-The product is impossible or uneconomical to manufacture as a single piece. -The product is easier to manufacture in individual components, which are then assembled, than as a single piece. -The product may have to be taken apart for repair or maintenance during its service life. -Different properties may be desirable for functional purpose of the product. -Transportation of the product in individual components as subsequent assembly may be easier and more economical than transporting it as a single piece.
*Welding process that uses a fuel gas, combined with oxygen to produce a flame as the source of the heat required to melt the metals at the joint. *The most common used gas is acetylene. *Typically used for structural sheet-metal fabrication, automotive bodies and various other repair works. *Filler metals are used to supply additional metal to the weld zone during welding. They are available as filler rods or wire.
The heat affected zone is within the base metal itself. It has microstructure different than the base metal because it has been subjected to elevated temperatures for a period of time during welding.
*Other fuel gases, such as hydrogen and methyl acetylene propadiene can also be used in oxy-fuel gas welding. However, the temperatures developed by these gases are low; hence they are used for metals with low melting points, such as lead and for parts that are thin and small
*Oxidizing flames form a thin protective layer of slag over the molten metal. *Carburizing flames is also used in cutting operations.
*One of the oldest, simplest, and the most versatile joining processes, currently about one-half of all industrial and maintenance welding is performed by this process. *The electrodes are in the shape of thin, long sticks hence this process is also known as stick welding. *The SMAW process is best suited for workpiece thicknesses of 3-19 mm, although this range can easily be extended by using multiple-pass techniques. *This process requires that slag( compounds of oxides, fluxes and electrode coating materials) be cleaned after each weld bead. *Slag should also be completely removed, such as by wire brushing, before another weld is applied for multiple-pass welding; thus labor costs are high as the material costs.
*The weld arc is shielded by granular flux(consisting of lime, silica, manganese oxide, calcium fluoride, and other elements) which is fed into the weld zone by gravity flow through a nozzle. *The thick layer of flux cover the molten metal and prevents weld spatter and sparks and suppresses the intense radiation and fumes. *The flux also acts as a thermal insulator, allowing deep penetration of heat into the workpiece. *Typical applications include thick-plate welding for shipbuilding and fabrication of pressure vessels. *The quality of the weld is very high, with good toughness, ductility and uniformity of properties. *The process provides very high welding productivity, depositing 4 to 10 times the amount of weld metal per hour as deposited by the SMAW process.
*Formerly called MIG welding (for metal inert gas) *In gas metal arc welding, the weld area is shielded by an external source of gas, such as argon, helium, carbon dioxide, or various other gas mixtures. *The consumable bare wire is fed automatically through a nozzle into the weld arc and multiple weld layers can be deposited at the joint. *The process is rapid, versatile and economical *Its productivity is double that of the SMAW process.
*This process is similar to gas metal arc welding, with the exception that the electrode is tubular in shape and is filled with flux. *The flux chemistry enables welding of many different base metals. *The flux-cored arc welding process combines the versatility of SMAW with the continuous and automatic electrode feeding feature of GMAW. *Economical and used for welding variety of joints with different thicknesses, mainly with steels, stainless steels and nickel alloys. *A major advantages of FCAW is the ease with which specific weld metal chemistries can be developed. *Easy to automate and readily adaptable to flexible manufacturing systems and robotics.
*Formerly known as TIG welding(for tungsten inert gas) *A filler metal is typically supplied from a filler wire. *It may be done without filler metals such as in close-fit joints. *Flux is not used, and the shielding gas is usually argon or helium or a mixture of the two. *AC is preferred for aluminum and magnesium because the cleaning action of AC removes oxides and improves weld quality. *Suitable for thin metals. *The cost of the inert gas makes this process more expensive than SMAW but it provides welds with very high quality and good surface finish.
*In AHW an arc is generated between two tungsten electrodes in a shielding atmosphere of flowing hydrogen gas. *Near the arc the hydrogen breaks down into its atomic form and absorb a large amount of heat from the arc. *The energy in AHW can easily be varied by changing the distance between the arc stream and the workpiece surface.
*A concentrated plasma arc is produced and directed toward the weld area. *Compared with other arc welding processes, PAW has a greater energy concentration hence deeper and narrower welds can be made, better arc stability, less thermal distortion and higher welding speeds. *A variety of metals can be welded, generally with thicknesses less than 6 mm. *Often used for butt and lap joints.
