Stampers: Consider Adding CNC Punching Machines

By: Louis A. Kren

Wednesday, May 22, 2019

Traditional metal stampers would do well to incorporate CNC punching into their production regimens, thus providing the ability to gain new short- and medium-run work without the expense of hard tooling.

Providing reasons for making the jump is Jeff Tyl, North American sales manager-fabrication for Murata Machinery USA. He’s met with and surveyed more than 200 metal stampers to help determine how CNC punching can be leveraged in a traditional metal stamping environment.

The majority of metal stampers surveyed do not employ punching-machine technology,” according to Tyl, with lack of process familiarity and capabilities a possible reason why.

“Stampers should understand that stamping presses and punching machines operate in the same manner—down and up motion,” Tyl offers. “The major difference: Instead of employing a single tool for a single hit as is the case with the components in a stamping die, punching-machines provide multiple tools for multiple hits for multiple parts. And, just like presses, punching-machine drives have evolved to employ hydraulic, mechanical and servo technology. In addition, these machines process similar materials with similar thicknesses. We need to remove the mindset that presses and punching machines are completely different pieces of equipment.

CNC punching machines provide a valuable complement to stamping operations, and an economical alternative for shorter part runs. Their part-nesting capability and use of sheet blanks also offer significant material savings.
“Punching machines perform a variety of operations, many similar to those employed in stamping presses,” he continues. “They can produce contours and rounds, and much more, with applications for all types of industries, including agricultural, medical and many others. And, the material need not only be metal. If it comes in a sheet —anything flat and not brittle—it’s a candidate for a punching machine.”

Take Back the Short and Medium Runs

In his detailed discussions with stampers, Tyl found that many see long-run tooling as a sweet spot, and stamping presses truly do excel in such applications.

“But stampers can miss the boat with short-run and middle-volume jobs, often opting to outsource this work,” he says. “One stamper told me that he outsources $300,000 in short-run work each year.”

The tooling capability of punching machines comes into play in these applications, and where the investment in CNC punching can produce a rapid ROI.

“For example,” Tyl says, “our standard 20-ton turret punch press houses 44 tools. Depending on the size of a tool, users can punch round holes in diameters from 0.5 to 4.45 in. without changing a tool in the turret. And, should a new tool be needed to produce a particular feature to accommodate a part-design change, tool changeout is a simple process. On the other hand, revising a hard tool brings a high cost. Many times, a tool component or feature in a progressive die is ‘one and done,’ meaning that it produces a feature for one particular part. A part revision means altering the die or building a new die, with significant costs in time and money.”

In the turret punch press, a complete toolset may run $1000 to $1200, according to Tyl. Revisions to hard tooling, or creating a new die may run from $10,000 to more than $100,000. On top of that, CNC punching tools may provide millions of hits and accept as many as 20 sharpenings throughout their useful lives, he says.

Tool cost and variety, along with ease of changeout, make profitability via CNC punching very possible on 2000 part/mo. jobs, for example, that stampers tend to outsource.

“Hard-tooling costs amortized across that amount of parts leads to the outsourcing decision,” Tyl says. “That part customer may have been buying long-run parts from a stamper for 50 years, but the stamper never sees the shorter-run business available from that customer. With CNC punching machines, these jobs make the money. With so many stampers taking themselves out of the competition and not even entertaining such work, lower part counts bring higher margins.”

Maximum Part Size, Minimal Material Waste

Another reason to consider the addition of CNC punching: press-bed size.

“Stampers are limited by the size of the press bed,” Tyl explains. “Should the part or tooling extend beyond that size, stamping is not possible. However, punching machines offer repositioning, where, with a 4 by 8 ft. table, a punching machine can produce parts longer than 8 ft. Just reposition the material and add tables to provide support. The sheet can be rearranged in any configuration as long as the work occurs in that 4 by 8-ft. area.”

In addition, while the amount of parts produced is limited by stamping-press tooling, nesting enables punching-machine production of multiple parts from a single sheet.

“This ability greatly reduces material usage,” says Tyl, leading into a discussion on material savings and efficiency when buying sheet as opposed to coil, as often is the case in stamping operations. “All service centers carry sheet inventory in standard sizes. When stampers buy slit material, that is limited to the width of the coil. And, buying material for a 5-in.-wide part means slitting off of a coil and purchasing that width for the entire coil length. If the job is 1000 parts but the coil yields 2000 parts, someone has to eat that scrap—paying for the unused portion of that slit coil.

“When buying for a punching machine,” he continues, “material in whatever width available from the mill is cut to a specific length, and from each of those sheets, thanks to nesting, umpteen parts can be produced. This significantly reduces scrap—no need to consider the entire length of a coil because a punching machine’s material needs are calculated on a per-sheet basis.”

Flexibility in Part Revisions

Of course, a revised stamped part means revising the tooling, a big-bucks proposition. Here, CNC punching can pick up the slack either by taking over the job using low-cost tool changeouts while new hard tooling is produced, or testing out new hard tooling options as an R&D operation.

In addition, a CNC punching machine may be able to accept a part revision simply though programming the relocation of a feature.

“Want to move a form 0.5 in.? Just program it,” Tyl explains. “Take the X axis and move it 0.5 in. via CNC programming. This technology enables changes on the fly, making CNC punching ideal not only for prototyping, but for these types of part revisions.”

Combine Processes

Stamping and CNC punching need not be a one-or-the-other decision. Numerous examples point out how CNC punching machines and stamping presses can be used together to make parts.

“Perform blanking on the stamping press and do the rest on a CNC punching machine, or vice versa,” Tyl says. “Punching machines do have form-height limitations, with the ability to form to 1 in. high, so consider that. But a punching machine may be able to handle 90 percent of the job, with transfer to a stamping press for a single process such as a deep form. Or, perhaps a stamping press performs 90 percent of the work. A punching machine can grip and orient a small piece, so following stamping, the punching machine can thread holes or create other features to finish the part. I have seen punching machines used as first, middle and end stages in part production.” MF


See also: Muratec Murata Machinery USA, Inc.

Related Enterprise Zones: Presses

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