Micro MIM (Micro Metal Injection Molding) technology is an advanced process that mixes metal powder and binder and injects tiny parts through a mold. This technology combines the high precision of injection molding and the material diversity of powder metallurgy to produce complex, tiny and highprecision metal parts, usually in the size of a few millimeters or even microns. Micro MIM technology plays an important role in the field of precision manufacturing, especially for the production of highprecision and tiny parts, meeting the needs of modern technology for lightweight and miniaturization.

Micro MIM technology is widely needed in fields such as medical, electronics and automobiles. In the medical field, it can be used to produce tiny surgical tools and implants; in the electronics industry, it can be used to manufacture micro connectors and mobile phone parts; in the automotive field, it can be used to produce highprecision sensors and engine parts. Due to its support for complex shapes and high precision, Micro MIM has become an indispensable process technology in precision manufacturing.

I. Introduction to Micro MIM Technology

Micro MIM (Micro Metal Injection Molding) technology is a precision machining technology specifically used to produce micro complex metal parts. Its basic principle is to mix metal powder with a binder to form an injection material, and then inject it into the mold. Because it can achieve highprecision and complexshaped micro parts manufacturing, Micro MIM technology is widely used in medical devices, electronic components and automotive parts.

II. Definition and Principle

Micro MIM technology, namely Micro Metal Injection Molding, is a manufacturing process that mixes metal powder with an organic binder to form a "feed material", and then produces highly precise micro metal parts through injection molding, degreasing, sintering and other steps. Its working principle is mainly:

1. Powder preparation: Select suitable metal powder and mix it evenly with a binder to form a feed material suitable for injection.
2. Injection molding: Inject the feed material into the mold and mold the initial structure of the part under high temperature and high pressure.
3. Degreasing: Remove the binder in the part by heating or chemical means to make it suitable for sintering.
4. Sintering: The degreased parts are heated to the sintering temperature of the metal powder to promote the fusion of the powder particles to form the final highstrength, dense micrometal parts.

Micro MIM technology effectively combines the advantages of powder metallurgy and injection molding processes, and can produce tiny and complex metal parts that are difficult to process with traditional manufacturing processes.

III. Material Selection

The materials of Micro MIM technology are mainly some metal powders with high strength and high precision requirements. Commonly used metal materials include: stainless steel, titanium alloy, copper alloy, tungsten alloy, nickel alloy and cobaltchromium alloy. The following is a detailed introduction to each metal material and its advantages and disadvantages:

1. Stainless steel

Stainless steel is an ironbased alloy containing chromium, which is known for its excellent corrosion resistance and high strength. It is often used in applications that require corrosion resistance and strength, such as medical devices, food processing equipment and building components. Common types used for Micro MIM include 304, 316 and other stainless steels.

Advantages:

• Corrosion resistance: Stainless steel contains chromium, which makes it have good corrosion resistance and is suitable for humid or highly corrosive environments.
• High mechanical strength: Stainless steel has high strength and is suitable for tiny parts that are subjected to large mechanical stress.
• Relative low cost: Compared with other materials, stainless steel has a low cost and is suitable for largescale production.
• Good machinability: Suitable for conventional powder metallurgy processes and easy injection molding.

Disadvantages:

• High density: Stainless steel has a high density, which may not be ideal in situations where lightweighting is required.
• High sintering temperature: Stainless steel sintering temperature is high, usually exceeding 1200°C, which increases the energy consumption and cost of the process.

2. Titanium alloys

Titanium alloys have extremely high specific strength (strength/weight ratio) and excellent corrosion resistance, and are widely used in aerospace, medical devices, and chemical industries. Common titanium alloys used for Micro MIM include Ti6Al4V.

Advantages:

• Biocompatibility: Titanium alloys do not cause rejection reactions in the human body and are ideal materials for manufacturing medical implants.
• High strengthtoweight ratio: Titanium alloys are high in strength and light in weight, making them very suitable for aerospace and miniaturized equipment.
• Excellent corrosion resistance: Titanium alloys have good resistance to seawater and chemical corrosion.

Disadvantages:

• High processing cost: The raw materials and processing costs of titanium alloys are high.
• High sintering process requirements: The sintering temperature of titanium alloys is high, requiring specific sintering equipment and precise temperature control.
• Low temperature brittleness: Some titanium alloys become brittle at low temperatures, which limits their use in extremely low temperature environments.

3. Copper alloys

Copper alloys are known for their good electrical and thermal conductivity and are often used in the electronics industry and communication equipment. Copper alloys used for Micro MIM include brass, bronze, etc.

