Page 572 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Machining Processes

and Machine Tools

Parts manufactured by the casting, forming, and shaping processes described in
Parts II and HI, including many parts made by near-net or net-shape methods, often
require further operations before the product is ready for use. Consider, for example,
the following features on parts and whether they could be produced by the processes
discussed thus far:

° Smooth and shiny surfaces, such as the bearing surfaces of the crankshaft
shown in Fig. IV1.
° Small-diameter deep holes in a part such as the injector nozzle
Before After
shown in Fig. IV2.
° Parts with sharp features, a threaded section, and specified close
dimensional tolerances, such as the part shown in Fig. IV3.
° A threaded hole or holes on different surfaces of a part for
mechanical assembly with other components.
° Special surface finishes and textures for functional purposes or for
appearance.
A brief review will indicate that none of the forming and shaping
processes described thus far is capable of producing parts with such spe-
cific characteristics and that the parts will require further manufactur-
ing operations. Machining is a general term describing a group of
processes that consist of the removal of material and modification of
the surfaces of a workpiece after it has been produced by various meth-
ods. Thus, machining involves secondary and #iris/Qing operations.
The very wide variety of shapes produced by machining can be
seen clearly in an automobile, as shown in Fig. IV4. It also should be
recognized that some parts may be produced to final shape (net shape)
FIGURE l\Ll A forged crankshaft before
and at high quantities by forming and shaping processes, such as die
and after machining the bearing surfaces.
casting and powder metallurgy. However, machining may be more
The shiny bearing surfaces of the part on
economical, provided that the number of parts required is relatively
the right cannot be made to their final
small or the material and shape allow the parts to be machined at high dimensions and surface finish by any of the
rates and quantities and with high dimensional accuracy. A good processes described in previous chapters
example is the production of brass screw-machine parts on multiple- of this book. Source: Courtesy of Wyman-
spindle automatic screw machines. Gordon Company.

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