JPH0994657A - Termination crack prevention method in single-sided butt welding - Google Patents

Abstract

(57) [Abstract] [Problem] To prevent terminal cracks and connect back beads. SOLUTION: The shape of the groove 3 is V type or Y type, the backing material 4 is brought into contact with the rear surface of the groove 3, and the outer diameter of the welding wire 6 is 2.0.
~ 3.2mm, welding current 500 ~ 1500A under the welding conditions, by high-speed rotating arc welding from the one end of the workpieces 1 and 2 to inward welding, after stopping the progress of welding at a predetermined position, the arc The welding current is reduced in a state where the rotation is stopped, the welding torch 5 is returned in the reverse direction at a higher speed than the welding speed, and the crater process is performed. Performs high-speed rotating arc welding from the end to the position where it overlaps with the stop position of the welding progress, stops the welding progress for a predetermined time while the arc rotation is stopped, is lower than the welding current, and faster than the welding speed. A method for preventing terminal cracking in single-sided butt welding, which comprises performing crater treatment after returning the welding torch in the opposite direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing terminal cracks in single-sided butt welding.

[0002]

2. Description of the Related Art It is desired to apply one-sided butt welding by gas shield arc welding, which is relatively easy to perform labor saving, automation, and welding robotization, as a method of joining plates to each other in shipbuilding and bridge member production processes. It's starting to happen.

However, in single-sided butt welding by gas shielded arc welding, tab plates are welded to the starting and ending ends of the material to be welded, and welding is performed from the starting tab plate to the terminating tab plate while continuously generating back waves. In this case, a vertical crack having a length of 50 to 150 mm may enter the center of the bead near the start end and the end. Of these, the cracking rate at the starting end is 10% or less and within 50 mm from the starting end (in the tab plate).
Since it often occurs at the same time, if the tab plate is cut, the defect of the vertical crack is also removed at the same time, so that there is no problem.

On the other hand, the crack at the terminal end is about 300 from the end.
It occurs in the area inside the welded material of mm and the crack length is 50 ~
The occurrence rate is considerably high at 150 mm.

This end cracking occurs at the joining portion of columnar crystals that grow parallel to the plate surface from the left and right melting boundary portions of the bead. The cause is a large tearing force and rotational deformation (welding heat source) generated at the end portion. Of the pear-shaped bead peculiar to the back bead enhances cracking susceptibility. It is said that

The following methods are known as measures for preventing the above-mentioned end cracking. A restraining bead is placed at the end by manual welding or carbon dioxide arc welding, and automatic welding is performed within that range without generating backwaters. A method in which the terminal tab plate is divided into two and completely welded to the material to be welded, and then pressure is applied from both sides of the tab plate to restrain the deformation of the terminal end portion. A method in which automatic welding is performed from the start end and the end, and both beads are associated in the middle of the welding line (crater association method).

[0007]

[Problems to be Solved by the Invention] However, as described above,
The method of and has the following problems. In this method, the welding of the end portion becomes intermittent, which is troublesome and inefficient. This method requires a special hydraulic device or a device for pressurizing the tab plate, which increases the number of work steps and may increase welding cost. The method of (1) has a problem that the back bead is not continuously spliced at the bead meeting, and the work of reworking is required.

Generally, in single-sided butt welding, it is important to form a good back bead in the initial layer welding.
When the back bead becomes intermittent, it is necessary to properly join the back beads.

The present invention has been made in order to solve the above problems, and solves the problem of terminal cracks and obtains a good back bead when performing single-sided butt welding by gas shield arc welding. The present invention provides a method for preventing terminal cracks in single-sided butt welding, which can be automated and highly efficient.

[0010]

[Means for Solving the Problems] The means for solving the above-mentioned problems is to perform inward welding from one end of a material to be welded in one-sided butt welding by gas shield arc welding and stop the progress of welding at a predetermined position. After that, the welding torch is returned in the reverse direction to perform crater processing, and thereafter, welding is performed from the other end of the material to be welded to a position that overlaps the stop position of the welding, and then the welding torch is returned in the reverse direction. It is a method of preventing terminal cracks in single-sided butt welding, which is characterized by performing crater processing.

That is, by bringing the end of welding to the middle of the welding line, a large tearing force or rotational deformation that normally occurs at the end is suppressed, and the occurrence of end cracking is prevented.

The trailing weld bead formed from the other end of the material to be welded is partially overlapped with the preceding weld bead, so that a good back bead can be spliced in the first layer welding.

When reversing the welding torch in the opposite direction, it is possible to reduce the welding current and increase the welding speed.
The height of the weld bead is not unnecessarily increased, which is preferable from the viewpoint of preventing hot cracking.

Further, when the trailing weld bead is wrapped with the leading weld bead and stopped there for a predetermined time, the leading weld bead is melted and a better weld bead splice can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front view according to an embodiment of the present invention. Reference numerals 1 and 2 denote welded materials to be welded on one side, in which a groove 3 is formed in a V shape and arranged. Is a backing material abutted on the back surface of the groove 3, and ceramics or copper is used.

Reference numeral 5 is a welding torch that rotates at a high speed, and 6 is a welding wire (consumable electrode) that rotates at a high speed within the groove 3 within the range of the dotted line.

