For the right applications laser welding has many advantages over other joining processes. One advantage is that very narrow welds can be made due to the small focused laser spot size. However, this advantage can also be a disadvantage. Small focused laser spot size requires great part fit-up. If the gap or space between two parts to be laser welded is too big, the laser beam will pass down the center and possibly not melt either side. Below is a video that shows a pulsed Nd:YAG laser weld with a focused spot size of about 0.008-inch being used to weld two pieces of 0.004-inch thick stainless. The welding starts out successful. The weld can actually be seen pulling the stainless pieces together ahead of the weld. However, a large gap between the two pieces near the end of the video prevents a weld from forming. A rough rule-of-thumb is that the allowable gap between the parts for laser welding should not exceed 10% the thickness of the thinnest component. Parts and tooling must be designed and built to reduce the gap.
Click on the image to see a video of pulsed Nd:YAG welding a butt joint of stainless steel that has an excessive gap. The weld cannot be made with this excessive gap.