Team Group 6 -Joining processes and Equipment-

Team Group 6 -Joining processes and Equipment- » Cedric Turcotte » Gavin Kurey » David Barboza » Marcos Gonzales » Kevin Archibeque Date: 04/12/2006

Presentation Overview Chapters Chap. 30: Fusion Welding Processes Chap. 31: Solid-State Welding Processes

Ch. 30 sections 1 -4 Fusion-Welding Processes: • What is welding? • Oxyfuel-Gas Welding • Arc-Welding (Nonconsumable Electrode) • Arc-Welding (Consumable Electrode)

Ch. 30 sections 1 -4 Introduction to Welding: • Partial melting/fusion of two members along a joint • Fusion welding – fusing material by means of heat • Fillers • Considerations • Limitations

Ch. 30 sections 1 -4 Oxyfuel-Gas Welding (OFW): • Any welding process using a fuel gas with oxygen to make a flame • Developed in the early 1900 • The flame produced is the source of heat • Common fuel gasses are propane, acetylene • Oxyacetylene-gas welding is the most common variant • Flame temperatures of 6000 F

Ch. 30 sections 1 -4 OFW Continued, Flame types and Fillers: • Oxygen to Gas Ratio • Neutral (1: 1) (oxidation risk!) • Reducing (less oxygen, less combustion) – low heat applications • Oxidizing (more oxygen) –only in copper applications • Filler rod or Wire • Flux • Pressure-gas Welding

Ch. 30 sections 1 -4 Arc-Welding (Nonconsumable Electrode): • Heat required for fusion is obtained from electricity • An electric arc is produced between the workpiece and an electrode • AC or DC power supplies • Polarity • Gas Tungsten Arc Welding - GTAW (TIG) • Plasma Arc Welding - PAW • Atomic Hydrogen Welding - AHW

Ch. 30 sections 1 -4 Gas Tungsten Arc Welding (GTAW): • Formerly TIG Welding • No flux, uses an inert gas (Argon, Helium, etc) • Filler Rod • DC @ 200 A or AC @ 500 A (Best for aluminum) • Can weld a variety of metals • Contaminated Electrode problems • Excellent surface finish and weld quality • Portable • Versatile

Ch. 30 sections 1 -4 Plasma Arc Welding (PAW): • Developed in the 1960’s • Temperatures exceeding 60, 000 F • Ionized hot gas containing equal shares of electrons and ions • Highly Concentrated • Filler fed into the arc, like GTAW • Shielding gas like Argon, Helium, etc • Transferred Arc, Nontransferred methods • Deep, Narrow Welds • Great stability • Low thermal distortion

Ch. 30 sections 1 -4

Ch. 30 sections 1 -4 Atomic Hydrogen Welding (AHW): • Arc generated between two tungsten electrodes inside a hydrogen atmosphere • Arc is maintained seperately from the work piece • Temperatures of 11000 F • Diatomic Hydrogen molecules breakdown under the heat of the arc and recombine when they hit the workpiece, releasing energy.

Ch. 30 sections 1 -4 Arc-Welding (Consumable Electrode): • Again, the heat necessary for fusion is derived from electrical energy • Electrode is consumed as process occurs (a filler) • Shielded metal arc welding (SMAW) • Submerged arc welding (SAW) • Gas metal arc welding (GMAW) (MIG) • Flux core arc welding (FCAW) • Electrogas welding (EGW) • Electroslag welding (ESW)

Ch. 30 sections 1 -4 Shielded metal arc welding (SMAW): • Oldest, simplest, most versatile welding process • 50% of all industrial and maintenance welding • Stick welding • Simple equipment • SLAG!

Ch. 30 sections 1 -4 Submerged Arc Welding (SAW): • Weld arc is shielded by granular flux • Flux could be lime, silica, manganese oxide, etc • Flux is fed to the weld via gravitational feed hopper • Flux can be reused

Ch. 30 sections 1 -4 Gas Metal Arc Welding (GMAW): • Commonly known as MIG Welding • Developed in the 1950’s • Uses a shielding gas (Argon, Helium, CO 2, etc) • Cosumable bare wire is fed through torch • Multiple weld passes are easily accomplished • Low temperatures • Easy to handle, very common • Ferrous and non-ferrous metals • Versatile, rapid, easy to learn!

Ch. 30 sections 1 -4 Flux-cored Arc Welding • Very similar to GMAW • Wire filled with a flux • Flux/slag is easily removed • Very versatile • Common steel welding process • Alloying can be accomplished • Easy Automation

Ch. 30 sections 1 -4 Electrogas welding (EGW): • A machine welding process • Vertical welding in one pass • Butt joints (edge to edge) • Flux-cored or shielding gas • Industrial applications • Reliable

Ch. 30 sections 1 -4 Electroslag Welding (ESW): • Similar in application to EGW • Arc is between machine and work piece • Flux is added/melted by arc • Arc is only “on” at the outset of the welding pass • Not strictly an arc-welding process • Excellent penetration • Good for thick pieces • Many industrial apps

Electrode for Arc Welding

Electrode for Arc Welding Electrodes are consumable and classified according to: • Strength of the deposited weld metal • Current (AC / DC) • Type of coating Identified by numbers and letters, or color code if they are to small to imprint.

Electrode for Arc Welding Typical coated-electrode dimensions: –From 6’’ to 18’’ in length; –From 1/16 to 5/16 in diameter. Electrodes are sold by weight. Selection and recommendations found in supplier literature or reference handbooks.

Electrode for Arc Welding

Electrode for Arc Welding

Electrode Coating Outside coating made of silicate binders and powdered materials (oxides, carbonates, fluorides, metal alloys, and cellulose) Functions Stabilize the arc Generate gases to act as a sheild against surrounding atmosphere. Control rate at which the electrode melts Acts as flux to protect against formation of oxides, nitrides, and inclusions Add alloying elements to the melt zone, enhance the properties of joint.

Electrode Coating Main electrode

Electrode Coating Flux coating (slag) must be remove after each pass to ensure a good weld. Should not be remove too quickly, let the joint cool down a little first.

Electron-Beam Welding

Electron-Beam Welding Heat is generated by high velocity narrowbeam electrons. The kinetic energy of the electrons is converted in heat as they strike workpiece. Usually performed in a vacuum. The greater the vacuum, the greater the penetration.

Electron-Beam Welding

Electron-Beam Welding Electron beam welding (EBW) EBW-HV: High vacuum EBW-MV: Medium vacuum EBW-NV: No vacuum

Electron-Beam Welding Properties: Workpiece can range from foil to 6’’ plate; Depth to width ratio between 10 and 30; Capacities or EBW guns range up to 100 k. W; No flux, filler or shielding gas required; Smaller heat affected zone; Good quality weld; Generates X-rays, hence periodic maintenance and monitoring Weld speed as high as 40 ft/min Ex: Aircraft, missile, nuclear component, gears and shafts.

Laser-Beam Welding

Laser-Beam Welding Laser-beam welding (LBW) utilizes a laser beam as the heat source. - Beam can be focused onto small area, it than has high energy for deeppenetrating capability. - This process is suitable for welding deep in narrow joints with depth-towidth ratio raging from 4 to 10. - Power level up to 100 k. W. - Welding speed up to 250 ft/min - Can weld foil up to 1’’ plate In automotive industry, it’s mostly use for welding transmission components

Laser-Beam Welding Advantages of LBW over EBW – No vacuum required; – Laser beam can be shaped, manipulated and focused. Easily automated; – Do no generate X-rays; – Better quality weld. Less tendency for incomplete fusion, spatter, porosity ans distortion.

Laser-Beam Welding Gillette Sensor razor cartridge Made with Nd: YAG laser Up to 3 million welds/hour 7 identical weld points/blade

Laser-Beam Welding Comparison: LBW or EBW a) over arc welding b)

Cutting

Cutting (oxyfuel-gas) A piece of material can be separated into two or more parts with various contours by removing a narrow zone in the workpiece. Other then mechanical means, heat source can be provided by torches, electric arcs, or lasers.

