120202a GTAW Process (Information Deck) Flashcards
Gas Tungsten Arc Welding (GTAW) Process
Overview:
* GTAW, often known as TIG welding, uses an electric arc for fusion welding.
* The arc is generated between a non-consumable tungsten electrode and the workpiece.
Shielding and Filler Rod:
* The electrode, arc, weld puddle, and adjacent heated area are protected from atmospheric contamination by an external gaseous shield.
* Filler rod may be added as required, either manually or automatically.
Development and Applications:
* Developed in the early 1940s for welding corrosion-resistant metals like aluminum and magnesium.
Arc Characteristics:
* GTAW arc can reach temperatures up to 19,427°C (35,000°F).
* The heat for welding is provided by the arc between the work and the electrode.
Visual Reference:
* See Figure 1 for the GTAW process in action.
GTAW Applications
Rising Popularity:
* Due to increasing use of high alloy metals and the demand for higher quality welds.
Key Uses:
* Ideal for critical weldments needing top-quality welding, such as pressure vessels and high-pressure piping systems.
Versatility in Metals:
* Suitable for welding a wide range of metals including:
- Aluminum, magnesium, stainless steel, carbon steel.
- Titanium, copper, copper alloys.
- Nickel, nickel alloys, low alloy steels.
Visual Reference:
* See Figure 2 for illustrations of GTAW applications.
Spot Welding with GTAW
- Application: Automated arc spot welding for thin materials, accessible from one side only.
- Uses: Automobile bodies, aerospace fuel ducts, thin-wall skins.
- Equipment: Requires an arc timer and a special torch.
- Advantages: Minimal distortion, one-side access, low spatter.
- Challenges: Crater cracking, concave weld surfaces.
Hot Wire GTAW
Mechanism: Automated process with filler metal fed into the puddle.
Setup: Uses a spool for filler metal, preheated by a separate AC power supply.
Benefits: Increased deposition rates, faster welding speeds, high-quality weld metal.
Visual Reference: Refer to Figure 3 for equipment setup.
Cold Wire GTAW
Mechanism: Similar to Hot Wire GTAW but with unenergized, ambient temperature filler wire.
Setup: Automatic wire feed to the puddle.
Visual Reference: See Figure 4 for the basic setup.
High Amperage GTAW
Usage: Commonly used for root passes in carbon steel pipe.
Method: Manual filler metal addition, mechanical pipe rotation, flat position with slight downhill progression.
Settings: Often exceeds 200 amperes.
Advantages: High-speed application, surpassing GMAW in some scenarios.
Advantages and Disadvantages of GTAW
Advantages:
Versatility: Joins a wide range of metals including aluminum, magnesium, and reactive metals like titanium.
Quality: Produces high-quality welds with excellent mechanical properties.
Control: Separate control of heat source and filler metal allows welding of thin materials with minimal distortion.
Applications: Suitable for manual, semi-automatic, and automatic welding.
Convenience: Simple equipment setups using conventional constant current sources.
Cleanliness: No flux use reduces post-weld cleaning, no spatter, and clear visibility of arc and weld pool.
Flexibility: Filler metal not always required; can use metal strips or scrap from parent metal.
Disadvantages:
Speed and Efficiency: Slow welding speeds and low deposition rates.
Skill Requirements: Requires excellent eyesight and higher skill levels for manual welding.
Cost: Needs expensive externally applied gas shielding.
Safety: Gas presents asphyxiation risk in confined spaces.
Contamination Risks: Electrode contamination can lead to erratic arc and tungsten inclusions in the weld.
Environmental Limitations: Not suitable for outdoor use or very low melting metals due to shielding gas requirements.
Special Precautions: Cast iron requires full preheating to prevent cracking.
Electric Shock Hazards in GTAW
Regularly inspect equipment to ensure all electrical connections are secure.
Disconnect primary power and install lockouts as per manufacturer’s recommendations.
Protective covers must be in place; welding machine properly grounded.
Check electrode holder, handles, and cables for condition and connection.
Ensure the electrode holder can handle the current without overheating.
Work lead should be in good condition and securely connected.
Protect hoses and cables; turn off power source when not in use.
Keep your body insulated from the workpiece and the torch.