*Heat is generated by high-velocity, narrow-beam electrons. *The kinetic energy of beams is converted into heat as the electrons strike the workpiece. *The process requires special equipment to focus the beam on the workpiece and a vacuum. *EBW has the capability of producing high-quality, deep and narrow welds that are almost parallel sided and have small heat-affected zones. *Distortion and shrinkage in the weld are minimal and the weld quality is good with very high purity. *Typical applications include welding of aircraft, missile, nuclear and electronic components.
*LBW uses a high-power laser beam as the source of heat to produce fusion weld. I*t has high energy density therefore deep penetration capability. *Suitable for deep and narrow joints. *The efficiency of the process decreases with increasing reflectivity of the workpiece. *LBW produces welds of good quality with minimum shrinkage and distortion. *LBW has good strength and is generally ductile and free of porosity. *Typical applications transmission shaft components, thin electronic parts, automotive body panels.
*Pressure is applied to the workpieces dies or rolls. *Preferably both work should be ductile, because of resulting deformation. *The work pieces should cleaned *Dissimilar metals can not join.
-The heat required for welding is generated through friction at the interface of two members being joined; thus, the source of energy is mechanical. -One of the components remains stationary and the other one rotated at a high constant speed. The two parts to be joined are then brought into contact under an axial force.
-A process which the heat required is produced by means of electerical resistance across the two components. -It doesn’t require; -consumable electrons -shielding gases -flux
-The strength of the joint results primarily from diffusion and to lesser extent from some plastic deformation of the faying surfaces. -Bond strength depends on pressure, temperature, time of contact and the cleanliness of the faying surfaces. - The requirements can be lowered by using filler metal at the interfaces.
Molten filler is drawn by capillary attraction into the space between closely adjacent surface of the parts being joined. -Strong soldered joint. -These process demand higher temperatures and require flame or other heating. -Clean surfaces The choice of filler metal and its composition is important. Because of diffusion, between the filler metal and the base metal proporties of joints can change and a well-defined interface no longer exists.
The filler metal fills the joint by capillary action between closely placed components. -Quick and useful. -The joints not very strong. -Can be used to join various metals and part thicknesses. -The joints cannot withstand heat because of low melting temperature solder.
*Adhesive bonding has been a common method of joining and assembling for applications such as bookbinding, labeling, packaging, home furnishing and footwear. *Aerospace, automotive, appliances and building products are common areas that this process is applied.
Two or more components are assembled in such a way that they can be taken apart during to production service life. Preferred because of its; 1.Ease of manufacturing 2.Ease of assembly, disassembly and transportation. 3.Ease of parts replacement, maintenance and repair. 4.Ease in creating design that require movable joints. 5.Lower overall cost of manufacturing the product.
1JoInING & FASTENINGPROCESSES
WHY JOINING? Ease of manufacturing part by part. Manufacture as a single then assembling. To take part apart for repair or maintenance. Different properties for functional purpose. Ease of transporting as individual part.Source: http://archives.frederatorblogs.com/the_finster_finster_show/files/2008/04/finster-weld-board.jpg
Oxy-Fuel Gas Welding•Fuel gas is used as the source of heat.•The most common used gas is acetylene.•For structural sheet-metal fabrication, automotivebodies and various other repair works.Source:http://www.corrosionist.com/oxyfuel%20gas%20welding.jpg
Heat-Affected Zone (HAZ)Source:http://www.china-weldnet.com/English/information/images/II-1553-05_img_3.jpg
• Hydrogen and methyl acetylene propadiene can alsoused for oxy-fuel gas welding.Source: http://www.roadkillcustoms.com/hot-rods-rat-rods/welding/fig11-4.gif
• Shielded Metal Arc Welding• Submerged Arc Welding• Gas Metal Arc Welding• Flux-Cored Arc WeldingArc Welding- Consumable Electrode
Shielded Metal Arc WeldingThe oldest, simplest and the most versatile joining process.Suited for work piece thicknesses of 3-19 mm this range canextend by using multiple pass technique.Slag should be cleaned after each weld bead.Source: http://www.everlastgenerators.com/images/smawwelding.jpg
Submerged Arc WeldingThe weld arc is shielded by granular flux.Flux prevents molten metal from spatter, sparks and fumes.Used in shipbuilding and pressure vesselsQuality of weld is very high with good toughness, ductility and uniformity of properties.Source:http://www.twi.co.uk/EasysiteWeb/getresource.axd?AssetID=9687&type=full&servicetype=Inline
Gas Metal Arc WeldingSource:http://www.weldingengineer.com/Mig%2006.JPG Known as MIG welding (formetal inert gas) The weld zone is shielded by anexternal source of gas. Multiple layers can bedeposited at the joint. Rapid, versatile & economical Its productivity is double ofSMAW process.
