Improvement of deep-drawing die design parameters and adjustment of heat treatment process
Deep drawing stamping is a special kind of stamping method, its principle is to rely on the press and die to apply external force to plates, strips, pipes, and profiles, etc., so as to produce plastic deformation or separation, thus obtaining the required shape and size of stamping and drawing parts, which is still relatively different from the common continuous stamping and single-action stamping.
First of all is the die; the die is composed of punch and concave die, one station a die, can reach about 18 stations, when designing the die usually consider using all the stations, so that the product forming is more stable and the effect is better; such split process reduces the load of equipment processing, while improving the efficiency and quality of processing.
The second is the material belt, deep drawing stamping is no material belt transmission, but placed directly in the mold, relying on the built-in robot to transfer between stations, the advantage of such a design is that it can better achieve arbitrary reversal of equipment, in the stretching process will also be more convenient, so you can design a more complex shape, such as thread, side holes, side grooves, end face of the reverse stretching.
Lastly, the overall control of deep drawing process, each step in the production process is controlled like an assembly line, so it is much simpler than the general stamping method in terms of the complexity of personnel operation and more comfortable in terms of equipment maintenance, and has the advantages of saving material cost, reducing scrap and lowering assembly cost compared with machined parts, cast parts, molded parts and ordinary stamping parts.
The first set of deep-drawing die concave and convex die clearance improvement
Firstly, the clearance between concave and convex die is Z = 1.2t (t is the nominal thickness of the sheet) for test drawing. Due to
Z is too small, the degree of deformation is too large, which not only makes the surface of the die and parts seriously strained, but also makes the bottom corner of the cone of the parts seriously thinned and cracked. For this reason, while improving the lubrication conditions and the surface quality of the die, Z = t + 0.26t (t is the middle value of the allowable deflection of the thickness of the sheet) was used to readjust the deformation.
(t is the middle value of the allowable deviation of the sheet thickness), the gap between the concave and convex die was readjusted and the experiment was successful, which solved the problem of thinning and cracking at the bottom corner.
In particular, in order to reduce the deformation resistance during the second deep drawing and make the workpiece less likely to be cracked, the semi-finished product of the first deep drawing is designed to be a good solution to the problem of bottom rounding and crack.
The first deep-drawing semi-finished product is designed with a 45° angle tapered bottom, which aims to improve the deep-drawing deformation performance of the material. Adjustment of clearance of concave and convex die for final drawing The maximum wall thickness of the first deep-drawn semi-finished products reaches 2.3 mm, and when the second set of deep-drawing die with the clearance of concave and convex die is 1.1 t is used for the final deep-drawing forming of the semi-finished products which have been hardened, because the formed parts are tightly wrapped on the convex die.
The strong demoulding caused the deformation of the cylinder wall, resulting in a convex belly (Figure 3). However, there was no strain on the working surface of the part and the die.
The forceful demoulding caused deformation of the barrel wall, resulting in a convex belly (Fig. 3). However, there was no strain on the working surface of the part and the mold. Figure 3 For this reason, while improving the lubrication conditions, the clearance of the concave and convex die of the second set of drawing die was adjusted according to Z = tmax + 0.12t, so that the deformation of the cylinder wall of the part could be overcome.
Adjustment of heat treatment process
In order to eliminate the internal stress, the part was finally annealed at low temperature of 650 °C .
Selection and use of lubricants
In the whole production process, in addition to the reasonable adjustment of the gap between concave and convex, another important factor for the successful drawing of parts is the reasonable selection and use of lubricants. The following
3 kinds of lubricants are used together to ensure the smooth completion of the deep drawing process. 1
The lubricant can separate the contact surface of parts and concave die, meanwhile, the volatile substance in it can take away part of the heat generated in the deep drawing process. 2, G0124 vinyl chloride is another lubricant used in the deep drawing process of stainless steel sheet. Coated on the surface of the blank or semi-finished product in contact with the working surface of the concave die to make up for the unevenness of HB221 in the formation of a protective film on the working surface of the concave die. Because HB221 protective film is formed during the deep drawing process, its uniformity is difficult to guarantee, plus the unevenness is inevitable when it is applied.
It should be noted that HB221 and G0124 can not wait until the lubricant is dry and solid on the coated surface before drawing, because it will affect the gap between concave and convex die, causing the parts to pull and crack or produce wrinkles and other defects. 3、No.25 machine oil. Mainly used for the second deep drawing, coated on the contact surface of convex die and forming parts, so as to smoothly release the die, thus avoiding deformation and strain . Summary Editor After exploration and repeated experiments, the production method finally succeeded in eliminating the intermediate heat treatment and deep-drawing the stainless steel cylindrical parts with ideal surface quality and used for mass production. Die life is also greatly extended, achieving good production benefits. After two successful deep-drawing t = 115 mm stainless steel barrel, and t = 018 mm and t = 1 mm stainless steel barrel has been deep-drawn three times, and basically successful. The difference is that after the second deep-drawing, a heat treatment of “box annealing” at 860 °C is required, while a heat treatment of “bright annealing” is not necessary.