Why are tack welds important in collision repair before performing a full MIG weld?

• A. To permanently seal the joints against water.
• B. To hold the panels in alignment, control distortion, and maintain fit-up during welding.
• C. To ensure a smooth paint finish.
• D. To remove surface contaminants.

Answer: (B)

Tack welds hold things in place while you weld, which is crucial because heat from welding can make sheet metal move, warp, or shift gaps. By placing temporary, spaced welds along the joint, you anchor the panels so their alignment and fit-up stay consistent during the full MIG weld. This helps control distortion, keeps gaps even, and ensures the panels come together the way they should when you finish the seam. After the final weld, these tacks can be removed or fully welded over and finished.

Sealing against water, removing surface contaminants, or directly ensuring a smooth paint finish aren’t the primary roles of tack welds. They’re about maintaining alignment and controlling distortion during the welding process.