Evolving The Surface Grinder
A creep feed/surface grinder proves a winning combination for airfoil machining cells.
Machinist Dave Beman removes the turbine blade from a Dominator machine in Blade Machine Cell No. 4 at Howmet Castings’ Corporate Machining facility. The machine’s compact design and easy accessibility were major considerations in its selection.
A gang of four grinding wheels used to grind the small blades is shown just above the Dominator’s table-mounted diamond dressing rolls.
Howmet’s Rich Dell’Agnese displays a vane segment produced on one of the plant’s six vane cells.
This Dominator machine in Blade Machining Cell No. 11 creep feed grinds four small blades at a time. Other components of the U-shaped cell are visible in the background.
A diagram of Cell No. 11 shows how the workstations are divided among the cell’s three operators.
Howmet Castings, a business unit of Alcoa Inc., is the world’s largest producer of precision castings, primarily for jet aircraft and industrial gas turbine engines. It’s Corporate Machining facility (Winsted, Connecticut), which specializes in precision machining of those castings, is embarked on a program expected to nearly double annual sales by 2003. To get the additional machining capacity needed to boost output, the firm is improving the efficiency of its existing plant. That includes selectively replacing aging grinders with new, more efficient and more versatile machines. Two new grinders, already installed in two of the facility’s machining cells, provide interesting insights into the features and capabilities that Howmet-and other firms similarly committed to cellular manufacturing-are looking for in today’s grinders.
The Winsted facility machines turbine engine blades, vanes and related components from near-net-shape investment castings, most of which are produced by Howmet at other plants. Parts range from small blades a few inches long and weighing less than 1 pound to vane segments 2 feet long, weighing about 20 pounds and incorporating several airfoils. The parts are made of Inconel and other nickel-based exotic alloys that chew up conventional cutting tools, thus they are processed almost exclusively on grinding machines.
Jobs typically involve parts for new engine build programs or spare part programs. Runs typically involve hundreds of pieces-an engine set usually requires about 100 blades and a smaller number of vanes-but can be as large as 1,500 pieces. For new engine build programs, the plant works in close support of the customer’s requirements. If the customer is building three engines per month, the plant supplies three sets of airfoils per month.
Since an engine set involves numbers of identical parts, you would expect to see parts processed in batches. However, the plant employs a “single-piece flow” processing method that consists of producing the blades and vanes one at a time in one of the plant’s many dedicated machining cells.
“We design a cell around a single part or family of parts, arranging the equipment needed to process the blade or vane in sequential order,” explains Gary Koeppel, engineering manager for the plant. “The production rate of the cell is based on customer requirements: If the customer needs 100 pieces per shift, we’ll design the cell to produce 100 pieces per shift. If the cell must produce a complete part, say, every 4 minutes, we’ll bring together the kind and number of machines required to achieve that 4-minute pace.
“We also calculate the number of operators required to run the machines in the cell,” Mr. Koeppel continues. “Each operator is responsible for one or more machines and performs related tasks such as inspecting machined parts and moving parts through the cell. Balancing the cell is critical. The machining operations, the number of operators and their activities are all analyzed to reveal and resolve imbalances that might disrupt production. We FOCUS on utilization of the whole cell, not on utilization of individual machines.”
The Howmet plant has 14 machining cells, eight for blades and six for vanes. Workpieces enter the cells as near-net-shape investment castings and emerge as completely machined turbine blades ready for heat treating. Machine tools in the blade cells consist mostly of surface grinders, used primarily to grind the root end of the blade, and creep feed grinders, used primarily to grind the shroud end of the blade. (Radial grinders may also be used to grind blade tips and other curved features.) The airfoil surfaces of the blade are not machined; they are used pretty much as cast. Each cell is as self-contained as possible: In addition to the grinders, it includes all necessary secondary equipment, such as inspection equipment, a deburring station and a permanent marking station.
The cells are U-shaped, and their openings front on a main aisle. “A long, U-shaped cell makes more efficient use of floor space than one that is more nearly square,” Mr. Koeppel explains. “It enables the part to be easily moved from one machine to the next, and at the same time it enables an operator working at one machine to turn around and tend another machine across from him. In a four-machine cell, one operator can tend machines 1 and 4 and another operator can tend machines 2 and 3. The cell arrangement minimizes the distance the operator must walk to get from one workstation to another; it saves not only time but also energy.”
Cellular manufacturing is a relatively new development at the Howmet facility, started as recently as the early ’90s. According to Mr. Koeppel, the plant’s model self-contained cell-including ancillary processes such as part inspection, chemical etching, fluorescent penetrant inspection, shot peening and so forth-was developed for a single, high-volume part. “The project succeeded, and we exceeded all of our performance targets for the cell,” he continues. “However, the four grinding machines within the cell were some of the oldest machines in the plant. As long as the cell was used to run the part it was designed for, it performed fabulously. However, volume requirements for the part declined, and other jobs were added to the cell to take advantage of its productivity.
“The introduction of more jobs to the cell necessitated setup changes, and the older machines did not support the changeovers very well,” Mr. Koeppel continues. “For example, as soon as the setup person would loosen a lock screw on a gib to make an adjustment, everything would begin to unravel.
“We not only had to be able to change over the cell to run different jobs, but we also had to be able to do it quickly,” Mr. Koeppel emphasizes. “We needed a new machine that would satisfy our changeover requirements and be compatible with our cellular manufacturing system.
“We prepared a list of features that the new machine needed for a best fit with our cellular manufacturing environment,” Mr. Koeppel continues. “We compared the features of several grinders from leading manufacturers and found that the Dominator Model 634 combination creep feed grinder and surface grinder from Jones Shipman Inc. (Meriden, Connecticut) came closest to satisfying our wish list.” (See below.)
“The decision was not based so much on the traditional performance specifications of the machines; they all met the requirements for accuracy, speed, spindle horsepower, control sophistication and so forth,” adds Rich Dell’Agnese, CNC manufacturing program engineer. “On the other hand, we were very interested in the footprints of the machines. The smaller the machine, the easier it is to fit in a cell. On conventional reciprocating grinders, the table traverses from side to side. If the machine has a 60-inch table, you need a 120-inch width to accommodate the travel of the table. With the Dominator, however, the table travels up and down instead of side to side, and the wheelhead carrier moves the wheel the length of the table so that the machine requires no more space than the width of its cabinet.
“We were also concerned about the shape of the footprint,” Mr. Dell’Agnese continues. “We wanted a machine with a narrow fa‡ade instead of a wide one, again to simplify placement in the cell. The bed of the Dominator is essentially a cube, which helps satisfy that requirement. The closer we can arrange the machines, the easier it becomes for the operator to move the part from one machine to the other.
“The Winsted facility is basically a job shop, and as our job mix changes we reconfigure our cells,” Mr. Dell’Agnese continues. “We move our machines frequently. Portability is therefore important to us. Some of our older surface grinders are so large that we must configure the cells around them; because of the Dominator’s compact size, we can move it where we need it fairly easily.
“For the same reason, we want our new machines to be self-contained,” he adds. “We don’t want any accessories that must be unwired and rewired, unplumbed and replumbed. Having everything mounted right on the machine, as it is on the Dominator, makes moving the machine that much easier.”
“Ergonomics is another important consideration,” adds Mr. Dell’Agnese. “On most surface grinders, the height of the worktable is fixed, and the wheelhead moves up and down on the machine column. On the Dominator, the table moves up and down to provide the Y-axis movement. That enables us to position the table at the most convenient (and comfortable) working height for the operator.
“The axis configuration of the Dominator is such that the work envelope is right in front of the operator, so there’s no reaching involved,” Mr. Dell’Agnese adds. (See photo) “Part loading is very comfortable.
“The Dominator incorporates some important features that weren’t included on our wish list,” he notes. “Its design is more rigid than the conventional moving-wheelhead machine configuration, making for improved accuracy. The design also does a good job of separating the grinding enclosure from the machine slides and ballscrews, so from a maintenance standpoint the machine should last longer than conventionally designed machines.”
A Utility Grinder
Probably the most important feature of the Dominator is its ability to perform both creep feed grinding and conventional reciprocating grinding. “We have had machines that could do both operations for years,” Mr. Dell’Agnese points out. “However, results were less than spectacular. For example, grinders with hydraulically driven tables could not deliver the positive drive that you get with a ballscrew, and older-technology ballscrews and controls could not efficiently support reciprocating grinding. Jones Shipman approached the design of the Dominator with the intent of building a machine that can operate in both modes without compromising performance in either mode.
“We have two Dominator Model 634 grinders, both in blade cells, and we use them for creep feed grinding and surface grinding,” Mr. Dell’Agnese affirms. “The mode that we use depends on the job. For one blade, we’ll use the Dominator in the creep feed mode; for another, we’ll use it as a surface grinder. And within a job there are times when we’ll run a combined cycle; that is, we’ll take a couple of creep feed passes and then shift over to surface grinding mode to spark out.”
The plant’s first Dominator is used in (blade) Cell No. 4. in the reciprocating mode to grind one feature (the root end) on one blade and another feature (the root bottom) on a second blade in the same cycle. To accomplish the task, the Dominator is equipped with two grinding wheels and a two-station fixture. After a blade is fixtured in the first station and ground, it is removed and placed in the second station (See photo) At the same time, a fresh blade is loaded in the first station. On the next and subsequent cycles, each blade will be ground by its respective wheel, and a finished part will be produced with every cycle.
“The Dominator was installed in Cell No. 4 to replace an aging surface grinder,” Mr. Dell’Agnese explains. “But it also provided the reliability of a new machine, ergonomic benefits for not only operating the machine but also setting up the machine, and the flexibility to be used either in creep feed mode or reciprocating mode, depending on the job. Because Cell No. 4 hosts multiple blades and will continue to do so, having the flexibility to grind in either mode may save us the trouble of having to move another machine when we’re changing over the cell. If we decide to process another blade in that cell, the odds are that the Dominator will be able to support whatever cycle we need to run.”
Howmet’s second Dominator is installed in (blade) Cell No. 11 where it is used to creep feed grind a different feature in each of four small blades mounted in a four-station fixture. In this application, the Dominator is equipped with four creep feed wheels, each of which has its own table-mounted diamond dressing roll (See photo).
At the end of each cycle, the operator removes a finished blade from the fourth fixture (closest to the wheels), advances each of the other blades to the next fixture in line and loads a “raw” blade into the first fixture. The operator has a limited time to move the blades in and out of the fixtures and the adjustable height of the grinding table, and the front-and-center location of the fixtures make this difficult task as easy as possible.
