Welding Industry Common Knowledge

Welding Industry Common Knowledge 

 Welding Classification：
⑴ Fusion welding

SMAW：Shielded metal arc welding
SAW：Submerged arc welding
TIG：Tungsten Inert-Gas arc welding
MIG：metal Inert-gas arc welding
⑵ Pressure welding

Cold welding

Friction welding

Diffusion welding

Explosive welding
⑶ Soldering/Brazing
such as: resistance brazing; torch brazing/ soldering
Other common welding: hot pressure welding; electroslag welding; electron beam welding, resistance welding; spot weld

Welded joint
1. Joint Type：Butt joint; Lap joint；Filit weld; T-joint/Tee joint；
(Butt joint is the most used one)
2. The joint whose welding surfaces of both welding parts are parallel is called butt joint.
(1) Butt joint without groove
1) Welding of thin steel sheets
If the product doesn’t need full penetration of welding, we can take single-side welding, and must make sure that the calculating thickness is more than or equal to 0.7δ(δ is the thickness of steel sheets) , If full penetration of welding needed, we can use carbon arc gouging to back chipping at the back of weld, after which welding can be taken, than the double-faced welding butt joint without groove is formed.
2) Welding of thick steel sheets
Butt joint with groove is used for thick welding parts which is needed full penetration of welding

Groove
1. Geometrical dimension of groove
(1) Groove face/surface
he surface of groove is named groove face
(2) groove face angle and  groove angle
The angle between the vertical surface of the welding part and the groove is called groove face angle.
The angle between the two groove faces is called groove face.
(3) Root opening/clearance
The clearance obligated for joint before welding is called root opening , whose function is to keep the root can be full penetration welded when backing weld is welded.
(4) When groove is made,the face without groove along the welding part direction is called root face

(5) The radius at the bottom of the J-groove or V-groove is called root radius.
(6) Groove type：
For the different of groove shape, we can classify the groove mainly into I-groove (without groove), v-groove, X-groove, U-groove.
V-groove is the most used one, which is easy to machine and no turn is needed, but distortion is easy to form
(7)  Groove Processing
Common Ways：oxygen cutting，carbon arc gouging， planing,    turning
oxygen cutting：The most used one, including manual, semi-automatic and automatic option
Weld
1. Classification：butt weld, fillet weld,plug weld，edge weld
2. Shape & Diameters

2.1  weld dimension:The dimension of weld is defined by a series of geometrical dimensions.
⑴  weld width
⑵  weld reinforcement
⑶  depth of penetration
⑷  weld depth
⑸ The shape an dimension of fillet joint
① weld calculating height
② weld convexity
③ The coefficient of weld moulding

The affection of welding procedure parameter to weld formation
Welding procedure parameter：The floorboard of all physical terms(as welding current,arc voltage,welding speed, energy definitions and so on)which are selected to assure the welding quality when welding is taken is called welding procedure parameter
1、 Welding current:When the other conditions don’t change, if the weld current is added,both the weld depth and weld reinforcement will increase, the weld width almost will not change. The reasons are:
⑴  When the welding current is added, the quality of heat of the arc will increase, so both the volume of molten puddle and the depth of arc crater will all increase, and the weld depth will increase when the weld is cooling.
⑵ When the welding current is added, the fusion quality of welding stick will increase, so the weld reinforcement also will increase.
⑵ When the welding current is added, on the one hand,the section of arc will more or less increase, so the fusion width will increase; on the other hand, the depth of arc crater will increase. For the welding voltage doesn’t change, so the arc length also will not change, and the arc will penetrate into the molten puddle, which will make the swing range small,so the fusion width will decrease. By the both effect, the fusion width is almost not changed practically.
2、 Arc voltage: :When the other conditions don’t change, the arc voltage is added, The width of the weld is significantly increased while the weld and reinforcement will be slightly reduced This is because an increase in the arc voltage means an increase in the length of the arc, so the arc swing range is expanded and the weld width increases. At the same time, after the arc grows, the heat loss of the arc increases, so the heat used to melt the base material and the welding wire is reduced, and the relative weld width and excess height are slightly reduced.

