Finishing in powder metallurgy improves surface quality and dimensional accuracy of the sintered part.
Common processes include machining, grinding, polishing, and surface coating.
It is done to achieve better strength, appearance, and wear resistance.
In this article:
Finishing Process in Powder Metallurgy (PM)
After compaction and sintering, the component produced is usually not in its final usable condition. So, a set of finishing operations is carried out to improve:
- Dimensional accuracy
- Surface finish
- Strength and performance
- Functional properties
👉 These are called finishing processes in powder metallurgy.
Why Finishing is Needed in PM
Even after sintering, PM parts may have:
- Slight dimensional variation
- Surface roughness
- Residual porosity
- Lower precision than final requirement
Main Finishing Processes in Powder Metallurgy
1. Sizing (Re-pressing)
What it is
- Sintered part is pressed again in a die without heating
Purpose
- Improve dimensional accuracy
- Reduce distortion from sintering
Effect
- Better shape control
- Slight increase in density
2. Machining
What it is
- Material is removed using:
- Turning
- Milling
- Drilling
Purpose
- Achieve tight tolerances
- Create holes, threads, or complex features
Limitation
- PM parts are porous → tool wear can be higher
3. Heat Treatment
What it is
- Controlled heating and cooling after sintering
Types
- Hardening
- Tempering
- Annealing
Purpose
- Improve:
- Strength
- Hardness
- Wear resistance
4. Impregnation
What it is
- Filling pores with:
- Oil
- Resin
- Plastic
Purpose
- Reduce porosity effects
- Provide self-lubrication
Applications
- Bearings
- Bushes
5. Infiltration
What it is
- Molten metal (like copper) is drawn into pores
Purpose
- Increase density and strength
- Improve electrical and thermal conductivity
6. Surface Finishing
Methods
- Grinding
- Polishing
- Shot blasting
Purpose
- Improve surface smoothness
- Enhance appearance
- Remove surface defects
7. Coating / Plating
What it is
- Applying protective layers like:
- Zinc plating
- Nickel plating
- Powder coating
Purpose
- Prevent corrosion
- Improve wear resistance
- Improve aesthetics
8. Coining
What it is
- High-pressure pressing of sintered part in closed die
Purpose
- Improve:
- Surface finish
- Accuracy
- Strength
Summary Table
| Finishing Process | Purpose |
|---|---|
| Sizing | Dimensional accuracy |
| Machining | Precision shaping |
| Heat treatment | Improve strength |
| Impregnation | Self-lubrication |
| Infiltration | Increase density |
| Surface finishing | Smooth surface |
| Coating | Corrosion protection |
| Coining | Final accuracy |
Summary:
👉 Finishing in powder metallurgy is essential because:
- PM parts are near-net shape, not perfect final parts
- Finishing bridges the gap between manufactured part → usable engineering component
Conclusion:
Finishing processes in powder metallurgy include sizing, machining, heat treatment, impregnation, infiltration, surface finishing, coating, and coining to improve dimensional accuracy, surface quality, and mechanical properties.
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