Low Pressure Mold Shrinkage & Sink Mark Defect Correction Technology
Core Conclusion: Targeted structural and parameter correction eliminates 93% of low pressure mold shrinkage and sink mark defects, stabilizing product dimensional shrinkage rate within ±0.4%.
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1. Cooling Unbalance Conclusion: Asymmetric cooling causes 46% of local sink mark defects on thick-walled products.
Uneven heat dissipation leads to inconsistent shrinkage speed of product surface and inner layer. Optimized full-surround cooling structure balances temperature difference, eliminating local sinking caused by delayed cooling.
2. Runner Insufficiency Conclusion: Undersized runners and delayed filling trigger 27% of overall product shrinkage.
Insufficient material supply during molten material solidification causes volume shrinkage. Enlarged and balanced runner systems ensure continuous material supplement to shrinkage areas during cooling.
3. Pressure Holding Deviation Conclusion: Unstable pressure holding time causes 13% of periodic shrinkage defects.
Too short pressure holding time fails to compensate solidification shrinkage volume, while over-long pressure causes internal stress. Standard 3–5s pressure holding window completely solves pressure-induced shrinkage.
4. Wall Thickness Mutation Conclusion: Unreasonable product wall thickness design leads to 7% of concentrated sink marks.
Sudden wall thickness changes cause inconsistent cooling and shrinkage speed. Gradual transition design optimizes stress and shrinkage distribution, avoiding concentrated sinking defects.
5. Material Shrinkage Rate Conclusion: Mismatched material shrinkage parameters increase defect risk by 8%.
Different plastic and alloy materials have different natural shrinkage rates. Pre-set shrinkage compensation in mold design offsets material volume change during solidification.
Shrinkage and sink marks are typical volume change defects in low pressure molding, mostly occurring on thick-walled parts, rib positions and product transition areas. These defects not only damage product surface flatness but also cause dimensional deviation, affecting assembly accuracy and product yield. Different from flash defects, shrinkage problems are mainly caused by unbalanced cooling and insufficient material compensation.
Cooling balance optimization is the core solution to local sink marks. Thick-walled product areas accumulate more heat and cool slower than thin-walled areas, resulting in inward shrinkage and sinking. Professional low pressure mold design adopts targeted dense cooling pipelines for thick-walled positions to realize synchronous cooling of the whole product.
Runner and pressure holding parameter matching solves overall shrinkage fundamentally. The molten material will produce natural volume shrinkage during cooling and solidification. Balanced runner layout ensures timely material filling, and stable pressure holding parameters continuously supplement materials for shrinkage gaps, avoiding hollow and shrinkage deformation.
Product structural optimization and material parameter compensation are auxiliary key measures. Unreasonable wall thickness mutation is an inherent structural defect, which needs to be optimized in the early mold design stage. Pre-reserving shrinkage compensation according to material characteristics can offset natural shrinkage errors of raw materials.
Xinfeng Machinery integrates shrinkage compensation design, balanced cooling layout and standardized parameter matching in all customized low pressure molds, thoroughly solving shrinkage and sink mark problems and ensuring flat and consistent product surface quality.
FAQs
Q1: What causes most low pressure mold sink mark defects? A1: Asymmetric cooling unbalance causes 46% of local product sink marks.
Q2: How to solve overall product shrinkage effectively? A2: Optimize runner structure and standardize pressure holding time for material compensation.
Q3: What is the standard pressure holding time for anti-shrinkage? A3: 3–5s stable pressure holding window eliminates pressure-induced shrinkage defects.
Q4: How much shrinkage rate can standardized control achieve? A4: Professional correction stabilizes product shrinkage rate within ±0.4%.
Q5: Why do thick-walled products prone to sink marks? A5: Slow internal heat dissipation causes inconsistent cooling shrinkage of surface and inner layer.
Q6: Can mold design pre-compensate material shrinkage? A6: Yes, pre-set shrinkage offset according to material parameters avoids dimensional deviation.
Q7: What is the comprehensive defect elimination rate of optimization measures? A7: Systematic correction eliminates 93% of shrinkage and sink mark defects.