“Airfoil parts are difficult to fixture,” Mr. Dell’Agnese notes. “It takes an experienced operator to load them the right way even when conditions are optimal. But when the operator must load fixtures in a work envelope that is dark and/or difficult to reach-frequently the case on older surface grinders-the task becomes more difficult, and the likelihood of quality problems increases. Part grinding errors are frequently attributed to operator misload; in fact, the errors occur because the operators have not been given the equipment they need to do the job right. As the Cell No. 11 application demonstrates, the Dominator not only makes the job easier to do, but it helps him do the job better as well.”
Mr. Koeppel estimates that each of the Dominators will save Howmet more than 32,000 annually. The single biggest chunk of that savings is attributed to improved productivity resulting from reduced walking, reduced reaching, eliminated bending and reduced fatigue. The total also includes improvements in setup costs and scrap reduction attributable to fewer “misloads.” eMr. Koeppel also notes that the Dominator has a 60 percent smaller footprint than another of the grinders considered in the buy decision. Howmet has determined that achieving its desired sales goal for 2003 will require a 21-percent increase in “sales per square foot. The Dominator contributes to the kind of machine density that will be needed to help Howmet make the numbers.
Checking Out Some New Moves
The idea seemed simple enough: instead of building a surface grinder with a reciprocating table that carries the work past a stationary grinding wheel, why not make the table stationary and pass the wheel over the workpiece? The interested party, grinding machine manufacturer Jones Shipman Inc., Meriden, Connecticut, was certain that the idea must have been used by some grinder manufacturer in the past, but research turned up no record of such a grinder ever being built. JS decided to bring the idea to market, and the result is the Dominator combination creep feed grinder and surface grinder.
The Dominator is based on a cube-shaped machine bed. (See drawing.) Main moving elements include the work table, which is supported from the front face and moves up and down (Y axis) on widely spaced preloaded slides; a saddle, which is mounted on top of the bed that supports the wheelhead carrier assembly and moves it in the Z-axis; and the wheelhead carrier assembly, which provides the X-axis movement for both creep feed grinding and reciprocating grinding.
Major benefits of the Dominator’s design include better structural rigidity (because there is no column) and a small footprint (because the table does not move in the horizontal plane), which saves on valuable floor space. Access for setup and part loading/unloading is also easier. Ability of the machine to perform both creep feed grinding and reciprocating grinding is credited to the machine’s utilization of the latest improvements in ballscrew technology.
The Dominator is programmed by Jones Shipman-developed software in a Microsoft Windows environment-a huge step forward from the menu-driven software of the previous generation of creep feed grinders and surface grinders. Windows allows simple-to-use, spreadsheet-style, setup routines for grinding and wheel-dressing operations and has made it easy for JS to incorporate special features for customers. The control system is a GE Fanuc CNC using a PC front end with a JS-developed graphical user interface.
How to Use a Surface Grinder Machine:
A surface grinding machine is used to produce a smooth accurate finish on either metallic or nonmetallic materials. It uses a round rotating abrasive grinding wheel that remains stationary (but rotating) while the feed table (with work attached) is run in a reciprocating motion (left and right) under the grinding wheel. The specific amount of material to remove is determined by lightly touching off on the work with the grinding wheel rotating and feeding the grinding head down a certain distance. W A R N I N G. If a grinding wheel is permitted to exceed the maximum safe speed, it may disintegrate and cause injury to the operator and damage to the grinding machine!
|On a Manual Surface Grinder, you will then need to run the table left and right with one hand wheel while cross-feeding with the other hand wheel.|
|On an Automatic Surface Grinder, you will then be able to run the table left and right automatically while cross-feeding automatically. All you need to do is set the down feed and stroke.|
Typically surface grinders can grind within.00010002 but not all surface grinders are created equal. The less expensive models may not hold up to tool room accuracies but could be used effectively to sharpen punches, dies or do repair shop work. The more expensive models will use higher quality spindle bearings and other components and will be better able to attain tool room accuracies.
To use the surface grinder, you must select the correct grinding wheel for the work to be ground. There are different wheels that are best suited for grinding:
High Speed Steel RC 50-68 400 Series Stainless Soft Steels RC 30-45 300 Series Stainless Cast Iron: Ductile Gray Nonferrous Alloys
In each of the categories above you will need to determine wheel type by deciding if you need heavy (.004), moderate (.002-.004) or light stock (.001) removal characteristics. Also, you will need to select a Grit size. 46 grit being for general purpose, 60 grit for commercial finish, 80 grit for fine finish and 120 grit for very fine finishes.
After selecting the correct wheel for your job, visually inspect the wheel for any damage or cracks. If no damage is found install the wheel on your surface grinder, tightening the left-hand spindle nut carefully with a spanner wrench. Make sure you replace the guard covering the wheel, put safety glasses on then turn the spindle on. Step away and let the spindle run for 1 minute to make sure the grinding wheel is running smoothly.
Once the grinding wheel has been dressed it is not recommended to turn the spindle off because turning off the spindle will require the wheel to be dressed again for some concentricity will be lost.
You are now ready to dress the wheel using a single point diamond dressing tool that is placed and held down by the magnetic chuck. A small amount of grinding wheel should be dressed off of the diameter in order to make the wheel run concentric. Place the diamond dresser under the rotating wheel and bring down the grinding head carefully so it just touches the dresser. Sweep the diamond dresser across the rotating wheel using the cross feed (y-axis). Feed the grinding head down.002 then sweep the diamond dresser across the rotating wheel. Repeat until the grinding wheel face is clean and running concentric.
After the wheel is dressed and running concentric you will then be ready to gently touch off on the work (using the spark or layout fluid method). Next, set your “zero” on the down feed handle, raise the head slightly to clear work then the cross feed handle to distance the work from the grinding wheel. Next feed the grinding head down a distance not more then.005. The amount of material being removed will determine how far you can feed the cross-feed in per pass.
The benefits of surface grinding are: You can grind very hard or abrasive materials High degree of dimensional accuracy Produces surface textures of very high finish Tooling is less expensive Work holding is easier because of magnetic chuck Can be done automatically
In short, you will most likely need a surface grinder if you need to provide precision ground surfaces, either for a high surface finish or attaining critical dimensions.
GRINDING MACHINES (originally written by the U.S. Army)
Grinding is the process of removing metal by the application of abrasives which are bonded to form a rotating wheel. When the moving abrasive particles contact the workpiece, they act as tiny cutting tools, each particle cutting a tiny chip from the workpiece. It is a common error to believe that grinding abrasive wheels remove material by a rubbing action; actually, the process is as much a cutting action as drilling, milling, and lathe turning. The grinding machine supports and rotates the grinding abrasive wheel and often supports and positions the workpiece in proper relation to the wheel.
The grinding machine is used for roughing and finishing flat, cylindrical, and conical surfaces; finishing internal cylinders or bores; forming and sharpening cutting tools; snagging or removing rough projections from castings and stampings; and cleaning, polishing, and buffing surfaces. Once strictly a finishing machine, modem production grinding machines are used for complete roughing and finishing of certain classes of work. Grinding machines have some special safety precautions that must be observed. These are in addition to those safety precautions described in Chapter 1.
Grinding machines are used daily in a machine shop. To avoid injuries follow the safety precautions listed below.
W A R N I N G. If a grinding wheel is permitted to exceed the maximum safe speed, it may disintegrate and cause injury to the operator and damage to the grinding machine! Wear goggles for all grinding machine operations. Check grinding wheels for cracks (Ring Test Figure 5-11) before mounting. Never operate grinding wheels at speeds in excess of the recommended speed. Never adjust the workpiece or work mounting devices when the machine is operating. Do not exceed recommended depth of cut for the grinding wheel or machine. Remove workpiece from grinding wheel before turning machine off. Use proper wheel guards on all grinding machines. On bench grinders, adjust tool rest 1/16 to 1/8 inch from the wheel. See figure 5-1.
TYPES OF GRINDING MACHINES
From the simplest grinding machine to the most complex, grinding machines can be classified as utility grinding machines, cylindrical grinding machines. and surface grinding machines. The average machinist will be concerned mostly with floor-mounted and bench-mounted utility grinding machines, bufting machines. and reciprocating surface grinding machines.
UTILITY GRINDING MACHINES
The utility grinding machine is intended for offhand grinding where the workpiece is supported in the hand and brought to bear against the rotating grinding abrasive wheel. The accuracy of this type of grinding machine depends on the operators dexterity. skill, and knowledge of the machines capabilities and the nature of the work. The utility grinding machine consists of a horizontally mounted motor with a grinding abrasive wheel attached to each end of the motor shaft.
The electric-motor-driven machine is simple and common. It may be bench-mounted or floor-mounted. Generally, the condition and design of the shaft bearings as well as the motor rating determine the wheel size capacity of the machine. Suitable wheel guards and tool rests are provided for safety and ease of operation. Grinding machines come in various sizes and shapes as listed below.
Floor Mounted Utility Grinding Machine:
The typical floor-mounted utility grinding machine stands waist-high and is secured to the floor by bolts. The floormounted utility grinding machine shown in Figure 5-1 mounts two 12-inch-diameter by 2-inch-wide grinding abrasive wheels. The two wheel arrangement permits installing a coarse grain wheel for roughing purposes on one end of the shaft and a fine grain wheel for finishing purposes on the other end this saves the time that would be otherwise consumed in changing wheels.
Each grinding abrasive wheel is covered by a wheel guard to increase the safety of the machine. Transparent eyeshields. spark arresters. and adjustable tool rests are provided for each grinding wheel. A tool tray and a water pan are mounted on the side of the base or pedestal. The water pan is used for quenching carbon steel cutting took as they are being ground. Using the 12-inch wheel, the machine provides a maximum cutting speed of approximately 5.500 SFPM. The 2-HP electric motor driving this machine has a maximum speed of 1.750 RPM.
Bench Type Utility Grinding Machine:
Like the floor mounted utility grinding machine, one coarse grinding wheel and one fine grinding wheel are usually mounted on the machine for convenience of operation. Each wheel is provided with an adjustable table tool rest and an eye shield for protection. On this machine, the motor is equipped with a thermal over-load switch to stop the motor if excessive wheel pressure is applied thus preventing the burning out of the motor. The motor revolve at 3.450 RPM maximum to provide a maximum cutting speed for the 7 inch grinding wheels of about 6,300 surface feet per minute (SFPM).
Bench-Type Utility Drill Grinding Machine:
The bench-type drill grinding machine is intended for drill sharpening. The accuracy of this type of grinder is not dependent on the dexterity and skill of the operator because the drill is placed in a holding device. The holding device places the drill in the correct position for the clearance and included angle. For more information on this machine refer to chapter 4.
