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Metal Injection Molding vs. Die Casting: A Comparison

Picture of Dean McClements
Written by
 7 min read
Published September 12, 2022

Learn more about the contrast of metal injection molding and die casting processes.

Die cast metal parts. Image source: patruflo/Shutterstock.com

Metal Injection Molding Background

Metal injection molding was first invented in the 1970s by Raymond Welch. It is used to create metal parts with a process similar to that of plastic injection molding. The key difference is that with MIM, the raw material is metal powder coated with a thermoplastic binder which will later be burned out, whereas, with conventional plastic injection molding, additive materials such as glass or ceramic fibers are incorporated permanently into the part to enhance its mechanical properties.

The granulated metal/binder mix is fed into an injection molding barrel. The barrel contains a screw with a shaft whose diameter increases from the material inlet to the outlet to the mold. As the screw rotates, the powdered feedstock is forced into incrementally smaller volumes. 

The compression generated by the screw is the primary mechanism responsible for heating and melting the plastic binder carrying the metal powder. The barrel is also heated to supply additional energy. Once enough material is melted, the screw retracts and then forces the metal powder suspended in the plastic binder into a two-part mold that is clamped shut during the injection, the plastic binder then transports the metal powder into the mold. Once cooled, the green part is ejected from the mold. To achieve its final properties, the binder must be removed from the structure. The empty spaces left by the binder must be filled by sintering to create a fully dense, structurally capable part. This green part is then exposed to solvents or a catalyst, and elevated temperatures help remove the thermoplastic binder, which is called the brown part. Finally, the part is placed in a furnace to sinter the metal powder particles together. During this process, the part can shrink from 15-30% (depending on the material used). After sintering, the part will have its final mechanical properties. Figure 1 below shows examples of metal injection molded parts:

Parts made with metal injection molding
Parts made with metal injection molding

Advantages and Disadvantages of Metal Injection Molding Compared to Die Casting

Listed below are some advantages of metal injection molding compared to die casting:

  1. MIM can manufacture a wide variety of small, complex parts with fine features using the same techniques in standard plastic injection molding. Die casting, on the other hand, struggles to produce fine feature parts.
  2. The MIM process only makes use of high temperatures during the sintering process.  A molten metal feedstock is not required like with die casting. This also means that materials with very high melting temperatures can be used without the challenges of processing and handling these metals in molten form. 

Listed below are some disadvantages of metal injection molding compared to die casting:

  1. Due to the complex high wear resistant tooling required for metal injection molded parts, metal injection molding (MIM) equipment can be expensive. MIM molds do not last as long as diecast molds because of the abrasive nature of the metal powder feedstock.
  2. MIM requires multiple post-molding steps to produce the final part. This adds cost to the final parts compared to those produced by die casting.  
  3. Metal injection molded parts shrink significantly during the densification process. Mold design requires an advanced understanding of the properties of the binder, the metal, and the interaction between the two during post-processing to produce final parts that can meet dimensional requirements.

Die Casting Background

Die casting is a process for manufacturing metal parts by injecting molten metal into a mold. This process was first invented in 1838 and was patented in 1849. The first die casting materials used were lead and tin. In 1914, the process was further developed to also accommodate the use of aluminum and zinc. Today magnesium, copper, and silicon are also used. Die casting is limited to non-ferrous materials. Die casting ferrous metals is possible, but is an uncommon practice.  

The molten metal to be cast can be injected under high pressure or simply flow in by gravity feed. Once the part has been allowed to cool, it can be ejected from the mold. This can take up to a minute, depending on part size and wall thicknesses. Excess material due to gates, runners, and parting line flash must be removed either using a manual process or a press die. To learn more, see our guide on the Process of Die Casting.

Advantages of Die Casting Compared to Metal Injection Molding

Listed below are some advantages of die casting compared to metal injection molding:

  1. Die casting molds last longer than MIM molds. In some cases, a single die-casting mold can be used to make a million parts, whereas a MIM mold can only produce a couple hundred thousand. 
  2. Diecast parts do not shrink the way MIM parts do. This means that molds can be more easily manufactured to the required size.

