1 welding arc welding head with groove preparation

Electrode arc welding of joints depends on the type and size of groove weld parts of the structure and thickness, the joint performance of the mechanical properties and metallurgical requirements, and construction conditions. Electrode arc welding joints are butt joints, T-joints, corner joints and lap joints four.
(1) butt joint
Butt joint is the most common form of a connector according to bevel different forms, can be divided into I-butt joints (no groove), V-shaped groove joints, U-shaped groove joint, X-shaped groove joints and double U-shaped groove joints. General thickness of 6mm or less, using non-open groove and stay in a certain space of double-sided welding; moderate thickness and large thickness of the components of the butt welding, in order to ensure penetration, must be open groove. V-shaped groove to facilitate the process, but after welding components prone to deformation; X-shaped groove weld cross-section as symmetry, the deformation of the workpiece after Types Of Welding Electrode and stress than the V-shaped groove is small, in the same conditions, thickness, X-shaped groove mouth than the V-shaped groove to reduce the 1 / 2 the amount of filler metal. U-shaped and double U-shaped groove, less the amount of weld filler metal after welding deformation is small, but the groove processing difficulties, generally used for critical structures.
(2) T-shaped connector
According weldment thickness and load conditions, T-shaped connector can be divided into not open groove, unilateral V-shaped groove and K-shaped groove in several forms. T-joint welds in most cases can only afford a smaller shear stress, or only as a non-load bearing welds, so the thickness of 30mm the following can not open groove. Required load for T-joints, in order to ensure penetration, should be based on the thickness of the workpiece, weld joint strength and deformation requirements to determine the form of the groove.
(3) corner joints
Different forms according to groove, do not open corner joints into groove, V-shaped groove, K-shaped groove and curling in several forms. Usually the thickness of 2mm below the corner joints, crimping type can be used; thickness of 2 ~ 8mm these corner joints, often do not open groove; large thickness and must penetration of the corner joints and corner joints important components should be groove, groove thickness of the workpiece according to the same form, structure and carrying case.
(4) lap joint
Less demanding on the lap joint assembly, but also easy to assemble, but the joint carrying capacity is low, generally used in important structures. Lap joint groove is divided into non-overlapping and plug welding of two types. Generally not open for lap groove below the steel plate thickness of 12mm, lap part of the length of 3 ~ 5δ (δ as the thickness)
2 electrode arc welding process parameters
Welding parameters (welding specification) is to ensure welding quality and selection of the welding parameters (welding current, arc voltage, welding speed and welding heat input, etc.) in general. Select the correct welding parameters, to improve the welding quality and productivity is very important. In the previous sections have described electrode model, type and polarity of the welding power source options, there is no longer introduction, the following describes several other welding process parameter selection.
(1) electrode diameter
Electrode diameter, according to the weldment thickness, joint type, weld position, weld-level factors such as selection. Weldment thickness greater choice of electrode diameter greater; T-shaped connector rod diameter than the butt joint of the big, standing welding, Yang flat welding and horizontal welding than when welding electrode diameter should be chosen smaller, generally the largest vertical welding electrodes diameter less than 5mm, horizontal welding, welding Yang does not exceed 4mm; multi-layer welding of the first selection of fine seam welding. The relationship between the diameter and thickness of the electrode shown in Table 2-6.
Table 2-6 electrode diameter and the thickness of the relationship between the weldment
Weldment thickness / mm 2 3 4 ~ 5 6 ~ 12 ≥ 13
Electrode diameter / mm 2 3.2 3.2 ~ 4 4 ~ 5 4 ~ 6

(2) The welding current

 
Electrode arc welding current is the most important process parameters, which directly affects the size of weld quality and weld. When the welding current is too large, more than a high increase in thickness and weld, the weld width decreases and may cause undercut, burn and other defects; when the Cast Iron Welding Electrode current is too small, narrow weld high, shallow pool, bad fusion , will produce incomplete penetration, slag and other defects. Choose the size of welding current, electrode to consider the type of electrode diameter, thickness and joint type weldment, weld position, weld-level and other factors. The most important electrode diameter, weld locations and weld the three-level factors.
â‘  welding electrode diameter, the greater the diameter, the greater the welding current.
Electrode diameter and welding current relationship

