Metal injection molding (MIM) merges the technology of plastic injection molding with powdered metallurgy. The process produces high volumes of small metal components with fine details and thin walls, allowing for greater design flexibility compared to die casting.

The metal injection molding process provides an economical choice for manufacturing high volumes of complex parts in less time. It overcomes the difficulties of machining metals like nickel iron, stainless steel, and titanium. It also produces less scrap with a shorter turn-around.

What is Metal Injection Molding?

Metal injection molding combines powdered metals with a polymer binder material to create metal parts. After the injection mold metal is melted, molded, and cooled, unwanted polymer material is eliminated by applying high heat to reveal a highly dense metal part. Recent process improvements now allow MIM to incorporate a wide variety of ferrous and non-ferrous alloys to produce non-corrosive metal parts with excellent strength and hardness properties.

The metal injection molding process can produce a near-unlimited variety of shapes and geometries

  • Preparing feedstock. Operators combine thermoplastic binder and metal powder to create feedstock, which is fed into the injection molding machinery. The feedstock is typically granulated for faster melting and efficient blending.
  • Injection molding. The feedstock is injected into the mold to form a physical metal component in a plasticized state. The automated process can fill multiple mold cavities and reduce product flaws and imperfections. At this stage, the green product is approximately 20% larger than the final component. After cooling, the product gets ejected from the mold.
  • Binder removal. At this stage, the intermediate binding material is thermally removed as the first step in the sintering process. The product is held at a specified temperature while the thermoplastic binding material evaporates through the pores of the component. The interconnected pore network is pre-engineered into the design to allow the plastic material to weep from the metal.
  • Sintering. The final stage of the metal injection molding process ramps up the furnace temperature to sinter or compact the metal powder particles, eliminating the pore volume left behind from the elimination of the plastic binding material. Product shrinkage at this stage is offset by the higher initial product volume. Further surface finishing or heat-treating processes can now achieve the final specifications for hardness, ductility, and other mechanical or physical properties.

Metal Injection Molding Applications

MIM manufacturing has applications in industries requiring small components that would be difficult or expensive to machine, stamp, or die-cast. Some of the ideal scenarios for MIM manufacturing include:

  • Medical devices. The process has extremely high repeatability, making it an excellent choice for FDA-approved medical devices.
  • Aerospace. The aerospace industry benefits from the high precision and complex geometries produced by metal injection molding, with typical tolerances exceeding 0.5% on production runs of 100,000 components.
  • Orthodontics. The one-off, custom design of orthodontic appliances is made affordable because of metal injection molding.
  • Electronics. MIM facilitates the cost-effective miniaturization of electronic components for millions of consumer products.
  • Consumer goods. Metal injection molded components can be found in a wide range of modern consumer domestic products like appliances, recreation equipment, watches, and jewelry.
  • Industrial. Industrial applications for metal injection molding include parts for automotive engines and transmissions and military-grade firearm and munition components.

Advantages of Metal Injection Molding

Metal injection molding offers numerous benefits over traditional machining and metalworking processes:

  • It is possible to manufacture high volumes of complex parts in less time with less scrap.
  • The singular production process saves on floor space, manpower, and material costs.
  • Powdered metals are equivalent to wrought alloys and exhibit superior mechanical properties compared to cast components.
  • Available master alloys and pre-alloys facilitate variable mechanical strength, hardness, ductility, magnetization, corrosion-resistance, and more.
  • Minimal finishing operations are required due to the inherent nature of injection molding.
  • The de-binding and sintering stages of the molding process removes the binder material and also conditions the metal.

Please contact us for more information about custom metal injection molding for the high-volume production of high-precision components.

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