Metal Injection Molding, or MIM, is considered a next level process when compared to powdered metal. The MIM process allows our customers to achieve the net shape they want without flash and surface imperfections typically associated with the powder metal process. It also allows for more complex geometries to be created in volume and without the need for secondary operations.
MIM Tooling & Metal Injection Molding Tool Making
Deep Experience
Since their finished goods are metal parts, MIM customers do not want to see the witness lines or flash typical of injection molding. MIM feedstock flashes easier than most thermoplastics, thus the need for extremely accurate, precise and perfectly aligned tooling. That’s where Matrix Tool’s expertise comes in. Our experience manufacturing high precision, tight tolerance, and very complex electrical connector molds is what really lends itself to producing high quality MIM tooling. Matrix has been producing MIM tooling for some of the biggest names in industry for over 25 years.
The Difference Is In the Details
The basics of MIM tool construction are identical to that of plastic injection molds, but there are several key exceptions. These include choice of cavity and core steel, fits for shut-off angles and slides, gate design and locations, venting depths, surface finish of the molding areas, and the correct choice of plating to be applied to the finished cavity and core details.
Cavity/Core Steel
The cavity and core steel must be able to withstand the abrasive wear of the molding material. Any steel that comes in contact with the molding compound, including the gates and runners, must be made from a high-wear resistance, high-hardness tool steel such as D-2 or A-2. High hardness H-13 will also work when plated with a high-hardness coating. Any details that do not come in contact with the molding compound can be constructed from a more standard tool steel such as S-7.
Shut Offs and Slides
Flash is a major concern with the MIM process and can be a real problem for the molder. To prevent this, good fitting on all shut-offs and slide areas is vital. All shut-offs must be within plus or minus .0001” of the steel print dimensions. Flash on a MIM part can result in a knife edge of steel on the finished part—which is clearly unacceptable and potentially harmful.
Vent Depths
A typical plastic mold may have vents ranging from .0005″ deep to .002″ deep, depending on the resin used. A MIM tool with these vent depths would certainly flash. Venting for a MIM tool is often .0001″ to .0002″ deep—nearly 5-10 times smaller than vents used in plastic molds—if venting is added at all. This requires a discipline and attention to detail at every level to achieve the desired results.
Polish and Shrink
One additional challenge with MIM tooling is the minimal amount of post mold shrinkage. For many of the MIM parts produced, overall shrinkage can be in the .001”/inch range or less. This can result in difficulties ejecting the part out of the mold. This requires excellent surface finishes—often needing a 600 compound finish, and at times a diamond finish. Matrix is capable of providing up to a mirror finish straight out of our EDM machines, where needed.
If all of this seems demanding, different and challenging, it is. That’s why engineering driven companies love working with Matrix Tool. High precision and attention to detail is promoted at all levels. From a strong foundation in the mold design through steel selection, tool construction and assembly, everything we do is driven by precision. There aren’t any shortcuts to producing highly precise MIM tooling!
For more information regarding a demanding MIM project that requires expert tooling, please Contact Us.
