Volume 16 - Machining Part 18 doc

Wear Mechanisms. A 10-year research program on tool materials for high-speed machining concluded that the two major wear mechanisms associated with high-speed machining are high-speed chemical dissolution wear and high-speed diffusion-limited wear (Ref 37). In the range of cutting speeds used in high-speed machining, the chemical dissolution of the tool material into the workpiece is the most important contributor to wear. In essence, the tool material dissolves into the flowing chip. The tool material that is the most resistant to dissolution exhibits the least wear. The second consideration is that of diffusion-limited wear. As the cutting speed is increased, the cutting temperature rises to a level at which seizure of the chip material occurs everywhere on the tool face. This layer of adherent material becomes saturated with tool constituents and serves as a diffusion-boundary layer, reducing the rate of transport of tool material into the chip and consequently the wear rate. The wear phenomenon becomes increasingly diffusion-limited, and the observed dramatic decrease in wear occurs with increasing speed. Because the diffusivity increases exponentially with temperature, a further increase in cutting speed beyond the speed for minimum wear produces a rapid increase in wear rate, as shown in Fig. 10. Fig. 10 Effect of cutting speed on the wear rate of cubic boron nitride tooling. Workpiece: AISI 4340 steel (35 HRC). Source: Ref 37 Cutting Tool Selection. Consideration of the wear mechanisms of tool materials during high-speed machining suggests three possibilities for tool development: • Pick a tool material that is so chemica lly stable with respect to the workpiece that chemical dissolution of the tool does not occur to a significant extent, even at the melting point of the workpiece • Promote the transition to the diffusion limited wear regime • Isolate the tool from the workpi ece rather than a modification of the tool material itself. If a protective layer could be introduced between the tool and the chip, transport of the tool constituents into the chip could be prevented. The use of viscous lubricants in the profile milling o f titanium has proved successful (Ref 38) Tool Systems for Aluminum Alloys. In aluminum alloys, the cutting temperature is limited by the low melting point and high thermal conductivity of aluminum. Chemical effects are minimal, and wear is primarily a result of the abrasion of the tool material by hard second-phase particles. Abrasion resistance increases with the hardness of the tool material; high-speed steel tooling and cemented carbide tooling are suitable for machining most structural alloys, and polycrystalline diamond is preferred for the highly abrasive cast aluminum-silicon (10 to 20% Si) alloys (see the article "Machining of Aluminum and Aluminum Alloys" in this Volume for a discussion of machining high-silicon aluminum alloys). Existing tool materials are adequate for machining aluminum alloys at any conceivable speed, with spindle speed and horsepower design limitations setting the upper limit on cutting speed. Tool Systems for Steel. The oxides are the only potential tool materials that are not limited by their chemical stability. Therefore, the most promising area for tool material development is in improving the toughness and flow strength of the oxides. A second possibility involves the development of tool materials with improved hot strength. The development of tool materials other than cubic boron nitride (CBN) with high hot strength in the range of 1300 to 1400 °C (2400 to 2600 °F) might allow a transition from dissolution-limited to diffusion-limited wear, with a corresponding increase in tool life. Finally, the wear of CBN in the machining of steels of moderate hardness (35 to 50 HRC) should be investigated to determine whether a transition to a low-wear regime (similar to that which has been observed in hard steels) occurs at sufficiently high cutting speeds. If so, machining in the range of 1200 m/min (4000 sfm) and above may be feasible. Tool Systems for Superalloys. The recommendations are similar to those for steel. The oxides are quite chemically stable with respect to nickel and cobalt, making the development of tough oxide materials