Designing a plastic part for injection moulding is very different from designing the same part for machining.
The plastic has to flow into the mould, cool, shrink and then release from the tool.
That is why manufacturing knowledge should influence the CAD model from day one.
## Keep wall thickness consistent
Large changes in wall thickness can contribute to uneven cooling and defects such as sink marks or warpage.
Where possible, aim for a consistent wall strategy rather than simply making everything thick.
## Add draft
A vertical wall may look perfectly fine in CAD but can become difficult to eject from a mould.
Draft helps the part release.
The required amount depends on material, surface finish, texture, depth and tooling.
## Use ribs carefully
Ribs are useful for increasing stiffness without making the entire wall thick.
But overly thick ribs can create visible sink marks.
The rib design should support the structure while respecting the material and process.
## Bosses need support
Bosses are commonly used for screws and locating features.
They should be designed with adequate support and appropriate wall thickness.
## Think about the parting line
The parting line affects tooling, appearance and sometimes the final geometry.
A good designer considers where the mould will open before finalising the shape.
## Check undercuts
Undercuts may require slides, lifters or other tooling solutions.
Sometimes that is completely acceptable.
Sometimes a small geometry change can eliminate the need for complex tooling.
## Design for the complete product
A moulded component is not finished when it comes out of the tool.
It still needs:
– Assembly – Fasteners – Inserts – Cosmetic requirements – Inspection – Packaging – Service considerations
That bigger picture is where strong product design happens.
2026 Engineering Update
Mechanical engineering is moving toward more connected design-to-manufacturing workflows. Three developments are especially useful for engineers:
- AI-assisted engineering: AI is increasingly being used alongside CAD, simulation and engineering data to explore designs and reduce repetitive work.
- Digital twins and digital threads: connected product and manufacturing data can help teams validate changes earlier and maintain better traceability from design through production.
- Design-for-manufacturing skills: engineers are increasingly expected to combine 3D CAD, simulation, GD&T, DFM/DFA, automation and data skills rather than work in isolated disciplines.
The practical takeaway: learn the fundamentals first, then use new digital tools to make engineering decisions faster, clearer and easier to validate.