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Classification standards for polishing of die-casting molds, roughness, process route, and appearance control

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  • وقت الإصدار: 2026-11-07

Classification standards for polishing of die-casting molds, roughness, process route, and appearance control
Polishing is not just about looking good, it directly affects the adhesion of aluminum, pulling, demolding, and surface quality of castings. There is no unified national standard for polishing grades in the industry, and foreign trade needs to agree on grades in advance.
1、 Polishing grading corresponds to roughness
180-400 sandpaper: rough polishing, removing knife marks, EDM spots, flow channels, and non appearance inserts; 800-1200: Medium throw, ordinary shell non appearance surface; 2000-3000: Fine polishing, ordinary appearance parts, Ra0.02–0.05μm; Mirror polishing (diamond paste): Ra ≤ 0.01 μ m, wheel appearance surface, A356 high anti sticking aluminum requirement. The appearance of alloy wheel mold generally requires mirror polishing.
2、 Complete polishing process route
CNC → EDM → Polish to remove white layer → Sandpaper to polish step by step → Diamond paste polishing; After ion nitriding, it should be lightly polished and not heavily ground, otherwise the nitride hardening layer will be worn off. Mirror polishing must be completed before PVD coating, and it is difficult to polish again after coating.
3、 Different polishing requirements vary in different regions
Internal gate and runner: Mid throw to reduce aluminum slag adhesion; Molding appearance surface: mirror surface; Deep reinforcement and dead corners: Moderate precision polishing, prioritizing demolding; Exhaust groove and overflow groove: Do not over polish, appropriate roughness is beneficial for gas discharge.
4、 Negative risks of polishing
Excessive polishing leads to stress concentration on the surface of the mold cavity, making it more prone to microcracks; The polishing pattern direction is perpendicular to the demolding direction, which can easily strain the casting; Mirror polishing has high costs and long working hours, and the quotation needs to be calculated separately.
5、 Agreement on Polishing and Acceptance of Foreign Trade Orders
It is not enough to only write 'mirror', the drawing should indicate the Ra value and attach reference blocks; Distinguish between A-side (primary appearance), B-side (secondary appearance), and C-side (internal non appearance). The appearance of the low pressure casting wheel hub also requires mirror polishing. Google's "die casting mold polishing standard" is aimed at polishing technicians and quality inspectors.
FAQ
Is it possible to directly mirror polish after EDM?
No, the EDM white layer has high brittleness and must be polished and removed first.
Does mirror polishing prevent aluminum from sticking?
Significantly reducing the probability, but A356 still requires coating coordination under high temperature conditions.
How to determine the direction of the polishing pattern?
Follow the demolding direction to prevent pulling.
Is it better to polish the exhaust groove more smoothly?
The exhaust groove is moderately rough, which is conducive to gas flow, and excessive polishing is actually detrimental.
Can mirror polishing still be achieved after nitriding?
It can only be lightly thrown to remove the surface white layer, and cannot be cut in large quantities.
6. Is there a large price difference between different polishing grades?
Mirror polishing takes 3-6 times more time than regular precision polishing.
Is the surface of the casting shiny and scratched related to polishing?
Chaotic patterns and inadequate polishing are common causes.
8. Will polishing change the cavity size?
Yes, trace removal of materials and reserved polishing allowance in advance for precision cavities.

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