topic7joiningprocessweldingbrazingsolderingfastening160214-150511104641-lva1-app6892.pdf
Content
JOINING PROCESSES
An all-inclusive term covering processes
such as:
Welding
Brazing
Soldering
Adhesive bonding
Mechanical fastening
Overview on Joining Processes
Why Joining Processes
Some (even simple) products are too large to be made
by individual processes ( 3-D Hollow structural member, 5 m
diameter)
Easier, more economical to manufacture & join
individual components (Cooking pot with handle)
Products to be disassembled for maintenance
(Appliances; engines)
Varying functionality of product (Carbide inserts in tool
steels; Brake shoes)
Transportation + assembly is less costly (Shelving units;
Machinery)
Product Example
Figure 8.1 Various parts in a typical automobile that are
assembled by the joining processes.
Product Example (Cont.)
Figure 8.2: Examples of parts utilizing joining processes. (a) A tubular part
fabricated by joining individual components. This product cannot be manufactured
in one piece by any of the methods described in the previous chapters if it consists
of thin-walled, large-diameter, tubular-shaped long arms. (b) A drill bit with a
carbide cutting insert brazed to a steel shank—an example of a part in which two
materials need to be joined for performance reasons. (c) Spot welding of
automobile bodies.
WELDING PROCESSES
BS 499 part 1 Welding terms
A union between pieces of metal at
faces rendered plastic or liquid by
heat,pressure or both.
Overview on Joining Processes
Figure 8.3: Joining Method (AWS A3.0:2001)
Fusion Welding
Fusion Welding
Fusion Welding
Fusion Welding
Any welding process that uses fusion
of the base metal to make the weld
(AWS A3.0: 2001)
Fusion Welding – Arc Welding
Arc Welding
A fusion welding process in which coalescence of the
metals is achieved by the heat from an electric arc
between an electrode and the work
Electric energy from the arc produces temperatures ~
10,000 F (5500 C), hot enough to melt any metal
Most AW processes add filler metal to increase volume
and strength of weld joint
An electric arc is a discharge of electric current across a
gap in a circuit
It is sustained by an ionized column of gas (plasma)
through which the current flows
To initiate the arc in AW, electrode is brought into
contact with work and then quickly separated from it by a
short distance
Fusion Welding – Arc Welding (Cont.)
A pool of molten metal is formed near electrode
tip, and as electrode is moved along joint,
molten weld pool solidifies in its wake
Figure 31.1 Basic configuration of an arc welding process.
Fusion Welding – Arc Welding (Cont.)
Two Basic Types of AW Electrodes
Consumable – consumed during welding process
Source of filler metal in arc welding
Nonconsumable – not consumed during welding process
Filler metal must be added separately
Fusion Welding – Arc Welding (Cont.)
Arc Shielding
At high temperatures in AW, metals are chemically
reactive to oxygen, nitrogen, and hydrogen in air
Mechanical properties of joint can be seriously
degraded by these reactions
To protect operation, arc must be shielded from
surrounding air in AW processes
Arc shielding is accomplished by:
Shielding gases, e.g., argon, helium, CO2
Flux
Fusion Welding – Arc Welding (Cont.)
Power Source in Arc Welding
Direct current (DC) vs. Alternating current (AC)
AC machines less expensive to purchase and
operate, but generally restricted to ferrous
metals
DC equipment can be used on all metals and
is generally noted for better arc control
Fusion Welding – Resistance Welding
(Cont.)
Resistance Welding (RW)
A group of fusion welding processes that use a
combination of heat and pressure to accomplish
coalescence
Heat generated by electrical resistance to current flow at
junction to be welded
Principal RW process is resistance spot welding (RSW)
Fusion Welding – Resistance
Welding (Cont.)
Figure 31.12 Resistance
welding, showing the
components in spot
welding, the main
process in the RW
group.
Fusion Welding – Resistance Welding
(Cont.)
Components in Resistance Spot Welding
Parts to be welded (usually sheet metal)
Two opposing electrodes
Means of applying pressure to squeeze parts between
electrodes
Power supply from which a controlled current can be
applied for a specified time duration
Fusion Welding – Resistance Welding
(Cont.)
Advantages:
No filler metal required
High production rates possible
Lends itself to mechanization and automation
Lower operator skill level than for arc welding
Good repeatability and reliability
Disadvantages:
High initial equipment cost
Limited to lap joints for most RW processes
Skilled operators are required
Bigger job thickness cannot be welded
Fusion Welding – Resistance
Welding (Cont.)
Applications of resistance welding
Joining sheets, bars and tubes.
Making tubes and metal furniture.
Welding aircraft and automobile parts.
Making cutting tools.
Making fuel tanks of cars, tractors etc.
Making wire fabrics, grids, grills, mesh
weld, containers etc.
Fusion Welding - Resistance Spot
Welding (RSW)
Resistance Spot Welding
Process in which fusion of faying surfaces of a lap joint is
achieved at one location by opposing electrodes
Used to join sheet metal parts using a series of spot welds
Widely used in mass production of automobiles,
appliances, metal furniture, and other products made of
sheet metal
Typical car body has ~ 10,000 spot welds
Annual production of automobiles in the world is
measured in tens of millions of units
Fusion Welding - Resistance Spot
Welding (RSW) (Cont.)
Figure 31.13 (a) Spot welding cycle, (b) plot of squeezing force & current
in cycle (1) parts inserted between electrodes, (2) electrodes close,
force applied, (3) current on, (4) current off, (5) electrodes opened.
Fusion Welding - Resistance Seam
Welding (RSEW)
Resistance Seam Welding (RSEW)
Uses rotating wheel electrodes to produce a
series of overlapping spot welds along lap joint
Can produce air-tight joints
Applications:
Gasoline tanks
Automobile mufflers
Various other sheet metal containers
Fusion Welding - Resistance Seam
Welding (RSEW)
Figure 31.15 Resistance seam welding (RSEW).
Fusion Welding - Oxyfuel Gas Welding
(OFW)
Oxyfuel Gas Welding
General term for welding operations that burn various fuels
mixed with oxygen
OFW employs several types of gases, which is the primary
distinction among the members of this group
Oxyfuel gas is also used in flame cutting torches to cut and
separate metal plates and other parts
Fusion Welding - Oxyfuel Gas Welding
(OFW)
Alternatives Fuel Gases for OFW
Acetylene
Gasoline
Hydrogen
MPS and MAPP gas
Propylene and Fuel Gas
Butane, propane and butane/propane
mixes
Fusion Welding - Oxy-acetylene gas welding
(OAW)
Oxy-acetylene gas welding (OAW)
Oxy-acetylene gas welding is a group OFW process that
used acetylene gas as a fuel gas
Most popular fuel among OFW group because it is capable of
higher temperatures than any other - up to 3480C
(6300F)
Fusion welding performed by a high temperature flame from
combustion of acetylene and oxygen
Flame is directed by a welding torch
Filler metal is sometimes added
Composition must be similar to base metal
Filler rod often coated with flux to clean surfaces and prevent
oxidation
Fusion Welding - Oxy-acetylene
gas welding (OAW)
Figure 31.21 A typical oxyacetylene welding operation (OAW).
Fusion Welding - Oxy-acetylene gas
welding (OAW)
Chemical reaction during burning
Two stage chemical reaction of acetylene and
oxygen:
First stage reaction:
C2H2 + O2 2CO + H2 + heat
Second stage reaction:
2CO + H2 + 1.5O2 2CO2 + H2O + heat
Fusion Welding - Oxy-acetylene
gas welding (OAW)
Oxyacetylene Torch
Maximum temperature reached at tip of inner cone,
while outer envelope spreads out and shields work
surfaces from atmosphere
Figure 31.22 The neutral flame from an oxyacetylene torch
indicating temperatures achieved.
Fusion Welding - Other Processes
FW processes that cannot be classified as arc,
resistance, or oxyfuel welding
Use unique technologies to develop heat for
melting
Applications are typically unique
Processes include:
Electron beam welding
Laser beam welding
Electroslag welding
Thermit welding
Fusion Welding - Thermit Welding (TW)
Thermit Welding (TW)
FW process in which heat for coalescence is produced
by superheated molten metal from the chemical reaction
of thermite
Thermite = mixture of Al and Fe3O4 fine powders that
produce an exothermic reaction when ignited
Also used for incendiary bombs
Filler metal obtained from liquid metal
Process used for joining, but has more in common with
casting than welding
Fusion Welding - Thermit
Welding (TW)
Figure 31.25 Thermit welding: (1) Thermit ignited; (2) crucible
tapped, superheated metal flows into mold; (3) metal solidifies to
produce weld joint.
Fusion Welding - Thermit Welding (TW)
Applications
Joining of railroad rails
Repair of cracks in large steel castings and forgings
Weld surface is often smooth enough that no finishing is
required
Solid State Welding (SSW)
Solid State Welding (SSW)
Coalescence of part surfaces is achieved by:
If both heat and pressure are used, heat is not enough to melt
work surfaces
Pressure alone, or
Heat and pressure
For some SSW processes, time is also a factor
No filler metal is added
Each SSW process has its own way of creating a bond at the
faying surfaces
Essential factors for a successful solid state weld are that the
two faying surfaces must be:
Very clean
In very close physical contact with each other to permit atomic bonding
Solid State Welding (Cont)
SSW Advantages over FW Processes
If no melting, then no heat affected zone, so metal
around joint retains original properties
Many SSW processes produce welded joints that bond
the entire contact interface between two parts rather
than at distinct spots or seams
Some SSW processes can be used to bond dissimilar
metals, without concerns about relative melting points,
thermal expansions, and other problems that arise in FW
Solid State Welding (Cont.)
