What parameter is critical for ensuring good fusion in a weld?

Heat input is a critical parameter for ensuring good fusion in a weld because it directly influences the melting of base materials and the filler metal at the joint interface. Adequate heat input ensures that the base materials reach their melting point properly and blend together, forming sound welds with good penetration and strength.

If the heat input is too low, the weld may be weak and not penetrate adequately, potentially leading to incomplete fusion or defects. Conversely, excessive heat input can lead to issues such as burn-through, distortion, or excessive grain growth in the heat-affected zone. Achieving the correct heat input is essential in creating a weld that meets the required specifications for structural integrity and performance.