Production Process Of Powder Metallurgy Automotive Parts

I. Process Overview and Scope of Application
Powder metallurgy automotive parts use metal powders as the core raw material. Through forming, sintering, and post-processing, near-net-shape forming and high-performance manufacturing are achieved. The process is compact, with high material utilization, making it particularly suitable for high-volume, structurally complex, and cost-sensitive automotive parts. Typical products cover engines, transmissions, chassis, and body accessories. The usage per vehicle in the European and American markets is approximately 20 kg, and this trend is continuously increasing. The main process routes include: raw material powder preparation, mixing, pressing, sintering, finishing/machining, heat treatment and surface treatment, inspection, and packaging delivery.

 

II. Raw Material Powder and Mixing

• Powder Preparation: Primarily using iron-based powders, commonly prepared by water atomization/gas atomization, followed by drying, sieving, annealing, and reduction treatments to reduce oxygen/carbon content and improve compressibility and consistency. Alloying elements can be introduced through pre-alloying or subsequent powder mixing.

• Mixing and Pretreatment: The base powder is uniformly mixed with alloy powders (such as Cu, Ni, Mo), graphite (C), and solid lubricants (such as zinc stearate and amide wax) to ensure stable composition and particle size distribution. The mixed powder must avoid segregation and oxidation to ensure batch consistency.

 

III. Pressing and Sintering

• Pressing: The mixed powder is loaded into a custom mold and pressed unidirectionally or bidirectionally on a hydraulic press. Typical unit pressing pressure is approximately 10–80 MPa, obtaining a green blank with the outline of the part. Forming must balance density uniformity, dimensional accuracy, and shape precision.

• Sintering Densification: The green blank is heated in a protective atmosphere (such as N₂/H₂) to 70%–90% below the melting point of the main components. The common sintering temperature range is approximately 1100–1250°C. Neck growth and porosity shrinkage are achieved through surface diffusion, grain boundary diffusion, and plastic flow. The conventional density can reach 90%–95% of the theoretical density, combining strength and toughness.

• Process Enhancement Methods: To improve density and performance, advanced technologies such as warm compression molding (100–300°C) and high-speed compression molding (HVC) can be introduced to increase the density of iron-based parts to approximately 7.4–7.5 g/cm³, significantly improving strength. This is suitable for critical load-bearing components such as valve seats, sprockets, gears, and connecting rods.

 

IV. Injection Molding (MIM) Route (Suitable for Complex Small Parts)

• Feed Preparation: Fine metal powder (<20 μm) is mixed with polymer binder in an internal mixer, followed by cooling, crushing, and granulation to form a uniform feed.

• Injection Molding: Molding is performed within a set temperature/pressure/holding pressure window. Controlling mold filling, venting, and holding pressure for shrinkage compensation avoids short shots, weld lines, and internal stress concentration.

• Debinding and Sintering: The binder is gradually removed through solvent/thermal/catalytic steps, followed by densification through sintering in a vacuum or inert atmosphere. MIM parts have high dimensional accuracy, with typical tolerances controllable within ±0.3%, and some critical dimensions reaching ±0.1%.

• Applicability Notes: MIM (Metal Injection Molding) is suitable for complex 3D shapes and minute features, but it has high requirements for mold investment, wall thickness uniformity, and batch production. It is commonly used for sensor housings, nozzles, clamps, and small transmission components.

 

V. Post-processing, Inspection, and Mass Production Control

• Post-processing: Depending on the working conditions and functional requirements, finishing/shaping, machining (critical mating areas), heat treatment (carburizing, quenching, tempering, sintering hardening), and surface treatment (coating, electroplating, phosphating, blackening) are performed to achieve target hardness, strength, wear resistance, and corrosion resistance. Oil-impregnated bearings/self-lubricating parts can be oil-immersed.

• Inspection and Quality Control: Sintered parts commonly experience linear shrinkage of approximately 20%, requiring control through dimensional and positional measurements, hardness/density testing, and non-destructive testing. For hidden defects such as sand holes, scratches, and dents in the inner walls of holes, an online combination of eddy current testing and fiber optic internal hole inspection can be used to improve detection rate and efficiency.

• Mass Production and Process Control: Automotive parts assembly typically follows IATF 16949 and APQP/PPAP processes, establishing FMEA, control plans, SPC/MSA, and other system documents. Closed-loop verification is implemented from tooling sample (OTS) to pilot production to mass production (SOP) to ensure process stability and traceability.