The Complete Guide for Metal Injection Molding

Metal injection molding is a process that involves injecting molten metal into a mold to form parts. It requires making a mold according to the shape of the product to be manufactured. After the metal liquid cools, it will take the shape of the mold cavity.
In this guide, you can find all the information about metal injection molding
Whether you want to learn about the history of metal injection, or want to understand its advantages, limitations, material selection, or final surface treatment methods — all the information you are looking for is here.
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Introduction to Metal Injection Molding 

Metal injection is a process where metal powder and binder are used as raw materials, injected into molds, and finally formed into final parts through sintering. It combines the advantages of plastic injection molding and powder metallurgy, allowing for the production of complex metal products. For large quantities of complex parts, the produced products have good mechanical properties, and a wide range of materials can be chosen.

History of Metal Injection Molding

 Metal injection molding was initially used in iron-based and nickel-based metal materials during World War II. By the 1970s, more manufacturers began using this process due to its ability to produce complex and high-performance products. A major proponent was Raymond Wiech, who further refined the process for large-scale commercial applications. In the last decade, the use of metal injection parts in electronic products, represented by iPhones and laptops, has driven the development of the metal injection industry.

proceso mínimo

Process of Metal Injection Molding (Mention Injection Molding Machine) 

The general metal powder metallurgy process is divided into four steps:

  • Preparación de materia prima 

The raw materials used in the MIM process are a mixture of metal powder and polymer binders. Metals like stainless steel, titanium, iron, and nickel, as well as some alloys, are used based on the product’s performance requirements. The binder materials are a mixture of thermoplastic plastics and waxes. The metal powder and binder are usually heated and mixed, then cooled and granulated. Raw material production often involves Sigma blade mixers or twin-screw extruders, as well as mixers and granulators.

  • Moldeo por inyección 

The production process is similar to plastic injection molding. The raw material granules are heated to a certain temperature, the binder melts, giving it fluidity. The molten material is injected into the mold cavity under high pressure, forming a part with the same shape as the mold, known as the “green part.”

  • Binder Removal (Debinding) 

The “green parts” formed after molding need to go through a debinding process to remove the binder, leaving the metal part. Binder removal can be achieved through thermal or chemical methods, or a combination of both, depending on the binder system used. This step is crucial as it prepares the workpiece for sintering while avoiding deformation or damage to the workpiece. Most of the binder can be removed through solvent soaking, heating, etc.

  • sinterización 

The final step is to sinter the debound parts in a high-temperature furnace, removing burrs. The parts are heated to just below the metal’s melting point, causing the metal particles to fuse and densify into a solid structure. These parts are called “brown parts.” At this stage, the parts are qualified, and there may be some shrinkage in size. Generally, the strength, dimensional accuracy, and final mechanical properties of the products can only be known after small batch testing. The sintering furnace chosen depends on the material, production scale, and complexity of the parts. Common options include vacuum furnaces, multi-gas furnaces, and box furnaces.

Beneficios del moldeo por inyección de metal

Beneficios del moldeo por inyección de metal 

Metal injection molding (MIM) is ideal for manufacturing complex, high-precision metal parts, especially for small-sized, high-volume products. 

Here are some main advantages:

  • Geometrías complejas y detalles intrincados: MIM can produce parts with complex shapes and intricate details that are difficult or impossible to achieve with traditional metalworking methods.
  • Alta Precisión y Consistencia: As a mold-based process, MIM ensures consistency, resulting in high-precision and high-quality products with tight tolerances.
  • Económico: MIM is an automated production process, requiring less labor compared to other processes. There’s minimal waste of materials, making it friendly for precious metals like titanium alloys. The high precision of MIM reduces the need for secondary machining and assembly, further saving costs.
  • Selección diversa de materiales: One of the biggest advantages of the MIM process is the wide range of materials available, including stainless steel, titanium, and various alloy steels, allowing engineers to choose the best material for specific applications.
  • Excelentes propiedades mecánicas: MIM parts have high density and therefore exhibit excellent mechanical properties, including strength and hardness, making MIM suitable for parts that need to withstand high stress and wear.

