Metal Injection Moulding – Process, Pros, Cons & More

The market for metal injection moulding (MIM) is experiencing significant growth, rising from US$1.5 billion in 2015 to US$4.6 billion in 2024—an impressive tripling. Back in 1986, the market was valued at just US$9 million. This remarkable increase can be attributed, in part, to recent advancements that have enabled MIM parts to achieve strength and durability comparable to those produced by traditional methods such as CNC machining and casting.

In this article, we will explore the fundamentals of metal injection moulding to better understand this remarkable process and its capabilities.

What Is Metal Injection Moulding?

Metal injection moulding is a specialised form of injection moulding in which metal powder, combined with binders to create a feedstock, is injected into moulds under pressure to form solid objects. These objects are then treated to remove the binder and strengthen the metal parts through processes such as sintering.

MIM’s ability to work with metals allows its components to outperform plastics in key properties such as strength and durability.

For high-volume production of parts weighing less than 100 grams, metal injection moulding is often more feasible than processes such as machining, investment casting, and stamping. This method enables a high density of up to 99%, excellent surface finish, and the creation of complex geometries. Additionally, it accommodates features such as external and internal threads, thin walls (as small as 100 micrometres), profiled holes, and fine markings.

However, it also comes with certain limitations, including high initial investment and part size restrictions. Before we delve into those aspects, let us first compare it with another similar process: die casting.

Metal Injection Moulding vs. Die Casting

Metal injection moulding and die casting share certain similarities but also differ in several key aspects. Both processes involve injecting a liquid feedstock into moulds, followed by solidification. However, in MIM, the feedstock consists of metal powder combined with binding agents such as wax and polypropylene, whereas die casting uses molten metal.

In both methods, high pressure is used to inject the material into moulds. MIM, however, offers several advantages, including higher precision, tighter tolerances, superior surface finishes, fewer design restrictions, lower scrap rates, and minimal post-processing. Additionally, MIM supports both ferrous and non-ferrous metals, while die casting is typically limited to non-ferrous alloys.

Die casting, on the other hand, has its own strengths. It is generally more suitable and cost-effective for larger components, offers longer mould life, and in some cases, allows the mould to be filled under gravity. It can also be faster than MIM in specific scenarios, as MIM requires additional steps, such as binder removal, before producing the final part.

MIM Applications

Most metals can be ground into powders, which can then be used in metal injection moulding (MIM). As a result, MIM is suitable for a wide range of metals. It is particularly effective for producing small parts (typically under 100 grams) intended for high-volume manufacturing. Stainless steel is one of the most commonly used metals in this process.

MIM is also highly efficient for fabricating components from expensive and specialised materials such as tungsten carbide, cobalt-chrome and titanium alloys. Common applications of metal injection moulding across various sectors include:

• Automotive – In the automotive industry, MIM is used to manufacture precision components such as turbocharger vanes, rocker arms, injector nozzles, shift levers, and various fittings and connectors.
• Aerospace – Aerospace applications often require specialised metals and alloy grades that are difficult to process using conventional methods. MIM is employed to produce critical engine parts, including turbine blades, nozzles, and combustion chambers. It is also used for airframe and avionics components such as latches, hinges, actuators, connectors, switches, and sensors.
• Agriculture – MIM has gained a foothold in the agricultural sector through parts like gears, bearings, and bushings used in equipment such as tractors. It is also applied in implements including nozzles, valves, couplings, harrow teeth, cultivator points, and ploughshares.
• Medical devices – MIM is capable of producing precise surgical instruments, implants, and diagnostic equipment for the medical field.
• Consumer products – The process is also used to manufacture highly durable and aesthetically pleasing consumer products, including mobile phones, watches, laptop hinges, and home appliances.

Metal Injection Moulding Process Steps

Metal Injection Moulding Process

The initial phase of the metal injection moulding (MIM) process closely resembles plastic injection moulding but includes additional steps to remove impurities and improve the quality of the final product. The full MIM process is typically divided into five distinct stages:

1. Blending Feedstock

Fine metal powder is blended with polymer binders, such as wax or polypropylene, to achieve a uniform consistency. The mixture is often granulated into pellets similar to those used in conventional plastic injection moulding, ensuring consistent flow during moulding. Additional controls are applied to preserve the characteristics and integrity of the metal powder throughout this stage.

