When work was first begun on moving the thermal spraying process to a low-pressure atmosphere, the question arose of what handling devices should be used, since humans could not enter the vacuum chamber when it was filled with argon, a rare gas. At first simple, electromechanical handling systems were used, operated from outside of the chamber using equally simple controllers.

Plasma coating in a vacuum

An operator places the workpiece on a turntable, which has been moved out of the chamber on a slide. Once the chamber is closed, the system evacuates the air, generates the prevacuum and then floods the chamber with argon until the pressure necessary for the coating process is reached. In the coating process, argon and hydrogen gases are fed in, creating a plasma jet. The system injects the coating material in the form of a powder into the jet as it is generated. While the robot guides its plasma spray gun along the contours of the workpiece, the controller of the KR 15 also moves the axis of the turntable at the same time. After the coating is applied, the system floods the chamber with argon up to a pressure of 500 mbar, and then up to 1,000 mbar with air. The workpiece would oxidize if only air were used for flooding. Lastly, the operator opens the chamber, moves the turntable forward and removes the component.

• KUKA KR 15 robot
• PC-based KUKA robot controller, including control panel with Windows interface
• Turntable
• Linear unit
• Motors and control modules for the external axes
• Modification of the robot
• Robot programming
• Commissioning    

• Vacuum-capable
  
  So that the KR 15 would operate in a low-pressure atmosphere just as it would in a normal one, it was adapted to the specific technology. This applies unconditionally with regard to service life, velocity and accuracy, and also includes the external axes controlled by the robot controller.
  
  
  
• High flexibility
  
  The superiority of the robot compared to other handling devices lies most of all in its excellent flexibility with regard to motion geometries, which makes it possible to coat even complex forms such as turbine blades and hip implants without problem.
  
  
  
• Exact reproducibility
  
  When a robot is used the processes, including the motion sequences, can be documented completely and reproduced exactly. It is also possible in this case to exploit the potential of off-line programming and process visualization.
  
  
  
• Consistent quality
  
  The robot achieves a more even coating thickness. This is important, because often for technical or economic reasons the parts cannot or must not be reworked.