Application of MIM Technology of Titanium Metal Powder Injection Molding in Medical Products
Jan 03, 2023
Application of MIM Metal Powder Injection Molding Technology in Medical Products
Minimally invasive surgical forceps
China is a country with a large population, and the aging phenomenon is getting more and more serious. In addition, the past pursuit of economic development has caused excessive damage to the environment, which makes people's health problems face huge challenges and stimulates the demand for medical products in the whole society.
How to improve the quality and reduce the cost of medical products has been a research topic for domestic and foreign scholars. The demand for medical products is large, and the structure of many products is also very sophisticated, so a new manufacturing technology is needed to replace the traditional production.
Metal injection molding (MIM) is a new near net forming technology, which can produce products with complex shapes in batches in a short period of time. It can meet the manufacturing requirements of medical products and become an ideal manufacturing method.
1 MIM technology
1.1 Technological process of MIM technology
MIM is a near net forming process developed rapidly in the 20th century. The general process is: powder+binder → mixing → injection molding → degreasing → sintering.
Firstly, the polymer and powder are mixed to produce the feed with sufficient fluidity, uniform mixing and meeting the injection requirements under certain conditions. Secondly, the appropriate injection temperature, injection pressure, injection speed and other process parameters are selected for injection molding. Then, the binder in the injection blank is removed and sintered to form metallurgical bonding of the powder. Finally, the qualified parts are obtained.
1.2 Features of MIM technology
MIM is a new near net forming technology for parts, which combines plastic forming technology, polymer chemistry, powder metallurgy technology, metal materials and other disciplines. It has the following characteristics:
① The parts formed by using MIM technology do not require follow-up processing or there is little follow-up processing. With high material utilization rate, they belong to near net forming technology and can produce high-performance and complex shaped parts.
② The filling process of feed and sintering of products can be simulated by computer, and the process can be optimized in the early stage [1-2] to obtain the best design scheme.
③ During the injection process, the pressure of each point in the cavity is equal, and the density is equal everywhere under the premise of uniform mixing of the feed, so there will be no density gradient, which is easy to achieve large-scale production.
2 Application of MIM technology in medical products
2.1 Medical products manufactured by MIM technology
Medical products generally require good usability and long enough service life, and flexible design in structure and shape design [3].
In the early 1980s, MIM technology was first applied in medical products, and has become the fastest growing area of the MIM market.
Figure 1 shows the proportion of MIM technology in different industries in North America in 2015 [4]. It can be seen that medical treatment and dentistry have become the main application fields of MIM in North America.
At present, most of the medical MIM products are made of stainless steel, the main brands are 316L and 17-4PH; There are also titanium alloys, magnesium alloys, gold, silver, tantalum, etc. [5].
2.1.1 Orthodontic bracket
| Orthodontic brackets produced by Qinhuangdao Zhongwei Precision Machinery Co., Ltd |
MIM technology was first used in medical treatment to make some dental orthopedic appliances. These precision products are very small in size and have good biocompatibility and corrosion resistance. The main material used is 316L stainless steel. Orthodontic brackets are still the main products in the MIM industry.
Forestadent, a German company, has produced a two-way hooked orthodontic bracket with MIM technology. The mechanical retention force can be increased by 30%. Polishing after one-time forming with MIM can greatly reduce the friction between the bracket and the arch wire. This product has been confirmed by BjornLudwig to play a positive role in orthodontic surgery [6].
2.1.2 Surgical tools
| Surgical tools produced by Qinhuangdao Zhongwei Precision Machinery Co., Ltd |
Surgical tools are required to have high strength, low blood pollution and be able to achieve aggressive disinfection procedures. The design flexibility of MIM technology can meet the application of most surgical tools. At the same time, it also has the advantages of technology. It can manufacture various metal products at low cost. It is gradually replacing traditional production technology as the main manufacturing method.
Qinhuangdao Zhongwei Precision Machinery Co., Ltd. has developed a kind of stainless steel claw [7] using MIM technology, which is made of 17-4PH stainless steel and has a density of more than 7.5g/cm3. It can be used to grasp objects in the human body during surgery and has the function of tweezers. Its design is quite complex and requires high production accuracy.
Sintering after forming with MIM technology can reach a high tolerance level, and does not require a large number of subsequent treatment processes to avoid damaging the linear and geometric shape of the claw.
It is difficult to produce this kind of stainless steel claw with complex shape by casting or machining, which requires a long production cycle and high cost. Using MIM technology to manufacture it can save 60% of the cost.
Disposable surgical tools need to develop a process that can be mass produced at low cost. Smith Metal Products Co., Ltd. uses MIM technology to produce a shaft assembly [8], which is used in a new type of disposable surgical instruments. The cost is only 1/4 to 1/5 of that of a Swiss CNC machine tool, the density is 7.5 g/cm3, the ultimate tensile strength reaches 1190MPa, the yield strength 1090MPa, the elongation is 6.0%, and the maximum hardness is 33 HRC.
The manufacturing process of this product is as follows: first, two 178mm long shaft parts are formed by MIM technology, then two parts are laser welded, and then the subsequent machining and heat treatment are carried out. In order to meet the requirements of good tolerance, shot peening and passivation are also required.
