1、ChapterModern Metalworking Machinery, Tools, and Measuring DevicesMetalworking machinery, tools, and measuring instruments haveadvanced considerably over the past 50 years. This chapter will showsome of the new machines, tools, and instruments used throughoutindustry today that allow us to produce p
2、arts faster and more accu-rately than was possible in the past. The widespread use and imple-mentation of microprocessors to control the actions of metalworkingmachinery is evident in many of the photographs of modern equipmentshown in this chapter. Photographs of other modern metalworkingmachinery
3、appear throughout this Handbook.1.1Metalworking Process OverviewWhen a metal part is fabricated, the part blank either can come froma near-net-shape manufacturing process or it can come in the form ofbars, rods, plates, etc. Metal casting processes such as die casting,sand casting, and investment ca
4、sting are the most common methodsof producing a part blank that is close to its final shape (i.e., near netshape). Recent years also have seen a flood of new solid freeform fab-rication (SFF) processes that are capable of directly producing near-net-shape functional metal parts without the need for
5、molds, dies,etc. (see Chap. 10). In the case of near-net-shape processes, rough11Walsh CH01 8/30/05 8:39 PM Page 1Downloaded from Digital Engineering Library McGraw-Hill ()Copyright 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the website.Sou
6、rce: McGraw-Hill Machining and Metalworking Handbookmachining of large amounts of stock is not necessary. Instead, it isonly necessary to finish machine those features that are critical tothe function of a part.1.1.1Primary processesDie casting.Small or medium-sized parts in nonferrous alloys suchas
7、 magnesium, aluminum, and zinc are injected under pressureinto a steel die. A machining allowance of 0.25 to 0.5 mm (0.010 to0.020 in) for critical features is typical.Sand casting.Molten metal is cast into a packed-sand mold. Partsweighing from just a few ounces to several tons can be sand cast. Th
8、emost commonly sand-cast metals include irons, stainless steels,aluminum, and nickel alloys. Since the surface of the cast part istextured, a machining allowance typically is provided for critical fea-tures. Recommended machining allowances for a variety of metalsare provided in Table 1.1.Investment
9、 casting.Both ferrous and nonferrous metals may beinvestment cast into a single-use refractory ceramic mold. High-temperature-reactive metals such as titanium typically are vacuuminvestment cast.Forging.Metals such as nonferrous alloys (e.g., aluminum, magne-sium, and brass), steels, and nickel allo
10、ys are relatively easy to forge.The slugs are essentially hammered by a die such that the metaldeforms to the shape of the die. Recommended machining allowancesfor a variety of metals are provided in Table 1.2.Powder metallurgy.Metal powder is compacted by a die and thensintered to hold its shape. T
11、he resulting parts are porous and option-ally are infiltrated to 100 percent density.Extrusion.A heated billet is forced through a die opening such thatthe length of the billet takes on the cross-sectional shape of the dieopening.1.1.2Metal-cutting processesCNC machining.The two most versatile machi
12、nes in the modernmachining industry are the computer numerical control (CNC)2Chapter OneWalsh CH01 8/30/05 8:39 PM Page 2Downloaded from Digital Engineering Library McGraw-Hill ()Copyright 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the webs
13、ite.Modern Metalworking Machinery, Tools, and Measuring Devicesmilling machine (Fig. 1.1) and the CNC lathe (Fig. 1.2). A key to theversatility of these machines is the automatic tool changer. Verticalmachining centers (VMCs) such as the one shown in Fig. 1.1 includea carousel that holds many differ
14、ent cutting tools such as millingcutters, drills, reamers, and taps. The automatic tool changerchanges cutting tools between machining operations without anyModern Metalworking Machinery, Tools, and Measuring Devices3TABLE1.1Sand Casting Allowances for Each SideAllowance, mm (in)Casting size, mm (in
15、)*Drag and sidesCope surfaceGray ironUp to 150 (up to 6)2.3 (332)3 (18)150300 (612)3 (18)4 (532)300600 (1224)5 (316)6 (14)600900 (2436)6 (14)8 (516)9001500 (3660)8 (516)10 (38)15002100 (6084)10 (38)13 (12)21003000 (84120)11 (716)16 (58)Cast steelUp to 150 (up to 6)3 (18)6 (14)150300 (612)5 (316)6 (1
16、4)300600 (1224)6 (14)8 (516)600900 (2436)8 (516)10 (38)9001500 (3660)10 (38)13 (12)15002100 (6084)11 (716)14 (916)21003000 (84120)13 (12)19 (34)Malleable Up to 75 (up to 3)1.5 (116)2.3 (332)iron75300 (312)2.3 (332)3 (18)300450 (1218)3 (18)4 (532)450600 (1824)4 (532)5 (316)Ductile Up to 150 (up to 6)
17、2.3 (332)6 (14)iron150300 (612)3 (18)10 (38)300600 (1224)5 (316)19 (34)600900 (2436)6 (14)19 (34)9001500 (3660)8 (516)25 (1)15002100 (6084)10 (38)28 (118)21003000 (84120)11 (716)32 (114)Nonferrous Up to 150 (up to 6)1.6 (116)2.3 (332)metals150300 (612)2.3 (332)3 (18)300600 (1224)3 (18)4 (532)600900
18、(2436)4 (532)5 (316)*Casting size refers to the overall length of the casting and not to the lengthof a particular measurement.SOURCE: Bralla, J., Design for Manufacturability Handbook. New York: McGraw-Hill, 1999.Walsh CH01 8/30/05 8:39 PM Page 3Downloaded from Digital Engineering Library McGraw-Hi
