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