It could just be that surfaces could soon be polished, coated or textured much faster by lasers. Within a European research project, Ultraface, two optics have been developed that allow the shape of a laser to be quickly and accurately adjusted a changing process conditions. The project also involved a Dutch party.
High precision and quality but too slow. That is a common complaint when it comes to laser processes. The Ultrasurface project has been looking for ways to improve this. Ten international partners from Germany, the Netherlands, Belgium, Israel and Switzerland joined forces in this. They have developed two new laser optics that will be available before the end of this year. These optics for the near-infrared range will reduce process times by up to a tenth and halve costs.
Polishing
One of the optics is specifically designed for polishing and machining thin layers with lasers. Here, the research team deploys a Piezoelectric Deformable Mirror (PDM), which can be continuously adjusted. This ensures that the laser can adjust to the process situation at intervals of less than 5 milliseconds. Extraordinarily fast, in other words. "The laser is reshaped depending on the beam angle so that its projection on the surface of the workpiece always has the same shape and the intensity is constant," explains Judith Kumstel, laser polishing expert at Fraunhofer ILT in Aachen, one of the organisations involved. This manipulation is important because only if the three-dimensional laser is constantly adjusted to the high machining speeds and hits the surface with a constant intensity will the result of laser machining always be the same, even with complexly shaped components and constantly changing beam angles. In contrast, if the laser projection distorts on skewed surfaces, the quality of the 3D surface machined also deteriorates.
Laser texturing
A different approach has been used for laser structuring. For this, a second new optic has been developed that allows four lasers to be used in parallel, instead of the usual single lasers, to increase machining speed and productivity. With a Diffractive Optical Element (DOE), the laser is split into four partial laser beams, which together form a square laser. In similar conventional multi-laser concepts, the optics at the end that focus the lasers on the part and the shape of the part create a distortion of the projected laser. The Ultrasurface project has now developed a special system that allows each individual part laser to be adjusted to its position in milliseconds, so that a square laser always remains for machining.
Industrial machine
Two compact optical modules are currently being developed. The Ultralaser team will test their potential in a new laser system in various applications until the end of 2018. A Swiss company is building an industry-ready machine that can be used to flexibly and cost-effectively polish, structure and coat at unprecedented speeds, thanks to its rapidly interchangeable optical modules. Judith Kumstel explains: "With the concepts developed in this project, surfaces will be able to be machined as well but much faster than with conventional systems. Thanks to the new optics and the new machine, machining will be ten times faster than before, so that finishing surfaces with lasers will be an alternative conventional methods of surface finishing; for many companies in different industries and even for small suppliers."
OKO Tech
OKO Tech is involved in the innovative project on behalf of the Netherlands. Flexible Optical B.V. (OKO Tech) is a small Dutch company active in the research and application-oriented development of high-resolution laser adaptors and adaptive optics. Since its founding in 1997, OKO has offered high-quality deformable mirrors with an extremely smooth surface with HR metal and dielectric coatings suitable for the most demanding image processing and high-performance laser applications.
One of the types of deformable mirrors manufactured by OKO are micro-milled membrane deformable mirrors (MMDM) with apertures in the range of 10 to 50 mm. MMDM represent an affordable high-quality solution for the correction of dynamic wavefront distortions in laser systems and telescopes and are successfully used in a number of applications. Due to their zero hysteresis, low light scattering and good switching capability (up to 500 W cw), MMDM are ideally suited for the feedforward intensity distribution control of the laser beam, required in the proposed project.
Within the project, OKO will improve the existing MMDM design and control electronics to meet the project requirements and supply the deformable mirrors including control electronics for the project purposes. Key persons are Dr Gleb Vdovin and Dr Oleg Soloviev.
Source: Metal News/Fraunhofer ILT
