Page 432 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

4|2 Chapter 16 Sheet-Metal Forming Processes and Equipment
Workpiece __§ constant wall thickness (that is equal to the clearance, except for some small
___
Side view
Top view
elastic recovery). Aluminum beverage cans, for example, typically undergo
two or three ironing operations in one stroke in which the drawn cup is
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pushed through a set of ironing rings.
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Containers that are too difficult to draw in one operation gen-
Redrawing.
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erally undergo redrau/ing (see Fig. 16.30). Because of the volume constancy
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of the metal, the cup becomes longer as it is redrawn to smaller diameters. In
reverse redrau/ing, the cup is placed upside down in the die and thus is sub-
Male die Female die
jected to bending in the direction opposite to its original configuration.
FIGURE l6.36 An embossing
Drawing without Blankholder. Deep drawing also may be carried out
operation with two dies. Letters,
numbers, and designs on sheet- successfully without a blankholder, provided that the sheet metal is sufficiently
metal parts can be produced by this thick to prevent wrinkling. A typical range of the diameter is
process. D, - DI, < sr, (16.14)
where T is the sheet thickness. The dies are contoured specially for this operation.
Embossing. This is an operation consisting of shallow or moderate draws made
with male and female matching shallow dies (Fig. 16.36). Embossing is used princi-
pally for the stiffening of flat sheet-metal panels and for purposes of decorating,
numbering, and lettering, such as letters on the lids of aluminum beverage cans.
Tooling and Equipment for Drawing. The most common tool and die materials for
deep drawing are tool steels and cast irons and include dies produced from ductile-iron
castings made by the lost-foam process. Other materials, such as carbides and plastics,
also may be used (see Table 5.7). Die-manufacturing methods are described in detail in
Section 14.7. Because of the generally axisymmetric shape of the punch and die com-
ponents (such as for making cylindrical cans and containers), they can be manufac-
tured on equipment such as high-speed machining on computer-controlled lathes.
The equipment for deep drawing is usually a double-action hydraulic press or
a mechanical press, the latter generally being favored because of its higher operating
speed. In the double-action hydraulic press, the punch and the blankholder are
controlled independently. Punch speeds generally range between 0.1 and 0.3 m/s.

CASE STUDY I6 I Manufacturing of Food and Beverage Cans

Can manufacturing is a major and competitive alone in a six-pack is 24 cents, which also indicates the
industry worldwide, with approximately 100 billion importance of recycling cans.
beverage cans and 30 billion food cans produced each Food and beverage cans may be produced in a
year in the United States alone. These containers are number of ways, the most common ones being two-
strong and lightweight (typically weighing less than piece and three-piece cans. Two-piece cans consist of
15 g), and they are under an internal pressure of 620 the can body and the lid (Fig. 16.37a). The body is
kPa-reliably and without leakage of their contents. made of one piece that has been drawn and ironed-
There are stringent requirements for the surface finish hence the industry practice of referring to this style as
of the can, since brightly decorated and shiny cans are D851 (drawn and ironed) cans. Three-piece cans are
preferred over dull-looking containers. Considering produced by attaching a lid and a bottom to a sheet-
all of these features, metal cans are very inexpensive. metal cylindrical body.
Can makers charge approximately $40 per 1000 cans, Drawn and ironed can bodies are produced
or about 4 cents per can. Thus, the cost of empty cans from a number of alloys, but the most common are