How do you quickly find laser beam focus? The first step is to establish the z distance for the position of focus, and the fastest way to do that is to make a series of spot welds in the z axis, through the focus, using thin shim stock, and then visually observing the level of penetration on the underside. Usually, 0.01-inch thick shim stock will do the trick.
Here are four simple steps you should take to use this shim method:
- Place the shim at a z distance definitely above or below the focus, and then step through in increments of 0.02-inch. Move the position of the weld on the shim so that each spot is on a new part of the shim.
- Once that is done, assess the rear weld width on the underside of the shim. If all the weld widths are very similar, reduce the peak power by 15 percent and repeat step 1.
- Continue until you clearly observe a trend of non-penetrating, penetrating, then non-penetrating welds, as the shim is moved through the focus.
- Tighten the z adjustment to 0.01-inch, centering the z distance in the range close to the penetrating part of the previous test.
Once established, this procedure can serve as a quick verification test that the laser and optics are OK, by re-testing using the shim and the same spot welding parameters for focus determination.
Similarly, when developing a new weld, one of the key verification methods is checking the weld cross section to establish weld penetration and general observation of weld. A quick way to do this is to select a shim thickness close to the required penetration and run testing. Although the thermal sinking may be different from the actual part, this will provide a good guide.
Just remember that this method does not replace sectioning, which should always be completed as part of qualifying the weld.