Metal Injection Molding (MIM) processing technology has a history of 35 years and is currently becoming a hot topic in the metal parts manufacturing industry. Generally speaking, the weight of MIM workpieces is below 250 grams, and the size of most MIM workpieces is similar to that of foldable phones. However, the number of larger MIM workpieces is increasing day by day.
If a large batch of workpieces needs to be produced (such as from 20000 to several million), and the workpieces have complex geometric shapes (such as 20-30 measurable dimensions), requiring more than 3 processing steps, then MIM machining is a feasible choice. Some workpieces that can be processed by MIM include: computer hard disk drive and other peripheral equipment parts, manual tool parts, gun parts, liquid syringe and spray parts, medical device parts and cutting tools.
MIM processing requires three steps:
(1) Inject a mixture of powdered metal and thermoplastic (or other binders) into the mold cavity under heating and pressure conditions (similar to thermoplastic injection molding).
(2) Remove the adhesive by heating or melting, leaving only the metal powder.
(3) Sintering of metal powder should be carried out at a temperature lower than the melting point of the metal, but sufficient to combine the metal powder into a solid metal (the actual density of the solid metal is greater than 96%).
MIM can be used for processing hard alloys, other metals, and metal alloys (including precious metals). Due to the fact that the particle size of metal raw materials used in MIM processing is much smaller than that of metal particles used in other powder metallurgy processes, it is more appropriate to refer to them as metal "micro powders", whose fineness is comparable to that of metallic pigment powders (particle size less than 20) μ m) .
The workpiece processed by MIM has the following characteristics:
(1) Belonging to net forming processing, the dimensional accuracy of the workpiece is very high.
(2) Large degree of freedom in forming, capable of processing blind or through holes, small arc radii, thin-walled and other complex geometric shapes.
(3) The mechanical performance is basically equivalent to that of workpieces processed by conventional cutting, welding, forging, and stamping.
According to different usage requirements, sintered workpieces can be hardened (including surface hardening), polished, and finely processed. In order to add structure, remove the mold support during sintering, modify the workpiece, or obtain the final size, it may be necessary to further process the workpiece.
The future development directions of MIM processing technology include: environmentally friendly adhesives; The continuous refinement of metal powder; Simplify processes and reduce costs; Design tools (including mold analysis software) that take into account the shrinkage factor of the workpiece during the machining process.