weld wire as the principle material delivery system. Robotic welding systems are a very mature capability and represent a highly supported industry. The primary challenges with robotic AM processes are the lack of integrated process controls and the difficulty of programming for complex parts.
High-Rate Throughput & Deposition Rates The up-time of robotic welding processes is very high, and the deposition rate for most alloys ranges from 7 lbs/hr to 25 lbs/hr. One operator can easily operate two to three robotic systems representing a low labor content.
However, one does not just take a robotic welder and become a qualified source for additive manufacturing processes. There are several other considerations required to make a capable AM system. Most significantly, closed-loop process controls need to be added to the robotic platform to build in a level of reproducibility and process consistency to provide confidence the material will be uniform. AM processes must be consistent, of predictable quality, be homogeneous throughout the AM build, consistently achieve minimum mechanical properties, and be equivalent from part-to-part, machine-to-machine and supplier-to-supplier. There are thousands of robotic welding systems throughout the country that could be placed into service performing AM processes, however without process controls, process specifications and procedures, qualification standards and certified mechanical property data bases, the output from these equipment platforms would be inconsistent, variable and lack reliability. The potential industry would falter and have strong negative perceptions.
The key elements needed for AM capability are process controls, written guidelines and specifications, and a solid path to qualification. Keystone is actively addressing these enhancements to make robotic pulsed-arc AM a qualified mainstream process.
The primary process controls that are needed to transform a typical industrial robotic welder to an AM capability are:
• Control of build height • Control and management of part temperature during an AM build • Monitoring the features of the melt pool during AM processing
Keystone has developed an integrated suite of sensors and control software that can be added to a welding robotic system and communicate with the robot’s controller through analog and digital I/O ports. Figure 2 shows the Keystone lightweight integrated sensor head mounted on the robot end arm to provide closed-loop build height control, closed-loop thermal management and control, and melt pool size and feature measurement and monitoring.
Figure 2. Keystone lightweight integrated sensor head mounted onto a robotic end arm
Using these controls, Keystone has successfully produced a significant range of AM parts in many important alloys including titanium, aluminum, steel, iron-based alloys, nickel superalloys, cobalt alloys, and copper-nickel alloys. Parts and tools with over 550 lbs of deposited material have been produced at Keystone for production applications. Figure 3 shows several examples of AM parts produced by Keystone using robotic pulsed-arc methods. This capability, combined with a focus on very low cost and non-critical hardware, has enabled Keystone to expand the range of parts and tooling appropriate for AM processing, critical for the directed-energy AM market.
Keystone has generated AM source and process qualification guidelines for the robotic pulsed-arc process and facilities and is currently developing certified B-Basis allowable mechanical
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