Advanced Technologies

Advances In Welding Technologies  	Six welding innovations to keep an eye on 	By Chris Conrardy
Welding technologies continue to evolve and improve, bringing to the forefront of the industry new innovations. EWI, the Edison Welding Institute, is dedicated to the research and development of materials joining and welding and assists members in the aerospace, automotive, government, energy and chemical, heavy manufacturing, medical and electronics industries. Below are six welding innovations that EWI is developing or are in the R&D phase.

friction stir welding  
Friction stir welding is now being used with hard metals such as steel and titanium alloys. FSW can achieve full penetration on thick sections (up to 1.5″) of aluminum in a single pass.  

Friction Stir Welding of Hard Metals
Friction stir welding (FSW) offers many advantages commonly found with other solid-state welding processes, including little distortion and weld shrinkage, reduction in consumable costs, property improvements, consistency and automatic operation. Over the last few years, the technology has been pushed to new heights. Not only can FSW be used to weld thick sections (up to 1.5 in.) of aluminum alloys in a single pass, but it is being used with hard metals, such as steel and titanium alloys.

As the tool material and design concepts for hard metals matures, engineers are developing a variable penetration tool, which can be retracted without leaving an exit hole. In order to use FSW on increasingly thicker sections of hard metals, refractory-metal tools were developed that meet the strength requirements for welding thick-section, high-strength structural steels. EWI has developed both single-sided (one-pass) and two-sided (two-pass) welding procedures for high-strength steels up to 0.750-in. thick. EWI has several different FSW applications for both titanium and steel nearing production, and many more in development and under consideration. In addition, this work is being extended to nickel-base alloys.

High-Power Hybrid Laser Arc Welding
Hybrid laser arc welding (HLAW), increasingly referred to simply as hybrid welding, is a high productivity welding process that combines the benefits of laser welding and gas metal arc welding (GMAW). As compared with conventional arc welding, this technology allows higher travel speeds and deeper

  high-power hybrid laser
  This high-frame-rate camera capture of laser-leading hybrid laser arc welding illustrates the laser keyhole and GMAW wire in the same weld pool.

penetration, lower heat input and less distortion, and less filler metal usage for a given thickness. As compared with conventional autogenous laser welding, hybrid welding provides greater gap tolerance as well as alloying and joint filling capabilities.

A great deal of hybrid welding work is being done with a focus on the application of a high-power (15 kW) fiber laser for deep penetration and high-speed hybrid welding. One effort involved developing a hybrid pipeline girth welding system by integrating off-the-shelf GMAW and fiber laser welding equipment. EWI engineers demonstrated the orbital welding system outdoors, with all of the equipment powered by a diesel generator to show the portability of the technology. Another important project involved characterizing the effects of multiple process variables to optimize welding of thick-section high-strength steel, aluminum and titanium alloys. High-speed video, non-destructive evaluation and mechanical testing are being used to assess process stability, weld integrity and properties. Custom laser optics and control strategies were tested to optimize the hybrid welding performance and weld quality for particular applications.

Resistance Weld Repair
Resistance welding processes employ large electrical currents and forces to heat the joint and produce a weld.

Resistance Weld Repair
Side view of resistance welding hole repair on 1.8mm Ti 6-4 sheet, post weld

This technology is being advanced for use as a repair process. These developed approaches have aerospace and other heavy manufacturers considering the advantages of resistance weld repair over previous techniques.

One exciting example is a resistance weld repair technique for bolt or rivet holes in aluminum, titanium and superalloys. Compared to manual arc welding repair processes, resistance weld repair does not require skilled operators or special techniques to achieve acceptable weld quality. Compared to friction plug welding, resistance weld repairs can be done on almost any location of a part and requires very little support tooling. The resistance weld repair technique also significantly reduces distortion, thanks to balanced heating and melting about both the neutral axis of the hole and the flange or sheet being repaired. Because matching filler metal slugs can be used, the repaired area properties more closely match that of the base material.
One method, known as conductive heat resistance welding, is particularly well-suited for weld repair of aluminum alloys. The method uses cover sheets made from a material having a higher electrical resistance and melting point to concentrate the resistance heating on the aluminum surface.

  dissimilar materials joining
  Magnetic pulse welding diagram for joining tubular members

Dissimilar Materials Joining
Joining of dissimilar materials is of increasing importance to many industry sectors. EWI has been investigating methods to join various dissimilar combinations of metal alloys, polymers, ceramics and composites for particular applications.

