Tack Welding the simple task but not simple.

Usually, "Tack Welding" is carried out before the main welding work to temporarily assemble the parts and maintain the accurate size of the products to be welded. Many people may think that tack welding is not important at all because it will be re-welded again by main welding. Actually, tack welding bead tends to contain many welding defects such as "crater crack", "porosities", "undercut", "overlap" and so on. This is because tack welding is not treated as important task as it should be.

Let's take a look at the suitable procedure for tack welding.

1. Tack welding electrode should be the same as the one for main welding. If low hydrogen electrode is to be used for main welding, it is required for tack welding as well.
2. The diameter of tack welding electrode should be smaller than the electrode used for main welding. This is to assure enough fusion at the root.
3. In case of groove welding butt joint, tack welding bead should not be laid in the groove. However, if it can not be avoided, tack welding bead should be completely removed before main welding is performed.
4. In case of fillet welding, where the tack welding bead may not be removed before the main welding is performed, tack welding should be minimized in both sizes and numbers.
5. The position of tack welding bead should be avoided at the stress concentration points as shown in the picture.

Following the above instruction, the quality of your welding work should be leveled up and welding defects should be minimized.