a priority. In addition, the transition to diffusion-limited wear is known to occur at high speeds; therefore, any new high hot strength compositions will likely find application in the machining of superalloys. A possible example is the class of tool materials based on silicon nitride (Si 3 N 4 ) and alloys of Si 3 N 4 and aluminum oxide (Al 2 O 3 ), referred to as SiAlON (see the article "Ceramics" in this Volume). These tool materials are very effective in machining nickel-base alloys at high speeds. In light of the relatively poor chemical stability of these materials, it is suspected that they represent the second example (in addition to CBN) of a tool material that has sufficient hot strength to enable the very high speed wear transition. Tool Systems for Titanium Alloys. Titanium has low thermal conductivity, low specific heat, and a high melting point. These properties ensure that cutting temperatures will be high at even moderate cutting speeds. In addition, titanium is highly chemically reactive with all known tool materials, causing rapid wear. It is quite likely that the most wear resistant materials tungsten carbide and diamond have already been identified. Therefore, the most promising area for investigation is the development of effective lubrication techniques to reduce the interaction between the tool and the chip. In addition, new tool geometries, such as the ledge tool described below, have also increased the productivity of machining titanium alloys. Alternative Cutting Tool Geometries (Ref 27, 28) Rapid tool wear remains a problem in the machining of titanium and other difficult-to-machine alloys, even though cutting speeds for titanium have been recently increased three- to fivefold through judicious choice of cutter grades and geometries, fluids, and machining parameters. Partial solutions to the tool life problem lie in new tool geometries and the use of rotating cutters. The Ledge Tool. The concept underlying the ledge tool (Fig. 11) is very simple: The tool contains a ledge that is allowed to wear away at a controlled rate with only minimal increase in force. Thus, tool wear has not been reduced, but tool life has been greatly increased. The size of the ledge (overhang) equals the depth of cut desired, and its thickness equals the ultimate flank wear width to be tolerated. In turning, the square tool with the ledged side is brought against the workpiece so that clearance is available between the edge of the ledge and the finished surface of the workpiece (that is, the end cutting edge angle, 1°), as shown in Fig. 11. Because the depth of cut is the same or less than the width of the ledge, only the ledge portion of the tool does the cutting and wearing. The ledge wear back is due to a combination of flank wear and microchipping wear. With this tool, cutting speeds for titanium alloys can be increased five times over conventional speeds, with long tool life ( 30 min) and good finish (Fig. 12). The sparking that accompanies tool wear at high cutting speeds has been eliminated by surrounding the tool/workpiece interface with inert gas (N 2 ) or by submerging the workpiece in a cutting fluid. A combination of a flood lubricant and an inert gas also serves to eliminate sparks and to keep the workpiece cool. Fig. 11 Schematic of ledge tool, which is designed to increase productivity during the high- throughput machining of titanium. (a) Ledge tool mounted on a conventional toolholder. (b) A turning operation using a ledge tool. Source: Ref 27 Fig. 12 Variation of ledge wear back with cutting time for different carbide grades when turning Ti-6Al- 4V at 180 m/min (600 sfm) with a depth of cut of 0.75 mm (0.030 in.) and a feed of 0.023 mm/rev (0.009 in./rev). Source: Ref 27 Ledge tools have also been evaluated in the face milling of forged Ti-6Al-2Sn-4Zr-2Mo. The results have been comparable to those in turning except the rate of ledge wear back was about three times faster in milling; on a microscopic level, the mode of tool wear is the same. Figure 13 shows the variation of ledge wear with cutting time and volume of material removed. Fig. 13 Variation of ledge wear back with cutting time (a) a nd with the volume of material removed (b) for different carbide grades when face milling a Ti-6Al-2Sn-4Zr- 2Mo alloy (36 HRC). Tool: 0.75 mm × 1.0 mm (0.030 in. × 0.040 in.). Cutting speed: 155 m/min (515 sfm). Chip load per tooth: 0.23 mm (0.009 in.). Axi al depth: 0.75 mm (0.03 in.). Source: Ref 28 Another incremental approach for increasing tool life when machining titanium alloys is a new cutting geometry comprised of a high clearance angle (10 to 15°) together with a high negative-rake angle (-10 to -15°). This geometry will also allow the use of a conventional insert on a modified toolholder (Ref 39). Rotary tool machining is another technique that holds promise for extending tool life. In this method, a tool with a circular cutting edge is allowed to rotate about its own axis, either self-propelled by the cutting process or driven externally at the desired speed. As cutting proceeds, new portions of the cutting edge are continuously brought into contact with the workpiece at the cutting zone. Thus, increased tool life can be anticipated because of lower temperatures and reduced chemical reactions at the moving chip/tool interface, and reduced cutting forces can be anticipated because of increased options for modifying the chip formation. Applications of High-Speed Machining (Ref 26) High-speed machining is used in the defense and airframe industries to manufacture aircraft engine propulsion components and in the automobile industry. When high-speed machining is accompanied by higher feed rates and spindle power, the higher spindle speeds allow higher removal rates. Increased productivity, however, necessitates high-speed, high-power, compact spindle designs; low-inertia feed tables; fast feed drives; quick-response numerical control; and a totally integrated machining system. A typical integrated machining system consists of multiple machining cells that will fabricate large machine parts under hierarchical computer control in an effective, cost-efficient manner (Ref 40). Benefits of the integrated machining system include: • Reduced labor requirements • Improved throughput with the application of high-speed and high-throughput machining • Enhanced production flexibility and reduced work-in-process through establishment of a serial production environment • Improved product quality and enhanced industrial base Figure 14 shows an isometric view of an integrated machining system. Such a system can take up to more than 9000 m 2 (100,000 ft 2 ) of floor space. Fig. 14 Integrated machining center for the high-speed and high- throughput machining of aluminum and titanium, respectively. AGV, automated guide vehicle; AS, automated storage; RS, retrieval system. Source: Ref 40 Airframe and Defense. Most airframe manufacturers have implemented high-speed machining. Its primary application is in end milling with small-size cutters. Aluminum alloys are the common work materials used, so tool wear is not a limitation, especially with carbide cutters. The ideal candidates for high-speed machining are parts whose machining time is a significant fraction of the floor-to-floor time. The ideal cuts are long, straight ones that enable the use of high feed rates and consequently high removal rates. Although some parts may fall under this category, there are others that are suitable for high-speed machining but require extensive pocketing and complex contouring. Both pocketing and contouring can involve frequent accelerations and decelerations in feed rates. Tool-changing time can be reduced by using as few cutters as possible, eventually using only one, smallest-diameter cutter capable of generating all the radii on the part. Modifying the design of the part may enable the use of high-speed machining and may be desirable if the modification can be achieved without compromising the part performance specifications. Further, although high-speed steel tools may be satisfactory for some applications, carbide cutters will not only extend tool life but also provide about three times the stiffness, which is essential for machining long, thin webs with slender end mills. The integrated machining system shown in Fig. 14 is used to machine both aluminum and titanium. For the high-speed machining of aluminum parts, metal removal rates of 3300 cm 3 /min (200 in. 3 /min) are possible using machines with up to 55 kW (75 hp) spindle drives and spindle speeds approaching 