Optimising your part design for strength, performance, and manufacturability
When designing a component for injection moulding, wall thickness and radii are two of the most important factors to get right. They influence not only the structural integrity of the part but also the efficiency of the moulding process, cycle times, and long-term product reliability.
At CJ Tool & Mouldings, we support design engineers and product developers across the UK to refine part designs, ensuring they are optimised for manufacturability without compromising performance.
Why Wall Thickness Matters
Uniform wall thickness is critical in injection moulding. Variations in thickness can cause issues such as warping, sink marks, voids, and uneven cooling. These defects not only affect the appearance of the part but also its strength and dimensional stability.
Key considerations:
- Consistency: Aim for uniform wall sections wherever possible to ensure even cooling and predictable shrinkage.
- Avoid thick walls: Excessive thickness increases cycle times and can cause sink marks or internal voids. Instead, use ribs or gussets to add strength without unnecessary material.
- Thin walls: While thin walls reduce weight and material costs, they must remain within the flow capabilities of the chosen polymer to avoid incomplete filling.
Typical guidelines:
- General purpose wall thickness: 2–4 mm
- Thin-wall moulding: as low as 0.5–1 mm (material-dependent)
- Structural components: up to 6 mm, but should be carefully designed to avoid defects
At CJ, our mould flow analysis helps identify potential wall thickness issues before tooling manufacture, reducing risk and avoiding costly redesigns later in the project.
The Role of Radii in Part Design
Sharp corners may look simple in CAD, but in injection moulding they create stress concentrations, hinder material flow, and shorten tool life. Incorporating radii (curved transitions) instead of sharp corners improves both the moulding process and part performance.
Benefits of adding radii:
- Improved material flow: Curved corners allow molten plastic to fill the cavity smoothly, reducing weld lines and voids.
- Reduced stress points: Radii distribute stress more evenly, improving durability and resistance to cracking.
- Tool longevity: Rounded features are less likely to damage or wear tooling compared to sharp corners.
Design tips:
- Internal corners should have radii of at least 0.5–0.6 x wall thickness
- External corners should be slightly larger than internal corners to maintain uniform wall sections
- Radii should blend smoothly to avoid abrupt geometry changes
By working closely with our customers during the design stage, we ensure radii are optimised not only for the part but also for the tool manufacture , saving time, cost, and complexity
Designing for Performance and Production
The best injection moulded parts are those that balance design intent with manufacturing practicality. Wall thickness and radii are fundamental to achieving that balance.
At CJ Tool & Mouldings, we combine technical expertise, mould flow analysis, and practical experience to guide design engineers through these critical considerations. By addressing potential issues early, we help reduce lead times, improve product quality, and ensure parts perform as intended from the first shot to full production.
Trusted by UK product designers and engineers.
If you’re developing a part and want expert advice on wall thickness, radii, or any aspect of injection moulding design then why not get in touch today? Our expert team can discuss your part design and put together a quotation for injection mould tooling and part production.
