Wire arc additive manufacturing (WAAM) continues to grow as a method for building large-scale metal parts. The as-printed surfaces of parts produced with WAAM are rough and may not be suitable for the final application. Thus, machining is needed to create the final working surfaces and geometry from the as-printed preform.
This work describes the development and testing of a new hybrid manufacturing work cell at the University of Tennessee, Knoxville which combines large-scale WAAM with five-axis machining to build large metal components with the final product ready to use in the desired application. The hybrid manufacturing work cell is comprised of three sub-systems: a robotic WAAM system, a metrology system, and a five-axis machining system. The robotic WAAM system is equipped with a Fronius CMT Advanced Twin Wire system mounted to a KUKA KR50 robotic arm. In addition, a two-axis part positioner is kinematically coupled to the robotic arm allowing for more complex parts to be built. The twin wire welding system provides the option of running two wires of the same material or two different materials simultaneously. When running two wires of the same material, higher deposition rates can be achieved which is useful when building large components. In the case of running two different materials, in-situ alloying is possible as well as depositing materials with different physical properties strategically throughout the part to enhance the component’s performance. The metrology system is a GOM ATOS Q structured light scanner. Using the two-axis positioner to manipulate the orientation of the part within the field of view of the scanner, a three-dimensional representation of the as-printed part is captured along with fiducials used to define a digital coordinate frame. By scanning the part after printing, the stock model used to inform the computer aided manufacturing (CAM) tool path creation is created. This allows for more accurate tool pathing for the machining process. Finally, a HAAS UMC-750 five-axis computer numerically controlled (CNC) machining center is used to machine the as-printed part to the desired final geometry.
The fiducials captured during the scanning process are probed by the machining center to recreate the digital coordinate frame used in CAM in the physical machine. Using a five-axis machine tool offers additional flexibility to create complex geometry which matches the complexity possible in the WAAM process. To demonstrate the feasibility of this process as well as test the new work cell, a simple propeller geometry is printed using ER70S-3 low carbon steel wire. Three blades are built onto a cylindrical hub to complete the propeller. Once the propeller is printed, it is moved to the metrology system for digital analysis. The scan of the as-printed part is compared to the desired propeller model to ensure that the final part is contained in the as-printed component. If the as-printed component is underbuilt in any area, the part may be sent back to the printing system for additional deposition in the needed areas. If no errors are found in the scan, an STL of the scan part is exported from the GOM Inspect software and imported into a CAM software. Here, the machining tool paths are generated to remove material from the as-printed part to reveal the final geometry. Once the tool paths are validated, they are executed on the machining center. The resulting geometry is again measured by the metrology system to ensure that the desired geometry is obtained. For wire arc additive manufacturing to become a widely used manufacturing practice, it must be coupled with traditional subtractive manufacturing to create a hybrid manufacturing process. The hybrid manufacturing cell described here couples these two processes through three-dimensional scanning and metrology. To demonstrate the capabilities of the system, a three-blade propeller is built. The resulting geometry is compared to the CAD design and shows that the hybrid manufacturing process can produce complex geometries that are ready for use in the desired application.
This work relates to Department of Navy award (Award number N00014-20-1-2836 in collaboration with Oregon State University) issued by the Office of Naval Research. The United states Government has a royalty-free license throughout the world in all copyrightable material contained herein. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the view of the Office of Naval Research.
Wire Arc Additive Manufacturing, Hybrid Manufacturing, Metrology, Subtractive Manufacturing