Processes under SSW group
Forge welding
Cold welding
Roll welding
Hot pressure welding
Diffusion welding
Explosion welding
Friction welding
Ultrasonic welding
Solid State Welding - Forge Welding
Forge Welding
SSW process in which
components to be joined are
heated to hot working temperature
range and then forged together by
hammering or similar means
Historic significance in
development of manufacturing
technology
Process dates from about
1000 B.C., when blacksmiths
learned to weld two pieces of
metal
Solid State Welding - Cold Welding
(CW)
Cold Welding (CW)
SSW process done by applying high
pressure between clean contacting
surfaces at room temperature
Cleaning usually done by degreasing
and wire brushing immediately before
joining
No heat is applied, but deformation
raises work temperature
At least one of the metals, preferably
both, must be very ductile
Soft aluminum and copper suited
to CW
Applications: making electrical
connections
Dies
Workpiece Workpiece
Before welding
After welding
Solid State Welding - Roll Welding
(ROW)
SSW process in which pressure sufficient to cause
coalescence is applied by means of rolls, either with or
without external heat
Variation of either forge welding or cold welding, depending
on whether heating of workparts is done prior to process
If no external heat, called cold roll welding
If heat is supplied, hot roll welding
Solid State Welding - Roll Welding
(ROW)
Applications
Cladding stainless steel to mild or low alloy steel for
corrosion resistance
Bimetallic strips for measuring temperature
"Sandwich" coins for U.S mint
Solid State Welding - Diffusion Welding
(DFW)
Diffusion Welding
SSW process that uses heat
and pressure, usually in a
controlled atmosphere, with
sufficient time for diffusion and
coalescence to occur
Temperatures 0.5 Tm
Plastic deformation at surfaces
is minimal
Primary coalescence
mechanism is solid state
diffusion
Limitation: time required for
diffusion can range from
seconds to hours
Work pieces
Force
A
B
Schematic representation of
diffusion welding using
electrical resistance for heating
Solid State Welding - Diffusion Welding
(DFW)
DFW Applications
Joining of high-strength and refractory metals in
aerospace and nuclear industries
Can be used to join either similar and dissimilar metals
For joining dissimilar metals, a filler layer of different
metal is often sandwiched between base metals to
promote diffusion
Solid State Welding - Explosion
Welding (EXW)
Explosion Welding (EXW)
SSW process in which rapid coalescence of two metallic
surfaces is caused by the energy of a detonated
explosive
No filler metal used
No external heat applied
No diffusion occurs - time is too short
Bonding is metallurgical, combined with mechanical
interlocking that results from a rippled or wavy interface
between the metals
Commonly used to bond two dissimilar metals, in
particular to clad one metal on top of a base metal over
large areas
Solid State Welding Explosion Welding (EXW)
Figure 31.27 Explosive welding (EXW): (1) setup in the
parallel configuration, and (2) during detonation of the
explosive charge.
Solid State Welding - Friction Welding
(FRW)
SSW process in which coalescence is achieved
by frictional heat combined with pressure
When properly carried out, no melting occurs at
faying surfaces
No filler metal, flux, or shielding gases normally
used
Process yields a narrow HAZ
Can be used to join dissimilar metals
Widely used commercial process, amenable to
automation and mass production
Solid State Welding Friction Welding (FRW)
Figure 31.28 Friction welding (FRW): (1) rotating part, no contact; (2)
parts brought into contact to generate friction heat; (3) rotation
stopped and axial pressure applied; and (4) weld created.
Solid State Welding - Friction Welding
(FRW)
1.
2.
Two Types of Friction Welding
Continuous-drive friction welding
One part is driven at constant rpm against
stationary part to cause friction heat at
interface
At proper temperature, rotation is stopped
and parts are forced together
Inertia friction welding
Rotating part is connected to flywheel,
which is brought up to required speed
Flywheel is disengaged from drive, and
parts are forced together
Solid State Welding - Friction Welding
(FRW)
Applications:
Shafts and tubular parts
Industries: automotive, aircraft, farm equipment,
petroleum and natural gas
Limitations:
At least one of the parts must be rotational
Flash must usually be removed
Upsetting reduces the part lengths (which must be
taken into consideration in product design)
Solid State Welding - Ultrasonic
Welding (USW)
Two components are held together, oscillatory
shear stresses of ultrasonic frequency are applied
to interface to cause coalescence
Oscillatory motion breaks down any surface films
to allow intimate contact and strong metallurgical
bonding between surfaces
Although heating of surfaces occurs,
temperatures are well below Tm
No filler metals, fluxes, or shielding gases
Generally limited to lap joints on soft materials
such as aluminum and copper
Ultrasonic Welding
Figure 31.29 Ultrasonic welding (USW): (a) general setup for
a lap joint; and (b) close-up of weld area.
Solid State Welding - Ultrasonic
Welding
Applications
Wire terminations and splicing in electrical and
electronics industry
Eliminates need for soldering
Assembly of aluminum sheet metal panels
Welding of tubes to sheets in solar panels
Assembly of small parts in automotive industry
Weld Quality
Concerned with obtaining an acceptable
weld joint that is strong and absent of
defects, and the methods of inspecting and
testing the joint to assure its quality
Topics:
Residual stresses and distortion
Welding defects
Inspection and testing methods
Weld Quality
Residual Stresses and Distortion
Rapid heating and cooling in localized regions during
FW result in thermal expansion and contraction that
cause residual stresses
These stresses, in turn, cause distortion and warpage
Situation in welding is complicated because:
Heating is very localized
Melting of base metals in these regions
Location of heating and melting is in motion (at
least in AW)
Weld Quality
Techniques to Minimize Warpage
Welding fixtures to physically restrain parts
Heat sinks to rapidly remove heat
Tack welding at multiple points along joint to create a
rigid structure prior to seam welding
Selection of welding conditions (speed, amount of filler
metal used, etc.) to reduce warpage
Preheating base parts
Stress relief heat treatment of welded assembly
Proper design of weldment
Weld Quality - Welding
Defect/Imperfection
Imperfection is any deviation from the ideal weld.
Defect is an unacceptable imperfection
A perfect weld joint, when subjected to an external force,
provide a distribution of stress throughout its volume which is
not significantly greater than parent metal.
Weld Quality - Welding
Defect/Imperfection
Cracks
Fracture-type interruptions either in weld or in base metal
adjacent to weld
Serious defect because it is a discontinuity in the metal that
significantly reduces strength
Caused by embrittlement or low ductility of weld and/or base
metal combined with high restraint during contraction
In general, this defect must be repaired
Weld Quality - Welding
Defect/Imperfection
Cavities
1.
2.
Porosity - small voids in weld metal formed by gases entrapped
during solidification. Caused by inclusion of atmospheric
gases, sulfur in weld metal, or surface contaminants
Shrinkage voids - cavities formed by shrinkage during
solidification. Cause by terminated arc at the end of a weld run
1
2
Weld Quality - Welding
Defect/Imperfection
Solid inclusions - nonmetallic material entrapped in
weld metal
Most common form is slag inclusions generated during AW
processes that use flux
Instead of floating to top of weld pool, globules of slag become
encased during solidification
Metallic oxides that form during welding of certain metals such
as aluminum, which normally has a surface coating of Al2O3
Weld Quality - Welding
Defect/Imperfection
Incomplete Fusion
Also known as lack of fusion, it is simply a weld bead in which
fusion has not occurred throughout entire cross section of joint
Weld Quality - Welding
Defect/Imperfection
o Lack of Smoothly Blended Surfaces
Weld Quality - Welding
Defect/Imperfection
o Miscellaneous defect
Misalignment
Spatter
Arc strikes
Burn Through
Inspection and Testing Methods
Visual inspection
Nondestructive evaluation
Destructive testing
Inspection and Testing Methods –
Visual Inspection
Visual Inspection
Most widely used welding inspection method
Human inspector visually examines for:
Conformance to dimensions
Warpage
Cracks, cavities, incomplete fusion, and
other surface defects
Limitations:
Only surface defects are detectable
Welding inspector must also determine if
additional tests are warranted
Inspection and Testing Methods –
Nondestructive Evaluation (NDE) Tests
Nondestructive Evaluation (NDE) Tests
Ultrasonic testing - high frequency sound waves
directed through specimen - cracks, inclusions are
detected by loss in sound transmission
Radiographic testing - x-rays or gamma radiation
provide photograph of internal flaws
Dye-penetrant and fluorescent-penetrant tests methods for detecting small cracks and cavities that
are open at surface
Magnetic particle testing – iron filings sprinkled on
surface reveal subsurface defects by distorting
magnetic field in part
Inspection and Testing Methods –
Destructive Testing
Destructive Testing
Tests in which weld is destroyed either during testing or
to prepare test specimen
Mechanical tests - purpose is similar to conventional
testing methods such as tensile tests, shear tests, etc
Metallurgical tests - preparation of metallurgical
specimens (e.g., photomicrographs) of weldment to
examine metallic structure, defects, extent and condition
of heat affected zone, and similar phenomena
Weldability Factors - Welding Process
Welding Process
Some metals or metal combinations can be readily
welded by one process but are difficult to weld by
others
Example: stainless steel readily welded by most AW
and RW processes, but difficult to weld by OFW
Weldability Factors – Base Metal
Base Metal
Some metals melt too easily; e.g., aluminum
Metals with high thermal conductivity transfer heat
away from weld, which causes problems; e.g., copper
High thermal expansion and contraction in metal
causes distortion problems
Dissimilar metals pose problems in welding when
their physical and/or mechanical properties are
substantially different
Weldability Factors - Other Factors
Filler metal
Must be compatible with base metal(s)
In general, elements mixed in liquid state that
form a solid solution upon solidification will
not cause a problem
Surface conditions
Moisture can result in porosity in fusion zone
Oxides and other films on metal surfaces can
prevent adequate contact and fusion
Design Considerations in Welding
Design for welding - product should be designed
from the start as a welded assembly, and not as a
casting or forging or other formed shape
Minimum parts - welded assemblies should
consist of fewest number of parts possible
Example: usually more cost efficient to perform
simple bending operations on a part than to
weld an assembly from flat plates and sheets
Arc Welding Design Guidelines
Good fit-up of parts - to maintain dimensional
control and minimize distortion
Machining is sometimes required to achieve
satisfactory fit-up
Assembly must allow access for welding gun to
reach welding area
Design of assembly should allow flat welding to
be performed as much as possible, since this
is fastest and most convenient welding position
Arc Welding Positions
Flat welding is best position
Overhead welding is most difficult
Figure 31.35 Welding positions (defined here for groove
welds): (a) flat, (b) horizontal, (c) vertical, and (d)
overhead.
