Welding and Leak Testing of Aluminum Honeycomb Panels

[KVARM]

I'm seeking insights and experiences on the welding and leak testing of thin aluminum honeycomb panels. Specifically, the panels are 45mm x 0.9mm thick with a 19mm cell core that is 0.06mm thick.

The panels are joined to an extrusion frame through welding and subsequently leak-tested. We have observed a gap between the extrusion and honeycomb panel, allowing for free airflow and enabling leak detection at vertical joints (corner junctions). However, the overlap of the panel and extrusion at horizontal joints creates a potential challenge for leak testing due to the presence of the honeycomb core.

Leak Testing:
Is leak testing of horizontal joints necessary or feasible given the potential airflow obstruction?
What leak testing methods are suitable for both vertical and horizontal joints?
How can airflow be optimized for effective leak detection?

Welding Techniques: What methods are best suited for thin aluminum honeycomb panels? How can heat input be managed to prevent core damage?

Any advice or experience in handling similar challenges would be greatly appreciated.

Thanks in advance,

 

[BEMPE16524]

Leak Testing of Honeycomb Panels

1. Leak Testing Feasibility for Horizontal Joints:

Airflow Obstruction Concerns: Given the presence of the honeycomb core, leak testing horizontal joints can indeed be challenging due to potential airflow obstruction. The core's structure may restrict air movement, making it difficult to detect leaks.
Necessity of Testing: Leak testing of horizontal joints may still be necessary depending on the application and required integrity of the structure. If these joints are critical to the overall seal, alternative methods or careful attention to test setup can be employed.

2. Suitable Leak Testing Methods:

Pressure Decay Testing: This method can be adapted for both vertical and horizontal joints. By sealing off sections of the panel and pressurizing them, you can monitor for any pressure drop indicative of a leak.
Helium Leak Testing: Helium is often used due to its small atomic size and ability to detect even tiny leaks. For horizontal joints, injecting helium on one side and using a mass spectrometer on the other can be effective, though the honeycomb core may require careful sealing and isolation.
Vacuum Box Testing: This method can be applied to flat surfaces and might be suitable for horizontal joints. A vacuum box is placed over the joint, and any leakage is detected by observing bubbles in a soap solution applied to the joint.

3. Optimizing Airflow for Leak Detection:

Ventilation and Channeling: Ensuring that there are clear paths for airflow within the honeycomb core or along the joints is critical. You may need to introduce small vent holes or channels that allow air or testing gases to flow freely during the test.
Selective Sealing: During the testing process, selectively sealing certain areas to focus the test on specific joints can help improve the accuracy of leak detection.
Welding Techniques for Thin Aluminum Honeycomb Panels

1. Suitable Welding Methods:

TIG Welding (GTAW): Tungsten Inert Gas (TIG) welding is a common method for thin aluminum, offering precise control over heat input. It's particularly useful for avoiding damage to the delicate honeycomb structure.

Laser Welding: Laser welding provides a high degree of precision with minimal heat input, making it ideal for thin materials like aluminum honeycomb panels. It allows for localized welding without extensive heat-affected zones.

Friction Stir Welding (FSW): This method involves using a rotating tool to join the materials without melting them. FSW is effective for thin panels and minimizes distortion or core damage.

2. Managing Heat Input to Prevent Core Damage:

Use of Backing Bars: Placing a backing bar or heat sink behind the weld area can help absorb excess heat, reducing the risk of damage to the honeycomb core.
Intermittent Welding: Applying welds in short bursts with cooling intervals can prevent overheating. This method is particularly effective with TIG welding.
Preheating: Preheating the material slightly can help control the cooling rate and reduce thermal stress, though it must be done carefully to avoid weakening the honeycomb structure.


If you're looking for authoritative sources, the following could be relevant for further reading:

ASM Handbook, Volume 6: Welding, Brazing, and Soldering – Provides comprehensive information on welding techniques, including those for aluminum and thin materials.
AWS D1.2/D1.2M: Structural Welding Code – Aluminum – This code covers welding requirements for aluminum structures, which may include techniques applicable to honeycomb panels.
ASNT (American Society for Nondestructive Testing) Leak Testing Handbook – Offers detailed information on various leak testing methods, including pressure decay and helium leak testing, which can be adapted for specialized applications.
Aluminum Design Manual by The Aluminum Association – This manual includes guidelines for working with aluminum, including joining and testing procedures.
These resources provide the technical foundations for the methods discussed and would offer more detailed and standardized procedures.



R.Efendy