1. Reasons for material turning and twisting during die casting In the progressive die, the shape of the punch is formed by punching the residual material around die casting parts. The reason for the blanking and twisting is the impact of the blanking force. During blanking, due to the existence of blanking clearance, the material is stretched on one side of the die (the material warps upward) and compressed on the other side of the punch. When using the unloading plate, the material is compressed by the discharging plate to prevent the material on the concave die side from warping upward. At this time, the stress condition of the material changes accordingly. With the increase of the material pressure of the unloading plate, the material on the convex die side is stretched (the compression force tends to decrease), while the material on the concave die surface is compressed (the tensile force tends to decrease). The flip of die casting is caused by the tensile of the material on the concave surface. Therefore, pressing and pressing materials is the key point to prevent the blanking parts from turning over and twisting. 2. methods to restrain the turning and twisting of die casting parts ( 1) . reasonable mold design. In the progressive die, the arrangement of blanking sequence may affect the precision of die casting. For the blanking of small parts of die casting parts, generally, large area blanking is arranged first, and then smaller area blanking is arranged to reduce the impact of blanking force on die casting parts forming. ( 2) . press the material. In order to overcome the traditional mold design structure, the discharge plate is opened with a material holding gap (that is, when the mold is closed, the discharge plate fits the die, and the gap between the discharge plate and the die where the material is contained is t-0.03-0.05mm). In this way, the unloading plate in die casting moves smoothly, and the material can be pressed again. In the key forming parts, the unloading plate must be made of inlay structure, so as to solve the wear (pressure) loss caused by die casting for a long time, and can not compress the material. ( 3) . add strong pressure function. That is, the thickness of the pressing part of the unloading insert (normal unloading insert thickness h+0.03mm) is increased to increase the pressure on the material at the concave side, thus inhibiting the deformation of die casting during blanking. ( 4) . the end of the edge of the punch is trimmed with a slope or arc. This is an effective way to reduce the blanking force. The reduction of buffer cutting force can reduce the tensile force on the material at the side of the die, thus the effect of suppressing the turning and twisting of die casting parts can be achieved. ( 5) . in daily die production, attention should be paid to maintaining the sharpness of the edge of punch and concave die. When the cutting edge is worn, the tensile stress of the material will increase, and the tendency of the die casting parts to turn over and twist will increase. ( 6) The unreasonable clearance or uneven clearance is also the reason for the material turning and twisting of die casting parts, which should be overcome.
