welding

Views:
 
     
 

Presentation Description

about welding process

Comments

Presentation Transcript

FUNDAMENTALS OF WELDING:

FUNDAMENTALS OF WELDING Overview of Welding Technology The Weld Joint Physics of Welding Features of a Fusion Welded Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Joining and Assembly Distinguished:

Joining and Assembly Distinguished Joining - welding, brazing, soldering, and adhesive bonding These processes form a permanent joint between parts Assembly - mechanical methods (usually) of fastening parts together Some of these methods allow for easy disassembly, while others do not Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Welding:

Welding Joining process in which two (or more) parts are coalesced at their contacting surfaces by application of heat and/or pressure Many welding processes are accomplished by heat alone, with no pressure applied Others by a combination of heat and pressure Still others by pressure alone with no external heat In some welding processes a filler material is added to facilitate coalescence Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Why Welding is Important:

Why Welding is Important Provides a permanent joint Welded components become a single entity Usually the most economical way to join parts in terms of material usage and fabrication costs Mechanical fastening usually requires additional hardware components (e.g., screws and nuts) and geometric alterations of the parts being assembled (e.g., holes) Not restricted to a factory environment Welding can be accomplished "in the field" Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Limitations and Drawbacks of Welding:

Limitations and Drawbacks of Welding Most welding operations are performed manually and are expensive in terms of labor cost Most welding processes utilize high energy and are inherently dangerous Welded joints do not allow for convenient disassembly Welded joints can have quality defects that are difficult to detect Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Generally, Welding is performed on parts made of the same metal However, some welding operations can be used to join dissimilar metals Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Types of Welding Processes:

Types of Welding Processes Some 50 different types of welding processes have been catalogued by the American Welding Society (AWS) Welding processes can be divided into two major categories: Fusion welding Solid state welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Fusion Welding:

Fusion Welding Joining processes that 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 added strength to the welded joint A fusion welding operation in which no filler metal is added is called an autogenous weld Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Some Fusion Welding Processes:

Some Fusion Welding Processes Arc welding (AW) – melting of the metals is accomplished by electric arc Resistance welding (RW) ‑ melting is accomplished by heat from resistance to an electrical current between faying surfaces held together under pressure Oxyfuel gas welding (OFW) ‑ melting is accomplished by an oxyfuel gas such as acetylene Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Arc Welding:

Arc Welding A manual arc welding operation Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Solid State Welding:

Solid State Welding Joining processes in which coalescence results from application of pressure alone or a combination of heat and pressure If heat is used, temperature is below melting point of metals being welded No filler metal is added in solid state welding Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Some Solid State Welding Processes:

Some Solid State Welding Processes Diffusion welding (DFW) –coalescence is by solid state fusion between two surfaces held together under pressure at elevated temperature Friction welding (FRW) ‑ coalescence by heat of friction between two surfaces Ultrasonic welding (USW) ‑ coalescence by ultrasonic oscillating motion in a direction parallel to contacting surfaces of two parts held together under pressure Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Principal Applications of Welding :

Principal Applications of Welding Construction - buildings and bridges Piping, pressure vessels, boilers, and storage tanks Shipbuilding Aircraft and aerospace Automotive Railroad Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Welder and Fitter:

Welder and Fitter Welder - manually controls path or placement of welding gun Often assisted by second worker, called a fitter , who arranges the parts prior to welding Welding fixtures and positioners are used to assist in this function Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

The Safety Issue:

The Safety Issue Welding is inherently dangerous to human workers High temperatures of molten metals In gas welding, fuels (e.g., acetylene) are a fire hazard Many welding processes use electrical power, so electrical shock is a hazard Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Special Hazards in Arc Welding:

Special Hazards in Arc Welding Ultraviolet radiation emitted in arc welding is injurious to human vision Welder must wear a special helmet with a dark viewing window Filters out dangerous radiation but welder is blind except when arc is struck Sparks, spatters of molten metal, smoke, and fumes add to the risks Ventilation needed to exhaust dangerous fumes from fluxes and molten metals Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Automation in Welding:

Automation in Welding Because of the hazards of manual welding, and to increase productivity and improve quality, various forms of mechanization and automation are used Machine welding – mechanized welding under supervision and control of human operator Automatic welding – equipment performs welding without operator control Robotic welding - automatic welding implemented by industrial robot Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

The Weld Joint:

The Weld Joint The junction of the edges or surfaces of parts that have been joined by welding Two issues about weld joints: Types of joints Types of welds used to join the pieces that form the joints Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Five Types of Joints:

Five Types of Joints Butt joint Corner joint Lap joint Tee joint Edge joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Parts lie in same plane and are joined at their edges Figure 30.2 Five basic types of joints: (a) butt Butt Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Parts in a corner joint form a right angle and are joined at the corner of the angle Figure 30.2 (b) corner Corner Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Consists of two overlapping parts Figure 30.2 (c) lap Lap Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

One part is perpendicular to the other in the approximate shape of the letter "T" Figure 30.2 (d) tee Tee Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Parts in an edge joint are parallel with at least one of their edges in common, and the joint is made at the common edge(s) Figure 30.2 (e) edge Edge Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Types of Welds:

Types of Welds Each of the preceding joints can be made by welding Other joining processes can also be used for some of the joint types There is a difference between joint type and the way it is welded ‑ the weld type Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Fillet Weld:

