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Influence of Mold Parting Surface Machining Precision on Injection Molding Stability

2026-06-30 10:37:38 Injection Molding
Over 60% of flash, leakage and dimensional deviation defects in injection workshops stem from unqualified parting surface machining precision. Key indicators include flatness, parallelism, surface roughness and uniform sealing gap, which jointly control mold closing tightness, exhaust efficiency and batch production consistency.
Excessive Flatness Deviation Triggers Continuous Flash and Mold Damage

Standard flatness tolerance for parting surfaces is 0.01–0.02mm per 100mm. Uneven protrusions and depressions from insufficient grinding create micro gaps after mold closing. Melt pressure ranges 80–120MPa, squeezing plastic out to form flash. Deviation between 0.02–0.03mm causes intermittent burrs requiring manual trimming to slow production rhythm; over 0.03mm deviation leads to persistent overflow, plastic residue blocking exhaust and subsequent sink marks, air bubbles and burning defects. Extruded plastic continuously impacts concave-convex areas to scratch and collapse the parting surface, widening gaps and forming a vicious cycle of deteriorating mold condition and more defects.

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Unqualified Parallelism Causes Product Wall Thickness and Size Drift
Precision mold parting surface parallelism must be controlled below 0.02mm. Out-of-tolerance parallelism creates uneven front-back and left-right mold clearance, shifting the entire cavity and generating inconsistent wall thickness and fluctuating product dimensions that fail assembly tolerance standards. For multi-cavity molds, offset leads to inconsistent forming status among cavities with mixed qualified and defective goods. Asymmetric force wears guide pins and sleeves unilaterally, causing mold opening jitter and frequent production readjustment.
Over Standard Roughness Leads to Batch Quality Fluctuation and Poor Exhaust
Precision mold parting surface Ra shall not exceed 0.8μm, while ordinary mass production molds require Ra ≤1.6μm. Unpolished tool marks form invisible tiny gaps to ooze fine flash and accumulate release agent and carbon slag, gradually weakening sealing performance. Stable initial quality declines after continuous 3–4 hours of production with recurring burrs, pits and weld lines. Chaotic exhaust through texture grooves prevents orderly air discharge via standard exhaust slots, trapping internal air to create bubbles and burnt spots that damage product appearance and structural strength.
Uneven Sealing Gap Amplifies Process Sensitivity and Accelerates Mold Wear

Uneven sealing gap from inconsistent parting surface processing causes local sealing failure. Operators have to raise clamping force and lower injection speed to restrain overflow, boosting internal product stress and inducing later warpage and cracking. Narrow adjustable process window makes small temperature or pressure changes alternately generate sink marks and flash, requiring constant parameter modification. Long-term high clamping force speeds up aging of mold plates, toggle mechanisms and guide pillars; parting surface wear rate doubles, shortening the mold polishing cycle from several months to a few weeks and disrupting production schedules.

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Benefits of Standard Precision Parting Surfaces
Parting surfaces meeting all precision standards achieve uniform full-area fitting, allowing lower clamping tonnage to reduce long-term equipment loss. Consistent mold closing, exhaust and sealing conditions unify forming status of all multi-cavity positions, cutting product appearance and dimensional fluctuation and reducing defect rate by around 50%. Less overflow residue extends mold cleaning intervals and shortens material switching debugging time. Slower mold wear lengthens repair cycles and improves continuous production efficiency, realizing stable long-term injection molding from quality, efficiency and equipment loss perspectives.

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