Designing a welded part for laser cutting

Laser cutting has changed welded fabrication: it produces precise outlines, complex shapes and internal cut-outs at a cost that depends mostly on cut length. Used well, it lets you design parts that position themselves at assembly. Fewer jigs, fewer measurements, fewer mistakes.

The principle: self-location

In conventional welded construction, you cut components to size, then position them using measurements, squares and jigs. With laser cutting, the position can be built into the geometry of the parts themselves: each component carries the features that locate it relative to the others.

The benefits are immediate:

• assembly is faster: you slot parts together instead of measuring;
• it is more reliable: a foolproofed part cannot be fitted the wrong way round;
• it is more repeatable: every unit in a batch has the same geometry;
• it paves the way for automation: a robot can place parts that slot together.

Tabs and slots

This is the basic technique. A tab is a tongue that protrudes from the edge of a plate; a slot is a cut-out in the other plate that receives it.

Sizing rules

• Cutting clearance: the slot must be slightly larger than the tab. The clearance depends on thickness, machine and material; ask your cutter for the value. Too tight and the fit has to be forced; too loose and it no longer locates anything.
• Tab length: no more than the thickness of the plate receiving it if you want a flush face. A protruding tab can serve as a weld point, but it gets in the way if a weld has to run there.
• Width: enough not to bend during handling, typically a few times the plate thickness.
• Number: two tabs per joint are often enough to fix the position; beyond that, you complicate the cutting without gaining accuracy.

Foolproofing

Make it impossible to assemble wrongly: tabs of different widths, asymmetrical spacing, or an extra tab on one side only. It costs nothing to cut, and it avoids scrapped parts.

Notches and half-depth slots

For cross members (two plates crossing each other), cut a slot to half height in each: they slot together at right angles, flush. The same principle applies to stiffeners passing through a web.

The inside corners of notches must allow for the beam radius: add small reliefs (“dog bones”) in the corners if the mating part has sharp edges.

Engraved marks

The laser can also mark without cutting: part numbers, assembly direction, position lines for a component without tabs. These engraved marks replace pencil marking-out and avoid drawing-reading errors.

Think about welding from the drawing stage

Interlocking must not compromise the weld:

• Do not put a tab under a continuous weld: it creates an irregular gap in the joint.
• Keep welds accessible: the torch must reach the joint at a correct angle. See our STEP preparation guide.
• Plan the assembly order: a component fitted last must not hide a weld that has to be made before it.
• Limit unnecessary welds: if the interlocking holds the position and the load is low, intermittent welds may be enough.

Nest to reduce cost

Cutting cost depends on the material used and the cut length. Components that nest well on the sheet, thicknesses grouped by part number and outlines without unnecessary detail reduce the bill. We go into the price factors in price of a welded part.

And for the robot?

Self-locating parts are ideal for a robotic cell: the handling arm places the components, the interlocking confirms their position, and the second arm tacks them. If your parts are already designed this way, send us the file: the online estimate reads it directly.

Key takeaways

Designing for laser cutting means transferring the know-how of the jig into the geometry of the parts. Tabs, slots, notches and engraved marks make assembly faster, more reliable and automatable, as long as you keep welding in mind from the drawing stage.