20,000 rev/min. For the high-throughput machining of titanium alloys, metal removal rates of the order of 165 cm 3 /min (10 in. 3 /min) using 95 kW (125 hp) spindle drives and up to 833 rev/min spindle speeds are possible. Many high-speed machining applications, however, do not require such machine capabilities. For example, a 15 kW (20 hp), 20,000 rev/min spindle is used to machine A7 wing spars made of 7057-T6 aluminum (Ref 26). The feed rate is 15,000 mm/min (600 in./min) on long, external tapered flanges and 7500 mm/min (300 in./min) in pocket areas; the metal removal rate is 1300 cm 3 /min (80 in. 3 /min). Retrofitted machining centers with 20 kW (26 hp), 18,000 rev/min high-speed spindles are used for the high-speed machining of 7075-T6 aluminum parts for the Trident missile (Ref 26). The worktable has a feed capacity of 5000 mm/min (200 in./min). The high-speed system incorporates such safety features as a double lock for the toolholder and sensors that can shut down the machine quickly if tool breakage creates an imbalance. A major commercial airline manufacturer uses six-axis machining centers for the contour milling of aluminum honeycomb for engine nacelles (Ref 26). The system has a 3.3 m (11 ft) diam rotary table capable of a full 360° rotation. The spindle is mounted on the gantry and can tilt 240° and rotate 360°. A unique feature of this system is the use of a graphite-fiber reinforced plastic ram. This ram provides the required stiffness and reduced weight necessary for the high feed rates of low-inertia parts. The high-speed machining systems utilize high-speed (24,000 rev/min) 11 kW (15 hp) spindles. Aircraft Engine Propulsion. Nickel-base superalloys and titanium alloys are the work materials most often used in aircraft engine propulsion components. These cause rapid tool wear at high speeds, which constitute a major limitation in the high-speed machining of propulsion parts. Until recently, the cutting speeds possible with nickel-base superalloys were about 30 m/min (100 sfm) with carbide cutters and about 9 m/min (30 sfm) with high-speed steel tools. The development of CBN and ceramics such as hot-pressed Al 2 O 3 plus TiC, SiAlON, and silicon carbide (SiC) whisker- reinforced Al 2 O 3 has made possible an increase in cutting speeds from 30 to 180 m/min (100 to 600 sfm) for machining nickel-base superalloys. These ceramic tool materials are much tougher and more consistent in performance than the ceramics introduced in the 1950s. SiAlON and SiC whisker-reinforced Al 2 O 3 are recommended for roughing, and hot- pressed Al 2 O 3 -TiC for finishing applications. Although new, tougher ceramic tool materials, perhaps based on ceramic composites, will undoubtedly be developed in the future, it is unlikely that cutting speeds will exceed 600 m/min (2000 sfm), because tool wear will continue to be a limitation. As described earlier in this article, innovative tool designs and geometries, such as the ledge tool, have improved productivity in titanium machining. Automobile Industry. High-speed machining in the automobile industry is performed on gray cast iron and aluminum alloys, especially the high-silicon type. Silicon nitride ceramic and polycrystalline diamond are the important tool materials that permit higher speed with longer tool life. Gray cast iron can be machined at a speed of about 1500 m/min (5000 sfm) with Si 3 N 4 tools, and aluminum alloys with high silicon content (10 to 20%) can be machined at about 750 m/min (2500 sfm) with polycrystalline diamond tools. In working with these materials, the current high-speed machining systems need to provide more power and stiffness and improved chip-handling means, controls, and safety features. High-speed machining with these materials may require spindle power from 150 to 375 kW (200 to 500 hp). Chip removal rates can reach 16,000 cm 3 /min (1000 in. 3 /in.), necessitating efficient chip disposal systems. Because products are mass produced in this industry, the nonmachining time should be minimal. Implementing High-Speed Machining (Ref 26) There are several factors to be considered by companies planning to employ high-speed machining systems. Whether high-speed machining is economically appropriate to the application, the relative value of various systems, and