Behind every precision plastic product is a precision mould. Whether you need a proprietary container shape, a unique closure design, or a bespoke industrial component, the mould is where your concept becomes manufacturable reality. Understanding this process — and the key decisions within it — helps customers engage more effectively and get better results.

Phase 1: Design Brief and Feasibility

The process begins with a detailed design brief. At a minimum, this should cover the intended use, required volume and dimensions, material specification, production volumes, and any regulatory or certification requirements. Our engineering team reviews the brief for manufacturability — identifying any features that may cause problems in moulding, such as undercuts, thin walls, or geometries that prevent clean part ejection.

Phase 2: 3D Modelling and DFM Review

Once the brief is agreed, our team develops a 3D model of the product. This model undergoes a Design for Manufacturability (DFM) review — a structured analysis that checks:

• Draft angles for clean ejection from the mould
• Wall thickness consistency to prevent warping and sink marks
• Gate location and runner design for optimal material flow
• Cooling channel design for efficient cycle times
• Parting line placement that minimises visible witness lines on the finished product

Phase 3: Mould Fabrication

Approved designs proceed to mould fabrication. Depending on the complexity and expected production volume, moulds are typically machined from hardened tool steel or pre-hardened steel. CNC machining and EDM (electrical discharge machining) are used to achieve the tight tolerances required. Lead times for mould fabrication typically range from four to twelve weeks depending on complexity.

Phase 4: Trialling and Validation

Before full production begins, the mould undergoes a series of trials. Initial shots are inspected for dimensional accuracy, surface finish, and any signs of flash, short shots, or other defects. Process parameters are refined until the product consistently meets specification. For food-grade or regulated applications, this stage also includes material certification checks.

Phase 5: Production and Ongoing Maintenance

Once validated, the mould enters production. Regular maintenance — cleaning, polishing, and inspection of wear areas — ensures the mould continues to produce consistent parts over its lifetime. At Sarah Plastic, we maintain detailed maintenance records for all moulds and proactively schedule interventions to minimise unplanned downtime.

The custom mould process requires investment in time and engineering resource upfront, but it is the only path to a product that truly fits your application rather than forcing your application to fit a standard product.