CHAPTER ONE
INTRODUCTION
1.1 THE BACKGROUND
Welding is a way of heating pieces of metal using electricity or a flame so that they melt and stick together. It can simply be defined as the process of joining two or more pieces of metal to make the act as a single piece. This is often done by melting the work pieces and adding a filler material to form a pool of molten material that cools to become a strong joint. Because of its strength, welding is used to join beams when constructing buildings, bridges and other structures. Welding can also be used to join pipes in pipelines, power plants at the construction sites and in home appliance. Furthermore, welding is used in shipbuilding, automobile manufacturing and repair, aerospace applications. There are many kinds of welding which include arc welding, resistance welding, gas welding among others. Emphasis will be laid on arc welding because it is the most common type of welding as well as the main aim of this project.
Arc welding is the process of welding that utilizes an electrical discharge (arc) to join similar materials together. Equipment that performs the welding operation under the observation and control of a welding operator is known as welding machine. To solve the problem of weight and size of conventional arc welding machine, it is necessary to design an inverter. The inverter provides much higher frequency than 50Hz or 60Hz supply for transformer used in welding. So transformer of much smaller mass is used to permit the handling of much greater output power. The welding noise produce by conventional arc welding machine is reduced by selecting the operating frequency over the hearing of human ability. The choice of 20Khz for the inverter type arc welding machine was determined to meet the above expectation. The output welding current is controlled by controlling the power supply for transformer at high frequency. This power supply is provided by a frequency inverter. Power switch IGBTs (Insulated Gate Bipolar Transistor) or MOSFETs is used for the inverter design due to its high switching. The control circuit use to control the output welding current is design to drive the power switch at high frequency. Insulated Gate Bipolar Transistor power switch is more efficient and less prone to failure than MOSFETs power switch.