Cutting (oxyfuel-gas) Oxyfuel-gas cutting (torch) • Similar to oxyfuel welding, but heat is now used to remove matter; • Suitable particularly for steels; • Heat is provided by reactions mainly from oxygen and iron. The heat generated is often not sufficient to cut steels. The workpiece therefore has to be preheated; • Higher the carbon concentration, higher cutting temperature required; • Cutting is obtain by the oxidation of the steel (burning, rusting); • Cutting thickness depends on gases used. Up to 2’ with some cases; • Process can be automated with multi-cutting piece.

Cutting (oxyfuel-gas) 200 mm thick plate

Cutting (oxyfuel-gas) None traditional pattern cutting made possible by automation.

Cutting (oxyfuel-gas) This process generates a kerf (wave pattern similar to that produce by saws) Kerf range from 0. 06’’ to 0. 4’’

Cutting (arc cutting) Based on same principale as arc welding Leave a heat-affected zone that have to be taken into account.

Cutting (arc cutting) In Air Carbon-Arc Cutting (CAC-A) • Carbon electrode is used; • Air is used to blow molten metal away, hence doesn’t have to be oxidize; • Noisy process; • Hazardous due to blown molten metal.

Cutting (arc cutting) Plasma-arc cutting (PAC) • Highest cutting temperature; • Used for rapid cutting of stainless steel and nonferrous plates; • Higher cutting productivity then oxyfuelgas cutting; • Most popular process utilizing programmable controllers;

Cutting (arc cutting) CNC plasma cutting system -> Plasma cutter

Cutting (arc cutting) Electron beams and Lasers • Use for accurate cutting; • Better surface finish; • Kerf is narrower.

Weld joint, quality, and Testing Weld Joint • Three distinct zones in weld joint: 1)Base metal 2)Heat-affected zone 3)Weld metal • Weld joint used without a filler is called autogenous.

Solidification of weld • The solidification process is similar to casting and begins with the formation of columnar grains • These are relatively long and form parallel to heat flow therefore lie parallel to the plane of the two components welded

Solidification of weld • Grain structure and size depend on the specific metal alloy, the welding technique, and type of filler metal. • The weld begins in a molten state; has a cast structure Cooled slowly Hoarse grains Low strength, toughness, and ductility r is the fille Here tile ost duc ith poor m w wever ho h strengt Here th most e filler is b with g rittle how ever reat s treng th

Solidification of weld • The resulting structure depends on the particular alloy, it’s composition, and thermal cycling to which the joint is subjected. • Preheating general weld area prior to welding can control cooling rates • Without preheating, heat produced during welding dissipates rapidly through rest of parts being joined

Weld Quality Some things that could cause Discontinuities, weaknesses in weld • Thermal cycling and microstructural changes • Inadequate or careless application • Poor training • Porosity • Slag inclusions • Incomplete fusion penetration • The Weld profile • Cracks • Tears

Weld Quality Overlap & Undercut Porosity • Gases released during melting of the weld area but trapped during solidification • Chemical reactions • Contaminants

Weld Quality Underfill, Crack & Incomplete fusion Slag Inclusions • Oxides, fluxes and electrode-coating materials that are trapped in the weld zone

Weld Quality Residual Stress • Distortion, warping, and buckling of the welded parts • Stress-corrosion cracking • If portion of welded structure is removed from sawing or machining • Reduced fatigue life of the welded structure

Testing of welds Types of tests: • Tension-shear • Bend • Fracture toughness • Corrosion and creep

Joint Design • Product should minimize number of welds • Weld locations should be selected to avoid excessive stresses and joining locations • Components should fit properly prior to welding • Weld bead size should be kept to a minimum to conserve weld metal

Joint Design Things to think about when welding:

Weld Quality

Chapter 31 Intro • Solid State Welding- Jointing at the interface without fusion. • Solid State Bonding- Involves one of the following phenomena: • Diffusion- Transfer of atoms across an interface. • Pressure- Plastic Deformation occurs at the interface. • Relative Interfacial Movements- Movements of the contacting surfaces occur

Cold Welding • Pressure is applied to the pieces through dies or rolls. • The interface is de-greased, wirebrushed and wiped to remove oxide smudges.

