Welding Test #2
24. What composition of SMA electrode should be used to make machinable type weld deposits on cast iron?
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31. How can a spark test be used to identify metals?
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Postheating
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Manganese steel
.30% carbon. Good fair weld ability. Post heat not needed
High carbon
.68%, poor weldability preheat 750/850F
Tool Steels
.80% carbon +, poor same as anovr
What metals were weldable only by the GTAW process before GMAW was developed?
.aluminum, magnesium, titanium, and some stainless steels
What amount of carbon,or more, in a steel would require that preheat and post weld heat treatment be performed for welding?
0.40%
Manganese 0.80%, molybdenum 0.40% is the composition of what alloy?
44xx
To get heat distribution of half in the work, half in the tungsten what type of current would be used?
AC
Dynasty 350
AC with DCEN/DCEP balance control for aluminum foot control Water cooled torch
Gas Metal Arc Welding aka
GMAW MIG- Metal Inert Gas Welding MAG- Metal Active Gas Welding Wire Welding-describes the electrode used
CC power source, work cable, liquid-cooled cable and torch, shielding gas supply with flow meter, related equipment" are the components of a _____welding system.
GMAW-P
Which process shifts between the globular and spray ranges?
GMAW-P
Aluminum, magnesium, titanium, and some stainless steels were weldable only by the what process before GMAW was developed?
GTAW
TIG is Slang for what process?
GTAW
GTAW class summary
GTAW was originally developed for metals that were difficult to weld by the and SMAW processes. Today it is widely used for clean, high-quality, precision welding applications in almost all metals used in construction and maintenance of ships and power plants.
Gas Tungsten Arc Welding
GTAW, TIG
A)
Gray Cast Iron B) Machinable C) OFW
a.)
Gray cast iron, b.) Machinable weld, a.)SMAW
22. What parts of a typical GMA welding gun can be replaced?
Gun Body Insulated Conductor Tube Conduit Contact Tube Gas Nozzle Gas Diffuser Gun Trigger
All inert gases are:
Hazardous: They displace air Same Density, colorless Odorless can asphyxiate
What setting should the XMT 350 be set on?
Stick welding (DCEP)
XMT350
Stick, MIG, TIG DC only not used for aluminum
What holds the molten ball of tungsten in place at the tip of the electrode during DCEP welding?
Surface Tension
"How might air be drawn into the shielding gas between the nozzle and the weld?"
The air can be drawn in under the nozzle if the torch is held at too sharp an angle to the metal.
Heat treatments to avoid cracking:
preheat ost weld heat treatments
In machine welding, which function is performed by the welder?
provide the joint guidance
Preparation to avoid cracking:
rust and paint removal
GMAW welding can be performed as:
semiautomatic machine automatic most commonly used in semiautomatic welding
If we want to increase penetration while keeping the wire feed speed the same when GMA welding, we could
shorten electrode extension
Liners for aluminum are
smooth teflon or nylon
round groove drive rolls are used for
soft wires to avoid distorting wire shape
Argon rich shielding gas,DCEP,and current above the transition current are required for what transfer mode in GMAW?
spray
Precipitation hardening steels are
stronger than austenitic
To get better shielding you can
switch to a larger cup you will need more flow: 17-20cfh
metallurgy
the combination of the base metal and filler metal
What would cause the cable of a GTAW torch to quickly overheat and melt through the hose?
the flow of cooling water has stopped.