Electrode diameter / mm 1.6 2.0 2.5 3.2 4.0 5.0 6.0
Welding current / A 25 ~ 40 40 ~ 65 50 ~ 80 100 ~ 130 160 ~ 210 260 ~ 270 260 ~ 300

â‘¡ thick plate welding position or T-joints and lap joints and low temperature welding, welding current should be larger; flat welding position welding, you can choose some of the welding current is too large; horizontal and vertical welding, when welding, welding current should be smaller than the current flat position welding of 10% to 15% overhead position welding, the welding current should be smaller than the current flat position welding of 10% to 20%; fillet weld current is slightly larger than the current flat position.
â‘¢ weld bead in multi-level or multi-layer multi-pass welding of backing weld, the weld back in order to ensure the quality and ease of operation, you should use a smaller current; weld bead filled, in order to improve efficiency, the use of more large welding current; capping, in order to prevent welding defects, should be used in smaller current.
In addition, when using alkaline electrodes, the electrode of the welding current than acidic by 10 percent.
(3) the arc voltage
Mainly affects the width of the weld arc voltage, arc voltage is higher, the more the weld width, weld thickness and reduce over high, splash increased weld difficult to control. Arc voltage depends mainly on the arc length, arc length, arc voltage will be high; short arc, arc voltage is low. There are long-arc welding arc and short arc of the points, when the arc length of the electrode diameter is 0.5 to 1.0 times, as short-arc; when the arc length is greater than the electrode diameter, known as the long arc. Generally in the welding process, arc length always want to make use of consistent and short arc welding.
(4) welding speed
Electrode welding speed depends on the melting rate and the required weld size, assembly and welding gap location. When the welding speed is too slow, the weld high and wide, irregular shape, easy to produce weld defects; when the welding speed is too fast, the low narrow weld, easy to produce defects such as lack of penetration. In practice, the welder should take the specific circumstances of flexibility to ensure the weld quality and appearance of size to meet the requirements.

 
(5) Welding heat input
Welding heat input is, by the welding energy input to the energy per unit length of weld. The formula is as follows:
E = = (J / cm)
Welding line of E-type energy, J / cm;
      q-arc effective power, J / s;
      v-welding speed, cm / s;
     η-arc active power factor;
I-welding current, A;
U-welding voltage, V.
Welding heat input affects the performance and quality welds, different steel, welding lines are not the same optimal range of energy, usually through the process tests to determine the line energy range, according to wire welding parameters to determine the energy range
(6) welding layers
When welding thicker pieces, welded to the multi-layer or multi-layer multi-pass welding. Multi-layer welding, weld layer after layer of weld heat treatment of the former role of grain refinement can improve the weld joints of plastic. For a number of important due to some structure, some good welding multi-layered, each layer thickness preferably not more than 4 ~ 5mm. Experience shows that when the electrode thickness of each layer is 0.8 to 1.2 times the diameter, the welding quality is best, most productive, and easy to operate.
3 position welding arc welding
Positioning before welding is a welding weldment fixed relative position of the welding operation, commonly known as tack welding. Tacking the formation of intermittent but short of the weld seam is called positioning. The manufacturing process in welded structures, almost all the parts are first assembled by tack welding, and then welded into one, thus positioning the quality of welding seam quality will affect the product quality as a whole, should be taken seriously enough. Positioning welding should be the main consideration the following factors:
(1) tack welding electrodes
Positioning of the weld seam is generally left in welding as a formal structure, and thus positioning welding electrodes used shall be the official welding electrodes used the same model, can not use damp, peeling, unknown type of electrode or welding head instead.
(2) positioning welding parts
Clear double-sided welding negative root of the weld, the weld as possible will be arranged in the opposite orientation; shape of symmetrical components, the positioning of the weld should say arranged; avoid end welds, angle and other areas likely to cause stress concentration to locate welding, can weld the weld intersection or dramatic changes in the direction of where to locate the welding, at least to leave these places is usually 50mm.
(3) positioning the weld size
Generally based on the thickness of the weldment to determine the positioning of the weld length, height and spacing. As shown in Table 2-8.
   Reference Table 2-8 Positioning the weld size unit: mm

