1) The design of the die-casting itself is unreasonable: the wall thickness, shape, fillet, draft angle, and hole size are inappropriate.
2) Problems with the performance of the die-casting machine: insufficient injection force and clamping force, improper casting pressure and filling speed, mismatch of die-casting machine capacity of casting size and projected area, etc.
3) Problems of die casting mold design and manufacturing: mold matching, grinding, machining accuracy, the effect of moving parts on the size of castings, and improper layout of cooling water channels.
4) Problems with the die-casting process: selection of parting surfaces, design of the pouring system, exhaust grooves, die-casting process parameters, paint, etc. are inappropriate.
5) Alloy material and smelting problems: improper alloy raw material composition, ratio of new and old materials, smelting process, etc.
6) Operation problems of die-casting workers: control of material temperature and mold temperature, control of process parameters, improper spraying, part taking, production cycle, etc.
One of the above factors is incorrect, or the combination of several factors is incorrect, will cause defects
Zinc alloy die castings are now being used in the periphery of various products, and various electronic and electrical appliances are all zinc alloy die casting products. Therefore, they have high requirements on the surface quality of castings and good surface treatment capabilities. The most common defect of zinc alloy casting products is blistering on the surface.
Defect characterization: There are raised small bubbles on the surface of die-casting parts. ① Found after die casting; ② Revealed after polishing or processing; ③ Appeared after spraying or electroplating; ④ Appeared only after being left for a while.
Most of the blistering on the surface of zinc alloy is caused by pores, and the pores are mainly pores and shrinkage pores. The pores are often round, and the shrinkage pores are mostly irregular.
1. The causes of air holes: ① During the filling and solidification of the metal liquid, due to the gas intrusion, the holes in the surface or inside of the casting are generated; ② the gas intrusion from the coating is invaded; ③ the gas content of the alloy liquid is too high and it precipitates during solidification.
2. Causes of shrinkage: ① In the process of solidification of the molten metal, shrinkage occurs due to the volume reduction or the final solidified part cannot be compensated by the molten metal; ②The casting of uneven thickness or partial overheating of the casting causes a certain part Solidification is slow, and concave holes are formed on the surface when the volume shrinks.
Because of the existence of air holes and shrinkage holes, when the die-casting parts are subjected to surface treatment again, who may enter the holes. When baking is done after painting and electroplating, ② the gas in the hole is heated to expand; or the water in the hole will become steam, which will cause blistering on the surface of the casting.
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