CM Metal Injection Molding Furnaces
CM furnace models like the CM 300 & CM 400 continuous series, or the 1500 series batch furnaces have supported the metal injection molding industry with their high temperatures, high temperature uniformity, and their ability to safely manage hydrogen and other atmospheres. To understand the role of the CM 200 series in the MIM process, understand the following typical process flow common to many.
- Formulation and mixing of feedstock from metal powder and binder
- Injection of feedstock into mold
- After pressing in the mold the so called “Green” Part appears.
- Debinding (Aqueous, Solvent, or Thermal, Catalytic) to remove major portion of proprietary binder. Depending on binder some debinding processes can also be done in a furnace. After this step the so called “brown” part is created
- The brown part is still fragile and filled with binder. Sintering removes the final binder elements by heating finished parts close to their melting point in a controlled atmosphere
- Finish or Coating operations as needed
Metal Injection Molding Process Components
The feedstock is mixed from fine metal powder, typically <22 micrometers, with a proprietary binding agent. The latter can be based on water, wax or other system. Different feedstocks will have specific characteristics, i.e., viscosity, injection pressure and temperature, and debinding process. The powder loading is 55-65% by volume or 90% by weight for steels.
With the ability to debind and sinter in one step at temperatures up to 1700C, CM offers both thermal and catalytic debinding systems for all feedstocks including BASF Catamold.
Molding is done in a conventional injection molding machine. The mold is designed similar to that for plastic but with allowances made for shrinkage and the cooling requirements for a feedstock highly loaded with metal particles. Molding can be done on both vertical and horizontal machines.
The parts are removed from the mold. At this point they are called “green” parts. Before the part can be sintered, the bulk of the binder has to be removed. Typically the binder has to be extracted by liquid or gaseous solvent, thermally or catalytic, or a combination thereof. The debound parts are called the “brown parts”.
The brown part is placed on a custom designed ceramic trays and processed in a high temperature furnace. Sintering is typically done in a high vacuum furnace or a continuous hydrogen furnace like our CM 400 pictured below:
Sintering temperatures can go up to 2500 degrees F. During the sintering process, the metal particles fuse together, the part shrinks 15% to 20% linearly, and density is increased to 98% or better.