1b1 Nonarc Process Continued

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

http://encarta.msn.com/find/Concise.asp?z=1&pg=2&ti=761578658

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 plumeMolten

material

shieldinggas nozzle(optional)

workpiece motion

Plasmakeyhole


Focusing the Beam

Heat Surface Welding Cuttingtreatment modification


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

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0

2

4

6

8

10

12

1 3 5 7Welding speed, m/min

Wel

d pe

netr

atio

n, 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


Electron Beam Welding (EBW)

0.1.1.2.1.T6.95.12

EB Applications

http://www.ahtc.com/page2.html

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


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


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

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.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


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


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


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

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)

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Hot Plate, Hot Gas, Infrared• Advantages

– Provide strong joints– Reliable– Used on difficult to

join plastics• Limitations

– Slow– Limited temperature

range

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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

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Ultrasonic• Advantages

– Fast– Can spot or seam weld

• Limitations– Equipment complex,

many variables– Only use on small parts– Cannot weld all plastics

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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

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

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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.

1b1 Nonarc Process Continued

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