19、ll ()Copyright 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the website.Modern Metalworking Machinery, Tools, and Measuring Devicesuser intervention, thus allowing several machining operations tobe executed in a single workpiece setup. Likewi
20、se, the CNC lathein Fig. 1.2 incorporates an automatic tool changer that can switchbetween tools that perform facing, knurling, grooving, boring, andmany other turning operations.Electric discharge machining (EDM).EDM comes in two formssinkerEDM and wire EDM. Sinker EDM uses spark erosion to machine
21、 aworkpiece with a graphite or copper electrode whose shape is thenegative of the cavity being machined. Wire EDM uses spark ero-sion with a wire to cut two-dimensional (2D) profiles.Laser machining.A powerful laser beam coupled with a CNC motion-control system is used to cut 2D profiles in sheet or
22、 plate material.4Chapter OneTABLE1.2Typical Machining Allowances for ForgingsForging size: Projected area at parting line, mm (in)Alloy To 640 cm2To 2600 cm2Over 2600 cm2family(100 in2)(400 in2)(400 in2)Aluminum0.51.5 1.02.0 1.53.0 (0.0200.060)(0.0400.080)(0.0600.120)Magnesium0.51.5 1.02.0 1.53.0 (0
23、.0200.060)(0.0400.080)(0.0600.120)Brass0.51.5 1.02.0 1.53.0 (0.0200.060)(0.0400.080)(0.0600.120)Steel0.51.5 1.53.0 3.06.0 (0.0200.060)(0.0600.120)(0.1200.240)Stainless 0.51.5 1.52.5 1.55.0 steel(0.0200.060)(0.0600.100)(0.0600.200)Titanium0.81.5 2.06.0 (0.0300.060)(0.0800.240)Niobium0.82.5 (0.0300.10
24、0)Tantalum0.82.5 (0.0300.100)Molybdenum0.82.0 2.03.0 (0.0300.080)(0.0800.120)SOURCE: Bralla, J., Design for Manufacturability Handbook. New York: McGraw-Hill, 1999.Walsh CH01 8/30/05 8:39 PM Page 4Downloaded from Digital Engineering Library McGraw-Hill ()Copyright 2004 The McGraw-Hill Companies. All
25、 rights reserved.Any use is subject to the Terms of Use as given at the website.Modern Metalworking Machinery, Tools, and Measuring DevicesModern Metalworking Machinery, Tools, and Measuring Devices5Figure 1.2CNC lathe.Figure 1.1Vertical machining center.Walsh CH01 8/30/05 8:39 PM Page 5Downloaded f
26、rom Digital Engineering Library McGraw-Hill ()Copyright 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the website.Modern Metalworking Machinery, Tools, and Measuring DevicesComplex, thin parts whose quantity does not warrant a hard dieare prod
27、uced using this method.Chemical milling.Large masses of metal may be removed effectivelyin producing a part using the etching action of chemicals. Very thinand delicate parts also may be produced with chemical milling oretching. A tough photoresistive substance covers the parts of themetal that are
28、not to be removed. Printed circuit board productionis actually a chemical milling operation.Waterjet machining.A very high pressure jet of water, loaded withmicrofine abrasives, is used to cut the sheet or plate material ofmetal, plastic, glass, or other composition. As is the case with lasermachini
29、ng, waterjet machining is useful when the production vol-umes do not warrant a hard die. The absence of a heat-affectedzone is advantageous as well. Figure 1.3 shows a nested pattern ofsheet metal parts being waterjet machined. Figure 1.4 shows acomplex geometric shape cut from plate.6Chapter OneFig
30、ure 1.3Waterjet machining operation. (Image courtesy of OMAX Corpo-ration, .)Walsh CH01 8/30/05 8:39 PM Page 6Downloaded from Digital Engineering Library McGraw-Hill ()Copyright 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the website.Modern
31、Metalworking Machinery, Tools, and Measuring Devices1.1.3Sheet metal parts fabrication methodsHard dies.A die set is used to stamp out the part in flat pattern. Pro-gressive dies also bend the part into the required shape after it isstamped in flat pattern. This is the most common, economical method
32、devised to mass produce large quantities of parts to great accuracy.Punch press.Large sheet metal parts may be made to accuratestandards using modern computer-controlled automatic multistationpunch presses. Programmers write the direct numerical control(DNC) programs for these machines, which are th
33、en loaded intothe machines computer or controller. The machine operator startsthe program and stands back to watch the machine go through thesequence of operations required to produce the finished part in flatpattern.Modern Metalworking Machinery, Tools, and Measuring Devices7Figure 1.4Complex water
34、jet-machined plate. (Image courtesy of OMAXCorporation, .)Walsh CH01 8/30/05 8:39 PM Page 7Downloaded from Digital Engineering Library McGraw-Hill ()Copyright 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the website.Modern Metalworking Machin
35、ery, Tools, and Measuring DevicesRoll forming.Flat strips of sheet metal are fed into the roll-form-ing machine, where they progress through a set of sequenced rollersto produce a long sheet metal part of constant cross-sectionalshape.Hydropressing.A sheet metal flat-pattern part is placed on a set
36、offorming dies, being located correctly with locator pins, and is thenpressed into shape by the action of the hydropress. Many aircraftsheet metal parts are produced in this manner. Lightening holesand shrink flutes are produced simultaneously with the part tocontrol the metal along curved surfaces.
