August 2026 Volume 8

EQUIPMENT & TECHNOLOGY

DESIGNING FOR DIE LIFE By Dan Ullrich

T ooling is a significant part of the cost of any forging. The cost of a set of dies divided by the number of forgings that can be made before the die needs to be replaced gives you the piece cost of the dies. In this article we will discuss some strategies to reduce the cost of the dies, as well as ways to extend their life. Die life can be defined as the maximum number of forgings that can be made before the die is no longer able to make parts that meet customer requirements. The end of a die's life can come about for a variety of reasons. The most common are wear and thermal fatigue, also known as heat checking. Other causes include cracks caused by stress, plastic deformation of the die, and die break-out, where a piece of the die literally breaks off. Ideally the failure will be due to wear or thermal fatigue, and the number of pieces made before the die ultimately fails will be repeatable. The best situation is when the dies last for an entire shift or an entire production run. This simplifies scheduling and makes it easier to keep a steady supply of dies in stock. Unpredictable die failures can lead to unscheduled downtime, loss of production, increased inspection, rework and scrap, and possibly overtime to make up for lost production. These all represent additional costs. Good die design starts with good forging design. The usual rules apply. Radii, both fillets and corner radii, should be as generous as possible. A small fillet in the forging translates to a small corner radius on the die, which will wear faster than a larger radius. A small corner radius in the forging translates to a small fillet in the die. Tight corners require increased cavity pressure to fill, which increases die stresses and can result in cracking. In addition, the

higher pressure increases the rate of die wear for the entire cavity. Thin ribs in the forging translate to narrow pockets in the die, which again require high cavity pressures to fill and can lead to cracking and increased die wear. Deep, narrow pockets in the forging translate to narrow ribs in the die. These features wear quickly. They also absorb a lot of heat from the forging but are unable to effectively transfer that heat to the main body of the die. This increased heating can lead to thermal fatigue, and in extreme cases can result in localized annealing of the die, causing plastic deformation. These features can also experience high stresses, which can result in the feature breaking off.

Figure 1: Increasing fillet and corner radii and eliminating finer detail results in an easier to forge design.

Figure 2: Maximum temperature of dies reduced by 178° F as a result of increasing fillet radii in the forging.

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