Tips for overcoming undercuts in manual arc welding

Undercut is a serious surface defect in welding, which will cause stress concentration, and cracks will occur when severe. He is mainly due to improper selection of welding process parameters, the operation process is not correct, and the grooves or depressions along the fusion line are generated on the base metal. Therefore, it is difficult to overcome in the operation, the welder is required to pay strict attention to the welding process parameters in the welding operation, and can better observe the melting condition of the molten pool, to ensure sufficient swinging time of the welding rod, and to have higher requirements on the welder's operation skill. Based on years of experience in teaching and welder training, we will introduce some tips for preventing undercut in electrode arc welding operations.

First, groove processing

1, common problems:

In butt welding, whether it is a V-shaped groove, a U-shaped groove or an X-shaped groove, these groove edges will form a sharp edge on the groove and the surface of the workpiece during processing. The side is the reference for the stay, which is used to ensure the straightness of the weld. At the beginning of the test, when the electrode is swung to this position, the sharp edge will melt quickly, and the molten metal will not fill the base material very quickly. Defects, if the metal and slag in the molten pool cannot be distinguished, the residence time of the electrode here cannot be guaranteed, and the undercut is bound to occur. If the residence time on both sides is too long, the weld seam is too high, and the temperature difference between the two sides is large due to the stay of the welding rod on both sides, and the welding wave on the surface of the weld is coarse, which affects the appearance quality.

2. Solution:

A 1×450 chamfer can be grounded at the edge of the edge by a sander to form a “buffering”, which can slow down the melting speed at the end of the groove and avoid undercutting. The residence time of the welding rod on both sides of the weld seam solves the problem that the temperature difference is too large due to excessive residence time and the welding wave is rough.

Second, the electrode swing and the angle of the transport bar

1, common problems:

(1) The choice of the position of the welding rod on both sides of the welding rod has a great influence on overcoming the undercut of the weld seam. If the welding rod stays at the edge of the groove, the base metal of the groove edge is sharp and easy to form the undercut; If it stays on the base metal outside the groove, it can be thickened accordingly due to the melting of the base metal, so that the melting speed of the base metal and the electrode metal is basically the same, which reduces the possibility of undercut, but it cannot be controlled. The width of the weld seam causes the width and width of the weld to exceed the standard, which affects the appearance and quality of the weld.

(2) For many beginners, when the welding rod is swung, the arc of the welding rod and the angle of the welding rod cannot be correctly judged. Therefore, it is easy to swing the hand and the wrist together during the swinging process, so that the arc of the welding rod is easily blown out to one side. The weld metal is high on one side and low on one side, and the undercut is easy to form undercut. The formation of the weld is also ugly and the quality is poor.

2. Solution:

(1) Allow the electrode to briefly stay at the edge of the groove when it swings, then swing to the edge of the other side to make a short stop, then continue to swing forward, and swing to the edge of the other side to make a stop. The weld pool of the weld is the same as the outer width of the previous weld pool, and at the same time, it should cover about three-quarters of the previous weld pool to ensure the fineness of the welding wave. At the same time, the electrode metal has been kept in a molten high temperature state, and the base metal has a corresponding cooling time, and the temperature is low, and the molten electrode metal can quickly fill the original undercut, which can effectively solve the undercut problem. . At the same time, when the welding rod stays on both sides of the weld, the straight edge of the groove is used as the reference to ensure the straightness of the weld; since the residence time of the electrode on both sides becomes shorter, the temperature difference between the two sides of the weld is not large, and the weld can be made The corrugations are fine and the appearance is well formed.

(2) When the welding rod swings, the welding rod should form a projection relationship with the welding seam to ensure that the welding rod is always in the center of the welding seam. When swinging, only the wrist swings, and the hand cannot swing. The arc is from the center of the weld to the sides. Blow out to prevent the base metal from flowing to the center of the weld to form a undercut.