Sharp corners on mold cavity are high‑risk locations for thermal‑fatigue crack. Fillet radius, local temperature‑swing, stress‑concentration and surface nitriding status jointly govern crack initiation life for LPDC, gravity and CPC counter‑pressure casting mold inserts.
Sharp internal corner produces severe stress‑concentration under cyclic thermal‑load. Simulation shows stress magnification‑factor reaches 2.7‑3.2 when fillet radius R＜1.0 mm; thermal‑fatigue crack preferentially nucleates right at corner root for EV structural‑part mold H13 inserts.
Local temperature swing amplitude dominates thermal‑fatigue life. At cavity sharp‑corner position, melt contact creates fast temperature rise; mold opening and spray‑cooling bring rapid cooling. Temperature swing over 220 ℃ sharply accelerates crack‑initiation for CPC counter‑pressure casting mold.
Fillet‑radius design recommendation for high‑load cavity corners: minimum inside fillet R≥1.5 mm. For functional geometry cannot achieve large fillet, adopt smooth blended transition to avoid right‑angle sharp root for gravity casting mold cavity design.
Nitriding‑layer brittleness amplifies corner‑crack risk. Stress‑concentrated corner superimposed with brittle nitriding compound‑layer; micro‑crack originates from nitriding‑layer and extends into H13 substrate under repeated thermal‑cycle for LPDC casting mold aluminum wheel inserts.
Over‑polishing at fillet corner must be prevented. Excessive manual‑polishing creates tiny grinding‑notches at corner root; grinding‑notch acts as crack‑initiation source even for fillet with theoretically qualified radius for aluminum casting mold.
Cooling‑channel layout near sharp‑corner zone: avoid placing cooling‑hole too close to corner root. Distance below 14 mm enlarges local temperature swing, aggravating thermal‑stress at fillet position for EV structural‑part mold.
Early warning feature of corner thermal‑fatigue crack: first appear as micro‑network crack along fillet surface. If continue production without maintenance, network‑cracks connect and develop into penetrating crack after additional 1000‑1400 cycles for CPC counter‑pressure casting mold.
Repair challenge for fillet‑zone thermal‑crack: simple surface polishing cannot remove crack root inside corner root. Crack tip remains under subsurface and propagates rapidly again under thermal‑mechanical‑load after short production time for gravity casting mold.
Weld‑repair at sharp‑fillet position: fully mill out crack network, adopt rounded weld‑bead transition, strictly implement pre‑heat and post‑weld stress‑relief. Re‑create smooth fillet geometry after repair‑weld for LPDC casting mold maintenance work.
Procast thermal‑stress coupled‑simulation marks high‑stress‑concentration corner zones. However simulation cannot fully reflect grinding‑notch, nitriding‑brittleness and other workshop‑introduced defects; on‑site periodic visual inspection remains irreplaceable.
Cross‑border mold procurement reminder: 2D drawing fillet‑radius annotation must be explicit. Many delivered molds carry invisible sharp root even drawing marks R‑fillet, caused by insufficient CNC‑machining tool radius compensation during mold manufacturing.
FAQ
Q: What stress‑magnification factor occurs for mold inner‑corner with fillet R＜1.0 mm?
A: Stress magnification factor reaches 2.7‑3.2 at sharp inner‑corner root position.
Q: What temperature‑swing threshold sharply accelerates fillet‑corner thermal‑fatigue crack?
A: Local cyclic temperature swing exceeding 220 ℃ accelerates crack‑initiation significantly.
Q: What minimum recommended inner‑fillet radius for high‑load mold cavity corners?
A: Adopt inner fillet radius R≥1.5 mm for high‑stress cavity corner geometry.
Q: What polishing‑related defect becomes hidden crack‑source at fillet corner root?
A: Over‑polishing‑induced tiny grinding‑notches act as thermal‑fatigue crack initiation origin.
Q: What cooling‑channel distance amplifies thermal‑stress risk nearby cavity sharp‑corner?
A: Cooling‑hole distance below 14 mm enlarges local temperature swing and thermal‑stress.
Q: What will happen if only surface polishing is applied to fillet‑zone thermal‑fatigue crack?
A: Sub‑surface crack tip survives and rapidly propagates again under cyclic thermal‑load.
Q: What manufacturing‑cause leads to sharp corner root despite drawing marked fillet radius?
A: Insufficient CNC tool‑radius compensation during mold machining generates invisible sharp root.
