FEATURED ARTICLE LOW-COST ROBOTIC AM For Large-Scale Parts BY RAYMOND WALKER & BRYANT WALKER
Expanding directed-energy additive manufacturing into very large parts based on a low-cost platform has been a thrust of Keystone Synergistic Enterprises, Inc. for the past decade. Keystone has successfully produced directed-energy additive manufacturing (AM) parts using a robotic pulsed arc platform enhanced by a suite of integrated process controls that provides a level of uniformity needed for a qualified additive manufacturing capability. To expand beyond laser powder, laser wire feed and electron beam (EB) wire feed AM processes, Keystone has established a very low-cost AM capability using the robotic arc-based process capable of making very large parts. Figure 1 shows the Keystone Robotic AM work cell for large-scale parts.
capital cost of electron-beam or laser AM equipment, few good examples of cost reduction were identified that would inspire an OEM to substitute AM processes for castings or forgings.
In that timeframe, it was becoming obvious that the effort to qualify additive manufactured parts for use in flight-critical airframe and engine applications was becoming a significant roadblock. This constraint coupled with the difficulty to identify pervasive cost reductions by substituting additive manufacturing for existing manufactured components, proved that directed- energy AM processes would struggle to be a sustainable business.
Keystone’s strategy was to expand the range and market of parts that could be made using directed-energy additive manufacturing, focusing more on non-critical parts, tooling and the reconstructive repair of non-critical components. This greater market segment would, however, require a significant reduction in the per-pound cost of AM deposited metal. A cost breakdown of an AM process reveals that the primary drivers are the cost of raw material, the cost of capital equipment, and the machine and labor-based cost of time in the equipment. These factors drove to a simple set of conclusions that defined the path forward for additive manufacturing to establish a foothold in the broader manufacturing industry beyond just aerospace.
Figure 1. Keystone Robotic AM work cell
In the late 1990s and early 2000s, additive manufacturing was being seriously considered for a limited number of F35 airframe components, but that small market of parts was far from being a sustaining business case for a supplier base in additive manufacturing. While numerous airframe and gas turbine engine makers were investigating additive manufacturing, only part demonstrations, test parts and the production of test blocks of AM material were produced, representing a very limited volume of AM parts.
Keystone participated in numerous detailed cost-benefit analyses with the OEM companies, reviewing part after part for suitability for AM processes and looking for compelling cost reductions that would be the foundation for a strong business case. Given the high cost of powder metal and welding wire, the high
16 LIATODAY FOCUS: INDUSTRIAL AM JULY/AUGUST 2016
Low-Cost Raw Material Welding wire is always a lower cost than powder metal and the cost for handling and management of the raw material stream is lower. There are far more alloys available as welding wire compared to powder metal. This raw material stream is highly mature, broadly distributed and is lower in cost.
Low-Cost Equipment for Large Parts Electron–beam and laser AM processes require expensive equipment driven by the high cost of delivered and focused energy from an EB gun or laser. This represents a significant cost compared to an energy source such as an electrical arc delivery. A robotic platform capable of 6 or 7 degrees of freedom of motion in a very large work space is a very low cost alternative to a gantry-based CNC system supplying motion in an equivalent work space. A highly capable robotic welding platform can be acquired for $100 K to $200 K compared to millions of dollars for EB and laser systems. This led to the utilization of a robotic gas metal arc welding (GMAW) system as a robust, mature starting platform for a low-cost AM process using traditional
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