314 Metal-Products Manufacturing Chap. 7 where d = grid circle diameter before pressing d; = major diameter of ellipse after pressing d, = minor diameter of ellipse after pressing It is frequently more convenient to express the resulting principal strains in terms of engineering rather than true or natural strain definition-that is, dj-d d,-d et=-d- and eZ=-d- If the analysis is made for the circles immediately adjacent to necked or frac- tured regions. a plot of major strain (el) against minor strain (ez) will yield a curve that separates the strain conditions for successful pressings from those that result in weakness or fracture (i.e., forming limits will be established). Thus. as indicated in the experimental press shop data of Figure 7.31, "safe" regions and "fail" regions for different materials and thicknesses can be established, It is informative to consider some day-to-day uses of the fanning limit diagram, The die setter can quickly determine, from a single pressing on a gridded sheet, whether a new component with its given set of tools is going to be easy, hard, or 140 0.35mm Thickness 1.95= 0.93mm 20 00 ~ w m ~ 00 COmpressive Tensile MinorsuIface strain (%) Fipre 7.31 Forming limit diagram. Different sheet thicknesses shown on right (data from Rose, 1974). 7.6 Mana_gementof Technology 315 impossible. Then it might be possible to argue quantitatively for a design modifica- tion or a change of material. Or, as discussed previously, it might be possible to move from failure to success by increasing one of the strain components through a slight change in die geometry. In many cases, special lubricants containing molybdenum disulfide can be locally applied to critical areas of the pressing, just to change the strain distribution near potential thinning and fracture points. In a different scenario it might be found that the material being used is too good and that a cheaper grade of sheet could be introduced. By keeping a satisfactory reference pressing, the die setter can also locate a source of trouble if,later on in the production run, the press gets out of adjustment or the properties of the sheet change. Finally, the training of press operators and die setters can be made considerably easier and quicker if gridded blanks are available for reference and demonstration. 7.6 MANAGEMENT OF TECHNOLOGY 7.6.1 Precision Manufacturing Services and Their Clients Today's clients for "high-tech" machine shops and metal fabrication shops include the medical industry, the biotechnology industry, mold-making industries that create the plastic casings of electromechanical consumer products, the aerospace industry, and the special-effects companies for Hollywood's movie industry. Small-batch high-precision machine shops are also the key suppliers of equip- ment for the semiconductor industry (Chapter 5) and PCB industries (Chapter 6). The stepper machines that increment the masks in photolithography are an excellent example of $1to $2 million machines that are initially fabricated by metal machining. This review of the "client base" for machining brings out a key historical obser- vation that will hold true in the future. Namely, the machine tool industry is a key building block for industrial society, since it provides the base upon which other indus- tries perform their production. This fact was especially true in the decades that fol- lowed the first industrial revolution (approximately 1780 to 1820). Throughout the period to the 19208, the machine tool industry was the foundation for the ship- building, railroad, gun-making, construction, automobile, and early aircraft industry. Since then it has also become the foundation for semiconductor fabrication and all forms of consumer product manufacturing. As these devices become more specialized and miniaturized, the construction of equally specialized equipment will still be performed at these "high-tech" machine shops and metal fabrication shops. Given this range of services, it is not surprising that a new awareness of preci- sion and optimization is emerging. Also, processes such as laser machining that were once regarded as specialized are now being used on a day-to-day basis for precision hole drilling (Chryssolouris, 1991). Overall, best practices include rapid links from design to G and M codes as indicated in Section 7.2.5, highly tuned economically operated machine tools as indi- cated in Section 7.4, and a greater appreciation for tooling design as indicated in Sec- tion 7.5.6. Deeper understandings of the physics of sheet-metal forming and 31. Metal-Products Manufacturing Chap. 7 machining-for example, the prediction of the cutting forces in Section 7.3.1-result in sensible investments in machine tools, forming machines, and rolling mills. 