Bench-Type Utility Grinding and Buffing Machine:
The bench-type utility grinding and buffing machine is more suitable for miscellaneous grinding, cleaning, and buffing It is not recommended for tool grinding since it contains no tool rests, eyeshields, or wheel guards. This machine normally mounts a 4 inch-diameter wire wheel on one end. The wire wheel is used for cleaning and the abrasive wheel is used for general grinding. One of the two wheels can be removed and a buffing wheel mounted in its place for buffing and polishing. The 1/4-HP electric motor revolves at a maximum of 3,450 RPM. The maximum cutting speed of the 4-inch-diameter wheel is approximately 3,600 SFPM.
Bench-Type Tool and Cutter Grinder:
The bench-type tool and cutter grinder, see Figure 5-4, was designed primarily to grind end mills. It can also grind a large variety of small wood and steel cutters as well as slitting saw cutters up to 12 inches in diameter using the saw grinding attachment. Capacity grinder is as follows: of the typical bench-type tool and cutter.
Grinding wheel travel. 7 l/2-inch vertical. Grinding wheel travel. 5 1/2-inch horizontal. Table travel. 6 inches. Slitting saws with attachment. 12-inch diameter. Distance between centers. 14 inches. Swing on centers (diameter). 4 l/2-inch diameter. Swing in work head (diameter). 4 l/2-inch diameter.
Nonspecialized cylindrical grinding machines in the Army maintenance system include the tool post grinding machine and the versa mil attachment.
Tool Post Grinding Machine:
The tool post grinding machine, see Figure 5-5, is a machine tool attachment designed to mount to the tool post of engine lathes. It is used for internal and external grinding of cylindrical workplaces. Refer to Chapter 7 for a description of this machine.
Milling and Grinding Lathe Attachment:
Also called a Versa-Mil this attachment is a versatile machine tool attachment that mounts to the carriage of a lathe. It performs internal and external cylindrical grinding among its other functions. Refer to Chapter 9 for a description of this machine.
SURFACE GRINDING MACHINE:
The surface grinding machine is used for grinding flat surfaces. The workpiece is supported on a rectangular table which moves back and forth and reciprocates beneath the grinding wheel. Reciprocating surface grinding machines generally have horizontal wheel spindles and mount straight or cylinder-type grinding abrasive wheels.
RECIPROCATING SURFACE GRINDING MACHINE:
The reciprocating surface grinding machine is a horizontal- automatic application and recirculation of a coolant to the type surface grinding machine. Workpieces are fastened to table and can be moved beneath the grinding abrasive wheel by hand or power feed. A magnetic chuck may be used for fastening the workpiece to the table. This grinding machine has an internal pump and piping network for automatic application and recirculation of a coolant to the workpiece and wheel. The grinding abrasive wheel, mounted to the horizontal spindle is straight and cuts on its circumferential surface only. Grinding wheel speeds are adjustable.
STANDARD TYPES OF GRINDING WHEELS:
Grinding wheels come in many different sizes, shapes, and abrasives (see Figure 5-7).
Straight: Straight wheels, numbers 1, 5, and 7, are commonly applied to internal, cylindrical, horizontal spindle, surface, tool, and offhand grinding and snagging. The recesses in type numbers.5 and 7 accommodate mounting flanges. Type number 1 wheels from 0.006-inch to l/8-inch thick are used for cutting off stock and slotting.
Cylinder: Cylinder wheels, type number 2, may be arranged for grinding on either the periphery or side of the wheel.
Tapered: Tapered wheels, type number 4, take tapered safety flanges to keep pieces from flying if the wheel is broken while snagging.
Straight Cup: The straight cup wheel, type number 6, is used primarily for surface grinding, but can also be used for offhand grinding of flat surfaces. Plain or beveled faces are available.
Flaring Cup: The flaring cup wheel, type number 11, is commonly used for tool grinding. With a resinoid bond, it is useful for snagging. Its face may be plain or beveled.
Dish: The chief use of the dish wheel, type number 12, is in tool work. Its thin edge can be inserted into narrow places, and it is convenient for grinding the faces of form-relieved milling cutters and broaches.
Saucer: The saucer wheel, type number 13, is also known as a saw gummer because it is used for sharpening saws.
The abrasive grains are the cutting took of a grinding wheel. They actually cut small pieces or chips off the work as the wheel rotates. The shape of each grain is irregular with several sharp cutting edges. When these edges grow dull, the forces acting on the wheel tend to fracture the abrasive grains and produce new cutting edges.
Most grinding wheels are made of silicon carbide or aluminum oxide, both of which are artificial (manufactured) abrasives. Silicon carbide is extremely hard but brittle. Aluminum oxide is slightly softer but is tougher than silicon carbide. It dulls more quickly, but it does not fracture easily therefore it is better suited for grinding materials of relatively high tensile strength.
Abrasive grains are selected according to the mesh of a sieve through which they are sorted. For example, grain number 40 indicates that the abrasive grain passes through a sieve having approximately 40 meshes to the linear inch. A grinding wheel is designated coarse, medium, or fine according to the size of the individual abrasive grains making up the wheel.
The abrasive particles in a grinding wheel are held in place by the bonding agent. The percentage of bond in the wheel determines, to a great extent, the hardness or grade of the wheel. The greater the percentage and strength of the bond, the harder the grinding wheel will be. Hard wheels retain the cutting grains longer, while soft wheels release the grains quickly. If a grinding wheel is too hard for the job, it will glaze because the bond prevents dulled abrasive particles from being released so new grains can be exposed for cutting. Besides controlling hardness and holding the abrasive, the bond also provides the proper safety factor at running speed. It holds the wheel together while centrifugal force is trying to tear it apart. The most common bonds used in grinding wheels are vitrified, silicate, shellac, resinoid, and rubber.
Vitrified: The majority of grinding wheels have a vitrified bond. Vitrified bonded wheels are unaffected by heat or cold and are made in a greater range of hardness than any other bond. They adapt to practically all types of grinding with one notable exception: if the wheel is not thick enough, it does not withstand side pressure as in the case of thin cutoff wheels.
Silicate: Silicate bond releases the abrasive grains more readily than vitrified bond. Silicate bonded wheels are well suited for grinding where heat must be kept to a minimum, such as grinding edged cutting tools. It is not suited for heavy-duty grinding. Thin cutoff wheels are sometimes made with a shellac bond because it provides fast cool cutting.
Resinoid: Resinoid bond is strong and flexible. It is widely used in snagging wheels (for grinding irregularities from rough castings), which operate at 9,500 SFPM. It is also used in cutoff wheels.
Rubber: In rubber-bonded wheels, pure rubber is mixed with sulfur. It is extremely flexible at operating speeds and permits the manufacture of grinding wheels as thin as 0.006 inch for slitting nibs. Most abrasive cutoff machine wheels have a rubber bond.
GRADES OF GRINDING WHEEL HARDNESS:
The grade of a grinding wheel designates the hardness of the bonded material. Listed below are examples of those grades:
A soft wheel is one on which the cutting particles break away rapidly while a hard wheel is one on which the bond successfully opposes this breaking away of the abrasive grain.
Most wheels are graded according to hardness by a letter system. Most manufacturers of grinding abrasive wheels use a letter code ranging from A (very soft) to Z (very hard). Vitrified and silicate bonds usually range from very soft to very hard, shellac and resinoid bonds usually range from very soft to hard, and rubber bonds are limited to the medium to hard range.
The grade of hardness should be selected as carefully as the grain size. A grinding abrasive wheel that is too soft will wear away too rapidly, the abrasive grain will be discarded from the wheel before its useful life is realized. On the other hand, if the wheel is too hard for the job, the abrasive particles will become dull because the bond will not release the abrasive grain, and the wheels efficiency will be impaired.
Figure 5-8 illustrates sections of three grinding abrasive wheels with different spacing of grains. If the grain and bond materials in each of these are alike in size and hardness, the wheel with the wider spacing will be softer than the wheel with the closer grain spacing. Thus, the actual hardness of the grinding wheel is equally dependent on grade of hardness and spacing of the grains or structure.
GRINDING WHEEL ABRASIVE
ABRASIVE WHEEL STRUCTURE
Bond strength of a grinding wheel is not wholly dependent upon the grade of hardness but depends equally on the structure of the wheel, that is, the spacing of the grain or its density. The structure or spacing is measured in number of grains per cubic inch of wheel volume.
Every grinding wheel is marked by the manufacturer with a stencil or a small tag. The manufacturers have worked out a standard system of markings, shown in Figure 5-9.
For an example use a wheel marked A36-L5-V23. The A refers to the abrasive which is aluminum oxide. The 36 represents the grain size. The L shows the grade or degree of hardness, which is medium. The 5 refers to the structure of the wheel and the V refers to the bond type.
STANDARD SHAPES OF GRINDING WHEEL FACES:
Figure 5-10 illustrates standard shapes of grinding wheel faces. The nature of the work dictates the shape of the face to be used. For instance, shape A is commonly used for straight cylindrical grinding and shape E for grinding threads.
SELECTION OF GRINDING WHEELS:
Conditions under which grinding wheels are used vary considerably, and a wheel that is satisfactory on one machine may be too hard or soft for the same operation on another machine. The following basic factors are considered when selecting grinding wheels, though it should be understood that the rules and conditions listed are flexible and subject to occasional exceptions.
Tensile Strength of Material:
The tensile of material to be ground is the main factor in the selection of the abrasive to be used. Two types of abrasives are suited to different materials as shown below.
Silicon Carbide: Gray and chilled iron Brass and soft bronze Aluminum and copper Marble and other stone Rubber and leather Very hard alloys Cemented carbides Unannealed malleable iron
Aluminum Oxide: Carbon steels Alloy steels High speed steels Annealed malleable iron Wrought iron Hard bronzes
Factors Affecting the Grain Size:
The softer and more ductile the material, the coarser the grain size. The larger the amount of stock to be removed, the coarser the grain size. The finer the finish desired, the finer the grain size.
Factors Affecting the Grade of Hardness:
The harder the material, the softer the wheel. The smaller the arc of contact, the harder the grade should be. The arc of contact is the arc, measured along the periphery of the wheel, that is in contact with the work at any instance. It follows that the larger the grinding wheel, the greater the arc of contact and, therefore, a softer wheel can be used. The higher the work speed with relation to the wheel speed, the milder the grinding action and the harder the grade should be. The better the condition of the grinding machine spindle bearings, the softer the wheel can be.
