This article is intended to introduce basic tool making knowledge
to beginner toolmakers, die maintenance technicians and press technicians.
We will first define what is a stamping die and difference type
of stamping dies exists in the market. Step by step introduce die
component and it function and application. It will also discuss
some terminologies use in the stamping industries such as cutting,
forming, lancing, ironing operations etc.
What Is a Stamping Die?
Basically, Stamping operation is a cold-forming operation, which
mean that, it runs under room temperature and no heat was introduced
to the entire operation intentionally. However, heat is still generated
from friction during the punching process. As such, proper lubricant
needs to be applied during the stamping operation to reduce heat
and wear rate of die members.
A stamping die is usually consists of a serious of precision punches
and dies that cuts and forms sheet metal into a desired shape or
profile within a specified dimension zone. The die members (punch
and die) are typically made from special types of hardened tool
steel. In some cases, die members are made of special material called
carbide to prolong tool life and enable it to runs in much higher
speed. ( 800- 1,500 spm in some cases)
A typical die set design can be seen on Figure 1.
Name of Tooling components:-
1. Top Die shoe
2. Top thrust plate
3. Punch holder plate or punch plate
5. Stripper backing plate ( some tools without this plate)
6. Stripper plate
7. Die plate
8. Die backing plate
9. Lower Die shoe
10. Guide pillar and bush
The part that the Die produced is called a piece part (see Figure
2). Usually, a Die can produces 1 part per cycle ( Stroke ) but
some Dies can produces more than one piece part per cycle and runs
as fast as 1500 strokes per minute with close tolerances up to +/-
0.05mm ( 0.0019 inch ).
Types of stamping Die.
There are many kinds of stamping dies exist in the market, all of
which perform a few basic operations, either cutting, forming, bending,
drawing or all of them. The Die can be runs manually ( manual loading
and unloading of piece part ) or automatically. The automatic Die
we called a Progressive Die. Which consists of many operations within
Cutting operation is perhaps the most common operation performed
in a stamping die. The component to be cut is placing in between
the punch and die. Desired shape and form is cut after two members
bypass each other. Usually, the Die is bigger than the punch to
allow smooth enter of the punch. The sizes difference between the
punch and die are called the cutting clearance.
Cutting clearances change with respect to the type of cutting operation
being performed, the metal's properties, and the desired edge condition
of the piece part. The cutting clearance often is expressed as a
percentage of the metal's thickness. Different clearances applied
to different material thickness and different type of material to
be punched. The most common cutting clearance used is about 5 percent
per side of the metal's thickness. In general, the harder the material
the bigger the cutting clearance will be applied.
Example 1. . A steel sheet of
1mm thickness ( 0.0393 inch ). Cutting clearance 5%.
Cutting clearance = 1mm ( 0.0393 inch ) x 0.05 = 0.05mm per side
( 0.00196 inch )
A Brass sheet of 1 mm thickness ( 0.0393 inch ). Cutting clearance
Cutting clearance = 1mm ( 0.0393 inch ) x 0.04 = 0.04mm per side
( 0.0015748 inch )
High punching force is needed to perform the cutting operation.
In general, the punching force can be calculated as follow:-
F = A X S
Cutting force = Area ( Perimeter of shape to be cut x thickness
of material ) x Shear strength of material
Note : Shear strength = 80% of the tensile strength.
3 show you a typical example of cutting condition.
1. Roll over : Plastic deformation state of material.
2.Penetration : A shinning cut band at the side of cut edge and
it is usually 1/3 of the total material thickness.
3. Fracture. Break off.
4. Burr edge.
There are still many different cutting operations, each with a special
purpose and application. Some common one are:
Trimming-The outer shape of the piece part is trim away to
give the piece part the desired shape.
In the progressive die, notching is applied on the outer edge of
the strip, unwanted part to be cut away to give the desired profile.
In some cases, notching is applied in the progressive die to provide
a stopper for material feeding. (see Figure 5).
Blanking- The term blanking is a cutting operation in stamping
die to cut out the desired piece part from the metal strip. The
dimension on the die profile is exactly the dimension of the component
wanted. The cutting clearance is applied on the punch. ( subtract
5% / side from die )
Cutting a hole onto the sheet metal or component. Some time called
perforating. The main difference between piercing and blanking is
that in blanking, the slug is used, and in piercing the slug is
discarded as scrap. The punch's size is exactly the hole size of
component wanted, cutting clearance added on the die side. (see
lancing, the metal is sliced or slit in an effort to free up metal
without separating it from the strip.
operation is to remove some small material from the component, usually
applied to provide better cut band. (see Figure 9).