http://72.3.142.35/mghdxreader/jsp/FinalDisplay.jsp;jsessionid=a-OrD... Cataloging-in-Publication Data is on file with the Library of Congress Walsh, Ronald A. McGraw-Hill machining and metalworking handbook / Ronald A. Walsh. and Denis R. Cormier—3rd ed. p. cm. ISBN 0-07-145787-9 1. Machining—Handbooks, manuals, etc. 2. Metal-work—Handbooks, manuals, etc. I. Cormier, Denis R. II. Title. TJ1185.W35 2005 2005051055 Copyright © 2006, 1999, 1994 by The McGraw-Hill Companies, Inc. All rights reserved. Printed in the United States of America. 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Copyright © 2006, 1999, 1994 by The McGraw-Hill Companies, Inc., McGraw-Hill 1 of 1 10/30/2007 6:41 PM Walsh CH01 8/30/05 8:39 PM Page 1 Source: McGraw-Hill Machining and Metalworking Handbook Chapter 1 Modern Metalworking Machinery, Tools, and Measuring Devices Metalworking machinery, tools, and measuring instruments have advanced considerably over the past 50 years. This chapter will show some of the new machines, tools, and instruments used throughout industry today that allow us to produce parts faster and more accu- rately than was possible in the past. The widespread use and imple- mentation of microprocessors to control the actions of metalworking machinery is evident in many of the photographs of modern equipment shown in this chapter. Photographs of other modern metalworking machinery appear throughout this Handbook. 1.1 Metalworking Process Overview When a metal part is fabricated, the part blank either can come from a near-net-shape manufacturing process or it can come in the form of bars, rods, plates, etc. Metal casting processes such as die casting, sand casting, and investment casting are the most common methods of producing a part blank that is close to its final shape (i.e., near net shape). 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 molds, dies, etc. (see Chap. 10). In the case of near-net-shape processes, rough 1 Walsh CH01 8/30/05 8:39 PM Page 2 Modern Metalworking Machinery, Tools, and Measuring Devices 2 Chapter One machining of large amounts of stock is not necessary. Instead, it is only necessary to finish machine those features that are critical to the function of a part. 1.1.1 Primary processes Die casting. Small or medium-sized parts in nonferrous alloys such as magnesium, aluminum, and zinc are injected under pressure into a steel die. A machining allowance of 0.25 to 0.5 mm (0.010 to 0.020 in) for critical features is typical. Sand casting. Molten metal is cast into a packed-sand mold. Parts weighing from just a few ounces to several tons can be sand cast. The most commonly sand-cast metals include irons, stainless steels, aluminum, and nickel alloys. Since the surface of the cast part is textured, a machining allowance typically is provided for critical fea- tures. Recommended machining allowances for a variety of metals are provided in Table 1.1. Investment casting. Both ferrous and nonferrous metals may be investment cast into a single-use refractory ceramic mold. High- temperature-reactive metals such as titanium typically are vacuum investment cast. Forging. Metals such as nonferrous alloys (e.g., aluminum, magne- sium, and brass), steels, and nickel alloys are relatively easy to forge. The slugs are essentially hammered by a die such that the metal deforms to the shape of the die. Recommended machining allowances for a variety of metals are provided in Table 1.2. Powder metallurgy. Metal powder is compacted by a die and then sintered to hold its shape. The resulting parts are porous and option- ally are infiltrated to 100 percent density. Extrusion. A heated billet is forced through a die opening such that the length of the billet takes on the cross-sectional shape of the die opening. 