Page 334 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Part III Forming and Shaping Processes and Equipment
forming processes, the starting material (usually called the workpiece, stock, or
blank) may be in the shape of a plate, sheet, bar, rod, wire, or tubing of various cross
sections. For example, an ordinary wire coat hanger is made by forming a straight
piece of wire by bending and twisting it into the shape of a hanger. As another exam-
ple, the metal body for an automobile typically is made of cold-rolled, flat steel sheet
which is then formed into various shapes (hood, roof, trunk, door panels) using a
pair of large dies.
Shaping processes typically involve the molding and casting of soft or molten
materials, and the finished product is usually at or near the final desired shape. It
may require little or no further finishing. A plastic coat hanger, for example, is made
by forcing molten plastic into a two-piece mold with a cavity in the shape of the
hanger. Telephone receivers, refrigerator-door liners, computer housings, and count-
less other plastic products likewise are shaped by forcing the molten polymer into a
mold and letting it solidify. Some of the forming and shaping operations produce
long continuous products, such as plates, sheets, tubing, wire, and bars with various
cross sections. Rolling, extrusion, and drawing processes (Chapters 13 and 15) are
capable of making such products, which then are cut into desired lengths. On the
other hand, processes such as forging (Chapter 14), sheet metal forming and stamp-
ing (Chapter 16), powder metallurgy compaction (Chapter 17), ceramic slip casting
and glass pressing (Chapter 18), and processes involving plastics and reinforced
plastics (Chapter 19) typically produce discrete products.
The initial material used in forming and shaping metals is usually molten
metal, which is cast into individual ingots or continuously cast into slabs, rods, or
pipes. Cast structures are converted to u/roug/vt structures by plastic-deformation
processes. The raw material used also may consist of rnetal powders, which then are
pressed and sintered (heated without melting) into individual products. For plastics,
the starting material is usually pellets, flakes, or powder, and for ceramics, it is clays
and oxides obtained from ores or produced synthetically.
The important factors involved in each forming and shaping process are
described in this part of the text, along with how material properties and processes
affect product quality (Table III.1). We also explain why some materials can be
processed only by certain manufacturing methods and why parts with particular
shapes can be processed only by certain techniques and not by others. The character-
istics of the machinery and the equipment used in these processes also significantly
affect product quality, production rate, and the economics of a particular manufac-
turing operation.