Welding Flashcards
(33 cards)
What processes does the term joining refer to?
Welding, brazing, soldering, and adhesive bonding
What is welding?
Welding is a materials joining process in which two or more parts are coalesced at their contacting surfaces by a suitable application of heat and/or pressure.
What is a weldment?
The assemblage of parts that are joined by welding
What are the main advantages of welding?
- Welding provides a permanent joint. The welded parts become a single entity.
- The welded joint can be stronger than the parent materials if a filler metal is used that has strength properties superior to those of the parents, and if proper welding techniques are used.
- Welding is usually the most economical way to join components in terms of material usage and fabrication costs. The alternative mechanical assembly is usually heavier than a corresponding weldment.
- Welding is not restricted to the factory environment. It can be accomplished “in the field”.
What are the limitations / disadvantages of welding?
- Most welding operations are performed manually and are expensive in terms of labor cost. Many welding operations are considered “skilled trades”, and the labor to perform these operations may be scarce.
- Most welding processes are inherently dangerous because they involve the use of high energy.
- Since welding accomplishes a permanent bond between the components, it does not allow for convenient disassembly.
- The welded joint can suffer from certain quality defects that are difficult to detect. The defects can reduce the strength of the joint.
What is the name for the surfaces that are to be joined through welding?
Faying surfaces
What are the two main groups of welding process?
Fusion Welding
Solid-State Welding
Give an overview of fusion welding
Fusion-welding processes use heat to melt the base metals. In many fusion welding operations, a filler metal is added to the molten pool to facilitate the process and provide bulk and strength to the welded joint.
What is a fusion-welding operation with no filler called?
An autogenous weld
What are the three main types of fusion welding operations?
Arc Welding
Resistance Welding
Oxyfuel Gas Welding
Give an overview of Arc Welding (AW)
Arc welding refers to a group of welding processes in which heating of the metals is accomplished by an electric arc.
Give an overview of Resistance Welding (RW)
Resistance welding achieves coalescence using heat from electrical resistance to the flow of a current passing between the faying surfaces of two parts held together under pressure.
Give an overview of Oxyfuel Gas Welding (OGW)
These joining processes use an oxyfuel gas, such as a mixture of oxygen and acetylene, to produce a hot flame for melting the base metal and filler metal
What is solid-state welding?
Solid-state welding refers to joining processes in which coalescence results from application of pressure alone or a combination of heat and pressure. If heat is used, the temperature in the process is below the melting point of the metals being welded. No filler metal is utilized.
Give an overview of Diffusion Welding (DFW)
Two surfaces are held together under pressure at an elevated temperature and the parts coalesce by solid-state diffusion.
Give an overview of Friction Welding (FRW)
Coalescence is achieved by the heat of friction between two surfaces.
Give an overview of Ultrasonic Welding (USW)
Moderate pressure is applied between the two parts and an oscillating motion at ultrasonic frequencies is used in a direction parallel to the contacting surfaces. The combination of normal and vibratory forces results in shear stresses that remove surface films and achieve atomic bonding of the surfaces.
What are the five basic types of joint
Butt Joint (Same plane) Corner Joint (Joined at a right angle) Lap Joint (Two overlapping parts) Tee Joint (T shape) Edge Joint (Joined at parallel edges)
What are the typical zones of a fusion weld joint in which filler metal has been used?
1) Fusion Zone
2) Weld Interface
3) Heat-Affected Zone
4) Unaffected Base Metal Zone
What are the characteristics of the fusion zone?
The fusion zone consists of a mixture of filler metal and base metal that have completely melted. This zone is characterized by a high degree of homogeneity among the component metals that have been melted during welding. The mixing of these components is motivated largely by convection in the molten weld pool.
What is a significant difference between solidification during welding compared to during casting.
Epitaxial grain growth occurs in welding
What is epitaxial grain growth?
In welding, by contrast, the nucleation stage of solidification is avoided by the mechanism of epitaxial grain growth, in which atoms from the molten pool solidify on pre-existing lattice sites of the adjacent solid base metal. Consequently, the grain structure in the fusion zone near the heat-affected zone tends to mimic the crystallographic orientation of the surrounding heat-affected zone.
Describe the Weld Interface?
A narrow boundary that separates the fusion zone from the heat-affected zone. The interface consists of a thin band of base metal that was melted or partially melted (localized melting within the grains)during the welding process but then immediately solidified before any mixing with the metal in the fusion zone. Its chemical composition is therefore identical to that of the base metal.
Describe the Heat-affected Zone (HAZ)
The metal in this zone has experienced temperatures that are below its melting point, yet high enough to cause microstructural changes in the solid metal.
