To weld or not to weld...

Perhaps the simplest idea is to not weld them together at all, just to electronically and mechanically jam them in between the extrusion nozzle and heater tube. If the wires only connect here electrically, then this will be the measuring point for the temperature. The thermocouples are not fragile, you just need to make sure that they only connect where you want to do your measurement. You can cut a thermocouple up into many new thermocouples if you join the ends (or jam them as I described). If you want to make thermocouples in general, or want a more stable setup, read on: