www.toolingandproduction.com Chapter 18/Tooling & Production 1 2 Tooling & Production/Chapter 18 www.toolingandproduction.com George Schneider, Jr. CMfgE Professor Emeritus Engineering Technology Lawrence Technological University Former Chairman Detroit Chapter ONE Society of Manufacturing Engineers Former President International Excutive Board Society of Carbide & Tool Engineers Lawrence Tech www.ltu.edu Prentice Hall- www.prenhall.com CHAPTER 18 Lapping and Honing Metal Removal Cutting-Tool Materials Metal Removal Methods Machinability of Metals Single Point Machining Turning Tools and Operations Turning Methods and Machines Grooving and Threading Shaping and Planing Hole Making Processes Drills and Drilling Operations Drilling Methods and Machines Boring Operations and Machines Reaming and Tapping Multi Point Machining Milling Cutters and Operations Milling Methods and Machines Broaches and Broaching Saws and Sawing Abrasive Processes Grinding Wheels and Operations Grinding Methods and Machines Lapping and Honing Upcoming Chapters FIGURE 28.1: Typical lapping machine. (Courtesy Engis Corp.) 18.1 Introduction Lapping is a final abrasive finishing operation that produces extreme dimensional accuracy, corrects minor imperfections of shape, refines surface finish, and produces close fit between mating surfaces. Most lapping is done with a tooling plate or wheel (the lap), and fine-grained loose abrasive particles suspended in a viscous or liquid vehicle such as soluble oil, mineral oil, or grease. A typical lapping operation is shown in Figure 18.1. Honing is a low velocity abrading process. Material removal is accomplished at lower cutting speeds than in grinding. Therefore, heat and pressure are minimized, resulting in excellent size and geometry control. The most common application of honing is on internal cylin- drical surfaces. The cutting action is obtained using abrasive sticks mounted on a metal mandrel. Since the work is fixed in such a way as to allow floating, and no clamping or chucking, there is no distortion. 18.2 Lapping Processes The principal use of the lapping process is to obtain surfaces that are truly flat and smooth. Lapping is also used to finish round work, such as precision plug gages, to tolerances of 0.0005 to 0.00002 inches. Work that is to be lapped should be previously finished close to the final size. While rough lapping can remove considerable metal, it is customary to leave only 0.0005 to 0.005 inches of stock to be removed. Lapping, though it is an abrasive process, differs from grinding or hon- ing because it uses a ‘loose’ abrasive instead of bonded abrasives like grind- ing wheels (Fig. 18.2). These abrasives are often purchased ‘ready mixed’ in a ‘vehicle’ often made with an oil-soap or grease base. These vehicles hold the abrasive in suspen- sion before and during use. The paste abrasives are generally used in hand- lapping operations. For machine lap- ping, light oil is mixed with dry abra- sive so that it can be pumped onto the lapping surface during the lapping op- eration. 18.2.1 Lapping Machines These machines are fairly simple pieces of equipment consisting of a rotating table, called a lapping plate, and three or four conditioning rings. Standard machines have lapping plates www.toolingandproduction.com Chapter 18/Tooling & Production 3 Chap. 18: Lapping and Honing from 12 to 48 inches in diameter. Large machines up to 144 inches are made. 1 to 20 HP motors run these tables. A typical lapping machine is shown in Figure 18.3. The lapping plate is most frequently made of high-quality soft cast iron, though some are made of copper or other soft metals. This plate must be kept perfectly flat. The work is held in the conditioning rings. These rings ro- tate as shown in Fig. 18.4. This rotation performs two jobs. First it ‘conditions’ the plate, that is, it distributes the wear so that the lapping plate stays flat for a longer time. Secondly, it holds the workpiece in place. The speed at which the plate turns is determined by the job being done. In doing very critical parts, 10 to 15 RPM is used, and when polishing, up to 150 RPM is used. one step. Also, less time is required for cleaning parts and processing waste; throughput, along with overall produc- tivity, is increased. Lapping plates are manufactured from various materials as described below, and are available in standard sizes from 6 to 48 inches in diameter. Plates are supplied with square, spiral, and concentric and radial grooves as shown in Figure 18.5. Iron - Aggressive Stock Removal: • Excellent primary/roughing lap plate, with long service life • Often used as an alternative to cast iron plates • Produces a good surface