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Metal Injection Moulding

What is Metal Injection Moulding (MIM)?

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What is metal injection moulding, and how does it work? Learn the basic principles and fundamental mechanics, as well as the key benefits and limitations of this manufacturing process.

What is Metal Injection Moulding?

Metal injection moulding, or MIM, was first developed in the 1970s by Raymond Wiech in the US, but it has only been used commercially in the last twenty years. It combines the geometrical complexity possible from injection moulded plastic with the mechanical properties of high performance metallic alloys. Components can be produced in a wide range of metals – steels, aluminum and titanium – and can be subjected to secondary treatments.

Despite there being a great contrast between the MIM and die casting processes, these two technologies are often compared as they are two of the most economical manufacturing processes for producing large bulks of complex-shaped metal components (over 100,000 parts).

How Does Metal Injection Moulding Work?

MIM involves four main steps: feedstock preparation, injection moulding, debinding and sintering. A simple concept, a complex process.

 

1. Feedstock Preparation – This stages involves blending very fine metal powders with polymer binders to achieve the desired material properties. The mix is then heated into a viscous mass. The mass gradually cools down and is processed into granular pellets to form the “feedstock.

2. Injection Moulding – Next, the feedstock is heated and injected into a mould cavity under high pressure, allowing for extremely complex shapes. Once the MIM component is removed, it is referred to as a “green” part.

3. De-binding – In this stage, the “green” part is put through a controlled process called “debinding” that involves removing the binder, preparing the part for the final step. Once, debinding is complete, the component is referred to as “brown.”

4. Sintering – After debinding, the brown part enters a continuous sintering process, where the parts are thermally processed in a controlled atmosphere to form a high-density metal component. During this sintering process, an approximate 16 to 18 percent shrinkage occurs, which results in products with densities approaching 98 percent of the theoretical density for a given alloy. It is vital to account for this shrinkage and ensure operating conditions and carefully controlled in order to achieve needed dimensional and performance requirements.

 

After the final MIM component is made, the characteristics and properties of the part can be further amplified or optimized by a wide range of secondary operations, including: heat treatment, physicochemical surface treatment, chemical surface treatment, mechanical surface treatment, nonmetallic coatings, metallic coatings, organic coatings, and wear resistant coatings.

Advantages and Disadvantages of Metal Injection Moulding

While metal injection moulding is a viable and even ideal manufacturing process for many applications, it’s not without its flaws. In this section, we cover its benefits and limitations.

Like plastic injection moulding, MIM demands a higher front-end cost but offers a significantly lower unit price. This makes it a cost-effective solution for producing higher volumes of metal parts. Due to the nature of the process, MIM can eliminate several product finishing (post-processing) steps, decreasing the time to manufacture ready-made components.

MIM offers excellent accuracy and precision. It is often used to produce intricate shape parts with very tight and precise tolerances, which makes it ideal for high-end applications, such as in the aerospace, aviation and automotive industries.

Generally speaking, any structure or shape that can be achieved using plastic injection moulding can be replicated in steel by MIM, but there are some limitations or design rules/considerations to keep in mind:

  • Although MIM has been used to produce parts weighing up to 453g, the process is recommended for producing parts under 100g. The weight reduction increases the precision of dimensional tolerances and reduces raw material consumption, which have significant effects on the total cost.
  • The maximum allowable radius is recommended for all edges, especially internal edges since sharp edges can be sources of potential cracks.
  • Section changes should be gradual, facilitating the flow of material during injection and avoiding isolated masses.
  • A flat face will facilitate the palletizing of the part inside the MIM furnace. The more stable this support is, the smaller the deformations will be and the more precise the dimensional tolerance will be.

MIM with HLH

Considering the metal injection moulding process for your project? Contact our team of experts at info@hlhrapid.com for advice or upload your CAD file here for a DFM and quotation. Use HLH’s MIM services to get custom industrial grade components in as fast as 3 weeks.

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