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Methods to reduce welding deformation and control.

1. Causes and types of welding deformation
The causes of welding deformation are:
Welding deformation refers to the deformation produced during welding and after welding.
During welding, the molten metal and thermal expansion of the parent material near the joint area produce plastic deformation. When solidification, the weld and the near seam zone metal shrink. Thus the longitudinal and transverse internal stresses are produced, and the internal stress is tensile stress. The weld is contracted longitudinally and horizontally, resulting in deformation of welds. Because the thermal expansion and contraction are inevitable during welding, the deformation caused by welding is inevitable. We can only control but can not completely eliminate welding distortion.
The harm of welding deformation:
1. influence the precision and function of welding parts.
2. reduce the quality of the assembly and even make the product discarded.
3. reduce the bearing capacity of the structure;
4. influence the beauty of welding parts.
5. progress makes the cost.
Types of welding deformation:
Types of welding deformation: 1. transverse contraction; 2. longitudinal contraction; 3. rotation deformation; 4. transverse bending deformation (angular deformation); 5. longitudinal bending deformation; 6. distortion; 7. wave deformation (unstable deformation).
1. lateral contraction
Transverse shrinkage refers to the deformation of the length of the weld line in the right direction.
The shrinkage will vary with the thickness of the groove, the form of the groove and the gap of the root.
The influence factors of transverse shrinkage deformation:
(1) relating to heat input: transverse shrinkage deformation increases with the increase of welding heat input.
(2) related to clearance: assembly clearance increased and transverse contraction increased.
(3) related to welding length: the transverse contraction of the weld is small to large from the direction of welding, and gradually increases to a certain extent.
(4) related to the degree of restraint: the longer the location weld, the smaller the transverse shrinkage deformation.
(5) related to the amount of metal filler: the transverse shrinkage of butt joint increases with the increase of weld metal volume.
(6) relating to weld form: the transverse contraction of fillet weld is much smaller than that of butt weld.
2. longitudinal contraction
Longitudinal shrinkage deformation: shortening the dimension along the axis of the weld.
The influence factors of longitudinal shrinkage deformation:
(1) relating to cross-sectional area: the larger the cross-sectional area of the weldment is, the smaller the longitudinal shrinkage of the weldment is.
(2) length: the longer the length of the weld, the greater the longitudinal shrinkage of the weldment.
(3) is related to the welding level: the compression plastic deformation of each weld is smaller than that of single layer welding.
(4) temperature dependent: the original temperature of the weldment is improved, and the longitudinal shrinkage after welding is increased.
(5) related to material properties: the material with large linear expansion coefficient has large longitudinal shrinkage after welding.
3. rotation deformation
Rotational deformation refers to the deformation of the groove widening or narrowing of the welding department which is not being carried out during the welding process.
Through strong and firm positioning, rotation deformation can be effectively prevented.
Automatic welding in artificial welding
4. transverse bending deformation (angular deformation)
Transverse bending is usually called angular deformation. It is due to the difference between the amount of deposited surface and back surface and the temperature change in the direction of thickness.
The influence factors of angular deformation:
(1) related to plate thickness: when the heat input is constant, the greater the plate thickness, the greater the angular deformation.
(2) related to heat input: the thickness of the plate is certain, the heat input increases, and the angular deformation increases.
(3) related to groove form: the welding seam of the butt joint groove cross section is erroneous, the angle distortion is large, the larger the groove angle, the greater the angular deformation.
(4) related to welding sequence: welding sequence also affects the size of angular deformation.
5. longitudinal bending deformation
The longitudinal bending deformation refers to the deflection caused by the weld deviating from the central line (central axis) of the cross section during the surfacing or corner welding.
6. distortion
For beam structure or slender member, due to welding sequence, welding direction or assembly reason, the welded section inclines to different directions to cause distortion of the member.
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