Weldment thickness of the seam height positioning positioning positioning of the weld seam length of the pitch
<4 <4 5 10 50 100
4 ~ 123 ~ 610 ~ 20 100 ~ 200
> 12> 615 30 200 300

(4) positioning welding process requirements
â‘  positioning weld short, cooling speed, and thus the welding current should be larger than the formal weld current 10% to 15%.
â‘¡ welding arc and positioned at the end of the transition should be smooth, the weld can not be too high, must ensure good fusion to prevent produce incomplete penetration, slag and other defects.
â‘¢ If positioning weld cracking, cracks at the weld must be repositioned after soldering to eradicate. After the tack welding, such as the emergence of missing the interface level, should be corrected before the official welding.
â‘£ avoid forced assembly to prevent the welding process, the positioning of the weld or weldment official weld cracking, if necessary, increase the length of the weld orientation and positioning of the weld spacing decreases, or the use of heat treatment measures.
4 basic operations electrode arc welding technology
(1) arc
Exposure to arc welding arc welding method using arc, there are scratch method and the Watch and French.
â‘  Scratch aligned arc welding method at first, reverse wrist look like a program that matches the same electrode at a slight scratch in the arc length of about 20mm, and then lift the height of 2 ~ 4mm arc ignition. Shown in Figure 2-15. Its characteristics are: easy to damage the welding surface is relatively easy to master, generally applies to alkaline electrode.

â‘¡ Watch aligned arc welding method at first, wrist bent under, so that the vertical rod to gently tap the workpiece, and then lift the height of 2 ~ 4mm arc ignition. . Its characteristics are: Arc welding is the starting point, to avoid damage to welding surface, but difficult to master, generally applicable to acidic electrodes or welding in a narrow place.
Arc, if the stick electrode welding parts, as long as the electrode from side to side several times, and you can out of weldments, if not from the weldment should be immediately out of the welding clamp weldment until the electrode cooling, the hand of its pull out; end if the rod when the drugs leather sleeve, the hand can wear gloves to remove the sleeve and then arc.
(2) from the weld seam

 
From the welding seam welding arc is ignited to normal after the operation before welding. Since the beginning welding weldment temperature is lower, after the arc can not quickly make this part of the metal temperature, thus they often result from the welding area porosity, incomplete penetration, weld width is not enough and higher weld defects. To avoid this phenomenon, generally can be used two ways:

â‘  Choose the correct arc weld points should be chosen from the starting point of about 10mm on parts to be welded, arc welding ignited after the move to the starting point, and then along the welding direction normal welding; weld connection points should be selected arc crater in the preceding weld 10mm at the front, moving the arc ignition at Crater, and then continue until the filled crater welding.
â‘¡ The arc plate that is welded and welded parts before assembling a same material and thickness of the metal plate, this board from the beginning arc, welding and then cut off.
This method is suitable for welding of welded structures important.
(3) transport of
In the welding process, in order to stabilize the arc length, keeping pool shape, weld control, in order to obtain uniform weld, electrodes must be some movement. Put this in the welding process, welding rod relative to the weld made by the general term for a variety of sports known as the transport bar.
â‘  operation of the transport of basic movements can be decomposed into three basic actions, namely: sent along the electrode axis, moves along the weld axis direction of the longitudinal and transverse oscillation
Table 2-9 Basic operation of the action

Operation of the transport direction of the action with the operational requirements for
Sent to the electrodes along the axis of the direction taken to control the arc length to the pool, so pool with good protection, to ensure continuous welding, weld requirements for electrode feed speed and electrode melting rate equal to, in order to maintain the arc the length of the same
Welding electrode moving direction of the longitudinal movement along the seam lines welding ensure and control the weld cross-sectional area of ??each road speed to be uniform due to the weld
Swing swing the control electrode of the horizontal weld penetration required, melting width, to obtain a certain width of weld, and to ensure that the weld groove on both sides and its swings between good fusion weld width should be based on the decision with the electrode diameter. Uniform horizontal swing and strive to get the width of neat welds. Weld width does not exceed the diameter of the electrode is generally 2 to 5 times.

â‘¡ operation of the method of operation of the method more use should be based on joint form, assembly space, welding position, electrode diameter and performance, size and welders welding current operating level may be.