3、 Welding speed
The welding speed has a significant effect on the thickness and width of the weld. When the welding speed increases, the thickness and width of the weld are greatly reduced. This is because when the welding speed increases, the heat input per unit time in the weld decreases.

4、 Other elements
① electrode diameter and welding stick outside elongation
② electrode (stick) obliquity
③ welding parts obliquity
④ groove shape
⑤ elements of protective gas
⑥ welding flux
⑦ elements of basic material

Welding arc
Arc is phenomenon of electric conductivity in the atmosphere, the fierce and permanent phenomenon of electricity discharge is called arc.
1、arc generation technique
⑴ arc generation technique of short circuit contaction
⑵ arc generation technique of high voltage pulse
2、the constitution of welding arc
⑴ anode area
⑵ cathode area
⑶ arc pole area

Welding Inner Stress & Deformation

1、Inner stress：Inner stress is the stress which balances the object interior without exterior stress.
2、 Deformation: The shape and size of an object changes under the influence of certain external conditions.

Deformation is divided into free deformation, visual deformation and inner deformation.
3、 Classification of welding residual deformatio

⑴ Longitudinal contraction deformation：The component contracts in the weld direction after welding.
⑵ Transverse/cross/lateral contraction deformation：The component contracts in the upright direction of weld after welding.
⑶ Bending deformation：The component bends in one side after welding.
⑷ Others
① angular deformation
② wave-like deformation
③ mismatching deformation
④ deflection deformation

The reasons of welding residual deformation

1、 Welding position: If the welding seam is symmetrically arranged in the structure and the welding sequence is reasonable, longitudinal shrinkage and transverse shrinkage deformation will mainly occur, otherwise, bending deformation will occur.

2、 Structural rigidity: The ability of a structure to resist deformation is called rigidity. Rigid structure has less deformation after welding. The rigidity of the structure depends on the shape, size and arrangement of the cross-section of the structure. The larger the cross-sectional area, the shorter the length and the greater the rigidity.

3、 Assembly—welding sequence:The configuration which had been whole assembled can decrease welding deformation for configuration rigidity had been added.
4、 Groove length and shape: If the weld is longer or the the vacuum of groove is larger, the welding deformation will be larger.
5、 Welding energy definition: If the Welding energy definition is larger ,the welding deformation will be larger too.

The measures of control welding residual deformation.
1、 Design measure: The right design scheme is the basical measure to control the deformation.
⑴ Choosing the reasonable weld dimension: The defornation will be increased when weld dimension is added;but if the weld dimension is too small, it will decrease reduce the load ability of weld and quicken the cooling speed of joint.
⑵ Decrease the weld number as possible: Choosing the right thickness of steel plate can reduce the rectification amount after welding
⑶ Arrange the weld position reasonably:
⑷ Remain the contraction in advance.
⑸ Remain the position of welding clamp in advance.
Measures to control welding residual deformation

4、 Procedure measure
⑴ Selecting the right assembly—welding sequence.
Different assembly-welding sequence will produce different residual deformation after welding. Generally, it is firstly point-fixed, and then symmetrical welding.

⑵ Selecting the right welding sequence.
① Take symmetrical welding.
② When the weld is not symmetrical, we should weld the side which has less weld.
③ Selecting the right welding direction.
Take welding from middle to both ends step by step may have the least deformation, or take welding from one section to another step by step may also reduce the deformation.
④ anti-deformation
⑤ rigidity fixed method
⑥ Selecting the right welding energy definition

Correction method of residual deformation after welding

1、Machine rectification: Machine rectification is using machine power to rectify deformation, which can be taken by hand hammering or machine pressure.
2、Flame heating correction method: The flame heating correction method uses the plastic deformation generated when the flame is locally heated, so that the longer metal shrinks after cooling to achieve the purpose of correction. The flame adopts oxygen-acetylene flame or other combustible gas flame. This method has simple equipment and easy operation, but it is more difficult.