Plastics manufacturing is a handful of processes that between them make almost every plastic object in existence, and choosing between them is nearly always a question about the shape of the part and the number needed. Getting that choice right at the start decides more about a product's cost than any negotiation afterwards.
The processes and the parts they make
Injection moulding makes detailed, dimensionally accurate parts in volume. Extrusion makes anything with a constant cross section continuously. Blow moulding makes hollow containers. Rotational moulding makes large hollow parts with cheap tooling. Thermoforming makes trays, covers and panels from sheet. Compression moulding handles thermosets and long fibre compounds. Casting makes small quantities from a soft tool.
How volume decides
Below a hundred parts, casting, machining or printing. Into the hundreds, soft tooled injection moulding or thermoforming. Into the thousands and beyond, injection moulding for detail, extrusion for constant sections, blow moulding for containers. The crossovers move with part size, because tooling cost scales with size much faster than part cost does.
The material follows the process
Thermoplastics can be melted and reformed, so they suit injection, extrusion, blow and thermoforming. Thermosets cure irreversibly, so they suit compression moulding, casting and reaction injection moulding. Elastomers split across both. A material chosen without reference to the process is a material that may not be processable that way at all.
Where the industry sits
The US plastics products sector is large enough that almost any process is available within reasonable distance, and the Census Bureau's business patterns data records the establishment counts by class. What varies regionally is not whether a process exists but how many suppliers of it are close enough to visit, which matters more than most buyers expect on a first tool.
Questions people ask about plastics manufacturing
Which plastics process should I use?
Start from shape and volume. Constant cross section means extrusion, hollow containers mean blow moulding, detailed parts in volume mean injection moulding, large panels mean thermoforming.
Can any plastic be used in any process?
No. Thermoplastics can be remelted and suit injection, extrusion and thermoforming. Thermosets cure irreversibly and suit compression moulding and casting.
At what volume does injection moulding win?
It depends on part size and the alternative, but the crossover against casting or machining commonly sits in the hundreds for small parts.
How do I find a supplier for an unusual process?
Start from the process rather than the geography. Specialist processes cluster, and being further from the supplier matters less than their having done your kind of part before.