Advances in Welding / Joining Process

NanoFoil Joining :

Many joining processes could be performed more effectively and with less damage to surrounding delicate microstructures if a localized and controllable heat source could be placed exactly where required—in the joint itself.

It appears that an innovative material capable of doing just that—NanoFoil—has been developed from long academic research (Livermore Labs) and industrial (RNT) development. It now is being introduced for high-temperature brazing or soldering critical heat management components in electronic applications. Other uses currently are in development for military and space applications.

At the heart of the method is a foil that comprises hundreds of alternate layers of aluminum and nickel, each layer a few nanometers thick. The foil is obtained by vacuum deposition using physical vapor techniques, such as magnetron sputtering and EB evaporation.

When the foil is ignited by one of several means, it develops an exothermal self-propagating reaction at controlled speed and temperature, depending on its exact makeup. This precisely localized heat source can be used for joining applications, in a way similar to other, long-known thermite reactions.

If the foil is sandwiched tightly between preplaced solder or brazing alloy layers deposited on the surfaces of metallic or ceramic elements to be joined together, the localized heat completely melts the filler metals and completes the joining process without heating the adjacent delicate structures.

Although this process seems limited at present to high-tech, demanding applications because of the high cost of the foil, industrial welding of more common material can be envisioned, if the correct forging temperature can be provided locally and a suitable upset pressure cycle can be applied.

Hybrid Laser-Arc Welding :

It may seem misleading to characterize hybrid laser-arc welding (HLAW) as innovative, since the original idea—essentially combining two well-known and -established unrelated processes, laser beam welding and gas metal arc welding—was first proposed almost 30 years ago.

In fact HLAW already has achieved resounding successes in many areas as a demonstrated, mature, and robust welding process. However, it is not yet an off-the-shelf technique. Note: At least one manufacturer does offer a hybrid laser welding head. However, before adopting this equipment, fabricators should investigate if it compares favorably with standard processes in terms of productivity, quality, and economy.

For each potential industrial hybrid laser-arc welding application, a specific procedure with optimized hardware and control capability has to be developed and tested, quality has to be assessed, and the economic advantage has to be validated.

It appears that the feasibility study alone is a major and costly project, and probably is the main deterrent to a larger acceptance. Researching and planning this solution for specific applications may seem daunting to all but established and resourceful industrial operations.

Another reason likely to limit a larger acceptance is that the high number of parameters to control to manage the combined processes is more feasible for a research institute’s capabilities than a manufacturer’s.

As stated in the conference paper “Recent progress and innovative solutions for laser-arc hybrid welding” by Dirk Petring and Christian Fuhrmann, “In spite of the simplicity of the basic idea of hybrid welding, the technical rules of arranging laser and arc in a proper way are quite complex, and their understanding is indispensable, if the full benefit of hybrid is to be realized.”

An overview HLAW for shipbuilding was presented in the article “Shipyard uses laser-GMAW hybrid welding to achieve one-sided welding” on thefabricator.com in 2003.

The benefits of HLAW exceed the advantages laser welding and GMAW offer individually. These benefits are:

• Welding from one side
• Increased tolerance to small but variable gap in joint fit-up
• Increased penetration
• Reduced filler metal
• Higher welding speed                                            
• Higher productivity
• Lower net heat input
• Reduced distortion
• Improved microstructure and properties
• Improved weld quality and process reliability