Metal powder injection molding process

       

Metal powder injection molding is a new type of injection molding process developed on the basis of traditional injection molding and powder metallurgy processes.



Metal powder injection molding technology has shown unique advantages in manufacturing near-net-type products with complex shapes, uniform structure, high performance, high strength, and high precision.

Flow chart of metal powder injection molding process

Preparation of metal powder



Metal powder injection molding has higher requirements for raw powder, including powder morphology, particle size, particle size composition, specific surface area, and bulk density.



There are two main methods of raw material powder for metal powder injection molding: hydroxyl method and atomization method. Metal powder injection molding requires very fine raw material powder, so metal powder injection molding requires high.



Binder



Binders play a key role in metal injection molding technology. Only after adding a certain amount of binder, the powder has certain fluidity to be suitable for injection molding. After molding, the binder plays a role in maintaining the shape of the product.



The requirements of metal powder injection molding for the binder include: small contact angle with the powder, strong adhesion; no two-phase separation with the powder; certain strength after cooling; no cracking of the green body during degreasing, Serious defects such as bubbling; the viscosity of the pure adhesive at the injection temperature should be less than 0.1Pa·s.



Mixing



Mixing is the process of mixing the raw material powder and binder under a certain device and a certain temperature and fully and effectively stirring them to make them uniform and meet the injection requirements. The nature of the feed determines the performance of the final product.



Therefore, the process step of mixing becomes very important, which will involve various factors such as the method and sequence of adding the binder and powder, the mixing temperature, the characteristics of the mixing device, and the final evaluation of the mixing process. An important indicator is the uniformity and consistency of the feed.



Commonly used mixing devices include double screw extruder, type B impeller mixer, single screw extruder, plunger extruder, double planetary extruder, double cam mixer, etc.



Injection molding



In the powder injection molding process, injection molding is an important process that determines the production of qualified green bodies. The mixture is stirred and heated by the screw in the injection molding machine, and the plasticized mixture is injected into the mold cavity through the injection molding machine feeding system, and the pressure is maintained to compensate for the cooling shrinkage.



When the part is cooled and solidified and the part has sufficient strength, the mold is opened and the part is ejected with a thimble to obtain a green body.



Degreasing



Degreasing is a process in which all the binders in the molded body can be removed by appropriate methods. There are two basic methods of degreasing: solvent extraction and thermal decomposition.



The most important indicator for evaluating various degreasing technologies is the degreasing time. In addition, if the formation of liquid phase can be avoided during debinding, the deformation of the green body can be effectively controlled and the dimensional accuracy after sintering can be ensured.



sintering



Sintering is an important part of powder metallurgy, and it is also the last process of metal powder injection molding process.



Through sintering, the metal powder injection molding product can reach full or close to full densification. In the sintering stage, the sintering temperature must be controlled to obtain high-density metal parts to avoid any surface cracks, while the parts can maintain the original Some shapes have the same size shrinkage.



In order to ensure the control of temperature changes, the sintering process is carried out in a vacuum furnace that can accurately control the heating temperature.



Source: China Powder Network