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Determining the right die clearance

Determining the right die clearance

Formula for calculating the right die measure:

M2 = M1 + f x tsheet thickness

M1 = punch measure
M2 = die measure
f = multiplier

f = multiplier for sheet type

Spring steel: f = 0,30 mm
Stainless steel (e.g. 1.4301): ≤ 2 mm (f=0,2)
>2 mm (f=0,25)
Steel (e.g. DC01): f = 0,20 mm
Aluminium: f = 0,15 mm

Calculation of punching force

Calculation of punching force

Formula for calculating the punching force:

F (in kN) = (U x t x Rm x 0,9 x f)/1000

F = punch force in kN

U = circumference or perimeter of the punch shape (in mm)

t = sheet thickness (in mm)

Rm = tensile strength (in N/mm²)

for Stainless Steel (1.4301) 720 N/mm²
for Steel (DC01) 420 N/mm²
for Alu (AIMg3) 220 N/mm²

f = factor between 0,5 - 0,95 when using punches with shear

Stanzkraftberechnung 1


Punches with shear for reducing the punch force and noise

Punches with shear for reducing the punch force and noise

Technical application:

Punches with shear are used for complete cuts in punching up to 6 mm sheet thickness.

System Trumpf - WT

Trumpf wt

System Trumpf - DOWT

Trumpf dowt

Corner edges on punches

Corner edges on punches

Punches are automatically produced with corner radius R = 0,15 mm. This process increases the life-time as the corner abrasive wear will be decreased considerably.


R = 0,5 mm instead of R = 0,15 mm for stainless steel in order to increase tool-life.
R = 0,05 instead of R = 0,15 mm for electronical parts.

e.g.: square- and triangle punch


Tool Variety

Tool Variety


HWS tools are made of a secondary hardened cold work steel with superior toughness. This type of steel is especially suitable for dies.

Advantage for customer:


H-PM® tools are produced with a steel made on a powder-metallurgical base with a high degree of purity.
This guarantees a segregational uniformed microstructure in the complete cross-section of the tool.

Advantage for customer:


X3-PM tools are made of an high-end powder-metallurgical steel with the best possible performance characteristics for punches in the punching technology due to the best possible degree of purity.
The segregational uniformed microstructure with high vanadium concentration in the complete crosssection of the punch guarantees best possible wear resistance regarding tool life-time.

Advantage for customer:


X8-PM tools are made of a high-end powder metallurgical steel with the best possible performance characteristics for dies in the punching technology caused by best possible degree of purity.
The high ductility of the segregational uniformed microstructure guarantees best possible fatigue limit. This kind of steel is especially suitable for dies with risk-breakage in regards to special contours.

Advantage for customer:

Coating versions to reduce material build-up

Coating versions to reduce material build-up

Punching tools are made of specially hardened powder metal steel to fullfil the highest punching demands.

Furthermore we attach great importance to a high quality hardening process by repeated temporing and deep-freeze subsequently. This process guarantees an extremely high hardness with an outstanding wear resistance of our punching tools. Associated with modern production methods (grinding of the cutting edges with special grinding wheels) we can ensure that the wide range of different sheet qualities can be punched up to 1.600 N/mm² - no matter if it concerns mild alloyed aluminium, mild steel, stainless steel or spring band steel.

A high punch hardness as well as an excellent grinding surface are important in order to counteract the problem with edge build-up.

Tests show us that the well-known TICN coating is a good coating to increase the lifetime (especially working with stainless steel). However, the problem of material buildup on the edges have not really been counteracted.

Built-up edges are known especially when working with

After specialized tests the below mentioned coatings turned out to be the most successful coatings:




for working with stainless steel


for dry processing with aluminium sheet


for working with copper


for working with galvanized sheet

Life-time of tools / regrind advice

Life-time of tools / regrind advice

For approximately 30 years we collected technical information from our customers which allows references to be made for operation times of tools and regrinding times.

Today we place this collected data at your disposal with the purpose to facilitate the estimated tool life. The following chart is compiled by indicating the recommended regrind after the relavant quantity of hits as there will be a difference for the regrind of the different machine types (tooling system).

The chart, however, should clarify as well that the punching process contains a big variety of in uencing factors affecting possibly more or less the increase or decrease of the punching hits.

A precondition by using this data is an optimal adjusted punching machine with a solid C- or O-frame.



Influencing factors



Zinc coated sheet / stainless steel with foil / aluminium anodized   0,5 - 0,8
No sheet-lubrication   0,4 - 0,6
Punch coating (TICN for stainless steel / T-MAX for zinc coated steel / A-Max for aluminium / C-Max for copper)   2,0 - 4,0
PASS punch made with special X3-PM steel   6,0 - 10,0
Nibbling   0,7 - 0,9
Corner-punching   0,5 - 0,7
Whisper Tool   0,8 - 0,9
Punching rate > 300 hits / min.   0,8 - 0,9
Cutting part with EDM surface   0,4 - 0,8
Cutting part with polished surface   1,5 - 3,0
Cutting part smaller than 1,5x sheet thickness   0,6 - 0,8
Cutting part smaller than 1,0x sheet thickness   0,3 - 0,5
Using of a too close radius   0,4 - 0,9

In the following example you will get an idea how the different in uencing factors can effect the tool life:
Factors: square punch / s = 2.0 stainless steel / nibbling / punching rate > 300 hits
A calculation can be variable depending of the factor which will be used:

Using the smallest factor (safety calculation):

22.000 x 0,7 x 0,8 =   12.320
(hit quantity (chart) x factor nibbling x factor punching rate > 300 hits)   hits until regrind

Using the biggest factor:

22.000 x 0,9 x 0,9 =   17.820
(hit quantity (chart) x factor nibbling x factor punching rate > 300 hits)   hits until regrind



Tools that release sheet stress and warping

Tools that release sheet stress and warping

You would like to produce a sheet with a large amount of holes. Sheet distortion results due to the small hole spacing. There is no patent solution for it. BUT: there are some countermeasures!

