Where the
world gathers for metal finishing
Q&As since 1989


-----

316SS MIM Part Galling Problem

 

Our company makes a product that uses 316SS metal injection molding parts. We recently encountered the following problem for several parts:

1. The assembled unit does not move smoothly and adjacent components appear to be galling. The parts all meet dimensional specifications and initial reports from the processor indicate that part densities match previous runs.
2. The surface of some parts has a dirty appearance, almost like corrosion.
3. Some of the parts that are galling have a "grainy" feel on mating surface edges.

I have several questions:

A. How much can MIM resin regrind affect the surface characteristics of mating MIM parts? We have used regrind in small percentages (10-20%) but have not controlled the size of regrind.
B. Can surface corrosion develop on MIM parts over time?
C. Can the sintering and debinding process affect part surface characteristics?
D. Are there any tests that can be completed post-processing to evaluate surface condition of parts?

Dave Hernon
- Houston, Texas

---

I don't know enough about MIM to answer your questions, but I do know that stainless steel is known for its propensity towards galling. What you didn't tell us is what the mating parts are made of.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

---

The mating parts are all 316SS MIM with identical surface finishes. We did not have galling problems in the first 12 months of production. We suspect regrind use may be a contributor but also want to check any other potential sources/issues.

Dave Hernon
- Houston, Texas
 

---

You may want to look into dryfilm lubricants such as molybdenum disulfide. These can be applied in bulk finishing or spray applied maintaining specific dimensions. Many dryfilms will give 100+ hours salt spray.

Wayne McKee
- Mississauga, Ontario, Canada
 

---

We have the same problem: The surface of some parts has a dirty appearance, almost like corrosion. Especially the underlayer. Did you find a solution?

Can the sintering and debinding process affect part surface characteristics?
You have a response?

Regards

Frank Sveid
- Brussels, Brabant, Belgium
April 28, 2010