how well the system can be integrated into existing operations must all be evaluated. Other areas to consider are the research and development support required, system reliability and maintenance, overall safety aspects, general acceptance on the manufacturing shop floor, capital and other investment costs, the skills required, corporate goals, and the financial health of the company. The overall goal should be to improve productivity, reduce costs, and produce parts of a given size, shape, finish, and accuracy at competitive cost. Productivity and overall costs depend on cutting time, noncutting time, labor, and overhead. High-speed machining can decrease cutting time by increasing cutting speed. Noncutting time can be decreased by the automatic loading and unloading of parts, automatic tool changing, in-process inspection, in-process sensing, and adaptive control. Labor costs can be decreased because with high-speed machining fewer operators are needed to work on fewer, more efficient machine tool systems. Similarly, overhead costs can be reduced by operating fewer, more efficient machine tools on two or more shifts and during holidays and at night. In order to evaluate the influence of cutting speed on productivity, floor-to-floor time can be regarded as the sum of the cutting time and the noncutting time. Figure 15 shows the percentage decrease in floor-to-floor time with an increase in cutting speed for different ratios of cutting time to floor-to-floor time, using conventional, currently used speeds of whatever the value may be for a given material and process as a base. When the cutting time is a significant fraction of the floor-to-floor time and when tool wear at high speed is not significant (solid lines, Fig. 15), the cutting speed can be increased considerably to effect a significant reduction in floor-to-floor time. If, however, this ratio is low (bottom curve, Fig. 15), an increase in cutting speed by even an order of magnitude or more will result in only a marginal decrease in floor-to-floor time. In this case, unless the noncutting time could be decreased significantly, high-speed machining would not be advantageous. Fig. 15 Variation of percent decrease in floor-to-floor time with cutting speed. See text for details. Source: Ref 26 When an increase in cutting speed does not contribute to a significant reduction in floor-to-floor time and when tool wear is significant at high speeds, as in the machining of titanium alloys (dashed line, Fig. 15), high-throughput machining can be adopted to reduce noncutting time and to increase productivity. Similarly, where heavier cuts can be made on the part without affecting either the part finish and accuracy requirements or the cutting tool performance, greater depths of cut (as in high removal rate machining) are recommended instead of higher speed (see the article "High Removal Rate Machining" in this Volume). Future Needs (Ref 1). High-speed machining can be cost effective only if other aspects of machining, including reduction of noncutting times and labor costs, can also be improved. For this reason, automated machining, such as the integrated machining system discussed earlier, is receiving much attention. Dynamic in-process inspection is an integral part of automated machining. Sensors and diagnostics have been identified as critical to effective in-process inspection. Recently, proximity sensors for measuring tool wear, vibration sensors for measuring tool-touch (between cuts), and lasers for measuring workpiece dimensions have been studied. The integrated machining system shown in Fig. 14 utilizes a coordinate-measuring machine as its inspection module. Some of the specific needs for the increased use of high-speed machining are: • Integrated sensing techniques for monitoring machining processes • Sensors and diagnostics for detecting tool breakage (including incipient tool breakage) • Linkage of signal analysis to tool wear mechanisms and machining variables • Self-teaching adaptive control systems • Faster response in machine tool controls when machining aluminum • Better cutting tools (composition and geometry) for machining titanium • Water-base cutting fluids for machining titanium • More reliability and predictability in cutting tools • Greater machine