BRAZING, SOLDERING, AND
ADHESIVE BONDING
1.
2.
3.
Brazing
Soldering
Adhesive Bonding
Overview of Brazing and Soldering
Both use filler metals to permanently join metal
parts, but there is no melting of base metals
When to use brazing or soldering instead of
fusion welding:
Metals have poor weldability
Dissimilar metals are to be joined
Intense heat of welding may damage
components being joined
Geometry of joint not suitable for welding
High strength is not required
Overview of Adhesive Bonding
Uses forces of attachment between a filler
material and two closely-spaced surfaces to bond
the parts
Filler material in adhesive bonding is not
metallic
Joining process can be carried out at room
temperature or only modestly above
Brazing
Joining process in which a filler metal is melted
and distributed by capillary action between faying
surfaces of metal parts being joined
No melting of base metals occurs
Only the filler melts
Filler metal Tm greater than 450C (840F) but
less than Tm of base metal(s) to be joined
Strength of Brazed Joint
If joint is properly designed and brazing operation
is properly performed, solidified joint will be
stronger than filler metal out of which it was
formed
Why?
Small part clearances used in brazing
Metallurgical bonding that occurs between
base and filler metals
Geometric constrictions imposed on joint by
base parts
Brazing Compared to Welding
Any metals can be joined, including dissimilar
metals
Can be performed quickly and consistently,
permitting high production rates
Multiple joints can be brazed simultaneously
Less heat and power required than FW
Problems with HAZ in base metal are reduced
Joint areas that are inaccessible by many welding
processes can be brazed; capillary action draws
molten filler metal into joint
Disadvantages and Limitations of
Brazing
Joint strength is generally less than a welded joint
Joint strength is likely to be less than the base
metals
High service temperatures may weaken a brazed
joint
Color of brazing metal may not match color of
base metal parts, a possible aesthetic
disadvantage
Brazing Applications
Automotive (e.g., joining tubes and pipes)
Electrical equipment (e.g., joining wires and
cables)
Cutting tools (e.g., brazing cemented carbide
inserts to shanks)
Jewelry
Chemical process industry
Plumbing and heating contractors join metal pipes
and tubes by brazing
Repair and maintenance work
Brazed Joints
Butt and lap joints common
Geometry of butt joints is usually adapted for
brazing
Lap joints are more widely used, since they
provide larger interface area between parts
Filler metal in a brazed lap joint is bonded to base
parts throughout entire interface area, rather than
only at edges
Butt Joints for Brazing
Figure 32.1 (a) Conventional butt joint, and adaptations of
the butt joint for brazing: (b) scarf joint, (c) stepped butt
joint, (d) increased cross-section of the part at the joint.
Lap Joints for Brazing
Figure 32.2 (a) Conventional lap joint, and adaptations of the lap
joint for brazing: (b) cylindrical parts, (c) sandwiched parts, and
(d) use of sleeve to convert butt joint into lap joint.
Some Filler Metals for Brazing
Base metal(s)
Aluminum
Nickel-copper alloy
Copper
Steel, cast iron
Stainless steel
Filler metal(s)
Aluminum and silicon
Copper
Copper and phosphorous
Copper and zinc
Gold and silver
Desirable Brazing Metal Characteristics
Melting temperature of filler metal is compatible
with base metal
Low surface tension in liquid phase for good
wettability
High fluidity for penetration into interface
Capable of being brazed into a joint of adequate
strength for application
Avoid chemical and physical interactions with
base metal (e.g., galvanic reaction)
Applying Filler Metal
Figure 32.4 Several techniques for applying filler metal in brazing:
(a) torch and filler rod. Sequence: (1) before, and (2) after.
Applying Filler Metal
Figure 32.4 Several techniques for applying filler metal in brazing:
(b) ring of filler metal at entrance of gap. Sequence: (1) before,
and (2) after.
Brazing Fluxes
Similar purpose as in welding; they dissolve,
combine with, and otherwise inhibit formation of
oxides and other unwanted byproducts in brazing
process
Characteristics of a good flux include:
Low melting temperature
Low viscosity so it can be displaced by filler
metal
Facilitates wetting
Protects joint until solidification of filler metal
Heating Methods in Brazing
Torch Brazing - torch directs flame against work in
vicinity of joint
Furnace Brazing - furnace supplies heat
Induction Brazing – heating by electrical
resistance to high-frequency current in work
Resistance Brazing - heating by electrical
resistance in parts
Dip Brazing - molten salt or molten metal bath
Infrared Brazing - uses high-intensity infrared
lamp
Soldering
Joining process in which a filler metal with
Tm less than or equal to 450C (840F) is
melted and distributed by capillary action
between faying surfaces of metal parts being
joined
No melting of base metals, but filler metal
wets and combines with base metal to form
metallurgical bond
Soldering similar to brazing, and many of the
same heating methods are used
Filler metal called solder
Most closely associated with electrical and
electronics assembly (wire soldering)
Soldering Advantages / Disadvantages
Advantages:
Lower energy than brazing or fusion welding
Variety of heating methods available
Good electrical and thermal conductivity in joint
Easy repair and rework
Disadvantages:
Low joint strength unless reinforced by
mechanically means
Possible weakening or melting of joint in elevated
temperature service
Filler metal / Solder
Usually alloys of tin (Sn) and lead (Pb). Both
metals have low Tm
Lead is poisonous and its percentage is
minimized in most solders
Tin is chemically active at soldering
temperatures and promotes wetting action
for successful joining
In soldering copper, copper and tin form
intermetallic compounds that strengthen
bond
Silver and antimony also used in soldering
alloys
Mechanical Means to Secure Joint
Figure 32.8 Techniques for securing the joint by mechanical means prior
to soldering in electrical connections: (a) crimped lead wire on PC
board; (b) plated through-hole on PC board to maximize solder
contact surface; (c) hooked wire on flat terminal; and (d) twisted
wires.
Functions of Soldering Fluxes
Be molten at soldering temperatures
Remove oxide films and tarnish from base part
surfaces
Prevent oxidation during heating
Promote wetting of faying surfaces
Be readily displaced by molten solder during
process
Leave residue that is non-corrosive and
nonconductive
Soldering Methods
Many soldering methods same as for brazing,
except less heat and lower temperatures are
required
Additional methods:
Hand soldering – manually operated soldering
gun
Wave soldering – soldering of multiple lead
wires in printed circuit cards
Reflow soldering –used for surface mount
components on printed circuit cards
Wave Soldering
Figure 32.9 Wave soldering, in which molten solder is
delivered up through a narrow slot onto the underside of a
printed circuit board to connect the component lead wires.
Adhesive Bonding
Joining process in which a filler material is used to
hold two (or more) closely-spaced parts together
by surface attachment
Used in a wide range of bonding and sealing
applications for joining similar and dissimilar
materials such as metals, plastics, ceramics,
wood, paper, and cardboard
Considered a growth area because of
opportunities for increased applications
Adhesive Bonding - Terminology
Adhesive = filler material, nonmetallic, usually a
polymer
Adherends = parts being joined
Structural adhesives – of greatest interest in
engineering, capable of forming strong,
permanent joints between strong, rigid adherends
Curing in Adhesive Bonding
Process by which physical properties of the
adhesive are changed from liquid to solid, usually
by chemical reaction, to accomplish surface
attachment of parts
Curing often aided by heat and/or a catalyst
If heat used, temperatures are relatively low
Curing takes time - a disadvantage in production
Pressure sometimes applied between parts to
activate bonding process
Adhesive Bonding - Joint Strength
Depends on strength of:
Adhesive
Attachment between adhesive and
adherends
Attachment mechanisms:
Chemical bonding – adhesive and
adherend form primary bond on curing
Physical interactions - secondary
bonding forces between surface atoms
Mechanical interlocking - roughness of
adherend causes adhesive to become
entangled in surface asperities
Adhesive Bonding - Joint Design
Adhesive joints are not as strong as welded,
brazed, or soldered joints
Joint contact area should be maximized
Adhesive joints are strongest in shear and tension
Joints should be designed so applied stresses
are of these types
Adhesive bonded joints are weakest in cleavage
or peeling
Joints should be designed to avoid these types
of stresses
Types of Stresses in Adhesive Bonding
Figure 32.10 Types of stresses that must be
considered in adhesive bonded joints: (a) tension,
(b) shear, (c) cleavage, and (d) peeling.
Joint Designs in Adhesive Bonding
Figure 32.11 Some joint designs for adhesive bonding: (a) through
(d) butt joints; (e) through (f) T-joints; (b) and (g) through (j)
corner joints.
