What is Metal Injection Molding (MIM)
Metal Injection Molding (MIM) is a near-net molding process suitable for the production of small, three-dimensional complex shapes and products with special performance requirements.
MIM is the development of traditional powder metallurgy process and modern plastic injection molding technology, the basic process is: a variety of fine metal powder (generally less than 20μm) according to a certain ratio and preset binder (a variety of thermoplastics, waxes and other materials) mixed homogeneously, made of feedstock with rheological properties, injected through the injection machine into the mold cavities (or multi-model cavities) molding parts blanks, blanks, after removing the binder. After removing the binder and high-temperature sintering, the blanks can be obtained as various metal parts with uniform microstructure and highly dense materials.
MIM development process
In the 1970s, American scholars Wiech first developed a metal powder injection molding powder metallurgy process. 1980s, the United States Rensselaer Polytechnic Institute began to carry out the theoretical basis of MIM technology and the application of basic research work. The United States Injectamax company and Germany BASF company will be degreasing time from tens of hours to a few hours, and conformability has been significantly improved, the dimensional accuracy of the product from ± 0.5% to ± 0.3%. 21st century, the MIM process has been further improved, the new materials, new processes continue to emerge, the industrialization of the rapid development. Complex shapes, smaller sizes and large yields, which are the strong points of MIM, have enabled it to find a large number of applications in light weapons, watches, hand tools, orthodontic brackets, automotive engine parts, electronic seals, cutting tools and sports equipment.
Examples of MIM applications in the electronics industry
The electronic instrument industry is the main application area for MIM parts, accounting for about 50% of MIM parts sales in Asia. The miniaturization of electronic devices requires the production of lower cost, better performance, smaller parts, which is where the advantages of MIM parts lie.
MIM development in China benefited from the electronics industry (such as the cell phone industry, etc.) driven from 2009, the whole industry rocketing; especially to the middle of 2011, but also by the Apple and Samsung Electronics two commodity competition, in the cell phone device in a large number of MIM parts, is never seen in the past boom. The following are examples of MIM products in the electronics industry.
In the 90’s, the most widely known MIM application was the tungsten alloy oscillator for the vibration motor of beeper, and after 2000, the stainless steel series began to be widely used, such as fiber optic connectors, hinge series of consumer electronics, cell phone buttons, and sim card holders, etc. Recently, there has been an investment boom in the MIM industry. The recent investment boom in MIM industry is due to the fact that MIM parts are widely used in the cell phone industry, as well as the assembly factories of 3C industry are also located in China, and the lowering of the investment threshold, which have attracted a large amount of capital inflow.
2020 Domestic smartphones using MIM parts
According to the market situation, only domestic cell phone parts (cartridge, button, lens ring, LED ring, spindle) reached RMB 10.55 billion in 2020, and the market demand for MIM products will further expand.
Optical fiber parts
Figure 5 is made of 17-4PH stainless steel thin-walled (wall thickness of less than 1mm), the shape of the complex optical fiber transceiver cover, is used in the network and telecommunications equipment in the ultra-high-speed transceiver paralleling optical modules. These thin-walled MIM enclosures are supported by 4 thin pillars supporting 2 parallel strips.
Other Typical Electronics Industry MIM Products
MIM products are also commonly used in the electronics industry such as disk drive components, cable connectors, electronic packages, cell phone vibrators, and computer print heads.
Key Guidelines for Selecting MIM Technology
The Metal Injection Molding Association of Japan, the United States, and Europe have jointly issued the ISO standard ISO22068 Material Specification for Sintered Metal Injection Molding, which is intended to provide design and materials engineers with the information they need to specify materials for parts manufactured by the MIM process. With regard to the selection of guidelines for the MIM process, the following major issues have been identified for consideration:
☆ Quality/large quantity
MIM is extremely effective in reducing production costs for parts that have high material loss in cutting or grinding.
Mold and creation costs are unaffordable for low production volumes. Therefore, MIM is most suitable when the annual production volume exceeds 20,000 pieces.
MIM is most attractive for parts designed for materials that are difficult to machine, such as titanium, stainless steel, and nickel alloys.
The MIM process is best suited for the manufacture of multi-axis parts with complex geometries and those that need to be repositioned during machining.
If usability is important, the performance of MIM’s high-density formation is often competitive.
Surface roughness reflects the size of the initial powder particles, however, unlike other competing processes, controlled weave may have little effect on cost.
When tight tolerances are required, the cost of MIM tends to increase due to the need for subsequent processing, and the tolerance of sintered parts is approximately ±0.3%.
In order to save inventory and assembly costs, it is beneficial to unite multiple parts into one.
Defects inherent to MIM must be kept in a non-critical position, or removed after manufacturing, such as gate marks, mold lifter marks, or joint lines.
☆New combination materials
MIM can produce new types of combination materials that are difficult to produce by conventional processes, such as laminated, two-material structures, or hybrid metal-ceramic materials for wear resistance.
Current situation and main problems of MIM in China
After more than two decades of development, China’s MIM practitioners have not only broken through the technological blockade, but also developed a large number of MIM products and expanded the market. In recent years, with the proposal of Made in China 2025, the market demand for MIM products has become increasingly strong, MIM companies are growing like a spring, the MIM industry presents a broader outlook and good potential for development.
However, from the overall situation of industry development, China’s current stage of MIM prospects are promising, but in some aspects there is still a gap with foreign countries.
1, the development of the industry is not standardized, product variety is small, poor quality, market competition is not strong;
2, the enterprise scale is small, backward level of technology and equipment, quality and efficiency is difficult to improve;
3, few professionals, poor scientific research and development capabilities, lack of energy for sustainable development.
Now the problem MIM improvement measures and suggestions
The United States, Europe and Japan and other industrially developed countries in the world in the early 1990s basically completed the transformation of MIM technology to the development of the MIM industry, China’s MIM industry and the overall level of foreign countries gap is about 10-15 years. At present, China coincides with the favorable period of manufacturing development, MIM technology application space, product market prospects, which undoubtedly accelerate the development of China’s MIM industry provides a rare strategic opportunity. To this end, we put forward the following measures and suggestions on how to promote the healthy development of MIM industry:
1, the establishment of new mechanisms for the integrated development of industry, academia, research and science, industry and trade
2, to strengthen the industry development planning research and scientific guidance
3, the implementation of high-tech industry development policies
- Actively seek international technical cooperation
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