Papers by Author: Hong Ming Gao

Abstract: The arc behavior in dry hyperbaric Gas Metal Arc Welding (GMAW) process was investigated by using a high speed camera system and welding electric signal acquisition system. The arc shape in hyperbaric argon environment of 0.1-2MPa shows quite different characteristic from that at normal pressure. With the increase of ambient pressure, the arc length turns shorter, arc column is contracted, and the arc brightness increases. At elevated ambient pressure, the arc length increases with increasing welding voltage. Arc voltage has a good linear relation with arc length. The sum of the fall voltages at ambient pressure of 0.4MPa, 0.8MPa, and 2MPa is nearly constant which is about 20.2-21.7V. The values of electric field strength of arc column at different ambient pressure were gained through the linear fit, which are increased with increasing ambient pressure. The arc static characteristics at elevated ambient pressure are raising characteristics, and it is shifted upward with increasing ambient pressure.

Abstract: The metal transfer behavior in hyperbaric GMAW process was investigated by using a high speed camera system with infrared laser as backlight. The metal transfer mode at 1-12bar argon environment shows different characteristics. Three kinds were observed: large droplet repelled transfer, projected repelled transfer and hyperbaric streaming transfer. Large droplet repelled transfer occurs mostly in the welding process with low feeding speed and relatively low welding voltage. Projected repelled transfer appears at middle feeding speed and high ambient pressure. Transfer tracks of former two modes deviate from the axial direction of welding wire. The spatter is produced more frequently in the projected repelled transfer mode. Hyperbaric streaming transfer is found meanly at high feeding speed and relatively high voltage. Because of its stability reflected from metal transfer process, hyperbaric GMAW process with hyperbaric streaming transfer mode should be employed preferentially.

Abstract: An hot-wire GMAW process is proposed in which the wire is preheated by a TIG arc to enhance the wire melting, and the process is aimed at high efficiency welding with a low level heat input. The welding system is designed, the wire temperature is monitored and the metal transfer and arc behavior is observed. The preheating effect on the wire temperature is analyzed, and the influence of the hot wire on the metal transfer, arc behavior, and the weld formation are analyzed, compared with conventional GMAW. The results show that the preheated wire can significantly enhance the wire melting, and thus several beneficial effects on the GMAW process.

Abstract: Welding seam tracking precision is a key factor influencing welding quality for master-slave robot remote welding system. However, it does not satisfy the welding requirement due to significant noises. To eliminate the influence of noises upon the seam tracking precision and improve the seam tracking precision, a master-slave robot remote welding system was built and Kalman filtering (KF) was applied to the seam tracking process. The experimental results show that the KF eliminated the influence of noises upon the seam tracking precision and improved the seam tracking precision.

Abstract: GMAW with strip electrode is a new method, which uses the flat wire with a rectangular cross-section to replace the conventional round wire as consumable electrode. In the present study, the welding system was established. Then the typical arc behavior and metal transfer were analyzed. After that, high-speed-high-current welding experiment was carried out in both GMAW with strip electrode and conventional round wire. The results show that, Compared with the conventional GMAW with round wire, the welding arc of GMAW with strip electrode has much lower arc pressure, and the impact of the droplet on the weld pool is weakened remarkably. These two characteristics make GMAW with strip electrode suitable for high efficiency welding on the basis of maintaining the original advantages of GMAW.

Abstract: 10mm-5A06 aluminum alloy was butt-welded in a single pass by the plasma-gas metal arc (plasma-MIG) welding procedure, the joints were subjected to X-ray inspection, the microstructure and mechanical performance of weld were also studied. The results indicate that plasma-MIG welding is superior to regular conventional MIG welding on the aspects of reducing weld porosity, increasing joint quality and improving deposition efficiency. Good weld joint with less porosity and excellent mechanical properties is obtained, which can reach as 92.62% tensile strength and 85.12% elongation percentage as base metal. Dimples in which the precipitated phase is the solid solution based on Al3Mg2 are observed in fracture scanning electron micrograph and the fracture mode is ductile rupture. α-Al and Al3Mg2 ,α-Al and eutectic structure are observed respectively in fusion area and in weld zone. The wire feed rate and melting rate can come to 14.5m/min and 80g/min respectively for the 1.6mm welding wire by the plasma-MIG welding process on the premise that the tensile strength of the joints meet the requirements.

Abstract: This paper presents a generic design and implementation of a telerobotic system application for the remote welding of unstructured and hazardous environment. The objective is to establish a remote welding telerobotic system that is flexibility to carry out welding seam tracing and welding remotely. According to the difference of welding task and environment, this paper presents human machine cooperative control strategies that integrate sensor and model-based computer assistance. The human operator decision and control commands participate into every control level of the teleoperation system. The specific control modes have been presented to integrate into human machine interface (HMI).

Abstract: In the near twenty years, with the rapid increase of Chinese economy, Chinese welding technology developed very fast. In 2003, the annual output of steel in China has reached 230 megatons and above 40 percent was manufactured by welding process. The main welding engineering projects include: the Three Gorges power station, bridges over the Changjiang River, high pressure heavy-duty chemical container, pipeline project of transferring natural gas from West to East and manned spacecraft etc. Meanwhile, Chinese annual output of welding materials exceeds 1,200 kilotons, welding equipments exceed 200,000 sets and the welding automation rate reached 40 percent. The State Key Laboratory of Advanced Welding Production Technology in Harbin Institute of Technology is the only welding laboratory of national level in China. It is the base of applied fundamental research and high quality welding technicians training. It has completed many projects of welding technology development and some significant applied engineering tasks. Every year, about 15-20 Doctors, 40-50 Masters and 70-100 Bachelors graduate from the Laboratory. Also, it is opened to the whole world.