7.6.2 Open-Architecture Manufacturing At the same time, more sophisticated control of the metal (cutting and metal) forming machinery is allowing these more traditional processes to keep pace with the SFF technologies described in Chapter 4. Some new developments in the last decade that have given more flexibility to CNC machinery controllers are now described. Today, factory-floor CNC machines are supplied by the machine tool compa- nies with "closed controller architectures." Fanuc, Mazak, and Cincinneti-Milaoron are some of the most often seen controllers. Specifically this means that a user or pro- grammer is constrained to work with the predefined library of G and M codes (now the RS 274 standard) that are supplied with each machine tool company's vendor- specific controller. This results in limited library functions, written in local fonnats. These are adequate today for routine production machining but they are not "open" to any arbitrary third-party software developers able,say, to supply C-based routines for new CAD geometries or new machining sensors coming onto the market. A broader "openness" to any outside third-party developer is one of the design goals of several U.S.government projects (Schofield and Wright, 1998; Greenfeld et al., 1989).The aim is to improve the productivity of the U.S. machine tool industry, not just by focusing on machine tool companies alone but also by expanding market opportunities for CAD companies, sensor companies, diagnostic software devel- open. and all ancillary product suppliers. The paradigm is the vastly expanding PC industry. It is anticipated that by using generic products and open systems, a large number of third-party product s willbe supported commercially, hence increasing the productivity of standard CNC machines and flexible manufacturing systems. "Open-architecture" machinery control (Figure 7.32) will allow faster access between high-level computer aided design (CAD), computer aided process planning (CAPP), and computer aided manufacturing (CAM) . •As a first example, especially for mold making and some aerospace parts, it is crucial to be able to take interesting, highly complex geometries from CAD and convert them into cutting tool motions. For example, a particular goal of the work by Hillaire and associates (1998) is the ability to take NURBS (nonuniform rational B-spline) curved surfaces from CAD and execute them on a standard three-axis milling machine. By contrast, with "closed architec- tures" it is likely that the user would be confined to the geometries and stan- dard interpolations in the machine tool company's lib:rary. • As a second example, open architectures allow a machine tool to automatically compensate for errors in the positioning of the workpiece and make possible the active control of the machining process by accepting inputs from external sensors-c-sometfung that the previous generation of controllers could not do. This results in faster production, more flexibility, and more opportunity for on- machine inspection and quality control. More flexibility in sheet forming can also be created with controllable die surfaces (Walczyk and Hardt, 1998). 7.6 Management of Technology 317 Design Tool path Cutter locations t ( Servo loop ) Voltage to drives Control signals Sensor information ( Machine tool ) F1glIre 7.3Z Control loops for open-architecture machine tools. Sensors and feedback are shown at six levels on the right (I-VI): (I) at tbe lowest level. vibration and force sensors monitor levels, and changes in speed or feed can be made "on the fly"; (II) at the next level, "on-the-machine touch probing after machining" can suggest changes in the cutter locations to compensate for form errors in the verticality of pocket walls; (UI) at the next level. undesirable bum can be compensated for by changing the entry and exit angles of the milling cullen: (JV) at Ihe ne1[1level_now within the process planing domain-it is often desirable to reallocate the proportion of