Tuesday, 24 January 2017

An Introduction to Welding from a Structural Engineering Perspective

Introduction

Welding is the process of joining metals in which the parent metals are fused together to form a single piece. Welding is used wherever strength is required, whereas soldering and brazing are primarily employed to handle only light loads. Structural engineers require knowledge of the welding process because many structural frames require field welding during assembling operations. Professional structural engineers preparing for their SE exam certification need the technical knowledge of various welding procedures. 

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Uses of Welding

Welding is: 
  1. A substitute for castings and forgings 
  2. A fabrication medium to join parts permanently and to form built up members 
  3. A connecting medium, in lieu of nuts and bolts 
  4. A repair medium to replace broken and worn out sections of members 

Types of Welded Joints

Welded joints are classified based on the welding method needed. Some examples include the following: butt, lap, strapped, tee, fillet, square butt, single and double V butt, single and double U butt, single and double bevel butt, single and double J butt, and corner joints. Technical and functional aspects of each joint are reviewed in SE exam review courses


Comparison of Riveted Joints and Welded Joints

When compared to riveted joints, welded joints are: 
  1. Lighter in weight 
  2. Stronger as there is no weakening of section due to punching or drilling 
  3. Laborless as several operations, such as punching, drilling, riveting, fullering, or caulking are replaced by a single operation, namely welding. 


Properties of Welding Materials

Many materials can be welded, but the ease of welding varies depending on the material. At a high temperature, the structure of a material changes, as well as the physical properties and corrosion resistance of the material. Gaseous oxides cause blow holes, soluble oxides in the molten metal reduce the strength of the weld, and insoluble oxide causes slag inclusion in the weld. 
  1. Metals, such as zinc, may vaporize and cause the weld to be more porous 
  2. Metals of high thermal expansion and low thermal conductivity are subjected to high cooling stress as the metal cools after welding 
  3. All carbon steels, except for spring steel and tool steel, can be welded satisfactorily, but the low carbon steels are most readily welded 
  4. Cast iron is difficult to weld, but satisfactory welds can be produced if due care is taken while pre-heating prior to welding 


Welding Processes for Different Metals

Arc welding, submerged arc welding, and electro-slag welding methods are employed for welding ferrous metals, as the gas welding process is used for welding metal alloys such as brass and bronze.

Types of welding processes, welding joints dimensions, and welding angle specifications are very important for professional engineers who plan to take the structural engineering certification exam.

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