Getting more punch life
Alternate tooling alloy and coating reduce friction, heat buildup
Augur Metal Products, a sheet metal fabricator that manufactures components for OEMs, punches large stainless-steel sheets for commercial separators. Its punches required sharpening after punching 10 to 15 sheets until it changed to Mate punches made from DuraSteel™ tooling with Maxima® coating and dies made with Mate's Slug Free® design. The new tooling allows the company to exceed 40 sheets between sharpenings and increase press speed by 20 percent.
Augur Metal Products, a custom fabricator in Independence Ken., performs a variety of processes for manufacturers. While the company's capabilities include shearing, cutting, forming, welding, and finishing, chief among them is sheet metal punching.
One of its processes involves punching 750 small holes in 33-inch by 36-inch 10-gauge stainless steel sheet panels used in the manufacture of large commercial separators. Because stainless steel is hard and abrasive, it heats up and puts stress on both the tooling and the punch press. With its previous tooling, the company was limited to punching just 10 to 15 panels before tool maintenance and sharpening were required. Stopping the line to sharpen punches often caused production bottlenecks.
On a different operation for perforating compressor panels, two 0.750-in. round punches were installed side by side in a turret so that when one tool became dull, the turret could be indexed to the next punch to continue punching without stopping the machine. When both the punches became dull, the machine had to be stopped and the punches removed for sharpening, at times disrupting part flow through the cell of five presses.
Augur Metal Products punches hundreds of holes in stainless steel sheets for commercial separators. Holding a punched panel is Joe Shotwell (left), senior purchasing buyer, and Pat Walker (right), press operator.
"Our punch press operators do a great job of maintaining constant work flow through our press department," said Joe Shotwell, senior purchasing buyer. "Premature tooling wear in the middle of a part run is disruptive. Our part runs vary and we punch a lot of different materials and thicknesses, everything from aluminum and mild steel to stainless steel. So continuous work flow minimizing press downtime for tool maintenance is a challenge we take seriously and try to improve on because it influences our quality and productivity."
Getting Longer Life From Tougher Punches
The company performed a trial run using Mate Precision Tooling's Strippit punches made of DuraSteel™ in an existing guide assembly to see if it could improve the hit count.
"We didn't have to touch the Mate punch until well after perforating 40 of the 10-gauge stainless steel panels," said press operator Pat Walker. "All 40 of the panels had between 650 and 750 holes punched in them. The holes are cleaner with less burr on them. And we're getting three to four times the tool life with the new Mate punches."
"Stainless is very abrasive to punch, creating a high degree of friction and heat in the punch when it penetrates the material," explained Tim Kraus, Mate sales representative. "Stainless dulls ordinary tools very quickly, especially at higher press speeds. Even if you slow the machine down, the abrasive effect continues and wears out the tool prematurely. You lose productivity two ways—with lower press speed and by having to maintain the tooling frequently."
The new punches resist the abrasive effects of the stainless material and reduce heat buildup in the punch. In addition to the DuraSteel punches, a special tool coating called Maxima™ was used to coat the punch. The coating bonds with the substrate and adds both durability and lubricity.
In addition to the DuraSteel punch and Maxima coating, the tools design affects productivity. For example, punch points are machined with a 1/4-degree back taper to reduce friction during the stripping phase of the punching cycle, which further extends tool life. Also, slug pulling is a longtime problem in the punching process, and thus the use of a special die design to counter this foe is useful. During punching the slug can pull back out of the die and then interfere with the next punching cycle. This is generically called slug pulling. Mate's Slug Free® die is designed with a slight hourglass shape that causes a pressure point that acts like a one-way door to keep the slug from pulling back out of the die. Once the slug is squeezed through the pressure point, it is free to fall down the slug chute as it should and away from where it could cause problems.
Using the new punches, Augur says it was able to increase press speed by 20 percent. Shotwell added that switching to the new Mate tooling actually cost 10 percent less than the old tooling. "When you add up the longer tool life, increased press output, and less downtime for tool sharpening, you've really improved overall productivity and profitability on that job."
DuraSteel is a trademark and Maxima and Slug Free are registered trademarks of Mate Precision Tooling Inc.
Photos courtesy of Mate Precision Tooling, Anoka, Minn.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.