Linear friction welding on a large scale
The linear friction welding machine might not look as imposing as its dimensions might suggest because most of it sits in a deep pit.
We can all stand to lose a little weight, and U.S. manufacturers are no different. That explains the growing interest in “lightweighting” of certain products.
It’s not hard to understand the interest: Remove weight from an aircraft, ship, or vehicle, and the end user doesn’t need as much fuel to power the mode of transportation. Even in the face of fuel costs that are below historic highs, everyone is interested in cost savings where they can get them.
Investigation into lightweighting has other benefits. New, less expensive materials are being investigated to see if they can deliver the same performance of long-used materials. In some instances, these alternatives also might show even better performance properties than the traditional materials they might replace. Also, research is being done to look at new technologies to cast, heat-treat, form/shape, join, and coat these new materials.
Detroit-based Lightweight Innovations for Tomorrow (LIFT) is leading the charge in this lightweighting research. It was created as a result of a consortium that won a Department of Defense program in February 2014. The American Lightweight Materials Manufacturing Innovation Institute, comprising manufacturing technology nonprofit EWI, the University of Michigan, and The Ohio State University, established its 100,000-square-foot facility almost a year later and formally announced its LIFT name. Since then the organization has been working to accelerate the transfer of new manufacturing technology from the research lab to the production floor.
LIFT recently got a big addition to its research efforts, and this new tool promises to have a huge impact on the way certain large metal parts are fabricated.
LIFT is installing what is believed to be one of the world’s largest linear friction welding (LFW) machines in its Detroit facility. In fact, Alan Taub, the former LIFT chief technology officer and now senior technical adviser to LIFT, said the high bay that was constructed in 2016 was built with this equipment in mind.
“We have industry companies that we call our gold and silver members, and we ran surveys with them over an 18-month period,” Taub said. “We asked them what type of equipment that they didn’t have access to and what they would like to see us put into our facility.”
The result is a machine that weighs 122,000 lbs., about the same weight as a Boeing 737. A majority of the machine sits in a 15-foot pit that was excavated the same time the high bay was constructed. It has a 22- by 8- by 14-ft. envelope, capable of joining some very large parts.
“This is not new technology,” said LIFT’s chief technology officer Hadrian Rori. “It’s been used for other joining processes and in research over the years. What makes this machine unique is that it has the largest envelope for fine-tuning some of these processes.”
MTI Welding, South Bend, Ind., built the equipment for LIFT. It is a manufacturer of friction welding equipment for other manufacturers and also offers contract manufacturer services. A couple of LFW machines are owned by large aerospace companies in North America, and other machines found around the world are mostly used for research and development purposes. None are believed to be as large as the LIFT equipment.
What is believed to be one of the world’s largest linear friction welding machines is delivered to the Lightweight Innovations for Tomorrow facility in Detroit.
So why friction welding for these lightweighting applications? The process creates a bond that is as strong as the parent material without the distortion that usually is associated with fusion welding technologies and their huge heat-affected zones. Additionally, this joining method avoids other conventional fusion welding shortcomings, such as shrinkage, solidification cracking, and porosity.
In the broad sense, friction welding of any kind is actually more like forging. Relative motion and high force are used to create frictional heat at the weld interface. When this occurs, the metal is plasticized, not necessarily melting but still receptive of alteration at the surface. The result is molecular intermixing at the weld interface and a forged-quality joint.
If you are talking about particular types of friction welding, most fabricators might be most familiar with friction stir welding, where a nonconsumable pin tool, attached to a spindle, is introduced to the joint between two clamped pieces of metal. When the rotating pin tool, accompanied by a consistent downward force, engages the weld path between the metal parts, it “stirs” the metal together, creating that plastic deformation that becomes the new joint.
In LFW, one metal part is held stationary while the other oscillates on a linear path. This linear motion creates the force needed to enable parts with varying geometries at the weld interface to be joined.
Taub said this force is why LIFT needed to specify such a large LFW machine. The forces needed to generate the movement required for friction welding of large metal components require a machine of substantial mass—if the machine is expected to stay in place during the process.
One of the current projects that will be investigated on the new LFW machine involves blisks, jet engine components comprising both a rotor disk and blades. As anyone who has flown on a plane lately can tell you, blisks can be quite large.
Traditionally, these items are machined from a single piece of material. When talking about titanium, this becomes a very expensive operation.
Taub said that the aerospace industry is looking to improve its “fly-to-buy” ratio. When it buys an immense titanium ingot that is then machined down to create a blisk, the aerospace company sees most of its original purchase go into the scrap bin in the form of shavings. The fly-to-buy ratio might be 20 percent.
The LFW equipment gives an aerospace company a better chance to create a near net shape that then can be machined down. Smaller titanium parts can be linear friction welded to a larger stationary part. The end result is a form that is closer in shape to the blisk, which means the aerospace company is not paying as much for its titanium blanks.
LFW also allows for the use of different metals that wouldn’t be compatible with conventional welding methods. Design engineers can consider metal combinations that can deliver strong performance properties and are less expensive than materials typically specified for such applications.
Rori said the new LFW machine has been set up to accommodate large and “unique” shapes. The rams, which hold the tooling to which the metal parts are adhered, are slightly offset. They look almost like a C-clamps. This design allows room for a variety of large and awkward shapes.
Taub said the new equipment is ready and qualified to work with different steel alloys as well. This was necessary in order to reach out to other manufacturers outside of the aerospace industry.
“We want to take these technologies and with our partners waterfall some of this stuff to other folks that might not otherwise be able to be part of this technology development,” Rori said.
Photos courtesy of Lightweight Innovations for Tomorrow, https://lift.technology.
MTI Welding, www.mtiwelding.com