What does the term weldability involve?
the metallurgy of the metal and filler metal, processes, joint design, preparation, heat treatments before and after
What does surface tension hold in place during DCEP welding?
the molten ball of tungsten
What problem can excessively large tungsten cause?
the temperature will be too low to establish a stable arc
What can happen if rolls of the wrong shape are used on aluminum?
the wire can become distorted, causing feeding problems
Joint Design's relation to cracking:
thicker - more cracking geometry: bevel vs. square to avoid cracking
Which condition could cause an unstable GTAW arc?
too much resistance overheating a small tungsten
The last two numbers in AISI steel classifications are
%carbon
1b.Malleable, 2a.non-machinable,3a.Smaw
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1A. Gray cast iron 2A. Non-machinable weld 3C. Brazing
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1A.) Gray Cast Iron 2A.) Non-machinable Weld 3A.) SMAW
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1A: gray cast iron 2a: non machinable 3a: SMAW
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1B) Malleable Cast Iron 2B) Machinable 3A) SMAW
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1B) Malleable Cast Iron. 2B) Machinable Weld. 3C) Brazing
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1C-(Nodular Cast Iron) 2B-(Machinable Weld) 1C- (SMAW)
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1b. Malleable cast iron; 2a. non-machinable ; 3c Brazing
...
Ways to prevent tungsten electrode erosion:
1. Having good mechanical and electrical contact. 2. Using as low a current as possible. 3. Using a water-cooled torch. 4. Using as large a size of tungsten electrode as possible. 5. using DCEN current. 6. Using as short an electrode extension from the collet as possible. 7. Using the proper electrode end shape. 8. Using an alloyed tungsten electrode.
divpWhat is the maximum recommended angle off perpendicular for the GTAW torch?/p/div
10
The flow on a XMT 250 machine should be set at
10CFH
8. Explain the steel classification number 1030:
1=Carbon The first two digits together indicate the series within the basic alloy group. The last two or three digits refer to the approximate permissible range of carbon content. So 30 would have .30% range of carbon content.
What is the maximum recommended gas flow for a 1/2 cup?
20 cfh
XMT 250 torch is limited to
200 amps
What type of filler metal would be good for joining austenitic to carbon steels?
310Cb
What type of filler metal electrode is best for salt water?
310L
What type of filler rod do we use?
316L any other austenitic stainless will work
Because the XMT 350 machine is set for DCEP, the maximum amperage is ___ or else the tungsten may melt up into the torch and damage it.
40 amps
19. What problems can occur to stainless steel as it is allowed to form carbide precipitation during welding?
A harder material with improved wear resistance. In this case there will be a loss in corrosion resistance.
GTAW Process
An arc is established between a nonconsumable tungsten electrode and the base metal which is called the work. The electrode doesn't melt, but the work does at the spot where the arc impacts its surface and produces a molten weld pool where it melts. Since hot tungsten is sensitive to oxygen contamination, a goodinert shielding gas is required to keep the air away from the hot tungsten and molten weld metal.
What type of shield gas is used to weld aluminum (GMAW)?
Ar or He
Which GTAW shield gas provides easier starts, longer arcs at low voltages, and is better for AC?
Argon
23. Why must cast iron weld metal be ductile?
Because of its application to materials that hold heavy loads and it often has a high carbon content.
15. Why are high carbon steels preheated before welding?
Because of the high carbon content, the heat affected zone can transform to very hard and brittle martensite. The welder can avoid this by using preheat and by selecting procedures that produce high energy inputs to the weld.
28. What makes helium difficult to use for manual welding?
Because penetration and bead profile are sensitive to the arc length and the long arcs needed for feeding filler wires are more difficult to control.
What type of shield gas is used to weld steel (GMAW)?
CO2 Ar/CO2 Ar/O2
What are the typical replacement parts of a GMAW gun?
CV power source, work cable, wirefeeder, gun, shielding gas supply with flowmeter, and related hoses, liners, cables
What can we do to melt the stainless and not the tungsten?
Change polarity to DCEN 2/3 heat in work
300 series
Chemical equipment, galley, furnace parts 18%Cr corrosion resistance 8%Ni austenitic (non-magnetic) at room temp 800-1500F begins to rust
21. What are the different uses for each of the three types of stainless steels?
Chromium-Nickel Austenitic: Ferritic Stainless Steels Martensitic Stainless Steels- used in applications requiring both wear resistance and corrosion resistance. Surgical knives and razor blades.
Cathodic cleaning action which removes high-temperature oxides is characteristic of what type of current?