2.1.3 Knee implant parts
| Knee bone implant parts produced by Qinhuangdao Zhongwei Precision Machinery Co., Ltd |
The progress of MIM technology in the field of human implantation is relatively slow, mainly because the certification and acceptance of products need a long period.
At present, MIM technology can be used to produce parts that partially replace bones and joints, and the metal materials used are mainly Ti alloys [9].
In terms of biocompatibility, Chen Liangjian et al. [10] prepared porous titanium with a porosity of 60% using MIM technology, and prepared gelatin sustained-release microspheres using an improved condensation polymerization crosslinking method and coated them on the surface of porous titanium.
The results showed that the gelatin sustained-release microspheres coated porous titanium had no cytotoxicity and could be used as a good material for medical implants.
Canadian MaettaSciences Inc has successfully used Ti-6Al-4V to produce knee sample parts for human implant [11]. The implant mainly bears pressure after entering the human body and has good biocompatibility. After MIM forming, hot isostatic pressing is carried out, followed by shot peening, polishing and anodizing to obtain better surface performance, reduce friction with human body, and improve compatibility and service life.
2.1.4 Hearing aid sound pipe
| Hearing aid shell parts produced by Qinhuangdao Zhongwei Precision Machinery Co., Ltd |
| Hearing aid tube produced by Qinhuangdao Zhongwei Precision Machinery Co., Ltd |
MIM technology can also be used to produce parts of various medical devices.
Indo MIM Company uses MIM technology to produce a hearing aid sound tube for Phonak Company in Germany [12], which has the effect of improving sound rate and promoting hearing.
This kind of hearing aid sound tube with complex shape can be obtained by sintering after MIM forming. In order to make the surface of the sound tube smooth, it is only necessary to go through a glass bead sand blasting process later.
The density of the acoustic tube is greater than 7.65 g/cm3, the maximum tensile strength can reach 480 MPa, the yield strength 150 MPa, the elongation 45%, and the maximum surface hardness 100 HRB. MIM technology can reduce the cost by 20% compared with the traditional production process before.
MIM technology can also be used to produce many products in medical field, including interventional therapy stent, radiation shielding of tungsten high-density alloy syringe, microsurgery manipulator, micro pump endoscope parts and drug inhaler [13].
2.2 New MIM technology applied to medical products
2.2.1 Metal micro injection molding
Metal micro injection molding, μ MIM) is a forming technology developed by IFAM Research Institute in Germany, which is to organically apply the MIM technology to the preparation of parts with dimensions up to micrometer level.
Generally speaking μ MIM can be used to produce two kinds of products:
① Parts with a size of micrometer and a mass of several milligrams;
② The appearance size of the part is similar to the size of the traditional injection molding part, but the size of the local structure is up to the micrometer level.
In recent years, micro injection molding has become a research hotspot in the field of injection molding. With the development of modern machinery towards miniaturization, the application of micro injection molding will be more and more extensive [14].
At present, Karlsruha Research Center has μ MIM technology has been successfully applied to the production of micro parts of medical devices [15], such as spectrometer, titration plate, etc. The structure size of the product has reached the micron level, and the minimum wall thickness is 50 μ m。
Figure 2 shows the use of IFAM in Germany μ The suture anchor [16] produced by MIM technology for surgical operation is only the size of match head.
2.2.2 Metal co injection molding
Metal co injection molding (Co MIM), originated in the 1990s, is a sandwich type powder injection molding technology.
This process is to simultaneously or in batches inject two materials with different characteristics into a mold for a composite injection molding. It can combine metal materials and a material with completely different properties in the same part.
The core/shell structure with functionality and complex shape can be obtained by this method, and subsequent processes such as coating, heat treatment and assembly of products are not required. Finally, a process can be realized to prepare functionally gradient materials, which greatly reduces the process and reduces the cost.
Co MIM technology provides a new idea for the development and design of functional parts. Li Yimin et al. [17] have proposed a new biological implant structure using Co MIM technology, which is widely used in dense cortical bone structures and cancellous bone structures with outer pores and inner pores.
This structure is conducive to the interface stress transmission between the implant bone and the surrounding bone structure. There are many outer layers, the porosity volume ratio of the pore structure is 5%~60%, and the largest pore is 400 μ m。
3 Outlook
According to BCCresearch's recent market research on metal and ceramic injection molding, the global market value of metal and ceramic injection molded parts will increase from 2.5 billion dollars in 2022 to nearly 3.9 billion dollars in 2028, with an average annual growth rate of 11.4%.
At the same time, with the decline of automobile sales, MIM technology will more enter the medical, aerospace, electronics and other fields.
In the new version of the European powder metallurgy industry roadmap, the European Powder Metallurgy Association pointed out that the medical market is an extremely important part of the injection molding industry [18].
With the continuous expansion of the market, the application of MIM technology in the medical field will be more and more in-depth, and various new materials and processes based on MIM technology will also be constantly developed.
Ultrasonic scalpel head
Qinhuangdao Zhongwei Precision Machinery Co., Ltd. is now a powerful manufacturer with rich experience in producing various kinds of medical device MIM products. In the future, it will also devote more efforts to metal powder injection molding precision products in the medical device industry.
Keywords: metal powder injection molding; Medical products; Metal micro injection molding; Metal co injection molding; Surgical instruments;
