Welding is an industrial process.
Any process where two separate parts penetrate into each other and forming bond that is as strong as surrounding material is welding. It is a common misconception by many people that welding is a process that requires heat or electric arc. In reality, heat is a secondary product or some time it is something that can aid welding.
Chemical or solvent welding.
The chemical solvent that is used for joining plastic pipes and various components like elbows, t – pieces and flanges together is designed not to stick to the pipe but to melt pipe and neighboring object so when you join them together their surfaced are welded.
Here is a video that shows this process in details.
Cold welding process.
Cold welding is the other welding process that does not require any heat and can be performed in the vacuum of space.
Live Biological Tisue welding.
The technology was invented and developed at the internationally renowned E.O. Paton Institute of Electric Welding, National Academy of Sciences of Ukraine at Kiev, Ukraine, headed by Professor B.E. Paton.
Surgeons at 10 Ukraine hospitals and clinics are using the tissue welding/bonding technology in clinical trials. They have completed more than 5,000 human surgeries using more than 70 types of open and laparoscopic surgical procedures and demonstrated that the technology is universal in its ability to repair soft biological tissue. The procedure involves little or no scarring while restoring the normal function of the body organ or tissue.