Adhesive Types
Natural adhesives - derived from natural sources,
including gums, starch, dextrin, soya flour,
collagen
Low-stress applications: cardboard cartons,
furniture, bookbinding, plywood
Inorganic - based principally on sodium silicate
and magnesium oxychloride
Low cost, low strength
Synthetic adhesives - various thermoplastic and
thermosetting polymers
Synthetic Adhesives
Most important category in manufacturing
Synthetic adhesives cured by various
mechanisms:
Mixing catalyst or reactive ingredient with
polymer prior to applying
Heating to initiate chemical reaction
Radiation curing, such as UV light
Curing by evaporation of water
Application as films or pressure-sensitive
coatings on surface of adherend
Applications of Adhesives
Automotive, aircraft, building products,
shipbuilding
Packaging industries
Footwear
Furniture
Bookbinding
Electrical and electronics
Surface Preparation
For adhesive bonding to succeed, part
surfaces must be extremely clean
Bond strength depends on degree of
adhesion between adhesive and adherend,
and this depends on cleanliness of surface
For metals, solvent wiping often used for
cleaning, and abrading surface by
sandblasting improves adhesion
For nonmetallic parts, surfaces are
sometimes mechanically abraded or
chemically etched to increase roughness
Application Methods
Manual brushing and rolling
Silk screening
Flowing, using manually operated dispensers
Spraying
Automatic applicators
Roll coating
Adhesive is dispensed
by a manually
controlled dispenser to
bond parts during
assembly (photo
courtesy of EFD Inc.).
Advantages of Adhesive Bonding
Applicable to a wide variety of materials
Bonding occurs over entire surface area of joint
Low temperature curing avoids damage to parts
being joined
Sealing as well as bonding
Joint design is often simplified, e.g., two flat
surfaces can be joined without providing special
part features such as screw holes
Limitations of Adhesive Bonding
Joints generally not as strong as other joining
methods
Adhesive must be compatible with materials being
joined
Service temperatures are limited
Cleanliness and surface preparation prior to
application of adhesive are important
Curing times can limit production rates
Inspection of bonded joint is difficult
Mechanical Assembly Technology
Threaded Fasteners
2. Rivets and Eyelets
3. Assembly Methods Based on
Interference Fits
4. Other Mechanical Fastening
Methods
5. Molding Inserts and Integral
Fasteners
©2007 John Wiley &
Sons, Inc. M P Groover,
6. ofDesign for Assembly
Fundamentals
1.
Modern Manufacturing
3/e
Mechanical Assembly Defined
Use of various fastening methods to
mechanically attach two or more
parts together
In most cases, discrete hardware
components, called fasteners, are
added to the parts during assembly
In other cases, fastening involves
shaping or reshaping of a
©2007 John Wiley
&
component,
and no separate
Sons, Inc. M P Groover,
Fundamentals of
fasteners are required
Modern Manufacturing
3/e
Products of Mechanical Assembly
Many consumer products are
assembled largely by mechanical
fastening methods
Examples: automobiles, large and small
appliances, telephones
Many capital goods products are
assembled using mechanical
fastening methods
Examples: commercial airplanes, trucks,
railway locomotives and cars, machine
tools
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Two Major Types of Mechanical
Assembly
1.
Methods that allow for disassembly
2.
Example: threaded fasteners
Methods that create a permanent
joint
Example: rivets
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Why Use Mechanical Assembly?
Low cost
Ease of manufacturing
Easy in creating design
Ease of assembly – can be
accomplished with relatively ease
by unskilled workers
Minimum of special tooling required
In a relatively short time
Ease of disassembly – at least for
the methods that permit
disassembly
Threaded Fasteners
Discrete hardware components that
have external or internal threads for
assembly of parts
Most important category of
mechanical assembly
In nearly all cases, threaded
fasteners permit disassembly
Common threaded fastener types
©2007 John Wiley &
are screws, bolts, and nuts
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Screws, Bolts, and Nuts
Screw - externally threaded fastener
generally assembled into a blind
threaded hole
Bolt - externally threaded fastener
inserted into through holes and
"screwed" into a nut on the opposite
side
Nut - internally threaded fastener
©2007 John Wiley
&
having
standard threads that match
Sons, Inc. M P Groover,
Fundamentals of
those on bolts of the same
Modern Manufacturing
3/e
diameter, pitch, and thread form
Screws, Bolts, and Nuts
Figure 33.1 Typical assemblies when screws and bolts
are used.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Some Facts About Screws and
Bolts
Screws and bolts come in a variety
of sizes, threads, and shapes
Much standardization in threaded
fasteners, which promotes
interchangeability
U.S. is converting to metric, further
reducing variations
Differences between threaded
©2007 John Wiley &
fasteners affect tooling
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Example: different screw head styles and
Head Styles on Screws and Bolts
Figure 33.2 Various head styles available on screws and
bolts.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Types of Screws
Greater variety than bolts, since
functions vary more
Examples:
Machine screws - generic type, generally
designed for assembly into tapped holes
Cap screws - same geometry as machine
screws but made of higher strength
metals and to closer tolerances
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Setscrews
Hardened and designed for
assembly functions such as
fastening collars, gears, and
pulleys to shafts
Figure 33.3 (a) Assembly of collar to shaft using a setscrew;
(b) various setscrew geometries (head types and points).
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Self-Tapping Screws
Designed to form or cut
threads in a pre-existing hole
into which it is being turned
Also called a tapping screw
Figure 33.4 Self-tapping
screws: thread-forming,
and thread-cutting.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Screw Thread Inserts
Internally threaded plugs or wire coils
designed to be inserted into an
unthreaded hole and accept an
externally threaded fastener
Assembled into weaker materials to
provide strong threads
Upon assembly of screw into insert,
insert barrel expands into hole to
©2007 John Wiley
&
secure
the assembly
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Screw Thread Inserts
Figure 33.6 Screw thread inserts: (a) before insertion, and
(b) after insertion into hole and screw is turned into insert.
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Washer
Hardware component often used with
threaded fasteners to ensure
tightness of the mechanical joint
Simplest form = flat thin ring of
sheet metal
Functions:
Distribute stresses
Provide support for large clearance holes
©2007 John Wiley& Protect part surfaces and seal the joint
Sons, Inc. M P Groover,
Fundamentals of
Increase spring tension
Modern Manufacturing
3/e
Resist inadvertent unfastening
Washer Types
Figure 33.8 Types of washers: (a) plain (flat) washers; (b) spring
washers, used to dampen vibration or compensate for wear; and
(c) lock washer designed to resist loosening of the bolt or screw.
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Bolt Strength
Two measures:
Tensile strength, which has the
traditional definition
Proof strength - roughly equivalent
to yield strength
Maximum tensile stress without
permanent deformation
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Stresses in a Bolted Joint
Figure 33.9 Typical stresses acting on a bolted
©2007 John Wiley &
joint.
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Over-tightening in Bolted Joints
Potential problem in assembly,
causing stresses that exceed
strength of fastener or nut
Failure can occur in one of the
following ways:
1.
2.
3.
Stripping of external threads
Stripping of internal threads
Bolt fails due to excessive tensile
stresses on cross-sectional area
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Tensile failure of cross section is
most common problem
Methods to Apply Required Torque
Operator feel - not very accurate,
but adequate for most assemblies
2. Torque wrench – indicates amount
of torque during tightening
3. Stall-motor - motorized wrench is
set to stall when required torque is
reached
4. Torque-turn tightening - fastener is
©2007 John Wiley &
initially tightened to a low torque
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
level and then rotated a specified
3/e
1.
Rivets
Unthreaded, headed pin used to
join two or more parts by
passing pin through holes in
parts and forming a second head
in the pin on the opposite side
Widely used fasteners for
achieving a permanent
mechanically fastened joint
Clearance hole into which rivet is
©2007 John Wiley &
Sons, Inc. M P Groover, inserted must be close to the
Fundamentals of
Modern Manufacturing
diameter of the rivet
3/e
Types of Rivets
Figure 33.10 Five basic rivet types, also shown in assembled
configuration: (a) solid, (b) tubular, (c) semi-tubular, (d) bifurcated,
©2007 John Wiley &
andInc.
(e)M compression.
Sons,
P Groover,
Fundamentals of
Modern Manufacturing
3/e
Applications and Advantages of
Rivets
Used primarily for lap joints
A primary fastening method in
aircraft and aerospace industries
Advantages:
High production rates
Simplicity
Dependability
Low cost
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Tooling and Methods for Rivets
1.
2.
3.
Impact - pneumatic hammer
delivers a succession of blows to
upset rivet
Steady compression - riveting tool
applies a continuous squeezing
pressure to upset rivet
Combination of impact and
compression
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Interference Fits
Assembly methods based on
mechanical interference between
two mating parts being joined
The interference, either during
assembly or after joining, holds the
parts together
Interference fit methods include:
Press fitting
©2007 John Wiley& Shrink and expansion fits
Sons, Inc. M P Groover,
Fundamentals of
Snap fits
Modern Manufacturing
3/e
Retaining rings
Snap Fits
Joining of two parts in which
mating elements possess a
temporary interference during
assembly, but once assembled
they interlock
Originally conceived as a method
ideally suited for industrial robots
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
During assembly, one or both parts
elastically deform to accommodate
temporary interference
Usually designed for slight
interference after assembly
Snap Fit Assembly
Figure 33.13 Snap fit assembly, showing cross-sections of two
mating
parts:
(1) before assembly, and (2) parts snapped together.
©2007
John Wiley
&
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Retaining Ring
Fastener that snaps into a
circumferential groove on a shaft or
tube to form a shoulder
Used to locate or restrict movement
of parts on a shaft
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Design for Assembly (DFA)
Keys to successful DFA:
1.
2.
Design product with as few parts as
possible
Design remaining parts so they are
easy to assemble
Assembly cost is determined
largely in product design, when
the number of components in
the product and how they are
assembled is decided
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Once these decisions are made,
little can be done in manufacturing
DFA Guidelines
Use modularity in product design
Each subassembly should have a
maximum of 12 or so parts
Design the subassembly around a base
part to which other components are
added
Reduce the need for multiple
components to be handled at once
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
More DFA Guidelines
Limit the required directions of
access
Adding all components vertically from
above is the ideal
Use high quality components
Poor quality parts jams feeding and
assembly mechanisms
Minimize threaded fasteners
Use
snap fit assembly
©2007 John
Wiley
&
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
An all-inclusive term covering processes
such as:
Welding
Brazing
Soldering
Adhesive bonding
Mechanical fastening
Overview on Joining Processes
Why Joining Processes
Some (even simple) products are too large to be made
by individual processes ( 3-D Hollow structural member, 5 m
diameter)
Easier, more economical to manufacture & join
individual components (Cooking pot with handle)
Products to be disassembled for maintenance
(Appliances; engines)
Varying functionality of product (Carbide inserts in tool
steels; Brake shoes)
Transportation + assembly is less costly (Shelving units;
Machinery)
Product Example
Figure 8.1 Various parts in a typical automobile that are
assembled by the joining processes.