Factors Affecting the Structure:
The softer, tougher, and more ductile the material, the wider the grain spacing. The finer the finish desired, the closer, or more dense, the grain spacing should be. Surfacing operations require open structure (wide grain spacing). Cylindrical grinding and tool and cutter grinding are best performed with wheels of medium structure (medium grain spacing).
Factors Affecting Bonding Material:
The factors described below affect the selection of bonding material for the wheel desired. Thin cutoff wheels and other wheels subject to bending strains require resinoid, shellac, or rubber bonds. Solid wheels of very large diameters require a silicate bonds. Vitrified wheels are usually best for speeds up to 6,500 SFPM and resinoid, shellac, or rubber wheels are best for speeds above 6500 RPM. Resinoid, shellac, or rubber bonds are generally best where a high finish is required.
Refer to Table 5-1 in Appendix A for specific requirements for typical grinding and materials (grinding wheel selection and application).
INSPECTION OF GRINDING WHEELS:
When a grinding wheel is received in the shop or removed from storage, it should be inspected closely for damage or cracks. Check a small wheel by suspending it on one finger or with a piece of string. Tap it gently with a light nonmetallic instrument, such as the handle of a screwdriver (Figure 5-11).
Check a larger wheel by striking it with a wooden mallet. If the wheel does not give a clear ring, discard it. All wheels do not emit the same tone; a low tone does not necessarily mean a cracked wheel. Wheels are often filled with various resins or greases to modify their cutting action, and resin or grease deadens the tone. Vitrified and silicate wheels emit a clear metallic ring. Resin, rubber, and shellac bonded wheels emit a tone that is less clear. Regardless of the bond, the sound of a cracked wheel is easy to identify.
MOUNTING GRINDING WHEELS:
The proper mounting of a grinding wheel is very important. An improperly mounted wheel may become potentially dangerous at high speeds.
The specified wheel size for the particular grinding machine to be used should not be exceeded either in wheel diameter or in wheel width. Figure 5-12 illustrates a correctly mounted grinding wheel
Note that the wheel is mounted between two flanges which are relieved on their inner surfaces so that they support the wheel only at their outer edges. This holds the wheel more securely with less pressure and with less danger of breaking. For good support, the range diameter should be about one-third of the wheel diameter. The spindle hole in the wheel should be no more than 0.002 inch larger than the diameter of the spindle, since a loose fit will result in difficulty in centering the wheel. If the spindle hole is oversize, select another wheel of the proper size. If no others are available, fit a suitable bushing over the spindle to adapt the spindle to the hole. Paper blotters of the proper size usually come with the grinding wheel. If the proper blotters are missing, cut them from heavy blotter paper (no more than 0.025-inch thick:) and place them between the grinding wheel and each flange. The blotters must be large enough to cover the whole area of contact between the flanges and the wheel. These blotters serve as cushions to minimize wheel breakage. When installing the grinding wheel on the wheel spindle, tighten the spindle nut firmly, but not so. tight that undue strain will be put on the wheel.
Grinding wheels wear unevenly under most general grinding operations due to uneven pressure applied to the face of the wheel when it cuts. Also, when the proper wheel has not been used for certain operations, the wheel may become charged with metal particles, or the abrasive grain may become dull before it is broken loose from the wheel bond. [n these cases, it is necessary that the wheel be dressed or trued to restore its efficiency and accuracy.
Dressing is cutting the face of a grinding wheel to restore its original cutting qualities. Truing is restoring the wheels concentricity or reforming its cutting face to a desired shape. Both operations are performed with a tool called an abrasive wheel dresser (Figure 5- 13).
The hand-held mechanical dresser has alternate pointed and solid discs which are loosely mounted on a pin. This dresser is used to dress coarse-grit wheels and wheels used in hand grinding operations.
Abrasive Stick Dresser:
The abrasive stick dresser comes in two shapes: square for hand use, and round for mechanical use. It is often used instead of the more expensive diamond dresser for dressing shaped and form wheels. It is also used for general grinding wheel dressing.
Abrasive Wheel Dresser:
The abrasive wheel dresser is a bonded silicon carbide wheel that is fastened to the machine table at a slight angle to the grinding wheel and driven by contact with the wheel. This dresser produces a smooth, clean-cutting face that leaves no dressing marks on the work.
The diamond dresser is the most efficient for truing wheels for precision grinding, where accuracy and high finish are required.
A dresser may have a single diamond or multiple diamonds mounted in the end of a round steel shank. Inspect the diamond point frequently for wear. It is the only usable part of the diamond, and is worn away it cannot dress the wheel properly.
Slant the diamond 3 to 15 in the direction of rotation and 30 to the plane of the wheel as shown in Figure 5-14 to prevent chatter and gouging. Rotate the diamond slightly in its holder between dressing operations to keep it sharp. A dull diamond will force the abrasive grains into the bond pores and load the face of the wheel, reducing the wheels cutting ability.
When using a diamond dresser to dress or true a grinding wheel, the wheel should be turning at, or slightly less than, normal operating speed never at the higher speed. For wet grinding, flood the wheel with coolant when you dress or true it. For dry grinding, the wheel should be dressed dry. The whole dressing operation should simulate the grinding operation as much as possible. Whenever possible, hold the dresser by some mechanical device. It is a good idea to round off wheel edges with a handstone after dressing to prevent chipping. This is especially true of a fine finishing wheel. Do not round off the edges if the work requires sharp corners. The grinding wheel usually wears more on the edges, leaving a high spot towards the center. When starting the dressing or truing operation, be certain that the point of the dressing tool touches the highest spot of the wheel first, to prevent the point from digging in.
Feed the dresser tool point progressively, 0.001 inch at a time, into the wheel until the sound indicates that the wheel is perfectly true. The rate at which you move the point across the face of the wheel depends upon the grain and the grade of the wheel and the desired finish. A slow feed gives the wheel a fine finish, but if the feed is too slow, the wheel may glaze. A fast feed makes the wheel free cutting, but if the feed is too fast, the dresser will leave tool marks on the wheel. The correct feed can only be found by trial, but a uniform rate of feed should be maintained during any one pass.
BUFFING AND POLISHING WHEELS:
Buffing and polishing wheels are formed of layers of cloth felt or leather glued or sewed together to form a flexible soft wheel.
Buffing wheels are generally softer than polishing wheels and are often made of bleached muslin (sheeting), flannel, or other soft cloth materials. The material is cut in various diameters and sewed together in sections which are put together to make up the buffing wheel. The buffing wheel is often slotted or perforated to provide ventilation.
Polishing wheels are made of canvas, felt, or leather sewed or glued together to provide various wheel grades from soft to hard. The harder or firmer wheels are generally used for heavier work while the softer and more flexible wheels are used for delicate contour polishing and finishing of parts on which corners and edges must be kept within rather strict specifications.
Buffing and polishing wheels are charged with abrasives for operation. The canvas wheels are generally suitable for use with medium grain abrasives, while felt, leather, and muslin wheels are suitable for fine grain abrasives. Buffing abrasives are usually made in the form of cakes, paste, or sticks which are applied to the wheel in this form. Polishing abrasives are fixed to polishing wheels with a glue.
A wire wheel consists of many strands of wire bound to a hub and radiating outward from the hub in the shape of a wheel. The wire wheel is used in place of a grinding wheel for cleaning operations such as removal of rust or corrosion from metal objects and for rough-polishing castings, hot-rolled steel, and so forth. The wire wheel fastens to the wheel spindle of the grinding machine in the same manner as a grinding wheel.
LAYING OUT AND MOUNTING WORK:
There are no special rules for laying out work for grinding operations. Most layout requirements will be dictated by the specific grinding machine to be used. In many cases, the workpiece will be turned on a lathe or machined in some other manner before grinding. The grinding is in preparation for the final finishing of the workpiece to the desired dimensions.
In planning work to be ground. the amount of metal to be removed should be based on the capabilities of the grinding machine. If the grinding machine is modern and in good condition, leave as much as l/32-inch or even more on large machine steel parts, but generally not more than l/64-inch on small machine parts.
If cylindrical grinding is to be performed, such as grinding of workplaces mounted in the grinding may be done with the workpiece set up between centers, held in a chuck and supported by a center rest, or clamped to a faceplate as in lathe setups.
Offhand grinding requires no mounting of the workpiece. Mounting for cylindrical, surface, and tool and cutter grinding is described below.
Mounting Workpiece for Cylindrical Grinding:
Cylindrical grinding may be done with the workpiece setup between centers, held in the chuck and supported by a center rest, or clamped to the faceplate as in lathe setups.
Use the following methods when mounting the workpiece between centers:
Use a dead center in the tailstock spindle. This method is preferred because it eliminates any error caused by wear in the machines spindle bearings. Before grinding check the accuracy and alignment of centers and correct if necessary. To grind the centers, follow the procedures for grinding lathe centers in Chapter 7. After the centers are accurate, align the centers by one of the methods prescribed for aligning lathe centers. Position the workpiece between the centers, and use a lathe dog to revolve the workpiece.
Use the following methods and procedures when mounting the workpiece for concial grinding.
Workpieces for conical grinding can be set up in a chuck or between centers. The table is swiveled to the required taper by means of the graduations on the end of the table (Figure 5-15). Since the table on a universal grinder is limited as to the degree that it can be swiveled, steep conical tapers are normally ground by swiveling the headstock to the angle of the taper desired (Figure 5-15). Remember when a workpiece is to be conically ground, the workpiece axis and the grinding wheel axis must be at the same height. Otherwise, the workpiece will not be ground at the correct angle.
Workpiece Mounted for Internal Grinding:
Internal grinding is done with the universal tool and cutter grinder with an internal grinding attachment (Figure 5-16). Note that the belt and pulleys are exposed; during actual operation, this area should be covered with a guard. Since internal grinding uses small grinding wheels, the spindle and quill must operate at a high speed to get the required SFPM. Most internal grinding attachments come with several sizes of quills. Use the largest one possible for the hole being ground. The smaller quills tend to spring away from the work easily and produce tapers and irregularities.
One condition that is more pronounced in internal grinding than in external grinding is that the larger area of contact may cause the wheel to load and glaze quickly which in turn causes vibration and produces poor surface finishes. Therefore, it is important to pay particular attention to the condition of the wheel and to use either a coarser grain wheel to provide more chip clearance or a softer grade wheel that will break down more easily. During grinding, let the grinding wheel run out of the end of the hole for at least one-half the width of the wheel face but not more than two-thirds. If the wheel clears the work each time the table reciprocates, it will grind bell-mouthed hole because of spring in the quill.
