Welding

Topics to be Covered

Welding Topics:

MIG

TIG

Stick

Diffusion

Friction

Explosion

MIG Welding

Metal Inert Gas (MIG) or Gas Metal Arc Welding (GMAW)

DC or AC (rare) Electric Arc

Consumable electrode

Shielding Gas

MIG - History

Developed in 1940’s to weld aluminum, magnesium, and other non-ferrous alloys

Use in steel was originally limited by cost of Inert gas – It the early 1950’s carbon

dioxide was used as shielding gas for steel greatly reducing the cost

Further developments through the 1960’s increased the versatility of the process – Today GMAW is the most

commonly used industrial welding process

MIG - Equipment

(1) Welding Torch – Controls arc, gas, wire feed

(2) Workpiece (3) Power Supply

-Typically constant voltage DC

(4) Wire Feed Mechanism (5) Electrode

– Usually similar material as workpiece

– Contains small amounts of deoxidizing metals (Si, Mg, Al)

(6) Shielding Gas – Typically argon-CO2 mix

MIG - Process

Arc creates weld pool to bond material – DC Constant Voltage with

positively charged electrode – reverse polarity requires special electrode

Shielding gas protects the weld pool from atmospheric gas effects – Porosity and embrittlement

Technique – Simple: electrode is fed

automatically – Torch is guided along weld area

keeping a constant tip to workpiece distance

MIG – Capabilities

Inexpensive machines ($500) Required skill level is relatively

low Can weld many ferrous and non-

ferrous materials – Different results and requirements

must be expected (shielding gas, technique, electrode, etc)

Power of machine will determine what it can weld – More power – thicker material

GMAW can be automated more easily than other methods

MIG - Industries

Automotive – Almost exclusive

Pressure Vessels

Heavy rail and construction equipment

At Home – Easy and inexpensive

Automobile/Agricultural repair

TIG - Welding

Tungsten Inert Gas (TIG) or Gas Tungsten Arc Welding (GTAW)

AC or DC Electric Arc

Non-consumable tungsten electrode

Shielding Gas

Hand fed filler

TIG - History

Early 1900’s welding non-ferrous materials was difficult – Reacted with air making

welds weak and porous

Process was improved in the 1930’s and 1940’s – Gas shielding increased

weld quality

– AC machines allowed for high quality welds on aluminum and magnesium

TIG - Equipment

Welding Torch – Directs shielding gas and holds

electrode

Power Supply – AC typically used for aluminum and

magnesium – DC with a negatively charged

electrode is typically used for steels

Electrode – Made from tungsten or tungsten

alloys – ISO standards for each alloy

Filler Rod Shielding Gas

– Argon is most common – Helium is sometimes used when

welding aluminum and copper

TIG - Process

Arc creates weld pool to bond material – AC or DC used depending on

base material

Shielding gas protects the weld pool from atmospheric gas effects – Porosity and impurities

Technique – Requires two hands – Torch is moved forward as filler

rod is dipped into the weld pool – Filler rod must remain inside

the gas shield at all times – Considered one of the most

difficult welding methods – low melt alloys increase difficulty

TIG – Capabilities

Produces welds with very similar material properties of the base metal

GTAW can produce high quality welds on materials such as aluminum, magnesium, titanium, copper, nickel, steel.

Dissimilar materials – copper and stainless Requires a skilled welder – considered to be

one of the more difficult types of welding Automation is possible, but not as common

as GMAW due to the increase complexities

TIG - Industries

Aircraft Spacecraft Bicycles

Crack repair – Aluminum wheels and

engine blocks

Shielded Metal Arc Welding (Stick Welding)

Common welding technique

Stick is synonymous with coated electrode

http://atpwelding.com/welding.jpg

Basic Principles

Arc created between metal and electrode

Metal is melted and coalesces to form weld

http://www.twi.co.uk/j32k/protected/band_3/jk2.html

Coating

Different coatings for different applications

Cellulosic, Rutile, and Limestone are common

Coatings ease process through slag creation, and help to strengthen weld

http://www.twi.co.uk/j32k/twiimages/jk82f1.jpg

Advantages/Disadvantages

Advantages:

Simple

Portable

Versatile

Inexpensive equipment

Disadvantages:

Limited shielding

Limited Deposition rates

Usually done by hand

Highly trained labor required

Diffusion Welding

Also known by: diffusion bonding, solid state bonding

Can be used to join metals and ceramics that otherwise can’t be joined

http://www.turktoz.gazi.edu.tr/en_makale_files/image037.jpg

Diffusion Welding

“Diffusion Welding is a solid-state welding process that produces a weld by the application of pressure at elevated temperature with no macroscopic deformation or relative motion of the work pieces.”