DCRP
What power supply is used in semioautomatic welding (GMAW)?
DCRP to melt electrode and provide transfer force, and provide cathode etching which is useful on aluminum
Perpendicular Direction of Travel
Deep Penetration, Narrow and High Bead Contour
Backhand Direction of Travel
Deep Penetration, Narrow and High Bead Contour.
GMAW-P, Pulsed Arc Metal Transfer
Dual pulsed current. One pulse of high current is for the axial spray transfer mode and the other lower pulse of current should not transfer any weld metal. The pulsing of the current levels permits the use of the high amperage transfer mode and the low current allows the weld pool to cool and contract slightly, so it is easier to control. It is relatively easy.
Cast Iron is very brittle so the weld must be____.
Ductile.
GTAW Electrodes
EWP = Pure Tungsten EWTh-1 = 1% Thorium Tungsten EWTh-1 = 2% Thorium Tungsten EWZr = 1/4% to 1/2% zirconium tungsten. EWCe-2 =2% cerium tungsten EWLa-1 = 1% lanthanum tungsten EWG = Alloy not specific
What is the ideal heat distribution with DCEP Welding Current?
Electrode absorbs 2/3 of the heat. Work absorbs 1/3 of the heat.
Other factors affecting weld ability
Filler metal Shielding atmosphere Fluxing material Preheat and postheat Welding procedure Welding process
How can heat be controlled remotely with the Dynasty 350?
Foot pedal
14. What must be done to steels before welding and after welding if they contain more than 0.40% carbon?
For steels containing more than 40% carbon, preheating and subsequent heat treatment generally are required to produce a satisfactory weld. Shielded arc electrodes can be used for welding this type of steel.
As argon became more plentiful, and DCEN was recognized as more suitable than DCEP, which process became more effective at reduced cost?
GMAW
To increase power without affecting desirable spray mode, what gas should be added to Argon shield gas?
Helium
EWZr - Brown, Zirconium Tungsten Electrode
Helps emit electrons freely. Same effect as thorium, but to a lesser degree. Are more easily melted than thorium tungsten so can be used with both AC and DC currents. They can be used with the balled end and are good for AC welding of aluminum and magnesium. Good resistance to weld pool contamination.
4068
High Carbon Poor weldability Preheat 750-850F low H flux heat input process postweld stress relief
12. What factors other than carbon affect a steel's ability to be welded?
High Maganese steel can crack easily. Chromium content generally improves weldability. Foreign matters such as oxides, slag, or dissimilar metals. Electrode polarity (reverse polarity typically preferred).
11. According to Table 26-3, at what level of carbon content does weldability become poor?
High carbon steel, carbon content of 0.5% to 1%.
Tool Steels
High carbon= poor weldability .80% C anneal above transformation range before welding
High Carbon =
High harden-ability and high strength high possibility of cracking
18. What properties does chromium and nickel produce in stainless steels?
High strength Less weight Chromium-Corrosion resistance Nickel-tough austenitic microstructure. Relatively easy to weld and weldable with many types of electrodes.
EWCeO2- Orange, Cerium Tungsten Electrode
Improves current carrying capacity. Not made of radioactive material. Improved arc starting and arc stability. Slightly higher voltage.
1. Why is usage of the term GMAW preferable to MIG for gas metal arc welding?
In the beginning the GMAW process was used to weld aluminum using argon (Ar) gas for shielding. As a result, the process was known as MIG, which stands for metal intert gas welding. The later introduction of CO2 and O2 to the shielding gas has resulted in the American Welding Society's preferred term, gas metal arc welding (GMAW).
Function of Inert Gas in GTAW welding:
Inert gas provides the needed arc characteristics and protects the molten weld pool. Because flexes are not used, the welds produced are sound, free of slags, and as corrosion resistant as the parent metal.
Why is thorium no longer used?
