Design for Sheet Metal
More parts are made from sheet metal than from any other material in the world. Most of the processes are well established, and design limits are well known and accepted. Many finishes are available, and customer acceptance and product life are well proven. More steel is produced than any other metal, with aluminum second in volume and in use in fabricating products. The weight of aluminum is approximately one third the weight of steel. In this subchapter we will concentrate our discussions on parts fabricated from these two materials. Although precision cold-rolled sheet is more expensive per pound that billets or bars, this can seldom offset the total part cost since sheet metal stampings are generally the lowest-cost parts to produce. Both the machinery and labor are relatively low in cost, and the production rates can be quite high.
One of the problems the author had in preparing this subchapter was separating design "do's and don'ts" from the "nuts and bolts" of the materials and fabrication processes. For the most part, the equipment and processes are described in Subchapter 15.1. Active participation by a manufacturing engineer (or other factory representative) in the design of a new product requires a knowledge of materials, processes, and costs as their most important contribution to the design team. This subchapter therefore will primarily provide guidance to the design features of sheet metal parts as seen from the manufacturing point of view. However, we must introduce sufficient material and process information to understand why the design comments are applicable.
Stampings
Stamping parts from sheet metal is a relatively straightforward process in which the metal is shaped through deformation by shearing, punching, drawing, stretching, bending, or coining. Production rates are fairly high, and little if any secondary machining is required to produce finished parts within tolerances. In most cases such parts are fairly simple in shape and do not tolerate extreme loads. However, stamped parts can be produced in complex shapes and sizes, and with load-carrying capabilities that rival parts made by other production processes. In some cases, unusual techniques have been developed to deform the metal to its required shape without exceeding forming limits. In other instances, ingenuity combined with good design practice have produced sheet metal parts that would be impossible to fabricate by other methods. Comparing cost impact of the several design variables is difficult. Figure 2.57 is an example of "minor" differences in the design of a sheet metal part which can double the part cost.
Quantity Considerations
The simple example shown in Figure 2.58 shows the influence of quantity production on the design and the manufacturing processes for producing a large tubular shape of large diameter and thin wall. Lowest unit cost is practical where substantial quantities are required for each production run. Welding may not be required in either the low or the high production design if locking tabs can be utilized.

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