I. Stainless steel plate bending key points
Due to the high yield point, high hardness and obvious cold hardening effect, the characteristics of the stainless steel plate bending are as follows:
1) because the thermal conductivity is worse than the ordinary low carbon steel, the elongation rate is low, resulting in the requirement of large deformation force;
2) the stainless steel sheet has a strong rebound tendency compared with carbon steel when bending.
3) the percentage of elongation of stainless steel plate is lower than the carbon steel, the bending angle of the workpiece (R) is larger than that of carbon steel, or there is the possibility of cracks.
4) due to the high hardness of stainless steel plate, with obvious cold work hardening effect, therefore, the tool steel should be chosen as the punch die, and the heat treatment hardness of the punch should reach more than 60 HRC, the surface roughness will be higher than that of carbon steel bending tools.
According to the above characteristics, generally speaking:
- Under the unit size, the thicker the plate, the larger the bending force is required, and the bending force of the plate should be larger as the plate thickness increases.
- Under the unit size, the larger the tensile strength, the smaller the elongation rate, the larger the required bending force, the larger the bend angle should be;
- If the designed plate thickness corresponding to the bending radius, according to the experience, the unfold size of workpiece with one bend should add the two right angle side, then minus two thickness, can completely meet the design accuracy requirement, according to the empirical formula computation quantity can simplify the calculation process, and greatly increased production efficiency;
- The greater the yield strength of the material, the greater the spring back, and the smaller the angle of the punch die should be designed for the angle of 90 degrees of the bending part.
Compared to carbon steel, for the same thickness of stainless steel, the bending angle is larger, special attention should be paid to this point, otherwise, the bending crack will appear, affecting the strength of the workpiece.
II. The spring back of the stainless steel
The return of stainless steel is indeed troublesome. It has to do with a lot of reasons:
- Hardness: the greater the hardness, the bigger the spring back.
Last time I used 301- EH stainless steel, and the spring back is 14 degrees.
- The bending radius thickness/stainless steel thickness: the larger the ratio, the larger the rebound
- The spring back of SUS301 stainless steel is bigger than SUS304 stainless steel. In the same situation, the spring back of 304 stainless is 2°less than 301 stainless steel. In addition, the spring back of Japanese 301 stainless steel is bigger than Taiwan’s stainless steel.
- There are also differences in shaping methods. The spring back of a one-step forming is larger than that of multiple forming.
- My habit is to revise the mold after the test, and change it accordingly, and pay attention to the angle rebound and radius rebound, and it should be analyzed based on the specific situation.
Of course, if the technician’s skill is good, he will adjust it in high efficiency, then notice the designer to make corresponding changes.
I usually try to move 5 pieces every time. This is much depending on the technician’s skill and experience.