Welding without jigs: is it possible?
Jigs are expensive for small batches. Tabs and slots, modular welding tables, magnetic tables, a second robot arm and 3D vision: the ways to do without them.
A welding jig has a simple job: holding the components in the right place while they are tacked and welded. In large series, it is indispensable and quickly paid back. In small batches, it becomes a problem: it has to be designed, built, set up and stored, and often remade at the slightest drawing change.
Can you do without it? Yes, as long as you replace each of its functions.
What a jig really does
A jig performs three distinct functions:
- Positioning: placing each component in the right place relative to the others.
- Holding: preventing the parts from moving during tacking.
- Restraining: limiting distortion during welding.
To weld without a dedicated jig, you need an answer to each of these three functions.
Positioning: letting the part locate itself
Tabs and slots
Laser cutting makes possible what shearing could not: precise interlocking shapes. A tab on one plate fits into a slot in the other and fixes the position without tooling. It is the most economical method, and it benefits the welder as much as the robot. We explain it in designing a welded part for laser cutting.
Modular welding tables
Tables with a grid of holes (16 or 28 mm systems) take modular stops, squares and clamps. You build a fixture for each part from standard elements, then take it apart. It is a “reusable jig”, quick to set up for an experienced welder, but it remains a manual set-up for every part number.
Holding: keeping the part still while tacking
Magnetic tables and tools
A switchable magnet (turned on and off on demand) holds a steel plate on the table or against a square without mechanical clamping. It is fast, leaves no marks on the part and is easy to automate: a robot can switch the magnet on and off.
The second robot arm
This is the most versatile solution: a robot arm picks a component, places it in its exact position and holds it while the second arm tacks it. Once a few tacks are in place, the part is rigid and the handling arm can move on to the next component. This principle, common in the automotive industry with expensive installations, is becoming accessible thanks to falling robot prices and progress in planning.
Restraining: controlling distortion
Without a rigid jig, distortion is controlled by method rather than by force:
- the tacking order: tacks spread symmetrically, placed in an order that balances shrinkage;
- the weld order: welding alternately on each side, from the centre outwards;
- sizing correctly: a smaller throat brings less heat and less shrinkage.
Tacking plays a central role here: see why tack welding determines weld quality.
And where does vision come in?
If the components arrive loose in bins, the robot needs to know where they are. A 3D camera locates each part and calculates how to grip it. Vision then replaces the precise arrangement of components, which would be another form of jig.
What it changes for the workshop
Combined, these techniques make the dedicated jig disappear:
| Function | With a jig | Without a jig |
|---|---|---|
| Positioning | jig stops | tabs and slots, robot arm |
| Holding | clamps | switchable magnet, robot arm |
| Restraining | jig rigidity | tacking and weld order |
| Changing part number | new jig | new file |
That is the principle of our robotic welding cell: a magnetic table, two arms, a 3D camera, and software that calculates the placement and tacking order from the STEP file.
Key takeaways
Welding without jigs is possible, as long as you address the three functions of a jig separately: positioning, holding, restraining. In small batches, it is often the key to making automation pay off, as we explain in why a welding robot does not pay off on small batches.