The basic concept of cold stamping:
First, the definition of cold stamping:
It is one of the basic methods of plastic processing. It is a pressure processing method that uses a mold installed on a press to apply pressure to the sheet to deform and separate, so as to obtain parts with a certain shape and size. Because the sheet metal stamping at room temperature is called cold stamping.
The hot forming process is to heat the steel sheet with an initial strength of 500-600MPa to the austenite temperature range (850°C), then punch it into the desired shape on a press, and quench it at a cooling rate of 20-30°C/sec. Hold the pressure for a period of time to ensure sufficient hardening, and finally the parts are cooled at room temperature, and the strength of the formed parts can reach about 1500MPa.
Second, the characteristics of stamping:
- It can punch out complex shapes that are difficult or impossible to process by other processing techniques.
- Stamping parts have stable quality and high dimensional accuracy.
- Stamping parts have the characteristics of light weight, high strength, good rigidity and small surface roughness.
- High productivity.
- High utilization rate of materials.
- Simple operation, easy to organize production.
- It is easy to realize mechanization and automatic production.
- The disadvantage of cold stamping is that the mold manufacturing cycle is long, the manufacturing cost is high, and it is not suitable for single-piece small batch production.
Three, stamping classification:
1. Separation process
Under the action of stamping force, the stress of sheet metal exceeds the extreme limit of strength and breaks along a certain contour line, which is called the separation process. It can be divided into blanking, punching and trimming and other blanking and separation processes.
2. Deformation process
Under the action of stamping force, the stress of sheet metal exceeds the yield limit (but lower than the strength limit) to produce plastic deformation, so as to obtain parts with certain shape and size requirements, which is called deformation process. Usually the deformation process is divided into three types: bending, drawing and forming.
Common product defects:
Compared with general stamping parts, automobile cover parts have the characteristics of thin material, complex shape, mostly space curved surface, large structure size and high surface quality requirements.
Defects of Covers:
The surface quality is good; the surface of the outer cover (especially the outer cover of the car) is not allowed to have defects such as waves, wrinkles, dents, scratches, abrasions, indentations, etc. The ridges should be clear and straight, and the curved surfaces should be smooth and smooth. The transition is even.
Blanking, punching, trimming defects
Defects and causes of separation process:
(1) The burr is too large
Too large or too small gap between punch and die; wear of cutting edge; poor guide accuracy; non-concentric position of punch and die, etc.
(The burr should consider factors such as punch (punch), die button (concave die), presser, wedge, guide, machine tool, buffer, etc.)
The pressure plate does not fit well with the concave model surface; the gap is too large, etc.
Defective die or punch; caused by positioning pins (offset or feed)
(3) Surface scratches
There are phenomena such as dragging and pulling during operation; the sheet is scratched during the shearing process, etc.;
(4) Size does not match
The feeding is not in place; the positioning device is damaged or loose, the position fluctuates, etc.
(5) Less holes
The punch is broken; the length of the punch is not enough; the stroke is not in place.
Flanging defects and causes:
The flanging is not vertical; the flanging height is inconsistent; the flanging is brushed; the flanging is broken, etc.
There are scars on the cutting edge; there are impurities on the surface of the part; the hardness of the cutting edge is too low; the flanging clearance is too small
The burr is large when trimming; the gap between the convex and concave die is too small; the shape of the flanging has a sudden change; the influence of the material fiber direction.
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