I have sub pannel for my two welders 30amp and 50 amp. I am basically using this as a junction box. Each welder has its own breaker. I ran 220 with a ground for this with no neutral. Will only be used for the welders. My question is should I use the bonding screw to bond the pannel to ground or just leave it floating.

First major question, is the sub-panel you are speaking about in the same building as the main service panel or is it in a different building?

If the sub-panel is in the same building, then you can use the existing grounding system at the main panel a do not "Bond the Sub-Panel". Sub -panels should be fed by a four conductor cable. Two hots, Neutral and ground.

If the sub-panel is in a separate unattached building, then the code is more specific.

You are required to run a four wire feed from the Main Service Panel to the Sub-panel. 2 Hots, Neutral and ground. The sub-panel is required ti use its own grounding system made up of one or two ground rods no closer that six feet from each other.

Also, you cannot bond the Neutral and Ground together in a sub-panel. Neutral must be isolated from Ground.

If the sub-panel has more than 6 breakers you need to protect the garage/shop by using a "Kill Switch" to kill power to the sub-panel or a main circuit breaker on the sub panel.