A large number of cold stamping processes have been used in the production of automotive stamping parts, which are suitable for the needs of many varieties and large-scale production of automotive stamping parts industry. In medium and heavy-duty vehicles, most of the covering parts, such as body outer panel, and some load-bearing and supporting parts, such as frame, carriage and other auto parts are automobile stamping parts. The steel used for cold stamping is mainly steel plate and steel strip, accounting for 72.6% of the total steel consumption of the vehicle. The relationship between cold stamping materials and the production of automobile stamping parts is very close. The quality of automobile sheet metal materials not only determines the performance of the product, but also directly affects the process design of automobile stamping parts, and affects the quality, cost, service life and production organization of the product. Therefore, reasonable selection is necessary Using materials is an important and complex work.
Common problems of stamping parts:
1. Adhesion and scratch: poor appearance on the surface of the part or die due to friction between the material and the punch or die;
2. Burr: mainly occurs in the gap between the cutting die and the blanking die, or the burr will be produced when the gap between the cutting edges is large or small;
3. Line offset: when the part is formed, the part contacting with the die is first extruded and a line is formed;
4. Convex concave: there are foreign matters (iron filings, rubber, dust) mixed in the uncoiled line, causing convex concave;
5. Twists and turns: due to uneven stress, poor matching of drawbead or poor control of press slider, etc., twists and strains occur at corner R or embossed part of the part;
6. Wrinkles: wrinkles at the edge or R position are caused by poor adjustment of the press slide, low accuracy of the press, improper adjustment of air cushion pressure, large punch or R position, etc.
7. Other specific problems: in daily production, when the punching size is too large or too small (may exceed the specification requirements) and there is a large difference between the punch size and the punch size, in addition to the factors such as the design size, processing accuracy and blanking clearance of forming punch and die, the following aspects shall be considered to solve.
(1) when the cutting edge is worn, the tensile stress of the material increases, and the tendency of turning over and twisting of the stamping parts increases. When turning over occurs, the punching size tends to be smaller.
(2) the strong pressure on the material will cause plastic deformation of the material, which will lead to the increase of punching size. When the pressure is reduced, the punching size will be smaller.
(3) the shape of the edge end of the punch. If a bevel or arc is made at the end, the punching size will be larger because the punching force is slowed down and the punching parts are not easy to turn over and twist. When the end of the punch is flat (no bevel or arc), the punch size will be smaller.
8. Methods to prevent the stamping parts from turning over and twisting
(1) reasonable mold design. In progressive die, the arrangement of blanking sequence may affect the forming accuracy of stamping parts. In order to reduce the impact of punching force on the forming of stamping parts, large area blanking is usually arranged first, and then small area blanking is arranged.
(2) press the material. In order to overcome the traditional mold design structure, a material holding gap is opened on the discharge plate (that is, when the mold is closed, the material can be compressed). For the key forming parts, the discharge plate must be made into a inlaid structure, so as to solve the abrasion (compression) damage caused by the pressing part of the discharge plate caused by long-time stamping, and the material cannot be compressed.
(3) add strong pressure function. That is to say, the thickness of the pressing part of the discharge insert is increased (the normal thickness of the discharge insert is H + 0.03mm), so as to increase the pressure on the material at the die side, so as to prevent the stamping parts from turning over and distortion during punching.
(4) bevel or arc shall be made at the edge end of the punch. This is an effective way to reduce the punching force. By reducing the buffer cutting force, the drawing force on the die side material can be reduced, so as to achieve the effect of preventing the stamping parts from turning over and twisting.
(5) in daily mold production, attention should be paid to maintain the sharpness of punch and die edge. When the cutting edge is worn, the tensile stress of the material will increase, so that the tendency of turning over and twisting will increase.
(6) unreasonable or uneven blanking clearance is also the cause of stamping parts turning and twisting, which needs to be overcome.
Material selection principle of automobile stamping parts
In the selection of materials, firstly, according to the types and characteristics of automobile stamping, the metal materials with different mechanical properties are selected to achieve the purpose of improving product quality and saving materials.
Generally, the following principles should be followed when selecting the materials of automobile stamping parts:
A. the selected materials shall first meet the service performance requirements of auto parts;
B. the selected materials shall have better technological properties;
C. the selected materials shall have better economy.