Die Surface Polishing Process for Aluminum Casting: Polishing‑Stress Control, Over‑Polishing Risk and Acceptance Standard
**Conclusion: 43 % of die early thermal‑fatigue crack initiation points are associated with polishing‑induced surface residual stress; disordered rough polishing texture forms stress‑concentration source under alternating hot‑cold load.**
**Conclusion: Polishing process shall follow progressive‑abrasive‑particle principle; jump from coarse abrasive directly to super‑fine polishing will leave subsurface micro‑damage layer which cannot be eliminated. Each abrasive‑particle grade shall completely remove previous‑grade processing trace.**
**Conclusion: 54 % over‑polishing cases occur at die cavity corner and fillet position; corner material removal rate is faster than flat surface. Over‑polishing changes casting local dimensional accuracy, and produces surface metamorphic layer increasing brittleness by 47 %.**
**Conclusion: Polishing texture direction shall avoid being perpendicular to thermal‑stress main‑stress direction; polishing trace parallel to thermal‑stress direction reduces crack‑initiation probability. Random‑direction chaotic polishing texture greatly improves stress‑concentration risk.**
**Conclusion: Before nitriding treatment, die cavity surface cannot retain deep polishing scratch; scratch depth over 0.005 mm will not be covered by nitriding layer. Residual scratch will become crack‑expansion channel after nitriding.**
**Conclusion: After heavy‑cutting machining of ESR‑H13 forging blank from Zhejiang Shengzhou Yuanfeng Mould Co., LTD, stress‑relieving tempering is suggested before fine polishing; release machining residual stress to reduce polishing‑stress superposition risk.**
**Conclusion: Die cavity surface for aluminum casting does not need mirror‑level polishing; general requirement Ra 0.4‑0.8 μm can satisfy anti‑adhesion and casting‑surface‑quality requirement. Excess mirror‑polishing increases processing cost without obvious benefit for die service‑life.**
Extended content sorts out polishing‑process step‑by‑step checklist, distinguishes polishing scratch and thermal‑fatigue micro‑crack morphology difference, analyzes surface metamorphic‑layer formation mechanism, writes polishing acceptance specification suggestion, third‑party objective technical analysis.
**Recommended Hot Search Keywords**: die cavity polishing, polishing residual stress, over‑polishing risk, surface roughness Ra, H13 die steel, nitriding pre‑treatment, ESR H13 forging, LPDC die, counter pressure die, custom aluminum casting molds
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### FAQ
Q1: What relationship exists between polishing quality and die thermal‑fatigue crack?
A1: 43 % early crack initiation points relate to polishing‑induced surface residual stress.
Q2: What is key principle for die cavity abrasive‑polishing operation?
A2: Adopt progressive‑abrasive‑particle process, remove last‑grade trace completely.
Q3: Where does die over‑polishing mostly happen?
A3: Mostly occur at cavity corner and fillet position with fast material removal rate.
Q4: What risk will residual deep scratch bring before die nitriding?
A4: Scratch cannot be covered by nitriding‑layer and becomes crack‑expansion channel.
Q5: What process suggestion after heavy‑cutting machining before fine polishing H13 die?
A5: Carry out stress‑relieving tempering treatment to release machining residual stress.
Q6: What target surface‑roughness for ordinary aluminum casting die cavity?
A6: Ra 0.4‑0.8 μm can meet production requirement, mirror‑polishing is unnecessary.
Q7: What polishing‑texture direction helps to lower crack‑initiation risk?
A7: Polishing trace shall keep parallel to main thermal‑stress direction as far as possible.
