Metal Joining Processes

Metal Joining Processes Objectives

• Identify the various discontinuities associated with common metal joining processes
• Compare the advantages and disadvantages of common metal joining processes
• Apply terminology and concepts to the types of welding and joining equipment
• Determine characteristics of an electrode using the AWS classification system
• Illustrate techniques of metal joining to the correct metal joining process

Introduction

• Experience and knowledge of joining and cutting processes is helpful for welding inspection
• Hands-on welding experience can be beneficial, but is not mandatory for welding inspectors
• Welding inspectors must understand aspects of joining and cutting processes
• It is important that the welding inspector knows the advantages and limitations of each welding process
• Welding inspectors should also be familiar with the equipment requirements for each process
• Knowing process fundamentals will equip them to perform visual welding inspections
• This aids in discovering problems early when correction costs are lower
• Experience with welding methods can help earn the respect of production welders
• Welders may be more open to bringing concerns to an inspector who understands the practical aspects of the process

Metal Joining Processes

• Many joining processes exist for fabricating metal products
• The American Welding Society (AWS) categorizes each welding and joining method into one of eight groups: arc welding, solid-state welding, resistance welding, oxyfuel gas welding, soldering, brazing, high energy beam welding, and other welding and joining processes

Welding Processes

• "Welding" refers to operations involving joining individual parts or components using heat and without pressure
• A weld joins by localized coalescence of metals; coalescence is when materials melt, mix, and solidify as one

Common Elements in Welding Processes

• All welding processes have common features
• A source of energy provides heating
• There is a means of shielding or protecting molten metal from the atmosphere
• There is a filler metal in most cases

Shielded Metal Arc Welding (SMAW)

• Shielded metal arc welding is commonly referred to as "stick welding"
• It utilizes heat from an electric arc between a covered metal electrode and the metals being joined
• Electricity flow creates an arc between the electrode and the workpiece
• The arc melts the base metal, electrode coating or flux, and filler metal
• Solidified weld metal is covered by slag, which is decomposed flux
• The electrode coating decomposes when heated and produces a shielding gas
• Together, the slag and shielding gas protect the molten metal from contamination

SMAW Filler Metals

• Electrodes are made of a metal core wire covered with granular flux held by a bonding agent
• Carbon and low alloy steel electrodes use similar core wire made of low carbon steel
• The dry electrode coating is a nonconductor of electricity
• Striking the arc triggers essential functions of the electrode

Essential Functions of the Electrode

• Shielding is when coating decomposes into a gaseous shield that protects the molten metal
• Deoxidation is when coating provides a fluxing or cleaning action to remove impurities and unwanted atmospheric gases
• Alloying is when the coating introduces elements into the weld pool which improves the characteristics of the weld deposit
• Ionization is when molten flux coating improves electrical characteristics to increase arc stability
• Insulation is when solidified slag provides an insulating blanket to slow the cooling rate of the weld metal
• Slag thickness influences the weld bead's appearance
• Molten filler metal droplets transfer across the arc magnetic pinch effect
• A circular magnetic field is induced when passing current through a conductor
• The magnetic field concentrates near the electrode's end, "pinches" droplets off, aiding metal transfer

SMAW Electrode Classification

• SMAW electrodes are classified using letters and numbers
• They communicate important details and usage information, such as tensile strength and chemical composition
• Most SMAW classifications have an "E" for electrode, followed by four digits
• The first two digits show the minimum tensile strength of deposited weld metal in thousands of pounds per square inch (psi)
• For example, E7018 means the tensile strength is at least 70,000 psi
• Some electrodes have five digits with the first three digits indicating tensile strength
• The next digit shows the welding positions in which the electrode can be used: "1" means any position, "2" means flat position for all welding joints and horizontal position for fillet welds
• "4" means the electrode is suitable for welding in a downhill progression
• The last digit describes electrode characteristics like coating composition, operating characteristics, electrical current, and polarity
• These polarities are alternating current (AC), direct current electrode positive (DCEP), and direct current electrode negative (DCEN)

Low Hydrogen Electrodes

• Electrodes ending in "5," "6," or "8" are low hydrogen types
• Low hydrogen electrodes are stored in the original factory-sealed metal container or an acceptable storage oven
• This oven is heated electrically and has temperature control between 225°F to 300°F
• Low hydrogen electrodes which are not used immediately should be put in the holding oven as soon as their container is opened
• Codes require keeping low hydrogen electrodes at a minimum oven temperature of 250°F after removal from the container
• Electrodes other than the low hydrogen type may be harmed if placed in the oven
• Some electrode types have a certain moisture level and eliminating the moisture will deteriorate its operating characteristics