It is radioactive
The L in the filler rod 316L stand for
Low carbon
Carbon steel
Low carbon, 10% carbon excellent weld ability preheat 70 min to 200 max
GMAW-S, Short Circuiting Transfer
Low currents allow the liquid metal at the electrode tip to be transferred by direct contact with the molten weld pool. This process requires close interaction between the wire feeder and the power supply. Most common on: Thin or properly prepared thick sections of material. On a combination of thick to thin materials. With a Wide Range of Electrode Diameters With a Wide Range of Shielding Gases.
Which name of a welding process became obsolete because of the introduction of 02 and CO2 in shield gas?
MIG
9. Referring to Table 26-2, what is the composition of the metal identified as 44XX?
Maganese 0.80; Molybdenum 0.40.
EWG - No color specified, Alloy not specified Electrode
Manufacturer specific alloys.
Effect of preheating cast iron
Metals such as cast iron that are brittle and can crack easily should be preheated. The preheating will reduce the stress caused by the weld and will help the filler flow.
EWLa-1- Black, Lonathium Tungsten Electrode
Not radioactive. Improved current carrying capacity. Slightly higher arc voltage than cerium and thorium.
For the Dynasty 350 and Miller XMT 350, the primary switch is always ____ when not in use.
Off
6. What ranges does the pulsed arc metal transfer shift between?
One pulse of high current is for the axial spray transfer. The other lower pulse of current should not transfer any weld metal and allows the weld pool to cool and contract slightly. The total heat input of the weld is lower than for the axial spray transfer method. The eight components of the Pulsed Arc Metal Cyle are Ramp Up Overshoot High Pulse Current High Pulse Time Ramp Down Step off Current Background Current Pulse Width
Electrode Tip Shape: DCEN DCEP AC
Pointed Rounded
Axial Spray Method
Pointing the wire tip from which very small drops are projected axially across the arc gap to the molten weld pool. There are hundreds of drops her second crossing from the wire to the base metal. The drops are propelled by arc forces at high velocity in the direction the wire is pointing.. Welding in vertical and overhead positions is possible without losing control of transfer.
Gas post flow is used to
Protect tungsten and the weld
1. What materials were weldable only by the GTAW process before GMAW was developed?
Reactive Materials (prone to contamination at welding temps). • Aluminum • Magnesium • Titanium • Some grades of Stainless Steel
Forehand Direction of Travel
Shallow Penetration- Wide and low bead contour.
3 types of arcs
Short Spray Pulse
7. What two organizations have developed systems for classifying standard construction grades of steel?
Society of Automotive Engineers (SAE)American Iron and Steel Institute (AISI)
EWTH-1 and EWTH-2 Yellow and Red, Thoriated Tungsten
Thorium oxide (ThO2), when added in percentages of up to 0.6% to tungsten, improves its current carrying capacity. The addition of 1% to 2% of thorium oxides improves electron emission. Thorium increases the serviceable life of the electrode. Easier arc starting. Work well with DCEN. Good for steel, steel alloys, nickel alloys, and most other metals other than aluminum or magnesium. Not suitable for AC.
High melting temperature and good electrical conductivity make which metal the best choice for GTA welding electrodes?
Tungsten
Which of the following are uses listed in the text for ferritic stainless steel?
ornamental applications, elevated temperatures such as heat exchangers
Globular Spray Metal Transfer
Used on thin materials and at a very low current range. The arc melts the end of the electrode, forming a molten ball of metal. The ball eventually falls across the arc, landing in the molten weld pool. This process is rarely used by itself.
1.What is meant when a metal is said to have good weldability?
Weldability describes the ease with which a metal can be welded properly.
•What does the term weldability involve?
Weldability is defined as "the capacity of a metal to be welded under the fabrication conditions imposed into a specific, suitably designed structure and to perform satisfactorily in the intended service." -Metallurgy of both the metal to be welded and the filler metal. -Welding Processes. -Joint Design. Weld Preparation Heat Treatments before and after welding, and many other factors, depending on the complexity of the welded system.
What does adding thorium oxide do for the tungsten electrode?
