Shujun Chen

Machine assisted manual torch operation: system design, response modeling, and speed control

Skills possessed by human welders typically require a long time to develop. Especially, maintaining the torch to travel in desired speed is challenging. In this paper, a feedback control system is designed to assist the welder to adjust the torch movement for the desired speed in manual gas tungsten arc welding process. To this end, an innovative helmet based manual welding platform is proposed and developed. In this system, vibrators are installed on the helmet to generate vibration sounds to instruct the welder to speed or slow down the torch movement. The torch movement is monitored by a leap motion sensor. The torch speed is used as the feedback for the control algorithm to determine how to change the vibrations. To design the control algorithm, dynamic experiments are conducted to correlate the arm movement (torch speed) to the vibration control signal. Linear model is firstly identified using standard least squares method, and the model is analyzed. A nonlinear adaptive neuro-fuzzy inference system (ANFIS) model is then proposed to improve the model accuracy. The resultant nonlinear ANFIS model can estimate the welder’s response on the welding speed. Based on the response model, a PID control algorithm has been designed and implemented to control the welder arm movement for desired torch speed. Experiments verified the effectiveness of the system for the desired speed with acceptable accuracy.

Measurement and Analysis of Plasma Arc Components

To better understand keyhole plasma arc (PA) and help improve the process, the authors recently observed that the electron flow may deviate from its ionized arc plasma which is electrically neutral. This phenomenon has been referred to as the arc separability which provides a better way to understand the arc fundamentally. Hence, in this study the authors designed an innovative experimental system to measure/record the heat and pressure from the separated arc components—arc plasma and electron flow. An algorithm was proposed to calculate/derive the distribution of the pressure from its bulk measurements that are easy to obtain accurately. Experiments were conducted to study the effects of welding parameters on the heat and pressure in the arc components. It is found that for the constrained PA, the heat applied into the work-piece through the arc plasma exceeds that from the electron flow and this dominance increases as the current increases. However, for the heat from the electron flow, the constraint on the arc does not change it significantly as can be seen from the comparison with that in free gas tungsten arc (GTA). For the pressure in PA, the arc plasma plays the dominant role in determining its amplitude, while the electron flow only primarily contributes to the distribution.

A novel method for testing the electrical property of arc column in plasma arc welding

The electrical property in arc column plays a fundamental role in understanding, controlling, and developing arc processes. In this study, a novel dual active probe method is proposed to measure the arc conductivity, as measured by the voltage-to-current ratio (V-I ratio), and study its electrical property distribution. The probes were partially coated except for their tips such that the electrical conductivity can be accurately tested with fine resolution. During test, the two probes moved into the arc column to detect the V-I ratio of selected zone between the probe tips. Since the speed of the movement is relatively slow, the moving probes are expected to have no significant interruption to the arc. The effect of the probe rotation angular velocity was examined. It was found that with the decrease of probe angular velocity, the instantaneous V-I ratio of the arc between two probes firstly decreases and then tends to be constant. Analysis suggests that the dynamics of the detection circuit is responsible. The testing current applied and the application positions (probe tips), as parameters of the detection circuit, were then analyzed using the circuit model. This novel method provides an effective new approach to study fundamental properties of welding.

Texture evolution and plastic deformation mechanism in magnetic pulse welding of dissimilar Al and Mg alloys

Texture evolution and plastic deformation mechanism of the weld zones of magnetic pulse welded dissimilar 1060 pure Al and AZ31B Mg alloy have been investigated in the present work. A much refined microstructure with smaller grains and higher hardness was observed near the weld interface which has different texture types compared to the BM (base material) at both the Al side and the Mg side. The intermetallic layers at the interface of the Al side and the Mg side have the highest hardness. The region near the weld interface has higher activity of both slip and twinning. Slip occurs on two planes (111) and (1¯

Interval model based human welder's movement control in machine assisted manual GTAW torch operation

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Double-Electrode Arc Welding Process: Principle, Variants, Control and Developments

11) in the Al BM, while the active slip systems in the Al region near the weld interface are on four planes (111), (111¯

Microstructure evolution during magnetic pulse welding of dissimilar aluminium and magnesium alloys

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