Four Golden Rules Of Plastic Part Wall Thickness Design

Many product structure designers often fail to determine accurate data for product wall thickness during the structural design process, leading to various issues in the final manufactured product. Wall thickness design for plastic parts is the most fundamental requirement for producing a good product. In simple terms, the wall thickness design of plastic parts prioritizes uniformity as the primary rule and avoids sudden changes. The main wall thickness typically ranges from 1.5-3mm (for general plastics), and can be slightly thinner for engineering plastics. The thickness of ribs should be controlled at 40%-60% of the main wall thickness, with transitions being gradual (transition length ≥ 5 times the wall thickness difference). Walls that are too thick are prone to sink marks, while walls that are too thin are prone to short shots; both can lead to warpage and internal stress issues.

I. Core Design Principles

The core points can be summarized in three words: Uniform (Uniformity First), Gradual (Gradual Transition), and Appropriate (Moderation is Best).

Principle of Uniformity (Most Critical)

All designs should revolve around considerations of material flow, cooling, and demolding. Uniform wall thickness is the foundation, without exception.

Non-uniform wall thickness leads to differences in cooling rates, causing defects such as sink marks, flow marks, internal stress, warpage, and deformation (approximately 40% of injection molding defects are directly related to this).

The difference in thickness between adjacent walls should not exceed 40%-60% to avoid sudden cross-sectional changes.

Principle of Gradual Transition

When a thickness change is necessary, use tapered or rounded connections. The transition length should be ≥ 5 times the wall thickness difference.

The fillet radius for transitions should be ≥ 1.5 times the wall thickness difference to prevent stress concentration.

For internal corners, use a radius of R1. For external corners, use a radius of R2 = R1 + t (where t is the main wall thickness) to maintain consistent wall thickness at corners.

Principle of Appropriateness (Thinner is Better)

The wall thickness should be as thin as possible while meeting strength requirements: saves material, shortens cycle time, and reduces costs.

Avoid simply increasing thickness: increasing wall thickness by 10% improves strength by about 33%, but beyond a certain point, strength may actually decrease due to sink marks/voids.

The recommended maximum wall thickness is ≤ 5mm, and should not exceed 8mm in special cases. For sections requiring greater strength beyond this limit, use ribs instead of simply increasing the wall thickness.

Principle of Functional Adaptation

Areas for connections, fastening, insert molding, or weld lines require sufficient thickness to ensure strength.

The part must be thick enough to withstand the impact of ejector pins and vibration during demolding.

It must withstand tightening forces during assembly.

Consider strength requirements during storage and handling.

Recommended Wall Thickness Values

By Product Material:

(Refer to the material-specific table provided )

By Product Type:

Small Precision Parts:​ 0.5-1.0mm

Medium-sized Housings (Small Appliances):​ 1.5-2.5mm (ABS commonly used)

Large Structural Parts (Automobile Bumpers):​ 3-4mm (Internal ribs are essential)