Cold Welding • It is preferred the mating parts be ductile • A weak and brittle joint occurs when two dissimilar metals are joined. • Applications: Wire Stock and Electrical Connections

Roll Bonding • A pair of rolls apply pressure to the material to form a weld. • Can be applied for both Cold and Hot temps. • Used to combine two different metals in order to obtain a metal suitable for different applications.

Roll Bonding • Process used in making U. S. quarters, which is made up of two outer layers of 75%Cu 25%Ni(Cupronickel) and a middle section of pure copper.

Ultrasonic Welding

Ultrasonic Welding • The two components are subjected to a static normal force and a oscillating shearing stress. • The shearing stress is applied at the tip of a transducer.

Ultrasonic Welding • The shearing stress breaks up oxide films and contaminants to allow for a strong bond. • Melting nor fusion take place • The temperature generated is in the range of 1/3 to 1/2 of the melting point of the metals joined

Ultrasonic Welding • Joining of thermoplastics- Melting does take place due to the lower melting temperature of plastics. • Applications: Bimetallic strips, plastics, packaging with foils, and lap welding of sheet, foil, and thin wire. • Moderate skill is required.

Friction Welding

Friction Welding • Friction at the interface of the joining components create enough heat to join the pieces. • One work piece is stationary while the other is rotated at a high constant speed.

Friction Welding • The two members are brought together by an axial force. • Once sufficient contact is established the rotating member is stopped and axial force is increased.

Friction Welding • The pressure at the interface and the resulting friction produce enough heat for a strong joint to form. • The Weld Zone depends on the following: • Amount of heat generated • Thermal Conductivity of the materials • Mechanical properties of the materials at elevated temperatures. • The shape of the welded joint depends on the rotational speed and axial pressure.

Inertia Friction Welding • The heat is supplied by the KE of a flywheel. • As friction slows the flywheel, the axial force is increased.

Inertia Friction Welding • The weld is complete when the wheel comes to a stop. • The timing for this sequence is extremely important in order to produce a good quality weld.

Linear Friction Welding • The interface of the components is subjected to a linear reciprocating motion.

Linear Friction Welding • This process is capable of welding square or rectangular components as well as round parts made out of metal and plastics.

Linear Friction Welding • One part is moved across the face of the other part using a balanced reciprocating mechanism.

Friction Stir Welding • A third body is rubbed against the surfaces to be joined. • A rotating non-consumable probe is plunged into the joint.

Friction Stir Welding • The contact pressures cause frictional heating, raising the temperature to 230 o to 260 o. C • The probe at the tip of the tool forces heating and mixing of the material at the joint.

Friction Stir Welding • Successful applications have been used for Aluminum, Copper, Steel and Titanium. • Developments may be made in uses for polymers and composite materials. • Used in the fields of aerospace, automotive, shipbuilding, and military.

Friction Stir Welding • Advantages: • High Quality • Minimal pores • Uniform material structure • Low distortion • Little microstructural changes • No shielding gases • No surface cleaning required • Thickness of weld in a single pass ranges from 1 mm to 50 mm

Explosion Welding • An explosive is used to provide the pressure to join the components together. • The explosive is attached to the flyer plate which strikes the mating component to produce a wavy interface.

Explosion Welding • The impact mechanically interlocks the two surfaces, which causes pressure welding by plastic deformation. • The bond strength is very high.

Explosion Welding • The explosive may be a flexible plastic sheet or cord or in a granulated or liquid form which is cast or pressed over the flyer plate. • Plates can be as large as 6 m X 2 m. • Pipes can also be joined to the holes of header plates by placing the explosive inside the tube, and when detonated the pipe expands joining the pieces together.

Diffusion Bonding • Achieved by movement of atoms across the interface (diffusion). • Temperatures are usually half of the absolute melting temperature.

Diffusion Bonding • The bond interface usually has the same physical and mechanical properties as the base metal. • The strength depends on the pressure, temperature, time of contact and cleanliness. • Electroplating the surface or applying a filler metal will increase the strength of the bond. • The parts are usually heated in a furnace or by electrical resistance.

