How to avoid welding defects

25 Oct 2021

What is a welding defect? In the welding production process of the welding machine,various welding defects often occur due to the structural design of the workpiece, welding parameters, improper preparation before welding, and improper operation methods. Welding defects exceeding the allowable range will directly affect product quality and safety and reliability, resulting in failure of the welding structure, and even damage accidents. The general technical regulations stipulate: cracks, lack of penetration, lack of fusion and surface slag inclusions are not allowed defects; undercut, internal slag inclusions and pores and other defects cannot exceed a certain allowable value, and excessive defects must be completely removed and Welding repair. Therefore, the purpose of welding construction can only be as far as possible to control welding defects within the allowable range. Welding defects mainly include: the surface size of the weld does not meet the requirements, undercuts, weld bumps, pits, burn through, arc scratches, incomplete penetration, incomplete fusion, pores, slag inclusions and cracks.

Let us first talk about what is the surface size of the weld that does not meet the requirements? What are the reasons and prevention methods? The surface of the weld is uneven, the width of the weld is not uniform, the size is too large or too small, and the size of the single side of the fillet weld and the weld foot do not meet the requirements, all of which are the weld surface size does not meet the requirements. The reason is that the weldment groove angle is incorrect, the assembly gap is not uniform, the welding speed is not correct or the method of transporting the strip is incorrect, the selection or change of the welding rod and the angle, and the incorrect selection of the submerged arc welding process will all cause this kind of defect. . The prevention method is to select the appropriate groove angle and assembly gap; correctly select the welding parameters, especially the welding current value; use the appropriate method and angle of the strip to ensure the uniform shape of the weld.

Then talk about what is a pore? What are the causes and preventive measures of stomata? The high temperature of the molten pool metal during the welding process is the gas that is absorbed and produced. During the cooling and solidification, the holes formed in the interior or surface of the weld metal due to failure to escape in time are called pores. The cause is that the oil, rust, and moisture on the surface of the welding wire and the base metal have oxidation in the molten pool; the protection of the welding zone is damaged; the welding material is damp and the baking is insufficient; the welding current is too large or too small, and the welding speed is too fast; In the case of low-hydrogen electrode, the polarity of the power source is wrong, the arc is too long, and the arc voltage is too high; the arc ignition method or the joint is bad. Preventive measures include improving operating skills to prevent interruption of shielding gas and flux delivery; carefully clean the base metal and welding wire surface oil, rust, etc. before welding, and properly preheat to remove moisture; strictly dry the welding material before welding, and low-hydrogen electrode must Put it in the welding rod insulation tube and take it as needed; use proper welding current, welding speed, and proper swing; when using low-hydrogen electrode, carefully check the power source polarity, and use short arc operation; use arc ignition plate or return arc Operation technology.

Then talk about what is scum? What are the causes and preventive measures of slag inclusion? The slag remaining in the weld after welding is called slag inclusion. The reason is that the welding current is too small, the welding speed is too fast, and the slag in the molten pool is too late to emerge to form point-like slag inclusions; in multi-layer welding, the slag between each layer of weld bead is not cleaned; welding groove angle Too small, poor welding bead formation; improper welding rod angle and transportation techniques, different weld widths, and too deep undercuts will cause slag inclusion. The preventive measure is to carefully remove the slag from each layer; select the appropriate welding current and welding speed to ensure that the slag in the molten pool has sufficient time to float; appropriately increase the welding groove angle, pay attention to the flow direction of the slag, and adjust the electrode angle at any time Improve the welding bead shape with the method of mixing and transporting the welding rod; select the welding rod with excellent slag removal performance.

Let's talk about what is a welding crack? What are the reasons and preventive measures for welding cracks? Under the joint action of welding stress and other brittle factors, during or after welding, the cracks that appear due to the destruction of the bonding force of the metal atoms in the local area of the welded joint are called weld cracks. Focus on welding cold cracks and lamellar tears. The cause of welding cold cracks is that the three factors of welding stress, hardened structure, and diffusive hydrogen work together to form cold cracks. The preventive measures are preheating before welding and reducing the cooling rate; selecting appropriate welding parameters; using low-hydrogen welding materials and strictly drying; thoroughly removing oil, rust and moisture in the welding area of the welding wire and base metal, and proceed immediately after welding. Heat or post-weld heat treatment; improve joint design and reduce restraint stress. Lamellar tearing is a kind of cold crack that is a stepped "platform" cracking along the rolling direction of the steel plate during welding and parallel to the surface. The reason is that there are layered inclusions along the rolling direction of the steel plate, and the welding stress perpendicular to the thickness direction is generated during welding. Preventive measures are to strictly control the sulfur content of the steel; improve the joint form and groove shape; pre-surfacing transition layer on the groove surface connected with the weld; use low-hydrogen welding materials with lower strength levels; use low welding heat input And welding preheating.

The above descriptions are the reasons and preventive measures for the formation of relatively common and typical welding defects. In addition, welding defects such as undercuts, weld bumps, pits, burn-through, arc abrasions, incomplete penetration, and incomplete fusion are all There are reasons and preventive measures. We should learn more about welding technology, lay the foundation for improving welding level, and work hard to be an excellent welder!

Keywords: welding machine

Originally published 25 Oct 2021, updated 25 Oct 2021.

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