tool rigidity for increased productivity • More notch-resistant cutting tools for superalloys In addition to the above-mentioned technical needs, significant reductions in noncutting time can be achieved by procedures that to a large extent involve improved management. These procedures include setup, part load/unload, queing, chip cleanup, tool change, maintenance, scheduling, and general operator efficiency. Until improvements in these procedures are achieved, cutting times will remain only a small fraction of the overall manufacturing sequence, and the full advantages of high-speed machining will not be realized. References 1. D.G. Flom, High-Speed Machining, in Innovations in Materials Processing, G. Bruggeman and V. Weiss, Ed., Plenum Press, 1985, p 417-439 2. B.F. von Turkovich, Influence of Very High Cutting Speed on Chip Formation Mechanics, in Proceedings of NAMRC-VII, 1979, p 241-247 3. The 12th American Machinist Inventory of Metalworking Equipment 1976-78, Am. Mach., Dec 1978, p 133-148 4. R.I. King and R.L. Vaughn, A Synoptic Review of High- Speed Machining from Salomon to the Present, in High-Speed Machining, American Society of Mechanical Engineers, 1984, p 1-13 5. R.L. Vaughn, Ultra-High Speed Machining, Am. Mach., Vol 107 (No. 4), 1960, p 111-126 6. R.L. Vaughn, "Recent Developments in Ultra- High Speed Machining," Technical paper 255, Vol 60, Book 1, Society of Manufacturing Engineers, 1960 7. R.L. Vaughn, "Ultra-High Speed Machining Feasibility Study," Final Report, Contract AF 33 (600) 3 6232, Production Engineering Department, Lockheed Aircraft Corporation, June 1960 8. R.L. Vaughn, L.J. Quackenbush, and L.V. Colwell, "Shock Waves and Vibration in High- Speed Milling," Technical Paper 62-WA-282, American Society of Mechanical Engineers, Nov 1962 9. R.L. Vaughn and L.J. Quackenbush, "The High- Speed Milling of Titanium Alloys," Technical Paper MR 66-151, Society of Manufacturing Engineers, April 1966 10. R.I. King and J. McDonald, Product Design Implications of New High-Speed Milling Techniques, Trans. ASME, Nov 1976 11. F.J. McGee, "Final Technical Report for Manufacturing Methods for High- Speed Machining of Aluminum," Technical Registry No. 6089, Manufacturing Methods and Technology Branch (DRDMI- EAT), U.S. Army Missile Research and Development Command, Feb 1978 12. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F33615-79-C-5119, GE Report No. SRD-80-018, Feb 1980 13. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Annual Technical Report, Air Force Contract No. F33615-79-C-5119, GE Report No. SRD-80-118, Aug 1980 14. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F33615-79-C-5119, GE Report No. SRD-81-018, Feb 1981 15. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F33615-79-C-5119, GE Report No. SRD-81-062, Aug 1981 16. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F33615-79-C-5119, GE Report No. SRD-82-027, Feb 1982 17. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Annual Technical Report, Air Force Control No. F33615-79-C-5119, GE Report No. SRD-82-070, Aug 1982 18. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F33615-79-C-5119, GE Report No. 83-SRD-012, Feb 1983 19. D.G. Flom, R. Komanduri, and M. Lee, "Review of Past Work in High- Speed Machining," Paper presented at the TMS-AIME Meeting (Louisville, KY), The Metallurgical Society, Oct 1981 20. R. Komanduri and J. Hazra, A Metallurgical Investigation of Chip Morphology in Machining an AISI 1045 Steel at Various Speeds up to 10,100 SFPM, in Proceedings of NAMRC-IX, Society of Manufacturing Engineers, 1981 21. R. Komanduri and B.F. von Turkovich, New Observations on the Mechanism of Chip Formation When Machining Titanium Alloys, Wear, Vol 69, 1981, p 179-188 22. R. Komanduri, "Titanium A Model Material for Studying the Mechanism of Chip Formation in High- Speed Machining," Paper presented at the TMS- AIME Meeting (Louisville, KY), The Metallurgical Society, Oct 1981 23. R. Komanduri, Some Clarifications on the Mechan ics of Chip Formation When Machining Titanium Alloys, Wear, Vol 76, 1982, p 15-34 24. R. Komanduri and R.H. Brown, The Mechanics of Chip Segmentation in Machining, J. Eng. Ind. (Trans. ASME), Vol 103, Feb 1981, p 33-51 25. R. Komanduri, T. Schroeder, J. Hazra, B.F. von Turkovich, and D.G. Flom, On the