Personal Protective Equipment for GTAW
Eye protection:
GTAW arc emits intense ultraviolet and infrared rays.
Use the recommended shade of filter plate for current ranges and materials.
Protect eyes from ultraviolet radiation, especially when welding aluminum or stainless steel.
Use blinds or screens to protect others in the area.
Face and body protection:
Protect skin from radiation that can cause sunburn-like effects.
Reflective metals like aluminum and stainless steel increase the need for protection.
Use appropriate clothing to shield the back of the neck and ears, especially in confined spaces.
Hearing protection:
Use approved earplugs or ear protectors in high noise areas.
Ensure they fit well and reduce noise to acceptable levels as per safety standards.
Protective clothing:
Wear dark-colored, tightly woven, flame-resistant clothing.
Avoid synthetic materials; use natural fibers that are less prone to burning.
Keep clothing free of oil and grease.
Use gauntlet gloves and steel-toed safety boots for additional protection.
TIG gloves are lighter and offer better dexterity but provide less protection than general-purpose welding gloves.
Fire Prevention in GTAW
Always have a suitable fire extinguisher available.
Remove or protect flammable materials in the immediate area.
Avoid welding near flammable vapors, dusts, or liquids.
Ventilation in GTAW
Ensure adequate ventilation to prevent toxic fume inhalation.
Be cautious of oxygen displacement by argon or helium, especially in confined spaces.
Ozone produced by GTAW can be toxic; proper ventilation is crucial.
Avoid exposure to fumes from metals like zinc, cadmium, lead, and beryllium.
GTAW Basic Equipment Requirements
Power Source: Conventional CC welding power source; AC capability for non-ferrous metals like aluminum and magnesium.
Torch: Air or water-cooled welding torch assembly.
Work Lead: Essential for connecting the torch to the power source.
Electrode: Non-consumable tungsten electrode.
Shielding Gas: Necessary gas with control equipment for protecting the weld area.
Filler Metal: Used as required for the specific welding application.
Visual Reference: Refer to Figure 5 for GTAW equipment setup.
Optional Accessories in GTAW
High Frequency Unit: For arc starting on DC and stabilization on AC.
AC/DC Selector & Polarity Switch: Allows switching between AC and DC, and polarity adjustment.
Automatic Stop-Start Switch: Manages arc initiation, water, and gas flow.
Remote Current Control: Adjusts amperage via foot control or torch handle switch.
Hot Start: Provides a high amperage burst for arc initiation.
Crater Fill: Lowers current before arc shut-off.
Spot Welding Timer: Controls the power source for set intervals in spot welding.
Up Slope/Down Slope Controls: Manages amperage increase and decrease around arc initiation and shut-off.
Post Purge: Controls gas flow after arc break to protect the electrode.
Pulse Control: For precision welding, managing high and background current levels and pulse timing.
Pulsed GTAW - Overview and Advantages
Working Principle:
Controls high peak and low background currents, with adjustable duration for each cycle.
Current rises to peak for penetration and metal flow, then drops to maintain the arc while cooling.
Typical pulsation rate: 2 to 10 pulses per second.
High frequency pulsing (200-500 pulses per second) in automatic applications creates a stiffer arc.
Advantages:
Prevents Burn-Through: Ideal for welding root passes and thin materials, especially in challenging positions.
Depth to Width Ratios: Short, high-current pulses enhance penetration in materials like stainless steel.
Narrow Heat Affected Zone (HAZ): Achieved by precise current and time adjustments.
Stirring Action in Weld Puddle: High pulse currents reduce porosity and incomplete fusion, improving weld quality.
Arc Stiffness for Low Current Welding: Minimizes arc wander associated with consistently low welding currents.
Visual References:
Figures 6 and 7 illustrate pulsed current and high frequency pulsed GTAW welding.
Orbital GTAW - Process and Advantages
Process Overview:
Orbital GTAW is semi-automatic or fully automatic, with the welding arc rotating 360 degrees around the work.
The process involves holding pipes or tubes stationary while an orbital weld head rotates the electrode.
Can be performed with or without filler wire. Without filler wire is known as autogenous welding.
Alignment precision is crucial for the quality of the weld.
System Components:
Includes a programmable power supply, orbital weld head, electric cables, gas hoses, and optional accessories.