finish on most materials, especially metals and ceramics. Copper - Moderate to Aggressive Stock Removal: • Most widely used, universal com- posite lap plate • Excellent when primary and fin- ishing lap are combined in a one step operation • Suitable for virtually any solid material: metal, ceramic, glass, car- bon, plastic, etc. Ceramic - Moderate Stock Removal: • Generally used to lap/polish ce- ramic parts and other stain- sensitive materials. • Used in applications where metal- lic-type contamination cannot be tol- erated • Affordable, more machinable al- ternative to ‘natural’ ceramic plates. Figure 18.3. Typical dual plate lapping ma- chine. (Courtesy Engis Corporation) Figure 18.2. Abrasive grit must be uniformly graded to be effective in lapping. Workpiece Lap A pressure of about 3 pounds per square inch (PSI) must be ap- plied to the workpieces. Sometimes their own weight is suf- ficient. If not, a round, heavy pres- sure plate is placed in the con- ditioning ring. The larger machines use pneumatic or hydraulic lifts to place and remove the pressure plates. Figure 18.5 shows various lapping plates. The workpiece must be at least as hard as the lapping plate, or the abra- sive will be charged into the work. It will take from 1 to 20 minutes to complete the machining cycle. Time depends on the amount of stock re- moved, the abrasive used, and the qual- ity required. Figure 18.6 shows a pro- duction-lapping machine. 18.2.2 Grit and Plate Selection Flatness, surface finish, and a pol- ished surface are not necessarily achieved at the same time or in equal quality. For example, silicon carbide compound will cut fast and give good surface finish, but will always leave a ‘frosty’ or matte surface. The grits used for lapping may occa- sionally be as coarse as 100 to 280 mesh. More often the ‘flour’ sizes of 320 to 800 mesh are used. The grits, mixed in slurry, are flowed onto the plate to replace worn-out grits as the machining process continues. The case for using diamond super abrasives rather than conventional abrasives such as aluminum oxide or silicon carbide can be summed up in three words. Diamonds are faster, cleaner, and more cost-ef- fective. With diamond slurries, the lap- ping and polish- ing phases of a finishing opera- tion can often be combined into Figure 18.4. Conditioning rings used in lapping operations. 4 Tooling & Production/Chapter 18 www.toolingandproduction.com Chap. 18: Lapping and Honing Tin/Lead - Fine Stock Removal: • Most widely used finishing lap/ polishing plate • Often used in place of polishing pads • Suitable for metal, ceramic and other materials. Tin - Fine Stock Removal • Often used where lead-type con- tamination cannot be tolerated • Suitable for charging of extra-fine particulates. 18.3 Advantages and Limitations Any material, hard or soft, can be lapped, as well as any shape, as long as the surface is flat. Advantages: There is no warping, since the parts are not clamped and very little heat is generated. No burrs are created. In fact, the process re- moves light burrs. Any size, diameter, and thickness from a few thousandths thick up to any height the machine will handle can be lapped. Various sizes and shapes of lapped parts are shown in Figure 18.7. Limitations: Lapping is still some- what of an art. There are so many variables that starting a new job re- quires experience and skill. Even though there are general recommenda- tions and assistance from the manufac- turers, and past experience is useful, trial and error may still be needed to get the optimum results. 18.4 Honing Processes As stated earlier, honing is a low velocity abrading process. Material re- moval is accomplished at lower cutting speeds than in grinding. Therefore, heat and pressures are minimized, re- sulting in excellent size and geometry control. The most common application of honing is on internal cylindrical surfaces. A typical honing operation is shown in Figure 18.8. Machining a hole to within less than 0.001 inch in diameter and maintain- ing true roundness and straightness with finishes less than 20 u inches is one of the more difficult jobs in manu- facturing. Finish boring or internal grinding may do the job, but spindle deflection, variation in hardness of the material, and difficulties in precise work hold- ing, make the work slow and the re- sults uncertain. Honing, because it uses rectangular grinding stones in- stead of circular grinding wheels, as shown in Figures 18.9a and 18.9b, can correct these irregularities. Honing can consistently produce finishes as fine as 4 u inches and even finer finishes are possible. It can re- move as little as 0.0001 inch of stock or as much as 0.125 inch of stock. However, usually only 0.002 to 0.020 inch stock is left on the diameter for honing. As shown in Figure 18.10, honing can correct a number of condi- tions or irregularities, left by previous operations. 