What does adding thorium oxide do for the tungsten electrode? • When added in percentages of up to .6% to tungsten, current carrying capacity is improved. • Further addition of thorium oxide to 1-2% helps with electron emission allowing it to carry approximately 20% more current. This results in a reduction of the electrode tip temperature, resulting in less tungsten erosion and subsequent weld contamination. • Also provide a much easier arc starting characteristic than pure or zirconiated tungsten. • They work well with DCEN and maintain a sharpened point well. Do not use with AC. • Very suitable for welding on steel, steel alloys, nickel alloys, and most metals other than aluminum and magnesium.
Why do older, transformer type GTA welding machines require high frequency for AC?
Why do older, transformer type GTA welding machines require high frequency for AC?
Argon when used with DCEP
acts as a cleaning agent. The electrons from the cathode surface lift the oxides that interfere with their movement.
divpWhat can happen if the TIG torch is held at an extreme angle off perpendicular to the work?/p/div
air can be entrained in the space between the nozzle and the work
Good Weldability
almost any process little control of procedures
ferretic
almost no nickle low carbon (heat exchangers, architectural)
What materials can be used to make nozzles for GTAW?
alumina, silicon nitride, or fused quartz
Too large of a diameter of an electrode will give
an unsteady arc
What early advancements made the GTA welding process more effective and reduced its cost?
argon became more plentiful, and DCEN was recognized as more suitable than DCEP.
"Deeper penetration, narrow and high bead contour," describes what GMAW gun angle?
backhand
What factors have led to increased usage of the GMAW process? (Note that GMAW does not include FCAW)
better filler metals, smaller wire, faster speed, higher deposition.
Why is argon's ease of ionization a benefit?
better for AC, easier starts, long arcs at low voltage
Why has GMAW seen an increase in use?
better quality welds faster welding speeds higher deposition rates lower equipment costs
How did the development of solid state electronics help the pulsed-arc process?
better, simpler, more economical way to control pulsing
How can the end of a tungsten electrode be shaped?
by grinding, alkaline solution, or remelting
What problem can occur in stainless when it is held at temperatures between 800 and 1500 degrees Farenheit?
carbide precipitation
Explain the steel classification number 1030.
carbon steel with 0.30% carbon
1010
carbon stell .10%carbon Low C= excellent weldability Preheat 70-200F
The new standard for welding Aluminum is
ceriated for AC and DC
GTA welding is the ____ of all the manual welding processes.
cleanest.
What properties does chromium produce in stainless steels?
corrosion resistance
Higher Heat Input reduces____.
cracking.
Which of the below is not listed as a typical replacement part for a GMA welding gun?
electrode
400 series
ferritic and Martensitic Stainless
Because there is no ____ used to clean the weld in GTA welding, all surface contamination such as oxides, oil, dirt, and so on, must be cleaned from the part being welded and the filler metal so they do not contaminate the weld.
flux
FCAW
flux inside freezes at lower temps than liquid metals, holding it in place can be used outdoors and on light rust and paint
"Wide, shallow penetration, with low bead contour" describes the cross sectional bead shape of what GMAW gun angle?
forehand
Why is CO2 added to argon when making GMA spray transfer welds on steel?
forms iron oxide, providing a stable site for the cathode
XMT350 torch is cooled by
gas,
What ranges does the pulsed gas metal arc welding shift between?
globular and axial spray
GMAW Electrode Liner -
guides the welding wire from the feed rollers to the gun.
serrated V-Grooved drive rolls are used for
hard wires
Liners for steel are
hard wound wire
EWP - Green, Pure Tungsten Electrode
has the poorest heat resistance and electron emission characteristics of all the tungsten electrodes. It can be used with AC for welding metals
GTA can be used to make extremely ___ quality welds.
high
Older transformer power supplies put out a sine wave AC welding current that would allow the arc to extinguish during voltage reversal. What is added to re-establish the ion path?
high frequency current
Why do we use a tungsten electrode?
high melting temperature good conductor
Which two of tungsten's properties make it the best choice for GTA welding?