Product Example (Cont.)
Figure 8.2: Examples of parts utilizing joining processes. (a) A tubular part
fabricated by joining individual components. This product cannot be manufactured
in one piece by any of the methods described in the previous chapters if it consists
of thin-walled, large-diameter, tubular-shaped long arms. (b) A drill bit with a
carbide cutting insert brazed to a steel shank—an example of a part in which two
materials need to be joined for performance reasons. (c) Spot welding of
automobile bodies.
WELDING PROCESSES
BS 499 part 1 Welding terms
A union between pieces of metal at
faces rendered plastic or liquid by
heat,pressure or both.
Overview on Joining Processes
Figure 8.3: Joining Method (AWS A3.0:2001)
Fusion Welding
Fusion Welding
Fusion Welding
Fusion Welding
Any welding process that uses fusion
of the base metal to make the weld
(AWS A3.0: 2001)
Fusion Welding – Arc Welding
Arc Welding
A fusion welding process in which coalescence of the
metals is achieved by the heat from an electric arc
between an electrode and the work
Electric energy from the arc produces temperatures ~
10,000 F (5500 C), hot enough to melt any metal
Most AW processes add filler metal to increase volume
and strength of weld joint
An electric arc is a discharge of electric current across a
gap in a circuit
It is sustained by an ionized column of gas (plasma)
through which the current flows
To initiate the arc in AW, electrode is brought into
contact with work and then quickly separated from it by a
short distance
Fusion Welding – Arc Welding (Cont.)
A pool of molten metal is formed near electrode
tip, and as electrode is moved along joint,
molten weld pool solidifies in its wake
Figure 31.1 Basic configuration of an arc welding process.
Fusion Welding – Arc Welding (Cont.)
Two Basic Types of AW Electrodes
Consumable – consumed during welding process
Source of filler metal in arc welding
Nonconsumable – not consumed during welding process
Filler metal must be added separately
Fusion Welding – Arc Welding (Cont.)
Arc Shielding
At high temperatures in AW, metals are chemically
reactive to oxygen, nitrogen, and hydrogen in air
Mechanical properties of joint can be seriously
degraded by these reactions
To protect operation, arc must be shielded from
surrounding air in AW processes
Arc shielding is accomplished by:
Shielding gases, e.g., argon, helium, CO2
Flux
Fusion Welding – Arc Welding (Cont.)
Power Source in Arc Welding
Direct current (DC) vs. Alternating current (AC)
AC machines less expensive to purchase and
operate, but generally restricted to ferrous
metals
DC equipment can be used on all metals and
is generally noted for better arc control
Fusion Welding – Resistance Welding
(Cont.)
Resistance Welding (RW)
A group of fusion welding processes that use a
combination of heat and pressure to accomplish
coalescence
Heat generated by electrical resistance to current flow at
junction to be welded
Principal RW process is resistance spot welding (RSW)
Fusion Welding – Resistance
Welding (Cont.)
Figure 31.12 Resistance
welding, showing the
components in spot
welding, the main
process in the RW
group.
Fusion Welding – Resistance Welding
(Cont.)
Components in Resistance Spot Welding
Parts to be welded (usually sheet metal)
Two opposing electrodes
Means of applying pressure to squeeze parts between
electrodes
Power supply from which a controlled current can be
applied for a specified time duration
Fusion Welding – Resistance Welding
(Cont.)
Advantages:
No filler metal required
High production rates possible
Lends itself to mechanization and automation
Lower operator skill level than for arc welding
Good repeatability and reliability
Disadvantages:
High initial equipment cost
Limited to lap joints for most RW processes
Skilled operators are required
Bigger job thickness cannot be welded
Fusion Welding – Resistance
Welding (Cont.)
Applications of resistance welding
Joining sheets, bars and tubes.
Making tubes and metal furniture.
Welding aircraft and automobile parts.
Making cutting tools.
Making fuel tanks of cars, tractors etc.
Making wire fabrics, grids, grills, mesh
weld, containers etc.
Fusion Welding - Resistance Spot
Welding (RSW)
Resistance Spot Welding
Process in which fusion of faying surfaces of a lap joint is
achieved at one location by opposing electrodes
Used to join sheet metal parts using a series of spot welds
Widely used in mass production of automobiles,
appliances, metal furniture, and other products made of
sheet metal
Typical car body has ~ 10,000 spot welds
Annual production of automobiles in the world is
measured in tens of millions of units
Fusion Welding - Resistance Spot
Welding (RSW) (Cont.)
Figure 31.13 (a) Spot welding cycle, (b) plot of squeezing force & current
in cycle (1) parts inserted between electrodes, (2) electrodes close,
force applied, (3) current on, (4) current off, (5) electrodes opened.
Fusion Welding - Resistance Seam
Welding (RSEW)
Resistance Seam Welding (RSEW)
Uses rotating wheel electrodes to produce a
series of overlapping spot welds along lap joint
Can produce air-tight joints
Applications:
Gasoline tanks
Automobile mufflers
Various other sheet metal containers
Fusion Welding - Resistance Seam
Welding (RSEW)
Figure 31.15 Resistance seam welding (RSEW).
Fusion Welding - Oxyfuel Gas Welding
(OFW)
Oxyfuel Gas Welding
General term for welding operations that burn various fuels
mixed with oxygen
OFW employs several types of gases, which is the primary
distinction among the members of this group
Oxyfuel gas is also used in flame cutting torches to cut and
separate metal plates and other parts
Fusion Welding - Oxyfuel Gas Welding
(OFW)
Alternatives Fuel Gases for OFW
Acetylene
Gasoline
Hydrogen
MPS and MAPP gas
Propylene and Fuel Gas
Butane, propane and butane/propane
mixes
Fusion Welding - Oxy-acetylene gas welding
(OAW)
Oxy-acetylene gas welding (OAW)
Oxy-acetylene gas welding is a group OFW process that
used acetylene gas as a fuel gas
Most popular fuel among OFW group because it is capable of
higher temperatures than any other - up to 3480C
(6300F)
Fusion welding performed by a high temperature flame from
combustion of acetylene and oxygen
Flame is directed by a welding torch
Filler metal is sometimes added
Composition must be similar to base metal
Filler rod often coated with flux to clean surfaces and prevent
oxidation
Fusion Welding - Oxy-acetylene
gas welding (OAW)
Figure 31.21 A typical oxyacetylene welding operation (OAW).
Fusion Welding - Oxy-acetylene gas
welding (OAW)
Chemical reaction during burning
Two stage chemical reaction of acetylene and
oxygen:
First stage reaction:
C2H2 + O2 2CO + H2 + heat
Second stage reaction:
2CO + H2 + 1.5O2 2CO2 + H2O + heat
Fusion Welding - Oxy-acetylene
gas welding (OAW)
Oxyacetylene Torch
Maximum temperature reached at tip of inner cone,
while outer envelope spreads out and shields work
surfaces from atmosphere
Figure 31.22 The neutral flame from an oxyacetylene torch
indicating temperatures achieved.
Fusion Welding - Other Processes
FW processes that cannot be classified as arc,
resistance, or oxyfuel welding
Use unique technologies to develop heat for
melting
Applications are typically unique
Processes include:
Electron beam welding
Laser beam welding
Electroslag welding
Thermit welding
Fusion Welding - Thermit Welding (TW)
Thermit Welding (TW)
FW process in which heat for coalescence is produced
by superheated molten metal from the chemical reaction
of thermite
Thermite = mixture of Al and Fe3O4 fine powders that
produce an exothermic reaction when ignited
Also used for incendiary bombs
Filler metal obtained from liquid metal
Process used for joining, but has more in common with
casting than welding
Fusion Welding - Thermit
Welding (TW)
Figure 31.25 Thermit welding: (1) Thermit ignited; (2) crucible
tapped, superheated metal flows into mold; (3) metal solidifies to
produce weld joint.
Fusion Welding - Thermit Welding (TW)
Applications
Joining of railroad rails
Repair of cracks in large steel castings and forgings
Weld surface is often smooth enough that no finishing is
required
Solid State Welding (SSW)
Solid State Welding (SSW)
Coalescence of part surfaces is achieved by:
If both heat and pressure are used, heat is not enough to melt
work surfaces
Pressure alone, or
Heat and pressure
For some SSW processes, time is also a factor
No filler metal is added
Each SSW process has its own way of creating a bond at the
faying surfaces
Essential factors for a successful solid state weld are that the
two faying surfaces must be:
Very clean
In very close physical contact with each other to permit atomic bonding
Solid State Welding (Cont)
SSW Advantages over FW Processes
If no melting, then no heat affected zone, so metal
around joint retains original properties
Many SSW processes produce welded joints that bond
the entire contact interface between two parts rather
than at distinct spots or seams
Some SSW processes can be used to bond dissimilar
metals, without concerns about relative melting points,
thermal expansions, and other problems that arise in FW
Solid State Welding (Cont.)