18.5 Honing Machines For most work, honing machines are quite simple. The most used honing machines are made for machining in- ternal diameters from 0.060 to 6 inches. However, large honing ma- chines are made for diameters up to 48 inches. Larger machines are some- times made for special jobs. The length of the hole that can be honed may be anything from 1/2 inch to 6 or 8 inches on smaller machines, and up to 24 inches on larger ma- chines. Special honing machines are made which will handle hole lengths up to 144 18.5.1 Horizontal Spindle Machines Horizontal-spindle honing ma- chines, for hand-held work with bores up to 6 inches, are among the most widely used. The machine rotates the hone at from 100 to 250 FPM. Figure 18.5. Typical lapping plates. (Cour- tesy Engis Corporation) Figure 18.7. Various sizes and shapes of lapped parts. (Courtesy Engis Corporation) Figure 18.8. Typical vertical honing operation. (Courtesy Sunnen Products Co.) Figure 18.6. Single plate lapping produc- tion machine equipped for diamond abrasive slurry use. (Courtesy Engis Corporation) www.toolingandproduction.com Chapter 18/Tooling & Production 5 Chap. 18: Lapping and Honing The machine operator moves the work back and forth (strokes it) over the rotating hone. The operator must ‘float’ the work, that is, not press it against the hone or the hole will be slightly oval. Sometimes the work- piece must be rotated. Horizontal-spindle honing machines are also made with ‘power stroking’. In these, the work is held in a self-align- ing fixture and the speed and length of the stroke are regulated by controls on the machine. As a hone is being used, it is ex- panded by hydraulic or mechanical means until the desired hole diameter is achieved. Various mechanical and electrical devices can be attached to the honing machine to control the rate of expansion, and stop it when final size is reached. On the simplest hand-held ma- chines, the operator may check the bore size with an air gage, continue honing, recheck, etc. until the size is correct. A horizontal-spindle honing machine is shown in Figure 18.11. 18.5.2 Vertical Spindle Machines Vertical-spindle honing machines are used especially for larger, heavier work. These all have power stroking at speeds from 20 to 120 FPM. The length of the stroke is also machine controlled by stops set up by the operator. Vertical honing machines are also made with multiple spindles so that sev- eral holes may be machined at once, as in automobile cylinders (Figure 18.8). Hone Body: The hone body is made in several styles using a single stone for small holes, and two to eight stones as sizes get larger (Fig. 18.9b). The stones come in a wide variety of sizes and shapes. Frequently there are hard- ened metal guides between the stones to help start the hone cutting in a straight line. Cutting Fluid: A fluid must be used with honing. This has several pur- poses: to clean the small chips from the stones and the workpiece, to cool the work and the hone, and to lubricate the cutting action. A fine mesh filtering system must be used, since recirculated metal can spoil the finish. A vertical honing operation was shown in Figure 18.8. A few of the parts honed on such a machine are shown in Figure 18.12. 18.6 Abrasive Tool Selection The abrasive honing stone must be selected for the proper abrasive type, bond hardness and grit size to deliver the fastest stock removal and desired surface finish. This selection is simple if done in the following three steps: Step One: Select the abrasive type with respect to the material composi- tion of the bore. There are four differ- ent types of abrasives: aluminum ox- ide, silicon carbide, diamond, and CBN. All four of these were discussed in the previous chapter. Each type has its own individual characteristics that make it best for honing certain materi- als. Some simplified guidelines for their use are: • Mild steel hones best with alumi- num oxide. • Cast iron, brass, and aluminum hone best with silicon carbide. • Glass, ceramic, and carbide hone best with diamond • High speed tool steels, and super alloys hone best with CBN. Mandrel Honing shoe Honing stone Workpiece (a) Figure 18.9a. Schematic illustration of the com- ponents of an internal hone. Figure 18.9b. Typical honing tool is shown be- ing Checked (Courtesy: Gehring L.P.) Alignment of tandem holes Correcting bellmouth Correcting taper Correcting rainbow-shaped holes Figure 18.10. Undesirable conditions that can be corrected by honing. 