Low Alloy Steel Electrodes

• Low-alloy steel electrode classifications have an alphanumeric suffix
• The suffix indicates the percentage of alloying elements present in the filler metal
• A system using numeric representations identifies stainless steel electrodes by the American Iron & Steel Institute (AISI)
• Additional suffixes are added when electrode characteristics are identified
• A suffix "L" identifies the electrode as being lower in carbon content than typical
• Suffixes "15" or "16" typically go with the AISI stainless steel number
• An "E308L-16" electrode is a low carbon 308 stainless steel that welds various other steels
• The E309L-16 electrode welds mild steel to any 18-8 stainless steel and used in high temperature service applications
• The E316L-16 electrode is a low carbon 316 stainless steel which is used in high temperature applications and where high strength and low creep is required

SMAW Equipment

• Equipment for shielded metal arc welding is simple
• A transformer-rectifier and an inverter power supply are used
• One lead from the welding power source connects to the piece being welded
• The electrode is melted by heat from the welding arc created between it and the workpiece when close
• The power source for shielded metal arc welding is a constant current with a "drooping” characteristic
• The volt-ampere curve helps understand the power source type
• Increased arc length increases the circuit's resistance and decreases the current flow
• Voltage supplied by the power source significantly increases which limits the drop in current
• Heat is the result of amperage, voltage, and time
• A long arc length results in more heat being produced than a short arc length

SMAW Techniques

• Arc length determines weld pool fluidity
• A long arc length causes heat loss in the weld pool due to loss of arc concentration
• An extremely long arc length causes arc instability and causes loss of molten pool shielding gases

SMAW Usage

• Shielded metal arc welding is used in many industries and for numerous applications
• It is used for most materials except some of the more exotic alloys
• Shielded metal arc welding will still be used in the welding industry even though some applications have been replaced

SMAW Advantages

• The equipment needed for SMAW is simple and cheap
• This helps in making the equipment very portable
• Shielded metal arc welding can be done in remote locations since some types don't rely on electrical input
• Power sources are small and lightweight so that the welder can carry them to the work
• This process is versatile because of numerous types of available electrodes
• With better equipment and electrodes, weld quality is consistently high

SMAW Limitations

• SMAW speed is limited due to the length of the electrodes since they must be periodically replaced, typically 9 to 18 inches in length
• Many applications have replaced it with semi-automatic, mechanized and automatic processes
• Solidified slag formed post-welding must be removed
• Requiring low hydrogen type electrodes means storage in a holding oven to maintain low moisture
• Metals with low melting temperatures are not welded well such as lead, zinc, and tin, will quickly vaporize
• SMAW is not suitable for reactive metals because the shielding is inadequate to prevent contamination of the weld

SMAW Problems

• One problem is presence of porosity where moisture or contamination is in the weld regions
• Elements could be in the electrode coating, material's surface, or in the welding operation's surrounding atmosphere
• Porosity occurs when the welder uses an arc length that is too long; using a shorter arc length aids in eliminating porosity of weld metal
• Porosity can result from arc blow which plagues the manual welder
• Electric current passing through a conductor develops a magnetic field
• The field develops perpendicular to electric current and is visualized as concentric circles surrounding the conductor
• The magnetic field is strongest when contained within a magnetically permeable material and when it resists having to travel through the air
• Distortion happens when welding material such as steel due to the arc approaching the edge of a metal plate, the end of a weld, or some abrupt change in contour of the part
• Arc blow effects are reduced by various alternative techniques: changing from DC to AC, holding a short arc as possible, reduce the welding current etc

Gas Metal Arc Welding (GMAW)

• Welding processes include porosity due to contamination and loss of shielding from short circuiting etc.
• Slag inclusions occur with SMAW because the process relies on a flux system
• Shielded metal arc welding is accomplished manually so discontinuities can result from improper electrode manipulation
• Gas metal arc welding, or GMAW, commonly referred to as “MIG” can be used as semi-automatic process
• An arc is created between a solid wire electrode, which is supplied through a welding gun, and the workpiece to deposit material in the weld joint
• An important feature for GMAW is that all shielding for the weld pool is provided by a protective gas atmosphere and shielding gas can be external

Gases for GMAW Usage

• These gases can be used individually or mixed
• Active gases, such as oxygen or carbon dioxide, can be mixed with an inert gas
• Carbon dioxide used as the shielding gas because of its relatively low cost compared to inert gases