Internal conical tapers can also be ground on a universal grinding machine, using a combination of the rules for external conical grinding and those for straight internal grinding. The main thing to remember is to be sure that the axis of the quill is at center height with the axis of the work.
Mounting Workpiece for Surface Grinding:
A workpiece for surface grinding is usually held to the reciprocating worktable by a magnetic chuck. It may also be held in a vise or clamped directly to the table.
The two types of magnetic chucks are permanent magnet and electric. The electric chucks are built in larger sizes and are more powerful. However, the permanent-magnet chucks are less dangerous, since accidental release of work (due to power failure) is not likely to occur.
Mounting Workpiece for Tool and Cutter Grinding:
A workpiece for tool and cutter grinding is usually held between centers or on a fixture clamped to the table. The workpiece is mounted in the same manner as for cylindrical grinding, except the lathe dog if not used. When a fixture is used, the workpiece is placed in the fixture and the fixture is clamped to the table.
GENERAL GRINDING OPERATIONS:
Efficient grinding depends primarily upon the proper setup of the machine being used. If the machine is not securely mounted, vibration will result, causing the grinder to produce an irregular surface. Improper alignment affects grinding accuracy, and it is good practice to check the security and plumb of the machine every few months. It is advisable to place a strip of cushioning material under the mounting flanges, along with any necessary aligning shims, to help absorb vibration.
When a grinding wheel is functioning properly, the abrasive grains cut very small chips from the workpiece and at the same time a portion of the bond of the wheel is worn away. As long as the bond is being worn away as fast as the abrasive grains of the wheel become dull, the wheel will continue to work well. If the bond is worn away too rapidly, the wheel is too soft and will not last as long as it should. If the cutting grains wear down faster than the bond, the face of the wheel becomes glazed and the wheel will not cut freely.
Precision and semiprecision grinding may be divided into the following classes:
Cylindrical grinding denotes the grinding of a cylindrical surface. Usually, Cylindrical grinding refers to external cylindrical grinding and the term internal grinding is used for internal cylindrical grinding. Another form of cylindrical grinding is conical grinding or grinding tapered workpieces.
Surface grinding is the grinding of simple plain surfaces.
Tool and Cutter Grinding:
Tool and cutter grinding is the generally complex operation of forming and resharpening the cutting edges of tool and cutter bits, gages, milling cutters, reamers, and so forth.
The grinding wheel for any grinding operation should be carefully chosen and the workpiece set up properly in the grinding machine. Grinding speeds and feeds should be selected for the particular job. Whenever practical, a coolant should be applied to the point of contact of the wheel and the workpiece to keep the wheel and workpiece cool, to wash away the loose abrasive, and to produce a better finish.
GRINDING MACHINE SPEEDS AND FEEDS:
In grinding, the speed of the grinding wheel in SFPM and the feed of the grinding wheel are as important as, and sometimes more important than, proper wheel selection. Occasionally, the grinder spindle should be checked with a tachometer to make sure it is running at its specified RPM. Too slow a speed will result in waste of abrasive, whereas an excessive speed will cause a hard grinding action and glaze the wheel, making the grinding inefficient. The feed of the grinding wheel will determine to a cetain extent the finish produced on the work and will vary for different types and shapes of grinding wheels.
Safety and Factors Governing Speed:
W A R N I N G. If a grinding wheel is permitted to exceed the maximum safe speed, it may disintegrate and cause injury to the operator and damage to the grinding machine!
The grinding wheel should never be run at speeds in excess of manufacturers recommendations, Usually, each grinding wheel has a tag attached to it which states the maximum safe operating speed.
Condition of the Machine:
Modern grinding machines and machines that are in good condition can safely turn a grinding wheel at speeds greater than machines that are older or in poor condition. Most grinding machines are equipped with spindle bearings designed for certain speeds which should not be exceeded. Poor quality will result from vibrations caused by inadequate rigidity or worn bearings that are not in the best condition. High speeds will intensify these defects.
Material Being Ground:
The material being ground will generally determine the grain, grade, structure, and bond of wheel to be selected. For example, if the wheel is too soft for the material being cut, an increase in speed will make the wheel act harder. Conversely, if the wheel is too hard, as lower speed will make the wheel act softer.
Type of Grinding Wheel:
The type of grinding wheel employed for a particular operation is one of the major considerations in the proper selection of cutting speed. In general practice, the wheel will be selected for the material to be cut. The recommended cutting speed can then be determined by the wheel type, bond, and grade of hardness (Table 5-1 in Appendix A).
Calculating Grinding Wheel Size or Speeds:
Both cutting speeds in SFPM and rotational speed in RPM must be known to determine the size wheel to be used on a fixed-speed grinding machine. To determine the grinding wheel size, use the following formula:
D = 12 x SDFPM divided by RPM
Where SFPM = Cutting speed of wheel (In surface feet per minute). RPM = Revolutions per minute of wheel. D = The calculated wheel diameter (in inches).
To obtain the cutting speed in SFPM when the wheel diameter and RPM are given, use the same formula in a modified form:
SFPM = D x RPM divided by 12
To obtain the rotational speed in RPM when the wheel diameter and desired cutting speed are known use the formula in another modified form:
RPM = 12 SFPM divided by D
NOTE: As a grinding wheel wears down and as it is continually trued and dressed, the wheel diameter decreases, resulting in loss of cutting speed. As this occurs, it is necessary to increase the rotational speed of the wheel or replace the wheel to maintain efficiency in grinding.
Work Speed for Cylindrical Grinding:
In cylindrical grinding, it is difficult to recommend any work speeds since these are dependent upon whether the material is rigid enough to hold its shape, whether the diameter of the workpiece is large or small, and so forth. Listed below are areas to consider when performing cylindrical grinding:
The larger the diameter of the workpiece, the greater is its arc of contact with the wheel. The cutting speed suitable for one diameter of workpiece might be unsuitable for another. The highest work speed that the machine and wheel will stand should be used for roughing. Higher work speeds increase the cutting action of the wheel and may indicate that a harder wheel and a smaller depth of cut be used to reduce wheel wear. The following cylindrical work speeds are only typical: Steel shafts, 50 to 55 FPM Hard steel rolls, 80 to 85 FPM Chilled iron rolls, 80 to 200 FPM Cast iron pistons, 150 to 400 FPM Crankshaft bearings, 45 to 50 FPM C rankshaft pins, 35 to 40 FPM
Work Speed for Surface Grinding:
Surface grinding machines usually have fixed work speeds of approximately 50 SFPM or have variable work speed ranges between 0 and 80 SFPM. As with cylindrical grinding, the higher work speeds mean that more material is being cut per surface foot of wheel rotation and therefore more wear is liable to occur on the wheel.
The feed of the grinding wheel is the distance the wheel moves laterally across the workpiece for each revolution of the piece in cylindrical grinding or in each pass of the piece in surface grinding. The following methods are recommended for determine feeds:
The feed should be proportional to the width of wheel face and the finish desired. In general, The narrower the face of the wheel, the slower must be the traverse speed; the wider the wheel face the faster can be the traverse speed. For roughing, the table should traverse about three quarter the wheel width per revolution or pass of the workpiece. For an average finish, the wheel should traverse one-third to one-half the width of the wheel per revolution or pass of the workpiece. In surface grinding with wheels less than 1 inch in width, the table traverse speed should be reduced about onehalf.
Methods for determining depth of cuts are recommended for determining feeds.
In roughing, the cut should be as deep as the grinding wheel will stand, without crowding or springing the work. The depth of cut also depends on the hardness of the material. In cylindrical grinding, in addition to these factors, the cut depends on the diameter of the work. In any case, experience is the best guide. Generally, a cut of 0.001 to 0.003 inch in depth is used, depending on the size and condition of the grinding machine. For finishing, the depth of cut is always slight, generally from 0.0005 inch to as little as 0.00005 inch. An indication of the depth of cut is given by the volume of sparks thrown off. Also, an uneven amount of sparks indicates that the workpiece or wheel is not concentric.
Most surface grinding machines are equipped with coolant systems. The coolant is directed over the point of contact between the grinding wheel and the work. This prevents distortion of the workpiece due to uneven temperatures caused by the cutting action. In addition, coolant keeps the chips washed away from the grinding wheel and point of contact, thus permitting free cutting.
Clear water may be used as a coolant, but various compounds containing alkali are usually added to improve its lubricating quality and prevent rusting of the machine and workpiece. An inexpensive coolant often used for all metals, except aluminum, consists of a solution of approximately 1/4 pound of sodium carbonate (sal soda) dissolved in 1 gallon of water. Another good coolant is made by dissolving soluble cutting oil in water. For grinding aluminum and its alloys, a clear water coolant will produce fairly good results.
Offhand grinding is the process of positioning and feeding the workpiece against a grinding wheel by hand. Offhand grinding is used for reducing weld marks and imperfections on workpieces, and general lathe tool, planer tool, shaper tool, and drill grinding. Deciding depth of cut and feed is based on the operators knowledge of grinding.
Offhand grinding is performed on utility grinding machines which generally have fixed spindle speeds and fixed wheel size requirements, so that the cutting speed of the wheel is constant and cannot be changed for different materials. Therefore, the operator must use care in feeding and not overload the wheel by taking too heavy a cut, which would cause excess wear to the grinding wheel. Similarly, he must be careful not to glaze the wheel by applying excessive pressure against the wheel.
The one variable factor in most offhand grinding is the selection of grinding abrasive wheels, although limited to one diameter. For example, a softer or harder wheel can be substituted for the standard medium grade wheel when conditions and materials warrant such a change. Lathe tool grinding is described in Chapter 7. Drill sharpening and drill grinding attachments and fixtures are described in Chapter 4.
TOOL AND CUTTER GRINDING:
Grinding Milling Cutters:
Milling cutters must be sharpened occasionally to keep them in good operating condition. When grinding milling cutters, care must be exercised to maintain the proper angles and clearances of the cutter. Improper grinding can result in poor cutting edges, lack of concentricity, and loss of form in the case of formed tooth cutters. Milling cutters cannot be sharpened by offhand grinding. A tool and cutter grinding machine must be used.
Bench-Type Tool and Cutter Grinding Machine:
The bench-type tool and cutter grinding machine described here is typical of most tool and cutter grinding machines. It is designed for precision sharpening of milling cutters, spot facers and counterbores, reamers, and saw blades. The grinding machine contains a l/4-HP electric motor mounted to a swivel-type support bracket which can be adjusted vertically and radically on the grinder column. The column is fixed to the grinder base which contains T-slots for attaching grinder fixtures used to support the tools that are to be ground.