high melting temperature and good electrical conductivity
What composition of SMA electrode should be used to make machinable-type weld deposits on cast iron?
high nickel, nickel-iron, or nickel-copper
Procedures to avoid cracking
higher heat input thinner joint design geometry of weld prep: rust and paint removal preheat and postheat
In what form is metal transferred across the arc in axial spray transfer mode in GMAW?
hundreds of small drops per second
tungsten is ceriated to
improve conductivity
Why is helium added to argon when making some spray or pulsed-spray transfer welds?
increase power without affecting desirable spray mode
Helium can be added to Ar, Ar/CO@, or ArO2 to
increase the power (heat) without changing transfer characteristics.
TIG uses an
inert gas shield
Why is Helium more difficult to use for manual GTAW than argon?
it is more difficult to ionize so starting is more difficult
What can be done to reduce tungsten erosion in the GTAW torch ?
keep it as cool as possible
When grinding a tungsten electrode, the grinding marks should run
lengthwise to get the arc to concentrate at the point, reducing tungsten in the weld.
Martensitic
low nickle more carbon wear and corrosion resistant (coal crushers)
In automatic welding, what provides the joint travel?
machine
The second number in AISI steel classifications is
major alloying element
What can be done when grinding a tungsten to reduce the tungsten contamination of the weld?
make the grinding marks run lengthwise on the tungsten electrode end
4440
manganese molybdenum (mag moly) .40% carbon Med C= Fair Weldability Preheat 400-500F Low H flux postweld heat treat stress relief at 1150F 1h/1in
1330
manganese steel 1.75% Mn .30% carbon Low/Med C= Good/ fair weldability Preheat 200-300F
A tractor cutting torch is an example of
mechanized equipment
Too small diameter of an electrode will
melt
Cast iron processes to get a ductile weld
nicke;, nickel iron, or nickle copper filler metal to get more ductile and machinable welds or braze cast iron preheat to 600-1200F or with nickel filler keep cast iron cool and peen each pass to relieve shrinking and wait between passes to cool down to touchable temp
The electrode in GTAW is:
non consumable.
What 3 parts are frequently replaced on a semiautomatic welding gun?
nozzle tip liner
What type of liner should be used for feeding aluminum wire?
nylon
What makes helium difficult to use for manual TIG welding/
penetration and profile are sensitive to arc length
Too much gas flow in a TIG machine will cause
turbulance
What is the heat distribution with DCEN welding current?
two thirds in the work, one third in the tungsten
The first number in AISI steel classifications is
type of steel
Gas Tungsten Arc Welding (GTAW)
uses a noncomsumable electrode made of tungsten. In GTA welding the arc between the electrode and the base metal melts the base metal and the end of the filler metal as it is manually dipped into the molten weld pool. A shielding gas flowing from the gun nozel protects the molten weld metal from atmospheric contamination. A foot for thumb remote control switch may be added to the basic GTA welding setup to allow the welder better controls. This remote control switch is often used to start and stop the welding current as well as make adjustments in the power level.
When sharpening a tungsten, what conditions should be avoided?
using a stone on which other metals have been ground.
A flowmeter is a tapered tube and must be ____ to read properly.
vertical
Because the tube of a flowmeter is tapered, how must the tube be positioned?
vertical with the end down so the gas can flow into it.
Cast iron
very brittle weld must be ductile
GTAW was developed to:
weld reactive metals; aluminum magnesium and some stainless which could not be welded otherwise.
Over half of the filler metals sold are
wire, to be used in semiautomatic, machine, and automatic welding equipment.
33. Using Table 15-4, determine the minimum gas flow rate for a 1/2'" (13mm) nozzle.
• 17-20 cfh, or 8-9.4 L/min
4. What three conditions are required for the spray transfer process to occur?
• Argon Shielding (or argon rich shielding gas mixtures) • DCEP Polarity • A current level above a critical amount called the transition current.
. What effect does shortening the electrode extension have on weld penetration?
• As the electrode extension distance is shortened, the weld heats up, penetrates, and builds up less.
