Plastic fabrication builds parts from stock sheet, rod and tube by cutting, forming, machining, welding and bonding, rather than by melting material into a tool. It needs no tooling at all, which makes it the right answer for one part, for a large part, and for anything that would never justify a mould.
What a fabricator actually does
Cuts sheet on a saw, router or laser. Line bends acrylic and polycarbonate with a strip heater. Machines features on a mill or router. Welds polypropylene, polyethylene and PVC with hot gas or extrusion welding. Bonds acrylic with solvent cement. Polishes and flame polishes edges. Most fabricators combine several of these to build tanks, guards, enclosures, display units and ducting.
Where it beats moulding
Very low quantities, because there is no tool. Very large parts, where a mould and a press would be impractical. Chemical tanks and ducting, where thick welded sheet is the normal construction. One off guards, covers and machine glazing. And anything where the design is still changing, since a modification is a new cut rather than a new tool.
The materials and their habits
Acrylic is clear, rigid, cuts and polishes beautifully and cracks if stressed or exposed to the wrong solvent. Polycarbonate is far tougher and scratches more easily. Polypropylene and polyethylene weld well and bond badly, which is why they are welded and not glued. PVC is easy to work and has its own handling requirements. Choosing the joining method starts with the material, not the drawing.
Getting a good fabricated part
Design for flat panels and simple bends where you can. Allow for the bend radius on heat formed sections. Do not put fasteners through a stressed acrylic panel without relief. Specify whether edges are sawn, machined or polished, because the difference is labour. And say what the part contacts in service, since chemical compatibility eliminates materials that otherwise look ideal.
Questions people ask about plastic fabrication
What is plastic fabrication?
Making parts from stock plastic sheet, rod and tube by cutting, forming, machining, welding and bonding, without any part specific tooling.
When is fabrication better than moulding?
At low volumes, at large sizes, and whenever the tooling cost cannot be justified. Moulding wins as soon as the volume amortises a tool.
Can all plastics be welded?
No. Polypropylene, polyethylene and PVC weld well. Acrylic is solvent bonded rather than welded. The material determines the joining method.
Why did my acrylic part crack around a screw?
Acrylic is notch sensitive and stress cracks. Clearance holes, no direct clamping load and avoiding solvent contact near stressed areas all help.