First, clean off the mud from the broken thread of the self-tapping screw. Use a center punch to make a center hole in the cross-section. Then, attach a 6-8mm HSS drill bit to the electric drill and drill a hole through the center hole in the cross-section, ensuring the hole is fully penetrated. After the hole is drilled through, remove the small HSS drill bit and replace it with a 16mm HSS drill bit. Expand and drill through the hole in the broken screw again.

Select welding wire with a diameter of 3.2mm or less. Use medium to low current to perform buildup welding inside the drilled hole of the broken screw, starting from the inside out. The buildup welding should gradually cover half the length of the broken screw. During the gradual buildup welding, avoid a long arc to prevent burning through the surface of the broken screw. After welding to the top surface of the broken screw, further weld to create a cylindrical shape with a diameter of 14-16mm and a height of 8-10mm.

After the surfacing is completed, strike the end face with a hammer to create vibrations along the radial direction of the broken screw. Due to the heat generated by the initial arc welding and the subsequent cooling, combined with the current vibrations, the broken screw will loosen between the outer threads of the screw and the human body.

Upon close observation, when a small amount of rust appears at the fracture upon tapping, you can remove the M18 nut sleeve and weld it onto the topped column.

After welding, while the material is still warm, use a梅花扳手 with a soft grip to oscillate back and forth on the bolt cap. You can also alternately oscillate and gently tap the cap end with small锤, allowing the broken screw to be removed.

After removing the broken screw, use a suitable tap to rework the threads inside the frame, removing rust and other debris from the holes.

Self-tapping screws, whether for small applications in electronic devices, general ones in household appliances, or large ones used in engineering projects, construction, road bridges, transportation equipment, airports, electric vehicles, and vehicles, play a crucial role in these industries.