Joiner of metals etc by heating (6)
I believe the answer is:
'joiner of metals' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for welder that I've seen before include "metalworker", "Tradesman who fuses metal using heat", "Skilled worker who fuses metals using heat", "Joiner of metals", "One joining".)