Advantages:
Increased Productivity: More efficient than manual welding.
Consistent Quality: Produces superior and uniform welds.
Operational Flexibility: Once set up by a certified welder, can be operated by others.
Specific Applications: Ideal for situations where the pipe cannot be rotated or access is limited.
Reliability: Suitable for applications requiring high precision and repeatability.
Visual Reference:
Refer to Figure 8 for an illustration of Orbital GTAW.
GTAW Power Source Types
Transformer Type: De-rated by 30% for GTAW due to heat buildup.
Transformer/Rectifiers: Commonly used, designed specifically for GTAW.
Inverter Type: Designed specifically for GTAW, offering advanced features.
Generators: Suitable for remote or outdoor GTAW applications.
Selection Factors: Based on welding requirements, material type, thickness, and manual or automatic operation.
Visual Reference: Refer to Figure 9 for a multi-process power source.
AC/DC Power Sources for GTAW
Usage: Alternating current for welding aluminum and magnesium; Direct current for ferrous and other non-ferrous metals.
AC/DC Capability: Essential for versatility in GTAW and SMAW processes.
Constant Current Output: Provides accuracy and repeatability, especially in automatic operations.
Visual References: Figures 10 and 11 for AC/DC GTAW power sources.
Control Panel Features of GTAW Power Sources
Amperage Adjustment: Sets output current, with panel/remote switch options.
AC Balance Control: Adjusts electrode polarity time for aluminum welding.
Spot Timer/Seconds: For precise control in spot welding.
Crater Time & Post Flow Timer: Facilitates cooling and filling of weld crater.
Arc Control: Automatic current increase to prevent arc outages.
High Frequency Start: Assists in arc starting and stabilization.
Visual Reference: Figure 12 for control panel details.
Specialized GTAW Power Sources for Automation
Fully Automatic Applications: Uses sophisticated, programmable power supplies.
Robotic Applications: Compatible with robotic hot or cold wire GTAW.
Visual Reference: Figure 13 for a full function GTAW power supply.
Remote Control Units in GTAW
Functionality:
Remote control units allow for control of gas flow, cooling media, and current at the work point.
Foot Control (Pedal):
Acts as an off/on switch when the power source is set at panel.
Functions like a vehicle accelerator, controlling current intensity.
Maximum current set via the amperage adjustment control on the power source.
Visual Reference: See Figure 14 for foot pedal remote control.
Remote Current Adjustment Control:
Used for adjusting current without affecting the contactor, shielding gas, or coolant flow.
Visual Reference: Refer to Figure 15 for remote current adjustment control.
Torch Handle Mounted Units:
Can be simple off/on switches or more complex units controlling main contactor, shielding gas flow, and amperage.
Visual Reference: Check Figure 16 for torch handle mounted units.
GTAW Welding Currents: AC, DC, and High Frequency
Overview of Current Types:
Amperage: Number of electrons flowing per second.
Voltage: Pressure needed to push electrons through a conductor.
Direct Current (DC):
DCEN (Direct Current Electrode Negative): Used for most metals except aluminum and magnesium. Provides deep penetration and narrow bead; 70% of heat at the positive side.
DCEP (Direct Current Electrode Positive): Rarely used in GTAW; beneficial for its cleaning action, especially on metals like aluminum.
Alternating Current (AC):
Used for welding aluminum and magnesium.
Alternates between positive and negative, offering a balance of penetration and cleaning action.
High Frequency Current:
Stabilizes the arc, especially useful in automatic GTAW applications.
Increases arc stiffness and reduces wandering.
Penetration Patterns:
Each current type affects electrode size and penetration patterns in welding.
Visual Reference: Refer to Figure 17 for penetration comparisons.
Ionic Bombardment (Cleaning Action):
Occurs in DCEP; positively charged gas ions break up surface oxides on materials.
GTAW with DCEN (Direct Current Electrode Negative)
Usage: Preferred for most metals except aluminum and magnesium.
Heat Distribution: 70% at positive side, resulting in deep penetration and narrow bead.
Electrode Cooling: Electrons flowing from electrode provide cooling effect.
Oxide Removal: Limited, making it unsuitable for aluminum and magnesium.
Visual Reference: See Figure 19 for DCEN illustration.
