Geometry and quality of welds

Common welding joint types are: square butt joint, single V- preparation joint, lap joint, T-joint.

Welds can be geometrically prepared in many different ways. Other variations exist as well – for example, double-V preparation joints are characterized by the two pieces of material each tapering to a single center point at one-half their height. Single-U and double-U preparation joints are also fairly common – instead of having straight edges like the single-V and double-V preparation joints, they are curved, forming the shape of a U. Lap joints are also commonly more than two pieces thick – depending on the process used and the thickness of the material, many pieces can be welded together in a lap joint geometry. Here are the examples of weld types.

Often, particular joint designs are used exclusively or almost exclusively by certain welding processes. For example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed on lap joints. However, some welding methods, like shielded metal arc welding, are extremely versatile and can weld virtually any type of joint. Additionally, some processes can be used to make multipass welds, in which one weld is allowed to cool, and then another weld is performed on top of it. This allows for the welding of thick sections arranged in a single-V preparation joint, for example.

The cross-section of a welded butt joint, with the darkest gray representing the weld or fusion zone, the medium gray the heat-affected zone, and the lightest gray the base material.

After welding, a number of distinct regions can be identified in the weld area. The weld itself is called the fusion zone – more specifically, it is where the filler metal was laid during the welding process. The properties of the fusion zone depend primarily on the filler metal used, and its compatibility with the base materials. It is surrounded by the heat-affected zone (HAZ), the area that had its microstructure and properties altered by the weld. These properties depend on the base material’s behavior when subjected to heat. The metal in this area is often weaker than both the base material and the fusion zone, and is also where residual stresses are found.

Most often, the major metric used for judging the quality of a weld is its strength and the strength of the material around it. Many distinct factors influence this, including the welding method, the amount and concentration of heat input, the base material, the filler material, the flux material, the design of the joint, and the interactions between all these factors. To test the quality of a weld, either destructive or nondestructive testing methods are commonly used to verify that welds are defect-free, have acceptable levels of residual stresses and have acceptable heat-affected zone properties. Welding codes and specifications exist to guide welders in proper welding and in how to judge the quality of welds.

5. Complete the definitions below with the highlighted words in the text:

__________ is a science of the properties and relations of lines, angles surfaces and solids.

__________ are the details or instructions for the design, materials or something to be made or done.

__________ is a state of being able to be able to exist together with somebody or something.

__________ is to be the form of a line of which no part is straight and which changes directions without angles.

__________ means directly, not in a curve or at an angle.

__________ means usual and ordinary, happening or found often in many places.

6. Put 3 questions to the text “Geometry and quality of welds”. Let your groupmates answer them.