Carbon Arc Fusion

One of our clients needed to develop a process for fabricating quartz vacuum vessels larger than the global supply chain could provide. They needed an automated system to precisely position three carbon electrodes within a rotating tube, ignite and maintain a 10,000 amp plasma arc, and use the heat from the arc to fuse silica sand into a quartz tube.

Featured Design Challenges

Load Capacity:

The customer’s initial concept for this system involved three separate robots, each positioning a single electrode. Our team determined that the challenge of perfectly coordinating an electrode on each of three robots would make them less effective than using one high-capacity robot with a single end effector to position all three electrodes.  To meet this requirement, Perellion was able to source one of the first Fanuc M1000 robots to be delivered to the US. This robot was the first in its series to use a serial link design, allowing it to have a greater range of motion compared to a parallel link.  However, even with this range of motion, the system required that the electrodes be cantilevered away from the end effector, creating a loading challenge even for this large robot. The Perellion design team needed to constantly manage the center of mass of the electrodes, balancing between the required performance and the load rating of the robot.

Cable Management:

Another issue with this system was supporting the “umbilical cord” to the end effector – the electrical cables and active cooling lines that supported the carbon arc fusion process. These cables were prohibitively heavy to be supported by the robot itself, so a separate support system had to be designed. The team at Perellion developed a series of counterbalanced arms that pivoted to passively follow the motion of the robot.

Heat Management:

The production of quartz generated a massive amount of radiant and convective heat, which needed to be managed in a variety of ways. The Perellion team designed multiple heat shields, a cooling plenum to contain heat during fusion, and an articulating insulated lid to facilitate controlled cooling after the cylinder was formed.

Harsh Environment:

An additional challenge that was considered throughout the design process was the harsh environment in which the robot would operate. In addition to the high heat load, there was also a high prevalence of raw quartz sand in the environment and adverse magnetic fields, due to very high currents being produced by the process. The design had to be resilient to these challenges.

Remote Control:

Due to the risk and high heat that would be produced by running this operation, the entire building had to be cleared while the arc system operated, which required that the system be controlled remotely from an adjacent building. Our controls team both developed a custom remote-control interface and supported the client to ensure that their facility’s network could accommodate the required connection.

Solution

Our team integrated a high load serial link Fanuc robot with a custom servo-driven end effector. We also designed a completely passive cable and cooling hose management system, as well as integrating multiple forms of heat management. To remotely control the system, a dependable and user-friendly app was developed.

One feature of our work on this project was our dedication to meet the client’s needs. This project’s needs changed throughout the initial design and long into the process development phase, and we were able to work smoothly with their team of engineers to continuously support the development effort. Our team is able to integrate smoothly with clients’ teams in a hybrid work structure in cases where concurrent engineering is required, the statement of work isn’t perfectly fixed, or when additional support is needed after initial installation.