It makes sense to stamp parts instead of machine them when production volumes are high and machining the parts would require multiple secondary operations. Good candidates for stamping include parts such as ball-bearing retainers, grid cups for cathode-ray tubes, and potentiometer and circuit-breaker components. These can be made from materials including aluminum, exotic metals, cold rolled and stainless steel, and red metals such as copper, brass, beryllium copper, phosphor bronze.

Process options involve traditional power presses with progressive dies, multislide presses running multislide tooling, or independent-cam-operated plunger presses with eyelet-transfer tooling. Selecting the correct process is critical for balancing economy and part quality. Here are a few considerations to help select a stamping method.

Progressive dies produce finished flat, formed, and drawn parts by combining several operations in one die. A strip of flat metal enters the die and is fed through one station at a time. Each station forms or cuts a particular feature such as a bend, notch, or hole. When the strip reaches the last station, the parts are complete and the tool cuts them free from the strip. One drawback: remaining scrap can reach up to 50%.

Any combination of operations such as notching, forming, coining, tapping, and assembly can be designed into a progressive die as long as the part configurations and tolerances remain acceptable. Our company stamps materials as thick as 0.1875-in. with this method.

But keep in mind it's sometimes necessary to perform a secondary press or machining operation to maintain a critical dimension that would otherwise be difficult to control in a die. And for low production quantities, it often makes sense to exclude a station because of tooling complexity. In these cases, finishing parts in a secondary operation makes sense, even though it involves more labor. It may also be necessary to exclude stations such as complex cam-actuated stations or those performing in-die tapping that require a lot of space because the die might become too long for the available presses.

Multislide tooling is a good choice for complex parts with extensive bending operations that would be difficult to perform in a progressive die. Multislide tooling is also good when parts are too costly to produce in single-station hand-fed tooling, or call for cam-actuated stations. The multislide process involves forming tools moving from multiple directions. Multislide tooling is less expensive and it produces parts with little or no scrap, a significant factor with high volumes and special metals.

Multislide machines can accommodate progressive dies to pierce holes, notches, or perform other operations before reaching the forming tools. Production pricing is about the same for complex parts that could typically be made complete in either progressive or multislide tooling. Variables include material usage and run rate. Our company processes material up to 0.125-in. thick and 2-in. wide with a multislide method.

Eyelet-transfer tooling is primarily for deep-drawn parts. These are transferred from station to station by “fingers,“ instead of a carrier strip as with progressive dies. This saves considerable raw material. Also, process control is greater because each station is independent. It's even possible to account for subtle changes in material properties to better maintain tolerances.

Punches in an eyelet machine are independently adjustable, while progressive-die punches are more difficult to adjust because they are mounted to a common holder. Depending on the part complexity and the number of stations required, the eyelet-transfer method produces a finished part that requires no secondary operations.

In fact, features such as side-pierced holes or notches, knife-edges, and coined edges or surfaces that would normally have required secondary press operations can be incorporated into the tooling. The only limitations are part size and complexity, material thickness, and the number of stations available in the press.

Eyelet tooling shines in adaptability. Tooling modifications from a revised part are less costly than with the other methods. This is particularly true when parts have the same shapes, but vary in size. It's easier to share tooling and produce only the necessary additional tooling. The eyelet-transfer method lets our company produce parts having a maximum depth and O.D. of 1.5 in.