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A Brief Analysis of Common Problems and Countermeasures in Gas-Shielded Welding
Release time:
2018-05-03
With the continuous improvement of welding technology in Chinese enterprises, gas-shielded welding processes have been steadily developing thanks to their advantages such as high quality, efficiency, energy savings, low costs, and minimal environmental pollution. In recent years, following the CO2 welding technology promotion and application exchange conferences, gas-shielded welding technology has been vigorously promoted and applied in the mechanical and metal structures industry, laying a solid foundation for the sustained, stable, and robust development of CO2 welding technology. Gas-shielded welding not only meets the demands of automation but also drives enterprise advancement and industrial upgrading, thus becoming the dominant welding method in many mechanical manufacturing and construction enterprises. However, in the...
With the continuous improvement of welding technology in Chinese enterprises, gas-shielded welding processes have been steadily developing thanks to their advantages such as high quality, efficiency, energy savings, low costs, and minimal environmental pollution. In recent years, following the CO2 welding technology promotion and application exchange conferences, gas-shielded welding technology has been vigorously promoted and applied in the mechanical and metal structures industry, laying a solid foundation for the sustained, stable, and robust development of CO2 welding technology. Gas-shielded welding not only meets the demands of automation but also drives enterprise advancement and industrial upgrading, thus becoming dominant in many mechanical manufacturing and construction enterprises. However, in its development, there are still some shortcomings that hinder its further progress.
1. Welding Personnel Factors
“People are the foundation of quality.” Every manufacturing and installation process that shapes quality relies on human operators and managers. The skills, quality awareness, rigorous work ethic, and psychological state of personnel are critical factors—and also the primary causes of defects. In enterprise production, it is common to encounter issues such as an inadequate staffing of welding personnel, improper scheduling of welding tasks, and insufficient skills and qualifications among welding staff.
The staffing of welding personnel should be tailored to the size of the enterprise and the scale of the welding projects. Welding personnel should include: welding administrative staff, welding technicians, welding quality inspectors, various types of welders (including spot welders, arc welders, repair welders, etc.), welding heat treatment specialists, and necessary support staff. To address the issue of insufficient skills and qualifications among welding personnel, efforts to enhance their training should be intensified.
2 Welding Equipment Factors
If the adjustments are improper, the welding machine may experience uneven wire feed, the wire-feed motor stopping altogether, the motor running without feeding the wire, uneven shielding gas flow, arc pits occurring during changes in welding parameters, the welding wire curling or knotting at the wire-feed rollers and the hose inlet, misalignment of the welding current, and other issues that fail to meet the specified requirements. Specifically:
2.1 Uneven wire feed
The causes are as follows: improper adjustment of the wire feed roller pressure, wear on the V-shaped groove of the wire feed roller, malfunction of the gearbox, loose power plug for the wire feed roller motor, poor contact in the welding gun switch or control circuit, looseness or blockage at the wire feed hose connector or inside the inner spring tube, improper winding of the welding wire—sometimes loose, sometimes tight, or bent—poor contact in the conductive parts of the welding gun, and an inappropriate diameter of the conductive nozzle hole.
Specific countermeasures: Adjust the wire feed roller pressure, replace the roller with a new one, inspect, tighten, repair, or replace an entire spool, or rewind and straighten the welding wire.
2.2 The wire-feeding motor stops running, or the motor runs but no wire is fed.
The causes are as follows: motor failure itself (including carbon brush wear), damage to the motor’s power transformer, blown fuse, slipping wire-feed roller, burned-out relay contacts or coil, welding wire and conductive nozzle fused together, poor contact in the welding gun switch or open circuit in the controller wiring, damaged control buttons, welding wire coil kinked and stuck in the wire-inlet tube, malfunction in the speed-control circuit, breakdown of silicon components, damage to the control transformer resulting in poor contact or open circuit, and poor contact in the potentiometer or breakdown of transistors and thyristors.
Specific countermeasures: Inspect or replace carbon brushes, fuse links, adjust the clamping force of the wire-feed roller presser, replace the conductive nozzle, replace switches, or inspect and repair the control circuit.
