A collaborative project including partners from research and industry has developed a laser machine that triples the rate at which embossing tools can be structured for use in the automotive industry.
The eight-axis machine developed within the ‘eVerest’ project – whose partners include entities such as Volkswagen, Fraunhofer ILT, Scanlab, Precitec Optronik, and Amphos – comprises an ultrashort pulse (USP) laser, a nanosecond laser, innovative scanner technology and OCT-based process monitoring.
The system dramatically increases the rate at which three-dimensional patterns can be applied to the embossing tools used in the automotive industry to apply textures to the plastic interior of vehicles. Such textures are used to convey an impression of superior quality.
While it takes automotive suppliers a matter of minutes to fabricate this kind of surface using injection moulding, manufacturing the metal tools required to produce them takes significantly longer – up to four weeks are usually required just to structure the tool. The three-dimensional texturing is either etched onto the tool in dozens of individual steps, or created by means of a laser process with ablation rates in the region of approximately 1mm³/min.
Since January 2016 the eVerest research project has therefore brought together five companies and three research institutions in order to radically improve the throughput of the laser structuring technology used in such applications, while also increasing its resolution to the micrometre regime.
Optimal structuring
The project partners optimised the laser structuring process in a number of ways.
Dead times in the current scan paths were reduced through the use of innovative scanner technology developed by Scanlab, which led to a tripling of the laser structuring throughput.
A USP laser was also introduced to accompany the nanosecond pulsed laser previously used in such processes. While such USP lasers have traditionally been criticised for their low productivity, a particularly powerful, actively cooled fibre-coupled USP laser from Amphos – a Fraunhofer ILT spin-off and Trumpf subsidiary – was used to obtain the same ablation rate per watt that was previously achievable using the nanosecond laser. The higher precision enabled by the USP laser also made it possible to reduce surface roughness to less than 0.5µm.
For quality assurance purposes, both during and post-processing, the partners included two fibre-coupled OCT systems from Precitec Optronik. The inline system facilitates resolutions of 5µm, while the post-process system is able to achieve resolutions as high as 1µm.
The individual components were incorporated into a machine based on the Lasertec 125 from DMG Mori. The goal here was to ensure that the machine was easy to operate without requiring any specialist expertise, and that the number of processes involved were reduced to a minimum.
The Lasertec 125 from DMG Mori. (Image: DMG Mori)
The simplicity of the resultant technology represents one of the main advantages over currently used etching techniques, which frequently rely on the instincts and dexterity of the machine operator. This simplicity was achieved through the development of special software tools at RWTH Aachen University, which enable users to simulate the desired structures precisely on the surfaces and visualise their appearance in real time.
The process itself is now being tested in collaboration with partners at Volkswagen, but the potential applications of the core technology extend beyond the automotive industry. From embossing rollers in the printing industry to large bearings for rotor shafts in wind turbines, structured and functional surfaces are required across a broad variety of sectors.
The eVerest project (‘Machine and systems technology for the efficient production of large-format 3D mould tools with design surfaces’) was funded by the German Federal Ministry of Education and Research (BMBF) and is set to conclude on 30 June 2019.
Additional project partners to those mentioned includes Sauer and the Photonics Laboratory at Münster University of Applied Sciences.