Metal Injection Molding is a near-net-shape manufacturing technology for metal parts that introduces modern plastic injection molding techniques into the powder metallurgy field. It is suitable for producing small, three-dimensionally complex-shaped components with special performance requirements.
Definition of Metal Injection Molding
MIM (Metal Injection Molding) is a process that combines metal powder with a binder for use in the injection molding process. Injection Molding = Powder Metallurgy + Plastic Injection Molding
It is a typical interdisciplinary innovation, combining two entirely different processing technologies (powder metallurgy and plastic injection molding). This integration enables engineers to break free from traditional constraints, allowing for the production of low-cost, intricately shaped parts made of stainless steel, nickel, iron, copper, titanium, and other metals through plastic injection molding. As a result, it offers greater design freedom compared to many different manufacturing processes.
Common Materials for Metal Injection Molding (MIM) Technology
| Material System | Alloy Grade / Composition | Application Field |
|---|---|---|
| Low Alloy Steel | Fe-2Ni, Fe-8Ni | Structural parts in automotive, machinery, and other industries |
| Stainless Steel | 316L, 17-4PH, 304 | Watch and clock components |
| Cemented Carbide | WC-Co | Cutting tools, watches, and clock parts |
| Ceramics | Al₂O₃, ZrO₂, SiO₂ | IT electronics, daily necessities, watches |
| Heavy Alloy | W-Ni-Fe, W-Ni-Cu, W-Cu | Military industry, telecommunications, household products |
| Titanium Alloy | Ti, Ti-6Al-4V | Military structural components |
| Magnetic Materials | Fe, Fe₁₄Nd₂B, SmCo₅ | Various magnetic components |
Advantages of Metal Injection Molding (MIM)
| Comparison Item | MIM | Powder Metallurgy | Casting | Machining | Stamping |
|---|---|---|---|---|---|
| Density | >98% | >86% | >95% | 100% | 100% |
| Tensile Strength | High | Low | High | High | High |
| Surface Finish | High | Medium | Medium | High | High |
| Miniaturization Capability | High | Medium | Low | Medium | High |
| Thin-Wall Capability | High | Medium | Medium | Low | High |
| Complexity | High | Low | Medium | High | Low |
| Design Flexibility | High | Medium | Medium | Medium | Low |
| Mass Production Capability | High | High | Medium | Medium-High | High |
| Supply Capacity | High | High | Medium | Low | High |
Limitations of MIM
| Long Process Cycle: The debinding and sintering steps in the MIM process are time-consuming, which can affect production efficiency to some extent. This poses challenges for products that require shorter production cycles.
| Size and Weight Limitations: The MIM process is primarily suitable for producing small to medium-sized parts. Larger components are prone to deformation and uneven shrinkage during the molding process, making it difficult to ensure precision.
| High Tooling Costs: The MIM process requires specialized molds, and the development costs for these molds are relatively high.
| Difficulties in Surface Treatment: The surface quality of MIM parts is relatively low, necessitating additional surface treatments to enhance their performance and aesthetic quality. However, due to the complex shapes of the parts, some traditional surface treatment methods may struggle to cover the entire surface completely, resulting in uneven treatment outcomes.
MIM Grades Sheets
| Grade | Magnetic Property | Application |
|---|---|---|
| 304L | Weakly magnetic | Internal & external structures, lens rings, protective covers / SIM trays |
| 316L | Weakly magnetic | Internal & external structures, lens rings, protective covers / SIM trays |
| 904L | Weakly magnetic | High-gloss components for smartwatches |
| PANACEA | Non-magnetic (after heat treatment) | PCB brackets, non-magnetic structural parts, lens rings |
| 310N | Weakly magnetic | Long-term heat-resistant applications (750-800掳C) |
| 420J2 | Strongly magnetic | Wear-resistant parts, pivot shafts for laptops/foldable phones |
| 440C | Strongly magnetic | Wear-resistant parts, pivot shafts for laptops/foldable phones |
| 2507 | Strongly magnetic | High-gloss components for smartwatches |
| 17-4PH | Strongly magnetic | Structural parts, connectors, and terminals |
| Grade | Magnetic Property | Application |
|---|---|---|
| Fe (SAE1010) | Medium magnetism, high induction | Internal structural parts requiring rust prevention / Inductive components |
| Fe-2Ni | Medium magnetism | Internal structural parts requiring rust prevention |
| Fe-8Ni | Medium magnetism | Internal structural parts requiring rust prevention |
| Fe-50Ni | High permeability | Internal structural parts requiring rust prevention |
| Low Alloy (Low non-ferrous content) | Medium magnetism, high induction | Internal structural parts requiring rust prevention / Inductive components |
| Grade | Magnetic Property | Application |
|---|---|---|
| Fe-50Co | Non-magnetic, high permeability | Connectors, terminals / EMC shielding |
| ASTM F75 | Non-magnetic, high permeability | PCB brackets, non-magnetic structural parts, lens rings |
| Inconel 718 | Non-magnetic, high permeability | Connectors, terminals, and internal structural parts |
| W-Ni-Fe | Low magnetism | Counterweights and vibration plates |
| Cu (Copper) | Non-magnetic | Heat dissipation & EMC shielding designs |
| W-Cu | Non-magnetic | Heat dissipation applications requiring low deformation & fast cooling |
| Ti (TA1) | Non-magnetic | Particularly for human-contact applications |
| Ti-6Al-4V (TC4) | Non-magnetic | Particularly for human-contact applications |
Process of Manufacturing
The manufacturing process can be described as “making metal like plastic.”
| Raw Materials: The metal powder used in MIM is not ordinary iron powder but micrometer-sized “spherical powder” (typically less than 10 microns in diameter, finer than a human hair). The powder must meet strict requirements, such as appropriate apparent density and uniform particle distribution.
| Mixing: The metal powder is blended with a “binder” (a mixture of wax and plastic) to coat each particle uniformly. The binder must ensure cohesion without reacting chemically with the metal and must be completely removable later.
| Injection Molding: The mixture is heated and softened, then injected into a precision mold like squeezing cream. The injection molding machine forms complex shapes, such as parts with small holes or grooves. After cooling and ejection, a “green part” with nearly the same shape as the final product is obtained, possessing strength similar to that of hard plastic.
| Debinding: The binder in the green part must be removed to prevent bubbling or cracking during high-temperature sintering.
After debinding, the green part becomes porous like a sponge and is then dried to remove residual solvents.
| Drying: The debound part is placed in an oven to evaporate residual extraction agents, ensuring no “moisture release” during sintering.
| Sintering: The dried part is placed in a vacuum or atmosphere furnace and heated (depending on the metal). The loose metal powder particles “attract each other” at high temperatures, gradually sintering into a dense metal component—shrinking in volume while significantly increasing strength and hardness, often surpassing the performance of forged parts.
Combination of Metal Injection Molding and Permanent Magnets
| Complex Shape Manufacturing: MIM can produce parts with intricate shapes, thin walls, and internal cavities that are difficult to achieve with traditional processes. When combined with permanent magnets, it enables the design of permanent magnets integrated with metal components, allowing for the incorporation of complex structures such as permanent magnets embedded in metal housings or attached to metal brackets. This meets the requirements of applications that demand high complexity in magnetic circuit design and structure.
| High Efficiency: The MIM process can consolidate multiple components into a single, precisely molded part, significantly reducing reliance on multiple manufacturers and lowering processing and assembly costs.
Metal Injection Molding Provider
At Tengye, we’re thrilled to be early participants in your new projects. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
Image Source: Alphaprecisionpm & Microtec-machining & Unionfab & Vectormagnets