roughing versus finishing cuts so that the last "slab" milled into the bottom of a pocket creates the desired surface fmish; (V) at the next level-e-still within the process planning domain-it is often desirable to reorder the sequence in which the several features of the part are cut, in order 10 improve accuracy or fixturability; (VI) at the design level, NURBS and new graphics routines can be directly sent to the open-architecture machine. Path planning Microplan Macroplan Design Constraint informatior Design features Plan Machine Ordered slabs Machining features Reference generation 318 Metal-Products Manufacturing Chap. 7 Since the mid·1990s.open-architecture machine tool controllers have thus been ccnuuerclally launched by some industrial companies including Hewlett- Packard, Allen-Bradley, Delta Tau, and Aerotech [e.g., see Delta Tau, 1994). Such new products are usually PC based, use either the UNIX or NT operating systems, and are open to third-party suppliers of sensors, diagnostic systems, programming interfaces, and software tools. Thrgeted at sophisticated users in industries such as aerospace, these open- architecture machine tools will be very useful as stand-alone machines, and they will provide powerful, networked-based machines for agile manufacturing. As individual systems they will be capable of producing small lot sizes of components with high accu- racy.They will also be the factory-floor building blocks of systems in which machines can communicate "bidirectionally" with the rest of the factory. Cole (1999) has empha- sized that such bidirectional knowledge exchange is the key to implementing TQM, lIT, and 6 sigma procedures, for the total integrati.on of quality in the factory. To close with an analogy, a banking machine or a telephone is useful not only because the machine itself is sophisticated but because it has been designed to allow bidirectional knowledge exchange all over a global network. Access to the network and all its services is actually more important than the local characteristics of the machine itself 7.7 GLOSSARY 7.7.1 Cemented Carbide Cutting Tools A family of sintered cutting tools that use a few percent of cobalt as the binder phase and a variety of hard carbide particles as the high-temperature, abrasion resistant phase.These may be tungsten carbide, titanium carbide, or tantalum carbide. Com- monly, these cemented carbide materials are additionally coated with thin, abrasion- resistant layers. 7.7.2 Ceramic and Cubic Boron Nitride (CBNI Cutting Tools A family of hard, nonmetallic stntered cutting tools that have higher abrasion resist- ance than carbides but relatively low toughness. 7.7.3 Chatter A machine tool vibration initiated by resonance with a machine tool element but worsened as the part surface becomes undulated and regenerative chatter occurs. 7.7.4 Chuck The clamping device in a lathe. 7.7.5 Cup The test part shape in methods that assess the stretching (Erichsen) and drawing (Swift) characteristics of sheets of metal. 7.7 Glossary 319 7.7.6 Deep Drawing Essentially the same as drawing hut often related to processes that use several repeated drawing operations so that long products can be formed. 7.7.7 Drawing The general term for sheet-metal forming and more specifically the behavior of material in the flange of a product that gets drawn into the die wall. 7.7.8 Deformed/Undeformed Chip Thlckne •• The geometry of machining can be described by the chip dimension (t e ) and the uncut dimension (t). If the rake angle is zero, then tan 4J = tlt e . 7.7.9 Depth-ol-Cut (dl In turning operations, the depth-of-cut is measured radially into the bar being machined. In milling it is the vertical depth into the block. 7.7.10 Feed R_If) In turning, the feed rate (f) is measured longitudinally along the bar, usually in mil- limeters or inches per revolution of the bar. In milling, the feed rate is usually the table speed in millimeters or inches per minute, so that it represents the relative motion between the tool and part in the plane being machined. 7.7.11 Fixture A work-holding device that supports, clamps, and resists the cutting forces between tool and work. 7.7.12 Flank Face/Flank Angle On a turning tool, the face is given a clearance angle at the side of a tool. This pre- vents it from rubbing on the shoulder being cut (usually to the left of the tool). 