NonArc Welding Processes Continued Introduction NonArc Welding Processes

Non-Arc Welding Processes Continued

Introduction Non-Arc Welding Processes • Resistive heating, chemical reactions, focused light and electrons, sound waves, and friction can also be used to join materials – – – – Resistance welding Oxy-Fuel Welding Friction welding (&Solid State) Laser and electron beam welding Brazing and soldering Plastics joining Adhesive bonding

High Energy Density Processes • Focus energy onto a small area • Laser – CO 2 gas: fixed position – Nd-YAG crystal: fiber-optic delivery • Electron Beam

High Energy Density Processes • These processes focus the energy onto a small area • Laser - 0. 0001 -inch thick stainless steel sheet • Electron Beam - 0. 030 -inch weld width on 0. 5 inch thick steel plate 0. 1. 1. 2. 1. T 2. 95. 12

Laser Beam Welding (LBW) Laser 0. 1. 1. 2. 1. T 3. 95. 12

High Energy Density Processes Laser Beam Welding (LBW) shielding gas nozzle (optional) • Single pass weld penetration up to 3/4” in Laser beam steel Plasma plume • Materials need not be Molten conductive material Plasma • No filler metal required keyhole • Low heat input produces workpiece motion low distortion • Does not require a Keyhole welding vacuum

High Energy Density Processes Focusing the Beam Heat treatment Surface modification Welding Cutting

Advantages • Single pass weld penetration up to 3/4” in steel • High Travel speed • Materials need not be conductive • No filler metal required • Low heat input produces low distortion • Does not require a vacuum 0. 1. 1. 2. 1. T 4. 95. 12

High Energy Density Processes Limitations • High initial start-up costs • Part fit-up and joint tracking are critical • Not portable • Metals such as copper and aluminum have high reflectivity and are difficult to laser weld • High cooling rates may lead to materials problems

Electron Beam Welding (EBW) EB Applications 0. 1. 1. 2. 1. T 6. 95. 12

High Energy Density Processes Electron Beam Welding (EBW) Advantages • Deepest single pass weld penetration of the fusion processes – 14 -inch-thick steel • Fast travel speeds • Low heat input welds produce low distortion

High Energy Density Processes Limitations • • • High initial start-up cost Not portable Part size limited by size of vacuum chamber Produces x-rays Part fit-up is critical High cooling rates may lead to materials problems

Turn to the person sitting next to you and discuss (1 min. ): • In laser welding, materials with high reflectivity reflect the beam right off the surface and no heat is absorbed and thus they are difficult to weld. What might we do to make these high reflectivity materials more weldable?

Introduction Non-Arc Welding Processes • Resistive heating, chemical reactions, focused light and electrons, sound waves, and friction can also be used to join materials – – – – Resistance welding Oxy-Fuel Welding Friction welding (&Solid State) Laser and electron beam welding Brazing and soldering Plastics joining Adhesive bonding

Brazing and Soldering Brazing (B) and Soldering (S) • In these processes, the base metals are heated but do not melt; only the filler metal melts – Brazing filler metals having a melting point above 840° F (450°C) – Soldering filler metals have a melting point below 840°F (450°C)

Brazing and Soldering 0. 1. 1. 2. 4. T 18. 95. 12

Application of Low Thermal Expansion Alloys • Thermal expansion mismatch in metalceramic joints can lead to cracks in the ceramic • Thermal expansion coefficients at 25°C (10 -6 mm / mm·°C) – – Alumina, 8. 8 Nickel, 13. 3 Iron, 11. 8 Kovar, 5. 0 Kovar lid Silicon chip Alumina substrate Brazed joints 0. 1. 1. 2. 4. T 20. 95. 12

Brazing and Soldering Brazing Specifications • AWS A 5. 8 Specification for Brazing Filler Metal – 8 well-defined groups (B) plus a vacuum grade (BV) • BAg-1 • BAu-1 • BCu. P-1 (44 -46 Ag, 14 -16 Cu, 14 -18 Zn, 23 -25 Cd) (37 -38 Au, remainder Cu) (4. 8 -5. 2 P, remainder Cu) – Standard forms: strip, sheet, wire, rod, powder – Joint design tolerances, generally ~ 0. 002 - 0. 006 inches – Uses for each braze material • AWS C 3. 3 Standard Method for Evaluating the Strength of Brazed Joints

Balchin & Castner, “Health & Safety…”, Mc. Graw Hill, 1993

Brazing and Soldering Advantages • Joins unweldable materials – Base metals don’t melt – Can be used on metals and ceramics • Joined parts can be taken apart at a later time • Batch furnace can easily process multiple parts • Portable when joining small parts

Brazing and Soldering Limitations • Joint tolerance is critical • Lower strength than a welded joint • Large parts require large furnaces • Manual processes require skilled workers • Flux Filler metal ring surrounded by flux

Turn to the person sitting next to you and discuss (1 min. ): • Why is joint tolerance so critical? • What happens if the joint space is too large? • What happens if the joint space is too small? Turn to the person sitting next to you and discuss (1 min. ): • What happens if we do not have sufficient flux?