Advantages:

• Excellent electrical conductivity: Copper alloys are materials with excellent electrical conductivity and are widely used in electronic components such as connectors and connectors.
• Good thermal conductivity: Copper alloys are superior in thermal conduction and help dissipate heat in electronic equipment.
• Relatively low sintering temperature: The sintering temperature of copper alloys is relatively low, usually below 1000°C, which reduces the energy consumption and equipment requirements of the process.

Disadvantages:

• Poor corrosion resistance: Copper alloys are prone to corrosion in humid or acidic environments, which may limit their service life.
• Low mechanical strength: Compared with stainless steel and titanium alloys, copper alloys have lower strength and are difficult to withstand large mechanical stresses.
• High density: Copper alloys have a high density and may not be suitable for applications with high lightweight requirements.

4. Tungsten alloys

Tungsten alloys have high density, high melting point and good wear resistance, and are often used in high temperature environments and applications requiring high hardness. Tungstenbased alloys are mainly used in aerospace, military industry and other fields.

Advantages:

• High density and hardness: Tungsten alloys have extremely high density and good wear resistance, and are suitable for parts requiring high hardness and high strength.
• High temperature resistance: The melting point of tungsten alloys exceeds 3000°C, which is suitable for high temperature occasions such as thermal spraying and high temperature parts.
• Good radiation shielding: The high density of tungsten gives it a good radiation shielding effect, which is suitable for nuclear industry and medical imaging equipment.

Disadvantages:

• High cost: Tungsten raw materials are scarce and expensive, and are not suitable for largescale and lowcost production.
• High sintering difficulty: The sintering temperature of tungsten alloys is extremely high, requiring special equipment and high energy consumption.
• High brittleness: Tungsten alloys have poor ductility and may fracture brittlely under greater stress.

5. Nickel alloys

Nickel alloys excel in corrosion resistance and high temperature resistance and are widely used in chemical processing equipment, turbine engine components, and parts in hightemperature environments. Common nickelbased alloys include Inconel, Hastelloy, etc.

Advantages:

• Good corrosion resistance: Nickel alloys can resist many acidic and alkaline corrosion environments.
• Good hightemperature strength retention: Nickel alloys can still maintain their strength in hightemperature environments and are suitable for hightemperature parts.
• Strong oxidation resistance: Nickel alloys can also effectively resist oxidation at high temperatures.

Disadvantages:

• Difficult processing: Nickel alloys have high hardness and density, and the processing and sintering process is complex and timeconsuming.
• High cost: The high price of nickel alloys limits their use in some lowcost applications.
• High density: Nickel alloys have a high density and are not suitable for weightsensitive applications.

6. Cobaltchromium alloy

Cobaltchromium alloys have high hardness and wear resistance, excellent biocompatibility, and are often used in medical implants such as artificial joints, dental alloys, etc. Its excellent corrosion resistance also makes it widely used in the marine and chemical fields.

Advantages:

• Excellent biocompatibility: Cobaltchromium alloys have good compatibility with human tissues and are the preferred material for manufacturing medical implants such as joints and teeth.
• High hardness and wear resistance: Cobaltchromium alloys have high hardness and are not easy to wear, and are suitable for applications with high friction.
• Strong corrosion resistance: It has excellent corrosion resistance in acidic and alkaline environments and is suitable for longterm use in the body or in harsh environments.

Disadvantages:

• High processing cost: Cobaltchromium alloys have high hardness, high processing difficulty, and more stringent equipment requirements.
• Poor elasticity: Cobaltchromium alloys are not as elastic as titanium alloys, and are not ideal for applications that require a certain degree of toughness and elasticity.
• High cost: Cobaltchromium alloys have high raw material and processing costs and are suitable for high valueadded applications.

Other Micro Metal Powder Materials

Brand	Phase structure	Magnetism	Heat treatment	Application
304L	Austenite	weak magnetism	No hardening effect	Internal structure and appearance, lens ring protective cover/card holder
316L/317L	Austenite	weak magnetism	No hardening effect	Internal structure and appearance, lens ring protective cover/card holder
904L	Austenite	weak magnetism	No hardening effect	Highlight parts for smart watches
P.A.N.A.C.E.A.	Austenite	no magnetism	No magnetic corrosion resistance	Circuit board bracket and nonmagnetic structural parts, lens ring protective cover
310N	Austenite	weak magnetism	No hardening effect	Heat resistant for long term use 750800°C
420J2	Martensite	strong magnetism	Water quenching hardening	Wearresistant parts, various cushions, product shaftslaptops/folding screen mobile phones
440C	Martensite	strong magnetism	Water quenching hardening	Wearresistant parts, various cushions, product shaftslaptops/folding screen mobile phones
2507	Duplex	strong magnetism	Water quenching hardening	Smart watch highlights
174PH	Duplex	strong magnetism	Precipitation hardening	Various structural parts/connectors and terminal ports

