Torch Height Research Articles

An analysis of the dynamic characteristics of an arc sensor for DC MIG/MAG welding in open arc mode: Study of improvement of sensitivity and reliability of arc sensors in GMA welding (2nd report)

Summary To improve arc sensor sensitivity and reliability, it is necessary to know how sensor characteristics vary depending on the welding circuit conditions, welding process variables, etc, since the arc sensor simply uses electrical signals ‐ the welding current and/or welding voltage ‐ to produce its outputs. This report theoretically analyses the relationships between these variables on the basis of non‐linear and linearised arc sensor models. The analyses are performed in the time and frequency domains. The results obtained suggest that the welding circuit inductance Lw has little effect on the arc sensor characteristics if the torch height variation frequency (f) is less than around 6 Hz but that its effect increases in the higher frequency range, increasing with an increasing f. The equivalent output electrical resistance of the power supply near the equilibrium point (slope of the static characteristic) Ks more strongly affects the arc sensor characteristics right across the frequency range. Any changes in the electrode wire material or welding conditions also affect the arc sensor characteristics, but less than do Lw and Ks. The real‐time behaviour of the arc sensor during welding in a V‐shaped groove is finally simulated, and the results are discussed through a combination of the arc sensor frequency characteristics and actual welding conditions. The results obtained suggest that, in the lower torch oscillation frequency range, the welding current gives better arc sensor output signals but that, in the relatively high torch oscillation frequency range, it may well be more advantageous to select the welding voltage. This is due to the fact that the current waveform generally exhibits greater asymmetry in relation to the groove centre and the current response also normally decreases with an increasing f.

プラズマアーク熱源特性のノズル形状による制御とその効果

This paper describes a guide line to make low bevel angle cuts in plasma arc cutting by changing of only nozzle conditions ; nozzle shape, electrode tip position in the nozzle and torch height (standoff distance). The idea was deduced from the view point of that the kerf shape is influenced by the radial heat distribution pattern that was established in our another report.First, a new and easy evaluation technique is proposed to be estimated the radial heat distribution pattern with information of cutting speed and top kerf width. Then, the adaptability is examined with some experiments.Secondary, actual radial distribution patterns are experimentally observed at various nozzle conditions. As a result, it is concluded that high throat length, small nozzle convergent angle, long distance between electrode tip to nozzle inlet and low torch height conditions are useful to realize more square type of radial heat distribution pattern with plasma arc.Finally, the relationships between torch conditions and bevel angles are examined. Then, it is indicated that more square radial heat distribution condition is effective to obtain lower bevel angle cuts.

Automatic simultaneous control of bead height and back bead shape using an arc sensor in one‐sided welding with a backing plate

Summary This paper describes an automatic welding system that can simultaneously control the bead height and back bead shape during one‐sided MAG welding with a backing plate. The system uses a high‐speed rotating arc welding process together with an arc sensing technique for seam tracking and torch height control. The arc sensing technique is also used to detect variations in the groove shape. The detection mechanism is described in detail in this paper. The system further uses a newly developed welding parameter control method in which only the wire feedrate and welding voltage are adaptively controlled, the other welding conditions being kept constant. This method is able to keep the bead height constant and retain the back bead shape even if the groove shape changes. Initial welding experimental results have shown the system to be effective and satisfactory for controlling the weld bead shape in one‐sided GMAW (MIG/MAG) with a backing plate.

アークセンサによる片面溶接のビード高さと裏ビード形状の同時自動制御

An automatic welding system that can simultaneously control the bead height and the back bead shape in one side MAG welding process with backing plate has been introduced in this paper. In the system, a high speed rotating arc welding method is used and the seam tracking and the torch height control are realized by utilizing arc sensing technique.On the other hand, the variations of groove shape is also detected by the arc sensing technique. The detecting mechanism is in detail discussed in the paper.Moreover, the system uses a new welding parameters control method that is developed by authors in which only wire feeding rate and welding voltage are adaptively regulated and the other welding conditions are all holded. The new method is able to keep the bead height constant and hold the back bead shape in the case of groove shape changing.The primary welding experimental results have proved that the system is effective and satisfactory for controlling the weld bead shape in one side GMAW process with backing plate.

