DEPENDING on the rate of heat input. A process with low rates of heat input will result in a large HAZ.The size of HAZ also increases as the speed of the welding process decreases. \({\rm{Size\;of\;HAZ}}\; \propto \frac{1}{{speed\;of\;welding}}\)So, order of welding processes in INCREASING speed isArc welding → SUBMERGED Arc welding → MIG welding → Laser Beam weldingImportant point:Butt welding: Joining of metal by its whole cross section side by side.