GTAW with DCEP (Direct Current Electrode Positive)
Usage: Rare in GTAW due to low current-carrying capacity of the electrode.
Heat Distribution: Concentrated at the electrode, less heat in the base material.
Cleaning Action: Effective in breaking up surface oxides, especially on aluminum.
Ionic Bombardment: Positively charged gas ions strike surface oxides, creating a sandblasting effect.
Visual Reference: Refer to Figure 20 for DCEP illustration.
GTAW with AC (Alternating Current)
Usage: Ideal for welding aluminum and magnesium.
Characteristics: Alternates between positive and negative, balancing penetration and cleaning.
Advantages: Combines benefits of both DCEN and DCEP, suitable for reactive metals.
High Frequency Current in GTAW
Role: Stabilizes the arc, reduces arc wandering.
Application: Essential in automatic GTAW for stiffer arc and better control.
Frequency Range: Typically 200 to 500 pulses per second.
Visual Reference: See Figure 7 for high frequency pulsed GTAW illustration.
GTAW Welding Current Basics
Amperage and Voltage:
Amperage: Measures the flow of electrons past a point per second.
Voltage: The pressure required to push electrons through a conductor.
Current Types in GTAW:
AC (Alternating Current): Switches direction periodically, used for materials like aluminum and magnesium.
DC (Direct Current): Flows in one direction, with two polarities:
DCEN (Direct Current Electrode Negative): Commonly used for most metals, offers deep penetration.
DCEP (Direct Current Electrode Positive): Rarely used in GTAW, beneficial for its cleaning action on certain metals.
Polarity Selection:
Depends on the type of metal being welded, desired penetration, and weld characteristics.
Each polarity type serves specific applications and has distinct advantages.
GTAW: Welding Current and Penetration Patterns
Impact of Current on GTAW:
The choice of current (AC or DC) and its polarity significantly influences welding characteristics.
Variations in current affect electrode size requirements and the resulting penetration patterns.
AC vs. DC in GTAW:
AC (Alternating Current): Offers a balance between penetration and surface cleaning, especially used for aluminum and magnesium.
DC (Direct Current): Provides different characteristics based on polarity:
DCEN (Direct Current Electrode Negative): Focuses more heat on the workpiece, leading to deeper penetration.
DCEP (Direct Current Electrode Positive): Concentrates more heat on the electrode, resulting in shallower penetration and wider bead.
Penetration Patterns:
Each current type creates distinct weld profiles, affecting depth and width of the weld bead.
Visual Reference: Refer to Figure 17 for illustrations of penetration comparisons among different current types.
Direct Current (DC) in GTAW
Definition of DC:
Direct current is an electrical current that flows in only one direction, from negative to positive.
Generation of DC:
Can be produced by a DC generator or through the rectification of AC current.
Characteristics in Welding:
Provides consistent and stable electron flow, crucial for controlled welding processes.
Essential for welding materials that require steady heat input and penetration.
Application in GTAW:
Often used for welding a variety of metals due to its stable arc and penetration properties.
Visual Reference:
Refer to Figure 18 for an illustration of AC current being rectified into DC.
Direct Current Electrode Negative (DCEN) in GTAW
Definition:
DCEN, also known as direct current straight polarity (DCSP), involves electron flow from the negative pole to the positive pole.
Applications:
Used for GTAW on most metals except aluminum, magnesium, and their alloys.
Heat Distribution and Weld Characteristics:
About 70% of heat is concentrated on the positive side, leading to deep penetration and a narrow bead.
Less heat at the electrode due to the cooling effect of electrons, allowing for higher current carrying capacity.
Example: A 1.6 mm (1/16”) electrode can handle up to 125 amps.
Limitations:
Limited oxide removal capability, making DCEN unsuitable for metals like aluminum and magnesium where oxide cleaning is crucial.
Visual Reference:
See Figure 19 for an illustration of DCEN in GTAW.
Direct Current Electrode Positive (DCEP) in GTAW
Definition:
DCEP, also known as direct current reverse polarity (DCRP), involves electron flow from the workpiece to the electrode.
Usage in GTAW:
Rarely used in GTAW due to the low current-carrying capacity of the electrode.
Requires larger electrodes for the same current (e.g., a 6.4 mm (1/4”) electrode for 125 amps).
