Manufacturing Extravaganza 2: Electric Boogaloo

FINAL

What is joining?

Welding, brazing, soldering, and adhesive bonding forming a permanent joint between parts

What is assembly?

Mechanical methods (usually) of fastening parts together; Some allow for easy disassembly

What is welding?

A joining process in which two (or more) parts are coalesced at teir contacting surfaces by applying heat and/or pressure

What are some key characteristics of welding?

Provides a permanent join

Usually most economical way to join parts

Not restricted to a factory environment

What are some limitations of welding?

Performed manually with high labor costs

Utilize high energy and are inherently dangerous

Do not allow for convenient diassembly

Joints can have quality defects that can be difficult to detect

What are the two types of welding?

Fusion & solid state welding

What is fusion welding?

Joining processes that melt the base metals

What is arc welding (AW)?

Melting of the metals by an electric arc (ie. stick welding, TIG, MIG)

What is the difference between TIG and MIG welding?

TIG (Tungsten Inert Gas) uses a non-consumable tungsten rod to make the arc.

MIG (Metal Inert Gas) uses a consumable wire electrode that becomes the filler metal.

What is resistance welding (RW)?

Melting by heat from resistance to an electric current between faying surfaces held together under pressure (ie. spot welding)

What is oxyfuel gas welding (OFW)?

Melting by an oxyfuel gas like acetylene

How does arc welding work?

During the weld, the base metal is melted and filler metal is added to the motel pool, protected by a shielding gas like argon

What is diffusion welding (DFW)?

Solid state diffusion between two surfaces held together under pressure at elevated temperature

What is friction welding (FRW)?

Using heat of friction to join two surfaces together

What is the welder & fitter?

Welder manually controls path & placement of welding gun

Fitter arranges parts prior to welding

What are some safety hazards with welding?

High temperatures of molten metals

Certain processes use fuels (acetylene in OFW) that are fire hazards

High electrical power can cause risk of shock

UV radiation from arc welding can be dangerous to eyes (requires welding helmet)

Sparks, smoke, fumes from metal & flux must be ventilated properly

What kind of joint is this?

Butt joint

What kind of joint is this?

Corner joint

What kind of joint is this?

Lap joint

What kind of joint is this?

Tee joint

What kind of joint is this?

Edge joint

How does fusion work with welding?

Fusion requires high density heat energy to cause localized melting of base metals with the least amount of energy possible

What is power density?

Power transferred to workpiece per unit surface area [W/mm²]

What happens if the power density is too high? Too low?

If it’s too high, localized temperatures vaporize metal in the affected region.

If it’s too low, heat is conducted into workpiece so melting never occurs.

What are the features of a fusion welded joint?

Fusion zone, weld interface, heat affected zone (HAZ), unaffected base metal zone

What is the heat affected zone?

Metal has experienced temps below melting but high enough to change the microstructure

Heat treated region that typically negatively affects the mechanical properties.

What is fusion welding?

Melting two parts to be joined & adding filler metal to the joint in some cases (ie. arc welding, resistance spot welding, oxyfuel gas welding)

What is solid state welding?

Using heat and/or pressure to join two parts together without any melting or filler metal being added (ie. forge welding, diffusion welding, friction welding)

What is Arc Welding (AW)?

Fusion process where coalescence of metals is done by heat from an electric arc between an electrode & the workpiece

Most AW processes add filler metal to increase volume & strength of joint

What are some problems with arc welding?

Weld joint quality & productivity can vary greatly

What is arc time?

Time the arc is on / hours worked

Manual Welding AT = 20%

Machine Welding AT = ~50%

What is a consumable electrode? Nonconsumable electrode?

Consumable electrodes are expended during welding process whereas nonconsumable electrodes are not

What are some forms of consumable electrodes?

Welding rods 9-18 & 3/8” or less in diameter

Welding wire continuously fed from spools with long lengths of wire

What are some forms of nonconsumable electrodes?

Made of tungsten which resists melting

Filler metal must be supplied by a separate wire fed into the weld pool

What is arc shielding?

Shielding gases like argon, helium, CO₂ & flux react to protect the arc from surrounding air in AW processes

What is flux?

A substance that prevents contaminants from reacting during the welding process by providing a protective atmosphere, stabilizing the arc, and reducing spattering

What are some application methods of flux?

Pouring granular flux onto the welding area

Stick electrode coated with flux material that melts during welding

Tubular electrodes where flux is contained in the core and released during welding

What power sources are used in arc welding?

Direct current (DC) used on all metals & generally has better arc control

Alternating current (AC) is cheaper to buy & operate but restricted to ferrous metals (Iron)

What are some consumable electrode AW processes?

Shielded Metal AW, Gas Metal AW, Flux-Cored AW, Submerged AW

What is Shielded Metal Arc Welding (SMAW)?

