Sheet metal design punching

Blanking is a basic stamping process that uses a mold to separate materials. It can be directly made into flat parts or prepare blanks for other stamping processes such as bending, drawing, forming, etc. It can also perform incisions, trimming, etc. on formed stamping parts. Blanking processing accounts for about 50% to 60% of the entire stamping process.

The depth and width of the protrusions and recesses of the blanking parts should generally be no less than 1.5t (t is material thickness). At the same time, avoid long and narrow interfaces and too narrow grooves to enhance the strength of the mold edge.

It is easier to ensure the accuracy between holes and shapes and between holes processed by composite molds, and the processing efficiency is higher. There are minimum wall thickness requirements for the distance between holes and between holes and shapes.

6. Punching bent parts When punching bent parts and deep-drawn parts, a certain distance should be maintained between the hole wall and the straight arm.

7. Hole margins on bent parts Punch first and then bend. The position of the hole is outside the bending deformation area to avoid deformation of the hole when it is completely empty. For the distance from the hole wall to the bending edge, refer to the table below.

8. Add process positioning holes In order to ensure the accurate positioning of the blank in the mold and prevent the blank from deflecting during bending and causing waste products, process positioning holes should be added in advance during design. Especially for parts that are formed by multiple bends, the process hole position must be positioned as a benchmark to reduce cumulative errors and ensure product quality.

⚡ Blanking and deformation process

When the gap is normal and the cutting edge is sharp, the blanking deformation process can be divided into three stages:

1. 1️⃣ Elastic deformation — stress < yield stress
2. 2️⃣ Plastic deformation — stress > yield stress

There is a gap between the convex and concave molds, and the deformation is complex. It isn't purely plastic shear deformation, but is also accompanied by bending, stretching, compression and other deformations of the convex and concave molds.

3. 3️⃣ Fracture separation — stress > strength limit

The crack first occurs on the side near the cutting edge of the die - the side near the cutting edge of the punch - the upper and lower cracks propagate and meet - material separation。

✨ Quality of blanking parts and its influencing factors

1. Factors affecting the cross-section quality of blanking parts

2. Dimensional accuracy of blanking parts and its influencing factors

Dimensional accuracy refers to the difference between the actual size of the blanking parts and the basic dimensions on the drawing. This difference includes deviations in two aspects: one is the deviation of the punched parts relative to the size of the punch or die; the second is the manufacturing deviation of the mold itself.

3. Shape error of blanking parts and its influencing factors

Shape errors of blanking parts refers to defects such as warping, distortion, and deformation.