Heat Distribution and Weld Characteristics:
Heat concentrates at the electrode, resulting in less heat in the base material.
Leads to shallow penetration and wider bead, making it suitable for welding thin materials.
Limitations:
Not commonly used due to electrode size requirements and specific heat distribution.
Visual Reference:
Refer to Figure 20 for an illustration of DCEP in GTAW.
Alternating Current (AC) in GTAW
Nature of AC:
AC changes direction at fixed intervals, known as cycles.
The intensity builds to a maximum in one direction, returns to zero, then builds to a maximum in the opposite direction, completing a cycle.
Frequency of AC:
In North America, AC typically operates at 60 cycles per second (60 Hz).
Relevance in Welding:
AC’s changing polarity makes it suitable for welding certain types of metals, particularly those with reactive or refractory surfaces like aluminum.
Used in GTAW for its ability to balance penetration with cleaning action.
Visual Reference:
Refer to Figure 21 for an illustration of AC current cycles.
Alternating Current (AC) in GTAW
Combining DCEN and DCEP Benefits:
AC in GTAW combines the deep penetration of DCEN and the cleaning action of DCEP.
Essential for welding metals like aluminum, magnesium, and beryllium copper.
Weld Bead Characteristics:
AC weld bead contour is a balance between the narrow, deep type of DCEN and the broad, shallow type of DCEP.
Electrode current-carrying capacity is intermediate between DCEN and DCEP.
AC Cycle Advantages:
DCEP Half-Cycle: Provides cleaning action, crucial for metals with heavy oxide coatings.
DCEN Half-Cycle: Offers deep penetration and higher current carrying capacity.
Stability Challenges:
Need for stable arc maintenance due to arc rectification, where the positive half-cycle is less intense than the negative.
Uneven electron transfer across the arc can lead to unstable arc conditions.
Visual References:
See Figure 22 for electrode details and Figure 23 for the uneven electron transfer in AC welding.
High Frequency Current for Arc Stabilization in GTAW
Purpose of High Frequency Current (HF):
Used to counteract arc rectification and maintain a stable AC arc in GTAW.
Characteristics of HF Current:
Consists of several thousand volts but only a fraction of an ampere of current.
Pulses at a high frequency, several thousand times per second.
Function in Arc Stabilization:
Superimposed on the welding power source’s output voltage.
Provides sufficient voltage to reignite the positive half-cycle, crucial for oxide removal.
Ensures stability of the arc by providing a continuous path for the welding current during the transition through zero in each AC cycle.
Visual Reference:
Refer to Figure 25 for an illustration of how HF is integrated with the power source output.
AC Square Wave Output in GTAW
Square Wave Output:
Modern GTAW power sources often include electronic circuits that enable a rapid transition between AC polarities.
This technology produces a sine waveform that closely resembles a square shape.
Advantages in Welding:
Allows for quicker polarity changes, enhancing arc stability and control.
The lower peak current of the square wave output expands the usable current range of the electrode.
Functionality:
These power sources, known as square wave output power sources, can vary the time spent on each half-cycle of the AC.
Benefits in GTAW:
Improves welding quality, especially for materials that require precise heat control.
Enhances electrode efficiency and longevity.
Visual Reference:
Refer to Figure 26 for an illustration of the square wave output and its effect on electrode current range.
AC Square Wave Output in GTAW
Square Wave Technology:
Modern GTAW power sources use electronic circuits for rapid polarity transition in AC, producing a nearly square sine waveform.
Advantages over Traditional Sine Wave:
Overcomes limitations of older non-square wave machines that struggled with arc stability at zero-crossing points.
Prevents issues like arc outages or tungsten splitting.
Benefits of Inverter-Based Technology:
Quick polarity switching improves weld quality and consistency.
Allows for deeper, narrower weld beads with better penetration (more DCEN).
Increases cleaning action and creates shallower, wider beads (more DCEP).
Application Variability:
Adjusting the time spent on each half-cycle (DCEN vs. DCEP) caters to different welding needs:
More DCEN for thick materials and faster travel speeds.
More DCEP for enhanced oxide removal on metals like aluminum.
Balance Control:
No fixed rules, but requires careful management to avoid melting tungsten (too much DCEP) or poor weld quality (too little DCEN).
