Page 35 - MetalForming June 2019

according to Tyl. Revisions to hard tool- ing, or creating a new die may run from $10,000 to more than $100,000. On top of that, CNC punching tools may pro- vide 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 avail- able from that customer. With CNC punching machines, these jobs make the money. With so many stampers taking themselves out of the compe- tition and not even entertaining such work, lower part-counts bring higher margins.”
Maximum Part Size, Minimal Material Waste
Another reason to consider the addi- tion 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 con-
figuration as long as the work occurs in that 4 by 8-ft. area.”
In addition, while the amount of parts produced is limited by stamp- ing-press tooling, nesting enables punching-machine production of mul- tiple parts from a single sheet.
“This ability greatly reduces material usage,” says Tyl, leading into a discus- sion on material savings and efficiency when buying sheet as opposed to coil, as often is the case in stamping oper- ations. “All service centers carry sheet inventory in standard sizes. When stampers buy slit material, that is lim- ited to the width of the coil. And, buy- ing 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 relo- cation 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 pro- gramming. This technology enables changes on the fly, making CNC punch- ing 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 punch- ing 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, per- haps 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
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MetalForming/June 2019 33
Fabrication: CNC Punching
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.