The motor shaft or wheel spindle accepts grinding wheels on each end. One end of the spindle contains a wheel guard and tool rest for offhand grinding of lathe tools and so forth. Cup, straight, and 15 bevel taper abrasive grinding wheels are used with this machine. Fixtures used for grinding tools and cutters include a center fixture for mounting reamers, taps, and so forth between centers; an outside diameter fixture for chucking arbor-type milling cutters and shanked peripheral cutting edge tools; and an end mill fixture for supporting end cutting tools to the grinder base.
Grinding Formed Milling Cutters:
Use the following methods and procedures when grinding formed milling cutters.
Formed milling cutters are usually ground with a cup or dish grinding wheel of medium grain (36 to 60 grain). It is important that formed cutters be ground only on the face, never on the land. Grinding the land destroys the shape of the cutter. Also important, the face must be ground so that the exact rake angle is retained or the cutter will cut unevenly. Formed cutters are ground by radial grinding. Correctly ground cutter teeth are shown at A and B, Figure 5-17. At A, the tooth is ground without rake; only cutters originally shaped without rake should be reground without rake. At B, a correctly ground tooth is shown with positive rake. Rake angles are commonly between 10 and 15 from the radius passing through the cutting edge, 12 being the most commonly used angle. The tooth shown at C, has excessive positive rake this tooth will gouge, making an excessively deep cut, and the cutting edge will dull rapidly with hard materials. The tooth shown at D, Figure 5-17 has negative rake; this tooth will drag and make a shallow cut.
On new cutters, the back (Figure 5-17) of each tooth should be ground accurately before grinding the face. This procedure is recommended so that an accurate reference surface is provided for the index finger of the grinding machine attachment. Another method of assuring this alignment is by mounting another cutter containing the same number of teeth on the same arbor with the cutter being ground. With the second cutter properly aligned and locked in place, the index finger can be used against the second cutters teeth.
NOTE: A positive rake angle is a rake angle that increases the keenness of the cutting edge. A negative rake angle is one that decreases or makes the cutting edge more blunt.
The grinding wheel should be set up so that the wheel traverse is aligned with the face of one tooth (Figure 5-18). The alignment should be checked by moving the grinding wheel away from the cutter, rotating the cutter, and rechecking the traverse on another tooth. After this alignment is accomplished, the depth of cut, is regulated by rotating the cutter slightly, thus maintaining the same rake angle on the sharpened cutter. The depth of cut should never be obtained by moving the cutter or grinding wheel in a direction parallel to the wheel spindle. Doing this would change the rake angle of the cutter.
Grinding Plain Milling Cutters:
Plain milling cutters with saw-tooth type teeth are sharpened by grinding the lands on the periphery of the teeth. The lands may be ground using a straight grinding wheel or a cupshaped grinding wheel.
The important consideration when grinding this type of cutter is the primary clearance angle or relief angle of the land (Figure 5-19). If the primary clearance angle is too large, the cutting edge will be too sharp and the cutter will dull quickly. If the primary clearance angle is too small, the cutter will rub rather than cut and excessive heat will be generated.
The primary clearance angle (Figure 5-19) should be between 3 and 5 for hard materials and about 10 for soft materials like aluminum. For cutters under 3 inches in diameter, a larger clearance angle should be used: 7 for hard materials and 12 for soft materials.
The clearance angle for end and side teeth should be about 2 and the face of these cutters should be ground 0.001- or 0.002-inch concave toward the center to avoid any drag.
To grind the lands of milling cutter teeth to primary clearance angle, the teeth are positioned against the grinding wheel below the wheels axis (Figure 5-20).
To obtain the primary clearance angle when grinding with a straight wheel, lower the indexing finger or raise the grinding wheel a distance equivalent to 0.0088 times the clearance angle times the diameter of the grinding wheel. For example, to find the distance below center of the indexing finger (Figure 5-20) for a cutter with a 5 clearance angle, being ground by a straight wheel 6 inches in diameter, the calculation is as follows: 0.0088 x 5 x6 = 0.264 inch. The indexing finger would then be set 0.264 inch below the wheel axis. The milling cutter axis should also be 0.264 inch below the wheel axis.
To obtain the primary clearance angle when grinding with a cup wheel, the formula for a straight wheel is used except that instead of wheel diameter being used in the formula, the cutter diameter is used. In this case, the index finger is set to the calculated distance below the axis of the milling cutter (Figure 5-20) instead of below the axis of the wheel.
Table 5-3 in Appendix A is provided to save time in calculating distances below center for primary clearance angles. The same figures can be used for straight wheel or cup wheel grinding, substituting the wheel diameter for the cutter diameter or vice versa.
The land of each tooth (Figure 5-19) should be from 1/32 to 1/16-inch wide, depending upon the type and size of the milling cutter. As a result of repeated grinding of the primary clearance angle, the land may become so wide as to cause the heel of the tooth to drag on the workpiece. To control the land width, a secondary clearance angle (Figure 5-19) is ground. This angle is usually ground to 30, although the exact angle is not critical. Generally, an angle between 20 and 30 is sufficient to define the land of the tooth.
Grinding End Milling Cutters:
The peripheral teeth of end milling cutters are ground in the same manner as the teeth of a plain milling cutter. When grinding the end teeth of coarse-tooth end milling cutters, the cutter is supported vertically in a taper sleeve of the end mill fixture and then tilted to obtain the required clearance angle. The end mill fixture is offset slightly to grind the teeth 0.001 to 0.002 inch lower in the center to prevent dragging. A dishshaped grinding wheel revolving about a vertical spindle is used to grind end milling cutters.
After the milling cutter is ground, the cutting edges should be honed with a fine oilstone to remove any burrs caused by grinding. This practice will add to the keenness of the cutting edges and keep the cutting edges sharper for a longer period of time.
Cylindrical grinding is the practice of grinding cylindrical or conical workplaces by revolving the workpiece in contact with the grinding wheel. Cylindrical grinding is divided into three general operations: plain cylindrical, conical grinding (taper grinding), and internal grinding. The workpiece and wheel are set to rotate in opposite directions at the point of contact (Figure 5-21).
Plain Cylindrical Grinding:
The step-by-step procedure for grinding a straight shaft is given below. The shaft has been roughly turned prior to grinding.
Check and grind headstock and tailstock centers if necessary. Check drilled centers of workpiece for accuracy. Place a grinding wheel of the proper grain, grade, structure, and bond on the wheel spindle. Place wheel guards in position to cover the wheel adequately. Set the proper wheel speed on grinding machine (Table 5-2 in Appendix A). Place the diamond dresser and holder on the machine table and true and dress the grinding wheel. Mount the headstock and footstock on the table. Attach the proper size drive dog on the headstock end of the workpiece. Mount the workpiece between headstock and tailstock centers. Use lubricant (oil and white lead mixture) on tailstock center. Make sure centers fit drill center holes correctly with no play. Set the proper rotational work speed on the wheel head. The general range of work speed for cylindrical grinding is 60 to 100 SFPM. Heavy rough grinding is sometimes performed at work speeds as low as 20 or 30 SFPM. Soft metals such as aluminum are sometimes ground at speeds up to 200 SFPM. Position the table trip dogs to allow minimum table traverse. The wheel should overlap each end of the workpiece not more than one-half the wheel width to assure a uniform straight cut over the length of the workpiece. Calculate the table traverse feed using this formula.
TT = (WW x FF x WRPM) 12 Where TT = Table travel in feet per minute WW = Width of wheel FF = Fraction of finish WRPM = Revolutions per minute of workpiece 12 = Constant (inches per foot)
The fraction of finish for annealed steels is 1/2 for rough grinding and 1/6 for finishing; for hardened steels, the rate is 1/4 for rough grinding and 1/8 for finishing.
For example, a l-inch-wide wheel is used to rough grind a hardened steel cylinder with a work RPM of 300.
Table travel = (1 x 1/4 x 300) 12 = (75) 12 = 6.25 FPM
After the calculations have been completed, set the machine for the proper traverse rate, turn on the table traverse power feed, and grind the workpiece. Check the workpiece size often during cutting with micrometer calipers. Check the tailstock center often and readjust if expansion in the workpiece has caused excessive pressure against the drilled center in the workpiece. The finishing cut should be slight, never greater than 0.001 inch, and taken with a fine feed and a fine grain wheel.
If two or more grinding wheels of different grain size are used during the grinding procedure, each wheel should be dressed and trued as soon as it is mounted in the grinding machine.
Most conical grinding is performed in the same manner as plain cylindrical grinding. Once the grinding machine is set up, the table is swiveled until the correct taper per inch is obtained. Steep conical tapers are normally ground by swiveling the headstock to the angle of taper. Whichever method is used, the axis of the grinding wheel must be exactly at center height with the axis of the work.
The internal grinding attachment is bolted to the wheel head on the universal tool and cutter grinder. The RPM is increased by placing a large pulley on the motor and a small pulley on the attachment.
The workpiece should be set to rotate in the direction opposite that of the grinding wheel. The following step-bystep procedure for grinding the bore of a bushing is outlined below as an example.
Set up the workpiece in an independent chuck and check and adjust its alignment. Mount the internal grinding attachment to the wheel head and adjust its position so that the grinding wheel is centered vertically with the mounted workpiece. True and dress the grinding wheel. Set the proper wheel speed on the grinding machine by adjusting the pulleys and belts connecting the wheel spindle to the drive motor shaft. Set the proper rotational work feed. The speed should be 60 to 100 SFPM. Be sure sufficient clearance is allowed when setting the traversing speed so that the grinding wheel will not strike any part of the workpiece or setup when the wheel is fed into and retracted from the workpiece.
If two or more grinding wheels are used to complete internal grinding, true each wheel after mounting it to the spindle of the internal grinding attachment.
Surface grinding or grinding flat surfaces, is characterized by a large contact area of the wheel with the workpiece, as opposed to cylindrical grinding where a relatively small area of contact is present. As a result, the force of each abrasive grain against the workpiece is smaller than that applied to each grain in cylindrical grinding. In surface grinding the grinding wheel should be generally softer in grade and wider in structure than for cylindrical grinding.
SURFACE GRINDING OPERATION:
The following sequence is provided as a step-by-step example of a typical surface grinding operation:
Adjust the surface grinding machine so that grinding head and worktable are absolutely parallel. Place a grinding wheel of the proper grain, grade, structure, and bond on the wheel spindle. Place the guard over the wheel and check security of all adjustable members of the grinding machine for rigidity and lack of backlash. True and dress the grinding wheel. Mount the workpiece to the worktable. Make sure the surface to be ground is parallel to the worktable and the grinding wheel. Adjust wheel speed, work speed, and work feed. Proceed with grinding, adjusting depth of cut as necessary. Check for accuracy between each cut and determine that the workpiece is square and the wheel is not out of alignment. If it is necessary to use more than one grinding wheel to complete the grinding, each wheel should be trued and dressed after it is mounted.
