There are two main reasons for strain during workpiece forming:
One is that the mechanical wear is formed on the surface of the workpiece and the surface of the die convex and concave die because of the macroscopic mechanical concave or uneven surface of the die convex or die surface or the inclusion of other hard particles between the forming material and the die convex surface and the die surface. The solution is to carefully grind the surface of the die convex and concave die and strengthen the production. The management of the environment.
Two is caused by the wear of the surface of the workpiece and the surface of the die convex and concave die. It is also the most common and difficult situation in production. The following detailed analysis of the formation of adhesive wear and some basic measures to reduce the adhesion wear. In order to solve the problem of strain in the forming process of mould and workpiece, the basic principle of reducing adhesive wear should be reduced, and the nature of contact pairs should be changed as the starting point.
The following three pairs of contact pairs are formed, namely, the raw material, the workpiece and the mold, and the mold.
1. through the surface treatment of raw materials, such as phosphating, spraying or other surface treatment of raw materials, forming a layer of non metal film on the surface of the formed material, it can greatly reduce or eliminate the scratch of the workpiece. This method often costs higher, and needs to add additional production equipment and increase production process. This method sometimes has some effect, but it is seldom applied in practical production.
2. adding a layer of PVC film between mold and forming material can sometimes solve the problem of workpiece pulling. For the production line, the continuous supply film can be achieved through the mechanism, and for the stamping equipment produced in the periodic production, each piece of production must be added a thin film to affect the production efficiency. The general cost of this method is very high, and a large amount of waste will be produced. It is advisable to adopt this method for the production of small large pieces of large pieces. In some occasions where the forming load is very small, sometimes the problem of pulling the workpiece can be solved by adding lubricating oil or adding EP (extreme pressure) additive lubricant.
3. by changing the die convex, die material or the surface treatment of the die convex and concave die, the formed material is changed with the convex and concave die. Practice has shown that this is an economical and effective way to solve the problem of pull injury, and is widely adopted at present.
(1) the hard alloy can be used to solve the problem of scratch of the workpiece from the die convex and die material. In general, the convex and concave die made of this material is very high in tensile resistance, and the problem is that the material cost is high and it is difficult to process. For the larger mold, it is difficult to burn the large hard alloy block. Even if firing is successful, there may be cracks in the process, and the yield is low, and some of them are almost difficult to form. In addition, the cemented carbide is brittle, and must be extremely careful in the process of handling, installation and use. In addition, because the structure of the hard alloy is composed of hard tungsten carbide particles and soft bonding phase cobalt, hard tungsten carbide particles have high wear resistance and bite resistance, while cobalt phase is low in hardness and poor in wear resistance. The cobalt phase will be worn first in the process of use, making the surface of convex and concave die uneven, so that the surface of the concave die is uneven. The surface of the workpiece will also show a tensile mark. At this time, the surface of the die and die should be polished and polished before being reproduced. The use of a suitable copper based alloy can also solve the problem of the work of the workpiece, but the hardness of the copper base alloy is low, and the wear and tear is easy to appear. In the case of mass production, the cost of the material is low. For the larger mold, such as the forming die of the automobile panel, the alloy cast iron is used in large quantities. The cast iron can only reduce the strain of the workpiece and can not eliminate the problem of drawing. However, the mould made by this way is usually short in life. After a period of time, if there is a strain, it is necessary to repair the mold and re treat the surface.
(2) it is an economical and effective way to solve the problem of scratch on the surface of the workpiece by the surface treatment of the die, especially the surface super hardening treatment of the die convex and concave die. There are many kinds of surface treatment methods, such as hard chromium plating, electroless nickel phosphorus, special alloy of brush plating and so on. Chemical heat treatment has various kinds of nitriding, boriding, sulphur and so on; surface super hardening treatment includes chemical vapor deposition (CVD), physical vapor deposition (VVD), physical and chemical vapor deposition (PvD), “ID”. Coating treatment. Electroplating, electroless plating and brush plating are different ways to form alloy coating on the surface of workpiece by electrochemical or chemical reaction. The properties of the alloy coating are different. As for wear resistance and occlusal use, hard chromium plating, electroless Ni-P plating and nickel tungsten alloy plating are widely used. These methods can sometimes achieve certain results for smaller forming load or larger die. The problem of such surface treatment is that on the one hand, the hardness of the surface hardened layer is low, and it is easy to wear. On the other hand, the coating is mechanically combined with the matrix material. In the case of large load, sometimes the coating will be flake with a few times, and the effect will be lost once the coating is peeled off. Chemical heat treatment is to heat and heat the workpiece in a medium containing some or some chemical elements. Through the physical and chemical effects of the workpiece and the medium, these or these elements are infiltrated into the surface of the workpiece, and then the appropriate square is used.
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