Welding and fabrication: design rules
Joining metal parts by fusion; used for frames, enclosures and structures.
Typical tolerance
Weld distortion is the main issue; machine critical surfaces after welding.
Files to send
STEP or DXF plus a drawing with weld symbols, weld sizes and the applicable code.
Common materials
Carbon steel, stainless steel, aluminium; keep stainless and carbon-steel tooling separate to avoid contamination.
The rules, with reasons
- Specify the weld. Mark weld type and size with standard weld symbols and name the code (for example AWS D1.1 for structural steel, EN 1090 in Europe). Why: Without a spec the shop chooses, and inspectors cannot check.
- Distortion. Machine critical faces after welding and ask the shop about fixtures and sequence. Why: Heat shrinks and bends the part.
- Access. Leave room for the torch and for inspection of every joint. Why: Hidden joints cannot be welded or checked properly.
- Closed volumes. Add vent or drain holes in sealed hollow sections. Why: Trapped air expands and can blow out, and liquids from cleaning or galvanizing are trapped.
- Inspection. State the inspection level (visual, dye penetrant, magnetic particle, radiographic). Why: It decides cost and lead time.
Before you ask for a quote
- Material and thickness
- Weld code and welder qualification
- Inspection and documentation
- Finish (paint, galvanize, powder coat)
- Quantity and drawings
Common mistakes
- No weld symbols on the drawing
- Welding after finishing
- Sealed hollow sections without vent holes
- Expecting flat, tight parts without post-weld machining
Request a quote Find manufacturers
Typical rules of thumb, not a guarantee. The manufacturer's own design guidelines override them: ask for them and check your design against both before ordering.