Working with Sterling Silver still frustrates the average person to no end from having to pull soft delicate stones for a simple sizing, to having to deal with heavily-plated silver the torch burns off. Then you have to re-plate, risking rhodium contamination or chipping or breaking the stone while re-setting, It is all too time consuming for what is typically charged.
Using your laser can be the trick for this troubled but popular metal. First cut or prep metal, then re-align the pieces. Then use 3M Scotch Brite wheel or Radial Bristle Brush to remove the shine from the desired welding area. (Using a marker to darken the area can work, but it does not consistent draw the energy into the metal as a roughed up surface will). Parameters on your Rofin laser, depending on thickness of metal, should range from 280-300V, 4.5ms, focus 8-18 (very narrow focus can create a hole straight through the metal). While preparing the piece, if the metal seems spongy or overly porous, use a ramp-down pulse shape. This will allow the metal to cool more slowly and form a greater bond. When filling in the seam with wire, using sterling weld hard wire instead of 925 Sterling. As the 925 Sterling is very reflective, you would have to use higher and higher voltage to flow the metal. This leads to pitting and cracking the piece. The slightly lower silver content of the silver weld hard will flow at lower voltage and with less splashing. Polishing should leave your sterling ring nearly seamless.
With sterling, like costume jewelry, always start with a test shot at a lower voltage and work up from there. This may take an extra two or three seconds of time but finding the exact temperature for each piece will make stronger joints in the long run.
Welding plated rings should not be a problem. Because the heat is isolated, you will not burn off the plating. After finishing your weld, sand and prep the seam as normal. But when polishing, only use red rouge to prevent removing any other plating. This should leave you with only a small area to pen plate at the end.