Norrish Advanced Welding Processes

1. Auflage 2006
ISBN: 978-1-84569-170-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 304 Seiten

Reihe: Woodhead Publishing Series in Welding and Other Joining Technologies

Advanced welding processes provides an excellent introductory review of the range of welding technologies available to the structural and mechanical engineer. The book begins by discussing general topics such power sources, filler materials and gases used in advanced welding. A central group of chapters then assesses the main welding techniques: gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), high energy density processes and narrow-gap welding techniques. Two final chapters review process control, automation and robotics.Advanced welding processes is an invaluable guide to selecting the best welding technology for mechanical and structural engineers. - An essential guide to selecting the best welding technology for mechanical and structural engineers - Provides an excellent introductory review of welding technologies - Topics include gas metal arc welding, laser welding and narrow gap welding methods

John Norrish is Professor of Materials Welding and Joining at the University of Wollongong, Australia.

Autoren/Hrsg.

Norrish, J.

Leseproben

1 An introduction to welding processes
Publisher Summary
This chapter discusses some of the basic concepts that are needed to be considered and it highlights some of the features of traditional welding methods. Welding and joining are essential for the manufacture of a range of engineering components, which may vary from very large structures such as ships and bridges, to very complex structures such as aircraft engines or miniature components for micro-electronic applications. A large number of joining techniques are available and, in recent years, significant developments have taken place, particularly in the adhesive bonding and welding areas. A wide range of welding processes is available and their suitability for a given application is determined by the inherent features of the process. 1.1 Introduction
Welding and joining are essential for the manufacture of a range of engineering components, which may vary from very large structures such as ships and bridges, to very complex structures such as aircraft engines or miniature components for micro-electronic applications. 1.1.1 Joining processes
The basic joining processes may be subdivided into: • mechanical joining; • adhesive bonding; • brazing and soldering; • welding. A large number of joining techniques are available and, in recent years, significant developments have taken place, particularly in the adhesive bonding and welding areas. Existing welding processes have been improved and new methods of joining have been introduced. The proliferation of techniques which have resulted makes process selection difficult and may limit their effective exploitation. The aim of this book is to provide an objective assessment of the most recent developments in welding process technology in an attempt to ensure that the most appropriate welding process is selected for a given application. This chapter will introduce some of the basic concepts which need to be considered and highlight some of the features of traditional welding methods. 1.1.2 Classification of welding processes
Several alternative definitions are used to describe a weld, for example: A union between two pieces of metal rendered plastic or liquid by heat or pressure or both. A filler metal with a melting temperature of the same order as that of the parent metal may or may not be used. [1] or alternatively: A localized coalescence of metals or non-metals produced either by heating the materials to the welding temperature, with or without the application of pressure, or by the application of pressure alone, with or without the use of a filler metal. [2] Many different processes have been developed, but for simplicity these may be classified in two groups; namely ‘fusion’ and ‘pressure’ welding as shown in Fig. 1.1, which summarises some of the key processes. A more extensive list of processes is reproduced in Appendix 1. [1]
1.1 Some important welding processes. 1.2 Conventional welding processes
A brief description of the most common processes, their applications and limitations is given below. The more advanced processes and their developments are dealt with in more detail in the remaining chapters. An international standard ISO 4063 [3] identifies processes by a numeric code. The first digit of this code specifies the main process grouping whilst the second and third digit indicate sub-groups. The main groups and some examples of sub-groups are shown in Table 1.1 and where appropriate the classification code is given in {}brackets in Sections 1.2.1 and 1.2.2. Table 1.1 Examples of numbering system from ISO 4063 {1} Arc welding {12} Submerged arc welding {13} Gas shielded metal arc welding {15} Plasma arc welding {111} Manual metal arc welding {131} Metal inert gas welding {141} Tungsten inert gas welding {2} Resistance welding {21} Resistance spot {22} Resistance seam {23} Projection welding {222} Mash seam welding {291} High frequency resistance welding {3} Gas welding {31} Oxy-fuel gas welding {311} Oxy acetylene welding {4} Welding with pressure {42} Friction welding {48} Cold pressure welding {441} Explosive welding {5} Beam welding {51} Electron beam welding {52} Laser beam welding {511} Electron beam welding in vacuum {521} Solid state laser welding {522} Gas laser welding {7} Other welding processes {71} Aluminothermic welding {75} Light radiation welding {753} Infrared welding {8} Cutting and gouging {81} Flame cutting {82} Arc cutting {83} Plasma cutting {84} Laser cutting {821} Air arc cutting {9} Brazing and soldering {91} Brazing {94} Soldering {912} Flame brazing {944} Dip soldering 1.2.1 Welding with pressure
Resistance welding {2} The resistance welding processes are commonly classified as pressure welding processes although they involve fusion at the interface of the material being joined. Resistance spot {21}, seam {22} and projection welding {23} rely on a similar mechanism. The material to be joined is clamped between two electrodes and a high current is applied (Fig. 1.2). Resistance heating at the contact surfaces causes local melting and fusion. High currents (typically 10000 A) are applied for short durations and pressure is applied to the electrodes before the application of current and for a short time after the current has ceased to flow.
1.2 Resistance welding system. Accurate control of current amplitude, pressure and weld cycle time are required to ensure that consistent weld quality is achieved, but some variation may occur due to changes in the contact resistance of the material, electrode wear, magnetic losses or shunting of the current through previously formed spots. These ‘unpredictable’ variations in process performance have led to the practice of increasing the number of welds from the design requirement to give some measure of protection against poor individual weld quality. To improve this situation significant developments have been made in resistance monitoring and control; these allow more efficient use of the process and some of the techniques available are described in Chapter 10. Features of the basic resistance welding process include: • the process requires relatively simple equipment; • it is easily and normally automated; • once the welding parameters are established it should be possible to produce repeatable welds for relatively long production runs. The major applications of the process have been in the joining of sheet steel in the automotive and white-goods manufacturing industries. Cold pressure welding {48} If sufficient pressure is applied to the cleaned mating surfaces to cause substantial plastic deformation, the surface layers of the material are disrupted, metallic bonds form across the interface and a cold pressure weld is formed. [4] The main characteristics of cold pressure welding are: • the simplicity and low cost of the equipment; • the avoidance of thermal damage to the material; • it is most suitable for low-strength (soft) materials. The pressure and deformation may be applied by rolling, indentation, butt welding, drawing or shear welding techniques. In general, the more ductile materials are more easily welded. This process has been used for electrical connections between small-diameter copper and aluminium conductors using butt and indentation techniques....