Die Surface Polishing Process for Aluminum Casting: Polishing‑Stress Control, Over‑Polishing Risk and Acceptance Standard

Die Surface Polishing Process for Aluminum Casting: Polishing‑Stress Control, Over‑Polishing Risk and Acceptance Standard

Die cavity polishing directly determines casting surface quality; improper polishing operation brings surface residual stress, local over‑polishing and micro‑groove defects, which become crack‑source under cyclic thermal‑shock in mass‑production.

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.