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TIG welding aluminum: What you need to Know

Plain ol Bill
17 Min Read
Professional TIG Welding Engineers Need to Learn to Control the Melt Pool
Professional TIG Welding Engineers Need to Learn to Control the Melt Pool

Manufacturing products using aluminum offers numerous advantages, such as extended part life, reduced weight, and enhanced integrity in cold temperatures. This makes aluminum an ideal choice for various applications, including truck and trailer manufacturing, cryogenic piping, and boat components.

Tips for sound, aesthetically pleasing welds

Welding Town

However, welding aluminum comes with its own set of challenges, including controlling heat input and dealing with the oxide layer that forms on the metal’s surface. Gas tungsten arc welding (GTAW), also known as TIG welding, has long been considered the preferred process for welding aluminum due to its ability to provide high weld integrity and an appealing appearance.

Achieving high-quality welds and the desired stacked-dimes appearance when welding aluminum with GTAW requires practice and skill. Following key best practices can greatly contribute to successful results.

Overcoming the Challenges of TIG Welding Aluminum

Gas tungsten arc welding (GTAW), or TIG welding, is known for its slower welding speed compared to other processes like gas metal arc welding (GMAW), or MIG welding. While GTAW may not be the go-to choice for high-production manufacturing, it shines in aluminum welding applications where the focus is on achieving superior quality and appearance rather than maximizing productivity.

One of the key differences between GTAW and GMAW is the way filler metal is added during the welding process. In GMAW, the filler metal is automatically fed into the weld puddle as soon as the welder activates the gun trigger. This quick introduction of filler metal can create “cold starts,” which may result in incomplete fusion and insufficient penetration, leading to weaker welds.

On the other hand, GTAW provides more control over the addition of filler metal. The welder can establish the weld puddle first, ensuring proper penetration before introducing the filler metal. This control over the filler metal addition adds complexity to the process and demands a higher level of operator skill compared to GMAW.

The ability to control the filler metal addition and the welding process’s slower speed make GTAW an excellent choice for aluminum welding projects that prioritize weld quality and appearance over production speed.

Proper heat input is a crucial factor in achieving successful aluminum welding with GTAW (TIG welding). Aluminum’s high thermal conductivity means that the heat from the weld puddle can dissipate quickly, making it necessary to apply a significant amount of heat to establish the weld puddle. However, it is equally important to control the heat to avoid issues like a runaway puddle or burn-through.

The heat in welding is determined by the combination of amperage and voltage. Higher arc voltage means more power is being delivered to the workpiece. Welding with a longer arc can increase the arc voltage, leading to more heat being produced. However, a longer arc also heats a larger area of the material, which can result in a runaway puddle that grows rapidly and may cause weld defects.

To prevent a runaway puddle and maintain control over the heat input, it is recommended to use a shorter arc length. By reducing the arc length, the heat is concentrated in a smaller area, allowing for better control of the weld puddle and preventing overheating of the workpiece.

In addition to controlling the heat input, here are some other tips to optimize the results when welding aluminum with GTAW.

Use the Right Polarity

Many welders, especially those who are new to aluminum welding, may not be aware that aluminum generates an oxide layer. This oxide layer appears as a dull silver color and is not as visible as red oxidation (rust) on steel. Additionally, the melting point of aluminum oxide is about three times higher than the melting temperature of the base material.

To achieve successful aluminum welding, it is crucial to clean the oxide layer before starting the welding process. This can be done using a dedicated stainless steel wire brush or a carbide cutter to remove the oxide from the surface. However, even with proper cleaning, the oxide layer begins to reform immediately, which can obstruct the welder’s view of the weld puddle.

To address this challenge, it is critical to use alternating current (AC) polarity when using the GTAW (TIG) process on aluminum. With AC polarity, the direction of current flow continuously changes during the weld. This AC polarity provides a cleaning action that helps to remove the oxide layer on aluminum, allowing the welder to see the molten weld pool clearly.

By using AC polarity, welders can improve their visibility of the weld puddle and ensure better control over the welding process. This allows for cleaner and more precise welds, contributing to the overall quality and appearance of the final weld on aluminum materials.

Adjust the Balance Control in Aluminum Welding

Setting the proper balance control is another crucial step in achieving a good aluminum weld. When welding in AC polarity with the GTAW process, there are two portions of the welding cycle: electrode-negative (EN) and electrode-positive (EP). EN is considered the welding side of the AC waveform, while EP is where the cleaning or oxide removal occurs.

Modern welding equipment provides a balance control feature that allows you to adjust the ratio between EN and EP based on what you observe in the weld puddle.

In the past, older equipment had a balanced 50-50 ratio of EN and EP. However, many modern GTAW power sources come with a factory preset balance control of 75 percent EN to 25 percent EP. If you notice small black flecks (peppering) in the weld puddle during welding, it indicates that the balance control is not adjusted properly. To address this, you can turn the balance control down, reducing the EN and increasing the EP. This adjustment helps to remove more oxide during welding and should reduce the occurrence of peppering.

When welding material that has been in service or exposed to the elements and has a thick oxide layer that wasn’t entirely removed during material preparation, you may need to turn the EN down to provide more cleaning action.

However, using a lower balance setting (more EP) puts the majority of the heat on the tungsten electrode, which can cause the tungsten tip to ball back. This can affect your ability to control the arc direction and placement of the weld.

It’s essential to note that adjusting the balance control does not replace the need for proper material preparation and cleaning when welding aluminum. Proper cleaning and preparation are still necessary to achieve high-quality welds on aluminum materials. The balance control serves as an additional tool to optimize the welding process and ensure the best results when working with aluminum.

Set the AC Output Frequency

Another important factor that contributes to easier weld placement in aluminum welding with GTAW is the AC output frequency. This setting can be adjusted on modern welding power sources and should not be confused with high-frequency arc starting, which is relevant only for initiating the arc.

