Influence of Mold Polishing Roughness on Casting Surface Quality

Mold cavity polishing roughness is a decisive factor affecting the surface finish of aluminum alloy castings, especially for automotive wheels and appearance structural parts with high surface quality requirements. The industry has formed clear polishing roughness matching standards for different casting product grades. For high-precision automotive appearance castings including wheels, the optimal mold cavity polishing roughness is controlled at Ra0.3-Ra0.4μm. Under this standard, the mold cavity surface is smooth and dense, which can effectively avoid molten aluminum adhesion, oxide residue deposition and surface scratch problems, controlling the casting surface defect rate below 1.2%. When the mold roughness reaches Ra0.8μm (conventional ordinary mold standard), the uneven microscopic grooves on the cavity surface will trap aluminum liquid oxide and residual release agent, forming a large number of micro-pit defects on the casting surface, with the defect rate increasing by 68%. Excessively pursuing ultra-high smoothness below Ra0.2μm will cause over-polishing, wear off the surface nitriding hardened layer, reduce mold high-temperature wear resistance, and shorten the overall service life by 22%. In addition, ununiform polishing with local roughness deviation exceeding 0.15μm will lead to inconsistent aluminum liquid flow and solidification state, causing local color difference and texture flaws on castings. Standardized and uniform Ra0.4μm fine polishing can not only significantly improve casting surface quality, but also reduce subsequent manual polishing and repair workload by 37%, optimizing comprehensive production efficiency.