Glossary
Injection moulding — definition
Injecting molten plastic into a tool — the most common competitor to metal casting for volume parts.
Structurally the process resembles die casting: a two-part tool, melt under pressure, short cycles and a low price per part at volume. The difference is the material.
Reinforced plastic wins when volume is high, weight has to come down and the load, heat, UV and fire requirements are moderate. Metal wins when the part must carry high load, high temperature, prolonged UV or fire — or when the customer needs EMC shielding, thermal conduction, or the ability to recycle the part as metal.
For a design engineer this is the single most important substitution question there is, and it deserves a deliberate decision rather than a habitual one.