Equipment Furthers Welding Research Discoveries
The work welding researchers do requires the use of a variety of specialized equipment in addition to power sources, wire feeders, filler metals, shielding gases, lasers, robots, computer numerical controls, and other more or less commonplace types of welding equipment and consumables. Depending on their areas of interest, researchers need equipment that can, among other things, simulate the conditions that occur during welding, see into the welds and base metals, monitor the welding process, and test the welds for a variety of conditions. The goal of these researchers’ work is to not only add to the body of knowledge about welding in general, but also discover solutions to problems and develop methodologies that will eventually find their way out of academia or government laboratories and into the private sector. The Welding Journal asked some prominent researchers to detail some of the special equipment they use and why they are useful, outline breakthroughs accomplished, and for their equipment “wish list.” Lehigh University The research at Lehigh University, Lehigh, Pa., “addresses fundamental issues of weldability and properties — mechanical properties and corrosion resistance — of fusion welds in advanced engineering alloys,” explained John N. DuPont, the R. D. Stout Distinguished Professor of Materials Science & Engineering and Associate Director of Lehigh’s Energy Research Center. “Our group also conducts research in additive manufacturing. Much of our research is conducted through the National Science Foundation Manufacturing and Materials Joining Innovation Center (M2aJIC),” for which DuPont is the Lehigh site Director. The university’s welding-related facilities and infrastructure are concentrated in six areas: microstructural characterization; thermal analysis, heat treating, high-temperature corrosion; mechanical testing; additive manufacturing; and microstructural modeling. “The Electron Microscopy Laboratory at Lehigh University houses one of the most advanced suites of electron microscopes in the world and includes four scanning electron microscopes two transmission electron microscopes, two scanning transmission electron microscopes (STEMs), one focused ion beam instrument, and an electron microprobe,” DuPont said. The pride of the facility is a JEOL JEM-ARM200CF aberration-corrected STEM, a state-of-the-art instrument purchased through a National Science Foundation MRI grant. The university also houses a modern light optical microscopy lab with a full range of reflection, transmission, polarized light, dark field, bright field, and Nomarski optical microscopes, as well as a Leco 2001 quantitative image analyzer. DuPont manages a complete welding laboratory with equipment for arc and laser welding, preparation of experimental alloys, weldability testing, and welding simulation. The lab also houses a Gleeble 3500 high-temperature thermo-mechanical simulator for a wide range of welding simulation and phase-transformation studies (see boxed item). In addition, DuPont said, “The Gleeble system has a high-speed dilatometer that is ideally suited to detect and measure phase transformation temperatures under the high heating and cooling rates associated with welding.” Also available is a varestraint tester for solidification cracking studies and a Thermonetics welding calorimeter for conducting transfer efficiency measurements. According to DuPont, the university has made a significant investment in developing a state-of-the-art Additive Manufacturing (AM) laboratory. Students, faculty researchers, and staff have access to this centralized facility. “The facility has capabilities for all major forms of additive processes,” DuPont explained. “As a central campus facility for AM, the laboratory also serves as a site for industry partners to learn about applications for AM technologies. The LU AML has facilities for vat polymerization, direct metal deposition, powder bed fusion, binder jetting, material jetting, and direct metal deposition.” DuPont emphasized the increasingly important role microstructural modeling plays in welding and AM research, stating it is used in nearly every project. “The modeling results are critical for more efficient design of experiments, interpreting experimental results, and designing new alloys with improved microstructures and properties. Through its current membership at the Lehigh M2aJIC site, ThermoCalc (Canonsburg, Pa.) provides Lehigh with the full suite of ThermoCalc and DICTRA software tools for conducting thermodynamic and kinetic simulations in multicomponent systems. In addition, ThermoCalc provides updated databases as they become available and provides technical assistance and mentoring of graduate students as they encounter new modeling challenges.” The university also has the MatCalc, Sysweld, and SOAR programs for conducting kinetic and heat flow simulations. Breakthroughs. Significant discoveries have recently been made in two areas that explained why premature failures occur in two types of high-temperature materials: dissimilar welds involving 9Cr alloys, and premature creep rupture failure in the new nickel-based Alloy IN740H. “These breakthroughs would not have been possible without Lehigh’s advanced electron microscopy laboratory and modeling capabilities,” according to DuPont. Wish List. “Lehigh University