SPECIAL OPERATIONS ON GRINDING MACHINES:
A wire wheel mounted to a utility grinding machine is used for cleaning operations such as removing rust, paint, or dirt from metal objects. If the utility grinding machine on which the wire wheel is to be mounted is equipped with wheel guards and tool rests, these parts should be removed or swung out of the way so that the objects to be cleaned can be brought against the wheel without interference.
To clean objects with a wire wheel, place the object firmly against the wire wheel. Work the object back and forth across the face of the wheel until all traces of rust, paint, or dirt are removed. Avoid excessive pressure against the face of the wire wheel to prevent spreading the steel wires. Keep the point of contact below the center of the wheel to avoid kickback of the workpiece.
POLISHING, BUFFING, AND LAPPING:
Polishing, buffing, and lapping are three closely related methods for finishing metal parts. The three different methods of finishing are listed below.
Polishing is an abrading process in which small amounts of metal are removed to produce a smooth or glossy surface by application of cushion wheels impregnated or coated with abrasives. Polishing may be used for reduction or smoothing of the surface to a common level for high finish where accuracy is not important, or it may be employed for removing relatively large amounts of material from parts of irregular contour. Rough polishing is performed on a dry wheel using abrasives of No. 60 grain (60 grains per linear inch) or coarser. Dry finish polishing is a similar process where No 70. grain to No. 120 grain abrasives are used. Oiling is the term applied to polishing with abrasive finer than No. 120 grain. In this process, the abrasive is usually greased with tallow or a similar substance.
Buffing is a smoothing operation which is accomplished more by plastic flow of the metal than by abrading. The abrasives are generally finer than those used in polishing and instead of being firmly cemented to the wheel are merely held by a grease cake or similar substance. Buffing is used to produce a high luster or color without any particular regard to accuracy of dimension or plane. Cut down buffing produces a Rapid smoothing action with fast-cutting abrasives and relatively hard buffing wheels. It is accomplished with high speeds and heavy pressures to allow a combined plastic flow and abrading action to occur. Color buffing is the imparting of a high luster finish on the workpiece by use of soft abrasives and soft buffing wheels.
Lapping, like polishing, is an abrading process in which small amounts of material are removed. Unlike polishing, however, lapping is intended to produce very smooth, accurate surfaces, and is never used instead of polishing or buffing when clearance is the only consideration. Lapping is accomplished by charging metal forms called laps with flourfine abrasives and then rubbing the workpiece with the lap. The lap may be of any shape and may be designed to fit into most power machine tools. The only requirements of the lap are that it be of softer material than the material being lapped, and that it be sufficiently porous to accept the imbedded abrasive grain. Common materials for laps are soft cast iron, copper, brass, and lead. Some laps are flat and others are cylindrical to fit on steel arbors for internal lapping of bores. A cutting oil is recommended for most lapping operations.
Polishing and Buffing Speeds:
The proper speed for polishing and buffing is governed by the type of wheel, workpiece material, and finish desired. For polishing and buffing in general where the wheels are in perfect balance and correctly mounted, a speed of approximately 1,750 RPM is used for 6-inch to 8-inch wheels; up to 6-inch wheels use 3,500 RPM. If run at a lower rate of speed, the work tends to tear the polishing material from the wheel too readily, and the work is not as good in quality.
The abrasive grains used for polishing must vary in characteristics for the different operations to which they are applied. Abrasive grains for polishing are supplied in bulk form and are not mixed with any vehicle. The abrasives, usually aluminum oxide or silicon carbide, range from coarse to fine (1 to 20 grains per inch).
Buffing abrasives are comparatively fine and are often made up in the form of paste, sticks, or cakes; the abrasive being bonded together by means of grease or a similar vehicle. The abrasive sizes for buffing are 280, 320, 400, 500, and 600. Some manufacturers use letters and numbers to designate grain size such as F, 2F, 3F, 4F, and XF (from fine to very fine). Pumice, rottenstone, and rouge are often used as buffing abrasives.
Only the finest abrasives are used for lapping. These may be either natural or artificial. Abrasives for lapping range from No. 220 to No. 600 or No. 800 which are very fine flours. Lapping compounds are generally mixed with water or oil so that they can be readily applied to the lap.
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R Series Surface Grinder
Description: Single disc grinder capable of self-rotation of part during grinding. Reduced thermal distortion of part.
Application Example(s): Spacer, Wafer
Industry: Automotive, Information Technology
Grinding Capacity: Grinding capacity up to Ø100mm
Description: Single disc grinder capable of achieving mirror like finish on small parts without excessive lapping. Optional full automation and vacuum chucking of the part.
Application Example(s): Spacer, Wafer
Industry: Automotive, Information Technology
Grinding Capacity: Grinding capacity up to Ø100mm
Description: Dual spindles for side by side single-disc grinding. Mirror-like finish on small parts without excessive lapping. Optional full automation and vacuum chucking of the part.
Application Example(s): Inner Ring, VVT Housing, VCT Rotor, VTC Sprockets, Stator, Inner Plate, Housing, Gear, Ring Ball Ramp, Stops Spacers, Pump Body
Industry: Automotive, Pump
Grinding Capacity: Grinding capacity up to Ø100mm
Description: Single disc grinder with the ability to grind two parts at a time. Indexing table with 2-4 jigs.
Application Example(s): Rotor, Wafer, Stator, Housing, Inner Plate, Ring Ball Ramp, Stops Spacers, Inner Ring, Gear
Industry: Automotive, Information Technology
Grinding Capacity: Grinding capacity up to Ø125mm
Description: Single disc grinder with indexing table capable of loading/unloading while grinding after indexing.
Application Example(s): Wafers, Stator, Housing, Inner Plate, Ring Ball Ramp, Stops Spacers, Inner Ring, Gear, Rotor, Vane Housing, VCP Stator, Sprocket Housing
Industry: Automotive, Information Technology
Grinding Capacity: Grinding capacity up to Ø125mm
Description: Dual spindles for side by side double-disc grinding. Capable of rough and finish grinding to achieve high accuracy and mirror-like finishes.
Application Example(s): Connecting Rod
Grinding Capacity: Grinding wheel Ø455 x 125mm
Description: Side by side double-disc grinder ideal for grinding larger parts. Indexing table and loader are synchronized for continuous full automation and high productivity.
Application Example(s): V-6 Engine Block
Grinding Capacity: Grinding capacity up to Ø600mm
Description: Slanted surface grinder ideal for V-6 engine block.
Koyo Machinery USA is a world leader in the development and manufacturing of custom Centerless, Surface and Specialty Grinders. We repair and install specialty grinders for a variety of industries including Automotive, Aerospace, Bearing, Construction, Energy and Medical Our products are used in manufacturing facilities throughout the world including: The United States, Canada, Mexico, South America and Europe
A surface grinder or a surface grinding machine is one of the most important machines in any precision machine shop. While it is not a versatile machine like a lathe or a milling machine, it is a piece of essential equipment for fine metalworking.
Do you know what makes the Grinding Machine stand apart compared to other machines?
Your Grinding Machine differs from the other machining processes in one major aspect. Unlike your Lathe or Milling machines, which are used to machine the work-piece to the desired shape by removing the material in the form of chips, grinding involves minimum material removal and for many components, it is the final operation.
- What is Grinding Process?
- Types of Grinding Machines
- Why we use Surface Grinding Machine
- How surface grinding machine works
- 1. Horizontal Spindle Surface Grinder (with Reciprocating Table)
- 2. Horizontal Spindle Surface Grinding Machine (with Rotary Table)
- 3. Vertical Spindle Surface Grinding Machine with Reciprocating Table.
- 4. Vertical spindle surface grinding machine with Rotary Table.
- 5. Disc surface Grinders
- Cutting Fluid / Coolant
- Applications of Surface Grinding
What is Grinding Process?
Your grinding machine involves a process of material removal in the form of minute chips by the cutting action of numerous abrasive particles bonded together in the form of a grinding wheel. The cutting action takes place when you feed the work-piece against a revolving grinding wheel. Your grinding machine is normally used for producing components of accurate geometric shapes with smooth, fine surface finish and close dimensional tolerances.
When the individual grains of your grinding wheel wear out during the abrasive action, the self-sharpening properties of the bonded abrasive particles become effective by releasing the dulled grains and exposing new sharper ones.
Types of Grinding Machines
Based on the nature of the work-pieces ground, your grinding machines are broadly categorized into:
- Cylindrical Grinding machines.
- Internal Grinding Machines.
- Surface Grinding Machines.
- Tool and Cutter Grinding Machines.
Cylindrical and internal grinding machines are used for grinding cylindrical diameters and bores (internal diameter). Centreless grinding machines come under the cylindrical grinding machine category.
Tool and cutter grinding machines are used for sharpening cutting tools.
Surface grinding machines are used for grinding flat surfaces.
Now, let us dive into the world of Surface Grinding Machines.
Surface Grinding Machines
You can do surface grinding of the components in any of the following types of machines
Why we use Surface Grinding Machine
You use Surface Grinding Machine for producing accurate flat surfaces with geometrical accuracy and good surface finish. With special accessories and fixtures, you can do an angular surface grinding operation. You can do form grinding on the work-piece surface by using specially formed wheels.
How surface grinding machine works
You use a surface grinding machine to grind flat surfaces, and for this, you need a rotating grinding wheel in horizontal or vertical axis and a moving table of rectangular or circular shape for mounting and feeding the work-piece against the rotating grinding wheel. Depending on the orientation of your surface grinding machine, cutting action is done by the abrasive particles on the periphery (horizontal spindle) or the face (vertical spindle). Your direction of work-piece feed will be opposite to the direction of grinding wheel rotation.
Types of Surface Grinding Machines
Horizontal Spindle Surface Grinder (with Reciprocating Table)
Your Horizontal Spindle Surface Grinding Machine consists of a base on which a bed made of high tensile strength cast iron (for better vibration damping and shock absorption) is assembled. In many designs, you will find that this bed houses a hydraulic reservoir and hydraulic pump to operate the table and power feeds.
Your machine saddle is mounted on the bed and can be moved in the transverse direction, and the table with T-slots is mounted on the saddle and has longitudinal movements. You can mount magnetic chuck, vice and fixture on the table for clamping the work-pieces or directly clamp it on the table using the T-slots.
