Welding defects
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This document discusses welding defects and welding processes. It describes various types of welding including arc welding, gas welding, resistance welding, thermit welding, solid state welding, and newer welding techniques. It then discusses common welding defects such as slag inclusion, undercut, porosity, incomplete fusion, overlap, underfill, spatter, excessive convexity/concavity, excessive weld reinforcement, incomplete penetration, and excessive penetration. For each defect it provides the potential causes and recommendations for prevention and repair.
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Welding defects
- 1. WELDINGWELDING DEFECTSDEFECTS International Training Centre, Butibori 9001:2008 CERTIFIED INSTITUTE
- 2. Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material. Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, boilers, general repair work and ship building. WELDING
- 3. CLASSIFICATION OF WELDING PROCESSES: (i). Arc welding • Carbon arc • Metal arc • Metal inert gas • Tungsten inert gas • Plasma arc • Submerged arc • Electro-slag (ii). Gas Welding • Oxy-acetylene • Air-acetylene • Oxy-hydrogen (iii). Resistance Welding • Butt • Spot • Seam • Projection • Percussion (iv)Thermit Welding (v)Solid State Welding • Friction • Ultrasonic • Diffusion • Explosive (vi)Newer Welding • Electron-beam • Laser (vii)Related Process • Oxy-acetylene cutting • Arc cutting • Hard facing • Brazing • Soldering
- 4. Equipments: A welding generator (D.C.) or Transformer (A.C.) Two cables one for work and one for electrode Electrode holder Electrode Protective shield Gloves Wire brush Chipping hammer Goggles
- 6. ARC WELDING Uses an electric arc to coalesce metals Arc welding is the most common method of welding metals Electricity travels from electrode to base metal to ground
- 7. 7 WELD TERMINOLOGY Joint and WeldJoint and Weld Heat Affected ZoneHeat Affected Zone
- 8. 8 TYPES OF JOINTS There are 5 types of joints …
- 9. FILLET AND GROOVE WELDS Groove and fillet welds can be made on many types of joints
- 10. TYPES OF DEFECTS Slag Inclusion Undercut Porosity Incomplete fusion Overlap Underfill Spatter Excessive Convexity Excessive Weld Reinforcement Incomplete Penetration Excessive Penetration
- 11. SLAG INCLUSION Cause:- Low amperage, improper techniques, slow travel rate Prevention:- Increase amperage, increase travel rate Repair:- Remove by grinding or other mechanical process
- 12. UNDERCUT Cause:- High amperage, wrong electrode angle, long arc length, rust Prevention:- Set machine on scrap metal to correct parameters, clean metal before welding Repair:- Weld with smaller electrode, sometimes must be low hydrogen with preheat.
- 13. POROSITY
- 14. INCOMPLETE FUSION Cause:- Low amperage, steep electrode angle, fast travel speed, short arc gap, lack of preheat, electrode too small, unclean base metal, arc off seam Prevention:- Eliminate the potential causes Repair:- Remove & reweld, being careful to completely remove the defective area.
- 15. OVERLAP Cause:- Improper welding technique, steep electrode angle, fast travel speed Prevention:- Overlap is a contour problem. Proper welding technique will prevent this problem
- 16. UNDERFILL Cause:- Improper welding techniques Prevention:- Apply proper welding techniques for the weld type & position. Use stripper beads before the cover pass. Repair:- Simply weld to fill. May require preparation by grinding.
- 17. SPATTER Cause:- High arc power, magnetic arc blow, Damp electrodes Prevention:- Reduce arc power, reduce arc length, use dry electrodes Repair:- Remove by mechanical process
- 18. EXCESSIVE CONVEXITY Cause:- Amperage & travel speed Prevention:- Observe proper parameters & techniques Repair:- Must blend smoothly into the base metal
- 19. EXCESSIVE CONCAVITY Cause:- Amperage & travel speed Prevention:- Observe proper parameters & techniques Repair:- Must blend smoothly into the base metal
- 20. EXCESSIVE WELD REINFORCEMENT Cause:- Travel speed too slow, amperage too low Prevention:- Set travel speed & amperage on scrap plate Repair:- Remove excessive reinforcement and feather the weld toes to a smooth transition to the base plate.
- 21. INCOMPLETE PENETRATION Cause:- Low amperage, low preheat, tight root opening, fast travel speed, short arc length Prevention:- Correct the contributing factors. Repair:- Back gauge and back weld