8-shaped
  Direction along the welding electrode end of the movement for the 8-shaped, widened the weld, butt joint corrugated appearance (thick weldments Welded)

(4) weld joints

After welding the first weld seam and the weld joints is called the junction. Welding process, due to the electrode length limitations or other factors, and sometimes can not complete a weld with a welding rod, and therefore, the weld joints is inevitable. In order to ensure the continuity of the weld, the weld to prevent excessively high, out of line, width inconsistencies and other defects, seam welding joints should be familiar with technology. There are four general weld joint connection,
â‘  the middle of the weld joint that is after the beginning of the tail and connected to the first weld. Joint approach is: the earlier weld crater near the front about 10mm arc, arc length slightly longer than the normal welding some (non-alkaline elongated rod, or easy to produce pores), then after the move to the original arc Crater 2 / 3, down the arc, a little swing, forward to fill the crater after normal welding. This joint method most used for multi-layer welding and soldering of the surface connector.

 
â‘¡ connector that is contrary to the beginning after the weld seam welding beginning with the first phase. Joint method is: first welding requires slightly lower at the beginning of the weld, weld joints, beginning at a little earlier before that arc, and slightly elongated arc, the arc towards the first weld joints, and cover The end of the first, to be welded at the beginning level, to raise the first weld to weld the opposite direction. .

 
â‘¢ Connector the opposite end of the weld after welding the first weld and adjacent to the end. Joint method is: When the weld after welding seam close to the first welding arc at the time, the welding speed should be slightly slower, the first weld to fill the crater, with its slightly faster forward speed and then welded period, and then extinction. Welded joints of extinction method
â‘£ sub-head that is welded back after the end of weld seam welding beginning with the first connected. Joint method is: request to close before welding weld seam welding beginning of time, change the electrode angle, electrode point before the beginning of the weld, elongated arc, until the formation of pool, and then arc down, move back, Finally, return to the original pool at the Crater.
(5) finishing the weld
The ending is a weld seam at the end of the end of operation method, also known as Crater. Such as improper finishing methods, the end will produce the weld crater, thereby reducing the weld strength, and easy to form a stress concentration resulting crater cracks. There are three common methods of finishing:
â‘  circled finishing method to move the weld electrode end, in the arc of a circle pit for exercise, play fill the crater and then pull off the arc. This method is suitable for thick plate welding, the sheet is easy to burn.

 
â‘¡ finishing law repeatedly broken arc welding electrode to move the finish line, repeated in the crater at extinction, arc several times, play a crater filled up. This method is suitable for sheet metal and high-current welding, but the basic welding rod should not be used, or easy to produce pores.
â‘¢ Move back electrode welding seam finishing finishing method to stop immediately and change the angle back to the welding electrode after a short extinction. This law applies to alkaline electrode.
6 Common welding defects in arc welding and prevention measures
(1) does not meet the required weld size
â‘  shape of the weld surface uneven, corrugated poor weld, the longitudinal width of the uneven, too high or too low than high, unilateral, and fillet weld leg size does not meet the requirements.

 
â‘¡ hazards unsightly weld, the weld and base metals affect the bonding strength, easy to produce stress concentration, reducing the carrying capacity of such joints.

â‘¢ causes weldment right angle bevel, uneven gap assembly, welding parameters inappropriate or incorrect operation of the other way.
â‘£ Select the appropriate measures to prevent the bevel angle and gap, improve the assembly quality, correct choice of welding parameters and techniques to improve the level of welding operations.
(2) crack
There are many cracks in the weld type, there are many causes of cracks, the crack on the theory of knowledge are described in later chapters, I will not say more. See Frequently Asked crack shape.
(3) undercut
 
â‘  shape along the weld toe on the base metal parts formed by arc melting into the depression known as trench mouth or side.
â‘¡ joint strength and reduce the risk bearing capacity, easy to produce stress concentration, the formation of cracks.
â‘¢ causes the inappropriate choice of welding parameters, welding current is too large, the arc is too long, rod angle is not correct and that the transport of inappropriate and so on.

