The exposure to fumes and gases is one of the hazards associated with welding operations. Apart from research conducted on the mechanism of fume and gas formation and the relationship between fume formation rates and common welding parameters, little is known about the exposure process during welding. This research project aimed to identify the factors that influence exposure, develop an understanding of their role in the exposure process and through this understanding formulate strategies for the effective control of exposure during welding. To address these aims a literature review and an experimental program was conducted The literature review surveyed epidemiological, toxicological and exposure data. The experimental program involved three approaches, the first, an evaluation of the factors that influence exposure by assessing a metal inert gas/mild steel welding process in a workshop setting. The second approach involved the study of exposure in a controlled environment provided by a wind tunnel and simulated welding process. The final approach was to investigate workplace conditions through an assessment of exposure and control strategies in industry. The exposure to fumes and gases during welding is highly variable and frequently in excess of the health based exposure standards. Exposure is influenced by a number of a factors including the welding process, base material, arc time, electrode, arc current, arc voltage, arc length, electrode polarity, shield gas, wire-to-metal-work distance (metal inert gas), metal transfer mode, intensity of the UV radiation (ozone), the frequency of arc ignitions (ozone), thermal buoyancy generated by the arc process, ventilation (natural and mechanical), the welding environment, the position of the welder, the welders stance, helmet type, and helmet position. Exposure occurs as a result of three processes: the formation of contaminants at or around the arc region; their transport from the arc region, as influenced by the entry and thermal expansion of shield gases, the vigorous production of contaminants, thermal air currents produced by the heat of the arc process, and ventilation; and finally the entry of contaminants into the breathing zone of the welder, as influenced by the position of the welder, the welders stance, helmet type, and the helmet position. The control of exposure during welding can be achieved by several means: through the selection of welding parameters that generate low contaminant formation rates; through the limitation of arc time; and by isolating the breathing zone of the welder from the contaminant plume through the use of ventilation, welder position or the welding helmet as a physical barrier. Effective control is achieved by careful examination of the workplace, the selection of the most appropriate control option, and motivation of the workforce.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 209-217).

An automatic system to weld multiple layers using Tungsten Arc (TIG) welding was in the process of being developed by Tool-Tec Welding Inc, prior to the company’s recent bankruptcy and subsequent closure. One of the project’s main concerns was the thermal expansion experienced by the part to be welded. To avoid having to install expensive sensors, it is necessary to predict the temperature and the dilatation of the mould during the welding process. The mould to be welded is preheated to prevent excessive stress due to extreme temperature differences in the material. As well, it is necessary to maintain the temperature of the mould during the welding process in order to avoid distortions or changes in size larger than 1 mm. Two models have been developed to predict the size of the preheat temperature of the mould and prevent mould size changes. One model uses the results of several simulations made with finite element analysis (FEA), while the other one takes advantage of Tool-Tec expert knowledge using the Fuzzy Logic method. Validation of both theories was done at the University of Waterloo, as Tool-Tec had at that point closed down. For the experiment, an MIG (Metal Arc Welding) robot was used, together with a medium-sized mould and an infrared camera. Using an IR camera is preferable to using sensors because a camera gives the whole temperature of the mould while the sensors provide information only about some points, and these may not necessarily be representative ones. However, an IR camera can record hundreds of pictures in a single experiment and analyzing them one by one to sort the useful from the useless is tedious work. Therefore, an automatic selection of the useful pictures and recognition of the mould was the best way to review the data. In the end, successful results were obtained since it was possible to maintain the preheat temperature of the mould within the required limits in order to avoid changes in size larger than 0.05mm. Nevertheless, future tests should involve larger and smaller moulds in order to tune the models presented in this thesis.

Gas Metal Arc welding (GMAW) is one of the primary techniques used to join structural components together. The major obstacle precluding full closed-loop control of GMAW has been the lack of robust techniques using non-destructive and non-contact sensors capable of operating in high temperature and harsh environments typical of GMAW processes. This research uses laser generated ultrasound and electromagnetic acoustic transducer (EMAT) to receive ultrasound. Previous research has focused on ultrasonic shear wave time of flight (TOF) techniques to determine weld penetration depth, a key measure of weld quality. The objective of this research was to use a new technique, frequency modulation of a laser phased array (FMLPA), to determine weld penetration depth. Theoretical background of the FMLPA was developed. An analytical model of the FMLPA was derived and validated through experimentation. The FMLPA was experimentally validated. However, both the FMLPA and shear wave TOF techniques have proven to be impractical for real-time control. These techniques are impractical because the required ultrasonic waves are difficult to acquire due to attenuation and interference from other waves. A new type of wave called the RGLS wave was discovered during the course of this research. The RGLS wave was used to create a new RGLS TOF method for measuring weld penetration depth. The RGLS TOF method for measuring weld penetration depth has proven to be highly accurate, precise, and repeatable. The RGLS TOF method for measuring weld penetration depth has been demonstrated to work both off-line after welding and real-time during welding. Although the FMLPA and shear wave TOF technique was proven to be impractical, the RGLS TOF method has met the ultimate goal of this research area. Other new methods such as the RGSL, RGLL, and RGSS TOF methods related to the RGLS TOF method was also developed. The RGLS TOF method is suited for non-destructive and non-contact sensing. It will help future researchers achieve closed-loop control and automation of the GMAW process, which will help to improve quality and efficiency of welding, and also reduce waste and cost of welding parts together.

We investigate the post-weld-shift(PWS) induced fiber alignment shift in butterfly laser packaging. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A novel measurement and compensation technique employing a high-magnification camera with image capturing system (HMCICS) to probe the post-weld-shift (PWS) induced fiber alignment shifts in high-performance butterfly-type laser module packages is studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The increased coupling efficiency after this PWS compensation was from 3% to 10%. This HMCICS technique has provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

A notch clip approach to compensate post-weld-shift(PWS) induced by laser welding process in butterfly type laser module packages is investigated. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the laser welding process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A notch clip approach and measurements employing a high-magnification camera with image capturing system (HMCICS) to probe the PWS induced fiber alignment shifts and welding compensation on notch in high-performance butterfly-type laser module packages are studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The overall coupling efficiency after this PWS compensation was from 80¢H to 90¢H. This notch approach and HMCICS technique have provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

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In this study, a particle welding tester has been employed to weld the 500 £gm diamond particle coated copper on the aluminum workpiece surface. The DC power supply is used as the welding energy to weld. The resistance material is added into the interface between the electrode and the diamond particle. Hence the welding energy can transfer from the diamond particle to aluminum surface so that the aluminum softens and the diamond particle is embedded into the surface under the applied force. In this experiment, the effects of the applied force (2-20 N), power (13-35 W) on the welding pattern and the behavior of welding interface. When the silicon carbide is used as the resistance material, the weld able region map is established in terms of the applied force and power. The map is divided into the insufficient heat input, the normal welding and the excess heat input. In the insufficient heat input region the power is less than 20 W, and the diamond can not be embed into the workpiece surface because the power is not enough. In the normal welding region, the power is in the range between 20 to 30 W, where the welding quality is quite good. In the excess heat input region, the power is greater than 30 W, where the welding quality is poor because the blowhole and the gas hole are generated on the surface. In the normal welding region, the embedded depth can be controlled by the different force during welding process.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: welding; ultrasonic. Includes bibliographical references (p. 100-101).

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 83-85).