Processes under SSW group
Forge welding
Cold welding
Roll welding
Hot pressure welding
Diffusion welding
Explosion welding
Friction welding
Ultrasonic welding
Solid State Welding - Forge Welding
Forge Welding
SSW process in which
components to be joined are
heated to hot working temperature
range and then forged together by
hammering or similar means
Historic significance in
development of manufacturing
technology
Process dates from about
1000 B.C., when blacksmiths
learned to weld two pieces of
metal
Solid State Welding - Cold Welding
(CW)
Cold Welding (CW)
SSW process done by applying high
pressure between clean contacting
surfaces at room temperature
Cleaning usually done by degreasing
and wire brushing immediately before
joining
No heat is applied, but deformation
raises work temperature
At least one of the metals, preferably
both, must be very ductile
Soft aluminum and copper suited
to CW
Applications: making electrical
connections
Dies
Workpiece Workpiece
Before welding
After welding
Solid State Welding - Roll Welding
(ROW)
SSW process in which pressure sufficient to cause
coalescence is applied by means of rolls, either with or
without external heat
Variation of either forge welding or cold welding, depending
on whether heating of workparts is done prior to process
If no external heat, called cold roll welding
If heat is supplied, hot roll welding
Solid State Welding - Roll Welding
(ROW)
Applications
Cladding stainless steel to mild or low alloy steel for
corrosion resistance
Bimetallic strips for measuring temperature
"Sandwich" coins for U.S mint
Solid State Welding - Diffusion Welding
(DFW)
Diffusion Welding
SSW process that uses heat
and pressure, usually in a
controlled atmosphere, with
sufficient time for diffusion and
coalescence to occur
Temperatures 0.5 Tm
Plastic deformation at surfaces
is minimal
Primary coalescence
mechanism is solid state
diffusion
Limitation: time required for
diffusion can range from
seconds to hours
Work pieces
Force
A
B
Schematic representation of
diffusion welding using
electrical resistance for heating
Solid State Welding - Diffusion Welding
(DFW)
DFW Applications
Joining of high-strength and refractory metals in
aerospace and nuclear industries
Can be used to join either similar and dissimilar metals
For joining dissimilar metals, a filler layer of different
metal is often sandwiched between base metals to
promote diffusion
Solid State Welding - Explosion
Welding (EXW)
Explosion Welding (EXW)
SSW process in which rapid coalescence of two metallic
surfaces is caused by the energy of a detonated
explosive
No filler metal used
No external heat applied
No diffusion occurs - time is too short
Bonding is metallurgical, combined with mechanical
interlocking that results from a rippled or wavy interface
between the metals
Commonly used to bond two dissimilar metals, in
particular to clad one metal on top of a base metal over
large areas
Solid State Welding Explosion Welding (EXW)
Figure 31.27 Explosive welding (EXW): (1) setup in the
parallel configuration, and (2) during detonation of the
explosive charge.
Solid State Welding - Friction Welding
(FRW)
SSW process in which coalescence is achieved
by frictional heat combined with pressure
When properly carried out, no melting occurs at
faying surfaces
No filler metal, flux, or shielding gases normally
used
Process yields a narrow HAZ
Can be used to join dissimilar metals
Widely used commercial process, amenable to
automation and mass production
Solid State Welding Friction Welding (FRW)
Figure 31.28 Friction welding (FRW): (1) rotating part, no contact; (2)
parts brought into contact to generate friction heat; (3) rotation
stopped and axial pressure applied; and (4) weld created.
Solid State Welding - Friction Welding
(FRW)
1.
2.
Two Types of Friction Welding
Continuous-drive friction welding
One part is driven at constant rpm against
stationary part to cause friction heat at
interface
At proper temperature, rotation is stopped
and parts are forced together
Inertia friction welding
Rotating part is connected to flywheel,
which is brought up to required speed
Flywheel is disengaged from drive, and
parts are forced together
Solid State Welding - Friction Welding
(FRW)
Applications:
Shafts and tubular parts
Industries: automotive, aircraft, farm equipment,
petroleum and natural gas
Limitations:
At least one of the parts must be rotational
Flash must usually be removed
Upsetting reduces the part lengths (which must be
taken into consideration in product design)
Solid State Welding - Ultrasonic
Welding (USW)
Two components are held together, oscillatory
shear stresses of ultrasonic frequency are applied
to interface to cause coalescence
Oscillatory motion breaks down any surface films
to allow intimate contact and strong metallurgical
bonding between surfaces
Although heating of surfaces occurs,
temperatures are well below Tm
No filler metals, fluxes, or shielding gases
Generally limited to lap joints on soft materials
such as aluminum and copper
Ultrasonic Welding
Figure 31.29 Ultrasonic welding (USW): (a) general setup for
a lap joint; and (b) close-up of weld area.
Solid State Welding - Ultrasonic
Welding
Applications
Wire terminations and splicing in electrical and
electronics industry
Eliminates need for soldering
Assembly of aluminum sheet metal panels
Welding of tubes to sheets in solar panels
Assembly of small parts in automotive industry
Weld Quality
Concerned with obtaining an acceptable
weld joint that is strong and absent of
defects, and the methods of inspecting and
testing the joint to assure its quality
Topics:
Residual stresses and distortion
Welding defects
Inspection and testing methods
Weld Quality
Residual Stresses and Distortion
Rapid heating and cooling in localized regions during
FW result in thermal expansion and contraction that
cause residual stresses
These stresses, in turn, cause distortion and warpage
Situation in welding is complicated because:
Heating is very localized
Melting of base metals in these regions
Location of heating and melting is in motion (at
least in AW)
Weld Quality
Techniques to Minimize Warpage
Welding fixtures to physically restrain parts
Heat sinks to rapidly remove heat
Tack welding at multiple points along joint to create a
rigid structure prior to seam welding
Selection of welding conditions (speed, amount of filler
metal used, etc.) to reduce warpage
Preheating base parts
Stress relief heat treatment of welded assembly
Proper design of weldment
Weld Quality - Welding
Defect/Imperfection
Imperfection is any deviation from the ideal weld.
Defect is an unacceptable imperfection
A perfect weld joint, when subjected to an external force,
provide a distribution of stress throughout its volume which is
not significantly greater than parent metal.
Weld Quality - Welding
Defect/Imperfection
Cracks
Fracture-type interruptions either in weld or in base metal
adjacent to weld
Serious defect because it is a discontinuity in the metal that
significantly reduces strength
Caused by embrittlement or low ductility of weld and/or base
metal combined with high restraint during contraction
In general, this defect must be repaired
Weld Quality - Welding
Defect/Imperfection
Cavities
1.
2.
Porosity - small voids in weld metal formed by gases entrapped
during solidification. Caused by inclusion of atmospheric
gases, sulfur in weld metal, or surface contaminants
Shrinkage voids - cavities formed by shrinkage during
solidification. Cause by terminated arc at the end of a weld run
1
2
Weld Quality - Welding
Defect/Imperfection
Solid inclusions - nonmetallic material entrapped in
weld metal
Most common form is slag inclusions generated during AW
processes that use flux
Instead of floating to top of weld pool, globules of slag become
encased during solidification
Metallic oxides that form during welding of certain metals such
as aluminum, which normally has a surface coating of Al2O3
Weld Quality - Welding
Defect/Imperfection
Incomplete Fusion
Also known as lack of fusion, it is simply a weld bead in which
fusion has not occurred throughout entire cross section of joint
Weld Quality - Welding
Defect/Imperfection
o Lack of Smoothly Blended Surfaces
Weld Quality - Welding
Defect/Imperfection
o Miscellaneous defect
Misalignment
Spatter
Arc strikes
Burn Through
Inspection and Testing Methods
Visual inspection
Nondestructive evaluation
Destructive testing
Inspection and Testing Methods –
Visual Inspection
Visual Inspection
Most widely used welding inspection method
Human inspector visually examines for:
Conformance to dimensions
Warpage
Cracks, cavities, incomplete fusion, and
other surface defects
Limitations:
Only surface defects are detectable
Welding inspector must also determine if
additional tests are warranted
Inspection and Testing Methods –
Nondestructive Evaluation (NDE) Tests
Nondestructive Evaluation (NDE) Tests
Ultrasonic testing - high frequency sound waves
directed through specimen - cracks, inclusions are
detected by loss in sound transmission
Radiographic testing - x-rays or gamma radiation
provide photograph of internal flaws
Dye-penetrant and fluorescent-penetrant tests methods for detecting small cracks and cavities that
are open at surface
Magnetic particle testing – iron filings sprinkled on
surface reveal subsurface defects by distorting
magnetic field in part
Inspection and Testing Methods –
Destructive Testing
Destructive Testing
Tests in which weld is destroyed either during testing or
to prepare test specimen
Mechanical tests - purpose is similar to conventional
testing methods such as tensile tests, shear tests, etc
Metallurgical tests - preparation of metallurgical
specimens (e.g., photomicrographs) of weldment to
examine metallic structure, defects, extent and condition
of heat affected zone, and similar phenomena
Weldability Factors - Welding Process
Welding Process
Some metals or metal combinations can be readily
welded by one process but are difficult to weld by
others
Example: stainless steel readily welded by most AW
and RW processes, but difficult to weld by OFW
Weldability Factors – Base Metal
Base Metal
Some metals melt too easily; e.g., aluminum
Metals with high thermal conductivity transfer heat
away from weld, which causes problems; e.g., copper
High thermal expansion and contraction in metal
causes distortion problems
Dissimilar metals pose problems in welding when
their physical and/or mechanical properties are
substantially different
Weldability Factors - Other Factors
Filler metal
Must be compatible with base metal(s)
In general, elements mixed in liquid state that
form a solid solution upon solidification will
not cause a problem
Surface conditions
Moisture can result in porosity in fusion zone
Oxides and other films on metal surfaces can
prevent adequate contact and fusion
Design Considerations in Welding
Design for welding - product should be designed
from the start as a welded assembly, and not as a
casting or forging or other formed shape
Minimum parts - welded assemblies should
consist of fewest number of parts possible
Example: usually more cost efficient to perform
simple bending operations on a part than to
weld an assembly from flat plates and sheets
Arc Welding Design Guidelines
Good fit-up of parts - to maintain dimensional
control and minimize distortion
Machining is sometimes required to achieve
satisfactory fit-up
Assembly must allow access for welding gun to
reach welding area
Design of assembly should allow flat welding to
be performed as much as possible, since this
is fastest and most convenient welding position
Arc Welding Positions
Flat welding is best position
Overhead welding is most difficult
Figure 31.35 Welding positions (defined here for groove
welds): (a) flat, (b) horizontal, (c) vertical, and (d)
overhead.
