I. Core Technical Principles of MIM

1. Preparation of Metal Powders Select ultrafine spherical metal powders with particle sizes ranging from 1 to 20 μm (such as stainless steel, iron-based alloys, titanium alloys, tungsten alloys, etc.). These powders have a large specific surface area, ensuring high densification after sintering (reaching 95% to 99% of the theoretical density).
2. Binder System Design Mix metal powder with a binder (wax-based, oil-based, or polymer-based) in proportion to produce a uniform mixture. Feeding (Powder volume fraction: 60%–65%) The binder serves to bond and plasticize the material, imparting fluidity to the feedstock for injection molding.
3. Injection molding The feed material is heated to a molten state (150–200℃), then injected under high pressure into a precision mold using an injection machine, and after cooling, it is obtained. Green body (green blank) The green body shape matches that of the final part, and its strength is sufficient to meet handling requirements.
4. Degreasing process By solvent degreasing, thermal degreasing, or catalytic degreasing, the binder is removed from the green body (degreasing rate > 99%), resulting in: Brown blank The brown blank has extremely low strength and a porous, loose structure, so it must be handled with care.
5. Sintering densification The brown body is placed in a high-temperature sintering furnace (at a temperature ranging from 70% to 90% of the metal’s melting point) and held under a protective atmosphere (such as nitrogen or hydrogen). Through atomic diffusion and rearrangement, the powder particles become densified, and the part typically exhibits a shrinkage rate of... 12%~25% Ultimately forming high-precision metal parts.
6. Post-processing (optional) Perform CNC finishing, heat treatment (quenching, carburizing), and surface treatments (plating, passivation) on parts requiring high precision.

II. Core Technical Features of the MIM Process

1. Molding Capability: Complex shapes can be formed in a single step, breaking through the limitations of traditional processes.

• Moldable features It can directly form complex structures that are difficult to achieve through conventional powder metallurgy and CNC machining, such as: Thin walls, blind holes, irregular grooves, threads, undercuts, complex curved surfaces Wait—part size ranges typically are: 0.1–200 g (Suitable for small, precision parts.)
• Comparative advantage Traditional powder metallurgy can only produce parts with simple geometric shapes; CNC machining of complex parts requires multiple processing steps and results in low material utilization (typically less than 30%), whereas MIM can achieve much higher material utilization. Over 95% 。

2. Dimensional accuracy and surface quality: Near-net-shape forming reduces post-processing.

• Dimensional accuracy : Tolerances can reach after sintering ±0.3% to ±0.5% Some high-precision parts can be controlled within [a certain range] through process optimization. ±0.1% ; No CNC finishing or only minimal CNC finishing required (e.g., for high-precision mating surfaces).
• Surface roughness The surface roughness Ra after sintering can reach: 1.6–3.2 μm After polishing, the surface roughness can be reduced to below Ra 0.4 μm, meeting the appearance and assembly requirements in fields such as medical and electronics.

3. Wide material compatibility: Covers multiple categories of metallic material systems.

4. Advantages of mass production: high efficiency, low cost

• Suitable for large-scale production The molds can be designed with multiple cavities, and a single mold can accommodate anywhere from 16 to 64 cavities. The injection molding cycle is short (10 to 60 seconds per mold), and daily production capacity can reach tens of thousands of parts.
• Cost structure optimization Compared to CNC machining, MIM... Large volume (>100,000 units) During mass production, there are significant cost advantages, enabling a reduction of 30% to 50% in manufacturing costs. However, when producing small batches, the high tooling costs make this approach less economically viable.

5. Performance Consistency: Uniform microstructure and excellent mechanical properties.

• After sintering, the parts exhibit high density (95% to 99% of theoretical density), with no macroscopic pores, a uniform microstructure, and no segregation defects typically found in castings.
• The mechanical properties of MIM parts are comparable to those of forgings. Taking 316L stainless steel as an example, MIM parts can achieve a tensile strength of 550–650 MPa and an elongation of over 20%, matching the performance of forged parts.

III. Limitations and Technical Challenges of the MIM Process

1. Limitation

• Part size limitations Suitable for small parts (typically weighing less than 200g and with maximum dimensions less than 150mm); large parts are prone to sintering deformation and uneven shrinkage.
• Mold costs are high. Precision mold design and manufacturing are costly (typically exceeding 100,000 yuan), making small-batch production cost-ineffective.
• Long degreasing cycle Traditional thermal degreasing takes dozens of hours, which limits production efficiency. Although catalytic degreasing is highly efficient, it is applicable only to specific binder systems (such as those based on polyoxymethylene).

2. Core Technical Challenges

• Feed formulation optimization It is necessary to balance the powder loading amount with its flowability. If the loading amount is too high, flowability will be poor, leading to insufficient material during injection; if the loading amount is too low, the sintering shrinkage rate will be high, making it difficult to control dimensional accuracy.
• Fat-free deformation control During the degreasing process, brown bodies are prone to cracking and deformation due to uneven removal of binders, so it is essential to precisely control the degreasing temperature and atmosphere.
• Sintering shrinkage consistency Multiple cavities or complex parts are prone to local shrinkage variations, which can lead to dimensional deviations. These issues need to be addressed through mold compensation design and optimization of the sintering process.

IV. Comparison of the MIM Process with Other Metal Forming Processes

V. Development Trends of MIM Technology

1. High-performance materials development Expand the applications of MIM technology to high-temperature alloys and ceramic-metal composites, meeting the demands of the aerospace and new energy sectors.
2. Innovative Fat-Removal Process Develop highly efficient degreasing technologies such as microwave degreasing and supercritical fluid degreasing, reducing the degreasing cycle to just a few hours.
3. Intelligent manufacturing Introduce AI-driven process optimization, using digital twins to simulate the entire manufacturing process—from injection and degreasing to sintering—enabling precise prediction of part shrinkage and deformation and enhancing dimensional consistency.
4. Large-part forming technology Develop layered injection and sintering-bonding technologies to break through the size limitations of MIM parts.
5. Green manufacturing Use environmentally friendly binders (such as water-based binders) to reduce organic solvent emissions and lower energy consumption during degreasing.