2.3 Uneven gas flow causes porosity.
The causes are as follows: gas blockage or leakage at connections, insufficient gas pressure inside the cylinder—or even a completely empty cylinder—malfunction of the solenoid gas valve, blockage of the nozzle’s internal orifice, failure to power on the preheater, inadequate gas flow rate, oil contamination on the workpiece, and strong air convection in the working area.
Specific countermeasures: Inspect the gas lines and tighten the connections; replace the cylinder with a new one; perform maintenance and repairs; clean the nozzle; inspect and repair the preheater circuit; increase the gas flow rate; clean the workpiece areas to be welded; install wind shields or other measures to block the wind.
2.4 Changes in welding parameters cause unstable arc during the welding process.
The causes are as follows: wear of the wire feed roller; improper welding parameters; severe wear of the contact tip; excessively large bending angle of the welding wire; contamination on the workpiece and welding wire; and poor electrical contact.
Specific countermeasures: Replace or adjust welding parameters; inspect and service the wire feed rollers; replace the contact tip; straighten the welding wire; clean the welding wire and the area to be welded.
2.5 The welding wire becomes curled and knotted at the feed roller and the hose inlet.
The causes are as follows: The wire feed roller, hose connector, and wire guide connector are not aligned in a straight line; the inner bore of the contact tip is too small; the contact tip is stuck to the welding wire; the wire feed roller pressure is too high; the welding wire is deformed; the inner bore of the wire feed roller is too small and blocked; or the distance between the wire feed roller and the inlet of the hose connector is too great.
Specific countermeasures: Straighten the component; replace the conductive nozzle; adjust the pressure; clean or replace the hose; shorten the distance between the two components.
2.6 Welding Current and Voltage Imbalance
The causes are as follows: failure of the wire-feeding motor or its wiring; fault in the welding circuit; fault in the thyristor speed-control circuit.
Specific measures: Replace the appropriate conductive nozzle; tighten the connectors; inspect the motor and power supply system; tighten the connections; tighten the nuts.
3 Welding Process Factors
3.1 The issues arising and their specific manifestations are as follows:
Lack of operational proficiency and unclear standards—such as not fully understanding the specific dimensions of fillet welds and the hazards of excessive weld height—can lead to issues like excessively high fillet weld dimensions and poor weld appearance. Excessively high gas flow rates will accelerate oxidation reactions in the weld, causing significant burn-off of carbon, manganese, and silicon elements, thereby reducing joint strength and frequently resulting in excessive undercut and numerous large arc pits. Furthermore, due to insufficient attention paid to spot welding quality and a superficial understanding of the requirements, improper welding procedures may be adopted, leading to poor quality sealing welds.
3.2 The following countermeasures are proposed in response to the above-mentioned issues:
The general principle is: strengthen training, standardize operational procedures, implement an assessment system, and combine self-inspection with mutual inspection. To address the issues of excessively high weld toe dimensions and their impact on appearance, the following standards are established: The dimensions of fillet welds shall be determined according to engineering requirements. When no specific requirements are provided by the engineering design, the thickness of the thinner workpiece shall prevail. Excessively high welds can lead to stress concentration, increased deformation, wastage of welding materials, and longer welding times. To tackle a series of problems caused by excessive current, appropriate welding operation instructions and welding process cards shall be developed based on relevant standards and welding procedure qualification results, clearly specifying the allowable ranges for welding current and welding voltage. Welding joints should be minimized as much as possible; where unavoidable, effective protection measures must be implemented at joint locations to conserve shielding gas, ensure aesthetically pleasing weld bead formation, and meet strength requirements. Moreover, before arc termination, the current should be gradually reduced, and the arc crater should be fully filled. Regarding excessive undercutting, operations must strictly adhere to the welding parameters specified in the process card, adjusting the torch angle appropriately, closely monitoring the molten pool during welding, and pausing longer on both sides of the joint. As for poor-quality sealing welds, on the one hand, sealing welds should be eliminated altogether, and the welding sequence reasonably arranged so that sealing welds can be replaced by direct transition welds or ordinary intermediate joints. On the other hand, when sealing welds are absolutely necessary, or if defects are found at sealing locations requiring repair welding, the welding current must be reduced, and short-circuit transition pulse welding techniques should be employed.
