1) The design of the die casting itself is unreasonable: the wall thickness, shape, round corner, demoulding angle and porosity are not appropriate.
2) Performance problems of die-casting machine: insufficient injection force and locking force, improper casting pressure and filling speed, mismatching of casting size and projected area of die-casting machine capacity, etc.
3) Problems in die casting mold design and manufacturing: mold matching, grinding, machining accuracy, impact of moving parts on casting size, and improper arrangement of cooling water.
4) Problems in die-casting process: improper selection of parting surface, design of gating system, exhaust slot, die-casting process parameters, coating, etc.
5) Alloy material and smelting problems: improper alloy raw material composition, new and old material ratio, smelting process, etc
6) Operation problems of die-casting workers: improper material temperature and mold temperature control, process parameter control, spraying, parts taking, production cycle, etc.
Incorrect one of the above factors or incorrect combination of several factors will lead to defects
Zinc alloy die-casting parts are now being used around various products. All kinds of electronic and electrical equipment are zinc alloy die-casting products. Therefore, it requires high surface quality of castings and good surface treatment ability. The most common defect of zinc alloy castings is surface blistering.
Defect characterization: there are convex bubbles on the surface of the die casting.
① Die-casting is discovered;
② Exposed after polishing or machining;
③ Appears after oil injection or electroplating;
④ Appears after a period of time.
Most of the blisters on the surface of zinc alloy are caused by pores, which are mainly pores and shrinkage pores. The pores are often round, while the shrinkage pores are mostly irregular.
1. Causes of porosity:
① During the filling and solidification process of molten metal, due to gas intrusion, holes are formed on the surface or inside of the casting;
② Invasion of gas volatilized from paint;
③ The gas content of the alloy liquid is too high and precipitates during solidification.
2. Causes of shrinkage:
① During the solidification process of molten metal, shrinkage cavity is generated due to the volume reduction or the final solidification part can not be supplemented by molten metal;
② The uneven thickness of the casting or the local overheating of the casting will cause the solidification of a certain part to be slow, and the surface will form a concave hole when the volume shrinks.
Due to the existence of pores and shrinkage holes, when the surface treatment of die castings is carried out, who may enter the holes. When baking is carried out after painting and electroplating, the gas in the hole expands due to heat; Or the water in the hole will become steam, which will cause the casting surface to bubble.