New Metal Forming Process: Introduction to MIM (Metal Powder Injection Molding) Process

New Metal Forming Process: Introduction to MIM (Metal Powder Injection Molding) Process

Editor's Note: Based on the current situation of MIM in China, some information has been supplemented.

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MIM is a near net metal forming process

MIM (metal injection molding) is the abbreviation of metal injection molding. A molding method that injects a plasticized mixture of metal powder and its binder into a model. It involves mixing the selected metal powder with an adhesive, then granulating the mixture, injecting the desired shape matrix, and then sintering at high temperature to obtain a strong metal part.

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MIM process steps

The MIM process combines the flexibility of injection molding design with the high strength and integrity of precision metals to achieve low-cost solutions for extremely complex geometric components. The MIM process is divided into four unique processing steps (mixing, molding, degreasing, and sintering) to achieve the production of components, and to determine whether further machining or surface treatment is required based on product characteristics

blend

Fine metal powder is mixed with thermoplastic and paraffin adhesives in precise proportions. The mixing process is carried out in a specialized mixing device, heated to a certain temperature to melt the adhesive. In most cases, mechanical mixing is used until the metal powder particles are uniformly coated with an adhesive and cooled to form a granular shape (called a raw material) that can be injected into the mold cavity.

CNPIM Note: Mixing is a very important process in the MIM process. Currently, there are several mixing systems with different additives, which require different degreasing methods to remove. The most commonly used wax and plastic bases correspond to thermal and catalytic degreasing, respectively.

forming

The equipment and technology of injection molding are similar to those of injection molding. Granular raw materials are fed into the machine for heating and injected into the mold cavity under high pressure. This process is formed by cooling the green part and demolding it. Only when the adhesive is melted (fully fused with the metal powder) at a temperature of about 200 ° C can the entire process be carried out. The mold can be designed to have multiple cavities to improve productivity. The shrinkage generated during the sintering process of metal parts should be considered in the design of mold cavity dimensions. The shrinkage changes for each material are accurate and known.

Degrease

Degreasing is the process of removing the adhesive from the molded part. This process is typically accomplished in several steps. Most of the adhesive is removed before sintering, and the remaining part can support the components to enter the sintering furnace.

Degreasing can be accomplished by various methods, the most commonly used being solvent extraction. The degreased components are semi permeable, and the residual adhesive is easily volatilized during sintering.

CNPIM Note: Currently, the most commonly used degreasing method is the Catalyst catalytic degreasing method launched by BASF, which requires the use of a dedicated catalytic degreasing furnace. (For more information, please visit the Zhongwei Precision official website.)

firing