MIM has established itself as a competitive manufacturing process in the past decades for large quantity production of small precision mechanical components with complex features.
The global market for MIM has exhibited spectacular growth over the last ~20 years.
The market size for MIM is expected to reach $ 3.7 billion by 2017 as shown in Figure 1.
Components produced using MIM technology are finding applications in industry sectors such as automotive, chemical, aerospace, business equipment, computer hardware, bio-medical and armaments.
The MIM process
It is carried out by mixing the powder (metal or ceramic) and binder (composed of several polymers such as PE, PP, PW, PEG, AS etc).
Following this, the powder binder mix is converted into solid pellets by granulation.
The objective of this step is to ensure that the whole surface area of each particle is coated with the binder in order to allow a good injection.
In industrial practice, the volume ratio (Vpowder/Vfeedstock) varies from 0.5 to 0.7.
It is conducted using the same machines as those are utilised in the plastic industry.
The injection temperature depends on the feedstock compositions.
Generally, the temperature varies from 130°C to 200°C.
It is carried out to eliminate the binder phase. It is the key step of MIM process and requires the most careful control to avoid defects in parts.
The process is typically performed in two steps.
- The first step involves dissolving of one of the polymers in the binder by a suitable solvent
- The latter stage consists of thermal decomposition of the remaining polymers
It is performed to provide the necessary strength in the finished products.
The process is carried out in controlled atmospheric furnaces at a temperature below the melting point of the metal.
Sintering in MIM is conducted via the same route as is done for the traditional PM parts.
Benefits of MIM
MIM combines the flexibility and high productivity (from 5000 parts/year for parts with high complexity to several 10000 parts/year for parts with low complexity) of thermoplastic injection moulding with the superior mechanical performance of metal parts.
This moulding process allows complex parts to be net shaped in a single operation with good dimensional tolerance control and high density.
MIM components achieve an excellent surface finishing (usually surface roughness values Ra< 1µm) without any subsequent operations.
Besides, the MIM process offers reduced production time compared to investment casting.
Owing to the fine particle size and high-sintered density, mechanical properties of the final parts are superior to that of the cast products.
There is also a wide range of materials (all materials used in PM industry, stainless steel, Ni alloys, titanium alloys, Tungsten heavy alloys etc) available to be processed for MIM applications.
Tooling costs generally limit the economic production volumes to greater than 10,000 parts
This is fully in line with MAESTRO’s objectives which are targeting large scale markets.
MIM and DMLS are two complementary technologies; while the latter allows creating complex shapes, the former saves the manufacturing time.
Hence, the objective of MAESTRO is to combine them in a single hybrid process chain.