Final answer:
The process where filler may or may not be required, and metal materials are joined with heat and possibly solder, is welding. Forge welding is a traditional example used by blacksmiths.
Step-by-step explanation:
The process described in the question, where filler may or may not be required, is known as welding. Welding involves the joining of metal materials using heat and sometimes a filler material called solder. Various forms of energy, such as gas, electricity, or laser, can be utilized to generate the necessary heat to fuse the materials together. An example of an ancient welding technique is forge welding, which has been used by blacksmiths to join iron and steel for millennia.