How to Get Better GTAW Welds Through Melt Pool Thermal Analysis

If you’re wondering how to analyze a GTAW or TIG weld pool during welding, you’re not alone.

Nearly every welder at some point has wanted to do some sort of analysis by measuring the size, shape, and location of the melt pool as a way of determining how well the GTAW process is performing. Often this is done by eye through a weld helmet, but recent technology has enabled the generation of such data from the output of a thermal weld camera that acquires thermal images of the welding process.

Thermal weld cameras offer temperature measurement information of the entire environment of the weld process. The high-contrast recorded video generated from a thermal weld camera has multiple uses as part of the welding quality control process. The recorded video itself can act as evidence that the weld was completed correctly and can be reviewed offline for quality analysis and process review. Using a thermal weld camera gives the welder an excellent, high-contrast view of the interaction of electrode, arc, parent materials, and the resulting melt pool that determines weld bead quality.

While a standard weld camera can capture a clear image of the melt pool during the welding process, a thermal weld camera offers an even more advanced solution. By using machine vision software algorithms, the same video can be analyzed to extract quantifiable data that measures the melt pool's characteristics. In this post, we’ll explore how to improve your GTAW welds by using a thermal camera to monitor and analyze the melt pool, and what to consider when selecting thermal weld monitoring equipment.

A thermal camera offers two main advantages over a standard camera when using it for GTAW weld monitoring:

(a) better image fidelity of the melt pool and

(b) thermal data that can be used to measure temperature at key points in and around the melt pool.

Fig. 1: Clear View of a GTAW Melt Pool from a SWIR Thermal Camera (Xiris)

Optimizing Orbital Welding with Thermal Cameras and Machine Vision

While nothing replaces hands-on experience, an apprentice welder can use a thermal camera to record and display proper weld techniques and best practices, or to compare the results of good and bad welding techniques. Using a thermal camera to view or record a weld is particularly useful for orbital welding procedures in several circumstances. It can enable management of remote welding in hazardous environments, giving the welder a real-time view of weld head activity and melt pool characteristics while the process is monitored from a safe location.

The melt pool itself is one of the most important features to be monitored in any GTAW weld process. While a good weld camera can assist the operator in seeing much of the detail of the melt pool, better image fidelity can be obtained with a thermal camera system that is able to show hotter objects in an image with greater brightness and contrast than cooler objects. As a result, the melt pool can be imaged with greater clarity and sharpness, making it easier to distinguish its boundaries from the tungsten electrode, weld arc, and other elements in the weld environment.

This better fidelity image allows the operator to better see details of the melt pool clearly and provide a more exact understanding of the health of the welding process.

The better image fidelity that helps operators see the melt pool better, is also valuable as an input to machine vision algorithms that can extract information about the melt pool for better decisions to be made. More precise images lead to more precise data that can be extracted about the melt pool, which typically include size, shape and location data.

Machine vision software, such as available from Xiris’ WeldStudio software, can analyze thermal images to detect temperature anomalies, monitor weld bead formation, and ensure consistent weld quality. This data-driven approach can lead to improved process control, reduced defects, and higher overall efficiency in welding operations.

Fig. 2: Clear View of the GTAW Cooling Bead from a SWIR Thermal Camera (Xiris)

Essential Features to Look for in a Thermal Weld Camera for Orbital Welding

The extreme heat and light associated with orbital welding and the constrained area of some welding operations require monitoring and recording systems specifically designed for the job. A High-quality thermal weld vision system should offer the following features:

High Dynamic Range SWIR imaging: The best thermal weld cameras use a combination of Short-Wave Infrared Imaging that captures the range of heat most suitable to hot metal, and High Dynamic Range (HDR) imaging that can extend the range of exposure through a larger temperature range that minimizes saturation. The result is a thermal weld camera that can provide good detail to the operator to clearly show any weld melt pool issues.
Cameras designed for the weld environment: The extreme temperatures and radiated heat from a weld and pre-heated substrate require thermal weld cameras that can tolerate the harsh environment. A water-cooled housing can protect the thermal weld camera from the intense heat of the weld arc is needed to protect the camera in temperatures up to 300°C / 550°F.
Calibrated Images: For most versatile results, the thermal weld camera should be calibrated to a precision heat source so that every pixel can report a temperature value that is within 2% of actual temperature. The camera must be calibrated with its optics assembled to ensure the same optics are used in the field as what was used for the calibration.
Optimized Optics: The camera’s optics should be optimized to operate specifically in the SWIR range of between 900-1700 nm, filtering out specific light frequencies in order to eliminate glare and show a clear view of the melt pool. A variety of lens configurations and camera controls should be available to provide different fields of view and working distances to allow operators to focus on the most critical areas of the weld process. The best thermal weld cameras will also automatically compensate for light intensity differences between welding and non-welding modes.
Configurability: The thermal weld camera systems should be adaptable to a variety of weld heads and welding applications. Proper camera angle relative to the weld head is critical in monitoring the melt pool quality.
Recording: The thermal camera system should communicate with the welding controller to simplify the monitoring and recording of the welding process data. Systems that record the date and time provide additional means of process verification in support of quality control and compliance. Some thermal weld cameras (such as Xiris’ XIR-1800) can take snapshots of the weld as well as record full raw or processed video.

A well-designed thermal weld monitoring system has the versatility to adapt to a wide range of welding applications. As with any new technology or system, it’s worthwhile to invest time in setting up a test environment prior to using the system for production-level monitoring and recording.

Testing a Thermal Weld Vision System

It will take some planning to position the camera such that it is in the best possible alignment with the weld head to obtain a high-quality thermal recording of a melt pool. Trial runs with many test pieces are recommended as the camera's placement, angle, and optics are adjusted to capture the best possible details of the melt pool. The factors of the welding process that need to be monitored about their effect on the melt pool will dictate the location and focus of a thermal weld camera. As you fine-tune the camera arrangement, consider these important decision factors:

Camera Location: Metal pool’s leading edge, trailing edge, or both sides.
The position, type, and feed rate of the wire feed can affect the quality of the final weld.
The torch alignment can change the weld.
The possible defects (undercut, lack of fusion, porosity, burn-through, or wet-out fluidity) that can occur.
Other factors like shielding gas interference or material defects which can result in weld defects.

Working with many test pieces will give you an idea of the camera's capabilities and assist in figuring out which camera configuration offers the best information for the areas of the melt pool that need to be monitored. When an optimal method for recording a melt pool has been established, operators may use this information for a variety of welding applications and benefit from real-time monitoring and recording.

Welding image of Preparing to Test a Thermal Camera (Xiris)

Fig. 3: Preparing to Test a Thermal Camera (Xiris)

Benefits of Learning How to Record a Melt pool

There are many advantages to recording a melt pool using thermal weld camera equipment. Regardless of the operator’s visual acuity, a purpose-built thermal weld camera system has the technology and capability to provide a clearer image of the welding process. Camera technology allows the operator to focus on aspects of the process that affect melt pool quality. Whether the purpose of the thermal camera is to record a weld for teaching or learning new techniques, or to monitor the process for quality assurance or operator safety, weld monitoring equipment can become an indispensable tool for welders intent on ensuring the quality and reliability of the work they undertake.

Welding image of An HDR View of the Melt Pool and Torch Tip in a GTAW Process (Xiris)

Fig. 4: An HDR View of the Melt Pool and Torch Tip in a GTAW Process (Xiris)

Summary

Gas Tungsten Arc Welding (GTAW or TIG welding) requires meticulous attention to detail in precise, clean environments. Thermal weld cameras are essential tools that surpass standard cameras by providing detailed images of the melt pool. They ensure high performance in welding operations, boosting safety, quality, and efficiency.