Factors that Affect the Success and Safety of the Punching Process

June 7, 2019

Seeking out punching precision, an engineering formula assures success. Procedurally, the factors accumulate as lots of smaller steps, not as some grand giant corrective leap. For instance, starting with a vital process optimizing initiative, we can use reverse-analysis testing to see how safe a punching tool is performing. We do this, not by examining the punch holes, but by looking at their ejected slugs.

Mirror-Image Slug Inspection

If a punch hole is the subtractive results of a complex tooling operation, then the slug is the positive leftovers of that tooling stroke. The punch has dropped like a hammer to an anvil, the slug has been cut free, and it’s ready to be cleared. Before that happens, a quality control technician examines this aperture mirror image. Is it a clean slug? Or are there distortions on its edges? Let’s view it side-on. From here, a microscope splits the planes of the edge into three distinct sections. There’s the fracture plane, where the cut was initiated. That edge should be straight and clean. A burr zone is there, too. This area should be practically undetectable. If there’s burring along the fracture plane, the punch tool isn’t operating safely or successfully. Finally, a burnished zone should indicate satisfactory punch clearance.

Factors That Affect Slug Edge Profiles

The burnished edge and fracture planes of a punch slug need to be clean. Furthermore, edge burrs are not allowable. One factor that influences the burnish zone has already been mentioned. That’s where the die clearance variable enters the punching formula. If the clearance isn’t optimized, tool life will suffer. Next, what about the tool holder system? An array of high-tolerance equipment parts orients the punch stroke so that it strikes safely and repeatedly. Unfortunately, probably thanks to the high expenditure of shock energy, this particular success-attenuating factor does sometimes fall out of alignment. As a corrective measure, initiate a scheduled planned maintenance program and incorporate an alignment checking procedure into that program.

The success, or lack thereof, of the punching process can’t be viewed as a whole-system operation. Instead, precision-based, quality-assured punching processes are divided into several operational domains. After checking the slugs for defects, die and punch clearance settings are tuned. Next, as the formula variables accumulate, there’s the tool holder system to maintain. The tool itself requires extra-special attention, for a fracture could mean the end of an expensive, hard to replace punch. Safely and successfully punching masses of clean and geometrically precise openings in hardened alloys, a tool-hardened punch won’t fracture prematurely or exhibit signs of fatigue if the above factors are continually monitored.

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