Solutions to Insufficient Filling in Thin-Wall Injection Molding
2026-04-15 15:37:18
Injection Molding
Thin‑wall plastic parts are widely used in electronic housings, automotive components, home appliances and connectors due to their light weight, material saving and compact structure. However, thin‑wall parts usually have a wall thickness between 0.3mm and 1.2mm, long flow distance and high flow resistance. Insufficient filling, short shots, sink marks, weld lines and burn marks are common defects. These problems not only damage appearance but also reduce structural strength and assembly performance. This article summarizes practical solutions from process, mold, structure and material aspects to help achieve stable filling.
Causes of Insufficient Filling in Thin-Wall PartsThe essence of insufficient filling is that flow power is less than flow resistance and cavity back pressure. When the melt enters the cavity, it cools rapidly and forms a solidified layer on the surface. If the injection speed is not fast enough or the pressure is not high enough, the melt cannot break through the solidified layer, resulting in incomplete filling. Low melt temperature or high viscosity will also increase flow resistance. Improper gate location or size will cause excessive pressure loss.
Unbalanced runner or sharp corners will further hinder flow. Poor ventilation causes trapped gas, which forms back pressure and prevents the melt from filling the end of the cavity. Extremely thin walls, sharp corners and deep ribs in product structure will also increase filling difficulty. In addition, materials with poor fluidity are more likely to cause insufficient filling in thin‑wall products.
Process Parameter Optimization
Process adjustment is the fastest and most cost‑effective method to improve filling. Increasing barrel temperature can reduce melt viscosity and improve flowability. Raising mold temperature delays the formation of the solidified layer and allows more time for filling. High‑speed injection is essential for thin‑wall parts, as it fills the cavity before the surface cools down.
Increasing injection pressure provides sufficient power to overcome flow resistance. Extending holding time ensures that the cavity is fully filled and compensated. Optimizing cooling ensures uniform temperature distribution and avoids local overcooling. Through reasonable parameter matching, most filling problems can be significantly improved without modifying the mold.
Mold Structure ImprovementMold optimization solves the problem fundamentally. Enlarging gate size and setting gates at the thickest and shortest flow position can reduce pressure loss. Using larger and smoother runners helps reduce flow resistance. Adding sufficient vents at flow ends and weld line areas allows gas to escape smoothly.
Polishing cavity surfaces reduces friction and helps melt flow. Using hot runners maintains melt temperature and pressure, which is very effective for long‑flow and thin‑wall parts. Avoiding sharp corners in the cavity can prevent turbulence and stagnation. Reasonable mold structure is the basis for stable production of thin‑wall parts.
Product Structure Optimization
Reasonable product design can greatly reduce molding difficulty. Maintaining uniform wall thickness, generally not less than 0.6mm, helps ensure stable filling. Controlling a reasonable flow‑length ratio prevents excessive pressure attenuation. Using rounded corners reduces flow resistance and helps melt pass through smoothly.
Avoiding deep and narrow ribs that are difficult to fill can effectively prevent short shots. For long‑flow parts, adding auxiliary gates can shorten the flow distance and improve filling balance. Product structure optimization is the most fundamental way to avoid insufficient filling.
Material Selection and PreparationChoosing high‑flow grades with high melt index is very helpful for thin‑wall parts. Fully drying hygroscopic materials such as PA and PC prevents bubbles and flow breakage. Ensuring uniform material and stable batch performance helps maintain consistent filling effect. Avoiding excessive moisture can prevent unstable flow and insufficient filling.
ConclusionInsufficient filling in thin‑wall injection molding can be effectively solved by systematic optimization. Increasing temperature, speed and pressure improves flow. Optimizing gate, runner and vent ensures smooth filling. Reasonable product structure reduces difficulty. High‑quality and stable production of thin‑wall parts can be achieved through comprehensive adjustment of process, mold, structure and material.