37、Hydraulic brakes.In this machine, a flat-pattern sheet metal partis given flanges or webs to produce the finished part. The modernbrakes have automatic back gauges and material-handling devicesto assist the operator in making the various bends and flangesrequired on the part.Hydraulic shears.The sta
38、ndard hydraulic shear cuts sheet metalaccording to the back gauge set by the machine operator and his orher accuracy in placing the sheet into the machine.1.2Measurement and GaugingThe preceding section provided an overview of many types of metal-working and machining processes. In a production envi
39、ronment,parts typically are fabricated according to specifications on thecomputer-aided design (CAD) drawing using one or more of theaforementioned processes. At certain points during the fabricationprocess, parts are inspected to verify that they satisfy the requiredgeometric and dimensional tolera
40、nces. In some cases, 100 percentof the parts are inspected. In many instances, however, it is suffi-cient to inspect a subset of parts using a statistical sampling scheme.This section describes some of the instruments used to performcomponent inspection.1.2.1Coordinate measuring machines (CMMs)CMMs
41、are highly versatile inspection machines. Although CMMs areavailable in numerous configurations, the typical CMM consists ofa probe that is positioned beneath a gantry. Depending on the type8Chapter OneWalsh CH01 8/30/05 8:39 PM Page 8Downloaded from Digital Engineering Library McGraw-Hill ()Copyrig
42、ht 2004 The McGraw-Hill Companies. All rights reserved.Any use is subject to the Terms of Use as given at the website.Modern Metalworking Machinery, Tools, and Measuring Devicesof CMM, the probe can be moved manually by the operators hand, orit can be moved automatically via a motion-control system.
43、 Theworkpiece being inspected is rigidly clamped to the CMMs granitetable.In manual mode, the operator tells the computer which feature(s)he or she is going to inspect, and the control computer will theninstruct the user as to what points need to be probed for a givenfeature. To measure the distance
44、 between two faces, for instance, theoperator must touch the probe to at least three points on the firstface (i.e., three points define the plane) and one point on the secondface (i.e., the perpendicular distance from a point on the secondsurface to the plane defined by the three points on the first
45、 surface).To measure the diameter of a hole, the user is prompted to touchthe probe to three or more points around the perimeter of the hole.For each feature, the CMM control computer prompts the user totouch the probe to the appropriate number of points for the featurebeing inspected.Fully automate
46、d CMMs are also available. With automatedCMMs, the inspection planner starts with the geometric and/ordimensional tolerances (GD&Ts) specified in the CAD model by themechanical designer. CMM software packages such as PC-DMISare now available that are capable of extracting GD&T specifica-tions from a
47、 CAD model. Using this software, the inspection planneridentifies each feature in the CAD model to be inspected in a givensetup on the bed of the CMM. The software then automatically gen-erates an inspection plan for that setup on the CMM. The processis very much like generating toolpaths for a comp
48、uter numericalcontrol (CNC) milling machine. In this case, the touch probe ratherthan a rotating cutting tool automatically follows the prescribedpath. After the workpiece has been inspected, the CMM softwaregenerates an inspection report. In many instances, companies willstore these inspection resu
49、lts in a central database for purposes oftraceability.Both rigid and touch probes are available on CMMs. With a rigidprobe, the operator must press a button manually so that the CMMcan capture the x,y,z coordinates of the probe at that instant. Witha touch probe, the probe automatically senses when
50、it has touchedthe part, and the x,y,z coordinates are sent to the control computerimmediately. Motorized touch probes are also available that cantilt and swivel in order to inspect features that otherwise would notbe accessible in a given setup orientation.Modern Metalworking Machinery, Tools, and M
