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

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.T2.95.12

Laser

Laser Beam Welding (LBW)

0.1.1.2.1.T3.95.12

High Energy Density Processes

Laser Beam Welding (LBW)

shielding gas nozzle (optional) Laser beam

• Single pass weld penetration up to 3/4” in steel

Plasma keyhole workpiece motion Plasma plume

• Materials need not be

Molten material

conductive • No filler metal required • Low heat input produces low distortion

Keyhole welding

• Does not require a vacuum

High Energy Density Processes

Focusing the Beam

Heat treatment Surface modification Welding Cutting

12 10 8 6 4 2 0

Advantages

6 kW CO2 2 kW Nd:YAG 1 3 5 7 Welding speed, m/min

• • • • • •

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.T4.95.12

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.T6.95.12

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 (450°C) 840° F – Soldering filler metals have a melting point below 840°F (450°C)

Brazing and Soldering

0.1.1.2.4.T18.95.12

Application of Low Thermal Expansion Alloys

• Thermal expansion mismatch in metal ceramic 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.T20.95.12

Brazing and Soldering

Brazing Specifications

• AWS A5.8 Specification for Brazing Filler Metal – 8 well-defined groups (B) plus a vacuum grade (BV) • BAg-1 (44-46 Ag, 14-16 Cu, 14-18 Zn, 23-25 Cd) • BAu-1 • BCuP-1 (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 C3.3 Standard Method for Evaluating the Strength of Brazed Joints

Balchin & Castner, “Health & Safety…”, McGraw 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

(Poly)ethylene

• 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

H H C=C

add H 2 O 2

H H ··· H H -C-C H H ···

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.T22.95.12

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.T23.95.12

Welding of Plastics

Hot Plate, Infrared Welding

Hot plate welding

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

Welding of Plastics

Vibration

• Advantages – Speed – Used on many materials • Limitations – Size – Requires fixturing – Equipment costly 0.1.1.2.5.T24.95.12

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.T25.95.12

•

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.T26.95.12

Curing of Adhesives

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

Adhesive Bonding

Stress Modes - Best to Worst

1. Compression 2. Shear 3. Tension 4. Peel 5. Cleavage

0.1.1.2.6.T29.95.12

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 Selection

Adhesive Bonding

• 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.T27.95.12

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.