Introduction to the Process Flow of Powder Metallurgy Metal Injection Molding

Introduction to the Process Flow of Powder Metallurgy Metal Injection Molding

1. Overview

The main process flow of metal injection molding technology includes mixing, injection molding, debonding agent, sintering, and post-treatment.

2. Mixing materials

In metal injection molding technology, the mixture formed by powder and binder is called feed. MIM has high requirements for raw powder, and the selection of powder should be conducive to mixing, injection molding, degreasing, and sintering, which are often contradictory. Research on MIM raw powder includes: powder shape, particle size and particle composition, specific surface area, etc. The characteristics of the feed are determined by four factors, including the properties of the powder, the composition and content of the binder, the mixing process, and the granulation process. To improve molding and ensure the final size of the parts, low molecular weight polymers are usually used to reduce viscosity and fill the particle space as much as possible, avoiding gaps and pores. Mixing is the process of mixing metal powder with binder to obtain a uniform feed. Due to the nature of the feed material determining the performance of the final injection molded product, the mixing process step is very important. This involves various factors such as the method and sequence of adding binder and powder, mixing temperature, and characteristics of the mixing device. At present, this process step has been stuck at the level of relying on experience and exploration, and an important indicator for evaluating the quality of the mixing process is the uniformity and consistency of the feed obtained. The particle size distribution of powder particles can be obtained by mixing two particles with different shapes. Excessive binder can reduce the viscosity of the feed, which is not conducive to molding. The key to the success or failure of injection molding is to coordinate the complete powder characteristics, binder composition, and powder to binder ratio. The properties of some of the powder characteristics in metal injection molding are shown in Table 1-1.

Choosing the appropriate adhesive can reduce defects and improve molding efficiency. Choosing the appropriate mixing process can fully mix the powder and binder, laying a solid foundation for injection molding and sintering, and avoiding defects such as density gradient, bubbles, and incomplete mold filling. Due to mixing at temperatures above 100 degrees Celsius, be careful not to burn.

1.4.3 Injection molding

Injection molding is a crucial step in the metal injection molding process. Currently, CAE technology is used to analyze the warping deformation of molds and injection molded blanks before entering production. Different material properties and plastic structure are the main reasons for the warping deformation and plastic iron separation of plastic parts. By adjusting the injection temperature control system and plastic structure, optimization is achieved to produce plastic parts that meet quality requirements. In this step, various problems arise due to different injection molding parameters and properties of powder and binder, such as insufficient injection, foaming, cracking, density gradient, fracture, etc. Some of these defects cannot be detected during the injection molding stage. And its existing problems will be addressed in the subsequent steps