 

Brand	Phase structure	Heat treatment	Application
Fe	Moderate Magnetic	Hardening according to carbon content	Internal structural parts, requiring various antirust treatments/inductor components
(SAE1010)	High magnetic induction
Fe2Ni	Moderate Magnetic	Hardening according to carbon content	Internal structural parts require various antirust treatments
Fe4Ni	Moderate Magnetic	Hardening according to carbon content	Internal structural parts require various antirust treatments
Fe8Ni	Moderate Magnetic	Hardening according to carbon content	Internal structural parts require various antirust treatments
Fe50Ni	High magnetic permeability	Hardening according to carbon content	Internal structural parts require various antirust treatments
FeSi3	High magnetic permeability	Hardening according to carbon content	Internal structural parts require various antirust treatments
Low Alloy	Moderate Magnetic	Hardening according to carbon content	Internal structural parts, requiring various antirust treatments/inductor components
((Low content of nonferrous elements))	High magnetic induction

 

Brand	Phase structure	Heat treatment	Application
Fe50Co	No magnetic conductivity	Annealing softening improves toughness	Connector and terminal port/EMC shielding
ASTM F75	No magnetic conductivity	Annealing softening improves toughness	Circuit board bracket and nonmagnetic structural parts, lens ring protective cover
Inconel 718	No magnetic conductivity	Annealing softening improves toughness	Internal structural parts such as connectors and terminal ports
WNiFe	Low Magnetic	Dehydrogenation improves toughness	Various counterweights and vibration plates
Cu	Nonmagnetic	Dehydrogenation improves toughness	Various heat dissipation and EMC screen wall cover designs
WCu	Nonmagnetic	Dehydrogenation improves toughness	Various heat dissipation and low deformation and fast heat dissipation are required
Ti (TA1)	Nonmagnetic	Dehydrogenation improves toughness	Especially for contact with human body
Ti6Al4V (TC4)	Nonmagnetic	Dehydrogenation improves toughness	Especially for contact with human body
High strength steel THOR	Nonmagnetic	Precipitation hardening	Axis

 

Each metal material has its own unique advantages and disadvantages. The selection of the appropriate material should be based on the specific application requirements and cost budget to optimize manufacturing costs while ensuring part quality.

IV. Molding Process

Micro MIM technology, or Micro Metal Injection Molding, is a highprecision manufacturing process specifically designed for manufacturing tiny, complex metal parts. It combines the advantages of powder metallurgy and injection molding technology, mixes metal powder with a binder, and produces complex small metal parts through injection molding. The following is the detailed working principle of Micro MIM technology and its main steps:

1. Mixing metal powder with binder

The first step of Micro MIM technology is to mix metal powder with an organic binder (binder) to form a plastic mixture called "feed". Commonly used metal powders include stainless steel, titanium alloy, copper alloy, etc., while the binder is usually composed of materials such as thermoplastic polymers, wax, and oil.

• Metal powder: The particle size is between 110 microns to ensure that it is suitable for precision machining.
• Binder: It plays a supporting role, allowing the metal powder to pass through the injection molding mold and maintain its shape during the molding process.

• Mixing process: Mix metal powder and binder in a certain proportion, and use high shear mixing equipment to evenly disperse the metal powder in the binder to form a homogeneous mixture. This mixture has fluidity when heated and can be shaped after cooling.

2. Injection molding

Injection molding is one of the core steps of Micro MIM. In this process, the mixture is heated to a certain temperature to soften the binder and obtain fluidity. The heated mixture is then injected into a precision mold through an injection machine to form the rough shape of the part.

• Mold design: The mold must be precise in order to obtain the required shape and details. It is usually made of high hardness materials to ensure accuracy and durability.

• Injection temperature and pressure: In order to ensure that the mixture can smoothly fill the mold cavity, it is usually necessary to inject at a higher temperature and pressure.

• Cooling and shaping: After the mixture is injected into the mold, it is immediately cooled to solidify. The solidified part is called "green blank", which contains a large amount of binder and maintains the shape of the metal powder.