Main Density Below

Tipo De Material Densidad (gramos por centímetro cúbico)
Acero y acero inoxidable. 7.6 a 7.9
Aleaciones de titanio 4.4 a 4.5
Aleaciones a base de cobalto 8.3 a 9.1
Aleaciones a base de cobre 8.4 a 8.9

Limitaciones del moldeo por inyección de metal

While metal injection molding offers many advantages, there are also some limitations to consider:

  • Initial Investment in Molds: MIM is more suited for high-volume production due to the need for molds, making it less friendly for small-batch products compared to machining or SLM.
  • Size Limitations for Parts: MIM is better suited for producing small to medium-sized parts. Typical part size ranges are as follows (for reference only):
    • Weight: MIM parts usually range from a few milligrams to a few hundred grams, with the most common range being 1 gram to 100 grams.
    • Dimensions: The minimum size can reach about 0.5 mm, while the maximum size is usually no more than 250 mm. The most common part size range is between 2 mm and 150 mm.
    • Wall Thickness: The minimum wall thickness achievable by MIM is about 0.1 mm, but a more common minimum is about 0.5 mm. The maximum wall thickness is generally no more than 10 mm.
    • Tolerance: MIM can achieve high dimensional accuracy, with typical tolerances ranging from ±0.3% to ±0.5%.
  • Longer Development Cycle for Products: Designing and making molds for MIM requires time, typically 30-40 days for simple products and longer for complex parts. If the trial mold is not satisfactory, it must be redesigned and modified, further extending the development cycle.
  • Challenges with Post-Processing, Debinding, and Sintering: In addition to the limitations mentioned above, there are various issues related to post-processing, debinding, and sintering in the production process.

compare with other solution

Comparación con otros métodos

 Let’s compare MIM with other processes, highlighting its unique advantages. Each process has its own strengths and limitations, and the choice often depends on factors like cost, material, and complexity.

Metal Injection Molding (MIM) vs. Die Casting:

Both processes require molds and can produce complex-shaped products, but MIM is more suited for small, intricate parts, while die casting is better for larger parts. In terms of material selection, MIM often uses iron-based, nickel, titanium, and alloy materials, while die casting is primarily used for non-ferrous metals like aluminum alloys. Surface finish is high for both processes, but die casting parts might require additional processing to remove flash or gates. In terms of physical properties, MIM parts have better impact resistance than die-cast parts.

Metal Injection Molding (MIM) vs. Powder Metallurgy (PM)

Both belong to powder metallurgy, but MIM uses finer powders and higher sintering temperatures, resulting in higher density and strength compared to traditional PM. MIM offers greater design flexibility, allowing for threaded and complex part shapes, while PM products are typically simpler and larger in size. MIM is more material-efficient, with minimal material waste.

Metal Injection Molding (MIM) vs. CNC Machining

In the actual production process, the two technologies are generally used in conjunction. CNC machining offers a wide range of material processing capabilities, including metals, plastics, and composites, and can produce products with complex geometries. It is often used for custom or small-batch production and plays an irreplaceable role in the product development stage. CNC machining does not require molds.

However, in the later stages of mass production, the MIM process can effectively ensure product quality, save materials, and have a much shorter delivery time compared to CNC machining.

Metal Injection Molding (MIM) vs. Selective Laser Melting (SLM)

SLM, as a new manufacturing method, can produce parts with even more complex internal structures and does not require molds for the initial stage. The melting and solidification process of metal in SLM ensures that the mechanical properties of the produced products are comparable to forged materials. However, the production efficiency of SLM is not as high as MIM, and the speed is not as efficient. Post-processing and surface treatment in SLM are more complicated than in MIM. Therefore, SLM provides an alternative for the production of complex components.

Metal Injection Molding (MIM) vs. Investment Casting

Both can be used to produce complex, precision parts, but MIM parts have tighter tolerances, higher detail, and more complex shapes with better surface finishes. However, MIM requires mold development, and it’s not suitable for larger parts. Both can be used for a variety of metals, including difficult-to-machine metals like TC-4, but MIM is more efficient in production and cost-effective compared to investment casting.

Materials for Metal Injection Molding and Their Performance 

There are many materials used for MIM production, each with unique properties.

  • Aleaciones a base de hierro: These include various types of steels such as tool steel, stainless steel, iron-nickel magnetic alloys, and special iron alloys like Kovar and Invar.
  • Aleaciones de tungsteno: Tungsten-based metal alloys, including tungsten-copper mixtures, are known for their high density, strength, good electrical and thermal conductivity, and excellent shielding capabilities, widely used in aerospace, military, medical, and nuclear industries.
  • Materiales de carburo: Carbide mixtures, such as cemented carbide (WC-Co) and metal ceramics (Fe-TiC), are used in MIM to produce highly durable and hard parts that are resistant to breakage under intense usage conditions.
  • Acero Inoxidable: Stainless steel, known for its excellent corrosion resistance, is one of the most popular MIM materials and is ideal for medical instruments, automotive parts, and various consumer goods.
  • Titanio: Titanium is chosen for its high strength-to-weight ratio and is used in aerospace and medical fields. MIM-produced titanium parts are strong, durable, and capable of withstanding extreme conditions.
  • Aleaciones de níquel: These alloys are used in applications requiring high temperature resistance, such as aerospace and energy industries.
  • Aleaciones de cobre: Copper and its alloys are known for their excellent thermal and electrical conductivity and are ideal materials for the electrical and electronics industries.

