Surface Treatment and Finishing Options for Sintered Metal Components

Finishing turns as-sintered MIM parts (matte, ~Ra 1.6 µm) into finished products by improving appearance, corrosion resistance, wear life and dimensional accuracy. Options include mechanical finishing (tumbling, blasting, grinding, polishing, CNC), heat treatment (quench and temper, nitriding, HIP, annealing), and plating/coatings (electroplating, electroless nickel, PVD, DLC, black oxide, passivation).

The as-sintered finish

Parts that come straight out of the sintering furnace have a matte, slightly rough surface — typically around Ra 1.6 µm. For many industrial applications that is perfectly serviceable, but for visible, wear-critical or corrosion-critical parts, secondary finishing is what turns a good MIM part into a finished product.

Why finishing matters

Finishing improves appearance, corrosion resistance, wear life and, in some cases, dimensional accuracy. Because metal injection molding produces near-net-shape parts, only a light secondary operation is usually needed — far less material removal than with conventional machining.

Mechanical finishing

• Vibratory and barrel tumbling — deburring and edge rounding, cheap and high-volume.
• Shot blasting / sand blasting — uniform matte finish and surface cleaning.
• Grinding and lapping — tightens dimensional tolerance to ±0.05 mm or better.
• Polishing — cosmetic surfaces down to Ra 0.4 µm or finer.
• CNC machining — critical features, threads and sealing faces to ±0.1% or tighter.

Heat treatment and hardening

• Quench and temper — raises hardness on martensitic grades such as 17-4PH or 420 stainless.
• Case hardening and nitriding — a hard, wear-resistant skin over a tough core.
• Hot isostatic pressing (HIP) — closes residual porosity and lifts density toward 99.5%.
• Solution annealing — restores corrosion resistance and uniformity after sintering.

Plating and coatings

• Electroplating — nickel, zinc, chrome or tin for corrosion protection and appearance.
• Electroless nickel — uniform coverage on complex geometries.
• PVD and DLC coatings — very hard, low-friction surfaces for tooling and wear parts.
• Black oxide and passivation — low-cost corrosion resistance, especially for stainless steels.

Choosing the right finish

The right combination depends on the material, the service environment and the cosmetic requirement. Stainless steel MIM parts often need only passivation or light polishing, while carbon and low-alloy steels usually receive plating or a hardening treatment. Tolerances, batch size and budget all play a role.

Get a quote

Ningbo Precision Tech runs in-house heat treatment, plating and machining alongside metal injection molding, so a single supplier can deliver fully finished parts. Send your drawing, material and finish requirement to Jack@precision-mim.com for a free DFM review and quote.

Frequently asked questions

What surface finish do MIM parts have as sintered?

As-sintered parts have a matte, slightly rough surface, typically around Ra 1.6 µm, which is serviceable for many industrial applications.

Why is secondary finishing needed for MIM parts?

Finishing improves appearance, corrosion resistance, wear life and sometimes dimensional accuracy, and because MIM is near-net-shape, only a light secondary operation is usually needed.

Which finishes suit stainless steel MIM parts?

Stainless steel MIM parts often need only passivation or light polishing, while carbon and low-alloy steels usually receive plating or a hardening treatment.