Page 25 - MetalForming March 2020

Punching Machines —An Evolution
The ability of CNC punch-
ing machines to quickly and accurately punch holes of unlim-
ited sizes and produce functional forms in sheet metal parts opened up a new world in manufacturing and sheet metal processing, offers Angel, who provides an overview of the technolo- gy’s development.
The first mechanical machines employed brute force for punching, with a large flywheel mechanism lit- erally throwing the punch, as Angel describes it, through the sheet metal. For each punch, hole or form, the ram would complete a full move from top dead center (TDC) to bottom dead cen- ter (BDC) and back to TDC. Any form- height adjustments required removal of the tool for shimming, then reload- ing and testing—a process repeated until achieving the needed form.
Next in the timeline: the hydraulically controlled ram. This development dra-
The simple
design of servo drives in
CNC punching machines deliver efficiency, speed and mainte- nance advantages over drive sys- tems in hydraulic and mechanical machines.
matically affected the punching process by enabling control of
ram positioning. Through control of the ram stroke during punching, hit rates improved from several hundred/min. to 1000/min. and more. Newly devel- oped tool styles could take advantage of this controlled stroke, thus improving the manufacturing process. Another development, electronic shimming, allowed adjustment of forming tools without removing them from the turret.
Unfortunately, “the beauty of hydraulics also was its downfall,” says
Angel. “Hydraulic units are more expensive to run, and fluctuations in pressure and temperature can impair ram accuracy. Maintenance needs and costs tend to be much higher, too, with machine longevity not meeting users’ expectations based on their experiences with mechanical
machines.”
The introduction of an electronic
ram drive employing a servo motor, Angel explains, resolved most issues with hydraulic drives while retaining the benefits. He notes that Murata introduced its servo-ram-controlled machine in 1994.
Before Angel details how servo-con- trolled machines differ, here’s a glimpse at just how servo-controlled punching machines improve upon their mechan- ical and hydraulic predecessors, according to Jeff Tyl, North American sales manager for fabrication at Murata Machinery USA. The company’s servo- controlled 33-ton turret punch presses (TPPs), he offers, use 40 percent less
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