Laser removal of TiN coatings from WC micro-tools and in-process monitoring

Current environmental challenges require sustainable and extended use and re-use of materials. For example, the service life of engineering tooling can be extended by using thin film coatings such as titanium nitride (TiN). However, when errors arise in the coating process or when the tooling needs to be re-used it is necessary to remove the coating. Decoating is also useful when a large batch of cutting tools needs to be re-directed for a different application, which requires a new generation of coating. Existing technology uses chemical methods which are not environmentally friendly or ideal for selective removal. In this work, excimer laser striping of TiN from coated tungsten carbide (WC) micro-tools has been demonstrated as a viable alternative to chemical methods. Also, in order to raise the integrity of the decoating process and to make the process more accurate and reliable, two online monitoring systems were developed exploiting probe beam reflection (PBR) and laser plume emission spectroscopy (PES). The online monitoring system facilitated a simultaneous prediction of surface elements as coating layers are progressively removed and ensures better control over the laser irradiation process so as to avoid under or over stripping of the coating.