Filler Metals

• Electrodes are solid wires that supplied on spools, coils or drums of various sizes
• American Welding Society classification system approves a standard for the identification of gas metals & arc welding electrodes
• American Welding Society classifications standards can be identified by ER - followed by two to three numbers, number and hyphen and finally another number
• Letter “E” identifies the wire as being in the electrode
• Letter “R” identifies the wire is adequate to be used as robotic GTAW
• Solid wire is identified by Letter 'S'
• Various amounts of deoxidizers such as manganese, aluminum, and titanium should be used to avoid formation of porosity due to oxygen in the shielding gas
• Gas metal arc welding electrodes run using direct current electrode positive (DCEP)

Equipment for GMAW Usage

• Critical factor is that the wire must be maintained and kept clean
• When a spool of GMAW wire feeders are placed a protective covering should be utilized for prolonged times of non-use
• Power supply that supplies GMAW is different from SMAW
• Gas metal arc welding uses a voltage power source

Equipment for GMAW Cont.

• Gas metal arc weld provides a presets value of voltage for a range of welding currents
• Combining power source and wire feeder creates a process that is automatic, semi automatic and fully automatic
• Gas metal arc is used with a bit more complex equipment compared to gas shielded welding
• Welding is adjusted with power source & wire feed speed at wire feeder
• By increasing wire feed it increases welding & vice-versa
• Electrode of melt-off rate is proportional to act current, where wire feed speed controls melt-off rate as well

Constant Voltage Power Source

• Constant voltage power addresses the issue of consistent current levels
• In a short circuit power source function the welding cannot be manually classified without adjustments
• Another option includes varying voltage setting & increasing speed voltage & vice cersa
• Argon in a shield gas will allow for wire speed feed compared to wire feed using CO2 as shield gas

Common Metal Transfers

• Molten metal can be transferred from the end of the electrode and across and to the top of the base
• Gas metal arc uses modes of metal transfer being that: short circuit, globular, spray, and pulsed spray.
• Modes are uniquely different as individual process

GMAW techniques

• Spray transfer needs at least 80% present in the gas
• Short circuit requires electricity wire that is between a 1/4 - 1/2 inches.
• Gas arc pulsed is best suited when power is being produced and current where the welder is programming
• The electrode extension will depend on wire size
• Globular Transfer & axial spray transfer use eletrode extnsions from ½‘ to 1” inch.

Metal Cored Electrodes in Metals

• Metal cored wire represents core deposit
• Focuses current outer diameter while wire creates a cone shape, creating molten droplets

Metal Cored Electrodes- Advantages

• Some advantages are high rates of deposit, the ability to bridge gaps, almost no splatter and has no slag
• Letter “E” represents impact strength, were the number designates metal gas

Metal Cored Electrodes-Advantages

• This versatility has resulted in ferrous and non ferrous metal use
• GMAW can be used on situations where hydrogen can be a problem, preventing arc coating after welding
• With new porting & numerous equipment the ability of gas arc have improved

Limitations of GMAW Usage

• If the base metal contaminated the shielding may prove insufficient preventing porosity occurance
• GMAW is sensitive with drafts, so it leaves metal unportable - so gas metal arc cannot be used as field welding

Problems With The Metal

• Primary issues of contamination and short circuit or arc
• Alleviated by taking precautions of the metals being cleaned
• Issue of open arc may think there is heating

Flux Cored Arc Welding (FCAW)

• Flux cored arc welding (FCAW) is very similar where the electrode is similar tubular
• FCAW has gas shielded and self shielded depending on the type of electrodes used

Just Like Gas Metal Arc Welding

• FCAW has wire being feed between electricity being produced.
• GMAW uses solid filler and FCAW tubular filler

FCAW - Fillers

• External Shielding must be used based on the type of electrode when welding (some electrodes are designed to provide self shielded)
• AWS provides many codes for the ID

Electrics for Electrode for Welding

• An E represents the start for the letter for the electrode
• Where the first number is referred to strength of 10,000 psi
• 0 means flat weld or horzinal and 1 indicates every potential
• Welding can be external whether auxillary is and its important

SMAW Processes

• Self shielded or with aid or addition of shielding

Equipment for Arc

• Same as GMAW, but higher capacities of amperage
• It will have a Gas capacity and the same with DC as electrodes
• Electrode can be DCEN or DCIP

FCAC Rapid Gain & Processes

• Is relatively done on contained face and improved deposition rates has replaced GMAW & SMAW
• is mostly on areas of flux for carbons & alloy with nickel and chromium

Process and Steps for FCAW

• Constant source is being used when method is semiautomatic
• Arc length is made by the voltage setting
• Not like industrial FCAW using short circuit increases for the inclusions of Slag
• Short circuit is for lower output Power sources

