Factors that Determine Metal Punching Quality

November 4, 2019

If a multi-tonnage press snaps down at breakneck speed, will a punch eject a razor-sharp blank? Not necessarily, not if there are certain quality-attenuating factors hindering the process. For one thing, what kind of shape is the die in? If it’s worn and chipped, then metal punching quality issues are going to surface. Anyway, let’s see what else could trip up a successful punching operation.

Source Sheet Metal Thickness

Before a new job starts, there’s an important retooling period to tackle. The punch and die are inspected and checked for damage. They’re aligned and tightened, too. Finally, is the tool configuration compatible with the sheet material being processed? If the alloy is overly dense or too thick, then the punch and die pairing must be able to overcome that hardness and thickness partnership. And not just once, the tool stroke must repeatedly cycle backwards and forwards for many hours.

Punch Profile Geometry

A featureless cylindrical punching tool distributes its energies evenly. As the punch stroke begins, a metal blank ejects cleanly. With more intricate die shapes, a balanced drop and retract stroke can easily become misaligned after hours of blank cutting operations. Continual system load monitoring is essential when carrying out such detail-oriented projects. Moreover, work and shear plane angles cannot go beyond a certain tolerance. Otherwise, edge and flank wear problems will shorten the lifespan of a hardened punch, even if it’s made out of heat-treated tungsten carbide.

Shock and Clearance Considerations

Switching to an orthogonal point of view, the clearance between the tool point, the sheet metal and the underlying die must all be carefully maintained. Adjusted and fine-tuned, metal punching quality factors are held perfectly in balance. If out of tolerance gaps do occur here, the tool and sheet metal meet and create an abrasive or rubbing effect. With tons of press load behind the stroke, tool lifespans shorten. Strike zone shock and edge stripping issues climb high when these provisional operating conditions are not fulfilled.

What else can be done to assure a clean cut on every single punch stroke? A volumetrically adjusted lubricant stream should be in place to wash away debris, keep the tools cool, and to keep the stroke smooth. If the blank edges do take on a ragged appearance, post-production grinding operations can eliminate the excess waste. However, by doing this, the job takes on an additional stage, which equals more time spent doing the same work. Alternatively, preferably, tool stroke velocity can drop slightly to accommodate the tougher work conditions. As an upshot of this choice, the tools will last longer.

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