Additive manufacturing by laser melting has now offered a new cost-efficient way to produce optical freeform surfaces, with applications such as automotive lighting. Selective laser melting (SLM) is an additive manufacturing technique that potentially enables new, complex-shaped geometries. It allows to build prototypes of freeform reflectors from polymer-based materials with functional surfaces to which we can then apply a coating. Alternatively, it can create aluminium-based prototypes that do not require coating. Both strategies would reduce the manufacturing time and the carbon footprint of complex-shaped optical elements.
To evaluate the opportunities and challenges of SLM for optical reflectors, an automotive high-beam module was considered, which comprised of four blue laser diodes emitting blue light onto phosphor placed at the focal point of the reflector. This leads to the emission of nearly parallel light. The advantage of a laser-based light source using phosphor to generate white light is that the emission point of the white light is smaller than for other light sources, such as LEDs.
In summary, the use of SLM for fabricating optical components was explored, and it was found to be an efficient method with a carbon footprint that compares favourably with that of conventional fabrication techniques. Although SLM makes it relatively easy to generate a rigid structure that serves as a mounting base for additional parts, the requirement for a high reflection grade is a serious challenge. The typical SLM aluminium alloy AlSi10Mg offers a reflection grade of 50–70% after polishing, depending on the process parameters and the wavelength of the light. Therefore, our future studies will centre on evaluating other alloys for this purpose.