3. Degreasing

Degreasing refers to the removal of binders in green blanks to obtain highdensity, pure metal parts. Debinding is usually divided into two steps: predebinding and main debinding.

• Predebinding: First, solvent debinding or thermal debinding is used to remove about 6080% of the binder in the green blank. It is carried out at a lower temperature to avoid damage to the part structure.
• Main debinding: High temperature or catalytic debinding technology is used to completely remove the remaining binder. At this time, the part becomes a "brown blank", which still maintains the connection of metal powder particles in structure, but the binder has been removed.

During the debinding process, especially in the predebinding stage, it is very important to avoid deformation or cracking of the green blank. Controlling temperature and time ensures that the part is uniformly debinded while maintaining its shape.

4. Sintering

Sintering is the last step of Micro MIM technology, which is to combine the metal powder particles in the brown blank into a dense metal structure through high temperature treatment. In this process, the powder particles in the brown blank diffuse at high temperature and combine with each other to form a part with high strength and density.

• Sintering temperature: Depending on the metal material, the sintering temperature is usually between 1100°C and 1400°
• Sintering atmosphere: To avoid oxidation or other reactions, sintering is usually carried out in a vacuum environment or under the protection of an inert gas (such as nitrogen or hydrogen).
• Volume shrinkage: During the sintering process, the parts will shrink to a certain extent, usually between 1520%. This shrinkage can improve density and strength.
• Final molding: After sintering, the density and mechanical properties of the parts are significantly improved to achieve the accuracy and quality required by the design.

5. Postprocessing (optional)

Depending on the application requirements, the sintered parts may require further postprocessing steps, such as:

• Heat treatment: Such as quenching or tempering to enhance hardness and mechanical properties.
• Surface treatment: Such as electroplating, polishing or oxidation treatment to improve surface quality or corrosion resistance.
• Machining: In special cases, minor machining adjustments may be required to obtain precise dimensions.

V.Advantages of Micro Metal Injection Molding

1. High precision:

 The general tolerance of MIM is ±0.5%, which is higher than ±1% of Lost Wax.

2. Complex shape manufacturing:

 MIM process can produce three-dimensional shapes with high degrees of freedom. Compared with other metal forming processes such as metal sheet stamping, MIM can form parts with highly complex geometric shapes. Including parts such as thin-walled structures and internal channels that are difficult to manufacture by traditional processing methods. In other words, MIM can also complete the complex part structure that can be completed by plastic injection molding.

3. Low-cost production:

MIM uses injection molding machines to mold green products, which greatly improves consumption efficiency, greatly reduces manpower and material resources, and reduces production costs; at the same time, the diversity and repeatability of injection molded products are good, thus providing a guarantee for large-scale and large-scale industrial consumption.

4. High material utilization rate:

Injection materials can be reused repeatedly, and the material utilization rate is almost 100%. There is basically no production waste, which can maximize the use of metal powder and reduce material waste.

5. Uniform microstructure, high density and good performance of parts:

 MIM is a fluid molding process. The presence of adhesive ensures the uniform arrangement of powder, thereby eliminating the uneven microstructure of the blank. The microstructure is uniform, without the coarse crystalline structure and component segregation that appear in the casting process, so that the density of the sintered product can reach the theoretical density of its material. Generally speaking, MIM can reach 95%~99% of the theoretical density, and for those with high carbon liquid phase sintering, almost 100% relative density can be obtained. High density can increase the strength of MIM parts, enhance toughness, improve ductility and electrical and thermal conductivity, and improve magnetic properties. The density of parts pressed by traditional powder molding can only reach 85% of the theoretical density at most. This is mainly due to the friction between the mold wall and the powder and between the powders, which makes the pressing pressure unevenly distributed, resulting in uneven microstructure of the pressed blank. This will cause the pressed powder metallurgy parts to shrink unevenly during the sintering process, so the sintering temperature has to be lowered to reduce this effect, resulting in large porosity, poor material density, and low density of the products, which seriously affects the mechanical properties of the parts.

6. High strength and high surface quality:

It can obtain mechanical strength close to that of the casting process, and its mechanical properties are significantly better than those of precision casting and traditional powder metallurgy; the product dimensional accuracy and surface finish are also better than those of precision casting products, which can reduce the need for subsequent processing. The surface roughness can reach Rmax6~8μm (Ra1.5 to 2).

VI .Application of Micro Metal Injection Molding Technology

1. Medical Devices

Medical devices are generally required to have good usability and a long enough service life, and to have flexible design in structure and shape design. MIM technology was first applied to medical products in the early 1980s, and has become the fastest growing area in the MIM market.

