Time:2023-12-13 Browse: 29
Zinc alloy die casting is a precision casting method that utilizes high pressure to force molten metal into complex-shaped metal molds. The causes of deviations in the surface roughness of zinc alloy die castings are relatively complex, involving multiple aspects such as molds, processes, and materials. Below, the editor from Aude Zinc Alloy Die Casting Factory elaborates on the specific reasons:
If the machining precision of the mold cavity surface is insufficient, with existing tool marks, grinding marks, and other defects, the molten zinc alloy will fill these surface flaws during the die casting process, resulting in increased surface roughness of the die castings.
Surface treatments such as nitriding and hard chrome plating on the mold can improve its surface hardness and finish. Improper surface treatment—such as uneven nitriding layers or pinholes in the chrome plating layer—will change the surface roughness of the mold, thereby affecting the surface quality of the die castings.
During die casting production, the mold is repeatedly scoured and impacted by molten zinc alloy, making it prone to wear. Wear is particularly severe in areas such as gates and runners. After wear, the mold's surface roughness increases, leading to defects like scratches and die sticking on the die castings, which adversely affects surface roughness.
Unreasonable design of the mold draft angle will cause excessive friction between the die casting and the mold surface during demolding, resulting in scratches on the casting surface and increased surface roughness.
Excessively high die casting temperature leads to overly good fluidity of the molten zinc alloy, which easily scours the mold surface. Meanwhile, the large shrinkage during the cooling process will cause defects such as blowholes and porosity on the casting surface, affecting surface roughness. Conversely, excessively low temperature results in poor fluidity of the molten zinc alloy and incomplete mold filling, leading to defects like cold shuts and misruns, which also deteriorate surface roughness.
An excessively high die casting speed causes the molten zinc alloy to impact the mold cavity at a high velocity, resulting in splashing and eddy currents that make the casting surface rough. An excessively low speed prolongs the mold filling time, making it easy for an oxide film to form on the surface and increasing surface roughness.
Insufficient pressure holding time means the molten zinc alloy cannot receive adequate pressure supplementation during solidification, leading to defects such as shrinkage marks and blowholes on the casting surface, which affect surface roughness. Excessively long pressure holding time makes demolding difficult and prone to scratching the casting surface.
Improper use of mold release agents also affects the surface roughness of die castings. Excessive or uneven spraying of the release agent will form an uneven film on the casting surface, impairing surface finish. Poor-quality release agents may chemically react with the zinc alloy, corroding both the mold and the casting surface.
Excessively high content of impurities such as lead, tin, and cadmium in the zinc alloy will reduce its fluidity and mechanical properties, making the casting surface prone to defects and increased roughness. In addition, uneven alloy composition will result in inconsistent performance and surface quality across different parts of the die castings.
High-purity zinc alloy exhibits better fluidity and formability, enabling it to fill the fine details of the mold cavity and produce die castings with a smooth surface. Insufficient material purity—characterized by high levels of impurities and gas—will cause defects such as blowholes and slag inclusions during die casting, affecting surface roughness.
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