JPS58138566A - Plasma key hole welding method - Google Patents

Abstract

PURPOSE:To easily execute titled welding without requiring any complicated welding condition control in case when welding is started, or providing a small hole and a cut groove on welding start point by using a gap provided in advance on a part to be welded of the welding start point of a base material, in place of a key hole. CONSTITUTION:On a welding start point of a part to be welded of butted base materials 3, 4, a small gap 7 of prescribed size is provided in advance. Subsequently, this gap 7 is used as a key hole, and welding is executed by a plasma arc torch 1. As a result, said state becomes same as the key hole exists immediately after start of arc, and plasma gas passes through the gap 7 and is jetted easily to the reverse side of the base materials 3, 4. At the point of time when the base materials 3, 4 are melted by this plasma 2, the base materials 3, 4 are brought close to the C and B directions, respectively, the gap 7 is closed, and welding is continued in the direction A. In this case, however, a key hole 8 is formed already by plasma 2, and a defect of the welding start part in case of forming a key hole as the case when there is no gap 7 is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma keyhole welding method in which base materials are butted and welded, and in particular to an improvement in the welding initiation method.

In plasma keyhole welding, it is extremely important to form a good keyhole at the welding starting point, and avoid defects such as cavities caused by the entrainment of plasma gas, molten metal being blown onto the back side of the workpiece, and molten metal falling off. Easy to occur.

Therefore, in order to prevent these defects from occurring, conventional methods require sufficient control of welding conditions at the start of welding, and small holes or kerfs that penetrate from the surface of the base material to the back surface of the welded part at the welding start point are required. A method has been proposed in which a predetermined hole or cut groove is used as a keyhole to supply plasma gas with a predetermined current, and welding is started with the predetermined current.

However, as a method for sufficiently controlling welding conditions at the start of welding, as shown in FIG.

In order to control the welding current I, the plasma gas flow rate Q, and the welding speed (2), a gradual increase control device for the welding current I and the plasma gas flow rate Q, and a sequence control device for these conditions are required.

The drawback is that the control device is complicated and expensive.

Furthermore, when starting welding, the method of creating a small hole or kerf for a keyhole in the welded part does not require complicated control of conditions at the start of welding, but it does require the process of creating a small hole or kerf in advance before starting welding. There were additional drawbacks.

That is, this method is shown in Figs. 2 and 3, where 01 is the plasma arc torch, 02 is the plasma ejected from the plasma arc torch 01, 03 and 04 are the base metal, o5 is the part to be welded, and 06 is the welded part. This is a small hole or kerf provided at the welding start point of the part to be welded 05, and since the small hole or kerf 06 is provided in this method, it is the same as a keyhole that exists immediately after the arc starts. , a good welding starting point can be obtained, but it requires a step of providing a small hole or kerf, which is not practical.

This invention was made in consideration of the above points, and the butt base metals at the welding start point are arranged in advance with a small gap,
A predetermined flow rate of plasma gas is supplied using the small gap as a keyhole.

By closing the gap after starting welding with a predetermined welding current, defects at the welding starting point are eliminated, a complicated welding condition control device is not required, and the weight part at the welding starting point is free from defects, especially in circumferential welding. A plasma keyhole welding method is provided.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 6.

FIG. 4 is a diagram showing the state at the start of welding, and FIGS. 5 and 6 are explanatory diagrams of the base metal arrangement before and after the start of welding. In the figure,
1 is a plasma arc torch.

2 is the plasma ejected from the plasma arc torch l, 3
- 4 is the base material, 5 is the part to be welded, and 7 is a small gap provided in the part to be welded 5.

Since a gap 7 of a predetermined size is provided in advance at the welding start point of the welded part 5 of the butted base metals 3 and 4, it is as if a keyhole exists immediately after the arc starts, and the plasma The gas easily blows out onto the back surfaces of the base materials 3 and 4 through this gap 7. When the base materials 3 and 4 are melted by this plasma 2, as shown in FIGS. The base metals 3 and 4 are brought close together in the C direction to close the small gap, and welding is continued in the direction of the arrow A, but the keyhole 8 has already been formed by the plasma 2 and the small gap 7 does not exist. No defects occur at the welding start point during keyhole formation.

As described above, in the method of this invention, a gap is provided in advance in the welded part at the welding start point of the base metal, and is used at the welding start point as a substitute for a keyhole. Requires no control and becomes
Further, there is no need for steps such as forming a small hole at the welding start point.

Especially for pipe butt automatic plasma keyhole welding, a pipe moving device is included.

No separate gap closing device is required. Therefore, according to the present invention, plasma keyhole welding can be easily performed without defects at the welding starting point.

[Brief explanation of the drawing]

1 to 3 illustrate a conventional welding method, and FIGS. 4 to 6 show an example of the present method. FIG. 4 is a schematic diagram of the welding start state, and FIGS. 5 and 6 are explanatory diagrams of base metal arrangement in the welding start state. 1: Plasma arc torch, 2: Plasma. 3/4: Base metal, 5: Welded part, 7: Small gap. 1st story 2nd story Shin 3 Sen 6 Ha 4 story

Claims (1)

[Claims] The butt base metals at the welding start point are arranged with a small gap, the small gap is used as a keyhole to supply plasma gas at a predetermined flow rate, and after welding is started with a predetermined welding current, the small gap is closed. Characteristic plasma keyhole welding method.