Simultaneous control of penetration depth and bead height by controlling multiple weld parameters

One of the important subject in the study of automatic arc welding is to establish control system of welding parameters for controlling bead shape, namely penetration depth, bead width and bead height, by detecting or predicting behavior of molten pool owing to change of groove shape.This report describes the study of simultaneous control system of penetration depth and bead height despite the variation of root gap in gas metal arc welding with X-groove. In this system, root gap width is detected by image processing with CCD (charge coupled device) camera, and welding current and welding speed are controlled in order to keep constant penetration depth and bead height. Furthermore in this system, wire feeding rate and terminal voltage are controlled by using equations proposed by Lesnewich and Halmφy so that both wire extension length and arc length can be kept constant during torch height control with ACC method. This control of both wire extension length and arc length is very efective to maintain stabilized welding arc.From the result of an experiment with X-groove of SUS304 stainless steel, both penetration depth and bead height can be simultaneously controlled to be almost constant despite the variation from 0 to 3 mm of root gap width.

多変数溶接パラメータ制御による溶込み深さとビード高さの同時制御

One of the important subject in the study of automatic arc welding is to establish control system of welding parameters for controlling bead shape, namely penetration depth, bead width and bead height, by detecting or predicting behavior of molten pool owing to change of groove shape.This report describes the study of simultaneous control system of penetration depth and bead height despite the variation of root gap in gas metal arc welding with X-groove. In this system, root gap width is detected by image processing with CCD (charge coupled device) camera, and welding current and welding speed are controlled in order to keep constant penetration depth and bead height. Furthermore in this system, wire feeding rate and terminal voltage are controlled by using equations proposed by Lesnewich and Halmφy so that both wire extension length and arc length can be kept constant during torch height control with ACC method. This control of both wire extension length and arc length is very efective to maintain stabilized welding arc.From the result of an experiment with X-groove of SUS304 stainless steel, both penetration depth and bead height can be simultaneously controlled to be almost constant despite the variation from 0 to 3 mm of root gap width.

溶込み深さの最適制御方法に関する基礎的検討

One of the important subject in the study of automatic arc welding is to establish control system of welding parameters for controlling bead shape, namely penetration depth, bead width and bead height, by detecting or predicting behavior of molten pool owing to change of groove shape.This report describes the effect of welding parameters on the bead shape and the study of simultaneous control system of penetration depth and bead height in the variation of root gap in gas metal arc welding. From the fundamental investigation of optimum penetration control method, following results were obtained.1) By the method of controlling additional filler wire feeding rate in order to maintain constant torch height during automatic current control (ACC), the penetration depth and the bead height can be controlled constant at the variation of root gap width in Y-groove.2) The penetration depth can be effectively controlled by the welding current control which is corelated to the welding speed control in order to keep constant bead height.

アークセンサーによる溶着量の自動制御 ＩＩ 多層ＭＡＧ自動溶接装置の開発

The automatic seam tracking system by arc sensor method developed by NKK has an original feature, that a weaving arc in a groove performs groove surface tracking under constant arc length control (AVC or ACC) and the turning point of weaving is controlled by the condition when torch height reaches to constant preset level. In this system, weaving width well corresponds to groove width independently to variation of deposited amount of metal. Namely, variation value of weaving width is same as that of groove width. Based on this relationship, welding speed control system has been developed. Where, only the variation value of weaving width is used as detected parameter, and optimum value of welding speed to keep bead height constant is calculated and output at every cycle of weaving. The pulsed MAG arc welding system for multi-pass welding of V shaped butt joint has been developed. Main function of this system is adaptive microcomputer control with above mentioned arc sensor method, such as seam tracking, weaving width control and bead height control for every pass of welding.In addition, following functions are also composed: built-up sequence control where number of passes is automatically decided from weaving width, simplified operating system by man-machine dialogic style with liquid crystal display and a key board, and use of a couple of optical fiber cable for transmission of multiple control signals. This system has been already applied to the fabrication of steel box columns.

ＩＴＶ画像処理システムによるパルス溶接のサンプル値制御

The problem for measuring and controlling the arc length and the torch height is important as a basis of research in automatic arc welding systems. Improvement of welding quality requires to keep constant optimum values of the length and current of the arc. In this paper, we discuss the stability and adaptability of the arc length in the MIG pulse arc welding system with a constant feeding speed of the electrode wire. Consequently, it is necessary to control the height of welding torch so as to keep the electrode extension constant for controlling both the current and length of the arc. We construct a basic visual robot which measures and controls the arc length and the torch height, using the personal computer, image processing device, and ITV camera as a sensor. Furthermore, we describe how to determine the characteristic of the digital controller, which controls the welding current and the digital servo motor for controlling the arc length and the torch height. We also introduce a basis of the electric techniques which incorporate the personal computer, image processing device, digital-analog converter, programmable current source, and digital servo motor.