7.7.13 Force. The main cutting force isF c ' acting on the tool face from the advancing tool in milling or the advancing work in turning. The tangential force, F n acts normal to the main cutting force. 7.7.14 Form Error Ideally the walls of a milled pocket should be vertical. However, form errors often occur because of fixture deflections, part deflections, or tool deflections, In the latter case, the walls often exhibit a "ski-slope" appearance related to the tool deflection shape. Similar form errors can occur in turning if the bar is slender and pushes away from the tool. Metal-Products Manufacturing Chap. 7 1.7.15 Forming Limit Diagram A plot of minor strain, on a +/-x axis, and major strain, on ay axis.The strains are measured from small circles that are etched onto a sheet prior to the test. The circles might become ellipses or bigger circles depending on the deformation that occurs.The diagram also notes at which combination of major and minor strain failure by tearing of the sheet occurs. This locus of failure points is the forming limit curve or diagram. 7.7.16 G Cod •• The standard low-end machine tool command set that gives motion; for example, G1 = linear feed. 7.7.17 Jig A modified work-holding device or fixture that additionally guides the cutting tool into ~ desired location on the surface of the part. 7.7.18 Machinability A relative term that judges the ease ofmachining of differentmateriaIs. Usually,the tool wear or tool life is the main objective function that appraises relative machinability. 7.7.19 M·Cod•• The standard low-end command set for machine tool operations that are not related to x, y, or z motion of the axes; for example, M6 = call tool into spindle. 7.7.20 Milling A machining process suited to prismatic parts. 7.7.21 nValue (the Work-Hardening Coefficient) Defines the slope of the stress-strain curve plotted on log axes. Physically, large n values occur with materials that work-harden a great deal during deformation. Austenitic stainless steels are in that category. 7.7.22 Power The power supplied by the lathe or mill is usually measured by the product of the main cutting force and cutting velocity. 7.1.23 Rake Angle The rake angle is measured from the face of the tool to the normal to the surface being cut. 7.7.24 RValue Defines a ratio between the strain in the plane of a sheet and the strain in the thick- ness of the sheet. Large R values indicate good drawability because the material will extend and draw down without thinning in the thickness direction. 7.7 Glossary 321 7.7.25 Roll Gap The area between the rolls where plastic deformation of the strip is occurring. 7.7.28 Roll Load The force between the rolls related to the deformation of the strip. 7.7.27 Shear Plane Angle, $ The shear angle $ is not a single plane but a narrow zone identifiable in micrographs. The shear angle is then measured between this zone and the direction of the tool/work velocity factor. • Primary shear: the main shear process that creates the chip • Secondary shear: the shear zone between the bottom of the chip and the tool face 7.7.28 Strain Defined as the extension divided by the original length: • Engineering strain: the extension divided by the original length • True strain: the extension divided by the current length as deformation increases 7.7.29 Stress Defined as the load divided by the area of contact of the two opposing load bearing elements: • Engineering stress: the load divided by the original area •True stress: the load divided by the current area as deformation increases 7.7.30 Stretching The deformation mode in sheet-metal forming in which an original square element of the sheet surface is deformed in both the x and y dimensions to become larger in all directions. 7.7.31 Surface Finish. Surface Roughness Cutting tools leave distinctive markings on the surface that are a function of feed rate and the nose radius of the cutting tool edge (see Armarego and Brown, 1969).A pro- filometer can be used to trace over the surface and measure the roughness. (Imagine the stylus of an old-style record player being dragged across the tracks rather than following the tracks.) The surface roughness can be measured by the arithmetic mean value (R,,)- which used to be known as the centerline average-or the root-mean-square average (R q ). To obtain these values, imagine that a cross section is like a rough or uneven sine wave about a centerline datum. The R" value is found by taking a large number, 322 Metal-Products Manufacturing Chap.7 A r1YCl\ f, h ij kl0 !II ~B lIbCdeUIW \V " Center (datum) line Figure7.]3 Surface finish. n, of amplitude or ordinate values of the rough sine wave (a + b + c + + n) and dividing them by n. The R q value is obtained by taking the square root of [(a 2 + b 2 + c 2 + + n 2 )/n j.Typical values of R" might be 125 rnicroinches for standard surfaces and 60 to 80 microinches for smoother, well-finished surfaces (Figure 7.33). 