Currently, most medical MIM products use stainless steel materials, with the main grades being 316L and 17-4PH; there are also titanium alloys, magnesium alloys, gold, silver, tantalum, etc. 

1.1 Orthodontic brackets

MIM technology was first used in the medical field to produce some orthodontic appliances. These precision products are very small in size, have good biocompatibility and corrosion resistance, and the main material used is 316L stainless steel. At present, orthodontic brackets are still the main products of the MIM industry.

A company uses MIM technology to produce a two-way hook-type orthodontic bracket, which can increase the mechanical retention force by 30%. The use of MIM one-time forming and polishing can greatly reduce the friction of the bracket on the archwire. This product plays a positive role in orthodontic surgery.

1.2 Surgical tools

Surgical tools require high strength, low blood contamination, and the ability to implement aggressive disinfection procedures. The design flexibility of MIM technology can meet the application of most surgical tools. It also has process advantages and can manufacture various metal products at low cost. It is gradually replacing traditional production technology and becoming the main manufacturing method. 

1.3 Knee implant parts

MIM technology has made slow progress in the field of human implants, mainly because the certification and acceptance of products requires a long period of time.

Currently, MIM technology can be used to produce parts that partially replace bones and joints, and the metal materials used are mainly Ti alloys.

In terms of biocompatibility, Chen Liangjian et al. used MIM technology to prepare porous titanium with a porosity of 60%, and used a modified condensation polymerization cross-linking method to prepare gelatin sustained-release microspheres and coated them on the surface of porous titanium.

1.4 Hearing aid sound tubes

MIM technology can also be used to produce parts for various medical devices.

Indo-MIM uses MIM technology to produce a hearing aid sound tube for Phonak in Germany, which has the effect of improving sound rate and promoting hearing.

After MIM forming and sintering, the complex-shaped hearing aid sound tube can be obtained. In order to make the surface of the sound tube smooth, it only needs to go through a glass bead sandblasting process.

MIM technology can also be used to produce many products in the medical field, including interventional treatment stents, radiation shielding for tungsten high-density alloy syringes, microsurgical manipulators, micro pump endoscope parts and drug inhalers.

2. Electronic Equipment

The electronic instrument industry is the main application field of MIM parts, accounting for about 50% of MIM parts sales in Asia. The miniaturization of electronic devices requires smaller parts with lower production costs and better performance, which is exactly the advantage of MIM parts.

The development of MIM in China has benefited from the promotion of the electronics industry (such as the mobile phone industry, etc.). Since 2009, the entire industry has been rising rapidly; especially after mid-2011, due to the competition between Apple and Samsung Electronics, a large number of MIM parts have been used in mobile phone devices, which is a trend never seen before.

2.1 Smartphones

In the 1990s, the most well-known MIM application was the tungsten alloy vibrator of the BP machine vibration motor. After 2000, stainless steel series began to be widely used, such as optical fiber connectors, hinge series of consumer electronics, mobile phone buttons, SIM card trays, etc. The recent investment boom in the MIM industry is due to the widespread application of MIM parts in the mobile phone industry, and the assembly factories of the 3C industry are also in China, and the lowering of investment thresholds have attracted a large amount of capital inflow.

2.2 Manufacturing of mobile phone cases

The mobile phone case is an important part of the mobile phone. The MIM process can produce high-precision, high-strength and lightweight mobile phone cases. During the manufacturing process, the MIM process is first used to manufacture the injection-molded blanks of the mobile phone case, and then the blanks are placed in the mold for injection molding, and finally surface treatment and assembly are performed.

2.3 Camera manufacturing

The manufacturing of mobile phone cameras requires high precision and miniaturization. The MIM process can manufacture high-precision miniaturized lenses and brackets. During the production process, the MIM process is first used to manufacture the injection-molded blanks of the camera bracket and lens, and then the blanks are placed in the mold for injection molding, and finally surface treatment and assembly are performed.

2.4 Manufacturing of card trays

The card tray is an important part of mobile phone electronic products. The MIM process can manufacture card trays with high precision, high strength and light weight. During the manufacturing process, the MIM process is first used to manufacture the injection-molded blanks of the card tray, and then the blanks are placed in the card tray mold for injection molding, and finally surface treatment and assembly are performed.