BRAZING, SOLDERING, AND
ADHESIVE BONDING
1.
2.
3.
Brazing
Soldering
Adhesive Bonding
Overview of Brazing and Soldering
Both use filler metals to permanently join metal
parts, but there is no melting of base metals
When to use brazing or soldering instead of
fusion welding:
Metals have poor weldability
Dissimilar metals are to be joined
Intense heat of welding may damage
components being joined
Geometry of joint not suitable for welding
High strength is not required
Overview of Adhesive Bonding
Uses forces of attachment between a filler
material and two closely-spaced surfaces to bond
the parts
Filler material in adhesive bonding is not
metallic
Joining process can be carried out at room
temperature or only modestly above
Brazing
Joining process in which a filler metal is melted
and distributed by capillary action between faying
surfaces of metal parts being joined
No melting of base metals occurs
Only the filler melts
Filler metal Tm greater than 450C (840F) but
less than Tm of base metal(s) to be joined
Strength of Brazed Joint
If joint is properly designed and brazing operation
is properly performed, solidified joint will be
stronger than filler metal out of which it was
formed
Why?
Small part clearances used in brazing
Metallurgical bonding that occurs between
base and filler metals
Geometric constrictions imposed on joint by
base parts
Brazing Compared to Welding
Any metals can be joined, including dissimilar
metals
Can be performed quickly and consistently,
permitting high production rates
Multiple joints can be brazed simultaneously
Less heat and power required than FW
Problems with HAZ in base metal are reduced
Joint areas that are inaccessible by many welding
processes can be brazed; capillary action draws
molten filler metal into joint
Disadvantages and Limitations of
Brazing
Joint strength is generally less than a welded joint
Joint strength is likely to be less than the base
metals
High service temperatures may weaken a brazed
joint
Color of brazing metal may not match color of
base metal parts, a possible aesthetic
disadvantage
Brazing Applications
Automotive (e.g., joining tubes and pipes)
Electrical equipment (e.g., joining wires and
cables)
Cutting tools (e.g., brazing cemented carbide
inserts to shanks)
Jewelry
Chemical process industry
Plumbing and heating contractors join metal pipes
and tubes by brazing
Repair and maintenance work
Brazed Joints
Butt and lap joints common
Geometry of butt joints is usually adapted for
brazing
Lap joints are more widely used, since they
provide larger interface area between parts
Filler metal in a brazed lap joint is bonded to base
parts throughout entire interface area, rather than
only at edges
Butt Joints for Brazing
Figure 32.1 (a) Conventional butt joint, and adaptations of
the butt joint for brazing: (b) scarf joint, (c) stepped butt
joint, (d) increased cross-section of the part at the joint.
Lap Joints for Brazing
Figure 32.2 (a) Conventional lap joint, and adaptations of the lap
joint for brazing: (b) cylindrical parts, (c) sandwiched parts, and
(d) use of sleeve to convert butt joint into lap joint.
Some Filler Metals for Brazing
Base metal(s)
Aluminum
Nickel-copper alloy
Copper
Steel, cast iron
Stainless steel
Filler metal(s)
Aluminum and silicon
Copper
Copper and phosphorous
Copper and zinc
Gold and silver
Desirable Brazing Metal Characteristics
Melting temperature of filler metal is compatible
with base metal
Low surface tension in liquid phase for good
wettability
High fluidity for penetration into interface
Capable of being brazed into a joint of adequate
strength for application
Avoid chemical and physical interactions with
base metal (e.g., galvanic reaction)
Applying Filler Metal
Figure 32.4 Several techniques for applying filler metal in brazing:
(a) torch and filler rod. Sequence: (1) before, and (2) after.
Applying Filler Metal
Figure 32.4 Several techniques for applying filler metal in brazing:
(b) ring of filler metal at entrance of gap. Sequence: (1) before,
and (2) after.
Brazing Fluxes
Similar purpose as in welding; they dissolve,
combine with, and otherwise inhibit formation of
oxides and other unwanted byproducts in brazing
process
Characteristics of a good flux include:
Low melting temperature
Low viscosity so it can be displaced by filler
metal
Facilitates wetting
Protects joint until solidification of filler metal
Heating Methods in Brazing
Torch Brazing - torch directs flame against work in
vicinity of joint
Furnace Brazing - furnace supplies heat
Induction Brazing – heating by electrical
resistance to high-frequency current in work
Resistance Brazing - heating by electrical
resistance in parts
Dip Brazing - molten salt or molten metal bath
Infrared Brazing - uses high-intensity infrared
lamp
Soldering
Joining process in which a filler metal with
Tm less than or equal to 450C (840F) is
melted and distributed by capillary action
between faying surfaces of metal parts being
joined
No melting of base metals, but filler metal
wets and combines with base metal to form
metallurgical bond
Soldering similar to brazing, and many of the
same heating methods are used
Filler metal called solder
Most closely associated with electrical and
electronics assembly (wire soldering)
Soldering Advantages / Disadvantages
Advantages:
Lower energy than brazing or fusion welding
Variety of heating methods available
Good electrical and thermal conductivity in joint
Easy repair and rework
Disadvantages:
Low joint strength unless reinforced by
mechanically means
Possible weakening or melting of joint in elevated
temperature service
Filler metal / Solder
Usually alloys of tin (Sn) and lead (Pb). Both
metals have low Tm
Lead is poisonous and its percentage is
minimized in most solders
Tin is chemically active at soldering
temperatures and promotes wetting action
for successful joining
In soldering copper, copper and tin form
intermetallic compounds that strengthen
bond
Silver and antimony also used in soldering
alloys
Mechanical Means to Secure Joint
Figure 32.8 Techniques for securing the joint by mechanical means prior
to soldering in electrical connections: (a) crimped lead wire on PC
board; (b) plated through-hole on PC board to maximize solder
contact surface; (c) hooked wire on flat terminal; and (d) twisted
wires.
Functions of Soldering Fluxes
Be molten at soldering temperatures
Remove oxide films and tarnish from base part
surfaces
Prevent oxidation during heating
Promote wetting of faying surfaces
Be readily displaced by molten solder during
process
Leave residue that is non-corrosive and
nonconductive
Soldering Methods
Many soldering methods same as for brazing,
except less heat and lower temperatures are
required
Additional methods:
Hand soldering – manually operated soldering
gun
Wave soldering – soldering of multiple lead
wires in printed circuit cards
Reflow soldering –used for surface mount
components on printed circuit cards
Wave Soldering
Figure 32.9 Wave soldering, in which molten solder is
delivered up through a narrow slot onto the underside of a
printed circuit board to connect the component lead wires.
Adhesive Bonding
Joining process in which a filler material is used to
hold two (or more) closely-spaced parts together
by surface attachment
Used in a wide range of bonding and sealing
applications for joining similar and dissimilar
materials such as metals, plastics, ceramics,
wood, paper, and cardboard
Considered a growth area because of
opportunities for increased applications
Adhesive Bonding - Terminology
Adhesive = filler material, nonmetallic, usually a
polymer
Adherends = parts being joined
Structural adhesives – of greatest interest in
engineering, capable of forming strong,
permanent joints between strong, rigid adherends
Curing in Adhesive Bonding
Process by which physical properties of the
adhesive are changed from liquid to solid, usually
by chemical reaction, to accomplish surface
attachment of parts
Curing often aided by heat and/or a catalyst
If heat used, temperatures are relatively low
Curing takes time - a disadvantage in production
Pressure sometimes applied between parts to
activate bonding process
Adhesive Bonding - Joint Strength
Depends on strength of:
Adhesive
Attachment between adhesive and
adherends
Attachment mechanisms:
Chemical bonding – adhesive and
adherend form primary bond on curing
Physical interactions - secondary
bonding forces between surface atoms
Mechanical interlocking - roughness of
adherend causes adhesive to become
entangled in surface asperities
Adhesive Bonding - Joint Design
Adhesive joints are not as strong as welded,
brazed, or soldered joints
Joint contact area should be maximized
Adhesive joints are strongest in shear and tension
Joints should be designed so applied stresses
are of these types
Adhesive bonded joints are weakest in cleavage
or peeling
Joints should be designed to avoid these types
of stresses
Types of Stresses in Adhesive Bonding
Figure 32.10 Types of stresses that must be
considered in adhesive bonded joints: (a) tension,
(b) shear, (c) cleavage, and (d) peeling.
Joint Designs in Adhesive Bonding
Figure 32.11 Some joint designs for adhesive bonding: (a) through
(d) butt joints; (e) through (f) T-joints; (b) and (g) through (j)
corner joints.
Adhesive Types
Natural adhesives - derived from natural sources,
including gums, starch, dextrin, soya flour,
collagen
Low-stress applications: cardboard cartons,
furniture, bookbinding, plywood
Inorganic - based principally on sodium silicate
and magnesium oxychloride
Low cost, low strength
Synthetic adhesives - various thermoplastic and
thermosetting polymers
Synthetic Adhesives
Most important category in manufacturing
Synthetic adhesives cured by various
mechanisms:
Mixing catalyst or reactive ingredient with
polymer prior to applying
Heating to initiate chemical reaction
Radiation curing, such as UV light
Curing by evaporation of water
Application as films or pressure-sensitive
coatings on surface of adherend
Applications of Adhesives
Automotive, aircraft, building products,
shipbuilding
Packaging industries
Footwear
Furniture
Bookbinding
Electrical and electronics
Surface Preparation
For adhesive bonding to succeed, part
surfaces must be extremely clean
Bond strength depends on degree of
adhesion between adhesive and adherend,
and this depends on cleanliness of surface
For metals, solvent wiping often used for
cleaning, and abrading surface by
sandblasting improves adhesion
For nonmetallic parts, surfaces are
sometimes mechanically abraded or
chemically etched to increase roughness
Application Methods
Manual brushing and rolling
Silk screening
Flowing, using manually operated dispensers
Spraying
Automatic applicators
Roll coating
Adhesive is dispensed
by a manually
controlled dispenser to
bond parts during
assembly (photo
courtesy of EFD Inc.).