For the automotive industry, government regulations and marketplace demands are forcing the automotive industry to develop frame structures that are stiffer, lighter weight, and offer improved crush resistance. To achieve this, frame designs are incorporating thinner and higher strength steels, as well as aluminum alloys. Successfully joining aluminum to steel will be critical to achieving the designed performance.

Two solid state welding processes—magnetic pulse welding (MPW) and friction welding (FW)—were evaluated for joining aluminum to steel tubular members. MPW is particularly well suited for joining thin tubular materials, while FW is capable of welding larger diameters and thicker sections. EWI engineers built a prototype next-generation automotive frame using MPW to successfully join thin (<2 mm) aluminum tubes to steel nodes throughout the frame. Other processes, such as resistance welding and precision GMAW, were used to produce similar metal joints in the frame structure. FW techniques have been developed that are suitable for producing aluminum to steel welds in pipe with wall thicknesses over 10 mm. Tensile testing was used to evaluate FW joint strength, and joint efficiencies of up to 90 percent were achieved.

screen shot  
Screen capture of spot weld inspection interface  

Inspection of Resistance Spot Welds
Phased array (PA) ultrasonic testing (UT) is an advanced non-destructive evaluation (NDE) method that has applications in inspection of structures and welds. Recent work has been done to determine if PA-UT can be used to reliably inspect resistance spot welds in advanced high-strength steel (AHSS) sheet. An improved NDE method is needed for this application because destructive testing is expensive and unreliable, and conventional NDE methods can be slow and incapable of reliably assessing weld size and quality.
Engineers at EWI have developed and validated 2-D matrix PA-UT technology for reliable inspection of resistance spot welds in various thicknesses of AHSS sheet. They used ultrasonic modeling and simulation to design high-frequency 2-D matrix PA probes. Prototype probes were built and used during the experimental validation phase. A classification algorithm was developed that would identify stuck welds with a high degree of accuracy. Experiments on thin gauge material (0.7 mm) showed that the algorithm provided real-time identification of good versus stuck welds with a probability of detection (POD) of 98 percent. POD was increased to 100 percent when operator input was added to the classification step. Similar results were obtained for thicker spot weld samples.

Additive Manufacturing
Additive manufacturing is a family of technologies used to produce net-shape components by successive build-up of materials. Additive manufacturing technologies can potentially revolutionize many sectors of U.S. manufacturing by reducing component lead time, cost, material waste, energy usage and carbon footprint. Additive manufacturing will enable improved product designs not producible with conventional manufacturing processes.

  test machine
  Test machine evaluates the feasibility of ultrasonic additive manufacturing of advanced, high-strength alloys.

Various processes are being studied for additive manufacturing. One unique capability being developed is very high power ultrasonic additive manufacturing (VHP-UAM). The process deposits successive layers of strip materials using a solid-state welding process to produce net-shapes. The latest machine design has a working envelope of about 2 meters by 2 meters by 1 meter tall. The very high power levels allow a range of metal alloys to be deposited, including stainless steel, titanium, copper and high-strength aluminum alloys. The process can produce net-shapes with internal cooling channels or embedded materials. Ongoing research involves developing a better understanding of UAM bonding mechanisms for different materials to optimize processing procedures.

EWI recently formed an Additive Manufacturing Consortium involving industrial end-users, suppliers, universities and government agencies to advance the manufacturing readiness of a range of additive technologies.

Gases and Welding Distributors Association
Chris Conrardy Meet the Author
Chris Conrardy is vice president for technology and innovation at EWI, an engineering and technology organization dedicated to materials joining and allied technologies located in Columbus, Ohio, and on the Web at www.ewi.org.