Welding Processes Handbook

K Weman

• Éditeur: Woodhead Publishing
• Année: 2011
• ISBN:
  9780857095183
• Édition: 2
• Sujet: Tecnología e ingeniería
• Sous-sujet: Ingeniería industrial

The first edition of Welding processes handbook established itself as a standard introduction and guide to the main welding technologies and their applications. This new edition has been substantially revised and extended to reflect the latest developments.After an initial introduction, the book first reviews gas welding before discussing the fundamentals of arc welding, including arc physics and power sources. It then discusses the range of arc welding techniques including TIG, plasma, MIG/MAG, MMA and submerged arc welding. Further chapters cover a range of other important welding technologies such as resistance and laser welding, as well as the use of welding techniques for cutting, surface cladding and hardfacing, soldering and brazing. A final group of chapters discuss more general issues such as mechanisation, safety, residual stress and distortion, welding design, costs and quality assurance, as well as the welding of steel and aluminium.The new edition of Welding processes handbook confirms its reputation as a concise, authoritative and practical introduction to welding and its applications for both students and engineers. It is designed to meet the requirements of Module 1: Welding processes and equipment of the International Institute of Welding (IIW) guidelines for the training of welding personnel at IWE, IWT, IWS and IWP level.

• This new edition has been substantially revised and extended to reflect the latest developments in the main welding technologies and their applications
• Reviews gas welding and discusses the fundamentals of arc welding, including arc physics and power sources, before covering the range of arc welding techniques, including TIG, plasma, MIG/MAG, MMA and submerged arc welding
• Examines a range of important welding technologies, such as resistance and laser welding and the use of welding techniques for cutting, surface cladding and hardfacing, soldering and brazing

1

Introduction to welding

1.1 The history of welding

Methods for joining metals have been known for thousands of years, but for most of this period the only form of welding was forge welding by a blacksmith.

A number of totally new welding principles emerged at the end of the 19th century. It became possible to combine and store safely gases such as oxygen and acetylene to produce a flame with enough heat. At the same time sufficient electrical current could then be generated for resistance welding and arc welding. The intensity of the heat source enabled heat to be generated in, or applied to, the workpiece quicker than it was conducted away into the surrounding metal. Consequently it was possible to generate a molten pool which solidified to form the unifying bond between the parts being joined. The basic welding methods of resistance welding, gas welding and arc welding were all developed during the time before World War I.

Figure 1.1 Thomson’s resistance welding transformer.

Resistance welding

The first resistance welding machines were used for butt welding. Elihu Thomson made the first welding transformer in 1886 in the USA and patented the process the following year. His transformer managed to output approximately 2000 A at 2 V open circuit voltage.

After the turn of the century Thomson continued to develop other types of machines such as spot welding, seam welding, projection welding and flash butt welding. Spot welding later became the most common resistance welding method and today is used mainly in the automotive industry but also for many other sheet metal applications. Figure 1.2 shows the principle: two copper electrodes apply a pressure to the overlapping plates and a high current melts the plates together. The first robots for resistance spot welding were delivered from Unimation to General Motors in 1964.

Figure 1.2 The principle of resistance spot welding.

Gas welding

Gas welding with an oxyacetylene flame was developed in France at the end of the 19th century. The first torch suitable for welding was made by Edmund Fouche and Charles Picard in about 1900. The use of acetylene and oxygen made it possible to produce a comparatively high flame temperature, 3100 °C, which is higher than that of other hydrocarbon based gases. The torch became the most important tool for welding and cutting of steel.

Acetylene gas had been discovered much earlier in England when Edmund Davy in England found that a flammable gas was produced when carbide was decomposed in water. The gas proved to be excellent for illumination when burned and this soon became the main use of acetylene.

However, numerous large explosions occurred when the gas was transported and used. It was found that acetone could dissolve large quantities of acetylene, especially if the pressure was increased. In 1896 Le Chatelier developed a safe way of storing acetylene by the use of acetone and a porous stone inside a cylinder (see Figure 1.3). The Swede Gustaf Dahlén at AGA changed the composition of the porous content and managed to make acetylene storage 100 % safe.

Figure 1.3 Equipment for gas welding.

Arc welding

Arc welding was initially carried out using carbon electrodes, developed by Bernardos, and then by the use of steel rods. The weld was however not protected from the air and there were problems with quality. The Swede Oskar Kjellberg made an important advance when he developed and patented the coated electrode. The welding result was amazing and arc welding using coated electrodes became the foundation of the ESAB welding company.

Figure 1.4 Principle of Manual Metal Arc (MMA) w...