Punching is a basic stamping process that uses a mold to separate materials. It can be directly made into flat parts or prepared for other stamping processes such as bending, deep drawing, forming, etc., and can also be cut, repaired on the formed stamped parts. Wait. The blanking process accounts for about 50% to 60% of the entire stamping process.

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Sheet metal process blanking
Written By Jasmine HL
Punching is a basic stamping process that uses a mold to separate materials. It can be directly
made into flat parts or prepared for other stamping processes such as bending, deep drawing,
forming, etc., and can also be cut, repaired on the formed stamped parts. Wait. The blanking
process accounts for about 50% to 60% of the entire stamping process.
First, the basic process
Punching is divided into blanking and punching. The punching method for obtaining a certain
shape or blank by punching is blanking; otherwise, the punching is obtained.
Technical design of stamping parts
1. The shape and size of the blanking parts are as simple as possible to minimize waste during
layout. The picture shows no waste layout.
2. Avoid sharp corners in the shape and inner hole of the blanking part. There should be a circular
link at the link of a straight line or a curve, and the arc radius R≥1.5t (t is the plate thickness).
3, punching parts should avoid narrow and long cantilever and slot
The depth and width of the convex part of the blanking part are generally not less than 1.5t (t is
the thickness of the material), and at the same time avoid narrow interfaces and excessively
narrow grooving to enhance the die edge strength.
4. For punching, round holes should be preferred. Punching should have minimum size
requirements.
5. Punching space distance and hole margin

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The precision of the hole and the shape and the accuracy between the hole and the hole
processed by the composite mold are relatively easy to ensure, and the processing efficiency is
high. The distance between the hole and the hole and the distance between the hole and the
shape have minimum wall thickness requirements.
6. When punching the bent parts and deep-drawn parts, keep a certain distance between the
hole wall and the straight arm.
The distances a1 and a2 should meet the following requirements: a1 ≥ R1 + 0.5t, a2 ≥ R2 +
0.5t.
7, hole margins on bent parts
Punching first and then bending, the position of the hole is outside the bending deformation area,
to avoid the hole from being deformed completely. Refer to the following table for the distance
from the hole wall to the bent edge.
8. Add process positioning holes in the design. To ensure the accurate positioning of the blank in
the mold and prevent the blanks from being offset during bending, the process positioning holes
should be added in the design. Especially for parts that are formed by multiple bending, the
process hole positioning reference must be used to reduce cumulative errors and ensure product
quality.
Third, the blanking deformation process
In the case of normal clearance and sharp edge, the blanking deformation process can be divided
into three stages:
1. Elastic deformation stage: The material stress in the deformation zone is less than the yield
stress.
2. Plastic deformation stage: The material stress in the deformation zone is greater than the yield
stress.
There are gaps between the convex and concave molds, and the deformation is complicated. It is
not pure plastic shear deformation, but also accompanied by deformation such as bending and
stretching, and compression of the convex and concave molds.
3. Deformation during fracture and separation: The material stress in the zone is greater than the
strength limit.
Cracks first occur on the side near the die cutting edge--the side near the punch cutting
edge--upper and lower crack growth meet--material separation
Fourth, the quality of blanking parts and its influencing factors
Blanking part quality: refers to the cross-section condition, dimensional accuracy, and shape
error.
Section condition: vertical, smooth, and small burr.
Dimensional accuracy: the tolerance range requirements specified in the drawing.
Shape error: the shape meets the requirements of the drawing; the surface is flat, that is, the
arch is small.
1. Influencing factors of blank section quality
(1) Influence of material properties

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For materials with good plasticity, cracks appear later during punching, and the material is
sheared to a greater depth, resulting in a larger proportion of bright bands in the cross-section.
(2) Influence of mold clearance
A small gap, secondary shearing occurs, producing a second bright band
The gap is large, and the second tension crack occurs, resulting in two slopes
(3) Influence of die edge state
When the punch edge is blunt, burrs will be generated on the upper end of the blanking part.
When the die cutting edge is blunt, burrs will be generated at the lower end of the orifice of the
punching part;
When the convex and concave die edges are blunt at the same time, burrs will be generated at
the upper and lower ends of the blanking part.
2. Dimensional accuracy of blanking parts and its influencing factors
The dimensional accuracy of the blanking part: the difference between the actual size of the
blanking part and the basic size on the drawing.
The difference includes two deviations:
The first is the deviation of the punched part from the size of the punch or die;
The second is the manufacturing deviation of the mold itself.
Influencing factors:
(1) Manufacturing precision of die (part processing and assembly)
(2) The nature of the material
(3) Blanking clearance
3. Shape error of punching parts and its influencing factors
Shape error of blanking parts: refers to defects such as warping, distortion, and deformation.
Warping: The blanking part is uneven.
It is caused by excessively large gaps, increased bending moments, increased deformation, and
increased bending components. In addition, the anisotropy of the material and the uncorrected
coil will also cause warping.
Distortion: The blanking part is distorted.
It is caused by uneven materials, uneven clearances, and uneven back friction of the die on the
materials.
Deformation: It is caused by bulging because of the edge punching of the blank or the distance
between the holes is too small.