12. Why should a grinding stone that is used for sharpening tungsten not be used for other metals?
• Because of the hardness of tungsten and its brittleness, the grinding stone chips off small particles of the electrode. A course grinding stone will result in more tungsten breakage and a poorer finish. If the grinder is used for metals other than tungsten, particles (of other metals) may become trapped on the tungsten as it is ground. The metal particles will quickly break free when the arc is started resulting in contamination.
8. Why does DCEP help with welds on metals such as aluminum?
• Cathodic cleaning action removes high temperature oxides.
What materials can be used to make nozzles?
• Ceramic such as Alumina or Silicon Nitride (opaque) • Fused Quartz (clear)
15. Describe the weld produced by a backhand welding angle?
• Deep penetration-narrow and high bead contour.
"How is the metal transferred from the electrode to the plate during the GMAW-S process?"
• Direct Contact with the molten weld pool
What is the heat distribution with DCEN welding current?
• Electrode absorbs 1/3 of the heat. • Work absorbs 2/3 of the heat.
24. What is the heat distribution with AC welding current?
• Electrode absorbs ½ of the heat. • Work absorbs ½ of the heat.
How can the end of a tungsten electrode be shaped?
• Grinding • Breaking • Remelting the end • Chemical Compounds Tungsten is easily broken so the welder must be careful when breaking it.
16. What components make up a GMA welding system?
• Gun • Electrode (wire) feed unit • Electrode (wire) supply • Power Source • Shielding gas supply with flowmeter/regulator • Control circuit • Related hoses, liners, and cables • Some have water cooling systems.
1. What early advancements made the GTA welding process more effective and reduced its cost?
• Improvement in gas composition (switching from helium to tungsten) and a better understanding of the importance of polarity (all three polarities are used, but differ for different applications) improved the effectiveness of the process and reduced its cost
9. Why is CO2 added to argon when making GMA spray transfer welds?
• It allows higher weld speed, better penetration, good mechanical properties, and costs less than the inert gases.
27. Why is argon's ease of ionization a benefit?
• It makes it suitable for alternating current applications and easier starts. It also permits fairly long arcs at lower voltages, making it virtually insensitive to changes in arc length.. Argon is also good for welding in deep grooves because it is denser than air.
Why should the grinding marks run lengthwise on the tungsten electrode?
• Lengthwise grinding reduces the amount of small particles of tungsten contaminating the weld.
3. In what form is metal transferred across the arc in the axial spray metal transfer method of GMA welding?
• Molten metal drops
21. What type of liner should be used for aluminum wire?
• Nylon
"What factors have led to the increased use of the GMAW process?"
• Quality and ease of mechanization
14. Describe the weld produced by a forehand welding angle?
• Shallow penetration-wide and low bead contour
"How have electronics helped the pulse-arc process?"
• Solid state electronics provided a better, simpler, and more economical way to control the pulsing process.
Why must AC welding power use high frequencies in order to work?
• The high frequency ensures that a voltage peak will occur reasonably close to the current reversal in the welding arc, creating a low resistance ionized path for the welding current to follow.
2. Which two of tungsten's properties make it the best choice for GTA welding?
• The high melting temperature and good electrical conductivity. Hardness Tensile Strength
What holds the molten ball of tungsten in place at the tip of the electrode during DCEP welding?
• The liquid tungsten surface tension with the larger mass above the molten ball holds it in place like a drop of water on your fingertip.
18. What can happen if rollers of the wrong shape are used on aluminum wire?
• The wire rollers are clamped securely against the wire to provide the necessary friction to push the wire through the conduit to the gun. Using the wrong rollers can damage the wire and cause it to not feed correctly.
7. What problem can an excessively large tungsten cause?
• They may result in too low a temperature for a stable arc.
7. Why is helium added to argon when making some spray or pulsed-spray transfer welds?
• Very hot arc for welds on thick sections, usually used in gas blends to increase the arc temperature and penetration. Helium produces a lot of heat.