The vertical column of your machine is assembled upright on the base and houses the drive system for the wheel head; the wheel head is mounted on the column. The grinding wheel of your machine may have more than one rpm.
Your machine saddle, table, and vertical column are provided with precision hardened and ground antifriction roller guide-ways for precision movement.
The movement in the vertical direction is given to the table and in some designs, it may be the wheel head.
The reciprocating movement of the table in the longitudinal axis is hydraulic and the table speed is infinitely variable. You can change the speed of table movement or stop the movement by using the lever.
There are two movable stoppers on the front of your machine table and they can be moved and locked at any position; the lever for reversing the direction of the table’s longitudinal movement is in between these two stoppers and during grinding, the stopper on the moving table strikes the lever to reverse the direction.
You have to position the two stoppers in such a way that the table movement is reversed as soon as the grinding wheel passes over the work-piece length.
You can move the table or the wheel head manually or through power including Rapid movement.
Your machine is provided with a coolant tank, coolant pump, piping, and coolant filtering arrangement for spraying the area of cutting with coolant.
You can feed the work-piece longitudinally against the rotating grinding wheel, using the reciprocating movement of the table.
You can give in-feed or depth of cut by using the vertical movement of the table or the wheel head. The hand-wheel will have a provision for giving fine in-feed.
When the width of your work-piece is more than the thickness of the grinding wheel, crossfeed is necessary and cross-feed is given by moving the table in the transverse direction. You can make the crossfeed automatic by synchronizing the crossfeed movement with the reversal of table movement. This means the crossfeed set by you occurs automatically when the table direction is reversed for a fresh cutting stroke.
Your machine is ideal for components requiring extremely accurate and highly finished flat surfaces and tool room applications. You can increase the rate of production by loading the components in a batch either in special fixtures or mounting them on the magnetic chuck.
Horizontal Spindle Surface Grinding Machine (with Rotary Table)
Your Horizontal Spindle Surface Grinding Machine with Rotary Table has a base on which a cast-iron bed is mounted; the bed is mounted with a saddle and a circular table on which magnetic chuck or fixtures can be mounted. The vertical column is mounted on the base and houses the wheel head.
The rotary table of your machine has rotary motion and the grinding head can be moved up and down in Rapid or at feed rate.
Your machine is suitable for surface grinding of thin parts of high accuracy and larger machines are suitable for mass production of pallets and surface plates.
In some designs, you will be able to tilt the table for concave or convex grinding (hollow grinding).
In smaller machines, the rotary motion of the circular table is sufficient for you to manage feeds and depth of cut. In bigger machines, you can move the circular table on the saddle horizontally towards or away from the grinding wheel head.
Your machine is provided with a coolant system.
You can make the in-feed of the wheel head (depth of cut) automatic at the completion of one revolution of the table or one cut on the components mounted on the table.
Your machine is generally not used for rough grinding operations.
Vertical Spindle Surface Grinding Machine with Reciprocating Table.
The base, bed, column, the hydraulic system for longitudinal movement of the table, and the coolant system of your Vertical Spindle Surface Grinding Machine with Reciprocating Table is similar to the Horizontal Spindle Surface Grinding Machine with Reciprocating Table.
The table of your machine moves on precision scraped or ground V and flat guide-ways with continuous forced feed lubrication. The wheel-head of your machine moves on rectangular precision guide-ways.
Arrangement of stoppers for reversing the direction of the reciprocating table (longitudinal axis) is the same as in the horizontal Spindle machine and you can set the stoppers suiting to the length of the work-piece.
Segmental Grinding Wheels are used in your machine for efficient grinding and better use of the coolant.
The wheel head of your machine has Rapid movement and also slow inching feed.
Your machine has a hollow spindle for better coolant supply to ensure full power utilization.
The table of your machine is provided with infinitely variable speed with smooth reversal by means of a hydraulic power pack and the table strokes are sensed by limit switches. You can regulate the table speed and also set the in-feed (depth of cut) to happen automatically at every cutting stroke.
Your machine has built-in safety interlocks.
Your machine can use Cup, Cylindrical or segmented wheels for fast stock removal where accuracies are not very stringent. Your machine is suited for heavy stock removal with a high degree of accuracy and faster rate of production for the grinding of the engine block, cylinder head, refractory bricks, and many other general engineering components.
Normally, the diameter of the wheel in your machine is sufficient to grind the complete width of the work-piece in a single stroke and hence crossfeed may not be necessary.
In many machines, built-in provision is made for wheel dressing.
Vertical spindle surface grinding machine with Rotary Table.
The basic construction of the machine viz. base, bed, column, and cooling system are similar to your earlier machines.
In your machine the diameter of the circular table is always bigger than the grinding wheel diameter, viz. grinding wheel diameter 450 mm and the table diameter750 mm and this gives you sufficient space for handling the work on the table. Also, there is a huge difference between the grinding wheel rpm and the table rpm, while the grinding wheel rpm is 960 table rpm is 7.5 or 15 rpm.
The rotary table of your machine operates on large circular ways well lubricated and carries an electromagnetic chuck with circular poles.
The construction of the wheel-head in your machine is very rigid and has provision for a segmented wheel or ring wheel.
The column of your machine houses the drive system for the wheel-head and the wheel-head moves vertically on precision guide-ways; manual or automatic in-feed of small increment is possible.
Your machine may have a built-in wheel dressing unit.
The wheel head motor of your vertical surface grinder has more power than the horizontal spindle grinder; however, the rpm is much less in the vertical wheel head. This feature helps you with heavy stock removal.
Your Vertical spindle surface grinder with rotary table, using a cup, cylinder, or segmental wheels, are widely used for high production applications; for finishing applications, the wheel axis is kept exactly perpendicular to the surface to be ground and for roughing purposes the axis is kept slightly tilted.
Disc surface Grinders
You use disc surface grinders for volume production of flat work-pieces. Here, you will be using the face of the grinding wheel to grind the work-pieces.
Your Single Disc Surface Grinding Machine will look like a horizontal spindle surface grinding machine albeit smaller in size since it does not need a reciprocating or circular table. The grinding action in your machine takes place by the abrasive particles on the face of the grinding wheel. You will be able to give the feed (depth of cut) by moving the wheel head.
You have to mount the work-pieces (small bushes of circular or of any other shape) securely on a fixture. Your fixture should be capable of holding the batch of components during the grinding process and suitable to the size of the grinding wheel. Like other surface grinding machines, one face of the work-piece can be ground at a time. You need to take care of the wheel dressing in between.
Your Double Disc Grinding Machine is similar to the single-disc grinding machine, except that you will have two-wheel heads mounted parallel to each other.
This arrangement helps you for simultaneous grinding of two parallel faces of the work-piece. Normally, the components ground on your machine are bushes of circular or any other shape.
Your machine is a highly productive machine and has an arrangement for continuous feed of components. You will complete the grinding of the work-piece in a single pass through the grinding wheels; cutting action takes place at the face of the grinding wheels.
Your Disc type grinding machines have a coolant system.
The grinding wheel acts as the cutting tool on a surface grinder. Unlike a lathe, drilling, or milling machine, the cutting tool on a grinder doesn’t produce curled chips. Instead, the abrasive particles on the periphery and/or the face of the grinding wheel peels off a small amount of material in the form of fine metal dust.
The type of abrasive particle on the grinding wheel depends on the type of material you want to grind, surface finish requirements, and cutting conditions (wet or dry grinding).
For a more detailed explanation on grinding wheels and how to select the right wheel, please refer to our guide on surface grinding wheels.
Cutting Fluid / Coolant
When you work on your Surface Grinding Machine, the surface of the work-piece in contact with the grinding wheel develops considerable heat.
The cooling system of your machine cools the work-piece, reduces the effect of friction, removes heat from the work-zone and increases rate-of-material-removal, without further damage to the work-piece surface finish.
The most commonly used grinding fluids in your machine are water-based emulsions and grinding oils.
Since the grinding process in your machine produces a lot of heat, flooding the coolant at the point of cut is most effective; the quantity of the coolant depends on the length of contact between the grinding wheel and the work-piece, larger the contact area more should be the quantity of coolant.
Safety Precautions in Grinding
Your Surface Grinding Machine and Grinding Wheels should always be used in accordance with the safety regulations prescribed by the machine manufacturer and also as stipulated by the local authorities in the labor department.
Some of the safety precautions are recorded here for your safety when you work on your machine.
- Wearing of goggles and face shields is a must when you are working on Surface Grinding Machines.
- You should never stand in front of the rotating grinding wheel; stand safe at the side of the machine.
- You should always wait for the grinding wheel to stop, before putting your hand into the work-piece for checking or removing.
- You should never run the grinding wheels at more than the speed specified on the wheel by the manufacturer. When you run the grinding wheel at higher than the specified speed, it may lead to high internal stresses and accidents.
- You must inspect the new grinding wheel for chips, cracks, and other defects. Clean the grinding wheel to remove dust or wetness and check visually for any physical defects like cracks. Hold the grinding wheel with your finger in the bore or on the mandrel and tap gently with a plastic hammer or screwdriver handle at a point approximately 45 degrees from the vertical center-line. In the case of an undamaged wheel, you can hear a clear metallic ring and a different dead sound if the wheel has a crack.
- You must do static balancing followed by the proper dressing of your grinding wheel, before using it for grinding.
- While mounting a new wheel on your Surface Grinding Machine, it is a safe practice for you to stand aside and run the wheel for a full minute before starting the grinding.
- Wheel mounting-You have to assemble your grinding wheel with the correct size of flanges (with no warpage) and use blotters between the flanges and the wheel surface for uniform distribution of flange pressure. Do not over-tight the flanges. Also, you must inspect the mounting of the wheel at intervals.
- Your Surface Grinding Machine generates minute chips in the form of dust and provision should be made to control it, especially in case of grinding without coolant.
- You must always use the wheel guard during your grinding process. You have to take care to see that the wheel guard is properly adjusted when you mount a new wheel or when the wheel is worn out.
- Your grinding machine should have adequate power to run the selected grinding wheel; this is important to avoid faster wheel wear out and accidents.
Applications of Surface Grinding
The primary use of a surface grinder is to remove material from a flat surface to finish the workpiece to the correct size with a fine surface finish. They are also used for sharpening cutting tools, grinding off small flanges and also big cylinder blocks, machine base and many other items.
Your Surface Grinding Machines are required in every industry, be it an automobile industry, a consumer goods industry, or manufacturer of machine tools.
Conclusion: You cannot think of any engineering industry without a Surface Grinding Machine. With the introduction of CNC Controls, your machine has become more accurate and productive.