2.5 Manufacturing of the shaft

Folding mobile phones are also a kind of electronic products. The shaft of its folding screen can also be manufactured using the MIM process. Some of the most precise parts require the use of MIM technology, and the accuracy of MIM technology can reach ±0.1%~±0.3%.

2.6 Button Manufacturing

The buttons next to smart watches are also used for 3C electronic products, such as the buttons below, which are also made by MIM technology.

2.7 Capacitive Pen Cap Manufacturing

The parts used in the capacitive pen equipped with iPad are also made by MIM technology.

2.8 Smart Watchband Manufacturing

Smart watchbands are a type of 3C electronic products. MIM technology can manufacture smart watchbands with high precision. And through subsequent processing, exquisite products can be obtained.

3. Optical Fiber Parts

Optical fiber technology is widely used in the fields of communication, sensing and medical treatment. Its core components must have the characteristics of high precision, high strength and miniaturization. Micro Metal Injection Molding (μMIM) has become an ideal choice for manufacturing optical fiber parts due to its high precision, complex geometric shape processing and mass production capabilities. This process combines powder metallurgy and injection molding to produce micro parts that meet the needs of modern optical fiber technology.

3.1 Connector Housing

Optical fiber connectors are one of the core components used to connect the ends of optical fibers in optical fiber communication systems. The connector housing is extremely small and requires high wear resistance, while also requiring good electromagnetic shielding. The μMIM process can produce precise and durable metal connector housings to ensure efficient transmission of optical signals.

3.2 Fiber fixtures and aligners

In optical fiber systems, precise alignment of optical fibers is essential for signal transmission. The μMIM process can be used to produce high-precision fiber aligners and fixtures. These parts usually have complex geometric structures. μMIM can be formed in one go, avoiding errors that occur during traditional processing and ensuring the accuracy of fiber alignment.

3.3 Fiber Adapters and Sockets

Fiber adapters are used to connect fiber plugs to devices. The precision and durability of the socket directly affect the stability of the fiber system. μMIM technology can not only produce adapters with complex shapes, but also provide good mechanical strength and durability to meet the needs of high-frequency use.

3.4 Sensor Package

In the fiber optic sensing system, the sensor package needs to be dustproof, waterproof and high-temperature resistant, while ensuring that the optical fiber maintains stable signal transmission during the sensing process. The μMIM process can produce packages with high strength and complex shapes, which not only meet the protection needs, but also do not affect the performance of the optical fiber.

3.5 Fiber Cutter and End Polishing Tool

Fiber optic cutting and end polishing tools require extremely high precision to ensure the flatness of the fiber end face and the efficient transmission of optical signals. The μMIM process can produce high-hardness, high-precision metal knives and polishing tools that can maintain stable performance for a long time and improve work efficiency.

4. Automobile Industry

Since MIM parts entered the automobile market in the early 1990s, after nearly 20 years of development, there are more and more manufacturers of MIM parts for automobiles. Compared with traditional processing methods, MIM parts have the characteristics of high precision, high strength, high shape complexity, material diversity and low cost, so MIM technology has been widely used in automobiles. At present, MIM parts used in automobiles are generally iron-based materials, mainly Fe-Ni alloy steel Fe-04C-1Cr-075Mn-0.2Mo alloy steel, pre-alloyed Cr-Mo-C steel Ni-Cr-Mo-C steel 316L, 17-4PH400 series HK series stainless steel conel713C nickel-based heat-resistant high-temperature alloy steel.

4.1 Turbocharger

The turbocharger is mainly composed of a turbine, a pump wheel, a rotor, an impeller, etc. The inertial force generated by the high-pressure exhaust gas discharged by the engine drives the pump wheel to rotate, and the rotor drives the turbine to rotate, so that the engine intake pressure increases. In recent years, the research and development and production of turbocharger MIM parts have become the focus of scientific research work. At the same time, turbochargers are also one of the iconic parts of MIM manufacturing. Its structure is extremely complex, the working environment is harsh, and the precision requirements are high. However, other processing methods are costly and difficult to control. Turbocharger parts are mainly composed of nickel-based ultra-high temperature alloys, chrystal alloys and other materials. MIM has made great contributions to turbocharger parts.

4.2 Automobiles

Many small precision assembly parts on automobiles can be manufactured using MIM technology. The manufacture of assembly parts is generally carried out by forging, precision casting and other methods. The manufactured parts are costly and have low precision, and cannot achieve good economic benefits. The use of MIM technology can improve production efficiency, improve precision, save materials, reduce processes and reduce costs. The electronically controlled gasoline injector on the automobile engine consists of more than 20 parts. Among them, the iron core, armature, magnetic guide sheet, guide body and other parts constitute the magnetic circuit structure of the injector. These parts are all made of soft magnetic alloy materials. The parts made of iron-based nanocrystalline soft magnetic alloy powder by MIM technology have improved the comprehensive performance of the injectors made by MIM technology compared with traditional gasoline injectors.

