MIG welding nickel and its alloys is a viable option, but it requires careful attention to various technical details and advanced techniques to ensure a successful weld. This comprehensive guide will delve into the nitty-gritty of MIG welding nickel, providing you with a detailed, expert-level manual for a hands-on approach.
Gas Selection for MIG Welding Nickel
When MIG welding nickel, the recommended shielding gas is straight argon. However, when using the MIG spray transfer mode, a gas mixture of argon with 1% CO2 is preferred for applications involving 3 to 6 mm thick materials. This gas mixture provides improved electron transfer and arc stability, effectively reducing the magnetic influence on the arc.
The choice of shielding gas is crucial as it affects the weld pool fluidity, bead appearance, and overall weld quality. Argon, being an inert gas, helps prevent oxidation and maintains a clean weld. The addition of a small amount of CO2 in the gas mixture can enhance the arc stability and penetration, particularly for thicker nickel alloy sections.
It’s important to note that the gas flow rate should be carefully monitored and adjusted to ensure adequate shielding of the weld pool, preventing contamination from atmospheric gases.
Weld Parameters for Nickel Alloys
Image source: Mig weld example
Nickel alloys are generally more sluggish and sensitive to oxidation compared to other metals, which can lead to extensive weld porosity. To mitigate this issue, it is recommended to use low to moderate weld parameters, such as:
- Welding current: 100-200 Amps
- Voltage: 18-24 V
- Travel speed: 15-30 cm/min
These lower weld parameters help minimize the risk of crack sensitivity and excessive oxidation, which can compromise the weld integrity.
It’s crucial to closely monitor the weld pool behavior and make adjustments to the parameters as needed to maintain a stable and controlled weld. Overheating or excessive heat input can lead to distortion, cracking, and other weld defects in nickel alloys.
Ensuring Cleanliness for Nickel Welding
Welding and post-weld heating of nickel alloys should only be carried out on surfaces that are clean and free of contaminants. Effective methods for cleaning the weld areas include:
- Grinding: Using dedicated grinding wheels or discs for nickel alloys to remove any surface impurities or oxides.
- Shot blasting: Utilizing a shot blasting system to clean the weld areas and remove any surface contaminants.
It’s crucial to use wire brushes or power brushes made of stainless steel to avoid introducing any foreign materials or contamination during the cleaning process.
Maintaining a high level of cleanliness is essential to prevent weld defects, such as porosity, inclusions, and cracking, which can be caused by the presence of surface contaminants.
Removing Surface Oxides in Nickel Welding
Surface oxides produced during the high-temperature welding process can be detrimental to the weld quality. These oxides should be removed between each pass during multipass welding. The recommended method for removing nickel alloy surface oxides is grinding.
Grinding the weld area with a dedicated grinding wheel or disc helps to remove the surface oxides and ensure a clean surface for the subsequent weld passes. This step is crucial in maintaining the weld integrity and preventing defects such as lack of fusion or poor bead appearance.
It’s important to note that the use of abrasive tools, such as wire brushes or grinding discs, should be limited to those specifically designated for nickel alloy welding to avoid cross-contamination.
Selecting the Appropriate Filler Material
When MIG welding nickel alloys, it is essential to use a filler material that contains deoxidants, such as aluminum and titanium. These elements help to reduce porosity caused by:
- Oxygen and nitrogen from air entrainment and surface oxides
- Hydrogen from surface contamination
Commonly used filler materials for MIG welding nickel alloys include:
- ERNiCr-3 (AWS A5.14 classification)
- ERNiCrMo-3 (AWS A5.14 classification)
These filler materials are designed to provide good weldability, corrosion resistance, and mechanical properties when joining nickel alloys.
It’s crucial to follow the manufacturer’s recommendations for the specific nickel alloy being welded and ensure the filler material is compatible with the base metal composition.
Maintaining Shielding Efficiency
When using argon as the shielding gas in both TIG and MIG welding of nickel alloys, it is essential to pay close attention to the shielding efficiency of the weld pool. This includes the use of a gas backing system to ensure complete coverage and protection of the weld area from atmospheric contamination.
In TIG welding, the use of argon-hydrogen gas mixtures can help produce cleaner welds by improving the arc stability and weld pool fluidity. The addition of hydrogen to the shielding gas can enhance the arc characteristics and promote better weld bead formation.
Ensuring proper shielding efficiency is crucial in preventing weld defects, such as porosity and inclusions, which can be caused by the introduction of atmospheric gases into the weld pool.
Achieving Proper Weld Fusion
Weld fusion is a primary concern when welding nickel alloys, as these materials can be more sluggish and challenging to fuse compared to other metals. To ensure proper weld fusion, it is essential to:
- Maintain the appropriate weld energy input: Adjust the welding current, voltage, and travel speed to achieve the optimal heat input for the specific nickel alloy and joint configuration.
- Promote an agitated weld pool: Utilize techniques, such as weaving or oscillation, to create an agitated weld pool, which can help improve the wetting and fusion of the base metal.
Proper weld fusion is crucial in preventing defects like lack of fusion, which can compromise the structural integrity and performance of the welded joint.
By following these advanced techniques and paying close attention to the critical details, you can successfully MIG weld nickel and its alloys, ensuring a high-quality and reliable weld.
References:
– Welding of Nickel Alloys
– Welding Steels and Nickel Alloys
– Nickel MIG Wire and Welding Cast Iron
– How to Weld Nickel Alloys
– Weldability of Materials: Nickel and Nickel Alloys
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