Uses consumable electrode consisting of filler metal rod coated with chemicals that provide flux & shielding

A.K.A. stick welding

What is the welding stick made of in SMAW?

Composed of filler metal close in composition to the base metal coated with a powdered cellulose mixed with oxides & carbonates held by a silicate binder

What are some disadvantages of stick welding?

Sticks must be changed periodically

High current levels may melt the exterior coating prematurely

What is Gas Metal Arc Welding (GMAW)?

Uses consumable bare metal wire as electrode shielded by flooding arc with a gas

Wire is fed continuously and automatically from a spool through the welding gun

A.K.A. Metal Inert Gas (MIG) welding

What are some advantages of GMAW (Gas) over SMAW (Shielded)?

GMAW has better arc time with continuous wire electrode (Doesn’t need to constantly swap sticks out)

More efficient use of electrode filler than SMAW (End of stick is tossed)

Higher deposition rates

Doesn’t need slag removal

Easy to automate

What is Flux-Cored Arc Welding (FCAW)?

Continuous consumable tubing containing flux in its core

Variation of SMAW (Shielded)
Self-Shielded FCAW - core of electrode has flux
Gas-Shielded FCAW - uses external shielding gas

What is Submerged Arc Welding (SAW)?

Uses continuous, consumable bare wire electrode with arc shielded by cover of granular flux that completely submerges operation

Flux introduced slightly ahead of joint by gravity from a hopper

What is Gas Tungsten Arc Welding (GTAW)?

Uses nonconsumable tungsten electrode and an inert gas for arc shielding

A.K.A. Tungsten Inert Gas (TIG) Welding

Filler metal is added externally but does not require filler for thin metals & thin gaps

What are the advantages & disadvantages of GTAW / TIG?

Advantages:

High quality welds
No splatter
Little to no post-weld cleaning without flux

Disadvantages:

Generally slower & more expensive than consumable electrode arc welding processes

What is Resistance Welding (RW)?

Fusion welding processes that use heat and pressure to join parts together

Heat is generated by electric resistance to current flow at junction

Principal RW process is Resistance Spot Welding (RSW)

What are the advantages & disadvantages of resistance welding (RW)?

Advantages:

No filler required
High production rates
Easy to automate with good repeatability & reliability
Low operator skill required compared to arc welding

Disadvantages:

High initial equipment cost
Limited to lap joints for most RW processes

What is Resistance Spot Welding (RSW)?

Fusion of faying surfaces of a lap joint is done at one location with opposing electrodes

Mainly used for joining sheet metal

What is the spot welding cycle?

Electrodes push two parts together → Current is turned on & off → Creates weld nugget between two joints

What is Resistance Seam Welding (RSEW)?

Uses rotating wheel electrodes to produce overlapping spot welds along a lap joint

What is Oxyfuel Gas Welding (OFW)?

Fusion welding operations that burn various fuels mixed with oxygen to join parts

What is Oxyacetylene Welding (OAW)?

Fusion performed by high temperature flame from combustion of acetylene and oxygen

What is Electron Beam Welding (EBW)?

Fusion performed by focusing high-intensity stream of electrons striking work surface

What are the advantages & disadvantages of electron beam welding (EBW)?

Advantages:

High-quality welds with deep narrow profiles
Limited heat affected zone & low thermal distortion
No flux / shielding gases needed

Disadvantages:

High equipment cost
Precise joint preparation & alignment is required
Needs vacuum chamber
EBW generates x-rays which can be dangerous

What is Laser Beam Welding (LBW)?

Fusion achieved by energy of concentrated, coherent light beam focused on joint

Normally performed with shielding gases to prevent oxidation

What is are the main advantages of LBW over EBW?

LBW doesn’t require a vacuum chamber or emit x-rays
Lasers can be focused & directed by optical lenses & mirrors

BUT EBW provides deeper & high depth-to-width ratio welds than LBW

What is Solid State Welding (SSW)?

Joining of part surfaces by pressure alone or with pressure & heat

Time is typically a factor

No filler metal is added

What are the advantages of solid-state over fusion welding processes?

Melt around joints retains original properties if no heat is used (only for some SSW)

SSW joints bond entire contact interface between parts instead of at specific spots or seams

Some SSW can be used to bond dissimilar metals more easily than FW

What is Friction Welding (FRW)?

SSW process using frictional heat & pressure to join parts together

Can be used to join dissimilar metals & easy to automate

Steps: Rotating part w/out contact → parts generate friction → rotation stopped when axial pressure applied → weld complete

What are the limitations of friction welding?

One of the parts must be in rotation

Flash (bulging) must be machined / removed afterwards

Upsetting reduces part lengths

What is Friction Stir Welding (FSW)?

Rotating tool is fed along joint line generating heat & stirring metal to form weld seam

What are the advantages & disadvantages of friction stick welding (FSW)?

