Nonstamping Blanking Methods. When quantities are small, it may be advantageous to produce the blank by nonstamping methods, even though subsequent piercing, forming, or other operations are produced by punch-press methods. Among these nonstamping methods are contour sawing, routing, laser-beam machining, other machining methods, flame cutting, and hand cutting and filing.

Master Die Set: Adjustable-Die Stamping. This is a useful method for secondary stamping operations (after blanking). Punching, notching, countersinking, and other operations can be performed. The system utilizes reusable punch-die combinations for each hole or other element stamped in the workpiece. These combinations are fastened to a master reusable die set. The number of punch-die sets used and their locations determine the configuration of the stamped workpiece. In each punch-die combination are incorporated stripper devices, which are bolted to the master die plates or held magnetically. Templates are often used to locate the punch-die combinations, particularly if the job is rerun periodically.

Special Short-Run Tooling Methods. These methods involve tooling that, although more or less conventional in principle, is constructed especially for short-run work. Differences between this kind of tooling and its operating method and that of high-production tooling can include some or all of the following:

1. Less expensive and more easily machinable materials can be employed.

2. Often no provision is made for regrinding. There is no need for regrinding if the whole lot can be run in one setup.

3. The quantity of tool members is reduced to the minimum possible. Often no die shoes, punch pads, guideposts, spring strippers, tripper stops, wear plate, etc., are used.

4. Formal die designs are omitted or greatly simplified. Die construction is left to the skill of the toolmaker.

5. Die sets may be omitted. The tightness of the punch press and the skill of the setup operator are replied upon to provide correct alignment of the punch and die.

6. Single-operation tooling is employed, Compound, progressive, and other multiple-operation tooling is not attempted.

If cleverly designed, metal stampings, like injection-molded parts and die castings, can contribute strongly to design for manufacturability (DFM). They can incorporate diverse functions that otherwise would require additional parts. Springs and other flexible sections, snap-fit elements, folding tabs, and press-fitable designs can be incorporated and can eliminate the need for other parts, including separate screw fasteners or other fasteners. Projection welding and spot welding are easily provided for. Such innovations can reduce the number of parts in an assembly and make the stamped part itself easy to assemble.

Perhaps the major characteristic of stamped-metal parts is the fact that with a few exceptions, the wall thickness is essentially uniform throughout. Finished stampings are sometimes quite intricate in shape, with many tabs, arms, holes of various shapes, recesses, cavities, and raised sections. In all cases, however, the wall thickness is essentially uniform. Thick bosses of the type found in many casting are absent. For drawn shells, there is almost and infinite variety of shapes.

The characteristic edge of a stamped part, should be kept in mind by the design engineer, especially if bearing surfaces at the edges are involved or if, for appearance or other reasons, smooth edges are needed. The designer also should be aware of the burr on one side of stamped pieces and be careful to design parts so that burrs either are easily removed or do not interfere with subsequent operations or function.

Stamping can be machined after blanking an forming if dimensions that are more accurate than can be produced by stamping or shapes not feasible purely by stamping are required. Examples are reamed center holes of stamped pulleys or gears, surfaces ground for flatness, and grooves or relief areas requiring a change in thickness of the part.

Conventional Stampings

Conventional stamping is a high-production process. Production is very fast, from 35 to 500 or more strokes per minute. If total production is sufficient to justify compound or progressive dies, all blanking and forming can be done in one press stroke. In these cases, parts can be produced complete at a rate of thousands per hour.

As progressive die for the production of parts similar to those requires high production rates to justify the investment. Conventional dies to produce such parts might consist of (1) a compound blanking and piercing die and (2) a pad-forming die, which together would cost only about half the price of the progressive die. As a general rule, a progressive die should not be considered unless two secondary press operations can be eliminated.

Forming dies vary greatly in cost, depending on their complexity and size. A simple conventional die to form one bend can be very inexpensive, whereas a complex forming or drawing die for a large part can require a major investment.

As a result of these often sizable tooling costs for metal stampings, coupled with low unit labor costs, even with multiple operations, conventional metal stamping is a high-production process.

Punch presses are relatively low in cost compared with other high-production equipment. However, press cost is not a significant factor in economic-lot-size calculations because presses are versatile. Almost any given press has a wide range of stamping-operation capabilities.