How to control porosity during gas tungsten arc welding (GTAW) with a welding robot?

In the Gas Tungsten Arc Welding (TIG/GTAW) process, porosity is a common welding defect, mainly caused by gas entrapment, contamination of the base material or welding wire surface, and failure of the shielding gas. Controlling porosity requires a multi-faceted approach, addressing welding materials, process parameters, operating methods, and the environment. The following are specific control measures:

I. Pre-treatment of Welding Materials (Root Cause Control)

1. Base Material Surface Cleaning

Removal of contaminants: Before welding, thoroughly remove oil, rust, scale, moisture, paint, etc., from the welding area and a 20mm radius around it.

Carbon steel / Stainless steel: Use sandpaper or a wire brush to polish until a metallic luster is revealed, or wipe with acetone or alcohol.

Aluminum alloy / Magnesium alloy: First remove the oxide film using a mechanical method (such as scraping), then clean with acetone, avoiding residual moisture.

Drying treatment: If the base material is damp, preheat to 100~150℃ to dry (especially stainless steel and aluminum alloys) to reduce hydrogen porosity caused by moisture evaporation.

2. Welding Wire Quality and Storage

Use qualified welding wire: Ensure the welding wire surface is free of oil, rust, and that the packaging is intact and not damp (aluminum welding wire is easily oxidized and needs to be stored in a sealed container).

Drying treatment: Damp welding wire (such as stainless steel welding wire) can be dried at 150~200℃ for 1~2 hours. When using, place it in an insulated container (≤100℃) to avoid secondary moisture absorption.

II. Shielding Gas and Gas Supply System Control

1. Gas Purity and Flow Rate Optimization

Gas purity requirements:

Argon purity should be ≥99.99% (impurities such as O₂, N₂, H₂O will cause porosity), especially when welding stainless steel, titanium alloys, and other sensitive materials, high-purity argon (99.999%) should be used.

Mixed gases (such as argon + helium) should be mixed according to process requirements to avoid gas ratio deviations affecting the shielding effect.

Flow rate adjustment:

The argon flow rate is usually 8~15L/min, adjusted according to the welding current and workpiece thickness:

For high current, thick plates, or outdoor work (windy conditions), the flow rate can be increased to 15~20L/min to enhance protection;

For thin plate welding (<2mm) or indoor environments without wind, the flow rate can be appropriately reduced to 8~10L/min to avoid air entrainment due to gas turbulence.

2. Gas Supply System Leak Check

Regularly check for leaks in gas pipes, gas cylinder valves, flow meters, and welding torch gas paths (use soapy water to detect leaks) to prevent air from mixing into the shielding gas.

The welding torch nozzle should be undamaged to ensure uniform gas flow. Replace the nozzle or flow guide as needed to prevent gas dispersion.

III. Welding Process Parameter Optimization

1. Current and Welding Speed Matching

Avoid excessive current: Excessive current will cause the molten pool temperature to be too high, gases (such as CO₂, H₂) in the molten pool will not escape in time, forming porosity. Overheating of the base material can also lead to burn-through.

Control welding speed: Too fast a speed will increase the cooling rate of the molten pool, preventing gases from escaping; too slow a speed will prolong the high-temperature dwell time of the molten pool, easily absorbing external air (especially during overhead and vertical welding).

Example: When welding a 3mm thick stainless steel plate, a recommended current of 100~120A and a speed of 150~200mm/min are recommended to ensure that the molten pool is elliptical and flows steadily.

2. Arc Length and Polarity Selection

Short arc welding: The arc length is controlled to 1~3mm (approximately equal to the welding wire diameter). Long arcs easily draw in air and have poor arc stability.

Polarity matching:

When welding carbon steel and stainless steel, DC positive connection (workpiece connected to the positive pole) is commonly used, resulting in stable arc and moderate penetration depth;

When welding aluminum and magnesium alloys, AC power (or DC reverse connection) should be used to utilize the cathode cleaning effect to break down the oxide film and avoid tungsten electrode burn-off caused by DC reverse connection.

IV. Operating Techniques and Environmental Control

1. Standardized Operating Procedures

Arc starting and ending techniques:

Start the arc at the edge of the bevel to avoid spatter and porosity caused by directly starting the arc on the base material surface;

When ending the arc, fill the crater (using decaying current or multiple wire feeds) to prevent crater shrinkage. Use a crater-filling plate if necessary.

Wire feeding time and angle:

The wire should be slowly fed into the front of the molten pool (slightly lower temperature area) to avoid the wire contacting the tungsten electrode (which will cause tungsten electrode contamination and tungsten inclusion porosity);

Maintain a 15°~20° angle between the welding wire and the workpiece to avoid blocking the shielding gas flow.

2. Environment and Wind Protection Measures

Welding area wind protection: For outdoor work or wind speeds > 2m/s, windbreaks or windshields should be set up to prevent the shielding gas from being blown away (use ribbons to detect airflow direction).

Control environmental humidity: When the air humidity is > 80%, it is easy to cause the weld to absorb moisture and produce hydrogen porosity. A dehumidifier or heating of the base material can be used to reduce humidity.