Catastrophic Shear Instability in High-Speed Machining of an AISI 4340 Steel, J. Eng. Ind. (Trans. ASME), Vol 104, May 1982, p 121-131 26. R. Komanduri, High-Speed Machining, Mech. Eng., Dec 1985, p 65-76 27. R. Komanduri, D.G. Flom, and M. Lee, Highlights of the DARPA Advanced Machining Research Program, J. Eng. Ind. (Trans. ASME), Vol 107, Nov 1985, p 325-335 28. D.G. Flom, "Advanced Machining Research Program (AMRP) Final Technical Report," Air Force Co ntract No. F33615-79-C-5119, GE Report No. 83-SRD-040, Oct 1983 29. D.R.C. Durham, "Physical Metallurgy of Deformation Localization," Topical report prepared for DARPA, UV-81-DD1, Aug 1981 30. B.F. von Turkovich, Influence of Very High Cutting Speed on Chip Formation Mechanics, in Proceedings of NAMRC-VII, 1979, p 291-297 31. D.R.C. Durham and B.F. von Turkovich, Material Deformation Characteristics at Moderate Strains and High Strain Rates, from Metal Cutting Data, in Proceedings of NAMRC-X, 1982, p 324-331 32. B.F. von Turkovich and D.R.C. Durham, Machining of Titanium and Its Alloys, in Proceedings of the Symposium on Advanced Processing Methods for Titanium (Louisville, KY), The Metallurgical Society, 1981, p 241-256 33. C.A. Brown, A Practical Method for Estimating Machining Forces from Tool-Chip Contact Length, Ann. CIRP, Vol 32 (No. 2), 1983, p 91-96 34. G. Meir, J. Hashemi, and P.C. Chou, "Finite-Element Simulation of Segmented Chipping in High- Speed Machining," Report MR88-120, Society of Manufacturing Engineers, 1988 35. T.A. Schroeder and J. Hazra, High Speed Machining Analysis of Difficult-to- Machine Materials, in Proceedings of NAMRC-IX, Society of Manufacturing Engineers, 1981 36. J.P. Kottenstette and R.F. Recht, Ultra-High-Speed Machining Experiments, in Proceedings of NAMRC-X, 1982, p 263-270 37. B.M. Kramer, On Tool Materials for High-Speed Machining, in High-Speed Machining, American Society of Mechanical Engineers, 1984, p 127-140 38. J. Jensen, "High-Speed Milling of Titanium," M.S. thesis, Massachusetts Institute of Technology, 1983 39. R. Komanduri and W. Reed, Jr., Evaluation of Carbide Grades and a New Cutting Geometry for Machining Titanium Alloys, Wear, Vol 92, 1983, p 113-123 40. Integrated Machining System An Overview, L TV Aircrafts Products Group, Military Aircraft Division, 1988 High Removal Rate Machining Introduction HIGH REMOVAL RATE (HRR) MACHINING involves the use of extremely rigid, high-power, high-precision machines, such as roll turning lathes, to achieve material removal rates far beyond the capacity of conventional machine tools. Material removal rates as high as 6000 cm 3 /min (370 in. 3 /min) have been reached using multiple ceramic cutters on high-carbon (0.8% C) heat treated cast steel rolls. This article will review the machine requirements, cutting parameters, and applications associated with HRR machining. Additional information can be found in Ref 1, 2, 3, 4, and 5. Acknowledgement The editors would like to thank Jack Binns, Sr., inventor of the "Super-Lathe," for his valuable contributions to this article. Machine Requirements The key to success in HRR machining is extreme rigidity in machine, workpiece, and cutting tool setups. Figure 1 shows a "Super-Lathe" capable of making cuts as deep as 25 mm (1 in.) at feeds up to 1.3 mm/rev (0.050 in./rev) on hardened steel and chilled cast iron rolls. Metal removal rates as high as 4500 kg/h (10,000 lb/h) can be achieved with such machines, which have power ranges from 100 to 450 kW (150 to 600 hp) and can produce up to 400 kN (95,000 lbf) of output torque at the spindle. Workpieces of softer materials can also be turned, producing large, segmented chips, as shown in Fig. 2. Fig. 1 Superlathe used for HRR mac hining. This 300 kW (400 hp) machine, which is computer numerically controlled, can perform rough cuts on 1290 mm (50.75 in.) diam rolls and finishing cuts on workpieces up to 1200 mm (47.25 in.) in diameter at maximum roll lengths of 7.8 m (25 ft, 7 in.). Courtesy of J. Binns, Sr., Binns Machinery Products [...]