4 Material factors
Welding materials primarily refer to base metals and welding consumables. The main issues that may arise are that the chemical composition and physical properties of both the base metal and the welding consumables fail to meet the required specifications.
With regard to the common issues that frequently arise with welding materials, it is essential to strengthen quality inspections of both base metals and welding materials. Under no circumstances should even a single nonconforming material be allowed to enter the welding work area. Welding materials should be stored in a dedicated area, and their issuance should be managed and distributed by specially designated personnel.
5 Common Faults That Easily Occur During Gas-Shielded Welding
Gas-shielded welding fails to meet the specified requirements in aspects such as porosity, burn-through, slag inclusion, cracking, excessive spatter, insufficient penetration depth, and weld bead formation. Specifically:
5.1 Stomata
Due to poor gas shielding, oil, rust, and moisture on the welding wire surface, low gas purity, insufficient manganese-silicon content in the welding wire, and excessive swing amplitude and improper angle of the welding torch, numerous porosity defects have appeared. To address these porosity issues, the following countermeasures are proposed: increase the gas flow rate, take care to shield against drafts and clean the nozzle; thoroughly clean both the workpiece and the welding wire before welding; ensure that the purity of the welding gas exceeds 99.5%, with CO2 and Ar gases each exceeding 99.95%; select appropriate welding wires; and provide training to improve operational skills and adjust the welding torch angle accordingly.
5.2 Burn-through
Burn-through occurred due to excessive root gap in the bevel, insufficient root face, excessively slow welding speed, and excessive current. To address this issue, the following countermeasures are proposed: adjust the current according to the process specifications; machine the bevel to increase the root face or reduce the current; and select parameters appropriately.
5.3 Slag Inclusions
Due to the failure to remove the slag from the previous weld layer, using a low current, welding at a slow speed, and applying excessive weld metal thickness; when employing the left-hand welding technique, the slag flows to the front of the molten pool; and excessive oscillation of the welding torch causes the slag to be entrained into the molten pool, resulting in slag inclusion. To address this issue, the following countermeasures are proposed: thoroughly remove the slag between layers; adjust the current and increase the welding speed; modify the operating method and angle; reduce oscillation amplitude, and perform multi-pass, multi-layer welding.
5.4 Cracks
Due to oil, rust, and moisture on the welding wire and workpiece, the weld penetration is excessive, resulting in significant residual stresses in the welded component after welding. In multi-layer welding, the first weld pass is too narrow, and the CO2 gas contains excessive moisture, leading to cracking. To address these issues, the following countermeasures are proposed: clean the workpiece thoroughly; select welding parameters appropriately; adopt a reasonable welding sequence; relieve residual stresses; improve the quality of the first weld pass; and dehydrate and dry the CO2 gas.
5.5 Large Splash
Due to excessive or insufficient inductance during short-circuit transfer, arc oscillation during welding, inadequate cleaning of the welding wire and workpiece, and significant spatter generation—addressing these issues involves adjusting the inductance, replacing the contact tip, and thoroughly cleaning both the workpiece and the welding wire.
5.6 Insufficient Penetration Depth
Insufficient penetration occurs due to reasons such as too low welding current, excessive wire extension length, uneven wire feeding, excessively high welding speed, insufficient bevel angle and root gap, and excessive root face. To address this issue, the following countermeasures are proposed: increase the welding current; adjust the wire extension length; inspect the wire feeding mechanism; slow down the welding speed; and adjust the bevel dimensions.
6 Conclusion
To ensure welding quality, it is essential to strictly control the five key aspects of welding operations: personnel, equipment, materials, methods, and environment. From welding supervisors and welding technicians down to welding operators, everyone must rigorously scrutinize each of these aspects and never overlook any factor that could potentially lead to welding defects. Welding supervisors and technicians should integrate standards with practical realities, establishing reasonable management systems and welding operation documents. Welding operators, meanwhile, should conduct thorough self-inspections and mutual inspections, exercising self-control over quality to ensure that welded products meet the specified requirements.
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