7.1.32 Taylor Equation (VT"=C1 The result of replotting cutting speed (V) against the tool life data (non log-log axes. 7.7.33 Tool Ute tn UsuaUy defined by 0.75 millimeter (0.03 inch) of flank wear. 7.7.34 Turning A machining process suited to. axisymmetrical parts. 7.7.35 Wear Mechanisms Tool wear by abrasion, attrition, and fracture occurs at lower cutting speeds. At higher speeds diffusion occurs especially at the rake face, where high-temperature conditions exist. 7.8 REFERENCES Armarego, E. 1. A. and R. H. Brown. 1969. The machining of metals. Englewood Cliffs, NJ: Prentice-Hall. Asada, H., and A. Fields. 1985. Design of flexible fixtures reconfigured by robot manipulators. In Proceedings of the Robotics and Manufacturing AutomationASME Winter Annual Meeting, 251-257. Backofen, W.A.1972. Deformation processing. Reading, MA:Addison Wesley. Cbryssolouris, G. 1991. Laser machining. New York: Springer-Verlag. Cole, R. E. 1999. Managing quality fads: How American business learned to play the quality game. New York and Oxford: Oxford University Press. Cook, N. H. 1966. Manufacturing analysis. Reading, MA: Addison-Wesley. Delta Tau Data Systems Inc. 1994. Product Literature: "PMAC-NC." Northridge, CA. Ernst, H., and M. E. Merchant. 1940-1945. In particular see M. E. Merchant 1945. The mechanics of the metal cutting process. Journal of Applied Physics 16: UJ7-275. 7.8 References 323 Goodwin, G. M. 1968. Application of strain analysis to sheet metal forming problems in the press shop. In Proceedings of the Fifth Biennial Congress 1.UD.R.G., Torino, Italy. Greenfeld, I., E B. Hansen, and P. K. Wright. 1989. Self-sustaining, open-system machine tools. In Proceedings oftke 17th North American Manufacturing Research Institution Conference, 17: 281-292. Grippo, P.M., B. S.Thompson, and M. V. Ghandi. 1988. A review of flexible fixturing systems for computer integrated manufacturing.lnter1Ultional Journal of Computer Integrated Manu- facturing 1 (2): 124-135. Hill, R. 1956. The mathematical theory of plasticity. New York and Oxford: Oxford University Press. Hillaire, R., L. Marchetti, and P. K.Wright. 1998. Geometry for precision manufacturing on an open architecture machine tool (MOSAIC-PC). In Proceedings of the ASME International Mechanical Engineering Congress and Exposition, 8: 605 610. Hoffman, E. G. 1985. Jig and fixture design. Albany, New York: Delmar. Johnson, W., and P.B. MeUor.I973. Engineering plasticity. London: Van Nostrand Reinhold. Lu, L., and S. Akella. 1999. Folding cartons with fixtures; A motion planning algorithm. In IEEE Conference on Robotics and Automation. Detroit. Meyer, R. H., and 1. R. Newby. 1968. Effect of mechanical properties of bi-axial stretchability on low carbon steel. Paper presented at the SAEAutomotive Engineering Congress. Paper No. 680094. Michler, 1.R., M. L. Bohn, A. R. Kashani, and K. 1.Weinmann 1995. Feedback control of the sheet metal forming process using drawbead penetration as the control variable. In Proceed- ings of the North American Manufacturing Research Institution, 23: 71-78. Miller, S. M. 1985. Impacts of robotics and flexible manufacturing technologies on manufac- turing cost and employment. In The Management of Productivity and Technology in Manage- ment, edited by P. R. Kleindorfer, 73-110. New York: Plenum Press. Mueller, M. E., R. E. DeVor, and P. K. Wright. 1997. The physics of end-milling: Comparisons between simulations (EMSIM) and new experimental results from touch probed features. In Tra1l.!lactions of the 25th North American Manufacturing Research Institution, 25; 123-128. See <http;/Imtamri.me.uiuc.edu>. Rose,F.A.1974. Grid strain analysis technique for determining the press performance of sheet metal blanks. In international Conference on Production Technology. Melbourne. Institution of Engineers. Rowe, G. W. 1977. Principles of industrial metalworking processes. London, Arnold. Sarma, S., and P. K. Wright. 