Post on 05-Jan-2016
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Non-Arc Welding Processes Continued
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
Introduction
High Energy Density Processes
• Focus energy onto a small area
• Laser– CO2 gas: fixed
position– Nd-YAG crystal:
fiber-optic delivery
• Electron Beam
High Energy Density Processes
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 Beam Welding (LBW)
0.1.1.2.1.T3.95.12Laser
Laser Beam Welding (LBW)• Single pass weld
penetration up to 3/4” in steel
• Materials need not be conductive
• No filler metal required• Low heat input produces
low distortion• Does not require a
vacuumKeyhole welding
Laser beam
Plasma plume
Moltenmaterial
shieldinggas nozzle(optional)
workpiece motion
Plasmakeyhole
High Energy Density Processes
Focusing the Beam
Heat Surface Welding Cuttingtreatment modification
High Energy Density Processes
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.T4.95.12
0
2
4
6
8
10
12
1 3 5 7Welding speed, m/min
Wel
d p
enet
rati
on
, m
m
6 kW CO2
2 kW Nd:YAG
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
High Energy Density Processes
Electron Beam Welding (EBW)
• 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
Advantages
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
High Energy Density Processes
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?
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
Introduction
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
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
Alumina substrate
Kovar lid
Silicon chip
Brazed joints
0.1.1.2.4.T20.95.12
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 (37-38 Au, remainder Cu)• BCuP-1 (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
Brazing and Soldering
Balchin & Castner, “Health & Safety…”,McGraw Hill, 1993
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 ringsurrounded by flux
Brazing and Soldering
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?
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
Introduction
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
HH
HH C=C
H H-C-C-H H
··· ···
add H2O2
(Poly)ethylene
Welding of Plastics
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
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
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.
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
Introduction
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
4. Peel 5. Cleavage
2. Shear1. Compression 3. Tension
0.1.1.2.6.T29.95.12
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)
Adhesive Bonding
Factors that Influence Process Selection
• Material joining needs
• Capabilities of available processes
• Cost
• Environment
• Required welding speed
• Skill level
• Part Fit-up
Process Selection
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
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
Adhesive Bonding
Do Homework Assignment 3 on “More Welding Processes” and Turn in by next class period.