currently collaborates with Northwestern University (NU) where NU conducts local electrode atom probe (LEAP) tomography. Lehigh would very much like to have a LEAP instrument of its own.” University of Kentucky Dr. YuMing Zhang’s work focuses on sensing and control of arc welding processes. Zhang is the James R. Boyd Professor in Electrical Engineering and director of the Welding Research Laboratory, Institute for Sustainable Manufacturing and Dept. of Electrical and Computer Engineering, University of Kentucky, Lexington. For the work he and his colleagues perform, they need welding power sources and wire feeders that can receive analog signals to control their outputs, high-speed cameras, and welding robots whose motion/trajectory can be controlled/adjusted in real time rather than being preprogrammed. Easy adjustment is key, Zhang explained. With regard to the power sources and wire feeders, “We need to easily adjust the welding parameters to adaptively control the welding process based on the feedback from the process.” For the robot, parameters such as speed, torch orientation, and torch position must be adjusted. High-speed cameras allow them to observe and analyze the welding process at the speeds they need. Breakthroughs. “We have developed a human-robot collaborative system where the robot follows the motion of a torch operated by a human welder,” Zhang explained. “In this case, the motion of the human welder is not planned in advance. We use a sensor to track the torch’s motion and command the robot to follow the motion in real time.” The robot Zhang’s group uses is a UR 5 from Universal Robots USA, Inc., East Setauket, N.Y. He prefers this robot because most industrial robots do not allow their motion to be changed in real time, but Universal Robots do. “Using this human-robot collaborative system, we can allow the robot to carry sensors to see the welding process. The measurement from the sensors can be displayed to the human welder and the human welder can adjust the welding parameters per the display. The adjustment will be realized by the robot. As such, the human welder will not carry sensors such that he can operate freely to adjust the welding speed and torch orientation per the feedback of the welding process. We will be able to record what the welder sees and how the torch responds to that to analyze how the welder operates,” Zhang explained. LeTourneau University The lab at LeTourneau University, Longview, Tex., contains a variety of specialized equipment such as a microwave welding machine, short-circuit detector, high-speed cameras, and infrared cameras. However, the school’s modified DSI Gleeble® 1500 thermal-mechanical simulator plays an important role in much of the work as does varestraint testing equipment. Professor Yoni Adonyi holds the Omer Blodgett Chair of Welding & Materials Joining Engineering at LeTourneau and is also Materials Joining Engineering Program Coordinator. According to Adonyi, “The main focus of our research has always been simulating welding and other manufacturing processes by ‘deconstructing’ the thermal and mechanical processes involved using the Gleeble. After collecting real data from welding processes, we feed them into the Gleeble software and simulate different processes by ‘reconstructing’ them, using different heat inputs, etc., without making any welds.” They focus their energies on finding mechanical, physical, and other properties under dynamic conditions such as high heating and cooling rates, or strain rates. Adonyi desribes physical simulations as the “missing link” between numerical simulations and real life. To illustrate what he means, he said, “Most computer models are inaccurate because they use static or not time-dependent material properties from handbooks (for example, slowly heating samples to high temperatures and then measuring their strength by slowly pulling on them). In reality, in welding and forging processes, heating rates of hundreds of degrees per second and strain rates of many feet/second occur and properties change dramatically. “To illustrate this difference, a steel heated to 1000°F can elongate like chewing gum when slowly pulled, reaching almost 100% elongation and no strength. On the other hand, if pulled at 3 ft/s, the same steel breaks like glass with no elongation or close to 0% and considerable strength. The Gleeble is able to produce these dynamic properties, and if we feed those results into computer models, they become more accurate.” In the case of the LeTourneau group, they did compressive loading and measured the deformation rates at different temperatures, then fed the data into a high-frequency (forge) weld model. Similarly, they found changes in the Curie temperature (the temperature at which ferromagnetic materials lose their magnetic properties on heating vs. cooling) as a function of heating rates. Recently, a U.S. patent was issued to Adonyi, Baylor University Prof. Seung Kim, and former students Ithamar Glumac and Allen Worcester for a closed-loop controlled standing-wave, 3-kW microwave welding machine. This type of research equipment was not available commercially, so the LeTourneau group designed and fabricated one. Breakthroughs. Dynamic recrystallization conditions for high-frequency weld optimization, plus dissimilar sold-liquid interface simulations for centrifugal casting and weld cladding. Wish