Vartanian and McDonald (2016) provided an industrial example of where the additive manufacturing (AM) industry is heading in order to guide further development activities in the materials community. The article published in JOM by The Minerals, Metals & Materials Society discussed the benefits of the combination of additive and subtractive metal working capabilities into one machine tool, how it came into existence and the current capabilities and advantages it offers.
The merger of AM technologies and traditional subtractive Computerized Numerical Control (CNC) methods, now known as Hybrid CNC machining, offers numerous advantages in terms of lower equipment acquisition costs, lower training time as it can be operated from a common Human Machine Interface (HMI), leverages capital assets to deploy AM technologies and provides more capabilities compared to either technology alone.
Two common methods for commercial use in laser-base AM technology are the Power Bed Fusion (PBF) and Power Fed Directed Energy Deposition (PF-DED) systems. The PBF and PF-DED systems offer different advantages; the PBF machines are better at building smaller and complex-shaped designs coupled with better surface finishes while PF-DED machines are better at building or adding materials to form large parts and repairing worn or defective metal components. The Laser Engineered Net Shaping (LENS) machines offered by Optomec are known to be a stronger candidate for PF-DED machines.
Optomec delivered a proposal to package LENS technology in a modular kit as a project call was issued to lower adoption barriers for laser metal AM. Optomec, in January 2014, were awarded an America Makes contract to package LENS technology into a modular print engine and to prove the concept by upgrading a legacy Fadel Vertical Mill into a Hybrid CNC machine tool.
Upgrading steps included interlocked access doors and ports to prevent possible exposure to the high-power laser beam in order to satisfy Class I Laser enclosure requirements, and a laser safety window for viewing the process and secondly, inclusion of a closed loop process monitoring system to control heat input and cooling rate as the AM build progresses.
The Hybrid Fadel Vertical Mill was delivered to TechSolve, a company with expertise in process improvement and CNC machines. Fast learning curve was observed as machine was installed and operational in a day despite TechSolve having no prior 3D printing experience. This was possible because the LENS Hybrid system utilizes a custom interface that enables 3D printing operations to be executed using traditional 3D CNC programing and G-codes commands already familiar to a machinist.
Live demonstration of the LENS Hybrid system by TechSolve showed the machine operating in subtractive mode as it did prior to upgrade, or in additive mode building a 3D part, or in Hybrid mode switching back and forth between subtractive and additive operations.
Repairing and selective finish machining of parts was seen as jaws of a stainless steel wrench were cut off and the resulting internal cavity of new jaws were grown back using integrated LENS printing and finish machined using the Hybrid machine’s milling capabilities.
The LENS Hybrid machine was evaluated by TechSolve to be MRL 6/7, the highest rating possible by a non-production entity. It offers enablement of the application of additive and Hybrid techniques for a wide range of structural materials at a significant lower cost.
Vartanian and McDonald (2016), noted the relevance of moving this technique forward even for AM only machines built on lower cost CNC platforms or for hybrid machines when dry machining is possible to build and finish the part on one machine. More research is required to study the thermal effects of lubricants on material microstructural integrity and how to remove resultant surface contamination prior to resuming AM operations after wet machining. However, lower cost and more flexible pathways for development and production will accelerate adoption of both additive and Hybrid fabrication methods.