Proper clearance between the Punch and Die is essential for piercing a well-made hole efficiently.
* Too much punch and die clearance results in more rollover deformation where the punch enters the material and a large burr on the die side.
* With proper clearance between the punch and die there will be minimal rollover deformation around the hole where the punch enters the material. As the punch cuts through the material, it creates a region of vertical burnishing until the fracture line created by the punch meets the fracture line defined by the size of the die at which time the material breaks creating the hole. On the die side there will be a minimal burr.
* With too little die clearance the fracture lines of the punch and die do not meet, thus requiring a secondary shear of the material to make the hole, and this secondary shear is at the expense of requiring more tonnage, and in severe cases within the hole it results in a second region of vertical burnish that will grip the punch as it’s being extracted, thus requiring (1) more stripping force to extract the punch from the hole and (2) additional wear on the punch. Indeed the extra tonnage needed to make the hole and the additional stripping force required to extract the punch can result in premature punch failure in the form of chipping or breaking of the punch.
To optimize the die clearance inspect the slug and hole. To correct an unacceptable burr on the die side of the hole requires tighter clearance. Looking at the side of the punched slug, the top 1/3” should be sheared and burnished and equal to the size of the punch, the remaining material is typically dull and torn and the size of the die. If there has been a secondary shear, there will be two regions of burnishing on the side of the slug. If on the side of the punched slug, more than about 1/3” of the side is sheared and burnished, or if there are two regions where the slug is sheared and burnished, die clearance is too tight. Die clearance can be made larger to reduce tonnage and improve tool life.
How to Estimate Die Clearance Required for Punching:
MILD STEEL: Material thickness X .2 (.250 x .2 = .050 Total Die Clearance)
STAINLESS: Material thickness X .25 (.060 x .25 = .015 Total Die Clearance)
ALUMINUM: Material thickness X .15 (.250 x .15 = .037 Total Die Clearance)
OBTAINING TONNAGE FOR PUNCHING HOLES
FORMULA: Mild Steel = 3.1416 X Diameter of the hole X material thickness X 25
EXAMPLE: 3.1416 X 2.000 X .250 X 25 = 39.26 Tons
FORMULA: Mild Steel = Perimeter X material thickness X 25
EXAMPLE: (2 + 2 + 2 + 2) x .250 x 25 = 5O Tons
METAL GAGES IN DECIMALS OF AN INCH
It’s easy to believe that if you get a few thousand more hits with a tool you will get more value. When tool cutting edges show .010 radius, they need to be sharpened. If this is not done, tool edge wear will increase rapidly requiring a greater amount to be sharpened off the tool, thus reducing overall life.
By following a few simple guidelines your tooling will last longer and create a safer workplace. Remove all sharp edges from moving parts. Make sure punch slide freely inside guide or bushing. We recommend Type GN metal assembly past or die grease. Apply GN past liberally to punch and slide through guide or bushing and wipe away excess. Make sure all debris are removed and reassemble.
#1125 Unipunch Punch and Die Grinder