Why design for mouldability matters (even at the “napkin sketch” stage)

In product development, there is a significant gap between a concept that looks good and part that is viable for commercial production. This ism why considering manufacturability, even at the “napkin sketch” stage, is a sensible habit to get into. Addressing these factors before a single minute is spent on CAD or prototyping saves significant time and money on design changes further down the line, so much so it can even be the difference to whether a product successfully makes it into production.

Concept design considerations

Tooling Simplicity: A key consideration in making an injection moulded viable is to design for a “straight-pull” mould tool. By considering the line of draw at the concept stage, you can often eliminate undercuts – features that prevent the part from being ejected directly. For example, replacing a side-hole with a “shut-off” slot or repositioning a clip can remove the need for complex moving elements like sliders, lifters, or hydraulic cores.

Wall Thickness: Thick sections stay hot longer, which can lead to internal stress, sink marks, or voids. Conversely, sections that are too thin can lead to structural failure. Aiming for a thin, uniform wall keeps cycle times fast and parts stable.

The Power of Radii: Sharp corners equate to localised stress and hindered material flow. Incorporating generous radii facilitates easier part ejection and reduces the risk of failure.

Ribs and Bosses: A more production friendly approach to strengthening a wall. To avoid surface defects, rib thickness should generally not exceed 50% of the adjoining wall. Similarly, bosses for assembly must be designed with specific wall ratios to prevent “sink” on the decorative surface.

Draft Angles: To ensure a part can be removed from the mould without scuffing, draft angles (typically 0.25° to 2°) are essential. This applies to every feature, including holes, ribs, and recesses.

Partnering with Skar

We believe the best way to ensure a project’s success is through early, transparent collaboration. As a leading and highly experienced plastic injection moulding company, we’re always happy to help, even at the concept stage. We can provide advice on design optimisation, material selection, and more.

For manufacturers in highly regulated sectors, our ISO 13485:2016 certification for medical device manufacturing serves as a guarantee of our commitment to quality, risk management, and traceability. Whether your project is a medical component or a complex industrial housing, you can be reassured that our processes are built to meet the most demanding global standards.