Common flaws and causes of spot welding：

　　1.Rosin joint：

　　Misaligned electrode

　　Low welding current

　　Short welding time

　　welding over-current (Thin plate-not more than 1mm)

　　Improper water cooling of electrode

　　2.Crack at welding point：

　　Direct cause: Metallic property of plate

　　Indirect cause: short duration, high welding pressure, small area of electrode head, long time of use of electrode

　　3.Piercing at welding point：

　　Direct cause: short duration, high welding current, low welding pressure, dirt attached to plate, metallic property of plate

　　Indirect cause: Overlong welding, large area of electrode head, long time of use of electrode, excess matching gap of plate, unloading of pressure on electrode before curing at welding point, one electrode is in position while another electrode is not ready when welding current flows and builds electric arc (Causing air breakdown) and resultant torch blasting

　　4.Twisted welding point：

　　Electrode and plate out of square

　　Misaligned upper and lower electordes

　　5.Deep indentation：

　　excess welding current

　　Small electrode end

　　Improper electrode pressure

　　Other welding quality defects：

　　1.patter between plates

　　Direct cause: short pre-pressing, low welding pressure, dirt attached to plate, improper matching gap, welding point near plate edge, lagged movement of welding torch, welding not at right angle

　　Indirect cause: high welding current, misaligned electrode, metallic property of plate, small area or rough surface of electrode end, high temperature rise of electrode due to consecutive spot welding

　　2.Spatter on plate surface (Electrode binding)：

　　Direct cause: short pre-pressing, overlong welding, short duration, low welding pressure, unsmooth cooling, dirt attached to plate, improper matching gap, lagged movement of welding torch, not welding at right angle, overlong use of electrode

　　Indirect cause: high welding current, misaligned electrode, metallic property of plate, unsmooth cooling

　　3.Upsetting of electrode with mushroom head：

　　Direct cause: overlong welding, low welding pressure, high welding current, small area of electrode head, unsmooth cooling, overlong use of electrode

　　Indirect cause: dirt attached to plate, lagged movement of welding torch

　　4.Low welding intensity：

　　Direct cause: short welding time, high welding pressure, low welding current, small area of electrode head, large area of electrode head, unsmooth cooling, improper matching gap, close welding points and etc

　　Indirect cause: welding point near plate edge, metallic property of plate, not welding at right angle