 
â‘£ Select the correct measures to prevent welding current and welding speed, arc can not be stretched too thin, to master the correct operation of the method and operation of the angle.
(4) lack of penetration
â‘  shape welding, the joint roots of the phenomenon called incomplete fusion of the lack of penetration.
â‘¡ harm could easily lead to stress concentration, cracks, impact strength and fatigue strength of joints etc.
â‘¢ mouth through the slope causes a small, blunt side of the gap is too small or too large; welding speed too fast; welding current is too small; arc voltage is low; welding with magnetic blow phenomenon; the root is not completely clear; electrode accessibility poor and so on.
â‘£ measures to prevent the correct choice of welding parameters, groove dimensions, the assembly must ensure that the gap, careful operation, carefully clean the floor or between the edge of the base metal oxides and slag and so on.
(5) lack of fusion
â‘  shape welding, the weld and parent metal or between weld and the weld between the fusion part of the not fully known as non-fusion. Primarily from the side of the weld and solder layer.

 
â‘¡ hazards easy to produce stress concentration, affect the joint continuity, reduce joint strength.
â‘¢ causes groove between layers and clean is not clean, low heat input welding, arc point deflection and so on.
â‘£ prevent measures to strengthen the groove between layers and clean up, correct selection of welding heat input, the correct operation.

 
(6) burn
â‘  shape of the welding process, the molten metal from the groove on the back out of the formation of defects known as the burn hole.
â‘¡ harm reduction effective cross-sectional area of ??the weld, reducing the carrying capacity of such joints.
â‘¢ causes the welding current is too large, the order is unreasonable welding, welding speed is too slow, the roots of the gap is too large, blunt edges are too small.
â‘£ Select the appropriate measures to prevent welding current and welding speed, narrow root gap and improve skills.

 
(7) weld
â‘  shape of the welding process to weld the molten metal flowing outside of the base metal is not molten metal formed on the tumor, known as the weld, also known as overflow.
â‘¡ hazards weld appearance, waste material, weld cross-section mutation, easy to form sharp corners, resulting in stress concentration and so on.
â‘¢ the root causes of the gap is too large weldment, welding current is too large, the operation of incorrect or improper operation.
â‘£ prevention measures to improve skills, select the appropriate welding current, improve the assembly quality.

 
(8) crater
â‘  shape of the weld produced at the ending part is called subsidence crater.
â‘¡ risk weakening the weld strength, easy to produce crater cracks.
â‘¢ causes extinction time is too short, ending improper methods, failed to fill the crater.
â‘£ prevention measures appropriate to choose the right welding parameters and arc quenching time, master the correct finishing methods.
â‘  shape of the welding process, the bubbles in the coagulation bath failed to escape and left behind the formation of holes, called stomata.
â‘¡ harm reduction weld cross-sectional area, reducing the joint density, reducing the carrying capacity and fatigue strength of joints etc.
â‘¢ causes weldment clean is not clean, wet welding, arc welding parameters of magnetic blow and irrational.

 
â‘£ careful trimming to prevent measures 10mm at each side of the rust and dirt, strict drying electrodes, choose the right welding process parameters.
(10) slag
â‘  shape in the weld after welding slag residue called slag.
â‘¡ weld cross-sectional area to reduce harm, reduce joint strength, impact toughness.
â‘¢ too small causes the welding current, welding speed too fast, improper groove design, weld deposition sequence improper.
â‘£ measures to prevent the correct choice of welding parameters, groove angle is not too small, do a good job when the multi-layer weld clean-up work.
(11) collapse
â‘  shape molten weld metal from the back of leakage, the weld front concave, convex back of the phenomenon known as collapse.

 
â‘¡ joint bearing area to reduce harm, reduce joint strength, affect weld appearance and so on.
â‘¢ causes excessive welding current, welding speed is too small, assembly gap is too large and so on.
â‘£ Select the appropriate measures to prevent welding current and welding speed, control and gap weldment assembly.
(12) pits
 
â‘  shape of the weld seam on the back of the formation of surface or below the surface of the base metal is called the local low-lying part of the pit.
â‘¡ welding work cross-sectional area to reduce harm, reduce carrying capacity and other joints.
â‘¢ causes arc pull too long, improper welding and assembly clearance angle is too large and so on.
â‘£ Select the appropriate measures to prevent the assembly space, enhance operational level