MIM PARTS

MIM is a near-net forming process, that not only can get high density, good mechanical properties, and small surface roughness parts, but also can produce large quantities, of high-efficiency complex parts, generally do not need to continue finishing, parts cost reduction, promote the development of automotive lightweight, reduce environmental pollution, and thus caused the attention of the automotive industry. Since the early 1990s, MIM parts into the automotive market, after nearly 20 years of development, automotive MIM parts manufacturers more and more.

 

According to a recent survey by the Metal Injection Molding Association, according to the quality score of shipments, MIM small arms parts accounted for 42.3%, medical and dental parts accounted for 14.0%, MIM automotive parts accounted for 13.0%, electronic instrument parts/telecommunications parts accounted for 10.0%, industrial parts accounted for 16.0%, and MIM small arms parts accounted for 14.0%. Defense and aerospace components accounted for 1.0%, and other components accounted for 3.7%

 

As an advanced technology in the field of powder metallurgy, MIM technology is gradually replacing traditional machining technology and is more used in the production of auto parts

 

Typical applications of MIM components mainly include power transmission parts, turbochargers, fuel injectors, airbag sensor inserts, pressure sensors, electric door lock combination parts, and other MIM parts

 

MIM inherits the advantages of traditional powder metallurgy and plastic injection molding and breaks through the limitations of traditional metal powder molding in the shape of parts. It can quickly manufacture small, complex shapes that cannot be machined by traditional methods or are difficult to machine

 

The compared results of important parameters in the production process

Argument MIM Powder metallurgy process Machining Investment casting
Relative density (%) 98 88 100 98
Tensile strength High Low High High
Elongation High Low High High
Hardness High Low High High
Complexity High Low High Medium
Surface roughness High Medium High Medium
Production capacity High High Low Medium
Material range Big Big Big Medium-Big
Cost Medium Low High Medium

Application of MIM component 

Compared with traditional machining methods, MIM technology has the characteristics of high precision, high strength, high shape complexity, diversified materials, and low cost, so MIM technology has been widely used in automobiles. The MIM parts currently used in automobiles are generally iron-based materials, The main products are Fe-Ni alloy steel, Fe-0.4C-1Cr-0.75Mn-0.2Mo alloy steel, pre-alloyed Cr-Mo-C steel, Ni-Cr-Mo-C steel, 316L, 17-4PH, 400 series, HK series stainless steel, Inconel713C Nickel base heat resistant high-temperature alloy steel.

2.1 Turbocharger

The turbocharger is mainly composed of the turbine, pump wheel, rotor, impeller, etc., which uses the inertia force generated by the high-pressure exhaust gas discharged by the engine to drive the pump wheel to rotate and drive the turbine to rotate through the rotor so that the engine intake pressure increases.

In recent years, the research development and production of turbocharger MIM parts have become the focus of scientific research work, and turbochargers are also one of the iconic parts manufactured by MIM. Its structure is extremely complex, the working environment is harsh, and the precision requirement is high, but other processing methods have high costs and accuracy is not easy to control. Turbocharger parts are mainly composed of nickel-based ultra-high temperature alloy, titanium alloy, and other materials, which were previously processed by traditional powder metallurgy technology.

The German company BASF has made a great contribution to the MIM turbocharger parts, and BASF uses the unique Catamold process to manufacture MIM turbocharger parts. The mechanical strength of MIM parts and precision cast samples were compared at room temperature, which proved that excellent material properties could be obtained by using the Catamold process.

In China, researchers use argon atomized K418 alloy powder as raw material, add self-designed multi-component paraffin-based binder, and use injection molding technology to prepare complex shape turbocharging turbines. Through the subsequent hot isostatic pressing and heat treatment process optimization, the supercharger turbine with dense structure, uniform composition, excellent mechanical properties, suitable contour, and good surface finish was prepared. Key technical difficulties such as die structure design, injection molding process parameter optimization, sintering densification, and dimensional accuracy control of complex shape turbocharging turbines have been broken through, and the comprehensive mechanical properties have been significantly improved compared with cast turbines.

