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Ask the Stamping Expert: Increasing progressive-stamping tooling life with the right lubricant

I get a lot of questions regarding how to maximize the life of progressive-stamping tooling, but no one response fits all.

We talk a lot about tooling materials, heat treatment, and coatings. But time and again, stamping lubrication is treated as relatively insignificant. Stampers put little time and effort into lubricant choice, often sticking with whatever is in-house or a lubricant that was used on a similar job.

While this might be sufficient, I don’t see the same effort and care put into choosing the lubricant as is put into determining tooling materials. In general, stampers put a lot of thought into the types of steel they use in cutting and forming components, heat treatment, coating application, clearances, and geometries to minimize burrs and maintain the robustness of the tooling. I have even seen stampers define the manufacturing processes for the tooling (such as jig grind, visual grind, lapping) to achieve quality, consistency, and the required surface finishes.

Do we take the same care with lubricant selection?

Do we define lubricant vendors based on quality and review the batch certification for quality and consistency? Do we review the tooling needs and define the lubricant based on functional requirements like we would for the tooling material? Do we fully understand how the lubrication might eat away or cause microscopic pitting of our tooling materials? Typically, no.

For some tooling applications, overcoming friction can use as much as 50 percent of the input energy. The surface finish, tooling life between sharpenings, and dimensional precision of the final product are directly related to friction. Changes in lubrication can alter the flow of material during forming and create or eliminate defects. Production rates, tool wear, process maximization, and product consistency depend on the ability to control process friction.

No surface is perfectly flat. There is always some degree of roughness. With the very lightest of loads between two surfaces, three points contact at a minimum, and friction is light. As the cutting, forming, or drawing load increases, eventually the entire surface is in physical contact, and friction remains constant at that load. Adding the right lubricant in the right amount can significantly reduce and possibly eliminate the effects of friction.

Tooling is expensive. When it wears, tolerance control is lost, and the tooling must be replaced. As friction increases, the required tonnage to complete the press cycle also increases. The product surface finish will degrade, and productivity will be lost while the tooling is out for service.

Lubrication is the life blood of the metal stamping process. It minimizes friction and tool wear, but it also can act as a thermal barrier between the tooling and stamping metal, and it can serve as a coolant by removing heat from the die. Lubricant also acts as a rust inhibitor both on the tooling and the stamped parts.

A lubricant’s performance depends on factors such as surface finish on both the tooling and stamping material, surface area of contact, the applied load, speed, temperature, and quantity of lubricant. In other words, while the lubricant is key, it is not the only major factor affecting a stamping process’s consistency and reliability. All the parameters need to be defined and controlled to maximize the number of hits between service.

Select your lubricant carefully. If you do not have an expert in-house, find one. Ask your lubricant supplier to provide a tribologist, an expert in the science and engineering of interacting surfaces in relative motion, to determine your lubrication requirements rather than a sales rep.

Evaluating and fine-tuning the lubrication used in a stamping process can double the number of parts stamped between tool service. Why would you not make the effort to do this upfront? How many of us do?

About the Author
Micro Co.

Thomas Vacca

Micro Co.

Has a shop floor stamping or tool and die question stumped you? If so, send your questions to kateb@thefabricator.com to be answered by Thomas Vacca, director of engineering at Micro Co.