1.1.2 Metal-cutting processes CNC machining. The two most versatile machines in the modern machining industry are the computer numerical control (CNC) Walsh CH01 8/30/05 8:39 PM Page 3 Modern Metalworking Machinery, Tools, and Measuring Devices Modern Metalworking Machinery, Tools, and Measuring Devices 3 TABLE1.1 Sand Casting Allowances for Each Side Allowance, mm (in) Casting size, mm (in)* Drag and sides Cope surface Gray iron Up to 150 (up to 6) 2.3 (3⁄32) 3 (1⁄8) 150–300 (6–12) 3 (1⁄8) 4 (5⁄32) 300–600 (12–24) 5 (3⁄16) 6 (1⁄4) 600–900 (24–36) 6 (1⁄4) 8 (5⁄16) 900–1500 (36–60) 8 (5⁄16) 10 (3⁄8) 1500–2100 (60–84) 10 (3⁄8) 13 (1⁄2) 2100–3000 (84–120) 11 (7⁄16) 16 (5⁄8) Cast steel Up to 150 (up to 6) 3 (1⁄8) 6 (1⁄4) 150–300 (6–12) 5 (3⁄16) 6 (1⁄4) 300–600 (12–24) 6 (1⁄4) 8 (5⁄16) 600–900 (24–36) 8 (5⁄16) 10 (3⁄8) 900–1500 (36–60) 10 (3⁄8) 13 (1⁄2) 1500–2100 (60–84) 11 (7⁄16) 14 (9⁄16) 2100–3000 (84–120) 13 (1⁄2) 19 (3⁄4) Malleable Up to 75 (up to 3) 1.5 (1⁄16) 2.3 (3⁄32) iron 75–300 (3–12) 2.3 (3⁄32) 3 (1⁄8) 300–450 (12–18) 3 (1⁄8) 4 (5⁄32) 450–600 (18–24) 4 (5⁄32) 5 (3⁄16) Ductile Up to 150 (up to 6) 2.3 (3⁄32) 6 (1⁄4) iron 150–300 (6–12) 3 (1⁄8) 10 (3⁄8) 300–600 (12–24) 5 (3⁄16) 19 (3⁄4) 600–900 (24–36) 6 (1⁄4) 19 (3⁄4) 900–1500 (36–60) 8 (5⁄16) 25 (1) 1500–2100 (60–84) 10 (3⁄8) 28 (11⁄8) 2100–3000 (84–120) 11 (7⁄16) 32 (11⁄4) Nonferrous Up to 150 (up to 6) 1.6 (1⁄16) 2.3 (3⁄32) metals 150–300 (6–12) 2.3 (3⁄32) 3 (1⁄8) 300–600 (12–24) 3 (1⁄8) 4 (5⁄32) 600–900 (24–36) 4 (5⁄32) 5 (3⁄16) *Casting sizerefers to the overall length of the casting and not to the length of a particular measurement. SOURCE:Bralla, J., Design for Manufacturability Handbook.New York: McGraw- Hill, 1999. millingmachine (Fig. 1.1) and the CNC lathe (Fig. 1.2). A key to the versatility of these machines is the automatic tool changer. Vertical machining centers (VMCs) such as the one shown in Fig. 1.1 include a carousel that holds many different cutting tools such as milling cutters, drills, reamers, and taps. The automatic tool changer changes cutting tools between machining operations without any Walsh CH01 8/30/05 8:39 PM Page 4 Modern Metalworking Machinery, Tools, and Measuring Devices 4 Chapter One TABLE1.2 Typical Machining Allowances for Forgings Forging size: Projected area at parting line, mm (in) Alloy To 640 cm2 To 2600 cm2 Over 2600 cm2 family (100 in2) (400 in2) (400 in2) Aluminum 0.5–1.5 1.0–2.0 1.5–3.0 (0.020–0.060) (0.040–0.080) (0.060–0.120) Magnesium 0.5–1.5 1.0–2.0 1.5–3.0 (0.020–0.060) (0.040–0.080) (0.060–0.120) Brass 0.5–1.5 1.0–2.0 1.5–3.0 (0.020–0.060) (0.040–0.080) (0.060–0.120) Steel 0.5–1.5 1.5–3.0 3.0–6.0 (0.020–0.060) (0.060–0.120) (0.120–0.240) Stainless 0.5–1.5 1.5–2.5 1.5–5.0 steel (0.020–0.060) (0.060–0.100) (0.060–0.200) Titanium 0.8–1.5 — 2.0–6.0 (0.030–0.060) (0.080–0.240) Niobium 0.8–2.5 — — (0.030–0.100) Tantalum 0.8–2.5 — — (0.030–0.100) Molybdenum 0.8–2.0 2.0–3.0 — (0.030–0.080) (0.080–0.120) SOURCE:Bralla, J., Design for Manufacturability Handbook.New York: McGraw- Hill, 1999. user intervention, thus allowing several machining operations to be executed in a single workpiece setup. Likewise, the CNC lathe in Fig. 1.2 incorporates an automatic tool changer that can switch between tools that perform facing, knurling, grooving, boring, and many other turning operations. Electric discharge machining (EDM). EDM comes in two forms—sinker EDM and wire EDM. Sinker EDM uses spark erosion to machine a workpiece with a graphite or copper electrode whose shape is the negative 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 plate material. Walsh CH01 8/30/05 8:39 PM Page 5 Modern Metalworking Machinery, Tools, and Measuring Devices Modern Metalworking Machinery, Tools, and Measuring Devices 5 Figure 1.1 Vertical machining center. Figure 1.2 CNC lathe. Walsh CH01 8/30/05 8:39 PM Page 6 Modern Metalworking Machinery, Tools, and Measuring Devices 6 Chapter One Complex, thin parts whose quantity does not warrant a hard die are produced using this