How to Choose Tig Welding Parameters?

1. Types and Size of Welding Current

The selection of welding current type and size is critical in achieving optimal weld quality and performance. The current type is primarily determined by the material properties of the workpiece, while the current size significantly influences the weld penetration depth and overall joint integrity.

Current Type:
The choice between alternating current (AC) and direct current (DC) depends on the workpiece material’s thermal and electrical properties. For instance, DC is typically used for steel and stainless steel, while AC is preferred for aluminum and magnesium alloys due to its cathodic cleaning action, which breaks down surface oxides.

Current Size:
The magnitude of the welding current is a crucial parameter that directly affects the weld penetration depth, bead geometry, and heat-affected zone (HAZ) characteristics. Its selection is influenced by several factors:

1. Material composition and thickness
2. Joint configuration (e.g., butt, lap, T-joint)
3. Welding position (flat, horizontal, vertical, or overhead)
4. Electrode type and diameter
5. Shielding gas composition
6. Travel speed
7. Desired weld properties (strength, ductility, corrosion resistance)

In manual welding processes like Tungsten Inert Gas (TIG) welding, the welder’s skill level can also play a role in determining the optimal current setting. Experienced welders may be able to work with higher currents, achieving deeper penetration and faster travel speeds.

It’s important to note that modern welding power sources often offer advanced features like pulsed current and waveform control, allowing for fine-tuning of the welding parameters to achieve optimal results for specific applications.

2. Diameter and End Shape of Tungsten Electrode

The end shape of the tungsten electrode is an important process parameter. Different end shapes are chosen according to the type of welding current used.

The size of the tip angle α affects the allowable current of the tungsten electrode, arc starting, and arc stability.

Table 1 lists the recommended current range for different tungsten electrode tip sizes.

When welding with low current, using a small diameter tungsten electrode and a small cone angle can make the arc easy to ignite and stable.

When welding with high current, increasing the cone angle can prevent the tip from overheating and melting, reduce loss, and prevent the arc from extending upward and affecting the stability of the cathode spot.

The tip angle of the tungsten electrode also has a certain influence on the depth and width of the weld. Reducing the cone angle reduces the depth of the weld and increases the width, and vice versa.

3. Gas Flow Rate and Nozzle Diameter

Optimizing gas flow rate and nozzle diameter is crucial for achieving superior weld quality and efficiency in gas metal arc welding (GMAW) processes. These parameters directly influence the shielding gas coverage, arc stability, and overall weld integrity.

The gas flow rate and nozzle diameter exhibit a symbiotic relationship, with an optimal range that maximizes the effective protection zone while minimizing turbulence and contamination. Insufficient gas flow compromises the shielding effect, leaving the weld pool vulnerable to atmospheric contamination. Conversely, excessive flow can induce turbulence, potentially entraining atmospheric gases and compromising weld quality.

When calibrating gas flow, consider the following factors:

1. Low flow rates: Inadequate for displacing ambient air, resulting in poor shielding and potential weld defects such as porosity or oxidation.
2. High flow rates: May create turbulence, leading to gas waste and potential weld contamination due to air entrainment.

Nozzle diameter selection is equally critical:

1. Undersized nozzles: Generate high-velocity gas streams prone to turbulence, limiting the protected area and potentially causing weld defects.
2. Oversized nozzles: Obstruct visibility, reduce gas flow velocity, and diminish the overall protective efficacy.

To optimize these parameters:

• Use computational fluid dynamics (CFD) simulations to visualize gas flow patterns and optimize nozzle design.
• Employ pulsed gas delivery systems to maintain coverage while reducing overall gas consumption.
• Consider the welding position, joint configuration, and material properties when selecting flow rates and nozzle sizes.
• Implement real-time monitoring systems to adjust gas flow based on welding conditions.

See Table 2 for the selection of hand-held gas tungsten arc welding nozzle aperture and protective gas flow rate.

4. Welding Speed

The selection of welding speed is primarily governed by the workpiece thickness and must be carefully coordinated with other critical parameters such as welding current, preheating temperature, and electrode type. This synergy ensures the achievement of required fusion depth and width, ultimately determining weld quality and strength.

In high-speed automatic welding processes, such as robotic TIG or laser welding, the impact of welding speed on shielding gas effectiveness becomes a crucial consideration. Excessive welding speeds can lead to a significant lag in the protective gas flow, potentially exposing the tungsten electrode tip, arc column, and weld pool to atmospheric contamination. This exposure can result in oxidation, porosity, and other weld defects that compromise joint integrity.

To mitigate these risks and maintain optimal protection, welders must implement appropriate countermeasures. These may include:

1. Increasing the shielding gas flow rate proportionally to the welding speed
2. Tilting the welding torch forward at a calculated angle (typically 10-15 degrees) to direct the gas flow towards the advancing weld pool
3. Utilizing advanced gas nozzle designs that provide laminar flow and extended gas coverage
4. Employing trailing shields or additional gas diffusers for enhanced protection in critical applications

5. Nozzle-to-Work Distance

The farther the distance, the worse the gas protection effect. However, if the distance is too close, it can affect the welder’s line of sight and easily cause the tungsten electrode to contact the weld pool, resulting in tungsten inclusion.

Generally, the distance between the nozzle end and the workpiece is between 8 and 14mm.

Table 3 lists the reference welding parameters for tungsten inert gas welding of several materials.