Process and Physical Aspects of Continuous Wave Laser Processing

Abstract

Laser processing embraces six major activities, namely 1) generation of light within the laser, 2) transmission to the workpiece, 3) quality assurance of laser beam parameters as delivered, 4) absorption at the workpiece, 5) the process itself, and finally 6) quality assurance of the finished product. Although each activity may be considered in isolation, one should ideally consider all six as parts of an overall laser process chain. The reasoning behind this integration of activities is that the activities are interrelated. As an example of what could occur to upset the normal state of affairs, consider a local change in the chemical composition of the material being processed giving rise to a high electron density at the absorption interface and plasma frequency reflections. The excess reflected light reaches the laser and changes its mode structure which affects both beam measurements and further absorption. In practice unwanted feedback can be minimised by careful design and consideration for each activity; however certain feedback is highly necessary, such as qua I ity assurance between activities 3 and 1 and 6 and 1. With this in mind, this chapter examines each activity from a process engineering viewpoint with particular regard to eliminating or optimising feedback as appropriate, and takes its examples from continuous power welding and surfacing using continuous carbon dioxide lasers.