• Improved accuracy Optimize the sintered-state tolerances (±0.1–0.3 mm) to ±0.01–0.05 mm (e.g., bearing bores, locating pin holes);
• Complex feature shaping : Fabricating structures that cannot be achieved through sintering (such as internal threads, inclined holes, irregular grooves, and high-precision chamfers);
• Surface quality optimization By precision milling and precision grinding, surface roughness is reduced (e.g., from Ra 3.2 μm to below Ra 0.8 μm), meeting sealing and assembly requirements.
• Assembly surface treatment Remove the oxide scale and flash from the sintered part’s surface to ensure proper fit.

3. The process constraints are stricter.

• Clamping restrictions Soft jaws, vacuum suction cups, or specialized fixtures must be used to prevent single-point stress that could cause deformation of the part. Multi-hole parts cannot be clamped using magnetic fixtures.
• Tool wear is rapid. Traditional high-speed steel tools are prone to chipping, so it’s necessary to choose carbide (WC-Co) or diamond tools (PCD). The tool life of these alternatives is 30% to 50% lower than that of tools used for machining dense steels.
• High cooling and lubrication requirements Dry cutting easily generates dust and causes high-temperature wear on the tool; wet cutting requires careful selection. Highly penetrative cutting fluid Avoid allowing cutting fluid to seep into pores, which could make subsequent rust prevention and degreasing more difficult.

II. Key Methods and Process Essentials for CNC Machining of Powder Metallurgy Parts

1. Pre-processing before machining (to reduce the difficulty of subsequent processing)

• Deburring and Degreasing First, use roller grinding and sandblasting to remove flash and oxide scale from the surface of sintered parts, thereby preventing hard particles from damaging the cutting tools. For oil-containing sintered parts (such as self-lubricating bearings), degreasing must be performed first to prevent the cutting fluid from mixing with the lubricant in the pores and rendering it ineffective.
• Heat Treatment Optimization For high-precision parts, you can first perform... Sintering hardening or Carburizing and quenching Increase the surface hardness (HRC 58–62), then perform CNC precision machining (note that deformation compensation is required after quenching).