In the process of welding, uneven heating makes the temperature of the weld and its vicinity very high, while most of the metal in the distance is not heated, and its temperature is still indoor. In this way, the unheated cold metal part will hinder the expansion and contraction of the metal in the weld and near-seam area; Therefore, after cooling, the weld produces different degrees of shrinkage and internal stress (longitudinal and transverse), causing various deformations of the welded structure. The volume change caused by the transformation of grain structure in metal may also cause the deformation of weldment. This is the root cause of welding stress and deformation.
2. Reason:
(1) Too many welding layers.
(2) Improper welding sequence.
(3) Inadequate construction preparation.
(4) The substrate is cooled too fast.
(5) The parent metal is overheated. (thin plate)
(6) Improper weld design.
(7) Too much welding metal.
(8) the way of restraint is not true.
3. Solution:
(1) Use covered electrode with larger diameter and larger current.
(2) Correct the welding sequence
(3) Before welding, fix the weldment with a fixture to avoid warping.
(4) Avoid cooling too fast or preheating the parent material.
(5) Choose welding materials with low penetration.
(6) Reduce the gap between welds and the degree of grooving.
(7) Pay attention to the welding size, so as not to make the weld bead too large.
(8) Pay attention to the fixed measures to prevent deformation.