Introduction to Metal Injection Molding Process

 The acetate glasses, metal glasses, titanium glasses, etc., that we often see are often connected by different parts, such as front frames, temples, hinges, and some decorative metal parts. As shown below:

We can see that many metal accessories for glasses are made of metal. These metal accessories are made through some traditional manufacturing techniques, such as metal stamping, cutting, corrosion, casting and other processes. The accessories (metal temple and bridge) of the metal sunglasses we made below are completed through stamping and corrosion processes.

The metal temples of the acetate sunglasses below have many honeycomb-shaped holes, which are made by corrosion and CNC cutting.

With the development of glasses technology, in addition to these traditional production technologies, are there any more advanced manufacturing technologies suitable for these eye frames accessories?

This article will take a look at the MIM process, which is often referred to as the metal injection molding process. Some of today's glasses metal accessories are made by MIM technology.

1. What is metal injection molding?

MIM, the full English name is Metal Injection Molding, refers to a new type of powder metallurgy near-net forming technology formed by introducing modern plastic injection molding technology into the field of powder metallurgy.

The low price of plastic injection molding technology makes it widely used in various fields, and is mainly used to produce products of various complex shapes. Because the strength of plastic products in the past was not high, in order to improve strength and wear resistance and obtain corresponding products, researchers added metal or ceramic powder to plastics to maximize the content of solid particles and completely remove the bonding during the sintering process. This new powder metallurgy forming method is called metal injection molding.

2. Key processes of metal injection molding

(1) Professional feeding: About 90% metal powder and 10% binder are mixed into a homogeneous feeding material. Compared with traditional powder metallurgy, the particle size of metal powder (micron level) and extremely low impurity content ensure that the sintering density of MIM reaches 98% of the theoretical density; and the specially formulated binder can provide good fluidity during injection. It can ensure efficient degreasing ability.

(2) Precision injection molding: Use an injection machine to heat the MIM feed and evenly fill it into the mold cavity. After cooling, the MIM injection blank is obtained. Matching molds that meet MIM characteristics and reasonable processes is the key to this process.

(3) Degreasing: A professional degreasing furnace is used to gradually and efficiently remove the main binder in the injection blank. The remaining skeleton binder maintains the shape of the product so that the degreased parts can be moved into the firing stage.

(4) Sintering forming: In the MIM vacuum furnace or atmosphere furnace, the skeleton binder is removed, and the metal powder is densified into a complete metal body at a temperature close to the melting point. After cooling, a sintered part with a nearly finished shape is obtained.

(5) Post-processing process: Carry out corresponding surface treatment or machining treatment on the appearance parts, such as sandblasting. Polishing, cleaning, PVD coating, tapping, CNC and other processes.

3. What are the advantages of metal injection molding?

A. More economical: For complex parts, traditional metal forming usually disassembles and produces individual parts before assembling them. MIM simplifies the processing procedures through overall processing and is more economical. In addition, the cost of traditional metal forming increases as the complexity of the parts increases. MIM ensures that the cost remains unchanged by increasing the complexity of the mold. The more complex the product, the more economical MIM is.

B. Product complexity is higher: Compared with other metal molding methods, MIM can manufacture parts with more complex shapes. Basically all structures that can be realized by injection molds can be applied to MIM, which is suitable for applications with higher product complexity. scene, it can produce features that cannot be achieved by investment casting, such as small holes, thin walls, and fine surfaces.

C. Wider material selection: MIM can use almost most metal materials and is suitable for application scenarios with high material performance.

D. Higher product density: Because the sintering density of MIM is very close to the theoretical density, its physical and chemical properties are also very good, such as mechanical strength, which greatly exceeds traditional powder metallurgy.

E. Higher dimensional accuracy: MIM can generally achieve a tolerance accuracy of ±0.5%. With other processing methods, higher dimensional accuracy can be obtained.

F. Mass production capacity is more flexible: MIM can flexibly adjust and quickly increase production, and can respond quickly from a few hundred pieces per day to more than hundreds of thousands per day.

G. Higher raw material utilization rate: The raw material utilization rate is close to 100%. It is a near-net shape technology that can effectively avoid the waste of materials.

4. Common metal injection molding products and application fields

(1) Consumer electronics: external components of smartphones (such as trays, side buttons, charging interfaces), internal structural parts, smart wearables (such as smart watch cases, straps, buckles, etc.)

(2) Automobile: turbocharger, fuel injector, sensor, clutch inner ring, rocker arm insert, shift fork cover, distributor cover, car airbag parts, car locks, etc.

(3) Military industry: missile tail fins, gun parts, warheads, powder covers, and fuze parts

(4) Aerospace: aircraft wing hinges, rocket nozzles, missile tails, ceramic turbine blade cores

(5) Medical treatment: orthodontic brackets, internal suture needles, biopsy forceps, radiation shields

(6) Communications: CPU heat sink/fan blades, fiber optic base, microwave cavity components, and isolation components for 4G/5G projects, etc.

5. Application of metal injection molding technology in the eyewear industry.

The picture below shows some metal accessories made by MIM technology, which are inlaid on glasses frame, such as acetate glasses, metal glasses, titanium glasses, etc.

The application of MIM technology in the glasses industry is mainly to produce some accessories, such as hinges, metal decorative blocks, crowns, etc., as shown in the picture above. Since glasses are non-standard products, the same model often cannot be mass-produced in different batches, so this is also It limits the development of MIM in the glasses industry.

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