MIM turbocharger parts

2.2 Fuel Injector

Many small precision components in automobiles can be manufactured using the MIM process. The manufacturing of composite parts is generally through forging, precision casting, and other methods, the manufacturing of parts with high cost, and low precision, can not achieve better economic benefits. When the MIM process is used, it can improve production efficiency, improve accuracy, save materials, reduce processes, and reduce costs.

The electronic gasoline injector on the automobile engine is composed of more than 20 parts, in which the magnetic circuit structure of the injector is composed of an iron core, armature, magnetic guide, and other parts, which are made of soft magnetic alloy materials.

Compared with traditional gasoline injectors, the overall performance of the injectors manufactured by MIM technology is improved by using iron-based nanocrystalline soft magnetic powder.

 

440C stainless steel MIM seal support for direct feed injector assembly. This is a complex structural part with multi-angle grooves and top holes, the sealing support manufactured with MIM has a structural shape close to the final shape, ρ 7.54 — 7.65 g/cm3, σb is 1600MPa, σs is 1400MPa. The MIM process saves nearly 30% to 40% in cost compared with other production processes. The nozzle for cooling the piston on the V-8 cylinder engine is also made of MIM.

Characteristic Min Max Optimum
Mass 0.01g 240g 0.1~50g
Wall Thickness 0.1mm 10mm 0.5~5mm
Annual Usage 10000 million >100 thousand

 

Dimension(mm) Standard Tolerance(mm) Special Tolerance(mm)
0~5 ±0.05 ±0.025
5~10 ±0.07 ±0.03
10~20 ±0.10 ±0.05
20~50 ±0.30 ±0.10
50~100 ±0.50 ±0.2

 

Characteristic Best(±) General (±)
Angle 0.1°

2.3 Sensor

With the progress of science and technology, the types and functions of sensors applied in automobiles tend to be diversified, intelligent, and miniaturized. Depending on the application area, the sensor housing is used in the engine, chassis, body, navigation, and other systems.

Many sensors in the engine, chassis, body, navigation, and other systems have been manufactured using the MIM process, such as pressure sensor components, airbag sensor inserts, oxygen sensors, steering sensors, cruise control sensor mounts, sensor housings, etc.

The airbag is a measure to protect the life of the driver when the car encounters an emergency, which can be divided into mechanical and electronic.

The mechanical type is triggered by the impact of the inertial ball on the firing pin, and the electronic type is triggered by the sensitive element. The airbag is composed of a D-shaped shaft, embedded splice, and ignition pin, which are all made of MIM17-4PH stainless steel [21]. After heat treatment, σb is 1170MPa, σs is 1100MPa, hardness reaches 38-41HRC, δ is 7.0%. The density is between 7.60 and 7.68g/cm3. The dimensional accuracy, stiffness, strength, and wear resistance of the parts meet the requirements of use.

Compared with the precision casting process, the MIM process has the advantages of good surface roughness, high tensile strength, parts combination, reducing the number of parts, reducing costs, and improving benefits.

General dimensional tolerances that MIM parts can achieve. In addition to the above parts, the ignition key, the engine rocker arm parts, the U-clamp of the steering device, the reverse synchronizer, the valve ejector rod, the piston ring, the combustion chamber cover, and the car holder are all manufactured by MIM process.

 

Prospect MIM parts

With the progress of science and technology, the main direction of automotive development is energy saving, environmental protection, comfort, intelligence and lightweight, MIM automotive products in the automotive application prospects are huge.

Using MIM technology, it is possible to design tiny auto parts into whole or multiple components and use the MIM process for injection molding, so that the parts can achieve micro, integrated, low cost, and other characteristics under the premise of meeting the performance. At the same time, the parts can be manufactured with external grooves, external threads, cross holes, blind holes, reinforced plates, grooves key pins, and other complex shapes.

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