Advantages:

Good mechanical properties in joint
No toxic fumes, warping, shielding issues
Little distortion or shrinkage
Good weld appearance

Disadvantages:

Exit hole is produced when tool is withdrawn
Heavy clamping of parts required

What do you look for when determining weld quality?

Looking for defects like:

Residual stress & distortion
Welding defects / cracks

What causes residual stress & distortion?

Rapid heating & cooling in localized regions during fusion welding leads to thermal expansion & contraction that causes residual stress

Leads to distortion & warpage

What are some ways to minimize warping?

Welding fixtures to physically restrain parts

Using heat sinks to remove heat

Tack welding at points to create rigid structure before seam welding

Changing speed, filler metal (amount & type) to reduce warpage

Preheating base parts

Heat treating after welding to relieve stresses

What are some examples of welding defects?

Cracks

Cavities

Solid Inclusions

Imperfect shape / contour

Incomplete fusion

What is metal forming?

Using plastic deformation to change the shape of metal workpieces using dies to form the desired geometry

What is bulk deformation?

Significant deformations and massive shape changes w.r.t. workparts with low surface area-to-volume ratios

What are the types of bulk deformation processes?

Rolling

Forging

Extrusion

Wire & Bar Drawing

What is rolling?

Slab is heated in a furnace & rolled between powered rollers until at desired thickness

What is forging?

Forming metal by impacting and/or squeezing a preheated part between two halves of a die

Multiple dies may be needed to achieve final shape

What is extrusion?

Billets are preheated and forced by a ram through one or more dies to achieve the desired cross-section

What is wire / bar drawing?

Cross-section of solid rod, wire, tubing is reduced or changed by pulling it through a die

What is sheet metalworking?

Forming operations done on metal sheets, strips, and coils

High surface area-to-volume ratio of starting metal

Also called pressworking as operations use presses creating stampings using punches & dies

What is sheet metal bending?

Straining of metal sheet or plate to create a specific angle

What is deep drawing?

Forming of flat metal sheet into hollow or concave shape by stretching the metal

What is shearing?

Cuts the workpiece using a punch and die

What is the flow curve?

Plastic region of stress-strain curve expressed as a curve using true stress & strain

σ = Kεⁿ

K - strength coefficient
n - strain hardening exponent

What is flow stress?

Instantaneous value of stress required to continue deforming the material

Strength increases due to strain hardening

Y_f = Kεⁿ

Y_f - flow tress (yield strength as a function of strain)

What is the average flow stress?

How does temperature affect the flow curve?

As temperature increases, strength (K) & strain hardening (n) exponents are reduced

Ductility is increased at higher temperatures

Any deformation operation can occur with lower forces & power at higher temperatures

What are the temperature ranges in metal forming?

Cold working

Warm working

Hot working

What is cold working?

Plastic deformation that typically occurs at room temperature

What are some advantages & disadvantages of cold working?

Advantages:

Better accuracy, surface finish & closer tolerances
Strain hardening increases strength & hardness
Grain flow during deformation can improve directional properties
No heating required

Disadvantages:

Higher forces & power required for deformation
Surfaces must be smooth & free of scale (black coating of oxide when heated) and dirt
Ductility & strain hardening can limit amount of forming possible
May require annealing to allow further deformation
Some metals might not be ductile enough to do cold forming

What is warm working?

Plastic deformation carried out at above room but below recrystallization temperatures (~30% of melting)

Compromise between cold & hot working

What are the advantages of warm working?

Advantages:

Lower forces than cold working
More complex geometries possible
Reduced need for annealing (can even be eliminated)

What is hot working?

Plastic deformation done above recrystallization temperature (above ~50% of melting)

Why would you use hot working?

Higher ability for plastic deformation of metal than cold & warm working

Lower strength coefficient (K) and strain hardening exponent (n) is almost zero improves ductility

What are the advantages & disadvantages of hot working?

Advantages:

Significant alteration possible
Lower force & power required
Metals that fracture in cold working can be hot formed
Strength properties are generally isotropic (not directionally dependent)
No strain hardening / strengthening

Disadvantages:

Lower dimensional accuracy
Higher total energy required from needing to heat the workpiece
Work surface oxidation (scale) results in poor surface finish
Shorter tool life

What is bulk deformation?

Metal forming operations that cause significant shape change by deforming metal parts with an initial bulk form rather than sheet

What is rolling?

Deformation process where work thickness is reduced by compressive forces exerted by two opposing rolls

What is flat rolling?

Used to reduce thickness of rectangular cross-section

What is shape rolling?

Workpiece is deformed into a contour cross section than flat (rectangular)

What is the draft?

Amount of thickness reduction

d = t₀ - t_f

What is the difference between hot & cold rolling?

Hot rolling - most common due to large amount of deformation possible

Cold rolling - produces finished sheet & plate stock

What type of rolling mill is this?

Two-high rolling mill

What type of rolling mill is this?

Three-high rolling mill