Modelling and control of laser surface treatment

The results of laser surface treatment may vary significantly during laser surface processing. These variations arise from the sensitivity of the process to disturbances, such as varying absorptivity and the small dimensions of the work piece. To increase the reproducibility of the process, a real-time feedback control system was designed and tested. Process models were developed to gain insight in the process behavior. As a test case, laser alloying of titanium (Ti6Al4V) with nitrogen was considered. Unfortunately, not all the desired processing results, such as the thickness of the alloyed layer, can be measured during processing. The quantities, which can be measured, are temperature related, e.g. the melt pool temperature and the melt pool surface area. Dynamic and steady-state models were developed, which relate the processing results to the measured quantities. A thermographic CCD camera was developed to measure the melt pool surface area in real-time. Pyrometers were applied to measure its temperature. The effects of the laser power, the beam velocity and the disturbances (absorptivity, thin work piece) on the temperature distribution and melt pool surface area, were analyzed theoretically, as well as experimentally. The width and length of the temperature distribution and the melt pool vary due to the disturbances. In the case of a thin work piece, the length varies more than the width. In the case of an absorptivity disturbance, the variation of the length and width are of the same order. In addition, it was found that the laser power can be best applied to counteract an absorptivity disturbance. The beam velocity can be best applied to suppress the negative effects introduced by small dimensions of the work piece. Based on these results, several controller algorithms, including multivariable algorithms, were implemented and tested. A mode-switch controller was able to produce a constant melt pool depth despite disturbances. This controller applied the laser power to suppress an absorptivity disturbance, and the beam velocity to counteract a geometrical disturbance. Hence, although it is not possible to measure the thickness of the alloyed layer directly, it is possible to control it by measuring and controlling temperature related quantities (temperature, melt pool area) at the surface

Laser induced die transferring and patterning

The benefits of the use of lasers in the field of assembly of heterogeneous microsystems is demonstrated, by two applications. First, a laser induced pyrolitic process successfully transfers an chip (semiconductior die) from its carrier onto a receiving substrate. Secondly, a laser induced photolitic processes creates a hyhdrophobic/phillic pattern required for fluidic self-alignment of micro-fabricated component

Snijden van metalen met hoogvermogen lasers

Het snijden van metalen met behulp van een hoogvermogen laser biedt vele voordelen ten opzichte van conventionele snijtechnieken. Zo is de snijsnelheid hoger, de snedebreedte kleiner, de bewerking nauwkeuriger en is de warmte beïnvloede zone in het materiaal kleiner. In de voorlichtingspublicatie VM 121 “Hoogvermogen lasers voor het bewerken van metalen” [1] worden verschillende (theoretische) onderwerpen die een rol spelen bij het bewerken (snijden, lassen, oppervlaktebewerken, enz.) van metalen gedetailleerd(er) behandeld. Deze praktijkaanbeveling wil met name inzicht geven in de praktische aspecten die bij het gebruik van een hoogvermogen laser voor het snijden aan de orde komen

Oppervlaktebewerkingen met hoogvermogen lasers

Het bewerken van metalen oppervlakken met behulp van een hoogvermogen laser biedt vele voordelen ten opzichte van conventionele technieken voor oppervlaktebewerken. Zo kan de bewerking zeer lokaal worden uitgevoerd, waardoor het product niet vervormt en worden oppervlakken van een hoge kwaliteit verkregen. In de voorlichtingspublicatie VM 121 “Hoogvermogen lasers voor het bewerken van metalen” [1] worden verschillende (theoretische) onderwerpen die een rol spelen bij het bewerken (snijden, lassen, oppervlakte bewerken, enz.) van metalen gedetailleerd( er) behandeld. Deze praktijkaanbeveling wil met name inzicht geven in de praktische aspecten die bij het gebruik van een hoogvermogen laser voor het oppervlaktebewerken aan de orde komen

High precision optical fiber alignment using tube laser bending

In this paper, we present a method to align optical fibers within 0.2 μm of the optimal position, using tube laser bending and in situ measuring of the coupling efficiency. For near-UV wavelengths, passive alignment of the fibers with respect to the waveguides on photonic integrated circuit chips does not suffice. In prior research, it was shown that permanent position adjustments to an optical fiber by tube laser bending meets the accuracy requirements for this application. This iterative alignment can be done after any assembly steps. A method was developed previously that selects the optimal laser power and laser spot position on the tube, to minimize the number of iterations required to reach the target position. In this paper, that method is extended to the case where the absolute position of the fiber tip cannot be measured. By exploiting the thermal expansion motion at a relatively low laser power, the fiber tip can be moved without permanent deformation (only elastic strain) of the tube. An algorithm has been developed to search for the optimal fiber position, by actively measuring and maximizing the coupling efficiency. This search is performed before each bending step. Experiments have shown that it is possible to align the fiber with an accuracy of 0.2 μm using this approach