The AC output frequency refers to how many times per second the power source switches polarity. Older GTAW power sources typically operate at 60 hertz, determined by the input power. However, modern equipment often comes with a factory preset of 120-Hz output frequency.

The AC output frequency significantly influences the stability and characteristics of the welding arc. A higher AC output frequency, such as 120 Hz, results in a more stable and tighter arc column. This enhanced stability allows for better directional control, making it easier to weld in tight spaces and achieve precise welds without the arc wandering.

Conversely, lowering the AC output frequency to around 80 or 90 Hz creates a wider arc cone. This broader arc cone can be advantageous when welding outside corner joints or in situations where a wider weld bead is desired.

Selecting the appropriate AC output frequency depends on the material thickness and the welding requirements. For thin materials that demand accurate weld placement and the prevention of overheating or burning through, an output frequency of 150 to 250 Hz is recommended. On the other hand, when welding thicker materials (around 3⁄8 inch and thicker), using a low AC frequency of 80 to 120 Hz is more suitable to achieve a wider weld bead profile.

By adjusting the AC output frequency according to the specific welding needs, welders can achieve better control over the welding process and produce high-quality welds on aluminum materials.

Use Appropriate Amperage

In gas tungsten arc welding (GTAW), the amperage is typically controlled using a foot pedal or fingertip control. However, it is essential to set the appropriate maximum amperage on the welding equipment to ensure proper welding performance. When working with aluminum GTAW, a useful rule of thumb is to use 1 amp for every thousandth (0.001) of material thickness. For instance, welding a base material that is 1/8 inch (0.125 inches) thick would require approximately 125 amps.

As the base material thickness exceeds 1/4 inch, the rule of thumb starts to deviate, and less amperage is needed. For example, you can weld 3/8-inch material with a 280-amp power source.

It’s important to note that joint geometry also plays a role in determining the necessary amperage. When welding a T-joint, the heat can flow in three directions due to the configuration, compared to a butt joint where the heat can only flow in two directions. As a result, a T-joint generally requires more heat input to achieve proper penetration and fusion.

By appropriately adjusting the amperage based on the material thickness and joint geometry, welders can ensure optimal heat input during aluminum GTAW welding. This attention to detail helps achieve high-quality welds and reliable results.

Set the AC Amperage Independently

Some modern welding power sources offer the capability to set the AC amperage independently, which provides greater control over penetration and productivity in gas tungsten arc welding (GTAW).

With this feature, welders can increase the amperage during the electrode-negative (EN) portion of the AC cycle to achieve deeper penetration in the weld. Higher amperage is generally associated with increased penetration.

This independent AC amperage control is particularly useful in higher-amperage applications, where lower amperage may be sufficient during the electrode-positive (EP) cycle for oxide cleaning, but higher amperage is desired during the EN cycle for better penetration.

By setting the AC amperage independently, welders can avoid the need to use larger tungsten electrodes, as most of the heat is focused on the tungsten during the EP cycle. This helps maintain the desired tungsten geometry and allows for more precise welding.

It’s important to understand that the balance control and independent AC amperage control serve different purposes. Adjusting the balance control influences the level of oxide cleaning during welding, while adjusting the AC amperage can enhance penetration while keeping the tungsten geometry intact.

Having these advanced features in a welding power source empowers welders to tailor their settings for different welding tasks, leading to improved welding performance and better overall results.

Add Filler Metal for the Stacked-dimes Look

To achieve the desirable stacked-dimes appearance when welding aluminum with gas tungsten arc welding (GTAW), one effective technique is to add more filler metal during the welding process.

Filler metal, which is in solid form, is consumed into a molten liquid during welding. This process requires energy, similar to how adding ice cubes to hot water results in the ice melting but also cooling the liquid.

The same concept applies to adding filler metal in GTAW. By introducing more filler rod into the weld puddle, it creates a cooling effect on the back side of the puddle, contributing to the formation of the stacked-dimes appearance in the finished weld. Adding more filler metal with each application produces a more pronounced stacked-dimes pattern, while using less filler metal results in a smoother appearance.

While it’s not mandatory, some welders use the foot pedal to vary the amperage during welding, which can also aid in achieving the desired stacked-dimes look. Different welders may employ various techniques, but the ultimate goal is to achieve similar aesthetically pleasing results in the weld.

Mastering the art of creating the stacked-dimes appearance in aluminum welding with GTAW requires practice, skill, and a good understanding of how filler metal interacts with the weld puddle. It adds a touch of craftsmanship to the welding process and often results in visually appealing welds.

Prioritize Safety When TIG Welding Aluminum

Although gas tungsten arc welding (GTAW) is known for its clean process with minimal spatter, it is essential to prioritize safety by wearing appropriate personal protective equipment (PPE). When welding aluminum, which is highly reflective and demands substantial welding energy, the intensity of the GTAW arc can cause sunburn on exposed skin.

To ensure safety and prevent potential harm, welders should wear safety glasses, a welding jacket, gloves, and a welding helmet. The welding helmet plays a crucial role in allowing the welder to clearly see the welding arc and puddle while protecting their eyes from harmful radiation.

Considering advancements in helmet technology, welders can opt for modern autodarkening helmets that offer improved visibility and clarity of the weld pool. These helmets use innovative features that allow more colors to pass through the lens, providing better contrast among objects in the viewing area.

By using such technology, welders can achieve better welding results while minimizing eye strain and fatigue. Enhanced visibility enhances the welder’s ability to precisely control the welding process and produce high-quality welds on aluminum and other materials.

Remember, safety is of utmost importance when engaging in any welding process, and using proper PPE and advanced helmet technology helps ensure a safe and productive welding experience.

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