Disadvantages of Die Casting Compared to Metal Injection Molding

Listed below are some disadvantages of die casting compared to metal injection molding:

  1. Die casting is typically used with non-ferrous metals. While ferrous metals like steel can be die-casted too, these materials have very high melting points. This can significantly reduce the life of the molds. This makes die casting of limited use for high-performance and high-temperature applications. 
  2. Molten metal injected at high pressures and temperatures will often entrap gasses within the material. This results in porosity which ultimately reduces the part’s mechanical strength. MIM parts have significantly less porosity as the pre-sintered part has a lot of room for air to escape during sintering.

Comparison Table Between Metal Injection Molding and Injection Molding

Table 1 below compares some common properties of metal injection molding and die casting:

Table 1: Metal Injection Molding vs. Die Casting Attributes
AttributeMetal Injection MoldingDie Casting
Attribute

Can process ferrous metals

Metal Injection Molding

Yes

Die Casting

Not Typically

Attribute

Wall Thickness 

Metal Injection Molding

0.040” to 0.120” 

Die Casting

0.04 to 0.2 “

Attribute

Low-cost production

Metal Injection Molding

No

Die Casting

Yes

Attribute

Multi-step process

Metal Injection Molding

Yes

Die Casting

No

Attribute

Materials

Metal Injection Molding

Any material that can be turned into a powder form, including some difficult special cases:

Tungsten
Stainless steel
Tool steel
Cemented carbides
Nickel superalloys
Precious metals

Die Casting

Aluminum
Zinc
Copper
Magnesium
Lead
Pewter
Tin

Metal parts made with metal injection molding
Metal parts made with metal injection molding

More Comparisons between MIM and Die Casting

  • Cost comparison: Due to the cost of mold manufacture for MIM and die casting, both technologies require relatively large production volumes to justify the mold costs. However, at medium to large volumes, both technologies produce very low-cost parts. Die casting is up to 30% less expensive than MIM due to there being no need for multiple post-processing steps as is the case with MIM.
  • Speed comparison: Comparing only the speed of the actual molding process, metal injection molding (MIM) is faster than die casting. However, MIM requires post-molding processes that make its overall cycle time to produce a finished part longer than for a finished diecast part.
  • Volume comparison: Metal injection molding and die casting are both high production-volume technologies. Typical production runs on a mold for both can easily reach hundreds of thousands or even millions of parts. MIM is ideally suited to high-volume production of intricate parts, whereas die casting is better suited to high-volume runs of larger, simpler parts. 
  • Materials comparison: Die casting typically only makes use of non-ferrous metals like aluminum, copper, zinc, magnesium, and lead. MIM can make use of ferrous metals as well as more advanced materials like titanium and nickel alloys. One of the most commonly used MIM materials is stainless steel. MIM can essentially be used with any metal that can be converted into powder form.

A Mutual Alternative to Metal Injection Molding and Die Casting

A mutual alternative to MIM and die casting is Selective Laser Melting (SLM). SLM is a 3D printing technique used to produce complex metal parts. It consists of a laser selectively melting metal powder in the shape of the part cross-section. Once a layer is complete, another layer of metal powder is deposited on top and the process repeats until the part is complete. SLM can produce fine features like MIM. 

Xometry provides a wide range of manufacturing capabilities including die casting services as well as CNC machining, 3D printing, injection molding, laser cutting, and sheet metal fabrication. Get your instant quote today.


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The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

Picture of Dean McClements
Dean McClements
Dean McClements is a B.Eng Honors graduate in Mechanical Engineering with over two decades of experience in the manufacturing industry. His professional journey includes significant roles at leading companies such as Caterpillar, Autodesk, Collins Aerospace, and Hyster-Yale, where he developed a deep understanding of engineering processes and innovations.

Read more articles by Dean McClements

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