Die Science – Stamping Die Essentials: The Process Layout

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Editor’s Note: This is the second in a series of articles introducing the basics of embossing die design and construction. Read the first part.

What is a process layout?

A process layout can be defined as the steps we expect to use to successfully manufacture a part. This can be a simple two-step process for a simple part, or it can require 20 to 30 different steps for a difficult part.

The exact number of steps for the process layout depends on the metal from which the part is made, the complexity of the part geometry, and the characteristics of the geometric dimensions and tolerance.

More than just doing the part

Keep in mind that process layout is about more than being able to successfully shape your part. You also need to determine how to cut the metal and properly dispose of the scrap. The scrap that is cut from the part must be separated from the sides of the tool or run through a free opening in the die shoe and must be able to fall freely onto a scrap collection system or directly onto the press bedplate. For this reason, only certain areas can include parallels to support the die shoe.

For some part shapes, you may need to add inactive stations to the process. These stations do not perform work, but allow more space for larger, more robust tooling sections and the necessary die components.

Additionally, if you are designing a progressive die, you will need to determine what type of carrier strip is best for your part geometry. To do this you will need to determine if there is any metal flow during the molding of the part and if there is a difference in height between die stations. If any of these conditions exist, you will likely need to design a flexible or stretchable carrier that allows the metal to flow into the desired part geometry without disturbing the critical centerline distance between each part, known as pitch or progression (see Figure 1). If the tape will remain flat over the entire progressive matrix, with no metal flow or up and down movement, you can use solid media (see Figure 2).

A process layout for a progressive die is called a strip layout. This layout defines the process, the type of carrier that will be used, how the scrap will be ejected, how the part will be carried through the tool, and how it will be ejected from the die. The strength of the carrier is important as it must be strong enough to move the part from station to station without dislocation, severe bending or deformation. Media development can be problematic, especially when dealing with large parts made of very thin metal; the metal does not have the necessary rigidity to hold the parts in the carrier steady or to feed them without dislodging. In such a case, it may be necessary to form reinforcing beads or ribs into the carrier strip to give the carrier the necessary rigidity.

If the part will be stamped using a fully automated system, such as a transfer system, you must carefully determine how the parts will be picked up and carried through the tool. You will also need to determine whether a 2-axis transfer or a 3-axis transfer is best for your part geometry. For larger, profiled parts, 3-axis transfer is generally preferred as it allows you to pick up the part and place it within the measurement limits or on a guide pin. You will also need to determine the pickup height for each matrix. This is the level at which the fingers of the transfer bars will engage your part. Normally, the grip height for each part is at the same level. Before the tool or die is designed, you will also need to determine methods for clamping and moving the parts and for scrap.

Consider the press

Whatever type of tool you design, it must fit within the confines of a particular press style and size. Before starting tool design, you need to understand the parameters of the press in which the tools will work. Each press has a specific bed size, tonnage, stroke length, closing height and drive method. Some presses offer scrap removal through the strut, while others do not. Press conditions will certainly affect many of the die design parameters.

If you don’t plan on scrap disposal, the press will likely be stopped every few cycles for scrap removal. If you design a die with parallels spaced apart to allow a large piece of scrap to fall, those parallels will not adequately support the die shoes. A better solution would be to think ahead and plan for the scrap to be cut into smaller pieces before it is ejected from the tool, thus allowing the parallels to be correctly placed for support.

As you can see, many details need to be clarified before the design of the tool can begin. Your best chance for well-performing dies begins with thorough planning.

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