KR20120131563A

KR20120131563A - Gma root pass welding method for overcoming root gap variation and stable back bead formation by controlling the relative arc force

Info

Publication number: KR20120131563A
Application number: KR1020110049826A
Authority: KR
Inventors: 조상명; 손창희; 김남규; 박효희
Original assignee: 부경대학교 산학협력단
Priority date: 2011-05-25
Filing date: 2011-05-25
Publication date: 2012-12-05

Abstract

The present invention relates to a butt joint GMAW superlayer welding method capable of controlling the relative arc force to overcome root gap variation and stably form the backside beads.

Description

GMA ROOT PASS WELDING METHOD FOR OVERCOMING ROOT GAP VARIATION AND STABLE BACK BEAD FORMATION BY CONTROLLING THE RELATIVE ARC FORCE}

Pipe structures are increasing in demand for offshore structures, piping, steel towers, design, and the like, and are required for productivity and precision to manufacture them.

The joint fabrication process between pipes consists mainly of root pass (straight layer) and fill pass (second pass) welding, which is heavily dependent on the experience of experienced operators due to the possibility of defects, The gas is welded by a gas tungsten arc process, and a semi-automatic gas metal arc welding method is applied to the fill path.

Butt joints in the welding process are joints joined together in a state where steels are joined together, ie, in a straight line, and a beveling is formed to fill the weld metal along the welded part. Weld with a root gap at the end.

When welding a pipe with butt joints, first, as shown in FIGS. 1 and 2, an improved surface 14 is formed to have a certain degree of improvement 12 to weld the pipe, and a welding bead is formed between the improved surfaces 14. We do welding while filling in (16). First, first layer welding 15 is performed between the root gaps 13 to fill the welding beads 16. Root pass welding at butt joints refers to welding of the first layer of deposited metal formed in one or more passes, as shown in FIG. 2.

In conventional butt joints, an improved surface having a root gap of 3 mm without a root surface when pipe welding is made, and an inert gas tungsten arc welding (GTAW) and a flux cored arc welding (FCAW) method are combined. However, in the conventional method, when high current and high speed welding is performed to increase productivity, unstable beads such as undercuts or humping beads appear. On the contrary, when the welding speed is lowered, heat input increases to increase deformation and residual stress of the weld. Problems have arisen.

Accordingly, Gas Metal Arc Welding (GMAW) has been used as a new approach. Gas metal arc welding (GMAW) is a welding method in which an arc is generated between a wire and a base material through an electric current while supplying a consumed electrode wire serving as a filler material to a molten material at a constant speed. 3 shows the principle of GMAW welding. As shown in FIG. 3, the wires continuously fed are melted by the high heat of the arc to be transferred through the arc column to the molten pool, and the molten site is protected from the surrounding atmosphere by the protective gas supplied through the gas nozzle. GMAW uses relatively narrow (0.9-1.6 mm) electrode wire, which is more efficient than other welding methods because of high current density and high welding speed. In addition, there is an advantage that welding automation is relatively easy using a welding robot or an automation device.

In GMAW, the first layer welding (root pass welding) is a factor that greatly influences the mechanical properties and integrity of the weld. In the case of the pipe welding member, an error may occur in the process of improving the pipe, and the welding line may be inclined at the temporary welding for welding. In addition, an error in the welding line due to the eccentricity of the rotating device for rotating the pipe may be caused. In addition, the root gap affects various welding parameters such as welding current, arc voltage, and the like.

Since the shape of penetration in pipe welding is very important in the case of pipe welding requiring pressure or airtightness, it is necessary to control the formation of the penetration in real time to maintain an appropriate penetration. For this reason, the operation of the automation device for pipe welding, which is currently applied, requires the welding worker to continuously position the torch as the welding line during the welding and change the welding conditions according to the size of the gap. . As a result, conventionally, a method of reducing the speed and current when the gap is enlarged and increasing the speed and the current when the gap is reduced is mainly used. However, a more accurate and detailed description of how the speed and the current are regulated as the gap changes is required.

The present invention provides a butt joint GMAW superlayer welding method that can form a stable back bead while overcoming fluctuations in the root gap generated during butt joints by controlling the relative arc force. It aims to do it.

The present invention for the above purpose,

The present invention provides a butt joint GMAW superlayer welding method that overcomes the root gap variation through the control of relative arc force and stably forms the backside bead. In the present invention, when the root gap is smaller, the relative arc force is increased, and when the root gap is larger, the relative arc force is controlled to be reduced.

In the present invention, when the root gap becomes smaller, the relative arc force is increased by increasing the current and the welding speed. In addition, when the root gap is small, the weld cross-sectional area is reduced in order to prevent the shortage of penetration caused by increasing the current and the welding speed.