Flux-Cored Arc WeldingTubular electrode filledwith flux is used.Many different basemetals can be melded.Economical & used fordifferent thicknesses.Specific weld metalchemistries can bedeveloped.Easy to automate andadaptable to flexiblemanufacturing systemsand roboticsSource: http://www.personal.psu.edu/jhk5143/edesgn100/project4/welding/pic3.jpg
Gas Tungsten Arc WeldingSource: http://www.personal.psu.edu/jhk5143/edesgn100/project4/welding/pic1.gif Known as TIG welding(for tungsten inert gas) Flux is not needed. In close-fit joints filler wire is not required. The cost of inert gas makes this process expensive.
Atomic Hydrogen WeldingSource: http://lateralscience.co.uk/AtomicH/atomicHpics/arc-atom.jpg Energy is gathered by atomic formed hydrogen. The energy can be varied by changing distancebetween arc and workpiece.
• Electron Beam Welding• Laser Beam WeldingHigh-Energy Beam Welding
Electron Beam WeldingSouce: http://www.joiningtech.com/wp-content/uploads/2012/08/electron-beam-welding-pic02.jpg Heat is generated by electron beams. Vacuum and special equipment are needed. High quality, deep and narrow welded joints. Minimal distortion and shrinkage.
Laser Beam WeldingHigh-power laser is used for source of heat.Good quality welding.Can be easily automated.Source:http://www.ustudy.in/sites/default/files/images/laser%20welding.jpg
The major advantages of LBW over EBW•The LB can be transmitted through air, hence avacuum is not required.•Because laser beam can be shaped, manipulated andfocused optically the process easily be automated.•The laser beam do not generate X-rays unlikeelectron beams.•The quality of the weld is better with laser beamwelding with less tendency for incomplete fusion -,spatter, porosity and distortion.
Cold Welding(CW)Pressure is applied to the workpieces dies or rolls.Preferably both work should be ductile, because of resultingdeformation.The work pieces should cleanedDissimilar metals can not join.Source:http://dc299.4shared.com/doc/1nmxrl0R/preview003.png
Ultrasonic Welding(USW)• -The faying surfaces of the components are subjected to astatic forces and oscillating shearing stress.• -Energy required increases with the thickness and hardness ofthe materials.• -Reliable and versatile for joining metals.• -Dissimilar metals can join.Source: http://static.ddmcdn.com/gif/ultrasonic-welding-1.gif
Friction Welding(FRW) Process can be fully automated. Can be used to join wide variety of materials.Source:http://www.kuka-systems.com/NR/rdonlyres/2DAC0F4D-BB7B-4916-A59D-91259B3391B5/0/reibschweissverfahren_250x200.jpg
Explosion Welding•-The necessary contact pressure is applied bydetonating a layer of explosive placed over one ofthe members being joined.•-The pressure developed are extremely high.Source:http://www.yuguangmetal.com/UploadFile/WebEditor/2012103115602.jpg
Diffusion BondingSource:http://www.substech.com/dokuwiki/lib/exe/fetch.php?w=&h=&cache=cache&media=diffusion_bonding.png Bond strength depends on-pressure-temperature-time of contact-the cleanliness of surfaces
BRAZING AND SOLDERINGBrazing Strong Clean surface The choice of filler metaland its composition Small and thin parts.Source:http://www.abbottfurnace.com/images/technology/fundamentals/brazing/fundamentals-brazing-fig-2.gif
SolderingSourcehttp://upload.wikimedia.org/wikipedia/commons/f/f8/Soldering_a_0805.jpg: Quick Useful Not very strong Various materials can be joint
Adhesive bondingBookbinding, labeling, home furnishing, packaging and footwear.Used in aerospace, automotive, appliances and building products.Source:http://aluminium.matter.org.uk/content/media/images/joinAdhesedMan.gif
Types of Adhesives;Natural:stucrh, dextrin, soya flourInorganic: sodium silicate and magnesium oxy-chlorideSynthetic: thermoplastics and thermosetting polymers.Process Capabilities; Similar and dissimilar, metallic and non-metallic materials canbe easily bonded. Curing time : few seconds at high temperatures, severalhours at room temperature.
Advantages, Provides a bond at the interface Reduces vibration and noise at the joints Eliminate localized stresses The external appearances of joined components is unaffected Very thin and fragile components can be bondedLimitations, The service temperature are relatively low The bonding time can be long Surface preparation is essential It is difficult to test adhesively bonded joints
Questions!1. For more strong joints, which process we should choose in order?(welding, soldering, brazing)2. Why mechanical fastening is most preferred process?3. What are differences between laser beam and electron beamwelding?