Understanding the Metal Injection Molding Process

In the last few decades, Metal Injection Molding (MIM) has become a popular manufacturing process for the production of small complex parts with remarkable accuracy and consistency. MIM combines the strength of metal with the flexibility of plastic injection molding, which is why it has found favor in many industries, including aerospace, automotive, healthcare, and electronics where versatility and precision are both of high importance.

In this post, we’re breaking down the metal injection molding process and discussing its advantages and limitations to make it easier for manufacturers to harness the potential of this revolutionary technology for their business. Let’s dive in.

What Is Metal Injection Molding?

Metal powder injection molding is an advanced manufacturing technique born from the amalgamation of powder metallurgy and plastic injection molding where a solution of metal powder and binder is injected into molds and then sintered to create an object. This allows the creation of intricate parts with higher accuracy and ease than traditional machining and casting. 

The metal injection molding process typically involves four steps – feedstock preparation, injection molding, binder removal, and sintering. However, post-processing is also a crucial step for achieving the desired surface finish and mechanical properties. 

Feedstock Preparation

First, a homogenous mixture, also known as a feedstock, is created by blending metal powder with a thermoplastic binding material at high temperature using a shear roll extruder or kneader. The feedstock is then granulated into small pellets. The type of metal powder used differs case-by-case but MIM allows the use of a wide variety including titanium, stainless steel, copper and superalloys. 

Injection Molding

Next, the pellets are fed into the molding machine where they’re heated before being deposited into the die cavity through a controlled nozzle. The mold is designed in the shape of the desired component.

Debinding

The molded object is heated to decompose or evaporate the binding material, leaving behind a ‘green’ part with an interconnected pore network. The porous part is weak during this stage and must be handled with care. Some binder may also be left over.

Sintering

During this last step of the metal powder injection molding process the green part is put in a furnace, generally at a temperature below the melting point of the metal, in order to fuse the metal particles together. This step eliminates the remaining binder material. It also causes the part to shrink in size by as much as 15% to 20% and become denser.

Post-Processing

Depending on the application, the sintered part is subjected to post-processing treatments, machining, plating, or heat treatment to improve its surface finish and mechanical properties like strength.

Advantages of Metal Injection Molding

The metal injection molding process has many key advantages that have made it an attractive choice for large scale production of intricate components in many industries:

• MIM parts are known for their accuracy, consistency, and reliability. The process yields parts with complex geometries and with a near-net shape. Even features such as undercuts, teeth, and engravings are possible without the need for secondary machining and fabrication processes.
• Manufacturers can create a variety of shapes and even multi-component parts at once.
• Metal powder injection molding process supports a wide range of metal powder. This allows manufacturers to customize it according to their specific requirements.
• MIM parts exhibit superior mechanical properties comparable to machined wrought alloy parts, even with minimal post-processing.
• Compared to machining processes, MIM produces much lesser material waste.
• This method is much faster and cost-effective than traditional manufacturing methods like machining, investment casting, and stamping for large scale production of intricate parts.

Disadvantages of Metal Injection Molding

• As mentioned earlier, parts created using the metal injection molding process shrink by up to 25%, which can lead to inaccuracies in some cases. But if the shrinkage in size is accounted for while designing the mold, the final product is of greater accuracy.
• MIM is only suited for the production of small to medium sized parts due to mold and furnace capacity.
• MIM can be more expensive than other manufacturing methods because of the costs associated with the feedstock and high temperatures required for sintering. This is why it’s best suited for large scale production to bring down the costs.

Is Metal Injection Molding Right for Your Business?

Metal injection molding has a few disadvantages but they’re offset in the face of the advantages offered by this manufacturing method. If your business requires small to medium sized parts with exceptional accuracy and reliability at high volumes, the metal injection molding process may just be what you need for better cost-efficiency and design flexibility. Explore MIM metal powder at KBM or talk to our experts to learn more about metal powder injection molding.