Advantages of Adhesive Bonding
Applicable to a wide variety of materials
Bonding occurs over entire surface area of joint
Low temperature curing avoids damage to parts
being joined
Sealing as well as bonding
Joint design is often simplified, e.g., two flat
surfaces can be joined without providing special
part features such as screw holes
Limitations of Adhesive Bonding
Joints generally not as strong as other joining
methods
Adhesive must be compatible with materials being
joined
Service temperatures are limited
Cleanliness and surface preparation prior to
application of adhesive are important
Curing times can limit production rates
Inspection of bonded joint is difficult
Mechanical Assembly Technology
Threaded Fasteners
2. Rivets and Eyelets
3. Assembly Methods Based on
Interference Fits
4. Other Mechanical Fastening
Methods
5. Molding Inserts and Integral
Fasteners
©2007 John Wiley &
Sons, Inc. M P Groover,
6. ofDesign for Assembly
Fundamentals
1.
Modern Manufacturing
3/e
Mechanical Assembly Defined
Use of various fastening methods to
mechanically attach two or more
parts together
In most cases, discrete hardware
components, called fasteners, are
added to the parts during assembly
In other cases, fastening involves
shaping or reshaping of a
©2007 John Wiley
&
component,
and no separate
Sons, Inc. M P Groover,
Fundamentals of
fasteners are required
Modern Manufacturing
3/e
Products of Mechanical Assembly
Many consumer products are
assembled largely by mechanical
fastening methods
Examples: automobiles, large and small
appliances, telephones
Many capital goods products are
assembled using mechanical
fastening methods
Examples: commercial airplanes, trucks,
railway locomotives and cars, machine
tools
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Two Major Types of Mechanical
Assembly
1.
Methods that allow for disassembly
2.
Example: threaded fasteners
Methods that create a permanent
joint
Example: rivets
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Why Use Mechanical Assembly?
Low cost
Ease of manufacturing
Easy in creating design
Ease of assembly – can be
accomplished with relatively ease
by unskilled workers
Minimum of special tooling required
In a relatively short time
Ease of disassembly – at least for
the methods that permit
disassembly
Threaded Fasteners
Discrete hardware components that
have external or internal threads for
assembly of parts
Most important category of
mechanical assembly
In nearly all cases, threaded
fasteners permit disassembly
Common threaded fastener types
©2007 John Wiley &
are screws, bolts, and nuts
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Screws, Bolts, and Nuts
Screw - externally threaded fastener
generally assembled into a blind
threaded hole
Bolt - externally threaded fastener
inserted into through holes and
"screwed" into a nut on the opposite
side
Nut - internally threaded fastener
©2007 John Wiley
&
having
standard threads that match
Sons, Inc. M P Groover,
Fundamentals of
those on bolts of the same
Modern Manufacturing
3/e
diameter, pitch, and thread form
Screws, Bolts, and Nuts
Figure 33.1 Typical assemblies when screws and bolts
are used.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Some Facts About Screws and
Bolts
Screws and bolts come in a variety
of sizes, threads, and shapes
Much standardization in threaded
fasteners, which promotes
interchangeability
U.S. is converting to metric, further
reducing variations
Differences between threaded
©2007 John Wiley &
fasteners affect tooling
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Example: different screw head styles and
Head Styles on Screws and Bolts
Figure 33.2 Various head styles available on screws and
bolts.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Types of Screws
Greater variety than bolts, since
functions vary more
Examples:
Machine screws - generic type, generally
designed for assembly into tapped holes
Cap screws - same geometry as machine
screws but made of higher strength
metals and to closer tolerances
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Setscrews
Hardened and designed for
assembly functions such as
fastening collars, gears, and
pulleys to shafts
Figure 33.3 (a) Assembly of collar to shaft using a setscrew;
(b) various setscrew geometries (head types and points).
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Self-Tapping Screws
Designed to form or cut
threads in a pre-existing hole
into which it is being turned
Also called a tapping screw
Figure 33.4 Self-tapping
screws: thread-forming,
and thread-cutting.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Screw Thread Inserts
Internally threaded plugs or wire coils
designed to be inserted into an
unthreaded hole and accept an
externally threaded fastener
Assembled into weaker materials to
provide strong threads
Upon assembly of screw into insert,
insert barrel expands into hole to
©2007 John Wiley
&
secure
the assembly
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Screw Thread Inserts
Figure 33.6 Screw thread inserts: (a) before insertion, and
(b) after insertion into hole and screw is turned into insert.
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Washer
Hardware component often used with
threaded fasteners to ensure
tightness of the mechanical joint
Simplest form = flat thin ring of
sheet metal
Functions:
Distribute stresses
Provide support for large clearance holes
©2007 John Wiley& Protect part surfaces and seal the joint
Sons, Inc. M P Groover,
Fundamentals of
Increase spring tension
Modern Manufacturing
3/e
Resist inadvertent unfastening
Washer Types
Figure 33.8 Types of washers: (a) plain (flat) washers; (b) spring
washers, used to dampen vibration or compensate for wear; and
(c) lock washer designed to resist loosening of the bolt or screw.
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Bolt Strength
Two measures:
Tensile strength, which has the
traditional definition
Proof strength - roughly equivalent
to yield strength
Maximum tensile stress without
permanent deformation
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Stresses in a Bolted Joint
Figure 33.9 Typical stresses acting on a bolted
©2007 John Wiley &
joint.
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Over-tightening in Bolted Joints
Potential problem in assembly,
causing stresses that exceed
strength of fastener or nut
Failure can occur in one of the
following ways:
1.
2.
3.
Stripping of external threads
Stripping of internal threads
Bolt fails due to excessive tensile
stresses on cross-sectional area
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Tensile failure of cross section is
most common problem
Methods to Apply Required Torque
Operator feel - not very accurate,
but adequate for most assemblies
2. Torque wrench – indicates amount
of torque during tightening
3. Stall-motor - motorized wrench is
set to stall when required torque is
reached
4. Torque-turn tightening - fastener is
©2007 John Wiley &
initially tightened to a low torque
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
level and then rotated a specified
3/e
1.
Rivets
Unthreaded, headed pin used to
join two or more parts by
passing pin through holes in
parts and forming a second head
in the pin on the opposite side
Widely used fasteners for
achieving a permanent
mechanically fastened joint
Clearance hole into which rivet is
©2007 John Wiley &
Sons, Inc. M P Groover, inserted must be close to the
Fundamentals of
Modern Manufacturing
diameter of the rivet
3/e
Types of Rivets
Figure 33.10 Five basic rivet types, also shown in assembled
configuration: (a) solid, (b) tubular, (c) semi-tubular, (d) bifurcated,
©2007 John Wiley &
andInc.
(e)M compression.
Sons,
P Groover,
Fundamentals of
Modern Manufacturing
3/e
Applications and Advantages of
Rivets
Used primarily for lap joints
A primary fastening method in
aircraft and aerospace industries
Advantages:
High production rates
Simplicity
Dependability
Low cost
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Tooling and Methods for Rivets
1.
2.
3.
Impact - pneumatic hammer
delivers a succession of blows to
upset rivet
Steady compression - riveting tool
applies a continuous squeezing
pressure to upset rivet
Combination of impact and
compression
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Interference Fits
Assembly methods based on
mechanical interference between
two mating parts being joined
The interference, either during
assembly or after joining, holds the
parts together
Interference fit methods include:
Press fitting
©2007 John Wiley& Shrink and expansion fits
Sons, Inc. M P Groover,
Fundamentals of
Snap fits
Modern Manufacturing
3/e
Retaining rings
Snap Fits
Joining of two parts in which
mating elements possess a
temporary interference during
assembly, but once assembled
they interlock
Originally conceived as a method
ideally suited for industrial robots
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
During assembly, one or both parts
elastically deform to accommodate
temporary interference
Usually designed for slight
interference after assembly
Snap Fit Assembly
Figure 33.13 Snap fit assembly, showing cross-sections of two
mating
parts:
(1) before assembly, and (2) parts snapped together.
©2007
John Wiley
&
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Retaining Ring
Fastener that snaps into a
circumferential groove on a shaft or
tube to form a shoulder
Used to locate or restrict movement
of parts on a shaft
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Design for Assembly (DFA)
Keys to successful DFA:
1.
2.
Design product with as few parts as
possible
Design remaining parts so they are
easy to assemble
Assembly cost is determined
largely in product design, when
the number of components in
the product and how they are
assembled is decided
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Once these decisions are made,
little can be done in manufacturing
DFA Guidelines
Use modularity in product design
Each subassembly should have a
maximum of 12 or so parts
Design the subassembly around a base
part to which other components are
added
Reduce the need for multiple
components to be handled at once
©2007 John Wiley &
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
More DFA Guidelines
Limit the required directions of
access
Adding all components vertically from
above is the ideal
Use high quality components
Poor quality parts jams feeding and
assembly mechanisms
Minimize threaded fasteners
Use
snap fit assembly
©2007 John
Wiley
&
Sons, Inc. M P Groover,
Fundamentals of
Modern Manufacturing
3/e
Sponsor Documents
Recommended
No recommend documents