Fillet Weld Used to fill in the edges of plates created by corner, lap, and tee joints Filler metal used to provide cross section in approximate shape of a right triangle Most common weld type in arc and oxyfuel welding Requires minimum edge preparation Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Figure 30.3 Various forms of fillet welds: (a) inside single fillet corner joint; (b) outside single fillet corner joint; (c) double fillet lap joint; and (d) double fillet tee joint. Dashed lines show the original part edges. Fillet Welds Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Groove Welds:

Groove Welds Usually requires part edges to be shaped into a groove to facilitate weld penetration Edge preparation increases cost of parts fabrication Grooved shapes include square, bevel, V, U, and J, in single or double sides Most closely associated with butt joints Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Figure 30.4 Some groove welds: (a) square groove weld, one side; (b) single bevel groove weld; (c) single V‑groove weld; (d) single U‑groove weld; (e) single J‑groove weld; (f) double V‑groove weld for thicker sections. Dashed lines show original part edges. Groove Welds Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Fused section between surfaces of two plates Used for lap joints Closely associated with resistance welding Multiple Spot Welds are required to join the parts Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Figure 30.6 (a) Spot weld Spot Weld

Physics of Welding:

Physics of Welding Fusion is most common means of achieving coalescence in welding To accomplish fusion, a source of high density heat energy must be supplied to the faying surfaces, so the resulting temperatures cause localized melting of base metals (and filler metal, if used) For metallurgical reasons, it is desirable to melt the metal with minimum energy but high heat densities Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Power Density:

Power Density Power transferred to work per unit surface area, W/mm 2 (Btu/sec‑in 2 ) If power density is too low, heat is conducted into work, so melting never occurs If power density too high, localized temperatures vaporize metal in affected region There is a practical range of values for heat density within which welding can be performed Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Comparisons Among Welding Processes:

Comparisons Among Welding Processes Oxyfuel gas welding (OFW) develops large amounts of heat, but heat density is relatively low because heat is spread over a large area Oxyacetylene gas, the hottest of the OFW fuels, burns at a top temperature of around 3500  C (6300  F) Arc welding produces high energy over a smaller area, resulting in local temperatures of 5500  to 6600  C (10,000  to 12,000  F) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Power Densities for Welding Processes:

Power Densities for Welding Processes Welding process W/mm 2 (Btu/sec-in 2 ) Oxyfuel 10 (6) Arc 50 (30) Resistance 1,000 (600) Laser beam 9,000 (5,000) Electron beam 10,000 (6,000) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Power Density :

Power Density Power entering surface divided by corresponding surface area: where PD = power density, W/mm 2 (Btu/sec‑in 2 ); P = power entering surface, W (Btu/sec); and A = surface area over which energy is entering, mm 2 (in 2 ) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Unit Energy for Melting:

Unit Energy for Melting Quantity of heat required to melt a unit volume of metal depends upon: Symbolized U m It is the sum of: Heat to raise temperature of solid metal to melting point Depends on volumetric specific heat Heat to transform metal from solid to liquid phase at melting point Depends on heat of fusion Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Heat Transfer Mechanisms in Welding:

Heat Transfer Mechanisms in Welding Not all of the input energy is used to melt the weld metal Heat transfer efficiency f 1 - actual heat received by workpiece divided by total heat generated at source Melting efficiency f 2 - proportion of heat received at work surface used for melting; the rest is conducted into work metal Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Heat Transfer Efficiency f1 :

Heat Transfer Efficiency f 1 Proportion of heat received at work surface relative to total heat generated at source Depends on welding process and capacity to convert power source (e.g., electrical energy) into usable heat at work surface Oxyfuel gas welding processes are relatively inefficient Arc welding processes are relatively efficient Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Melting Efficiency f2 :

Melting Efficiency f 2 Proportion of heat received at work surface used for melting; the rest is conducted into the work Depends on welding process but also influenced by thermal properties of metal, joint configuration, and work thickness Metals with high thermal conductivity, such as aluminum and copper, present a problem in welding because of the rapid dissipation of heat away from the heat contact area Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Heat Available for Welding:

Heat Available for Welding H w = f 1 f 2 H where H w = net heat available for welding; f 1 = heat transfer efficiency; f 2 = melting efficiency; and H = total heat generated by welding process Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Energy Balance Equation:

Energy Balance Equation Net heat energy into welding operation equals heat energy required to melt the volume of metal welded H w = U m V where H w = net heat energy delivered to operation, J (Btu); U m = unit energy required to melt the metal, J/mm 3 (Btu/in 3 ); and V = volume of metal melted, mm 3 (in 3 ) Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

PowerPoint Presentation:

Figure 30.8 Cross section of a typical fusion welded joint: (a) principal zones in the joint, and (b) typical grain structure. Typical Fusion Welded Joint Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

Features of Fusion Welded Joint:

Features of Fusion Welded Joint Typical fusion weld joint in which filler metal has been added consists of: Fusion zone Weld interface Heat affected zone (HAZ) Unaffected base metal zone Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

FUSION ZONE :

FUSION ZONE Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com Consist of a mixture of filler metal and base metal

WELD INTERFACE:

WELD INTERFACE Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com A narrow boundary that separates the fusion zone from heat affected zone. It consists of a thin band of base metal that was melted or partially melted.

Heat Affected Zone:

Heat Affected Zone Metal has experienced temperatures below melting point, but high enough to cause microstructural changes in the solid metal Chemical composition same as base metal, but this region has been heat treated so that its properties and structure have been altered Effect on mechanical properties in HAZ is usually negative, and it is here that welding failures often occur Rattandeep singh (Mechanical engg.)Email:-rsrattanvirdi@gmail.com

authorStream Live Help