Advantages of FCAW

• High acceptance because what production offers
• High productivity with greater amount of weld & electrode which increases time when producing semi auto
• A gas is a helper which contaminates by less amount
• FCAW less sensitive due to contamination by the loss of shielding

Limit of Process and Inspections

• There by a Flux layer so solidified Slag or other visual will need to be inspected
• Prolongs when smoke is generated

Discontinutities of FCAW Process

• Travel speeed is too fast to allow maintenance of arc
• Lack of maintenance

Gas Tungsten Arc Welding

• Gas Tungsten Arc Welding has several interests and basic processes
• Gas electrode is what is often used for the weld electrode but it has ability to produce temperature (arc)
• Electrode does not occur - heat is created electrode/work

Electrode

• Electrode will have wire feed system. Is made of inner is produced of gas that is surrounding the process
• Beak will not be removed because no flux is ever produced/used

Equipment for Arc

• All fillers are some with metal fillers (GMAW)

Material Usage

• Weld metal is the same as GMAW and electrode metals being produced
• Same used by 36” inch parts and metal wire spool

Material & Electrode- Equipment cont.

• AWS will identify in this manner. - are mostly diff. code as well

Material & Welding cont.

• The equipment to similar when it is for GTAW power source is source that will need to be with required a plasma controlled
• PAW will require liquid the torch and torch will need to be created carbon arc

Material & Welding Cont.

• The process is used by DCEN with thoriated metal, electrode

Metal Welding Arc & GMAW:

• Applications are the one when source will also have similar is heat source
• In automatic is done at speed speed can be higher with arc

Limitation With The KeyHole

• It is limited but does have better range and can be difficult like key hole closure.
• The range of issues is not always proper like the other issues of welding

Electroslag Welding

• Is where arcs will make heat and melt
• Process is to start operation is for flux it will be welded in that method
• Will become resistance heating for alloys or metals

Electrode in filler of electro

• Filler is continuous Electrode either metal or solid

Important for Electro

• Must use Oscillate & provide great electrode on the welding surface

Important for ESW Cont.

• Need both constant & voltage, with either both or dc current of pole that is being affected with both bead face etc.
• The equipment for this has similar but must do other work- which is for high welding

Equipment Cont. of ESW:

• This will give metal is in water location for side by side is mostly of cars

Disadvantages in the ESW Process

• Has highest level of any welding type
• Source & each electrode have it source, the cutting face or sharp- its all easy and aligned

Oxyacetylene Welding

• Often are welding is a way a high heat or energy torch creates flames Will also heat and will act shielded no flex
• Not like alminum however when high flex needs other steps or items
• This welding is often as all piping welds- welding and maint

Torch Design and Uses

• 2 designs. Can be found a different lengths which needs to be added- 80 degrees or other
• When is set, need be sure damage isn't It needs transport

Technique for Torch

• Needs will heat the side up, then other (as need the welding) all as to with other item

Cont for oxyacetylene:

• Needs a 45 degree or something similar, in the tip the heat must melt to be in the spot

More Processes w Equipment;

• Some the control what heat and may not use metal if not heat the welding of the steel or other types

Important in Heat Contamination:

• Must follow what the rules to be be as well and not to use for metal etc

Some Dis of use

• Has is set of its item etc and its limited in items as well, no flex and no quick parts

Discontuties and welding- Process types

Important Factors

• Should have flame to be made proper by flame
• All needs follow what set of rules

Stud Welding (SW)

• Process with studs welds. Can be made to both faces and the weld face as weld type of heat
• Can have many advantages depending with shapes being avail

Cont. advantages for welds parts and welds:

• Build and bridges are SW with shear areas etc, with members

What Parts Are Used in process:

• Parts all are based on either DC source or some other sort

Benefits:

• With parts and things is simple

Process of Use & Equipment, Uses & steps:

• Is in various types of equipment. But can also break the proper areas or other stuff if something doesn’t work.

Welds

• Becomes the welds parts that need to be correct on some level etc or no flash

Laser Beam Welding

• Is what is in the metal the form of light that has the heat, the heat has beam and is easy to weld
• Does however doesn’t have metals
• Is very complex
• Needs the laser to have a electric parts

Laser Beam ( cont)

• The light will get increased every level, that will get to some other part being able to used
• Small surface that goes over other part and not broken apart

Process, benefits and uses

• Must have more for light , single pass welds, small weld of areas , very laser beam can be easy moved

Dis, issues & benefits

• Face be proper etc etc, cant connect copper alloy

EBW cont.

• This can make to weld and is very specific a wide place the type of space etc, it also what to be and no radiation