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Metal injection molding is a combination of plastic injection molding and powder metallurgy.
Metal injection molding combines the most useful characteristics of powder metallurgy and plastic injection molding to facilitate the production of small, complex-shaped metal components with outstanding mechanical properties.
The molding process allows high-volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debonding) and densify the powders. Finished products are small components used in many industries and applications.
The metal injection molding market has grown from US$9 million in 1986 to US$382 million in 2004 to more than US$1.5 billion in 2015. A related technology is ceramic powder injection molding, leading to about US$2 billion in total sales. Most of the growth in recent years has been in Asia.
Tooling For MIM
The basics of MIM tool construction are same of plastic injection molds, but there are several key exceptions.
Tool dimensions are generally increased to allow for shrinkage during sintering, but angles are usually maintained. The complexity of mold design extends beyond just increasing the dimensions. The following features require many critical decisions.
- Parting line location
- Gate size and location
- Taper or draft to part
- Ejector pin’s location
- Slider requirements for multiple critical shape
The Metal Injection Molding Process Consists of the Following Steps :
1. Feedstock Preparation
The MIM process starts with the feedstock preparation process. Formulation of feedstock from appropriate metal powders and thermoplastic binder.
The binder is only an intermediate processing aid and must be removed from the products after molding process. The properties of the powder determine the final properties of the Metal Injection Molded product.
2. Injection molding
Molding of feedstock into tooling that is designed for the final part and includes dilation of the size in anticipation of sintering shrinkage. The actual parameters of injection have to optimize based on the feedstock, part geometry and dimensional control needed.
Once Molding is complete,The molded part known as “Green Part”.Green part size aprroximatly 20% larger to allow for shrinkage during the final sintering phase. The srinkage percentage is different for each raw material grade.
3. Debinding
Through this process binders are removed from the green part. The state of the art Catalytic Debinding system resulting in less cycle time for debinding process with strict safety standards.
Once debinding is complete, the component is known as “Brown Part”. After debinding process ,the part is now semiporous and the remaningg binder easily leaches out during sintering process.
4. Sintering
Sintering process generates in high temperature controlled environment for metal particles to weld together and provide the necessary strength for the finished product. To prevent oxidation and to protect the metal, the process is usually carried out in a vacuum or a controlled atmosphere at a temperature close to the melting point of the metal. Since the brown part is very porous, a large shrinkage occurs during sintering. This shrinkage has to be controlled strictly, and the mold cavity size has to be planned accordingly during the design stage.
SECONDARY OPERATION
After Sintering Operation, if any secondary process is required, they are as follow:
- Coining process (Thickness Coining, Profile Coining, Wedge Coining, Position Coining)
- Heat Treatment (Hardening, Surface Carburization, Hot Isostatic Pressing)
- Surface Finishing (Sandblasting, Grinding, Polishing, Lapping)
- Coating (Thin Film Technology, Electroplating, Varnishing)
- Joining (Laser welding, Soldering, Assembling)
- Machining (Turning, Milling, Drilling, Grinding, Rubbing, Honing, Tapping)
- Shaping (Plastic Deformation, Calibration)