4.3 Sensors

With the advancement of science and technology, the types and functions of sensors used in automobiles tend to be diversified, intelligent and miniaturized. According to different application areas, sensor shells are used in engine chassis, body navigation and other systems! Many sensors on engine chassis, body navigation and other systems have been manufactured by MIM process, such as pressure sensor components, airbag sensor inserts, oxygen sensors, steering sensors, cruise control sensor seats, sensor shells, etc. Compared with precision casting process, MIM process has the advantages of good surface roughness, high tensile strength, and can realize part combination, reduce the number of parts, reduce costs and improve efficiency.

In addition to the above parts, the ignition key, engine rocker arm parts, steering device U-clip, reverse synchronizer, valve push rod, piston ring combustion chamber cover, car fixer, etc. on the car are all manufactured by MIM process.

5. Precision Machinery

MIM technology can produce metal parts with complex three-dimensional geometric shapes with high complexity, high precision, high strength, exquisite appearance and miniature specifications in large quantities, with high efficiency and low cost, and is widely used in various precision instruments. These gears are usually in millimeter diameter or even smaller, with complex design, requiring high strength, high wear resistance and precise meshing performance. With the advancement of science and technology, micro gears play a vital role in electronic products, medical equipment, aerospace and other fields.

5.1 Precision timing device

In the watchmaking industry, especially in high-end mechanical watches, micro gears are one of the core components. Through precise gear meshing, mechanical watches can maintain highly accurate timing functions. Due to the limited internal space of mechanical watches, the size of the gears needs to be very small and the operation is extremely smooth. The high precision and low friction performance of micro gears are crucial.

5.2 Microscopes and optical instruments

The focusing system and precise adjustment of optical elements used in microscopes rely on the transmission of micro gears. The accuracy of micro gears directly affects the magnification adjustment of the microscope and the clarity of the image. Micro gears are also widely used in the fine-tuning mechanism of optical instruments to ensure precise control of the optical path.

5.3 Medical Devices

In minimally invasive surgical equipment, micro gears are used to drive various tiny robotic arms and surgical tools. These gears are extremely small in size, but require extremely high precision and reliability to ensure accuracy and safety during surgery. Micro gears are also widely used in micro drill adjustment systems and blood pumps in dental equipment.

5.4 Robots and Automation Equipment

Micro robots are often used in surgery, manufacturing, and laboratory automation. These robots require flexible joints and precise motion control. The micro gear system is the core component of these robots, helping them achieve complex movements and operations. Due to the compact structure of the robot, the high efficiency and low noise characteristics of the micro gears are particularly important.

6. Consumer Electronics

Electronic communication products are an important market for MIM parts. Almost all mobile phone manufacturers will purchase a large number of MIM products, and the miniature and multifunctional parts in communications are suitable for the advantages of MIM technology. MIM injection molding can achieve the advantages of reducing production costs, improving production efficiency, and making parts smaller and lighter. The advantages that mobile phone developers strive for are to achieve thinness, reduce weight, and improve the feel of parts. Mobile phone project development is very rapid, and only MIM technology can produce so many parts in a short period of time.

In addition to the card tray, the hinges used in the currently popular folding screen mobile phones are also MIM parts. Of course, in addition to the above typical ones, there are many other applications of MIM parts in consumer electronics.

VII. Challenges and limitations

1 High equipment costs

High mold cost:

 The μMIM process requires the use of high-precision molds to ensure molding accuracy. The cost of making and maintaining these molds is high, especially for parts with complex geometries and small batch production. Mold costs may account for the overall production a larger proportion of the cost.

Material waste and low utilization rate: In the production process of micro parts, it is difficult to completely recover the material loss generated during degreasing and sintering. Especially when using precious metal materials (such as titanium, precious metals), this material waste will increase significantly. production costs.

Machinery and equipment are expensive:

Micro metal injection molding (μMIM) equipment usually requires a sophisticated micro injection molding machine, a sophisticated sintering furnace and an efficient degreasing system. Not only do these devices require huge investment in manufacturing, but they also require additional costs during maintenance and use.