Aleaciones a base de hierro

Aleación Tipo Grado Resistencia a la tracción (MPa) Densidad (g / cm³) Características
Acero bajo en carbono 1008, 1010 340 - 420 ~ 7.87 Good formability and weldability, suitable for general parts and structures.
Acero al Carbono Medio 1045, 1050 620 - 750 ~ 7.85 Medium strength and hardness, suitable for parts requiring some strength and toughness.
Acero de baja aleación Fe-2Ni Medium strength and toughness, suitable for general industrial parts.
Fe-8Ni High strength and good toughness, commonly used for automotive parts, tools, etc.
Herramienta de acero M2 High-speed steel with high hardness and wear resistance, suitable for cutting tools, drills, etc.
4605 Low alloy tool steel with good hardness and toughness, suitable for various molds and tools.
Acero estructural de aleación 8620 Good strength, toughness, and wear resistance, suitable for gears, bearings, etc.

Aleaciones de tungsteno

Aleación Tipo Densidad (g / cm³) Resistencia a la tracción (MPa) Alargamiento (%) Aplicaciones
Tungsten-Nickel-Iron (W-Ni-Fe) 17 - 18 900 - 1000 1 - 5 Balance weights, radiation shielding, high-temperature furnace parts, etc.
Tungsten-Nickel-Copper (W-Ni-Cu) 16 - 17 600 - 800 2 - 10 Electronic packaging materials, radiation shielding, etc.

Carburos

Aleación Tipo Dureza (HRA) Resistencia a la flexión (MPa) Densidad (g / cm³) Aplicaciones
Tungsten Carbide-Cobalt (WC-Co) 88 - 92 1400 - 2400 13.5 - 15 Cutting tools, drill bits, abrasives, etc.
Tungsten Carbide-Nickel (WC-Ni) 86 - 90 1200 - 1800 13 - 14 Corrosion-resistant tools, molds, mining equipment, etc.
Tungsten Carbide-Nickel-Chromium (WC-Ni-Cr) 85 - 89 1000 - 1600 12.5 - 14 Tools and components in high-temperature, high-wear environments.

Acero Inoxidable

Grado Resistencia a la Corrosión Fortalecimiento Aplicaciones
316L Bueno Alta Medical instruments, food processing equipment, etc.
17-4PH Bueno High, can be enhanced through heat treatment Aerospace, chemical industry, etc.
304L Bueno Construction, furniture, etc.

Titanio

Grado Resistencia a la tracción (MPa) Densidad (g / cm³) Aplicaciones
Pure Titanium (Grade 1-4) 240-550 (varies by grade) ~ 4.5 Medical instruments, chemical equipment, aerospace, etc.
Ti-6Al-4V (Grade 5) ~ 900 ~ 4.43 Aerospace, biomedical implants, high-performance sports equipment, etc.
Ti-6Al-7Nb ~ 900 ~ 4.5 Medical implants, orthopedic implants, etc.

Aleaciones de níquel

Aleación Resistencia a la tracción (MPa) Densidad (g / cm³) Aplicaciones
Inconel 718 ~ 1350 ~ 8.2 Aerospace, nuclear reactors, petrochemicals, high-temperature environments.
Inconel 625 ~ 930 ~ 8.4 Chemical industry, aerospace, seawater equipment, etc.
Hastelloy C-276 ~ 790 ~ 8.9 Chemical processing, pollution control, wastewater treatment, corrosion-resistant environments.

Aleaciones de cobre

Aleación Tipo Resistencia a la tracción (MPa) Densidad (g / cm³) Aplicaciones
Copper-Beryllium (Cu-Be) Approximately 410-1380 (depends on beryllium content and heat treatment) ~ 8.3 Non-sparking tools, aerospace components, electronic connectors, etc.
Brass (Copper-Zinc, Cu-Zn) Approximately 350-750 (depends on zinc content and processing state) ~ 8.4-8.7 Decorative items, valves, fittings, etc.
Copper-Nickel (Cu-Ni) Approximately 220-500 (depends on nickel content and processing state) ~ 8.9 Seawater system components, heat exchangers, coins, etc.
Bronze (Copper-Tin, Cu-Sn) Approximately 200-750 (depends on tin content and processing state) ~ 8.8-8.9 Gears, bearings, statues, etc.

design consideration

Design Considerations for Metal Injection Molding 

Design considerations for metal injection molding (MIM) are crucial for ensuring the successful production of high-quality, functional, and cost-effective parts. These considerations range from material selection to part geometry and surface treatments. Here are some key factors to consider during the design process:

  • Selección de material

Choose the appropriate metal or alloy that matches the part’s function, considering cost, strength, durability, and other performance characteristics.