list. A Gleeble® 3500. Canadian Centre for Welding and Joining The Canadian Centre for Welding and Joining (CCWJ), associated with the Dept. of Chemical and Materials Engineering at the University of Alberta, Edmonton, is “located right at the epicenter of manufacturing for the oil sands operations, and is the central point for weld-related issues in the oil sands,” related Prof. Patricio Mendez, the center’s director, and Program Manager Dr. Goetz Dapp. “The CCWJ holds a preeminent place in Canada in carrying out welding research in direct interaction and collaboration with the industry,” Dapp said. The center functions “as a liaison between the industry, equipment manufacturers, consumable manufacturers, and the global research community, and plays a key role in introducing technological advances and new technologies to the industry to drive innovation, increase productivity, and optimizing process and procedures. We offer the unique ability to combine fundamental research with practical, industry-related and industry-driven applications, and with our excellent connections in the international welding and research communities ensure that the industry can benefit from developments that reach far into the future.” The connection to Canada’s oil sands region has resulted in a research specialization in wear protection overlays. “Our high-speed videography of welding processes is being used in welding education by institutions around the world, and recently received a lot of attention when we started to lead a renewed effort in high-speed videography of submerged arc welding,” Mendez said. (See Mendez, et al. 2015. High-speed video of metal transfer in submerged arc welding. Welding Journal 94(10): 325-s to 332-s.) The center also conducts research into metal transfer and effects of shield gases, analysis of welding arc plasma, laser cladding, metallurgy and failure mechanisms of creep-resistant, high-alloyed steels (X80, X90), and dilatometry. The CCWJ also works on the development of predictive tools for procedure development. “This interdisciplinary research uses a scaling approach and complex mathematics to create relatively simple tools an engineer can use in procedure development to calculate the effects of welding parameters within a small error margin without having to rely on complex and expensive simulations on a computer,” Mendez explained. “The fundamental nature of this research creates a large applicability to a wide range of industrial applications.” Donations from welding equipment manufacturers and suppliers combined with government grants and local industry support, a lab with equipment for all arc welding processes, a Fanuc GMAW robot, and a friction stir welding machine has been established. “Our Lincoln S500 with advanced waveform module, as well as a Miller XMT 450 make it possible to work complex waveforms,” Dapp said. “In addition, we have highly specialized characterization equipment in our lab such as a Linseis dilatomer that allows us to study phase transformations; a Bruker G8 Galileo oxygen/nitrogen/ hydrogen gas chromatographer that gives us precise readings of O/N/H content in steels and other metals; hardness mappers for accurate hardness readings even in complex configurations, a Tukon 2500 automated hardness tester; a cryogen Instron CEAST 9350 impact tester with up to 1800 J that allows us to do full-size Charpy samples; and servo-hydraulic testing equipment for dynamic (fatigue) and fracture toughness testing. We also have two very high-precision Alicat flow meter systems that are synchronized with our data-acquisition systems and allow us to mix up to four different gases on the fly. The capability to do high-resolution data acquisition is essential for any welding-related research, and we have multiple systems operating at any given time, including several National Instruments USB 6351-X series. The data we obtain in our experiments is then synchronized with our high-speed video cameras, a Phantom V210 and a Miro eX4, and forms an invaluable tool to understand weld-stability and metal transfer.” Breakthroughs. The center’s ability to perform welds under controlled circumstances has been possible because of the donation of welding machines and consumables, the understanding of metal transfer in wire-based processes would not have been possible without the high-speed cameras, and the understanding of overlays would not be complete without the hardness mapper. “Our creative contributions to the theory of measurement of phase transformations is based on our dilatometer,” Mendez related. Wishlist. “As research progresses there are always new tools that can help to gain insights into areas previously impossible and to take research projects to new levels,” Dapp noted. Following is the center’s current wish list:- High-speed cool-sensor thermal imaging camera that would help to understand weld temperature distributions
- High-temperature confocal laser scanning microscope that would allow for true metallurgical undestanding of welding processes, particularly overlays and precipitation in steels
- A lighting system to improve high-speed video of the laser cladding/welding process
- Laser beam profiler to get accurate measurements for power density in the beam for modeling purposes
- Image analysis software
- Offline programming for welding robots
- Laser profilometer for surface textures.
