Welding angle steel of steel structure attic shall be welded with flat I-beam. In the welding process of steel structure attic, if angle steel and I-beam need to be welded together, flat welding is usually needed. Flattening means that after two or more metal materials are connected together by welding, the convex part of the weld is ground flat with appropriate tools and methods to make its surface smooth. The purpose of welding leveling is to ensure the strength and flatness of welded joints and improve the stability and reliability of the whole structure. For steel attic, welding leveling can increase the bearing capacity and seismic performance of welded joints, and reduce the possibility of uneven deformation and stress concentration of the whole structure. Therefore, welding angle steel and I-beam is a common practice.