What Die Clearances Should Be Used?
“Die Clearance,” as we define it, is the total less stripping pressure, and minimum press
difference between the Punch and Die tonnage which is an important feature since
dimensions. Many studies have been made the Units usually are used in multiple
throughout the Metalworking Industry setups.
regarding the proper amount of clearance Other materials require different die PUNCH & DIE CLEARANCE
to be allowed between Punch and Die. clearances depending on the shear 1) WHAT IS DIE CLEARANCE?
Results vary considerably due to the many strength and characteristics of the It is the dimensional difference
variables involved such as type and between the punch & die.
material. 2) INDUSTRY STD. –
hardness of material, type and speed of always total clearance
press, design of Punching Tools, finish on Copper, brass, soft aluminum and
3) UNITIZED TOOLING STANDARD
Punches and Dies, etc. Through continued other low shear strength materials is usually 20% of material thick-
research and experience, we have arrived tend to drag on the Punch and Die ness for 50,000 p.s.i. mild steel
at the following recommendations for the causing galling of punches, and
various styles of tooling. slugs tend to fuse together. 15% of PUNCH
material thickness is recommended MATERIAL
for these materials.
The UniPunch Tooling System When punching materials with high DIE
This is generally used on a wide variety shear strength such as stainless
of metal thicknesses, in short and medium steel, we recommend 25% of material
runs, using built-in springs to strip the die clearance. This helps to reduce 1/2
Punches from the material. These conditions punching tonnage and aid Punch and THE TOTAL
suggest maximum practical Die clearance of Die life. EXAMPLE:
.060 THICK MILD STEEL
20% be used when punching mild steel For quick selection of stock sizes with 1.000 DIA. PUNCH
(50,000 psi). Generally, this clearance pro- 15% to 20% clearance, see“Tech- DIE CLEARANCE = .060" X 20% = .012"
DIE SIZE = 1.012
vides maximum Punch and Die life, requires nical Data Die Clearance” pages.
How Often Should Punches and Dies be Sharpened?
Punch and Die life can be extended consid- and will have a frosted appearance. This
erably by prudent sharpening at the ideal indicates that the metal in the immediate
time. The number of holes produced vicinity is fatigued. At this time the Punch
between sharpening will vary according to and Die should be sharpened.
the material thickness and hardness from Tools not sharpened at the proper time will
conceivably 400 on very heavy material to also allow tool edges to deteriorate rapidly
about 25,000 on thin material. Punches and create extreme pressure on the cutting
require more frequent sharpening than Die edges and will increase punching pressure
Buttons by almost two to one. requirements. This in turn will decrease
On a new or sharpened Punch or Die, the quality and quantity of holes produced
shearing edges are square and sharp. along with creating poor stripping conditions
These edges are rather fragile considering in the Unit.
that they must withstand the impact and Therefore, frequent sharpening and minimum
tonnage required fracturing the material material removal is by far the least
being punched. After considerable punching, expensive and produces consistent high
observation of this edge will show a slight quality holes.
rounding (approximately .010"/.015" radius),
PH: (800)828-7061 • (716)825-7960 • FAX: (716) 825-0581 • www.unipunch.com
The Hole Thing / 113