Injection molding

1. Product Design

The most fundamental approach is to avoid excessive wall thickness or keep wall thickness as uniform as possible.

If the product's function allows, wall thickness can be reduced through hollowing or ribbing. For example, converting a solid thick wall into a thin-walled structure with reinforcing ribs maintains strength while reducing material accumulation. Rib thickness is typically controlled at 50% to 70% of the main wall thickness — too thick tends to cause sink marks at the rib base, while too thin fails to provide adequate reinforcement.

If a thick wall is truly necessary, consider designing it as a hollow structure, or adding process holes in non-functional areas to reduce the actual wall thickness. Wall thickness transitions should be as gradual as possible, avoiding abrupt changes from thick to thin, since sudden transitions are high-risk zones for stress concentration and deformation.

2. Mold Design

The core of mold design is to achieve uniform cooling and effective packing.

The design of cooling channels is critical. Thick-walled areas should receive enhanced cooling, with channels positioned as close to the cavity surface as possible and arranged evenly. For complex product geometries, conformal cooling channels can be considered to follow the shape of the part more closely and reduce cooling variation between different areas.

Gate location and quantity also affect warping. Gates should be positioned in thick-walled areas so that molten material flows from thick to thin sections, making it easier for packing pressure to reach the areas that need compensation. For large thick-walled parts, multiple gates can be considered to shorten flow paths and reduce shrinkage variation.

The ejection system must be balanced. The number, position, and speed of ejector pins should ensure uniform force during ejection, avoiding mechanical deformation caused by unbalanced ejection.

3. Injection Molding Process

The core of process adjustment is to achieve more complete and uniform cooling.

Appropriately extending cooling time ensures the core is fully solidified before ejection. For thick-walled parts, this is the most direct and effective measure. While it sacrifices some cycle time, it delivers stable quality in return.

Optimize packing parameters. Increase packing pressure and extend packing time so that core shrinkage is more fully compensated. The packing switchover point must be accurate, ensuring material compensation is completed before the gate freezes off.

Appropriately reducing melt temperature and mold temperature can reduce total shrinkage, but care must be taken to balance flowability and molding quality, avoiding short shots or weld lines caused by excessively low temperatures.

For parts that are particularly prone to warping, post-ejection measures such as cooling fixtures or annealing can be used. Cooling the part in a fixture to set its shape, or annealing to relieve internal stress, are both effective remedial measures.

Summary

Warping in thick-walled parts cannot be solved by a single measure — it requires systematic optimization across design, mold, and process. The core logic always revolves around two principles: more uniform cooling and more consistent shrinkage. Achieve these two, and the warping problem can be effectively controlled.