  • Geometría de la pieza

Consider the flow of molten material during molding for complex geometries to prevent voids or incomplete filling.

  • Espesor de la pared

Aim for uniform wall thickness, typically ranging from 0.3 mm to 8 mm, to prevent defects during sintering.

  • Ángulos de calado

Design with draft angles to facilitate part ejection, especially for tall parts.

  • Ubicación de la puerta

Optimal gate location is crucial for controlling the flow of molten material and impacting the part’s appearance and quality.

  • Parting Lines and Ejector Pins:

Consider the placement of parting lines and ejector pin marks to avoid affecting the part’s aesthetics or functionality.

  • Acabado superficial y textura

Achieving ideal surface finish and texture can be challenging for complex geometries and different materials.

  • Shrinkage Effects

Account for shrinkage during sintering, with an average shrinkage rate of around 20%.

  • Estructuras de apoyo

Design support structures for parts during sintering or binder removal to prevent deformation.

application of MIM parts

Applications of Metal Injection Molding Parts 

  • Metal injection molding (MIM) is widely used across multiple industries, with numerous applications in our daily lives. Its products are mostly small, complex, and precision metal parts.
    The automotive industry is a major user of MIM, utilizing it to manufacture engine, transmission, fuel injection, and steering system components such as gears, brackets, connectors, pulleys, sensors, synchronizers, and fuel injectors, which require high precision and durability.
  • In the aerospace industry, MIM is used to produce small, high-precision, and complex parts like injectors, valves, actuators, and electronic connectors, characterized by high strength-to-weight ratios, high-temperature resistance, and corrosion resistance.
  • The medical industry employs MIM to manufacture surgical instruments, endoscopic and laparoscopic equipment, dental crowns, and custom fasteners for orthopedic implants, with parts featuring biocompatibility, high precision, and sterilization capabilities.
  • In the consumer goods sector, MIM is suitable for producing watch cases, laptop hinges, radiators, buttons, vibrators, and lanyard rings, as well as eyeglass components and toys.
  • Additionally, MIM is applied in the intricate internal mechanisms of electronic products, fine and durable components for the firearms industry, industrial machinery and equipment, sports equipment, fire sprinkler systems for buildings, military and defense applications, and the manufacturing of various soft magnetic components.
  • The versatility of MIM in producing sturdy, durable, and complex parts makes it an essential manufacturing process for various applications demanding precision and material performance.

Surface Finishes Available for the MIM Process

  • chorro de arena: Involves blasting the surface of MIM parts with abrasive materials such as sand or glass beads to achieve a uniform, matte, and slightly textured surface finish.
  • Pulido: Utilizes polishing wheels and compounds to polish the surface of MIM parts, resulting in a smooth, shiny, and highly reflective surface finish.
  • Recubrimiento PVD: Involves depositing a thin layer of metal onto the surface of MIM parts through physical vapor deposition (PVD). This can include coatings of chromium, nickel, gold, and various colors.
  • Anodizado: Involves anodizing the surface of MIM parts by immersing them in an electrolytic bath and passing an electric current through it. This process creates a hard, protective oxide layer on the surface of MIM parts, enhancing their corrosion resistance and durability.

EMITECH’s Capabilities in MIM Part Production 

With years of experience in MIM part production, EMITECH can assist you with:

  • Design: Helping you select suitable metal raw materials and providing rapid design and mold-making capabilities.
  • Communication: Ensuring smooth communication throughout the project.
  • Equipment: Investing in precise, fast, and manufacturing equipment to offer limitless capabilities in MIM part production. Whether you need large or small batches, EMITECH can deliver high-quality MIM parts for the global market.
  • Collaboration: Working closely with your team to meet strict tolerances and deadlines. EMITECH provides customized solutions for businesses of all sizes.
  • OEM Services: Offering a variety of solutions, including OEM services.
  • Quality Control: Starting from selecting high-quality raw materials to inspecting the quality of manufactured parts.
  • Competitive Pricing: Providing competitive prices for all MIM parts.

Conclusión  

In summary, MIM processing is an advanced manufacturing technique that requires knowledge of MIM part design, alloy material selection, material properties, and proper surface treatment. It is essential for engineering and technical personnel.

MIM processing will be an effective and versatile method for producing parts and components in the future.

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