Page 26 - MetalForming-Mar-2018-issue

FABRICATION
ThreeThingsYou Need to Know to Prolong
Punch Life
Understanding these basic reasons for premature wear will enable you to get
the most from your tools.
Precision-machined punches and dies require mainte- nance with proper grinding
wheels and a coolant, as heat is a primary cause of wear.
To increase the life of punching tools, fabricators must under- stand the reasons why tools wear prematurely. While there are many, for this article we will focus on three.
Die Clearance
The number-one reason why tools wear prematurely? Improper die clear- ance, whether too tight or too loose. This fact requires that machine oper- ators understand the physics of punch- ing presses.
Too tight of a die clearance is hard on the punch, causing it to wear quick- ly. Galling also occurs as the punch rubs against the hole. Tight die clear- ance also increases the required punch- ing tonnage, resulting in increased press maintenance and effort.
Too loose of a die clearance causes the die to wear more quickly because
material rolls into the die before frac- turing occurs. The result: excessive burrs, deposited debris and part defor- mation. An understanding of press physics will allow companies to avoid these mistakes.
Turret Alignment
Numerous factors are involved with punching a hole in the center of the die: shot pins, bores, guides, punches, lower-die holders and auto-index sta- tions. All of these provide opportunities
24 MetalForming/March 2018
www.metalformingmagazine.com
Too tight of a die clearance causes the punch to wear quickly, as shown here.