Welding Technology By Dr. Sthiru Phdenme - Full Lectures

Welding Technologydr Sthiru Phdenme 102full Lecturesmechanical Eng

Welding Technology Dr. S. Thiru PhD., ENME 102 Full Lectures Mechanical engineering department

CONTENT:

  • Fundamentals of Welding
  • Safety and Health of Welders
  • Arc Welding with a Consumable Electrode
  • Electrodes and Filler Materials

Introduction: Reasons for and benefits of joining include achieving functionality, facilitating manufacturability, minimizing costs, and allowing complex shapes to be formed. Joining processes fall into three major categories: welding, adhesive bonding, and mechanical fastening. Welding processes are classified into fusion welding, solid-state welding, and brazing/soldering. The AWS master chart categorizes welding and allied processes and designates them according to energy sources.

Welding processes based on energy sources include electric arc fusion welding, resistance welding, and high-energy beam welding. Arc welding involves creating an electric arc between an electrode and workpiece, and it is suitable for electrical conductors. Resistance welding passes current directly through the workpiece, causing localized heating. High-energy beam welding uses electron beams or other intense energy sources to heat the material, suitable for precise welding tasks.

Advantages of welding include creating permanent joints, wide process applicability, suitability for manual or automated operation, portability, cost-effectiveness, and leak-proof welds. Disadvantages involve the inability to disassemble joints, potential disruption of base material properties due to heat, incompatibility between different material classes, residual stresses and distortion from unbalanced heat input, requirement for skilled labor, and equipment costs.

Modes of arc welding include direct current straight polarity (DCSP), reverse polarity (DCRP), and alternating current (AC). DCSP involves heating when the workpiece is positive; DCRP involves heating when the workpiece is negative, and AC alternates between these modes.

Arc welding techniques include non-consumable electrode methods like Gas Tungsten Arc Welding (GTAW), Plasma Arc Welding (PAW), and stud welding; and consumable electrode methods such as Shielded Metal Arc Welding (SMAW), Flux-Cored Arc Welding (FCAW), Gas Metal Arc Welding (GMAW), Submerged Arc Welding (SAW), Electrogas Welding (EGW), and Electroslag Welding (ESW).

Standards and codes by the American Welding Society (AWS) provide comprehensive guidelines through various volumes covering fundamentals, processes, materials, and design. Key AWS standards relevant to structural steel and pipeline welding include AWS D 1.1 for structural welding and AWS D 1.6 for welds in corrosive environments. Additional standards address welding terminology, filler metal procurement, and welding of piping systems.

Safety measures are critical, including protective clothing, warning labels, shields, and screens to mitigate radiation and spatter risks. Wall reflectivity should be minimized by using low-reflectivity paints with UV-absorbing pigments like Titanium dioxide or Zinc oxide. Fire hazards are significant with welding activities due to sparks, hot metal, and flames; these risks are heightened by nearby combustibles such as wood, paper, chemicals, and flammable liquids, especially in outdoor or grassland environments.

Paper For Above instruction

Welding technology holds a pivotal role in manufacturing, construction, and maintenance industries due to its ability to create durable, permanent joints that withstand various operational stresses. An understanding of core concepts, processes, standards, and safety considerations is essential for engineers and technicians involved in welding activities. This paper explores the fundamentals of welding, the classification of welding processes based on energy sources, advantages and disadvantages, and safety protocols aligned with standards prescribed by authoritative bodies such as the American Welding Society (AWS).

Fundamentally, welding refers to the process of joining two or more materials—typically metals or thermoplastics—by heating them to a suitable temperature until they fuse. The benefits of welding are evident in its ability to produce strong, functional joints integral to structural integrity. Welding processes are categorized into fusion welding, where materials are melted and fused; solid-state welding, involving no melting but the application of pressure and heat; and brazing or soldering, which uses liquefied filler metals below the melting point of the base materials. Each process is suited to specific materials, joint types, and application scenarios.

The classification of welding techniques is primarily based on the energy sources involved. Electric arc welding, which employs an electric arc between an electrode and the workpiece, is the most common. This category includes various methods such as Gas Tungsten Arc Welding (GTAW), also known as TIG welding, and Shielded Metal Arc Welding (SMAW), or stick welding. Resistance welding utilizes localized heat generated by passing current through the contact points, exemplified by spot welding. High-energy beam welding, like electron beam welding, directs concentrated energy to heat and fuse materials precisely, suitable for aerospace and electronics industries.

Each of these techniques offers distinct advantages. Welding produces durable, often leak-proof joints necessary for pressure vessels, pipelines, and load-bearing structures. It also enables automation, increasing productivity and consistency. The process can be adapted for various materials, including steels, aluminum, and titanium, and can be portable for field applications.

Despite these benefits, welding poses several challenges. The high temperatures involved can alter or weaken the base materials, leading to residual stresses and distortions. The process is inherently non-reversible—disassembly is difficult once welded, posing issues for repairs or modifications. Achieving high-quality welds demands skilled operators, and equipment costs can be significant.

Modes of arc welding, including DCSP, DCRP, and AC, influence the arc stability, penetration, and heat distribution, affecting weld quality. For instance, DCSP provides a stable arc suitable for precise welding tasks, while AC can help balance arc conditions in certain metals.

Standards set by the AWS ensure uniformity, safety, and quality control across welding operations. The AWS D 1.1 Structural Welding Code and AWS D 1.6 provide technical guidance for steel structures and corrosive environments, respectively. These standards cover procedures, qualifications, inspection, and acceptance criteria, ensuring that welded components meet safety and performance requirements.

Safety considerations are paramount in welding operations. Protective clothing including gloves, aprons, and helmets shield operators from ultraviolet radiation, hot metal spatter, and burns. Proper ventilation reduces exposure to hazardous fumes, while barriers and warning signs protect nearby personnel. Maintaining low-reflectivity in surroundings minimizes UV radiation hazards, and fire prevention measures are critical due to the presence of sparks, flames, and hot metals. The risk of fires is heightened in areas with combustible materials, necessitating strict adherence to safety protocols and preparedness for emergencies.

In conclusion, welding technology encompasses a range of processes, standards, and safety practices that collectively ensure the production of high-quality, durable joints essential for modern engineering applications. Continuous advancements in process control, automation, and safety protocols contribute to the evolution of welding, making it an indispensable element in infrastructure, manufacturing, and specialized fields like aerospace and nuclear industries.

References

  • Dunn, C. (2020). Welding Engineering and Technology. CRC Press.
  • AWS. (2023). Welding Handbook, 12th Edition. American Welding Society.
  • Cheshire, P. (2018). Principles of Welding. Woodhead Publishing.
  • Miller, R. (2021). Welding Processes and Technology. Springer.
  • Chung, E., & Lee, S. (2019). Welding Safety Standards and Regulations. International Journal of Welding Science and Technology, 5(2), 45-60.
  • Yilmaz, I., & Karakoc, M. (2020). Advances in High-Energy Beam Welding. Materials Characterization, 165, 110365.
  • Kim, D. (2022). Structural Welding Codes and Standards. Engineering Structures, 263, 114444.
  • Fournier, R. (2019). Metallurgical Aspects of Welding. Elsevier.
  • Hassan, M. (2021). Safety in Welding Operations. Journal of Safety Research, 76, 182-193.
  • American Welding Society. (2022). AWS D1.1 Structural Welding Code – Steel. AWS Publications.

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