Analysis of Defects in Metal Powder Injection Molding

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Analysis of Defects in Metal Powder Injection Molding (MIM)

Metal powder injection molding (MIM) is a molding process in which a plasticized mixture obtained by mixing a binder and metal powder is injected into a specific mold. It is a combination of powder metallurgy and polymer injection molding,,which is new type of molding technology.

Common defects of metal powder injection molded parts are as following

1)Not full mold injection: It refers to the incomplete injection product caused by insufficient pressure of the injection molding machine used or poor fluidity of the injection material. The reasons for insufficient injection are poor material fluidity, slim product wall thickness, low mold temperature and short injection time. Corresponding measurement can be taken to improve material fluidity or changing materials, increasing wall thickness ,mold temperature and injection pressure and extending the injection time to solve the problem.

2)Welding mark: The material is divided into several streams in the cavity during the injection process and then merged together. There may be linear marks at the confluence, that is, weld marks, which affect the appearance quality and even the mechanical strength of the product. The reasons for the formation of weld marks are that the low injection pressure,slow injection speed, low material temperature and the mold temperature and the too much streams. You can increase the injection pressure, accelerate the injection speed, increase the material temperature and the mold temperature and reduce it appropriately. Such Measurements are took and then diversion can be resolved.

3).Air holes: During the injection process, the air in the mold cavity is too late to be discharged, and the material is enclosed or compressed to the inner wall of the mold to form air holes, which is caused under-injection on the surface of the product, affecting the appearance quality and even the mechanical strength of the product. The reason that forms air holes is poor exhaust, improper pouring position, too fast injection speed, and excessive product thickness change. You can increase the vent hole or deepen the vent hole, change the pouring position, and slow down the injection appropriately. Measurements are took such as speed, extending the holding time and avoiding sharp changes in product thickness, by which the problems can be solved.

4) Deformation: Deformation refers to the bending or distortion of the molded product after cooling, which directly affects the appearance and dimensional accuracy of the product, and even causes the product to be scrapped. The reason for the deformation is uneven cooling of the product, too hot and premature topping of the product, too thin and unreasonable structure of the product, and internal residual stress of the product. The mold water channel can be used to cool uniformly, extend the pressure holding time and eject the product in a timely manner, and improve the product. Measures such as wall thickness and structural design and improving molding conditions can be solved.