FIG. 2 is an operation diagram of the welding torch 5 showing the welding sequence according to the method for preventing terminal cracks in single-sided butt welding according to the present invention.

In FIG. 2, welding is performed in the following order. (1) First, the first layer welding is performed from the left side a toward the center of the material to be welded, the movement of the welding torch is stopped at the position b, and immediately the predetermined amount L1 is returned to the position c. At this time, the rotation of the arc is stopped and the welding current (wA) returns to a value lower than the value of the first layer welding. The returning speed (v) is higher than the initial layer welding speed. The reason why the welding current is reduced by L1 is that if the welding current is stopped as it is, the welding current is high and crater cracking occurs.

(2) Next, the position c returned by L1
Then, a crater process is performed so that the penetration in the next step is favorably performed.

(3) Next, the first layer welding is performed from the right side (end side) direction toward the center of the material to be welded, and the first layer welding from the left side a in (1) above is stopped at a predetermined position b. It wraps by the value l and stops moving at the position e which has advanced, and stops the rotation of the arc.

(4) After the progress stop time (t1), the welding current (wA) lower than the current value of the first layer welding is used to return in the reverse direction by the predetermined amount L2 in the same manner as described above, and the crater processing is performed at the position f. The return speed (v) in this case is also higher than the initial layer welding speed, as described above.

By programming the above welding sequence as a sequence of the welding device (welding robot), the back bead can be automatically spliced well without any defects, and defects such as high temperature cracks at the splicing part of the back bead can be performed. Does not occur.

As an example, the values of the above-mentioned data when a welding wire having an outer diameter of 2.0 mm is used are as follows. Predetermined amount of return L1, L2: 40 mm Welding current wA: 250 A Return speed v: 70-100 cm / min Lap amount l: 10-15 mm Stop time (t1): 1 second The above various data changes when the welding wire diameter changes. Therefore, a value corresponding to the diameter of the welding wire may be experimentally obtained before performing the one-sided welding.

The position at which the back bead is joined is not particularly limited as long as it is located inward of about 300 mm from the end position of the material to be welded.

In the welding sequence described above, one welding torch is used to weld from one end of the material to be welded, and after the crater treatment is completed, the welding torch is moved to the other end of the material to be welded.
Welding may be performed inward from the other end, or welding may be performed from one end and the other end by separate welding torches in accordance with the above welding sequence.

When welding with one welding torch, the efficiency is slightly lowered, but the equipment cost is low, and it is advantageous in the case of a welded material having a short welding length.

In the case of welding from one end and the other end of the material to be welded with two welding torches, the equipment cost is slightly increased, but in the case of a large material to be welded, which is efficient and has a long welding length. Is advantageous.

Examples of the present invention are as follows. Example 1 Material to be welded: Mild steel 50 kg class (plate thickness 16 mm) Groove shape: V groove 60 ° Gap: 0 mm (standard) Backing material: Ceramics Welding wire: Metal cored wire 2 mmφ Shielding gas: Carbon dioxide gas 100% Arc rotation speed: 50 Hz Welding current: 600 A Welding speed: 40 cm / min Welding method: Using the above-mentioned data, one welding torch was used to advance the one-sided first layer welding from one end to the middle by the high-speed rotating arc welding method. Approximately 30 from the end of welding of the workpiece
At the position of 0 mm, the progress of welding is stopped, the welding current of the welding wire (consumable electrode) is immediately lowered to 250 A, the return speed is 80 cm / min, the distance is 40 mm back, and then the welding wire is flipped up for cratering. It was After that, welding is performed from the other end (end side) in the above-mentioned crater treatment direction (the intermediate direction of the material to be welded), and the welding is continued by wrapping it for 10 mm at the position where it is associated with the first layer weld bead portion from the above one end. After that, the welding current is reduced to 250 A, the movement of the welding torch is stopped in the arc igniting state for 1 second, and then the return speed is 80 cm / min, and the back is made 40 mm, and then,
The welding wire was flipped up to carry out crater treatment, and the back bead splicing welding at the crater joining part in the middle part was completed.

Example 2 Under the same conditions as in Example 1, using the above-mentioned data, the welding was started with two welding torches by a high-speed rotary arc welding method with a time lag from both ends to the middle to start welding. Welded back bead welding was completed at the crater joint.

In each of Examples 1 and 2, there was no end crack, and good back bead joining was performed.

[0031]

As described above, according to the present invention, in the termination crack prevention method by the association method, the joining of the back beads at the bead association portion can be automatically performed without causing defects, and It can prevent cracking.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of the present invention.

FIG. 2 is a plan view of FIG. 1; (Welding procedure diagram)

[Explanation of symbols]

 1.2 Material to be welded 3 Groove 4 Backing material 5 Welding torch 6 Welding wire (consumable electrode)

Claims (1)

[Claims] 1. In single-sided butt welding by gas shield arc welding, welding is performed from one end of a material to be welded inward, the welding progress is stopped at a predetermined position, and then the welding torch is returned in the reverse direction to perform crater treatment. After that, after performing welding from the other end of the material to be welded to a position where it overlaps with the stop position of the welding, and then returning the welding torch in the opposite direction to perform crater processing, in one-sided butt welding End crack prevention method.