The manufacturing industry is using metal injection moulding as one of its common processes. This involves combining the functions of plastic injection moulding with the strong points of pressed and manufactured, small yet complex metal parts. The process is also a hybrid between the plastic moulding and powder metallurgy. Plastic binders and powdered fine metals are injected to a plastic moulding machine. The binders are taken out of the equation through thermal and solvent processes. The metal particles remain bound though they are not melted. The powder is turned into a compact material through forging, extrusion, hot and cold isostatic pressing, rolling, pressure less compaction, and injection moulding.

Once the powder turns compact, it can be formed into various complex shapes. These metal powders can be used to develop a feedstock if combined with binders.

Process for MIM
MIM involves five steps in its process.

1. Mixing. This involves mixing the metallic powders with a binding agent. The metallic powders are chosen based on their strengths; wear resistance properties, impact strength, hardness, temperature properties, machinability and other inherent properties. Mixing is necessary to make sure that the weaknesses of metals will be compensated by the strengths and benefits of the resulting mixture. The feedstock is developed and is injected to the moulds. At this stage, the mixture will show a green part.

2. Debinding. The green part created in the previous stage is immersed into the water to remove the binder.

3. Cross-linking. The binder removed from the process is put under the ultraviolet light. To do this, MIM only uses thermoses metal powders.

4. Sintering. The debound part is heated in the furnace up to more than 2000 degrees-Fahrenheit. After this stage, the metal parts are already in compact form.

5. Finishing. All the imperfections on the surface are removed.

Guidelines
Usually, the design’s wall thickness may change which can lead to warpage or distortion. To avoid this, the wall thickness should only be at most 5 mm. Sharp changes in wall thickness should be prevented. Sink marks may be created by sharp edges and corners. There should be one flat side in the design. In designing the draft angles, the mould release should be carefully considered.

Uses
MIM is usually used in defence, aerospace, dental, automotive, electronic heat sinks, hermetic packages, fibre optic connectors, industrial tools, electrical connector hardware, power hand tools, pharmaceutical devices, fluid spay systems, sporting equipment, and surgical instruments. The process is also used in the medical field, particularly in making dental brackets, biopsy jaws, surgical instruments and laparoscopic cutting tips. It has electronic applications too as it is used in creating RF connectors, fibre optic transmitter, microwave packaging, and disc drive components.

Advantages
The process of metal injection moulding is advantageous for its high performance, good surface finish, complex geometries, close porosity, and high final density.

MIM gives the manufacturing process more freedom and flexibility in creating things. This is best used in making complex shapes when the finished item should only be as light as 100 grams. However, this process can also be used to finish things up to 453 grams.

This process usually uses copper, tungsten, copper-molybdenum, kovar, and stainless steel.

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