The welded parts will be failed due to various reason such as to improper welding procedures, composition of filler metal and base metal, selection poor work operator are some causes of weld joint failure. The discontinuities can be serving as weld failure of arc welding parts may be occurred.
The welding discontinuities occur in welding joint:
- Slag inclusions
- Porosity in welding process
- Grove over fill or under fill
- Incomplete fusion and penetration.
The small shapes of slag trapped inside the weld part during solidification process occur. In this cause for shielding gases are not properly during the welding and environmental contamination also contributed. Slag inclusion can be prevents by following procedure as followed
- Bead surface cleaned before the next layer deposition.
- Sufficient shield gases are provided
- Joint design properly.
porosity in welding process:
During the welding process the absorption of gases and chemical reaction to occur porosity or pores or fine holes in the weld metal. The metal susceptible to porosity can dissolve more quantity of gas in molten welding. The most of gas rejected during the solidification. Aluminum alloy to create more porosity than any other material. Cooling of welding metal affect by the volume of porosity.
what causes porosity in welding during machining:
The major sources of weld metal such as paints, rust, moisture, oils, hydrogen and oxygen and their chemical reaction.
The porosity in welding can be prevented as follow:
- Weld speed reduced to allow escape gas.
- Welding codes are followed properly
- To allow standard of work man ship
- Improve welding technology such as weld area are preheated and input heat increases.
Incomplete fusion and lack of penetration welding:
The improper manipulation of electrode and insufficient input heat to occur incomplete fusion. It is one of common discontinuities of welding process. During welding presence of contamination on the surface also. The insufficient of weld joint depth occur to lack of penetration.
lack of penetration welding and incomplete fusion can be improved by
- Shielding gases provide in sufficiently
- During the welding speed will be reduced
- Weld design modified
- Before welding process, the weld area will be cleaned together.
- To raise the weld temperature smoothly.
crack weld provide on the surface:
In weld area the crack occurred in various location and direction as result of cold cracking or hot tearing.
The shrinkage of metal during solidification process the hot tearing or hot crack provided from internal stress induced on cooling of area. In this defect will occur at more temperature in solidus of alloy hydrogen cracking or cold cracking is provide after freezes and residual stress cause cracks.
It crack weld caused by following:
- Large depth to wide ratio
- Poor ductility of weld metal expansion.
- Welding fixtures are not permit contraction of welding during cooling process.
Minimize hot crack weld as follow:
- Reduce carbon, phosphorus, sulfur and niobium in minimum sufficient amount.
- Tensile restraint exert reduced
- Maintain the ratio of adequate manganese to sulfur.
Under cut and under fill:
what is undercut in welding during machining process:
Sharp edged hole will be leaved on surface
The insufficient of filler metal to allow during the welding process that may result speed more welding.
residual stress in welding affect the weld strength:
The welding area expansion or contraction together from heating or cooling of metal during welding process. That caused by residual stress.
After complete weld, the thermal cycle of weld metal will be considered for residual stress which either distorts or restrains.
To minimize the distortion by using various technique in welded metal as follow by
- The welded assembly parts stress relief heat treatment
- Preheating the welding parts, that to allow reduce the thermal stress.
- Welding fixtures are restraining movement during the welding.
- Track welding process the joint of multiple point create a rigidly structure to continuous welding.
The small metal particles consider for surface of weld part are thrown and deposited around the weld bead together from filler metal.
weld spatter is avoided as follow:
- To maintain correct arc length
- Gas shield must be used
- Electrodes are used for properly
- The correct power supply according to metal thickness.