# Arc Shape Characteristics with Ultra-High-Frequency Pulsed Arc Welding
## 2 Methods  
Figure 1 shows the diagrammatic drawing of a visual inspection system for the gas tungsten arc welding (GTAW); snapshot (a) is the simplified model of (b). The system contains two parts: Part 1, which is included by red rectangle, is the welding system, consisting of a welding source, tungsten welding electrode, shielding gas, weldment, and workspace. It is used for providing the experiment with a stable welding arc plasma. Conventional and pulsed current of 60 and 80 A are both used in the experiment, with argon as the shielding gas and Ti-6 Al-4V titanium alloy as weldment. Part 2, which is included by blue rectangle, reveals the visual measuring system, which consists of high-speed camera and computer. Dimmer filter ND4, which is in front of the high-speed camera lens, is used for decreasing the arc brightness. The high-speed camera collects the real-time image processing signal of the welding process and transmits the signal to the computer via USB. The computer is able to control the time of exposure, sampling time, and some other parameters of the high-speed camera and save the video signal. Average pulsed current of 60 A has a peak current of 80 A and a base current of 40 A, average pulsed current of 80 A has a peak current of 110 A and a base current of 50 A, and the peak duration is all 50%. Finally, conventional and pulsed frequencies of 20 and 40 kHz, both under currents of 60 and 80 A, are used in the GTAW, and the video information is obtained.  
Figure 1: _Cont._  
In the process of obtaining the GTAW images using the high-speed camera, there are always some noise signals, including natural lighting, the influence of arc welding voltage and current, and so on, affecting the brightness of arc. The final result will be affected by noise signals. In this paper, MATLAB, manufactured by American corporation MathWorks (Natick, MA, USA), is used for image de-noising by using the method of median filtering [20], which is a nonlinear signal processing technology to suppress the isolated noise, effectively based on order statistical theory. The feature of median filtering is, at first, to establish a square neighborhood, which is centered on any point. Then, the filter takes every point in the neighborhood, also called the filtering window, in order, substituting the median value for the original one. The image could be subject to a smoothing process when the window moves. The median filtering method has simple arithmetic, low time complexity, and self-adaptive simplification. Based on this, the paper uses the method of median filtering to suppress the noise using a 3 \(\times\) 3 filtering window. Based on MATLAB, the images will be processed in two steps as follows:  
1. Make a welding arc regionalization for de-noised images, the core region is locate near the medial axis of the welding arc plasma, where the arc has the highest temperature, most concentrated plasma, largest current density, most drastic ionization thermal motion, and highest energy. It is also a prime source of energy for the melt of the base material. The shape, voltage, and force, or some other parameters of welding arc, vary with the welding arc core region.  
2. Calculating the ratio of the welding arc core region with respect to the total. The ratio represents the energy transfer efficiency from the welding cathode to the base material. Plenty of scholars have tried to improve the energy transfer efficiency and a number of papers have been published about it. As a result, it is rather valuable to research and discuss matters about the ratio of the core region to the total.