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Eliminate the defects of zinc die castings
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Zinc zinc die castings can be manufactured into precise near-net-shaped parts with a wide range of surface quality. It can achieve mass production and achieve continuous high quality.Coupled with the wide physical and mechanical properties of zinc die castings, this makes zinc castings the first choice for high-volume parts such as electronics, lock safety and door and window hardware, hydraulic and pneumatic connections and accessories, and decorative parts for the automotive industry.
However, the pursuit of high-quality decorative surfaces makes the surface quality standards more stringent, which affects the casting cost and increases the scrap rate. When producing zinc die castings, eliminating surface defects is a key requirement. Die-casters should consider the following possible causes of casting defects:
The chemical properties of the alloy. Excessive amounts of iron, lead, tin, cadmium, manganese, and intermetallic compounds / oxides are all causes of surface defects.
Metal temperature / metal processing. Changes in temperature and temperature affect the quality of castings. Adding ingots or scrap to the furnace at the wrong time or under the wrong conditions will also affect the quality of the casting.
Casting design. Variations in cross-sectional thickness, no rounded corners, surface texture and morphology may all cause surface defects.
Mold design. Runner and gate size calculations, machine performance, gate position relative to the casting, mold temperature heating / cooling, use of overflow wells and vents all play a key role in reducing defects.
Push out. Sufficient ejection force, the size and position of the ejector rod, the thickness of the ejection part, and reduction of mechanical damage / scratch during ejection are all factors affecting defects.
Mold lubrication. The die-caster must control the amount and type of lubricant to prevent deposition / carbonization / waxing on the mold surface.
Secondary operation. Defects can occur during removal / breaking, grinding, polishing, and shot blasting. These factors must be considered during the casting / mold design stage.
Defects after casting
In order to achieve a higher surface quality of zinc alloy die castings, the effects of multiple stages must be considered after the casting is completed. Most of these stages are to identify, produce or reject defective castings after the castings are processed.
Secondary operations include shearing, de-gate, grinding and polishing, vibration or shot blasting, machining and plating / painting, etc. In these operations, scrap may occur, but from a final point of view, some forms of scrap can be ignored (such as processing waste due to dimensional errors).
Casting movement and casting process usually also produce the same amount of scrap or castings with surface defects. Multiple clamping points will also damage the casting unless very careful during the transportation of the casting. Normally, polishing or shot blasting is not enough to eliminate edge cuts, small pits, and pinching during transportation.
After a casting cycle is completed, the casting is ejected. In some cases, castings fall onto conveyors or pallets and stainless steel or plastic storage trays. During the casting process, due to the slight impact of the corners of the steel disc and the casting, this may cause dents or pits on the sensitive surface or edge. The designer of the die casting mold should consider this factor when designing the positioning of the casting in the die casting mold. When the casting is pushed forward, the sliding edge of the jack, face jack and sand core should be adapted. The same principle applies during the cutting process. Assuming the same precautions are in place, using robots to pick and place can reduce the risk of impact damage in many cases.
Remedy:
Control of metal chemical composition, regular pre-furnace analysis and operating procedures will reduce the risk of defects.
Reduce oxides generated by turbulence in filling. In order to maintain these conditions, die-casters must establish consistent process conditions, cycle times, and uninterrupted operation.
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