Overhead welding is welding in which the welding position is below the level, and it is also the most difficult welding among the four basic welding positions.
Since the molten pool is located under the weldment, the gravity of the molten metal of the electrode will hinder the excess of the molten droplet, and the molten pool metal will also fall under its own gravity. During overhead welding, the back of the weld is prone to dents, and the front weld bead appears with weld bead, which makes it difficult to form the weld bead.
Overhead welding is one of the most difficult welding positions to operate. During welding, the weld pool is located above the combustion arc, the welder has poor vision when welding in the upward position, and the arm holding the welding handle is from near to far (low to high), which increases the difficulty of operation.
In addition, the height of the person from the workpiece should be moderate. If the height is low, it is inconvenient to observe the weld pool. If the height is high, the arm will be raised higher and higher when welding, which will reduce the stability and increase the labor intensity.
During bottom welding, due to the gravity of the metal droplet of the electrode, it will hinder the transfer of the droplet, and the phenomenon of sticking to the electrode is easy to occur; and the molten pool is suspended under the weldment without solid metal support, and the molten metal is under the action of gravity. , easy to flow down; the molten pool only exists by relying on the surface tension and arc blowing force of the metal solution. The higher the melt pool temperature, the lower the surface tension.
Therefore, the shape and size of the molten pool are not easy to control, and defects such as slag inclusion, incomplete penetration, bottom depression, surface protrusion, and undercut are prone to occur, and it is difficult to form welds. Therefore, when operating, use short arc welding.
In overhead welding, the diameter of the electrode and the welding current should be correctly selected, and the diameter of the electrode should not exceed 4mm; the welding current is 15%-20% smaller than the flat welding current.
The larger the diameter of the electrode, the more difficult the droplet transfer of the electrode; if the welding current is large, the temperature of the molten pool will be high, the volume will increase, and the fluidity of the molten metal will increase, which will easily cause the molten pool metal to drip down, making the bottom layer of the molten hole large, The welding seam is concave, and the filling and cover surface layer is convex; if the welding current is too small, the root will not be easily penetrated, resulting in defects such as slag inclusion and poor welding seam formation.
Overhead welding operation skills
01 During overhead welding, you must pay attention to maintaining the correct operating posture. The welding point should not be directly above the person, but should be upward and forward, and the welding seam should be inclined to the right side of the operator. The electrode holding method of overhead welding is the same as that of vertical welding.
02 Use small-diameter electrodes and low-current welding. Generally, the welding current of overhead welding is between the welding current of flat welding and the welding current of vertical welding.
03 Use short arc welding to facilitate droplet transfer.
04Maintain the proper angle of the electrode and the correct way of transporting the electrode, as shown in the figure below
For butt-overhead welding without groove, the straight line should be used when the gap is small, and the reciprocating straight line should be used when the gap is large. When multi-layer welding is used for open groove butt overhead welding, the first layer of welding seam adopts a linear or linear transport method according to the size of the groove gap. The rest of the layers are in a crescent or zigzag manner. Multi-layer multi-pass welding should be carried out in a straight line.
For the T-joint with smaller welding foot size, single-layer welding is adopted, and the straight-line transport method is used. When the fillet size is large, multi-layer welding or multi-layer multi-pass welding is used. The first layer should use straight-line transport, and the other layers can adopt oblique ring or triangular transport.
05 When the temperature of the molten pool is too high, the arc can be slightly lifted to slightly lower the temperature of the molten pool.
06 When using an oblique circle, the head of the electrode should be consciously pointed to the upper plate first, so that the molten droplet first merges with the upper plate. A uniform fusion can be obtained over and over.
07A short arc welding of 0.5~1mm should be maintained when the rod is transported in a straight line. Do not drag the electrode head on the welding seam to prevent narrow and convex welding seams.
08 Keep the correct electrode angle and uniform welding speed, keep a short arc, and the upward feeding speed should be consistent with the burning speed of the electrode.
09 It is best when the surface of the molten pool seen during welding is flat or slightly concave. When the temperature is high, the surface of the molten pool will bulge or protrude. In severe cases, weld flashes will appear. The solution is to accelerate forward. The speed of the swing and the dwell time on both sides are shortened, and the welding current is reduced if necessary.
10 During multi-pass welding, in addition to carefully cleaning the slag at the bottom, do not clean the slag on the cover surface. The center of the electrode of the next welding is pointing to the edge of 1/3 or 1/2 of the previous welding seam.
11 During the preheating process of start-up welding and continuous connection, it is easy for the slag to mix with the molten metal. At this time, the angle between the electrode and the upper plate should be reduced to increase the arc blowing force, and the arc must not be extinguished. If the start of the weld is too high or has a weld flash, it should be cut off with an arc.