In the present invention, when the root gap is increased, the relative arc force is reduced by reducing the current and the welding speed. In addition, when the root cap is increased, the weld cross-sectional area is increased in order to prevent melting by reducing current and welding speed.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Arc welding has a relatively small penetration depth and a slow welding speed because a small amount of energy is applied to a large area, and therefore, a large amount of heat is required as well as a large amount of welding labor is required when welding steels of the same thickness. As a result, the weld metal and the heat affected zone are widely formed, and thermal deformation is severely generated, which requires a large number of subsequent airlifts to correct them. Therefore, in arc welding, as the amount of heat input in the welding process decreases, deformation in the welding process can be minimized.

The heat input amount refers to the amount of heat applied to the weld portion from the outside during welding, also referred to as welding heat input. In arc welding, the arc represents the electrical thermal energy Q (J / mm) generated per unit length of the weld bead. If the arc voltage is E, the arc current is I, and the welding speed is v (mm / s), the heat input can be expressed as follows.

Heat input Q (J / mm) = E (V) * I (A) / v (mm / s)

It can be seen from the relational expression representing the heat input amount that the heat input amount is kept constant when the current I and the welding speed are deformed in inverse proportion.

In comparison, the relative arc force according to the present invention refers to a force proportional to the square of the current and a voltage as shown in FIG. 4, and is a force that pushes the molten metal downward when there is a gap during butt welding.

Although the relative arc force and the heat input change in common with the current and voltage, there is a big difference that the relative arc force is changed according to the welding speed, while the heat input is not changed by the welding speed. Therefore, by adjusting the welding speed, the amount of heat input does not change and only the relative arc force is increased, thereby making it possible to control the backside bead formation.

In other words, in the present invention, when the root gap becomes smaller than the reference root gap of 1.5 mm, a force that pushes the molten metal downwards further between the smaller root gaps is required, so that the current and the welding speed are increased to increase the relative arc force. To increase. However, as the current and the welding speed are increased, the shortage of penetration may occur accordingly, so that the current surface and the welding speed may be increased while simultaneously controlling the small welding cross-section to form the backside beads stably without the shortage of the penetration.

On the other hand, if the root gap is larger than the reference root gap of 1.5 mm, the relative arc force required to push the molten metal downward between the root gaps decreases, thus reducing the current and welding speed. However, as the current and welding speed decrease, the likelihood of melting increases, so that the weld cross-sectional area is increased to reduce the likelihood of such melting. This prevents the melt while increasing the amount of deposition, and reduces the current and voltage, thereby reducing the relative arc force, resulting in stable backside bead formation.

In the butt joint GMAW first layer welding of the present invention, the butt joint has one of the following shapes: Y-groove, I-groove, V-groove and U-groove. In order to form good weld beads, the shape of the grooves must be appropriate.

The butt joint GMAW superlayer welding method according to the present invention can form a stable back bead while controlling the relative arc force while overcoming the fluctuation of the root gap generated during the butt joint.

1 and 2 show a cross section during welding with butt joints.
3 shows the principle of GMAW welding.
4 shows the relative arc force.
5 shows the relationship between the relative arc force and the heat input amount according to the current in the same amount of deposition in Examples 1-1 to 1-3 of the present invention.
6 shows the weld results and the shapes of the welded portions in Examples 1-1 to 1-3.
FIG. 7 shows the result of performing the plate butt welding while changing the relative arc force by changing the voltage when the root gap is 1.5 mm.
FIG. 8 shows the result of performing the plate butt welding while changing the relative arc force by changing the voltage when the root gap is 0.5 mm.
FIG. 9 shows the result of performing the plate butt welding while changing the relative arc force by changing the voltage when the root gap is 2.5 mm.
Figure 10 shows the relationship between the relative arc force and the bead shape as the root gap changes in the embodiment of the present invention.
FIG. 11 shows the relationship and relationship between the size of the root gap and the required relative arc force for stable bead formation at each root gap size in Examples 2-4 of the present invention.
12 shows the shape of the U groove applied in this embodiment.
Fig. 13 shows the results of the first layer welding under the conditions of the present invention.

Example One. Root gap 1.5 mm Relative to copper plate when Arc Change experiment

In order to investigate the effect of relative arc force on the backside bead formation when the current and the welding speed were increased proportionally, the plate butt welding was performed under the standard root gap of 1.5 mm using a 200 mm × 50 mm × 5 mm copper plate. . The relative arc force was changed while changing the current and voltage under the conditions of Table 1, and the shape of the backside beads was observed.

As the current was increased, the welding speed was proportionally increased to maintain a constant cross-sectional area of the deposited metal at 10.5 mm ² , and in each case, the heat input was calculated as follows.

