1. Defect Overview

2. Main Cause Analysis

2.1 Molding Process Factors (Priority for On‑site Troubleshooting)

• Low holding pressure: Insufficient melt delivery to thick‑wall rib zones, poor shrinkage compensation.
• Insufficient injection pressure: Poor cavity packing, leaving large shrinkage allowance in rib areas.
• Too‑short holding time: Early gate freeze‑off cuts off melt feeding, so thick sections receive no supplementary material.
• Inadequate cooling time: Ejection before full part solidification; post‑ejection shrinkage manifests as depressions.
• Excessive barrel temperature: Higher melt temperature increases molding shrinkage rate.
• High mold temperature: Slow melt cooling amplifies shrinkage discrepancy between thick and thin sections.

2.2 Inherent Product & Mold‑Design Factors

• Unreasonable wall‑thickness transition: Excessive thickness difference between rib roots and outer part walls creates heat traps. Industry best practice: rib thickness shall not exceed 60 % of nominal wall thickness.
• Improper gating design: Undersized gate cross‑section or long flow distance from gate to defect zones causes substantial pressure loss and insufficient feeding to remote ribs.

3. Graded Improvement Countermeasures (Optimize process first; perform mold modification if process tuning reaches limits)

Process Optimization (Low‑cost & Quick Implementation)

• Appropriately increase holding pressure to enhance shrinkage compensation for thick ribs.
• Raise injection pressure reasonably to improve overall cavity packing density.
• Extend holding time to guarantee continuous feeding before gate solidification.
• Prolong cooling cycle to ensure full solidification prior to ejection.
• Reduce barrel temperature within material allowable range to lower melt shrinkage rate.
• Decrease mold temperature properly to accelerate surface skin solidification and suppress surface sinking.

Mold‑Structure Optimization (When process tuning cannot resolve defects)

• Revise rib geometry: Thin down reinforcing ribs to reduce wall‑thickness jump; apply core‑out design for heavy sections.
• Enlarge gate cross‑section and relocate gates closer to sink‑mark‑prone zones to minimize pressure loss.
• Optimize mold cooling channels to improve heat dissipation in concentrated rib regions.

4. Konger Molding‑Solution Advantages

• Closed‑loop servo pressure control supports multi‑stage holding pressure. Pressure is dynamically adjusted according to filling and cooling phases, providing precise and sustained feeding for thick‑wall zones. It effectively mitigates sink marks on ribs and mesh structures while avoiding residual stress and flash.
• High‑precision stable pressure‑and‑flow output delivers fast pressure response with low fluctuation. Holding pressure can be reliably transmitted even through long flow paths, greatly reducing sink marks on remote ribs caused by pressure decay. Well‑suited for mass production of large crates and housings with heavy ribs.
• Intelligent segmented temperature control enables independent fine‑tuning for each barrel zone. Stable output curves facilitate quick parameter tuning for shrinkage‑related issues, shortening mold‑tryout cycles and cutting scrap rates.
• Professional process‑engineering service: Konger’s experienced molding‑engineering team provides process support for automotive‑parts, logistics‑packaging, consumer‑goods and home‑appliance customers. On‑site process guidance covering sink marks, voids and warpage is available during pre‑sales mold trials and mass‑production phases. We deliver not only machinery but also complete molding solutions.
• Broad model coverage: Clamping force ranges from 100 T to 1400 T. Models match small enclosures as well as large fruit crates and logistics totes with dense reinforcing ribs, satisfying one‑stop production requirements for plastic articles of varying dimensions.

5. Summary