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Coating Makes Drawing Stainless Painless

Wednesday, August 01, 2012
 

Metalformer Penn United Technologies, Cabot, PA, produces laminations and complex parts to exacting specifications. In many cases, stainless steel comprises the part material. For difficult stainless-steel forming, the company has chosen to employ a physical-vapor-deposition (PVD) tool coating.

To form stainless-steel parts such as these for a medical customer, Penn United Technologies had to overcome issues with galling and part tearing. A new tool coating fit the bill, and increased tool life exponentially.
The coating (from Phygen Coatings, Inc., Minneapolis, MN) prevents galling while maintaining critical part tolerances, and also enables operations such as drawing to proceed tear-free. And the coated tools exhibit increased life, allowing for more productive part runs without the need for stoppages to replace or repair worn tools, according to company officials.

In two plants, Penn United leverages state-of-the-art stamping presses, ranging from small bench machines to 300-ton workhorses, with bed sizes to 96 by 42 in. To meet required high part volumes, presses churn at speeds to 2000 strokes/min. Parts produced on these presses are destined for customers in medical, defense, aerospace, automotive, hardware, electronic and other markets. Penn United also designs and fabricates stamping tooling inhouse.

Finding Answer to Improve Stainless Draws

The company produces many parts stamped from stainless steel. Demands in dealing with this material have presented challenges. For example, in 2004 Penn United was struggling to deep-draw cups in a progressive die. Trying to draw the cups in a four-station die on a 100-ton mechanical press, the company could not consistently complete the drawing operation without galling or tearing the 0.003-in.-thick Type-304 part material. Perhaps a tool coating was the answer. Jim Marraccini, project engineer at Penn United, recalls the challenge.

“This part, a 0.5-in.-dia., 0.5-in.-deep cup for a medical device, often would tear,” he says. “We make about 50,000 of these parts in a run and probably 10 times that annually, so we needed a fix.”

Coated tools at Penn United Technologies have enabled the company, on one job in particular that draws 0.5-in.-deep stainless-steel cups, to increase from 15,000 to millions of hits before the tools require maintenance.
The company searched for a solution, and eventually identified a coating for its affected carbide tools. That initial solution, however, didn’t last long. “Our initial coating selection lasted for about 15,000 hits before we needed to pull the tools for repair,” he says. Back to the drawing board, which put Penn United on the doorstep of another tool coater—Phygen Coatings.

“What’s the problem with forming stainless steel?” asks Dave Bell, Phygen president. “Stainless has significant chrome content, and tool steel also contains chrome. What happens when you combine similar metal alloys under high forming pressures and heat? The alloys weld together. You need to prevent that from occurring.”

For this and subsequent tool challenges at Penn United, Phygen employed what Bell refers to as a custom-engineered solution. Under this process, Phygen uses laboratory tools and research facilities to perform failure analysis to determine the root cause of a particular tool-part failure. Then, the tool-coating company works with the customer to tailor its coating capabilities to meet specific application needs.

“We can perform component modeling and also analyze substrate material,” explains Bell. “In some cases we recommend that the metalformer specify higher-quality tool material that provides a superior platform for applying the tool coating. Then we use our laboratory tools to analyze tool surfaces prior to applying the coating.”

In general, coatings provide an inert tool surface. This eliminates the welding effect Bell describes that occurs between similar tool and part materials, removing galling as a problem.

“It is virtually impossible to form stainless steel into complex shapes without using some sort of coating solution,” says Bell.

The Right Coating for the Application

Jim Marraccini, right, tooling engineer at Penn United Technologies, works with Chris Morrow, tool and die maker, to ready a die for production.
For Penn United’s difficult deep-draw medical-part application, analysis led to the selection of Phygen’s FortiPhy PVD process to coat affected tools. One reason stems from the fact that for coatings to work in difficult applications such as the cup draw, adhesion is key.

The FortiPhy process creates a dense, thin nanocrystalline coating structure that, according to Bell, adheres to virtually any tool-steel substrate. The plasma-arc-acceleration coating process reportedly eliminates as much as 90 percent of macro particles and occlusions present in the normal structure of PVD deposition arc coatings. Instead, creation of highly energetic nanoparticles of 14 to 40 nm in size enables high density and improved adhesion—reportedly a level of adhesion three times higher than is possible with conventional coating processes.

Another plus for Penn United and its exacting forming needs: The coating can be applied consistently at the same thickness. That provides tolerance control, a difficult proposition for higher-temperature chemical-vapor-deposition (CVD) and thermal-diffusion (TD) coating processes. In addition, the FortiPhy coating provides a low coefficient of friction, less than 0.1 in typical lubricated conditions.

Successful Draws, Time after Time

In a nutshell, Penn United has found that the tool coating delivered to properly form the cups improves metalforming characteristics and tolerance control, while providing minimal alloy pickup and prolonged tool life. With the new tool coating, tearing and galling problems were eliminated, according to Marraccini. And though he does not have precise numbers, he says that, “the coated tools last for millions of hits.”

Penn United continues to produce the part, and success on this project has led to additional stainless-steel-part jobs benefiting from the same tool coating. Punches comprise the majority of the tools undergoing the coating process, as well as some form tools.

Turnaround time for the coating process is important to Penn United, according to Marraccini. Inhouse capabilities at Phygen, such as polishing and the ability to strip its own coating, not only have contributed to quick turnarounds, but to coating quality as well.

“Expert polishing provides the ability to remove machining marks, grind lines and other impediments to material flow,” according to Phygen sales engineer Chuck Cathcart. “Properly forming stainless steel requires that all of that must be removed from the tooling to allow the coating to work optimally. Farming out stripping of the coating would add days to turnaround. Plus, you’re looking at bringing in another vendor that may or may not take the care required to minimize any surface irregularities.” MF

Information for this article provided by Phygen Coatings, Inc., Minneapolis, MN: 888/749-4361; www.phygen.com.

 

See also: Phygen Coatings, Inc., Penn United Technologies, Inc.

Related Enterprise Zones: Materials/Coatings, Tool & Die

 


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