Development of an ultrafast laser ultra-precision machining platform

Abstract

Ultra-precision manufacturing is commonplace in today’s society. It is used in a huge number of applications from electronics, medical devices to energy devices. Most devices manufactured using ultra-precision methods are made in high quantities where the volume of the components is required to outweigh the cost of the production equipment. However, there are few technologies targeting the manufacture of prototypes or small batches and those that are costly in terms of time or resources. Thus, there is a demand for a high speed, flexible manufacturing platform that is capable of ultra-precise manufacture. Currently, manufacturing techniques using ultrafast lasers are limited with regards to accuracy and repeatability. This body of work investigates how to develop an ultra-precision ultrafast laser manufacturing platform. From literature it was found that there are a significant number of avenues that could be investigated to improve the precision of an ultrafast laser machining process. This included the integration of metrology to perform closed-loop processing, studies of laser stability, new machining strategies and the effect of processing on plume formation. A significant proportion of the research presented was focused on the development of the ultra-precision platform. This work was carried out to provide a basis for this research but also for those that will use the platform in the future. One of the key outputs from this development was a graphical user interface that integrated with the range of devices on the platform such as the laser, 5-axis stage and beam diagnostic tools. This interface provides methods for automatic tilt correction, autofocus for the laser, angular ablation machining methods and other diagnostic tools. The interface is setup to capture the required data to provide traceability and diagnostics on the laser machining process. This aided the research carried out into improving the accuracy and repeatability of the laser-based process. First, an investigation into the characteristics of the laser installed on the ultra-precision platform was undertaken to determine the long-term stability of the laser with regards to the pointing stability, power stability and beam diameter stability. These characteristics are significant because they all affect the fluence at the focal spot which is responsible for ablating material. Variance in any of those parameters can have an effect and therefore influence the accuracy and repeatability of the process. The effect of duty cycle on power repeatability and the implications of this on machining was examined. Finally, a simulation was created to demonstrate the effect of laser stability on quality of machining. The ability to machine on angled planes enabled an investigation of the effect of angle on plume formation and the ablation threshold of the material. The ablation threshold for silicon was found at angles between normal and 45 degrees. It was found that the threshold could not be correlated with change of incident angle on the area of the focal spot. A range of different powers and angles were captured using the holographic camera and the effect on plume development was assessed. Overall, a range of tasks was completed which enabled several developments of the ultra-precision platform. These included in-process monitoring, the establishment of a novel machining strategy, and the capture of the effect of angular ablation on plume formation using a holographic camera. The platform is now placed to continue further development and integrate with other metrology technologies to provide closed-loop machining capabilities which will lead into a laser-based process which will be used for MEMS and similar device manufacture.