Aluminium welding, most commonly performed using the Tungsten Inert Gas (TIG) or Metal Inert Gas (MIG) processes, requires specific techniques and settings due to the unique properties of aluminium. TIG welding provides precise control, making it ideal for thinner materials and intricate work, while MIG is faster for thicker sections.
This guide focuses primarily on the TIG welding process for aluminium, incorporating insights into electrode placement for effective filler metal addition.
Understanding Aluminium Welding
Aluminium is challenging to weld because it:
- Has a low melting point.
- Transfers heat rapidly.
- Forms an insulating oxide layer that melts at a much higher temperature than the base metal.
- Can easily absorb hydrogen, leading to porosity in the weld.
Proper preparation, machine setup, and technique are crucial for successful aluminium welding.
Essential Equipment for TIG Welding Aluminium
- TIG Welder: Requires AC (Alternating Current) output to break through the aluminium oxide layer. Many modern machines offer AC balance and frequency control.
- Tungsten Electrode: 2% Ceriated, 2% Lanthanated, or Zirconiated tungsten are common choices. Pure tungsten used to be popular but is less common now. Ensure the tip is balled or slightly rounded (for older machines or lower AC frequency) or pointed/truncated cone (for modern machines with higher AC frequency and balance control).
- Filler Metal: Choose an aluminium filler rod compatible with the base aluminium alloy (e.g., 4043 or 5356 are common).
- Shielding Gas: Pure Argon (Ar) is the standard shielding gas for TIG welding aluminium.
- Safety Gear: Welding helmet, gloves, jacket, etc.
TIG Welding Aluminium Process Steps
Successfully TIG welding aluminium involves several key stages:
-
Preparation:
- Cleanliness: This is paramount. Aluminium must be meticulously cleaned of all grease, oil, paint, and the oxide layer. Use a stainless steel brush dedicated only to aluminium and a solvent like acetone. The oxide layer reforms quickly, so weld soon after cleaning.
- Fit-up: Ensure parts fit together well with minimal gaps. Bevel thicker sections (>1/8") for full penetration.
- Preheating (Optional but Recommended for Thicker Sections): Preheating (typically 250-350°F) can help reduce cracking and improve penetration on thicker or complex parts.
-
Machine Setup:
- Polarity: Set the machine to AC (Alternating Current). The AC cycle provides both penetration (electrode positive) and cleaning action (electrode negative).
- Amperage: Set your initial amperage based on the material thickness and joint type. Start slightly higher than estimated as aluminium dissipates heat quickly.
- AC Balance: This setting controls the ratio of electrode positive (cleaning) to electrode negative (penetration). More cleaning action helps remove the oxide layer but puts more heat on the tungsten. Find a balance that provides sufficient cleaning without overheating the tungsten.
- AC Frequency: Higher frequency creates a tighter, more focused arc, which can improve control and bead appearance.
- Gas Flow: Set argon flow rate (e.g., 15-25 CFH depending on cup size and draft).
-
Welding Technique:
- Arc Start: Use a foot pedal or hand control to start the arc. The high-frequency start helps initiate the arc without touching the material.
- Establish the Puddle: Hold the arc on the joint until a molten puddle forms. The cleaning action will be visible as a bright white area around the puddle.
- Adding Filler Metal: Once the puddle is established and wide enough, you can add filler metal.
- Introduce the filler rod into the leading edge of the molten puddle.
- According to welding techniques, one method involves pointing the tip of the electrode right at the top of the little point that's going to be used for filler metal. This directs the arc energy efficiently towards where the filler will melt into the puddle.
- Feed the rod smoothly as needed, withdrawing it before breaking the arc but keeping it within the gas shield to prevent oxidation.
- Moving Along the Joint: Advance the arc smoothly along the joint, maintaining a consistent puddle size. Add filler metal rhythmically as you move.
- Torch Angle: Maintain a slight push or drag angle (usually 10-20 degrees from vertical).
- Arc Length: Keep a short arc length for better heat concentration and shielding.
- Finishing: Slowly taper off the current using the foot pedal or control at the end of the weld to prevent crater cracking.
Common Techniques in TIG Aluminium Welding
Different techniques are used depending on the joint and material thickness:
- Dab/Dip Method: The most common method, where the filler rod is repeatedly dipped into the leading edge of the puddle.
- Pushing the Puddle: Often preferred for fillet welds, moving the arc forward while adding filler.
- Walking the Cup: A technique where the ceramic cup is rested on the material and rocked back and forth to control arc movement, often used for pipe welding or tight spaces.
Troubleshooting Common Aluminium Welding Issues
| Issue | Cause | Solution |
|---|---|---|
| Porosity | Contamination (oil, water, oxide), hydrogen absorption, insufficient shielding gas | Thorough cleaning, proper gas flow, correct filler metal, preheating |
| Cracking | Wrong filler metal, rapid cooling, joint restraint | Use appropriate filler alloy (e.g., 4043 for crack resistance), preheat, slower cooling |
| Lack of Penetration | Low amperage, incorrect travel speed, poor joint fit-up | Increase amperage, slow down travel speed, improve fit-up |
| Excessive Cleaning Band | Too much AC balance (too much electrode positive) | Reduce AC balance setting |
| Tungsten Contamination | Dipping tungsten in puddle/filler, wrong tungsten type, incorrect polarity (DC- on AC) | Adjust technique, use correct tungsten, check polarity, increase AC balance if needed |
By focusing on meticulous preparation, proper machine setup, and refining your technique – including specific electrode placement like pointing the tip towards the filler metal feed point – you can achieve strong and clean aluminium welds.