Diffusion Bonding • Method used by blacksmiths when the made filled gold (gold over copper) • Used for reactive metals and composite materials such as metal-matrix composites. • Generally used for complex parts in low quantities, but is now automated for moderate-volume production. • Equipment cost is in the range of $3 to $6 per mm 2

Diffusion Bonding/ Super plastic Forming • • Combines diffusion bonding with super plastic forming to fabricate sheet-metal structures. The Process: 1. The sheet metal is diffusion bonded 2. Formed into a die with stop-offs 3. The stop-off regions are expanded in a mold by air. • These structures have high stiffness to weight ratio

Diffusion Bonding/ Super plastic Forming

Diffusion Bonding/ Super plastic Forming • Useful in aerospace and aircraft applications • First developed in the 1970 s, currently more advanced for titanium structure • Ti-6 Al-4 V and 7475 -T 6 are commonly used for the titanium structures. • Various other alloys are used for aerospace applications.

Economics of Welding Operations • Costs in welding and joining processes depend on such factors as: • Equipment Capacity • Level of automation • Labor skill required • Weld quality • Production Rate • Preparation Required

Economics of Welding Operations • Welding and Joining Costs: –High- brazing and fasteners • They require hole-making operations and fastener cost –Intermediate- arc welding, riveting, adhesive bonding –Low- resistance welding, seaming, and crimping • They are simple to perform and automate

Economics of Welding Operations • Equipment Costs for Welding: –High- ($100, 000 -$200, 000) Electron-Beam and Laser-Beam Welding –Intermediate- ($5, 000 -$50, 000) Spot, Submerged Arc, Gas Metal-Arc, Gas Tungsten Arc, Flux. Cored Arc, Electro-gas, Electro-slag, Plasma Arc, and Ultrasonic Welding –Low- ($1, 000+) Shielded Metal-Arc and Oxyfuel. Gas Welding

Economics of Welding Operations • Labor Costs are usually higher in welding compared to other metalworking operations due to operation skill, welding time and preparation required. • In robotic controlled welding the welding time is 80% of the overall time; whereas in manual welding only 30% of the overall time is spent welding.

Economics of Welding Operations • Labor Costs–High to Intermediate- Oxyfuel-Gas Welding and Shielded Metal-Arc Welding –High to Low- Electron-Beam and Laser-Beam Welding and Flux-Cored Arc Welding –Intermediate to Low- Submerged Arc Welding

31. 5 Resistive Welding Definition: Resistance welding covers a number of processes in which the heat necessary is produced by electrical current being passed through the materials being welded.

Spot Welding Two metals sheets are clamped together and current is sent through the metal sheets. Typically spot welds are characterized by a small round discoloration and depression.

Spot Welding This is called the weld nugget. They are used extensively in industry especially automotive manufacture.

Spot Welding

Testing Spot Welds 4 types of spot weld tests. Tension test: most common because it is cheap and easy Cross-Tension test: Twist test: Both are good at finding flaws, cracks and porosity in the weld area Peel test: Commonly used for thin sheets.

Testing Spot Welds

Seam Welding Resistance Seam Welding (RSW) uses two wheels instead of two electrode probes to create a long single weld. The two sheets of metal are passed through the wheels while electrical current is applied.

Seam Welding

High- Frequency Resistance Welding This is similar to seam welding except high electrical frequency (up to 450 KHz) is used. Typically it is used to create butt welded tubing.

Projection Welding Resistance Projection Welding (RPW) One of the metal sheets have one or more projections embossed into it and causes weld nuggets to form at those points. After enough heat is created then the sheets are pressed together.

Projection Welding

Flash welding Flash Welding (FW) This is sometimes referred to as flash butt welding Heat is generated from the arc as the two pieces make contact. When sufficient heat is created the ends of the two pieces of metal are pressed together.

Stud Welding (SW) A small part, typically a threaded rod, hanger or handle acts as one of the electrodes. The metal sheet acts as the other electrode and after enough heat is generate the stud is pressed until a sufficient weld is created.

Percussion Welding uses a capacitor to provide electrical current instead of a transformer. The advantage is that localized heat is created making this type of welding ideal for parts that are next to heat sensitive areas such as electronic assemblies.

References Manufacturing Engineering and Technology, Fifth edition, Serope Kalpakjian & Steven R. Schmid. Picture from web site related to the book & Internet.