6 Tooling & Production/Chapter 18 www.toolingandproduction.com Chap. 18: Lapping and Honing Diamond and CBN are considered super abrasives because they are much harder than conventional abrasives. They cut easily and dull slowly, there- fore allowing them to hone certain materials much faster and more effi- ciently than conventional abrasives. However, as shown above, super abra- sives are not suited to honing all mate- rials. For instance, diamond does not hone steel very well, and CBN may not be as economical as using aluminum oxide to hone soft steel. Step Two: Use the stone hardness suggested in the manufacturer’s cata- log. If the stone does not cut, select the next softer stone; if the stone wears too fast, select the next harder stone. Stone hardness does not refer to the hardness of the abrasive grain, but to the strength of the bonding material hold- ing the abrasive grains together, as discussed in the previous chapter. A bond must be strong enough to hold sharp abrasive grains in position to cut, but weak enough to allow dulled grains to be sloughed off to expose underly- Figure 18.13. Plateau honed finish surface at 100x (Cour- tesy: Gehring L.P.) Figure 18.12. Parts honed on a vertical honing ma- chine. (Courtesy Sunnen Products Co.) Figure 18.11. Horizontal-spindle honing machine (Courtesy Sunnen Products Co.) ing sharp grains. If the bond is too hard, the dulled abrasive grains will not be allowed to fall off, and the stock removal rate will be reduced. If the bond is too soft, the stone will wear excessively because sharp abrasive grains fall off before they are fully used. Diamond and CBN abrasive grains dull so slowly that standard ceramic or resin bonds may not be strong enough when honing rough out-of-round bores in hard materials, or when CBN is used to hone soft steel. Metal bonds are best suited for these applications because the grains are held in a sintered metal matrix that is much stronger than stan- dard bonds. As with choosing abrasive type, stone bond hardness must be matched to the application to maxi- mize life and stock removal rates. Step Three: Select the largest abra- sive grit size that will still produce the desired surface finish. Surface finish is a function of the height of microscopic peaks and valleys on the bore surface and honing can produce al- most any degree of rough- ness or smoothness through the use of different abrasive grit sizes. Honing oil can improve stock removal rates by help- ing the cutting action of the abrasive grains. It prevents pickup (spot welding of tool to bore) and loading (chips coating the stone). Honing oil does this, not by acting as a coolant, but through chemical activity. The ingredients in the oil produce this chemical activity. Whenever the temperature rises at one of the microscopic cutting points, the sulfur in the oil combines with the iron in the steel to form iron sulfide, an unweldable compound, and weld- ing is prevented. The antiwelding property of honing oil also pre- vents chips from stick- ing together and coat- ing the stone. Water based coolants cannot produce this type of chemical activity. Use of water-based coolants will result in welding of metallic guide shoes to the part and loading of vitrified abrasive honing stones. 18.7 Cylinder Block Honing Bores sometime require a prelimi- nary rough honing operation to remove stock, followed by finish honing to get the desired surface finish. A character- istic feature of a honed surface finish is crosshatch, which makes an excel- lent oil retention and bearing surface. The crosshatch pattern is generated in the bore surface as the workpiece is stroked back and forth over the rotat- ing honing tool. Plateau Honing: A few years ago a special surface finish generated inter- est in the engine rebuilding market. With this finish, the valleys are deep and the peaks have been removed to form plateaus, giving the name plateau honing or plateau finish as shown in Figure 18.13. A recent test by a ring manufacturer has shown that an engine with a true plateau finish consumed one-tenth the oil and had 80 percent less cylinder bore wear than the en- gines with conventional finishes. Laser-Honing: With this process, considerably better results are achieved compared to traditional hon- ing. Precisely defined surface struc- tures can be obtained with Laser tech- nology. Laser-honing is a combination of honing and Laser processing. This process generates Laser-produced lu- bricant reservoirs into a specifically defined area in order to achieve an ideal plateau surface finish. Such a hydrodynamic system can be produced exactly where it is required as shown in Figure 18.14. Application of the Laser-honing process requires three steps. In the first step – rough honing – the macro-form www.toolingandproduction.com Chapter 18/Tooling & Production 7 Chap. 18: Lapping and Honing Figure 18.15. Single-stroke honing tools use expandable diamond-plated sleeves on a ta- pered arbor. (Courtesy Sunnen Products Co.) Figure 18.14. Laser generated honed finished surface (Cour- tesy: Gehring L.P.) of the bore is produced. In the second step, precisely defined lubricant reser- voirs are produced with the Laser. In step three –finish honing – an ex- tremely fine surface finish is obtained, resulting in increased engine life by reduction of wear in the cylinder sur- face and on the piston rings. 