JPS5916668A - Method for cutting prepared hole for branch pipe - Google Patents

Abstract

PURPOSE:To cut the prepared hole for a branch pipe with the arc kept at a specified length by setting the reference value of the arc length with a contact type sensor, detecting the change in the arc voltage in the stage of cutting and controlling the distance between the torch and a main pipe. CONSTITUTION:The space between a main pipe and a plasma torch is set with a contact type sensor 9 and the reference value of an arc length 10 is determined prior to starting of cutting of a prepared hole. The change in the arc length 10 that arises with a change in the space during cutting is detected as a fluctuation component of the voltage with an arc voltage detector 11, by which a torch lifting device 12 is controlled to maintain the specified arc length 10. The malfunction by the transient voltage fluctuation in the stage of changing the pilot arc to the main arc is eliminated and the prepared hole for the branch pipe is plasma-cut with the arc kept at the specified length.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a branch pipe pilot hole cutting device, and particularly to a method of keeping the arc length constant when a plasma cutting method is employed.

[Prior art]

As shown in FIG. 1, the method of cutting a pilot hole using X-θ, two-axis control requires the installation of sensors 3 on both sides of the torch 2. If contact type sensors are used for these two sensors, there is a risk that the weld bead 4 will get caught if there is a weld bead 4 in the cutting direction.

When using a non-contact magnetic sensor, when cutting a pilot hole in the joint of dissimilar materials such as stainless steel 5 and mild steel 6 as shown in Figure 2, it is difficult to cut a pilot hole in the joint of different materials such as stainless steel 5 and mild steel 6, because the magnetic properties of the materials are different between stainless steel and mild steel. There was a problem in that the sensor response changed and the arc length could not be kept constant. Furthermore, since a certain distance t must be maintained between the torch 2 and the sensor 3 for heat resistance reasons, there is a problem in that the sensor 3 cannot detect the vicinity of the end of the main pipe.

We also considered detecting the arc voltage from the beginning and trying to keep the arc length constant, but when switching from the pilot arc to the main arc at the start of cutting, the voltage fluctuation was greater than the arc voltage fluctuation over the cutting width. It was found that it was impossible to set the initial value of the arc length because it was extremely large.

[Purpose of the invention]

The present invention is capable of keeping the arc length constant, X-θ, 2
The object of the present invention is to provide a method for cutting a branch pipe pilot hole using axis control.

[Summary of the invention]

The present invention is a pilot hole cutting method using X-θ, two-axis control.
A reference value for the arc length is set using a contact sensor, and the distance between the torch and the main pipe is adjusted when the voltage is proportional to the arc length, avoiding transient voltage fluctuations at the start of cutting. It is something to control.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic diagram of the pilot hole cutting device. The main tube 1 rotates around the central axis (θ axis), and the torch 2 rotates in the central axis direction (
(X-axis). A servo motor is used for the movement in the two axes of X-θ, and the pilot hole is cut by controlling this with a microcomputer according to the input data.

In this case, the arc length 10 changes depending on the roundness of the main tube, and cutting may not be performed smoothly.

In order to prevent this, it is necessary to control the arc length using the arc voltage. First, in order to determine the appropriate arc length, as shown in Figure 4 (a) and (b), a reference value of arc length 10 is determined using a contact sensor, and then (c)
When the contact sensor is evacuated and the arc voltage reaches a steady state, changes in the arc voltage are detected by the arc voltage detector 11.
By detecting this and controlling the torch lifting device 12,
The aim is to perform cutting while keeping the arc length constant.

Fifth. '1100 shows a modified example of application of the present invention. FIG. 5 shows an attempt to cut the saddle-shaped curve 16 of the branch pipe by rotating the main pipe vertically and moving the torch in the vertical direction. FIG. 6 shows that in order to facilitate insertion of the diagonal pipe 13,
The torch angle can be changed using an angle changing plate 15.

〔Effect of the invention〕

According to the present invention, in a branch pipe pilot hole cutting device, a series of 9 operations are performed by bringing the torch closer to the main pipe, switching from the pilot arc to the main arc, and then cutting at an appropriate arc length. This can be done using a contact type sensor for arc length detection and an arc voltage detection device, thereby eliminating malfunctions caused by transient voltage fluctuations when switching from the pilot arc to the main arc.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a conventional profiling method, Fig. 2 is a schematic diagram of a conventional profiling method, Fig. 3 is a schematic diagram of a pilot hole cutting device, and Fig. 4 is a schematic diagram of an embodiment of the present invention. Figure, 5th. 6th
The figure is a schematic diagram showing another embodiment of the invention. 7...θ-axis, X-axis, 9...Contact sensor,
10... Arc length, 11... Arc voltage detector, 1
2...G Figure 1 Figure 2 Figure 3 Figure 4 (A) (B) (C) Figure 5 Figure 6 Port 351-

Claims (1)

[Claims] 1. In a method for cutting a branch pipe prepared hole in the main pipe by moving at least a plasma torch for cutting in the longitudinal direction of the main pipe and rotating the main pipe in the circumferential direction, The gap between the plasma torch is set using a contact sensor before the start of cutting, and after the voltage fluctuation when switching from the pilot arc to the main arc at the start of cutting has subsided, changes in the arc length caused by the gap change during cutting are measured. A method for cutting a pilot hole in a branch pipe, characterized in that the p-arc length is kept constant by detecting the voltage variation and controlling the voltage variation.