Heat input Q (J / mm) = E (V) I (A) / v (mm / s)

The relationship between the relative arc force and the heat input amount according to the current in Examples 1-1 to 1-3 is shown in FIG. 5, and the shape of the welded part in Examples 1-1 to 1-3 is shown in FIG. 6. . When the current and the welding speed are proportionally increased in FIGS. 5 and 6, there is almost no difference in heat input, but in FIG. 6, the relative arc force increases with the increase of the welding speed, so that the depth of penetration deepens. can do.

Example 2. Standard Root gap 1.5 mm Relative to mild steel sheet Arc Measurement experiment

In order to investigate the backside bead formation due to the change in relative arc force when the root gap is 1.5 mm, the voltage is reduced when the setting current is 120 A using a 150 mm × 50 mm × 3 mm mild steel plate as in Example 1 above. Plate butt welding was performed while changing the relative arc force.

Each condition and the shape of the welded portion are shown in FIG. 7. As shown in FIG. 7, when the relative arc force was 303K, the output current 126A, and the output voltage 19.4V, the shape of the beads was most stable.

Example 3. Root gap 0.5 mm in Relative Arc Change experiment

Except that the root gap is 0.5 mm was measured in the same manner as in Example 2, and the results are shown in FIG. As shown in FIG. 8, the bead shape was most stable in the welding condition at the 510k output current 152A and the output voltage 22.0V where the relative arc force increased from the reference root gap of 1.5 mm.

Although the heat input amount was lower than that of Example 2 having a root gap of 1.5 mm, the relative arc force was increased, and stable backside beads could be obtained by increasing the relative arc force as the root gap was decreased.

Example 4. Root gap 2.5 mm in Relative Arc Change experiment

Except that the root gap is 2.5 mm was measured in the same manner as in Example 2, and the results are shown in FIG. As shown in FIG. 9, the welding condition was found to be the most stable in the shape of the bead when the relative arc force is reduced to 197k, the output current 109A, the output voltage is 16.6V, than the reference root gap 1.5mm. The root gap was welded so that the relative arc force was reduced as the root gap was increased in size compared to Example 2 having 1.5 mm, thereby obtaining stable backside beads without melting.

The relationship between the relative arc force and the bead shape as the root gap is changed in Examples 2 to 4 is shown in FIG. For each root gap, it can be seen that the height and width of the beads have a constant relationship with the relative arc force.

The relationship between the size of the root gap in Examples 2 to 4 and the arc penetration force for stable bead formation at each root gap size is shown in FIG. 11. As shown in FIG. 11, it can be seen that there is an inverse relationship with the size of the root gap and the arc penetration force.

Example 5. U Groove Butt Joint Welding Experiment

When the root gap is 0.5mm, 1.5mm, 2.5mm, as shown in FIG. 12, U groove butt joint welding was performed under the most stable conditions of the back bead shape in Examples 2 to 4.

The shape of the U groove applied in this embodiment is shown in FIG. 12, and the results of welding are shown in FIG. 13. The U groove shape applied to the present embodiment has a root gap of 1.5 mm and a root surface of 3 mm. When the root gap is larger than the reference root gap 1.5 mm under the conditions of the present invention as shown in FIG. 13, the reference root gap 1.5 is used. When welding is performed under the condition that the relative arc force is reduced than the relative arc force at mm, and when the root gap is smaller than the reference root gap 1.5 mm, the relative arc force is reduced than the relative arc force at the reference root gap 1.5 mm. , It was confirmed that stable backside beads were produced in the first layer welding.

Claims

Butt Joint GMAW Superlayer Welding Method of Controlling Relative Arc Force to Overcome Root Gap Variation and Form Stably Backside Beads

The method of claim 1,
Butt joint GMAW that overcomes the root gap variation and stably forms the bead by controlling the relative arc force, characterized by increasing the relative arc force as the root gap decreases and decreasing the relative arc force as the root gap increases. Ultralayer welding method

The method of claim 2,
Butt joint GMAW superlayer welding method of controlling relative arc force to overcome root gap variation and stably forming backside beads by controlling the relative arc force by increasing the current and welding speed as the root gap decreases.

The method of claim 3, wherein
Butt joint that overcomes root gap variation and stably forms backside beads by controlling the relative arc force, characterized in that the weld cross section is reduced to prevent shortage of penetration by increasing current and welding speed when the root gap is reduced. GMAW Ultralayer Welding Method

The method of claim 2,
Butt joint GMAW superlayer welding method which controls relative arc force to overcome root gap variation and stably forms backside beads by controlling relative arc force, which decreases current and welding speed as the root gap increases.

The method of claim 5, wherein
Butt joint GMAW superlayer that overcomes the root gap variation and stably forms the backside bead by controlling the relative arc force, which increases the weld cross-sectional area to prevent melting by decreasing the current and welding speed as the root gap increases. welding method

The method of claim 1,
The butt joint has a groove in the form of one of Y-groove, I-groove, V-groove and U-groove to control relative arc force to overcome root gap variation and stably form a back bead Joint GMAW superlayer welding method.