Additive approach to machining Ti6Al4V

To demonstrate that additively manufactured steel cutting tools can machine Ti6Al4V equal to or better than their conventionally manufactured HSS counterparts, Jimmy Toton, a mechanical and manufacturing engineering Ph.D. candidate at the Royal Melbourne Institute of Technology in Australia, conducted research. Using laser metal deposition equipment at RMIT University’s Advanced Manufacturing Precinct, the director of which is Toton’s supervisor, professor Milan Brandt, Toton 3D-printed tool blanks with the chemical composition Fe25Co15Mo. Sutton Tools Pty. Ltd., Thomastown, Australia, then ground the blanks on a CNC tool and cutter grinder to produce endmills. Toton has worked at Sutton Tools as an intern.

Once the tool blank is 3D-printed via laser metal deposition, it is centerless-ground, and then the tool’s features are produced on a CNC grinder. Image courtesy of RMIT University

According to the definition from the American National Standards Institute, the material is not technically HSS but closer to the definition for maraging steel. “It is carbon-free and strengthened by the precipitation of nanosized intermetallics through artificial aging,” Toton stated in an email.

Steve Dowey, technology manager at Sutton Tools and a senior lecturer and industry fellow at RMIT University, said Toton targeted a substrate material that provides an intermediate high hot hardness between HSS and carbide.
“The substrate has thermomechanical properties that make it a suitable material for titanium machining, such as a higher hot hardness and resistance to thermal softening than all high-speed steel grades,” Toton added.

Printing with the material, however, wasn’t easy. “Creating a straight, long, thin cylinder without any defects was quite an interesting challenge, and Jimmy took that on and spent a long time optimizing the deposition conditions,” Dowey said.

To overcome the issues he faced in getting the deposited metal layers to print properly and bond strongly, Toton noted he employed high-temperature substrate heating to manipulate solid-state transformations with a microstructure during printing and prevent crack formation.

“All of optimization of printing doesn’t come in the manual,” Dowey said, adding that manufacturers of additive equipment are becoming better at providing more information. “It is a bit of a dark art.”