method. Chemical milling. Large masses of metal may be removed effectively in producing a part using the etching action of chemicals. Very thin and delicate parts also may be produced with chemical milling or etching. A tough photoresistive substance covers the parts of the metal that are not to be removed. Printed circuit board production is actually a chemical milling operation. Waterjet machining. A very high pressure jet of water, loaded with microfine abrasives, is used to cut the sheet or plate material of metal, plastic, glass, or other composition. As is the case with laser machining, waterjet machining is useful when the production vol- umes do not warrant a hard die. The absence of a heat-affected zone is advantageous as well. Figure 1.3 shows a nested pattern of sheet metal parts being waterjet machined. Figure 1.4 shows a complex geometric shape cut from plate. Figure 1.3 Waterjet machining operation. (Image courtesy of OMAX Corpo- ration, www.omax.com.) Walsh CH01 8/30/05 8:39 PM Page 7 Modern Metalworking Machinery, Tools, and Measuring Devices Modern Metalworking Machinery, Tools, and Measuring Devices 7 Figure 1.4 Complex waterjet-machined plate. (Image courtesy of OMAX Corporation, www.omax.com.) 1.1.3 Sheet metal parts fabrication methods Hard 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 is stamped in flat pattern. This is the most common, economical method devised to mass produce large quantities of parts to great accuracy. Punch press. Large sheet metal parts may be made to accurate standards using modern computer-controlled automatic multistation punch presses. Programmers write the direct numerical control (DNC) programs for these machines, which are then loaded into the machine’s computer or controller. The machine operator starts the program and stands back to watch the machine go through the sequence of operations required to produce the finished part in flat pattern. Walsh CH01 8/30/05 8:39 PM Page 8 Modern Metalworking Machinery, Tools, and Measuring Devices 8 Chapter One Roll forming. Flat strips of sheet metal are fed into the roll-form- ing machine, where they progress through a set of sequenced rollers to produce a long sheet metal part of constant cross-sectional shape. Hydropressing. A sheet metal flat-pattern part is placed on a set of forming dies, being located correctly with locator pins, and is then pressed into shape by the action of the hydropress. Many aircraft sheet metal parts are produced in this manner. Lightening holes and shrink flutes are produced simultaneously with the part to control the metal along curved surfaces. Hydraulic brakes. In this machine, a flat-pattern sheet metal part is given flanges or webs to produce the finished part. The modern brakes have automatic back gauges and material-handling devices to assist the operator in making the various bends and flanges required on the part. Hydraulic shears. The standard hydraulic shear cuts sheet metal according to the back gauge set by the machine operator and his or her accuracy in placing the sheet into the machine. 1.2 Measurement and Gauging The preceding section provided an overview of many types of metal- working and machining processes. In a production environment, parts typically are fabricated according to specifications on the computer-aided design (CAD) drawing using one or more of the aforementioned processes. At certain points during the fabrication process, parts are inspected to verify that they satisfy the required geometric and dimensional tolerances. In some cases, 100 percent of 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 perform component inspection. 1.2.1 Coordinate measuring machines (CMMs) CMMs are highly versatile inspection machines. Although CMMs are available in numerous configurations, the typical CMM consists of a probe that is positioned beneath a gantry. Depending on the type