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Novel Welding, Joining Techniques Focus on Machining and Additive Manufacturing

Novel technologies will be featured during the Welding and Allied Technologies panel at TITANIUM EUROPE 2015, taking place the 11th – 13th May at the Hilton Birmingham Metropole Hotel National Exhibition Centre in the UK.  Ian D. Harris, Ph.D., technology leader, arc welding, for Edison Welding Institute (EWI), Columbus, OH, serves as moderator for the session.

Harris’ colleague, Matt Short, EWI ultrasonics technology leader, will discuss the EWI ultrasonic-assisted machining processes that can be retrofitted into standard machine tools. Short said EWI has developed a system that “sends a longitudinal wave through the tool generating an intense oscillating motion at the material interface. Research conducted on titanium and many other materials and processes have shown significant improvements in tool life, feed rates, surface finish, and quality.”

Known as “Acoustech™ Machining,” Short said the technology “dramatically improves metalworking capabilities by bringing ultrasonic performance to new and existing manufacturing equipment,” which is designed to fit existing metalworking equipment and tooling.

Designed especially for hard-to-machine metals, like titanium, Acoustech, developed in recent years by EWI, is a patented system that provides acoustical vibrations to conventional cutting tools, bringing the many benefits of ultrasonic technology to today’s plant floor. Benefits of the system include accelerated production rates and extended tool life, according to Short. He said manufacturers can increase output and profits “without purchasing new machining centers, because this patented Acoustech tool holder was specifically engineered to work with standard equipment installed throughout the manufacturing industry.”

Benefits from the Acoustech system include lower operating forces, increased feed rates, improved chip extraction and reduced burr formation and improved surface finish of machined components. EWI describes Acoustech as a “green” technology that does not involve slurry abrasives or coolants.

Bertrand Flipo, senior project leader for The Welding Institute (TWI), Cambridge, UK, will provide an update on his group’s “Friction and Forge Processes,” which will provide recent developments and economical assessments in the joining of titanium alloys using linear friction welding (LFW). Flipo said the production of near-net shape aerospace components represents the focus for this technology.

LFW is an automated, self-regulating, self-cleaning and highly repeatable friction welding process, which delivers fast cycle times (under five minutes), according to Flipo. It preserves the forged microstructure of aerospace parts and can be post-weld heat treated and makes use of common stock plates for producing a range of parts.

Flipo explained that many tight-tolerance aerospace components typically are machined from solid blocks of titanium alloys, which results in relatively poor buy-to-fly ratios. He said the use of near-net shape parts produced by LFW can significantly reduce production costs for a wide range of aerospace components.

He said the buildup of near-net shape parts by LFW also provides the opportunity for selection of appropriate dissimilar alloys in different parts of the structure. This approach allows the production of tailored components, resulting in both functional and economic benefits. Examples range from simple LFW fabrications, to more complex components produced by sequential LFW of multiple parts.

Key findings showed that the average interface force and coefficient of friction during each phase of the process were insensitive to the rubbing velocity; and the interface of the work pieces reached a temperature of approximately 1000 C during the friction phase. TWI said this work has enabled a greater insight into the underlying process physics and will aid future modeling investigations.

EWI’s Ian Harris will provide an overview of other welding and joining additive manufacturing projects currently under development at his group—projects that are in the process of being transitioned into full commercial manufacturing systems. He said EWI is performing directed energy deposition (DED) additive manufacturing with laser, arc, and ultrasonic energy sources.

The thrust and focus for these development efforts, according to Harris, is to significantly increase additive manufacturing deposition rates (up to 40 pounds per hour), in order to produce high-value, complex parts—such as pumps and valves—from titanium alloys and nickel-based superalloys. Part size would fit into a 4 by 4 foot production cell. The cell employs a six-axis robot and gas tungsten arc welding (also known as tungsten inert gas welding, or TIG) with preheated wire. Harris pointed out that is less expensive and more readily available in the supply chain compared with powder metal.

“We’re addressing market needs (for new generations of additive manufacturing),” Harris said. “We look to identify technologies that seem promising, but need additional commercial development work.” He also noted an inherent advantage of additive manufacturing is the reduction of scrap rates, compared with traditional machining, which would result in a potential 50-percent per-part cost reduction, reducing the buy-to-fly ratio. 

In his conference presentation Harris will explain that “the ubiquitous use of robotic arc welding, with added CAD-to-part capability, can become a significant additive manufacturing resource for the supply chain in aerospace, oil and gas, and other markets. EWI is developing the software linkage for true CAD-to-part additive manufacturing using six-axis robotics, as well as the bead size/spacing to achieve both the desired microstructure and properties, and the build strategy/path.”

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