Metal Injection Molding: Transforming the Medical Industry

Application of metal injection molding in the medical industry

The purpose of the medical profession is to protect and improve the health of patients, and to prevent and treat disease. So it has always been at the forefront of innovative technology. The combination of metal injection molding (MIM) technology development and the medical industry has sparked a new spark. We see more and more surgical instruments, surgical tools and medical devices adopting this technology. This technology not only improves the efficiency of production, but also reduces the cost of production, and can maintain the consistency of products, from size to mechanical properties. Thereby raising the manufacturing of medical equipment to a new level, which is used to better benefit mankind.

medical injection molding

In this article, we discuss what MIM is, its applications in the medical industry, and its advantages and disadvantages compared to traditional CNC machining processes.

 

What is Metal Injection Molding?

The MIM process can be used to manufacture a variety of materials and alloys, for example, iron, stainless steel, aluminum alloys, titanium alloys, etc.

Once the right material for fabrication has been selected, it starts with the ingredients—metal powder and binders (usually a combination of wax and other polymers) are mixed and cooled to form raw pellets.

The raw material particles are passed through the injection machine, the raw material particles are heated into a fluid state, and injected into the mold, and the product parts are formed.

The product parts are then placed in a debinding oven to remove the adhesive from the product. Finally, through the sintering furnace, the powder metallurgy parts are heated to 1300-1600°C, so that the parts shrink by about 20%, and the pores of the degreased products are filled to form the final product.

The sintering process is the most technically difficult process in powder metallurgy, so the mold design of the MIM process must comprehensively consider the product mold design, product structure, sintering temperature, and shrinkage rate.

Since the product is produced by the mold, the product tolerance is small (usually up to 0.3-0.5% of the size), powder metallurgy injection molding technology can produce products with complex structures as easily as simple parts. It is especially suitable for the manufacture of medical metal products whose product weight is not more than 300g. Of course, if there is a higher technical requirement, an additional CNC process will be used to ensure

The following is the specific use of powder metallurgy parts in the medical industry

1.Application of MIM in Surgical Instruments

Surgical instruments are usually made of stainless steel, which has the characteristics of high strength, high hardness, good corrosion resistance and easy disinfection. Surgical instruments need to maintain wear resistance and sharpness, so MIM-420 material is the best choice.

Instrument Type of Stainless Steel
Cutting
Chisels 302, 303, 410, 416, 420, 440
Curettes 302, 303, 410, 416, 420
Cutters, bone-cutting forceps, 420
Dissectors 410, 416, 420
Knives 302, 303, 420, 440
Osteotomes 410, 440
Reamers 410, 630
Rongeurs 410, 420
Scalpels 420, 440
Scissors 410, 420, XM-16
Noncutting
Cannulae, needle vents 302, 303, 304
Forceps 302, 303, 304, 410
Retractors 302, 303, 304, 410, 416, 420, 431, 440
Specula 302, 303, 304, 316
Spreaders 302, 303, 304, 410, 416, 440
Clamps 303, 304, 410, 416, 420
Drills 303, 440, XM-16
Handles 303, 304
Hammers, mallets, rulers, screws, tunnelers 303
Punches 303, 410, 416, 420
Skin hooks 303, 410, 416, 420
Suction tubes 303, 304
Probes, tongs 303, 440
Holders 304, 410
Clip applicators, dilators 410
Elevators 410, 420
Burrs 420F
Orthopedic instruments 430
Needles 420, XM-16
Table I. Types of stainless steels used for medical instruments.1

 

The early surgical instruments made by powder metallurgy include scalpel handles, bipolar forceps, surgical jaws, U-shaped clips, etc. With the continuous advancement of powder metallurgy technology, they are constantly being used in minimally invasive surgical instruments. Products with miniaturization and complex structures are increasing, especially for laparoscopic instruments for grasping, cutting, and suturing. Such as tweezers, scissors, and clips with high dimensional accuracy and repeatability. These are difficult to achieve by traditional methods.

Generally, low-carbon materials are used, namely MIM-304L and MIM316L. The reason is that the injection molding process works best at low carbon, which improves corrosion performance. If the medical device needs to achieve high hardness, you need to use MIM-420 and MIM-440C), if the hardness is higher, then use MIM 17-4PH, the material, through additional heat treatment to further strengthen the hardness of the product.

medical injection parts

Moreover, metal injection molding can produce several complex product parts as one product, reducing the welding steps of several parts, thereby eliminating the risk of heterogeneous corrosion at the welding position.

Surgical tools, such as drills, saws, and reamers, require high strength and wear resistance to withstand surgical stress. MIM can use stainless steel, titanium alloy, and other materials to produce high-strength, wear-resistant surgical tools. MIM can also produce tools with complex geometries, such as hollow structures and internal channels, which are difficult to achieve with traditional machining methods.

The mass production efficiency of MIM, realizing scalpel handles, clips, drills, scissors, etc., reduces the cost of products, resulting in affordable, high-quality products that ultimately benefit patients.

Stents Bone plates, screws, staples, and rods Heart valves and pacemaker casings Electrodes

Material Implant Applications
316L Bones, plates, screws, staples, pins, and nails
Co-28Cr-6Mo Prosthetic replacements of hips, knees, elbows, shoulders, ankles, and fingers
Unalloyed Ti Bone plates, screws, rods, and staples
Ti-6Al-4V Prosthetic hips, knees, elbows, shoulders, ankles, and fingers
Unalloyed Ta Wire, foils, sheets, clips, staples, and meshes
Table III. Materials used for medical implants12

medical parts

2. MIM Applications in Medical Implants

Metal injection molding is also suitable for medical implants, such as orthopedic implants and dental implants, but due to the more complex and harsh environment inside the human body, the implants have high biocompatibility, corrosion resistance, and mechanical strength. 316L stainless steel has been widely used for short-term implants. MIM can use titanium alloy, cobalt chromium alloy, and other materials to produce medical implants with high biocompatibility as long-term implants. MIM can also produce implants with complex geometries, such as porous structures and internal channels, with high implant stability.

The table is a list of materials commonly used for metal injection molded implants.

 

Advantages and disadvantages of MIM in the medical industry compared with CNC

In the medical industry, MIM offers several advantages over CNC machining.

First of all, MIM can produce products with complex product structures, which is difficult to achieve with CNC machining.

Second, MIM can produce parts with complex features and internal channels, which cannot be achieved with CNC machining.

Third, MIM can use stainless steel, titanium alloy, cobalt-chromium alloy, and other materials to produce high-strength, high-wear-resistant parts.

Fourth, the production cost of products can be reduced through large-scale production.

However, MIM also has some disadvantages compared to CNC machining. First, MIM has long lead times due to the time required for mold design and manufacturing. Second, MIM has higher tooling costs due to the complexity of the tooling required to produce complex parts. Third, MIM has limited material options compared to CNC machining due to the need for a powder that can be mixed with a binder.

in conclusion

MIM is a cost-effective method for producing complex components with high precision and accuracy in the medical industry. It can be applied to surgical instruments, surgical tools, and medical implants. Overall, MIM is a promising technology that can improve the quality and efficiency of medical device manufacturing. For the right projects, use the MIM method to help CMO and OEM customers to gain more competitive market advantages.

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