Methods to reduce welding deformation and control

2019-12-20 14:02:59

I. causes and types of welding deformation


The causes of welding deformation are as follows:


Welding deformation refers to the deformation of weldment during and after welding.


During welding, the molten metal and the base metal near the seam expand and produce plastic deformation. During solidification, the weld and the metal near the seam contract. This is the longitudinal stress and the transverse stress. Make the weld longitudinal and transverse shrinkage, so that the weldment deformation. Because the heat expansionand cold contraction during welding is certain, so the deformation produced during welding is certain. We can only control but not completely eliminate welding deformation.


Hazards of welding deformation:


1. Affect the accuracy and function of weldments;


2. Reduce the assembly quality and even make the products scrapped;


3. Reduce the bearing capacity of the structure;


4. Affect the appearance of weldments;


5. Improve manufacturing cost.


Types of welding deformation:


Types of welding deformation: 1. Transverse shrinkage; 2. Longitudinal shrinkage; 3. Rotation deformation; 4. Transverse bending deformation (angular deformation); 5. Longitudinal bending deformation; 6. Distortion deformation; 7. Wave deformation (instability deformation).


1. Lateral contraction


Transverse shrinkage refers to the deformation of length reduction in the right angle direction with the welding line.


The shrinkage will vary with the thickness of the plate, the form of groove and the root gap, that is, the amount of deposit.


The influencing factors of transverse shrinkage deformation are as follows


(1) it is related to heat input: the transverse shrinkage deformation increases with the increase of welding heat input.


(2) it is related to the clearance: with the increase of assembly clearance, the transverse contraction also increases.


(3) it is related to the welding length: the transverse shrinkage of the weld increases from small to large along the welding direction, and then tends to be stable after reaching a certain degree.


(4) it is related to the degree of restraint: the longer the tack weld is, the smaller the transverse shrinkage deformation is.


(5) it is related to the amount of metal filling: the transverse shrinkage of butt joint increases with the increase of the amount of weld metal.


(6) related to the form of weld: the transverse shrinkage of fillet weld is much smaller than that of butt weld.

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2. Longitudinal contraction


Longitudinal shrinkage deformation: the reduction of dimension along the weld axis.


The influencing factors of longitudinal shrinkage deformation are as follows


(1) it is related to the cross-sectional area: the larger the cross-sectional area of the weldment, the smaller the longitudinal shrinkage of the weldment


(2) it is related to the length: the longer the weld length, the greater the longitudinal shrinkage of the weldment;


(3) it is related to the welding level: the compressive plastic deformation of each layer of welding seam is smaller than that of single layer welding.


(4) it is related to temperature: the original temperature of the weldment is improved, and the longitudinal shrinkage after welding increases.


(5) it is related to the material properties: the material with large coefficient of linear expansion has large longitudinal shrinkage after welding.


3. Rotation deformation


Rotary deformation refers to the deformation of groove widening or narrowing in the welding department during the welding process.


Rotation deformation can be effectively prevented by strong and firm positioning


Manual welding and automatic welding


4. Lateral bending deformation (angular deformation)


Transverse bending deformation is generally called angular deformation. It is due to the different amount of deposit on the surface and back and the temperature change in the direction of plate thickness during welding.


The influencing factors of angular deformation are as follows


(1) it is related to the plate thickness: when the heat input is constant, the larger the plate thickness, the greater the angular deformation.


(2) it is related to heat input: when the plate thickness is fixed, the heat input increases and the angular deformation also increases.


(3) it is related to the form of groove: if the cross-section of butt joint groove is wrongly balanced, the greater the angular deformation, the greater the angle deformation.


(4) it is related to the welding sequence: the welding sequence also affects the angular deformation.


5. Longitudinal bending deformation


Longitudinal bending deformation refers to the bending deformation caused by the weld deviating from the central line (central axis) of the cross-section during surfacing or fillet welding.


6. Distortion


For beam structures or slender members, the cross-section inclines to different directions after welding due to welding sequence, welding direction or assembly reasons, resulting in distortion of members.


This article comes from the manual welding equipment of water tank http://www.abbzs.com/


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