In the mold processing, the wire electric discharge machining technology has been widely used, but in the online cutting process, the mold is prone to deformation and cracks, resulting in scrapping of parts, resulting in cost increases and other problems. Therefore, the problem of deformation and cracking of the mold in the wire cutting process has attracted more and more people's attention. For many years, people have not enough understanding of the deformation and cracking of the wire cutting process, which often causes a line between the wire cutting processing department and the incoming material processor. Repelling responsibility and creating contradictions.
In fact, the causes of deformation and cracking are various, such as material problems, heat treatment problems, structural design problems, process arrangement problems, and the problem of workpiece clamping and cutting line selection during wire cutting. Among these many factors, can we find the law of deformation and cracking of wire cutting? The author has proposed the following measures to prevent deformation and cracking through intensive research for many years.
1. The main factors that cause deformation and crack
In the production practice, the author has analyzed a large number of examples and found that the deformation and crack generated by the wire cutting process are related to the following factors.
1.1 related to the structure of the part
1) Where the narrow and long concave molds and punches are easily deformed, the magnitude of the deformation is related to the shape complexity, the aspect ratio, and the width ratio of the cavity to the frame. The more complicated the shape, the larger the aspect ratio and the ratio of the cavity to the frame width, and the larger the deformation amount of the mold. The law of deformation is the middle of the cavity, and the punch is usually warped;
2) Any quenching cavity with complex shape and clear angle is prone to cracks at sharp corners, and even prone to bursting. The frequency of its occurrence is related to the composition of the material, the heat treatment process, and the like;
3) The cylindrical wall thickness is better than that of the book parts. If it is cut on the inner wall, it is easy to deform, and it generally changes from a circle to an ellipse. If it is cut into the gap, it will easily burst when it is about to cut through;
4) The deeper notch cut from the outside of the part is prone to deformation, and the law of deformation is the end of the mouth. The amount of deformation is related to the depth of the notch and the material properties.
1.2 Related to the hot processing process
1) When the mold blank is forged, the forging temperature is too high or too low, and the final forging temperature is low;
2) The final forging temperature is too high, the grain grows, the cooling rate is too slow after the final forging, and there is a mold blank in which the net carbide precipitates;
3) The forging blank annealing is not carried out according to the spheroidizing annealing process, and the spheroidized pearlite has more than 5 grade parts;
4) The quenching heating temperature is too high, the austenite grains are coarse, the material toughness is lowered, and the brittleness is increased;
5) Parts that are not tempered and tempered in time due to quenching of the workpiece.
1.3 related to the machining process
1) The die with a large area is cut off in the middle and has not been hollowed out beforehand. Due to the large volume in the frame, the frame size will produce a certain deformation;
2) Where there is no shape starting point in the blank, it has to be cut from the outside of the blank, no matter how the tempering and shape of the punch is, it is generally easy to produce deformation, especially the quenching part is severely deformed, even in the cutting;
3) For the grinding parts after heat treatment, there are no grinding wheel particle size, feed amount, cooling method and other technical requirements. After grinding, there are parts such as burns and micro cracks.
1.4 related to materials
1) There is serious carbide segregation in the raw materials;
2) Materials with poor hardenability and easy deformation, such as T10A, T8A, etc.
1.5 related to the wire cutting process
1) The wire cutting path is improperly selected and is prone to deformation;
2) The clamping method of the workpiece is not reliable, and the selection of the clamping point is improper, and the deformation is easy to occur;
3) The electrical specifications are not properly selected and are prone to cracks.
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