2. Moulding

The granulated feedstock is fed into a hopper and transported to the injection unit, where it is melted and pressurised using heating elements and a reciprocating screw. The molten material is then injected into the die cavity. The moulded component, known as the “green part,” cools and solidifies within the mould before being ejected.

At this point, the green part is a solid piece composed of both metal powder and binder. The process can be adapted to fill multiple cavities in a single cycle for increased production efficiency.

3. Debinding

In this stage, the binder is removed from the green part using thermal, chemical, or catalytic processes, or a combination thereof. As the binder is eliminated, the component becomes porous. Since the binder typically comprises 30–45% of the green part’s volume, a comparable level of porosity is expected following debinding.

4. Sintering

To eliminate porosity and strengthen the part, the component undergoes sintering. During this phase, it is heated to near its melting point—for example, stainless steel (melting point 1,530 °C / 2,786 °F) is generally sintered at around 1,350–1,400 °C (2,462–2,552 °F), depending on the alloy.

The high temperatures cause the metal particles to diffuse across their boundaries, densifying the part. Some variations of the process apply mechanical pressure during sintering to further enhance densification.

Sintered MIM parts typically reach densities of 96–99% and demonstrate mechanical properties comparable to wrought materials produced through conventional metalworking. However, sintering also causes shrinkage, making parts significantly smaller than their original “green” size. This shrinkage is accounted for during the mould design phase to ensure dimensional accuracy.

5. Secondary Processing

After sintering, MIM components can be further enhanced through standard post-processing and heat treatment methods—similar to those used for traditionally manufactured metal parts. These may include annealing, carburising, nitriding, plating, passivation, and precipitation hardening, depending on the application requirements.

Advantages of Metal Injection Moulding

Metal injection moulding (MIM) has carved out a niche in manufacturing by enabling the cost-effective production of high-strength components using a wide range of metals. Below are its key advantages:

✅ High density with smooth surface finish – MIM parts can achieve densities of up to 99%. Surface roughness can be minimised to below 1 micrometre Ra.

✅ Excellent mechanical properties – MIM components offer superior mechanical characteristics, including high strength and durability, making them suitable for demanding and safety-critical applications.

✅ Intricate geometries & fine features – MIM enables the production of intricate metal parts that are often unattainable through conventional methods. It supports detailed features such as profiled holes, thin walls, external and internal threads, as well as surface textures like knurling, engravings and markings. Tapping internal threads after moulding remains more precise and cost-effective than using unscrewing cores. The process also allows for easy embossing or debossing of fine details, including product codes, serial numbers and date stamps.

✅ Wide range of metals supported – MIM is a highly versatile process that accommodates both common and specialised metals, including materials like tungsten carbide. This versatility allows manufacturers to tailor components for specific needs such as strength, wear resistance, durability, and corrosion resistance.

✅ Reduced lead times – MIM integrates multiple operations into a single workflow, reducing production lead times. Additionally, part-to-part variation is minimal.

✅ Low scrap, high material efficiency – MIM generates significantly less material waste compared to traditional methods like casting or machining. Its high material efficiency positions it as a green and sustainable manufacturing solution.

Disadvantages of Metal Injection Moulding

While metal injection moulding offers numerous advantages, it also has limitations that can make it unsuitable in certain contexts. It’s important to understand these constraints when considering MIM as a manufacturing method:

❌ High initial investment costs – MIM involves high setup and tooling costs, making it less cost-effective for low-volume production. In such cases, alternative methods like CNC milling or turning may be more appropriate.

❌ Size and weight limitations – The process is best suited for small components—typically under 100 grams. MIM is not efficient for producing larger parts.

❌ Part shrinkage – As noted earlier, MIM parts shrink during the sintering stage. However, this shrinkage is predictable and can be compensated for during the mould design phase to ensure dimensional accuracy in the final product.

Conclusion

Metal injection moulding (MIM) has transformed the way manufacturers produce small, durable components across a variety of applications. By combining the design flexibility of plastic injection moulding with the strength of conventional metalworking techniques, MIM offers a precise and highly efficient manufacturing solution.

Its ability to process a broad range of metals, including titanium, tungsten carbide, and stainless steel alloys, makes it suitable for diverse industries, from aerospace and automotive to consumer goods.

Alongside these capabilities, MIM delivers other key advantages, such as excellent surface finishes, strong compatibility with mass production and exceptional material efficiency. These qualities position MIM as a distinct and valuable method in modern manufacturing. As processes and materials continue to advance, MIM is expected to play an increasingly significant role in high-performance engineering and production worldwide.