Fundamentally you should keep in mind that:

Should all of these points not be enough, there is the option to use tools that release sheet stress and warping.
In this case there are toolings with convex surface:

Stripper is produced concave
(Attention: use only active stripper)

On each hit the sheet will be pretensioned and adjusted against the usual emboss.


Richtwirkung 1Richtwirkung 2

Max. depth of countersinks

Max. depth of countersinks

Countersinks in sheets are possible (e.g. for countersink screws). Please note the following information:

Senkung 1

1. In order to make deformations (material deformations) it is necessary to pre-punch the clearance hole. This pre-punch is normally bigger than the finished clearance hole.

2. Technical guidance value for 90° countersinks:

Alu sheet:   min. 0,25 mm zyl. part or depth
max. 90% of s
Steel:   min. 0,25 mm zyl. part or depth
max. 80% of s
Stainless:   min. 0,55 mm zyl. part or depth Steel
max 66% of s
Senkung 3

3. If the screw head height is higher than the sheet thickness there are two possibilities to create the countersink:

  • A bigger screw thread clearance hole is required as DIN or ISO forces. Keep in mind that the surface area for the head support is reduced and the strength calculation must be adjusted accordingly.
  • The sheet can be embossed to create the countersink. Be aware that a raised emboss may create problems with further sheet handling.

Problems with pulling slugs

Problems with pulling slugs

There are special, technical possibilities to avoid pulling slugs, e.g. on machines without vacuum or punching with the vacuum offline.

Stanzbutzen 1

1. punch with rubber ejector pin

Stanzbutzen 2

2. rooftop shear or inverted rooftop shear

 Stanzbutzen 3  

3. Dies with slug-stop / slug-snap

a) slug-stop
PASS dies are produced in standard version with slug-stop version for machines without extraction. This means that the upper part of the cutting part is produced with a negative angle. The pulling slug will be held with the complete circumference in the die.

This is not recommended for:

  • shapes smaller 4 mm
  • clearance smaller/ equal 0,1 mm
 Stanzbutzen 4  

b) slug-snap
Alternatively we offer our slug-snap version (additional costs).
In this case special holding bolts are included in the die, clamping the pulling slug positively (better than the slug-stop version).

The slug-snap version is also more convenient for:

  • shapes smaller than 4 mm
  • clearance smaller/equal 0,1mm

Low-scratch material handling: polish, brush, soft pads

Low-scratch material handling: polish, brush, soft pads

There is often a problem with the die causing scratches on the sheet. Of course you can order steel with protective films, however there are other options with the tooling.

Krazer 1

1. Polishing the die

The entire horizontal surface is polished. Furthermore, a large radius is blended onto the edge of the die and this is also polished.

Krazer 2

2. Adapter rings (for dies) with brush inserts

The adapter ring is  tted with a „brush ring“ with several brush inserts in order to lift the sheet above the cutting surface of the die.

 Krazer 3

3. Using PASS Soft Pads

With a special foil pad which can be sticked directly on the die, stripper or adapter ring, scratches can be minimized. These pads are available in different versions.


Kratzerarme Bearbeitung mit Umformwerkzeugen

Low-scratch material handling with PASS Emboss Tools

For machines without active die or without ram from below respectively, Emboss Tools are normally produced with springloaded die.

Krazer 4

However, there is always the problem that scratches appear on the bottom part of the sheet due to the heightened lower part of the tool as the sheet material will always galling by moving the sheet.

In order to counteract this problem the machine user has several possibilities:

  • Working with polished stripper made of ampco-material. However, the procedure of the galling can only be delayed in this case but not eliminated.
  • The second possibility is to use soft pads. But this is still only a temporary solution and only suitable for a short time of operation.

In order to eliminate this long-term problem the engineers of PASS developed a simple, inexpensive, favourable and extremely effective solution.

Typically the evidence of galling always transpires on the extreme outer edge of the plate. Within this area a compressible rubber insert is integrated in the die from PASS, which raises the sheet material within about 0,01 mm.

On the one hand this elastic rubber insert has the characteristic to support the sheet material weight when moving the sheet plate in order to suppress the contact of metal to metal.
On the other hand the rubber insert will be coincide with compression as soon as the upper part imposes the necessary pressure. This procedure guarantees that no marks on the sheet will occure within the processing step.
Both of these factors are the crucial point in order to obtain low-scratching sheet handling.

This fantastic development helps to solve two problems:

  1. Scratches on the buttom part of the sheet are minimized. Only stress marks can arise.
  2. The small metal chips which occure during the punching operation and damage the tool will no longer be a problem. These chips will no longer be able to  nd a way into the lower base of the tool. Ensuring a non-material build-up within the lower base of the tool.


Punching press-fit holes

Punching press-fit holes

Exact size or press fit holes can be punched relatively simple.

Passung 1

1. Tool (first hit)

Producing a pre-hole with a standard tool

Passung 2

2. Tool (second hit)

Calibrating with restricted clearance and coated punch