1997. Algorithms for the minimization of setups and tool changes in 'simply Iixturable' components in milling. Journal of Manufacturing Systems 15 (2); 95-112. Schofield, S. M., and P. K. Wright. 1998. Open architecture controllers for machine tools, part I: Design principles. ASME Journal of Manufacturing Science and Engineering, 120; 425-432. Stevenson, M. G., P. K. Wright, and 1. G. Chow. 1983. Further developments in applying the finite element method to the calculation of temperature distribution in machining and com- parisons with experiment. Transactions of theASME, Journal of Engineering for Industry 105: 149-154. Stori,1.A.I998. Machiningoperation planning based on process simulation and the mechanics of milling. Ph.D. dissertation, University of California, Berkeley. [...]...Metal-Products 32 Trent, E M., and P K Wright 20 00 Metal cuuing, Manufacturing Chap 7 4th ed Boston and Oxford: Butterworths Wagner, R., G Castanouo, and K Goldberg 19 97 Fixture.Net: Interactive computer aided design via the WWW.lnternationalJournalon Human-Computer Studies 46: 77 3 -78 8 Walczyk, D E and D E Hardt 1998 Design and analysis of reconfigurable discrete dies for sheet metal forming Journal of Manufacturing. .. Automation 12( 1) Wagner, R., G Castanotto, and K Goldberg 19 97 FixtureNet: Interactive computer aided design via the WWW International Journal on Human-Computer Studies 46: 77 3 -78 8 A modular fixture consists of a metal lattice with holes spaced at even intervals (Figure 7. 34a), three locators (Figure 7. 34b), and a clamp (Figure 7. 34c), which make four contacts and hold objects in "form closure." Figure 7. 34d... example,1 ,2, 3 or 1 ,2, 4 or 1 ,2, 5 or 1,3,4or2,3,4.Foreach triplet,call the edges a, b, c This will give us all possible arrangements of the three locators in contact with the three edges of the part Step 4: Without the loss of generality, assume edge a is in contact with a locator at (0,0) Fwd aU possible positions for L2 in contact with edge b First trans- 321 7. 13 Review Questions Flgu~ 7. 3$ Screen... O(n5d5), where n is the number of edges and d is the diameter of the part in lattice units Question: Can all polygonal parts be fixtured? Specific assignment: Use FixtureNet to design two modular alternative fixtures for a part Compare these and explain why one might be preferable Metal-Products 328 7. 13 REVIEW Manufacturing Chap 7 QUESTIONS L In forming, forging, and extrusion operations, a popular... Interactive 325 Further Work 2: "Hxturenet" Complete the table for the following 12 cases: RakellllglC' a (degrees) o +45 +45 +45 +6 +6 +6 -6 Friction coefficient: 1.1.(0 to 1) Friction Write angle: in (degrees) SheBl'anglc: Write in (degrees) o o 0.5 1.0 o 0.5 1.0 o -6 0.5 -6 - 42 - 42 1.0 o 1.0 7. 12 INTERACTIVE FURTHER WORK 2: "FIXTURENET" Modular fixturing on the World Wide Web is by Dr Kenneth Goldberg... (Johnson and Mellor, 1 973 ; Rowe, 1 977 ; Hill, 1956) The upper bound technique can also be used to make an estimate for the force necessary to form the chip in metal cutting The analysis first enlarges the center section in Figure 7. 36 and then considers the complete shear band OD, which has a total length of (s) Show that the final result for the force Fc is found as: k·V 'S (7 .24 ) F, ~ ~ In this equation,... The conditions that allow the strip to go in and be rolled require that the friction component be greater than the pushingout component F'lprft7.36 plene, Stress element at the shear 329 7. 13 Review Questions Roll Entry of strip, h1 E~tofstrip,h2 Figuft 7. 37 Sheet rolling: material on the left enters the roll gap and is plastically deformed by an amount (h,-h, = dh) Show that because of the balance... is . thinning in the thickness direction. 7. 7 Glossary 321 7. 7 .25 Roll Gap The area between the rolls where plastic deformation of the strip is occurring. 7. 7 .28 Roll Load The force between the rolls. [(a 2 + b 2 + c 2 + + n 2 )/n j.Typical values of R" might be 125 rnicroinches for standard surfaces and 60 to 80 microinches for smoother, well-finished surfaces (Figure 7. 33). 7. 1. 32 Taylor. data (non log-log axes. 7. 7.33 Tool Ute tn UsuaUy defined by 0 .75 millimeter (0.03 inch) of flank wear. 7. 7.34 Turning A machining process suited to. axisymmetrical parts. 7. 7.35 Wear Mechanisms Tool