Visual References:
Refer to Figures 26, 27, and 28 for illustrations of square wave outputs and their effects on weld bead and electrode efficiency.
AC Unbalanced Wave Control in GTAW
Description of Unbalanced Wave:
Alters the natural AC cycle to focus more on either the electrode negative or positive half-cycle.
Results in a sine wave that is not evenly distributed (Figure 29).
Adjustments and Effects:
More time on electrode negative: Greater penetration, less cleaning action.
More time on electrode positive: Enhanced cleaning action (Figure 30).
Advantages:
Allows higher current use with a given electrode size due to reduced heating during the positive half-cycle.
Improved penetration due to extended negative half-cycle.
Cost-effective compared to balanced wave machines.
Visual Reference:
Refer to Figure 30 for an illustration of unbalanced wave adjustment.
AC Balanced Wave Control in GTAW
Description of Balanced Wave:
Achieves a completely balanced AC waveform, equalizing the duration and magnitude of both half-cycles (Figure 31).
Configuration:
Utilizes multiple capacitors connected in series.
Equal magnitude and duration of positive and negative half-cycles.
Advantages:
Excellent oxide cleaning due to a strong positive half-cycle.
Smoother and more stable arc, aided by higher open circuit voltage for reliable arc re-ignition.
Ideal for high-speed, high-quality production welding due to consistency and repeatability.
Visual Reference:
Refer to Figure 31 for an illustration of balanced AC wave control.
GTAW Torches and Cooling Systems
Heat Generation in GTAW:
GTAW produces significant heat, part of which is absorbed by the torch.
Need for Cooling Systems:
To handle this heat, GTAW torches are equipped with cooling systems.
Types of GTAW Torches:
Air-Cooled Torches:
Have a heavier power cable compared to water-cooled torches.
Cooling is aided by shielding gas flowing around or within the power cable.
Some models have finned handles for better heat dissipation.
More versatile but limited in current handling due to lack of water cooling.
Water-Cooled Torches:
Operate at much lower temperatures, reducing electrode erosion.
Can handle higher currents with smaller cable size.
Cooling water circulates through the torch body, removing heat efficiently.
Require a consistent water supply from a city line, central system, or recirculation system.
Additional Notes:
Air-cooled torches are generally more maneuverable due to flexible cable assemblies.
Water-cooled torches need proper maintenance to avoid leakage and contamination issues.
The water pressure in the torch assembly should not exceed the manufacturer’s recommendations.
Torch Current-Carrying Capacity and Head Design in GTAW
Current-Carrying Capacity:
GTAW torches are rated based on their ability to carry current.
Air-cooled torches: Rated up to 200 amps at 60% duty cycle.
Water-cooled torches: Rated up to 350 amps at 100% duty cycle.
Larger torches can handle higher current ratings.
Using a torch too small for the current can lead to overheating and early failure (Figure 33).
Torch Head Design:
Torch head angles vary to suit different welding needs.
Common angle is 120° for manual torches.
Flexible heads available for adjustable angles, enhancing comfort and joint access.
Straight-line heads (pencil type) used for restricted access.
Mechanized or robotic GTAW torches often lack handles and have specialized designs for automated operations.
Example: Mechanized orbital GTAW torches mounted on an internal track for precise movement (Figure 34).
Application in Welding:
Choice of torch and head design is critical for efficient and comfortable welding, as well as for accessing different joint types.
Components of Air-Cooled GTAW Torches
Common Components:
Torch Cap: Encloses and secures the internal parts of the torch.
Torch Body: Main structure holding the components together.
Collet Body & Electrode Collet: Secures the electrode in place and aids electrical conduction.
Gas Nozzle: Directs the shielding gas flow to the weld pool.
Gas Lens: Enhances gas coverage around the weld area.
Features:
Popular for lower amperage (up to 200 amps).
Preferred for field welding due to portability.
Visual Reference:
Figure 35 shows the components of an air-cooled torch (Courtesy of Miller Electric Mfg. Co.).
Components of Water-Cooled GTAW Torches
Common Components:
Same as air-cooled torches, with an additional cooling system for water circulation.
Features:
Designed for high current welding (up to 500 amps, some up to 700 amps).
Heavier and more expensive than air-cooled torches.
