Daniel Schaeffler Daniel Schaeffler

Opportunities Outweigh Apprehension When Forming New Metal Alloys

November 3, 2021

There is something reassuring about staying inside our comfort zone, especially as it relates to the stamping of metal-alloy parts. The engineering, manufacturing, quality, and purchasing teams can copy and paste from prior parts, with reasonably high confidence that whatever worked then will work again. However, are these parts the ones your company should pursue?
Review each of your parts with a critical eye as to the value they bring to you and your customer. Customers love low-cost stampings, but these jobs likely will cause metal formers to compete on price. Maybe these parts will reduce your fixed-cost plant burden, but running them also prevents you from using your line time and resources in a manner more beneficial to your bottom line.

Friction-SurfacesOne way to seek-out manufacture of value-added stampings is to target those parts formed from advanced metal alloys, such as high-strength steels or aluminum and stainless-steel grades. Doing so effectively requires understanding how stamping these grades differs compared to your current approach.

For example, it may be tempting to take a one-size-fits-all approach to tooling and tool construction, but doing so will result in a sub-optimal solution. A D2 tool steel, for example, works well for many plain-carbon-steel parts. However, this alloy contains about 12 percent chromium, as do many stainless steels—and that is the root of the problem. As the sheet metal flows over the tool during stamping, the chromium in the stainless sheet  and the tool may weld together, leading to adhesive metal transfer. Addressing this requires using applying a surface coating to the tool or selecting a different tool steel.

Tool surface-finish procedures also should change based on the chosen sheet-metal alloy. If the sheet and the tool have a high roughness, then the peak tips may break off as the sheet flows across the tool, leading to a high friction condition. High friction also exists with a low-roughness sheet and tool-steel combination, since the forming pressure squeezes out the lubricant between the surfaces. The ideal friction condition is when one surface has a relatively higher roughness compared with the other surface (see the accompanying illustration). However, the typical roughness of sheet aluminum and stainless-steel alloys is lower than that of plain-carbon steels. Aluminum also is softer than steel, so the roughness peaks may smear during forming. This results in particle buildup and an associated reduction in sheet metal flow.  The chosen sheet alloy should influence the tool surface finish to minimize this effect.

Further, steel mills and other material-production facilities add mill oil to the sheet surface as a rust-preventive measure; this oil does not add lubricity.  Stamping plants use press-applied lube in the hopes of reducing friction and improving material flow. Although having only one lubricant in the plant may be convenient, stamping plants forming multiple metal alloys should optimize their lubricant choices based on the types of materials processed and the parts they form. Lubricity is a function of surface chemistry, which differs among plain-carbon steels, stainless steels and aluminum alloys. Furthermore, engineered lubricants accentuate performance in extreme-temperature or extreme-pressure environments —a must when stamping the advanced metal alloys available today.

Considering new metal alloys means evolving cutting clearance beyond the rule-of-thumb recommendation of 10 percent of sheet thickness. Newer grades are more sensitive to cut-edge quality, resulting from their microstructure, an issue taking on increased importance.

Opportunities and Caveats

Expanding the types of sheet metals formed in a stamping plant allows the plant to consider entry into new markets. This diversification is a form of risk management, as many OEMs work in cyclical industries. Concurrent downturns in automotive, aerospace and agriculture, among other industries, happen infrequently, allowing for a steadier stream of business opportunities.
Of course, there are no free lunches.  These new metal alloys, already higher priced than plain-carbon steels, have experienced a recent runup in pricing.  That makes scrap quite costly, raising the cost of poor quality. Beyond simply the financial cost, consider the lack of availability of replacement sheet metal, with lead times for some products stretching to three months and beyond.

As a company transitions to advanced grades, metal forming simulation becomes an indispensable tool to optimize the forming process and minimize the production of bad parts. Blank shape and nesting optimization help to reduce engineered scrap from these more-costly sheet metal grades. And, stampers do not need to have the talent and software licenses inhouse, since many independent companies offer simulation as a service.

Don’t Forget the Training

Your workforce knows how to work with the materials and processes currently in use. You can leapfrog their troubleshooting skills by familiarizing them with the characteristics and nuances associated with newer metal alloys. Online resources such AHSSinsights.org offers a plethora of best practices, free of charge.  

In addition, seminars and workshops offered by the Precision Metalforming Association and MetalForming magazine provide great opportunities to learn and brainstorm with others facing the same issues. 

For example, I will be speaking about advanced materials at the upcoming Hot Stamping Experience and Tech Tour (November 2-3, 2021, in Ann Arbor, MI), and the Metal Stamping and Lubrication Technology Conference (January 18-19, 2022, in Cincinatti, OH). Hope to see you there. MF

Industry-Related Terms: Alloys, Blank, Form, Forming, Nesting, Scrap, Surface, Thickness, Transfer
View Glossary of Metalforming Terms


See also: Engineering Quality Solutions, Inc., 4M Partners, LLC

Technologies: Materials


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