... X-, Y-, and Z-axes The Z-axis is perpendicular to both X and Y in order to create a right-hand coordinate system For example, in a vertical drilling machine (as one faces the machine), a +X command moves the worktable from left to right, a +Y command moves it from front to back, and a +Z command moves the drill up, away from the workpiece The X-, Y-, and Z-axes are always assigned to create a right-hand... of considerable importance The part programmer must be familiar with the function of NC machine tools and machining processes and must decide on the optimum sequence of operations The part program can be written manually, or a computer-assisted language, such as the automatically programmed tool language, can be used In NC machines, the part dimensions are presented in part programs by integers In CNC... Tool and Manufacturing Engineers, 1964 4 J Binns, Sr., Super-Lathe for Roll Turning, Iron Steel Eng., Oct 1961 5 D.G Flom, Ed., "Advanced Machining Research Program," Annual Technical Report, Air Force Contract No F3361 5-7 9-C-5119, General Electric Co Report No SRD-8 2-0 70, Aug 1982 Numerical Control Yoram Koren, The University of Michigan Introduction THE METAL CUTTING INDUSTRY changed drastically during... higher-quality parts and makes possible the accurate manufacture of more complex designs without the usual loss in accuracy encountered in conventional manufacturing Producing a part that must be cut with an accuracy of 0.01 mm (0.0004 in.) or better may take a considerable amount of time using conventional methods In numerical control using single-axis motion, obtaining such accuracies is the state-of-the-art,... standard RS-273-A ("Interchangeable Perforated Tape Variable Block Format for Positioning and Straight Cut Numerical Controlled Machines") provides a line format for point-to point (PTP) and straight-cut NC machines A typical line according to this standard is as follows: N102 G01 X-52000 Y9100 F315 S717 T65432 M03 (EB) The letter and the number that follows it are referred to as a word For example, X-52000... Williams, Numerical Control and Computer-Aided Manufacturing, John Wiley & Sons, 1977 4 N.O Olesten, Numerical Control, Wiley-Interscience, 1970 5 M.P Groover, Automation, Production Systems, and Computer-Aided Manufacturing, Prentice-Hall, 1980 6 J Pusztaai and M Sava, Computer Numerical Control, Reston Publishing, 1983 7 Y Koren, Robotics for Engineers, Mc-Graw-Hill, 1985 8 J.T Beckett and H.W Mergler,... selected based on the worst-case conditions for that particular part Fig 2 Comparison of feed rates in adaptive and conventional (nonadaptive) milling when cut varies (a) Variable depth (b) Variable width Source: Ref 3 Some typical results demonstrating the economic benefits of adaptive control are given in Fig 3 These compare machining costs in adaptive and conventional (non-adaptive) machining and show... the machining of stainless steel with a 0.25 mm (0.01 in.) tolerance and a cut 2.5 mm (0.1 in.) deep and 25 mm (1 in.) wide Bar graphs (c), (d), and (e) compare a Bendix system with nonadaptive methods when variable-depth cuts (top graph) and a 1 mm (0.05 in.) depth of cut (bottom graph) are used Machining conditions are as follows: (c) machining of 4140 steel with a high-speed steel cutter, (d) machining. .. of the slash and contains modifiers to the major portion For example, a point can be defined by: POINT/X-coordinate, Y-coordinate, Z-coordinate An example of a corresponding geometric statement is: PT2 = POINT/3,4 where PT2 is the symbolic designation of a point whose X-coordinate is 3 and whose Y-coordinate is 4 A line can be defined by a point and a tangent circle (Fig 3): LINE/symbol for a point,... in machining The objectives of these adaptive controls are to increase productivity in rough machining and to improve part accuracy in fine cutting (Ref 13) The article "Adaptive Control" provides a more thorough discussion of adaptive control for machine tools References 1 Y Koren, Computer Control of Manufacturing Systems, McGraw-Hill, 1983 2 P Ranky, Computer Integrated Manufacturing, Prentice-Hall, . F3361 5-7 9-C-5119, GE Report No. SRD-8 0-1 18, Aug 1980 14. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F3361 5-7 9-C-5119,. SRD-8 1-0 62, Aug 1981 16. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F3361 5-7 9-C-5119, GE Report No. SRD-8 2-0 27,. F3361 5-7 9-C-5119, GE Report No. SRD-8 1-0 18, Feb 1981 15. D.G. Flom, Ed., "Advanced Machining Research Program (AMRP)," Semi- annual Technical Report, Air Force Contract No. F3361 5-7 9-C-5119,