Ideal for intensive, high-current applications.
Visual Reference:
Figure 36 (not provided here) would illustrate the components of a water-cooled torch.
Torch Cap in GTAW Torches
Purpose:
Prevents accidental arcing of the tungsten electrode at the torch’s back.
Aids in tightening the collet onto the electrode.
Design:
Equipped with an O-ring for a gas-tight seal.
Available in various configurations, including long back caps for full-length electrodes and short button caps for restricted access (Figure 37).
Function:
Ensures shielding gas integrity and prevents atmospheric contamination.
Visual Reference:
Figure 37 illustrates different types of torch caps (Courtesy of Tweco/Arcair A Thermadyne Company).
Collet Body and Electrode Collet in GTAW Torches
Collet Body (Figure 38A):
Holds and positions the electrode collet.
Establishes electrical contact and directs gas to the nozzle.
Electrode Collet (Figure 38B):
Secures the electrode when the torch cap is tightened.
Made of copper alloy or heat-resistant alloys.
Must match in size with the collet body for effective function.
Tapered design for secure fit and effective current transfer.
Usage:
Ensure matching sizes for collet body and collet with the electrode.
Tighten back cap snugly by hand; excessive force may indicate need for repair or replacement.
Gas Nozzles in GTAW Torches
Function:
Directs shielding gas into the weld zone.
Constructed from heat-resistant materials.
Varieties:
Available in different diameters, lengths, and shapes.
Sizes range from 4.2 mm (number 3) to 19 mm (number 12).
Types of Gas Nozzles:
Ceramic Nozzles (Figure 39):
Most common and least costly.
Made from Grade A lava, good for confined spaces.
Can become brittle and chip after repeated use.
Alumina Nozzles:
Made of aluminum oxide.
Good electrical insulation and heat resistance.
Suitable for most welding applications.
Fused Quartz Nozzles:
Transparent for better weld vision.
Can become brittle and clouded from metal vapors.
Metal Nozzles:
Sleeve type with limited current-carrying capacity.
Water-cooled metal nozzles can handle up to 500 amps.
Susceptible to crossfiring with high frequency current.
Considerations:
Select size based on electrode and weld pool size.
Smaller nozzles for stability and restricted areas; larger nozzles for better shielding at lower gas flows.
Caution: Use the smallest nozzle that won’t melt from arc heat.
Gas Lenses in GTAW Torches
Purpose:
Fits around the electrode or collet inside the nozzle.
Contains a porous diffuser, often resembling a fine mesh screen.
Function:
Creates a laminar flow of shielding gas.
Promotes a longer, undisturbed plume of gas, enhancing gas coverage (Figure 41).
Advantages:
Allows for greater nozzle-to-work distances.
Improves access to confined joint areas.
Results in better shielding, especially in complex welding tasks.
Visual Reference:
Figure 40 shows various gas lenses (Courtesy of Tweco/Arcair A Thermadyne Company).
Figure 41 illustrates gas flow with and without a lens (Courtesy of ESAB Welding & Cutting Products).
Maintenance:
Regular inspection and cleaning are necessary to prevent clogs from fine spatter or contaminants.
Ensuring clean gas lenses is critical for maintaining effective and efficient gas flow during welding.
Gas Regulators in GTAW
Purpose:
Reduce source pressure to a working pressure.
Maintain constant delivery pressure despite source variations.
Deliver gas at any desired pressure within its capacity.
Design:
Constructed with corrosion-resistant materials for durability and safety.
Often colour-coded pressure gauges for easy identification.
Valve seating materials tailored for specific gases.
Types:
Single-Stage Regulators:
Reduce source pressure to working pressure in one step.
Controlled by an adjustment screw.
Two-Stage Regulators:
Provide more uniform gas supply than single-stage.
First stage set by manufacturer to an intermediate pressure.
Second stage controlled by adjustment screw for precise pressure settings.
Visual Reference:
Figure 42 illustrates a typical gas regulator (Courtesy of ESAB Welding & Cutting Products).
Caution:
Must be used only for their designated service.
Regulators control pressure, not flow rates.
Flowmeters in GTAW
Purpose:
Measures the rate of flow of shielding gas.
Calibration:
Indicate flow rates in litres per minute (L/min) or cubic feet per hour (cfh).