Introduction Non-Arc Welding Processes • Resistive heating, chemical reactions, focused light and electrons, sound waves, and friction can also be used to join materials – – – – Resistance welding Oxy-Fuel Welding Friction welding (&Solid State) Laser and electron beam welding Brazing and soldering Plastics joining Adhesive bonding

Welding of Plastics Joining Plastics • Polymer - a single building block (mer) is repeated to form a long chain molecule – Thermoplastic polymers soften when heated, harden when cooled • 2 -liter bottles – Thermosetting polymers don’t soften when heated • Car tires, caulking compound (Poly)ethylene H H C=C H H add H 2 O 2 HH ··· -C-C- ··· HH

Joining of Plastics • Plastic (polymer) is a material in which single building blocks (mers) join to form a long chain or network molecule • Thermoplastic polymers soften when heated and harden when cooled – Foam cups (polystyrene), 2 -liter bottles (polyethylene), Leisure suits (polyester) • Thermosetting polymers become permanently hard when heat is applied and do not soften upon subsequent heating – Car tires (isoprene, isobutene), Epoxy, Caulks (silicones) 0. 1. 1. 2. 5. T 22. 95. 12

Hot Plate, Hot Gas, Infrared • Advantages – Provide strong joints – Reliable – Used on difficult to join plastics • Limitations – Slow – Limited temperature range 0. 1. 1. 2. 5. T 23. 95. 12

Welding of Plastics Hot Plate, Infrared Welding Hot plate welding

Welding of Plastics Hot Gas Welding • Thermoplastics (hotmelts) – Adhesive is heated until it softens, then hardens on cooling • Hot gas softens filler and base material • Filler is pulled or fed into the joint

Vibration • Advantages – Speed – Used on many materials • Limitations – Size – Requires fixturing – Equipment costly 0. 1. 1. 2. 5. T 24. 95. 12

Ultrasonic • Advantages – Fast – Can spot or seam weld • Limitations – Equipment complex, many variables – Only use on small parts – Cannot weld all plastics 0. 1. 1. 2. 5. T 25. 95. 12

Turn to the person sitting next to you and discuss (1 min. ): • Make a list of some thermoplastic items you have recently seen that have been wlded.

Introduction Non-Arc Welding Processes • Resistive heating, chemical reactions, focused light and electrons, sound waves, and friction can also be used to join materials – – – – Resistance welding Oxy-Fuel Welding Friction welding (&Solid State) Laser and electron beam welding Brazing and soldering Plastics joining Adhesive bonding

Adhesives • Thermosets form long polymer chains by chemical reaction (curing) – Heat is the most common means of curing – Ultraviolet light, oxygen - acrylics – Moisture - cyanoacrylates • Thermoplastics (hotmelts) – Adhesive is heated until it softens, then hardens on cooling -Polyethylene, PVC 0. 1. 1. 2. 6. T 26. 95. 12

Adhesive Bonding Curing of Adhesives • Thermosets form long polymer chains by chemical reaction (curing) – Heat (epoxy) – Ultraviolet light, oxygen (acrylics) – Moisture (superglue)

Stress Modes - Best to Worst 1. Compression 4. Peel 2. Shear 3. Tension 5. Cleavage 0. 1. 1. 2. 6. T 29. 95. 12

Adhesive Bonding Why Adhesive Bonding? • Dissimilar materials – Plastic to metal • Materials that can be damaged by mechanical attachments • Shock absorption or mechanical dampening • Laminate structures – Skin to honeycomb structure

Adhesive Bonding Adhesive Selection • Adhesive selection is based primarily on – Type of substrate – Strength requirements, type of loading, impact requirements – Temperature resistance, if required • • • Epoxy Cyanoacrylates Anaerobics - metals Urethanes Silicones Pressure sensitive adhesives (PSAs)

Process Selection Factors that Influence Process Selection • • Material joining needs Capabilities of available processes Cost Environment Required welding speed Skill level Part Fit-up

Advantages • Joining dissimilar materials - plastic to metal • Materials that can be damaged by mechanical attachments • Blind joints • Shock absorption or mechanical dampening • Temporary alignment • Laminated structures • Thin substrates - skin-to-honeycomb construction • Stress distribution 0. 1. 1. 2. 6. T 27. 95. 12

Adhesive Bonding Limitations • Adhesives don’t do work, they distribute work; they are not structural materials • Environmental degradation – Temperature – Oxidation • Difficult to repair • Curing or setting time • Surface preparation

Do Homework Assignment 3 on “More Welding Processes” and Turn in by next class period.