The Plasma Arc Facility
The 300,00-watt Plasma Arc Lamp in the Infrared Processing Center (IPC) at Oak Ridge National Laboratory (ORNL) is a unique piece of equipment. The lamp can deliver up to 3.5 kW/cm2 over areas up to 35cm by 3.175cm. The technology utilizes the radiant output from a stabilized DC plasma for transient materials processing (to see more on the basics of this technology, review the January 2000 JOM publication). The lamp is mounted on a Cincinnati-Milacron model T3-776 robot using a Universal Robot Controller (URC) developed and built by Robot Workspace Technologies in Fort Meyers, FL. Using the robot in conjunction with the Plasma Arc Lamp allows for a variety of experiments to be performed in a short amount of time. Using the URC to program the robot results in a turn around time, between experiments that require different programs, of a matter of minutes. The robot also allows samples of various shapes and sizes to be processed using the lamp.
Also included at the IPC are a number of tools to further enable processing using the arc lamp. An enabling tool used in processing is a protective water window. This water window, essentially an air knife that drives water across a piece of quartz to be drawn off the other side by a vacuum, allows materials that outgas to be readily processed. There is also a variety of processing boxes available for processing specimens in different atmospheres using the plasma arc lamp.
Other equipment available at the IPC to increase its processing capabilities include: A six axis, Cincinnati Milacron T3-726 robot which can be used in conjunction with the T3-776 robot for processing specimens with more complex geometries. Communication between the two robots is made possible using the URC. A 16" model CY Monarch lathe is available for rotating parts as they are being processed. Three different lamp heads are available for processing, a 35cm arc lamp capable of power densities of up to 600W/cm2, a 20 arc lamp capable of power densities of up to 1200W/cm2, and a 10cm arc lamp capable of power densities of up to 3500W/cm2. There are currently two different styles of reflectors available at the IPC, the elliptical reflectors which produce a narrow, high intensity beam, and the uniform irradiance reflector which produces a more diffuse beam (20cm by 10cm) that can be used to process non-uniform surfaces.
The power of the arc lamp is continuously variable from about 1.5% to 100% power with power changes taking place in less than 20ms, allowing for tight control of processing. Combined with the ease at which the scan speed of the robot can be reset, just about any processing parameters can be obtained.
The work cell is designed with safety interlocks on the door and pass throughs, cutting off the lamp instantaneously if somebody inadvertently tries to enter the cell while the arc lamp is on. Retractable welding curtains on the side windows are interlocked so that they must be down before the lamp can be started. Also, the top of the cell is guarded by infrared beams to halt work if the robot should leave its predetermined work area, or if something should unintentionally enter the cell from the top during processing.
On-line video monitoring is available for recording experiments from different locations inside the enclosure. This allows for qualitative data to be obtained during processing.