Each flowmeter is calibrated for a specific gas due to varying gas densities.
Some models have multiple calibrated scales for different gases.
Function:
Provides volume flow measurement, distinct from the pressure indication of regulators.
Essential for ensuring the correct volume of shielding gas to displace the atmosphere around the weld zone.
Types:
Commonly of the floating ball type for easy visual measurement.
Figure 43 shows examples of different types of flowmeters (visual reference not provided here).
Note:
Selection of the appropriate flowmeter is crucial to ensure accurate measurement for the specific shielding gas used in welding.
Combination Regulator/Flowmeters in GTAW
Purpose:
Combines the functions of both a regulator and a flowmeter.
Use Case:
Ideal for stand-alone welding units.
Provides cost-efficiency in large volume manifold systems with individual workstation flowmeters.
Design:
Regulator is preset to a pressure compatible with the flowmeter.
Indicates cylinder pressure and flow rate (in L/min or cfh).
Commonly used for gases like argon.
Types:
Single-Stage Regulator/Flowmeter:
Suitable for general applications (as shown in Figure 44).
Two-Stage Regulator/Flowmeter:
Used for applications requiring very accurate flow readings.
Accuracy:
More accurate than gauges that operate on pressure converted to volume.
Essential for precise control of gas flow in welding processes.
Visual Reference:
Figure 44 and 45 illustrate combination regulator/flowmeter units (visual reference not provided here).
Hoses in GTAW
Purpose:
Transfer shielding gas from the source to the GTAW torch.
Types:
High-Pressure Hoses:
Connect cylinders to manifold systems.
Designed to handle high pressure (Examples in Figure 46A and B).
Low-Pressure Hoses:
Commonly used from the flowmeter to solenoid valves.
Shown in Figure 46C.
Integrated Hoses:
Part of the welding torch cable assembly.
Connects solenoid valve to the torch head.
Material:
Typically made of plastic to prevent gas loss, especially for gases like helium.
Rubber is not preferred for high-pressure applications.
Usage:
Must be used as per manufacturer’s recommendations for safety and efficiency.
Compressed Gas Cylinders for GTAW
Storage and Handling:
Store in well-ventilated areas, upright and secured.
Ensure labeling with gas type and WHMIS symbols.
Do not transfer gas between cylinders. Use appropriate equipment and fittings.
Return with valves closed, protective caps on, and residual pressure maintained.
Types and Storage:
Made of alloy steel with extrusion construction.
Gaseous shielding gases stored at 2.9 MPa - 41.37 MPa.
Cylinder sizes vary based on job requirements.
Argon and helium commonly used; CO2 stored in liquid state.
Cylinders must be vertical for proper gas extraction.
Cylinder Valves:
Control gas flow; open fully when in use and close when not.
Protective caps required when not in use.
Metal rupture disc for safety in excessive pressure.
Connections and Safety:
Specific connections to prevent incorrect attachment.
Safety considerations include proper ventilation and secure upright storage.
Return protocols: close valves, attach caps, replace outlet caps, maintain pressure.
Shielding Gas Flow Rates for GTAW
Optimal Flow Rates:
Argon: 5.8 L/min - 16 L/min (12 cfh - 35 cfh).
Helium: 11.5 L/min - 24 L/min (25 cfh - 50 cfh).
Adjusting for Job Conditions:
Ensure adequate gas coverage without creating turbulence.
Low flow rate can cause porosity due to inadequate gas coverage.
High flow rate can create turbulence, mixing shielding gas with air, leading to porosity.
Cylinder and Supply Considerations:
A single cylinder may not suffice for high flow rates over extended periods.
Use of manifold system to connect multiple cylinders for consistent supply (Refer to Figure 51 for manifold system setup).
Gas Mixes for GTAW
Usage of Mixed Gases:
Mixing two or more shielding gases for GTAW.
Common in various welding applications.
Obtaining Mixed Gases:
Available pre-mixed from suppliers.
Option to mix gases on-site.
On-Site Mixing:
Use of gas mixers to achieve correct proportions (refer to Figure 53 in source material).
Advantage: Ability to customize gas proportions for specific jobs.
Selection of Gas Mixing System:
Based on the volume and types of gases required.
Determines the size and type of the gas mixing system.