18.8 Production Honing Honing will not only remove stock rapidly, but it can also bring the bore to finish diameter within tight tolerances. This is especially true if the honing machine is equipped with automatic size control. With every stroke, the workpiece is pushed against a sensing tip that has been adjusted to the finish diameter of the bore. When the bore is to size, the sensing tip enters the bore and the machine stops honing. Size repetition from bore to bore is .0001 inch to .0002 inch. The operator sim- ply loads and unloads the fixture and presses a button; everything else is automatic. Single-Stroke Honing: A still faster and more accurate method of honing a bore to final size is Single-Stroke hon- ing. The Single-Stroke tool (Fig. 18.15) is an expandable diamond plated sleeve on a tapered arbor. The sleeve is expanded only during set up, and no adjustments are necessary dur- ing honing. Unlike conventional hon- ing, where the work- piece is stroked back and forth over the tool, in Single-Stroke hon- ing the rotating tool is pushed through the bore one time, bring- ing the bore to size. The return stroke does nothing to the bore ex- cept get the workpiece off the tool. Single- Stroke honing is so ac- curate and consistent, that honed bores do not require gaging. Although Single- Stroke honing has many advantages, it is limited in the types and volumes of material that can be removed. The size and overall volume of chip produced in one pass must be no more than the space between the diamond grits, or the tool will seize in the bore. Workpieces are best suited for Single-Stroke honing when they are made of materials that produce small chips, such as cast iron, and that have interruptions that allow chips to be washed from the tool as the bore is being honed. Conventional honing should be used whenever the material to be honed produces long stringy chips, or the amount of stock to be removed is large. 18.9 Advantages and Limitations Honing has developed into a produc- tive manufacturing Process, some advantages and limi- tations will be discussed below: Advantages: The workpiece need not be rotated by power, there are no chucks, faceplates, or rotating tables needed, so there are no chucking or locating errors. The hone is driven from a central shaft, so bending of the shaft cannot cause tapered holes as it does when boring. The result is a truly round hole, with no taper or high or low spots, provided that the previous operations left enough stock so that the hone can clean up all the irregularities. Honing uses a large contact area at slow speed compared with grinding or fine boring, which use a small contact area at high speed. Because of the combined rotating and reciprocating motion used, a cross hatched pattern is created which is excellent for holding lubrication. Diameters with 0.001 to 0.0001 inch and closer accuracies can be repeatedly obtained in production work. Honing can be done on most materi- als from aluminum or brass to hard- ened steel. Carbides, ceramics and glass can be honed by using diamond stones similar to diamond wheels. Limitations: Honing is thought of as a slow process. However, new ma- chines and stones have shortened hon- ing times considerably. Horizontal honing may create oval holes unless the work is rotated or supported. If the workpiece is thin, even hand pressure may cause a slightly oval hole. . possible. It can re- move as little as 0.0001 inch of stock or as much as 0. 125 inch of stock. However, usually only 0.0 02 to 0. 020 inch stock is left on the diameter for honing. As shown in Figure 18.10, honing. Figure 18.11. 18.5 .2 Vertical Spindle Machines Vertical-spindle honing machines are used especially for larger, heavier work. These all have power stroking at speeds from 20 to 120 FPM. The length. (Fig. 18.9b). The stones come in a wide variety of sizes and shapes. Frequently there are hard- ened metal guides between the stones to help start the hone cutting in a straight line. Cutting