2 Molding accuracy and size restrictions

Although the μMIM process excels in processing micron-scale parts, it still faces some accuracy and size limitations:

Dimensional shrinkage and deformation:

The μMIM process will cause the volume of the metal powder to shrink significantly during the degreasing and sintering processes, usually around 15% to 20%. This shrinkage will have an impact on molding accuracy, especially in complex geometries and thin-walled parts, where uneven deformation is more likely to occur.

Surface finish and microstructure processing difficulty:

The surface of sintered micro parts often has problems with high roughness and obvious graininess. To achieve optical-level finish and fine-structure accuracy, additional surface treatment steps are often required, such as electroplating, polishing, etc.

3 Material selection restrictions

The μMIM process has high requirements on material selection. The metal powder used in this process needs to have the following characteristics:

Extremely fine and uniform particles:

 Generally speaking, the diameter of metal powder particles used in the μMIM process is less than 10 microns, but too fine powder particles are easy to agglomerate, making it difficult to distribute evenly during the mixing process, thus affecting the molding quality.

Difficulty of processing special alloy materials: Some high-performance alloys (such as titanium alloys, aluminum alloys) are difficult to carry out powder sintering and degreasing in the μMIM process due to their high activity or easy oxidation characteristics. Therefore, there are still limitations in the applications of these materials.

Material compatibility issues: The compatibility between the binder and metal powder used in the μMIM process needs to be very high, otherwise it will affect the fluidity of the part during molding and the mechanical properties of the final part.

4 Manufacturing process control is complex

The manufacturing process control of the metal injection molding process (MIM) is quite complex, mainly reflected in the precise management of multiple key steps. First, compounding and injection molding require mixing the metal powder with the binder and ensuring its uniformity to avoid molding defects. The temperature, pressure and speed during the injection process need to be strictly controlled to ensure that the material can fully fill the mold while preventing the generation of bubbles and voids. If you are not careful, these factors may lead to surface defects or uneven internal structure of the part. In addition, the design of the mold is also crucial, especially parts with complex geometries and fine features that require extremely high mold precision.

The subsequent debinding and sintering processes are even more challenging. Degreasing is the removal of the binder used during the injection process to leave the metal skeleton. This step requires long-term heating and precise time control. Slight fluctuations in temperature and atmosphere during the degreasing process can cause cracks or pores to form inside the part. The sintering process requires densifying the metal powder at high temperatures to ultimately achieve the mechanical strength and precision of the finished product. The control of sintering temperature and time is extremely critical. Too high a temperature will cause deformation of the part, while too short a time may not allow complete densification. Taken together, the meticulous control of each step directly affects the quality and performance of the final part.

VIII. Future Development

1 Technological Progress

With the continuous advancement of technology, the micro metal injection molding (μMIM) process has achieved significant improvements, especially breakthroughs in material science, equipment precision and process optimization. The research and development of high-quality metal powder makes the powder particles smaller and more uniform, which greatly improves the surface finish and structural strength of the parts. In addition, debinding and sintering technology has been improved to reduce production defects and improve process reliability and consistency through more efficient and precise control. At the same time, the introduction of intelligent manufacturing technologies, such as automated monitoring and parameter optimization, has further improved the efficiency of the μMIM process, making the mass production of micro-complex parts more stable and economical.

2 Development of New Materials

The development of new materials in the micro metal injection molding (μMIM) process mainly focuses on the research and application of high-performance alloys and composite materials. In recent years, in response to the special requirements for strength, corrosion resistance and electrical conductivity of micro parts, researchers have developed new materials such as titanium alloys, stainless steel and high-temperature alloys suitable for the μMIM process. These materials offer better mechanical properties and processability while reducing defects that occur during sintering and debinding. In addition, the development of biocompatible metal materials also provides new options for the manufacturing of micro-parts in medical, electronics and other fields. By improving the material formula, these new materials not only improve product performance, but also optimize the production efficiency and cost control of the μMIM process.

3 Enhance Production Efficiency

In order to improve the production efficiency of the micro metal injection molding (μMIM) process, technical improvements mainly focus on process optimization and equipment upgrades. Advanced automated injection equipment combined with a precise temperature control system makes the injection molding process faster and more stable, reducing the rate of defective products. At the same time, the introduction of rapid degreasing and sintering technologies, such as microwave sintering and vacuum degreasing, significantly shortened the production cycle. In addition, the application of intelligent monitoring and data analysis technology in the process allows key parameters in production to be adjusted in real time to ensure efficient and continuous production. These technological improvements not only improve production capacity per unit time, but also improve product consistency and quality stability.