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ME364_combining_fusion - Valery Marinov Manufacturing...

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Fusion Welding 153 Valery Marinov, Manufacturing Technology 8.2 FUSION WELDING Types of welding processes Welding is a material joining process for a permanent combining of two (or more) parts that involves melting and subsequent solidification of the material from two parts thus forming a strong joint between them. The assemblage of parts is called a weldment . There are two groups of welding processes according to the state of the base material during the welding process: Liquid-state welding ( fusion welding ), and Solid-state welding. Fusion welding is by far the more important category. In fusion welding, the base material is heat to melt. The most important processes in this group fall in the following categories: v Oxyfuel gas welding: an oxyfuel gas produces a flame to melt the base material; v Arc welding: heating and melting of the material is accomplished by an electric arc; v Resistance welding: the source of heat is the electrical resistance on the interface between two parts held together under pressure. In solid-state welding , two parts are jointed together under pressure or a combination of pressure and heat. If heat is applied, the contact temperature is below the melting point of the base metal. Two welding processes are the most popular from this group, v Diffusion welding: parts coalesce by solid-state diffusion; v Friction welding: coalescence is achieved by the heat of friction between two parts; Most of the processes for fusion welding and for solid-state welding are discussed in the present section. Oxyfuel gas welding Oxyfuel gas welding is the term used to describe the group of fusion operations that burn various fuels mixed with oxygen to perform welding or cutting and separate metal plates and other parts. The most important oxyfuel gas welding process is oxyacetylene welding. Oxyacetylene welding (OAW) is a fusion welding process performed by a high-temperature flame from combustion of acetylene and oxygen. The flame is directed by a weld- ing torch and a filler metal in the form of rod is added if the process is applied to weld. Composition of the filler must be similar to that of the base metal. A typical oxyacetylene welding operation is sketched in the figure. Oxyfuel gas welding operation.
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Fusion Welding 154 Valery Marinov, Manufacturing Technology Oxyacetylene welding uses equipment that is relatively inexpensive and portable. It is therefore an economical, versatile process that is well suited to low-quantity production and repair jobs. It is rarely used on the welding of sheet and plate stock thicker than 6 mm because of the advantages of arc welding in such applications. Although OAW can be mechanized, it is usually performed manually and is hence dependent on the skill of the welder to produce a high-quality weld joint.
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