one way would be to use two SingleProcs, one for the assembly and one for the welding.
You can give the assembly an entry control which sets the entrance to locked and you can reopen it in the exit control for welding. This way you avoid that a new part is assembled while the real station is still in the process of welding.
The exit control for welding should be rear triggered, so you make sure that the part already has left the welding station. (And because it already has left don't use @.move to move the part.)
You could split the work in two sub-cycles and change the service list of the machine after each sub-cycle. You could move the part after the first sub-cycle back to the same machine and use the entrance control (before actions) to make the settings.
See here a sample for the sub-cycles:
freelance simulation specialist