-American Welding Society description

Basic Principles

Two materials are heated and pressed upon one another

Pressure causes heated atoms to diffuse into surface, creating a bond upon recrystalization

D=D0e-(Q/KT)

Messler 1999

Equipment

A press is needed, which can create pressure in a variety of ways

Heat needs to be generated as well

Fixturing system required

http://frisch-gmbh.de/images/sinteranlage.jpg

Advantages/Disadvantages

Advantages

“Perfect” weld possible

Special material properties

Even weld properties throughout material

Close tolerances

Expensive materials

Disadvantages

Only perpendicular surfaces

Specially designed components

Requires inert atmosphere

Expensive

Friction Welding (FW)

Solid state welding process Generates heat through friction between moving surfaces Heat in combination with lateral force called “upset” fuses two materials together First Patent for the development of FW was applied for in 1891

http://www.fortunecity.com/village/lind/247/weld_book/fig10-79.gif

Types of Friction Welding

Spin Welding (inertia, rotational, inertial friction)

Linear Friction Welding (LFW)

Friction Stir Welding

Friction Surfacing

Spin Welding

Involves the rotation of one surface relative to another while applying pressure along the axis of rotation

Work pieces are held by chucks in spin welding machines

Flywheel is used to store the energy produced by the motor

Requires circular joining points

Linear Friction Welding

Image: http://www.eurotradeglobal.com/content/1124976586.jpg

Image: http://www.twi.co.uk/j32k/twiimages/spswksep99f9.gif

Lateral motion of surfaces rather than rotational

Most surface can be joined

Friction Stir Welding

A cylindrical probe rotates and constant speed and fed at a constant rate across the joint of two components

Parts must be rigidly clamped together to prevent them from being forced apart from welding process

Image: http://www.hitachi-cable.co.jp/ICSFiles/afieldfile/2005/12/26/1_1.gif

Image: http://www.boeing.com/news/frontiers/archive/2004/september/

photos/sept_i_tt.jpg

Friction Surfacing

Coating of material applied to surface of another material

Rod composed of coating material is rotated under pressure across the surface of a separate material

Closely resembles a hot forging process so problems associated with more traditional welding process are avoided

Image: http://www.frictec.co.uk/frictec-whatisfr.html

Fast joining times

Small heat affected zones

Joined with little preparation of surfaces

Believed that “flash” carries away dirt and debris from surfaces

Welding of dissimilar metals

Aerospace - Aluminum and Steel

Nuclear - Copper and Steel

Uneconomical for short production runs due to high equipment costs

Excludes delicate and intricate part

Advantages/Disadvantages

Explosion Welding (EXW)

Solid state welding process

Plates are bonded through pressure created from a controlled detonation of explosive charge

Originates from WWI when it was discovered that pieces of shrapnel were welded to armor plating on tanks

Later development occurred in the decades following WWII

Primarily used to clad inexpensive structural material with corrosion resistant material

Image: http://www.metalwebnews.com/howto/explosive-welding/fig1.gif

Welding Process

Image:http://content.edgar-online.com/edgar_conv_img/2007/03/08/0001104659-07-017391_G57151FCI001.JPG

Advantages/Disadvantages

Large surfaces may be welded

Produces a high quality bond

Low cost

Simple

Little surface preparation required

Dissimilar metals can be welded

Brittle materials cannot be processed

Only simple shapes

- Plates and Cylinders

Thickness of flyer plate is limited

There are many safety concerns when storing and detonating explosives

Common Bi-Metals Produced

Copper to Steel

Nickel to steel

Aluminum to steel

Tungsten to steel

Titanium to steel

Copper to aluminum

Other

SS/Al Ring

Commercially Available Combinations

Chart: http://www.aps.anl.gov/Facility/Technical_Publications/lsnotes/ls237/Images/ls237_t2.gif