In recent years, the micro-metal injection molding process (μ-MIM) has been developed with the goal of manufacturing metals and alloys that can be used for mass production of micro-parts and micro-structure surfaces. μ-MIM greatly increases the availability of metals and alloys for micro-applications, such as new materials with high temperature stability, strength and toughness, as well as thermal conductivity and magnetism.

In addition, compared with the plastic micro-injection molding, the bimetal production process developed by the μ-MIM enables two different metal materials to be connected together (bimetal co-injection) during the injection molding process.

 1.  Two-Component MIM (2C-MIM)

The surface is porous and the inner core is dense

As a method of manufacturing bimetallic parts, people have developed the 2C-MIM (Two-Component MIM) process. The main advantage of the 2C-MIM process is that two materials with different properties can be directly combined in a single production process, thus reducing subsequent joint operations (such as welding, riveting, fastening assembly, etc.).

The parts that 2C-MIM can manufacture range from hollow parts with complex internal structures to flexible detachable components.

The aim of all research is to produce functional enhanced engineering parts at a favourable cost. For parts that are easy to wear, you can only locally strengthen the key parts such as the friction surface with harder or more wear-resistant materials, and other structural parts with relatively low-cost materials.

To manufacture bimetal parts, simply understanding the injection molding shape of the two injection materials is not enough, the key is that the two materials must be able to be sintered in the same furnace and in the same sintering atmosphere. Because the shrinkage rate of the two parts is not the same during sintering, it may lead to delamination or cracking. And when a harmful phase is formed, alloyed elements can also spread along the boundary, which reduces the properties of the material.

Figure 17-4PH/316L composite tensile sample prepared by co-injection

By coordinating the machining factors, the quality of 2C-MIM parts is optimized. Due to its unique ability to make a part with different material properties without any assembly work, the 2C-MIM process is certain to expand the application market of the MIM industry.

If the particle size range of the powder is below 1um, special injection materials should be used to adapt to the problems caused by the large surface area of the powder injection molding and degreasing.

2.Micro Metal Injection Molding Process (μ-MIM)

Microinjection stainless steel reaction dish

Products and systems are becoming miniaturized, which means that structural and functional parts in complex systems are becoming smaller and smaller.

This requires not only the use of advanced materials with appropriate physical properties, but also micro-miniaturized geometric features in order to increase the number of integrated functions.

Therefore, it is necessary to develop highly effective and reliable methods for manufacturing micro-parts or micro-structure parts, and micro-structure parts manufactured with μ-MIM can be used to replace plastic parts to obtain the advantages of mechanical properties, corrosion resistance or high temperature properties of metal materials.

The success of this new manufacturing process is based on the fact that its competitive process is limited by machinable materials or mass production capacity, and there is no alternative to μ-MIM.

LIGA technology (a combination of lithography and electroforming) is usually only suitable for 2D geometry, and is limited by electroforming in terms of material selection.

Other techniques, such as electrochemical micro-manufacturing methods, micro-milling and micro-grinding, come from the silicon-based microelectronics industry and have the ability to solve features as small as 1μm, but they are not suitable for mass production of 3D parts.

Now, micro parts produced with μ-MIM can be as small as 5μm in feature size. However, in order to optimize performance, such as maintaining shape according to flow characteristics or parts, special injection materials have been developed that are fully possible for the submicron or nanometer required for μ-MIM.

In general, for micro parts, MIM can replicate features of about 10 times the average particle size, which is particularly suitable for micro parts, if you want to create smaller features, you need to apply a smaller powder. Now, the available metal powder is 1μm. Some powders are too reactive to produce powders in this particle size range (e.g., Ti), while other metal powders are easier to produce with special aerosol vaporization (e.g., stainless steel).

If the particle size range of the powder is below 1um, special injection materials should be used to adapt to the problems caused by the large surface area of the powder injection molding and degreasing.

Picture microinjection stainless steel gear and impeller

At present, μ-MIM is still in the incubation stage and is largely developing in parallel with the 2C-MIM process. First, both processes are now in production, but both are undergoing technology rollout and feasibility studies for a wide variety of micro-parts or micro-structural parts.

Initial competitive research and development goals are critical on their way to market success, but only through the development of materials and production processes around the possibilities of 2C-μ-MIM in the industry, coupled with the education of engineers and technicians, can real breakthroughs be achieved.

In the past six months, with the application of ceramic and 3D glass in mobile phones getting more and more attention, there are also many double-sided 3D glass and ceramic structure models. More and more enterprises have this industry, showing the flourishing of a hundred flowers, some new technologies, new processes, new materials have been developed, such as: stainless steel, titanium alloy, MIM frame, ceramic back cover, process aspects such as, glass decoration process texture development, ink spray new process, printing and antenna fusion; How to improve the 3D glass pass rate, reduce energy consumption, and improve efficiency has become a difficult problem for the entire industry.

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