Injection Moulding — Plastic Part Manufacturing

Why companies use it

• ·Enables production of complex plastic geometries at very low per-part cost in high volumes (typically >10,000 parts)
• ·Excellent part-to-part repeatability once the mould and process are optimised
• ·Wide material selection — hundreds of engineering thermoplastics available for specific mechanical, thermal, and regulatory requirements
• ·Can integrate multiple functions into one moulded part, eliminating assembly steps (snap fits, living hinges, wall mounts)

What hiring managers look for

• ·Mechanical engineers who design plastic parts must understand DFM for injection moulding — poor design leads to sink marks, warp, short shots, and flash
• ·Understanding the mould design (gate location, runner system, cooling channels, ejection) helps engineers communicate effectively with toolmakers
• ·Knowledge of shrinkage, warpage, and residual stress in injection moulded parts is essential for dimensionally accurate plastic designs
• ·Experience managing NPI from tool design through first article inspection (FAI) is expected for product engineers working with moulded parts

Typical interview questions

Common mistakes

• ·Designing without draft angles — parts with zero draft cannot be ejected from the mould without damage
• ·Thick wall sections with thin walls joining them — creates sink marks, voids, and warpage during cooling
• ·Sharp internal corners — stress concentration points that cause cracking; use fillets of at least 0.5× wall thickness
• ·Not considering shrinkage in nominal dimension specification — most engineering thermoplastics shrink 0.4–2.0% after cooling
• ·Placing the gate in a cosmetic area — weld lines and gate vestige are unavoidable; gate in hidden or non-critical areas

Real engineering example

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