The gas selection depends upon a number of factors like laser power, beam quality, material, weld depth requirement etc. Please provide some more info.
I am basically (circular) seam welding a 430F Stainless to a 304 stainless. Power is approximately @ 900W and 40 RPM with a 1/4" radius on the part. The beam is @ 30degree from the seam.
What is the desired weld depth? Helium is generally best for plasma suppression but it is expensive. One of the main sources of the spatter is the beginning of the weld. Do you ramp in and out the power? Ramping helps to reduce the spatter and get a smooth beginning of the weld. Is the work-piece already moving when the beam comes to it? Do you have cross-jets to protect your focussing optics? Are you contrained to have an angle of 30° between the beam and the part? This may mean that your cover gas does not cover the weld in an optimal way. Consider and additional cover gas feed close to the weld.
thanks for replying.
The piece is not constrained to the 30 degree, from this angle the required depth is 0.014". As for the cross jet, there is one across the lens and it is the only gas flow. The workpiece starts to move before the beam reach and is ramped up to the set power then ramped down. Can a Nitrogen flow directed on the weld region help?
Sure. Blowing some nitrogen at very low pressure thro an orifice of quarter inch opening will surely help to limit the plasma, improve the weld depth and appearance both.
I suppose the cross jet that you mention is compressed air flowing across the lower surface of the lens and perpendicular to the beam direction is meant to protect the lens from back splatter.
You mention weld depth of 0.014". This looks too small. What is the thickness of the parts?
The cross jet is a transverse nitrogen flow on the beam axis through the shield cone. I did try a nitrogen flow on the weld but it did not help with spatter. As for penetration, it is two components press fit together then butt welded @ a 30 degree angle. The thickness is of no concern they are small components (relative). It is the the spatter all around the welded part that I am looking for a solution to.
The cross jet, being perpendicular to the beam direction will keep the spatter away from the focussing optics but will not provide protection to the weld pool against oxidation from atmospheric air. Normally compressed air is used for cross-jet and an inert gas, also called cover gas (Helium, Nitrogen, Argon) for weld pool protection. I am still not clear the way you are bringing the cover gas to the weld area.
Are you trying to improve the weld seam appearance (spatter around the weld seam) or back spatter towards to the focussing optics?
If the weld appearance is not good (smooth and regular) may be you have too much of power. Here comes the beam quality into the picture. If the beam quality is not good, you will have to use extra power to reach the desired weld depth but at the same point the material at the surface overheats and causes spatter. Using Helium as cover gas may help, it cools the weld pool, limits the plasma and improves the weld depth. If the component is small, this becomes more tricky because the total thermal mass is low.
Hello;
That last post has a lot of useful information I can use.
I am going to try my best to describe the configuration. The cone where the laser comes out has a gas inlet orifice. At the top of the cone, is the lens facing down. This orifice is perpendicular to the beam axis. The nitrogen comes in the cone, as it may serve 2 purpose. At first, it is protecting the lens. Second, if there is enough flow it will reach the weld region.
The spatter issue is the fact that as the components are rotating, they are welded. throughout the rotation, you can see the spatter flying around and it is sticking to the wall on the inside of the part which does not meet quality standards.
Correct me on this: if the surface overheats, it will cause spatter.
It is a combination of the weld pool temperature and the cover gas conditions. Hard to tell you which one is responsible in your case without seeing the process. May be you want to play with the parameters and check whether there is any improvement.
