Many factors contribute to determining how much metal stamping will cost to produce your parts at high volume. While most factors such as material, tooling investment, labor, and overall part count are well known, many businesses fail to include the cost of die maintenance in their calculation for overall cost per part. Several aspects of the metal stamping process inherently cause wear. Without a strong die maintenance plan, you’ll end up spending even more than you calculated – because you’ll need to replace your tooling. Here are some areas that contribute to the overall cost of die maintenance.
Wear Stamping Die Failure Modes
Your tooling goes through a high friction and cyclical load process to create your parts. This creates natural wear on your die that causes the tooling surface to lose material as the part material is compressed and slides between the surfaces of the die to create your part features. This is called abrasive wear. Excessive abrasive wear can lead to fatigue cracking originating near complex notch features. Adhesive die wear occurs when the heat generated between the die and the part material during the stamping process create microwelds originating from the surface roughness of the two materials, that cause material to be “torn” away from the die. As this process continues the tooling surface is continuously degraded until maintenance is required to maintain part quality. The material hardness of the die, any coatings used, and the overall hardness of the part material determine the amount of wear per strike. Galling is the opposite of adhesive wear and occurs when the sheet metal being formed adheres to the tooling surface. Again, the friction and heat generated in the metal stamping process creates physical or chemical adhesion based on the material and the tool steel used in the die. Abrasive wear, adhesive wear, and galling can be controlled and minimized by using the correct coatings or surface treatments on your tooling – but ultimately, all dies need maintenance from wear.
Destructive Stamping Die Failure Modes
When proper manufacturing process best practices or maintenance schedules are not applied correctly, it can lead to more extensive die damage. Deformation of tooling occurs when the compressive force of the press applied to the die exceeds the compressive yield strength of the tool steel used to make the die. While the proper tooling material helps avoid this issue, operator error can create an issue like this that requires extensive maintenance. Chipping of the die can happen when there are excess metal flakes or scrap from cuts that are not properly cleared from the die after a strike. This can also occur by exceeding the strikes that the tooling is rated for, thus surpassing the fatigue strength of the tool steel. Chipping typically appears along the edges or corners of the tool as stress lines carry there from the high contact areas. Cracking of the die happens when the press impact force exceeds the fracture point of the material. In this scenario, sharp corners and radii in a die design enable cracks to form and spread until there is some level of tool failure.
As your tooling goes through an average of 1,000,000 strikes prior to requiring maintenance, it is designed to handle repetitive thermal and mechanical stress – but even the best dies wear out over time. When maintenance of your die is required, the team must take it offline and take it apart to repair the wear. The tooling for your part needs to be maintained properly so it can continue to produce high quality parts for your business. Planning the down time into your annual schedule allows you to properly care for your die (or multiple dies for progressive die stamping), project your overall cost per part, meet your lead times, and reliably fulfill on orders for your customers.