Analysis of common defects in metal powder injection molding
Common defects of metal powder injection molded parts are as follows.
1. Underinjection: Underinjection refers to incomplete injection products caused by insufficient pressure of injection molding machine or poor fluidity of injection materials. The causes of underinjection are poor fluidity of materials, too small wall thickness of products, too low mold temperature and too short injection time, which can be solved by measures such as improving fluidity of materials or changing materials, increasing wall thickness, raising mold temperature, increasing injection pressure and prolonging injection time.
2, welding mark: the material in the injection process in the cavity is divided into a number of material flow and then converged together, the junction may appear linear traces, that is, welding mark, affect the appearance of the product quality and even mechanical strength. The reasons for forming weld marks are too low injection pressure, too slow injection speed, too low material temperature and mold temperature and too many material flow, which can be solved by corresponding measures such as increasing injection pressure, speeding up the injection speed, increasing material temperature and mold temperature and appropriately reducing shunt.
3. Air pocket. In the process of injection, the air in the cavity of the mold can not be discharged, and it is wrapped with the material or compressed to the inner wall of the mold to form air holes, causing under-injection on the surface of the product, affecting the appearance quality and even mechanical strength of the product. The main causes of air holes are poor exhaust, improper gate position, too fast injection speed and too big change of product thickness, which can be solved by adding or deepening the vent, changing the gate position, slowing down the injection speed, prolonging the pressure holding time and avoiding the sharp change of product thickness.
4, deformation. Deformation refers to forming products after cooling bending or distortion, directly affect the appearance of the size of the product accuracy, and even cause the scrap of the product. The reasons for the deformation are uneven cooling of the products, too hot and premature topping, too thin and unreasonable structure of the products and residual stress in the products, which can be solved by measures such as uniform cooling of the mold channel, prolonging the pressure holding time and timely ejecting the products, improving the wall thickness and structure design of the products and improving the forming conditions.