Study of the effects of laser micro structuring on grinding of silicon nitride ceramics B. Azarhoushang *, B. Soltani, A. Daneshi Institute of Precision Machining (KSF), Hochschule Furtwangen, Villingen-Schwenningen, 78054, Germany Submitted by Dr. Goverdhan D Lahoti 1. Introduction High performance ceramics (HPC) like Si 3 N 4 are highly demanded in different industries owing to their high mechanical strength as well as thermal and chemical stability. Due to the high hardness of these materials, they are finished by the grinding process. High tool wear and high grinding forces, along with the high sensitivity of the ground surface to crack propagation are the challenges associated with the grinding of Si 3 N 4 [1,2]. Hybrid grinding technologies like laser assisted grinding (LAG) were introduced to reduce grinding forces and tool wear [3,4]. In conventional LAG, the laser radiation heats up the workpiece surface prior to the cutting process and soften the surface of the workpiece. The softened zone with lower mechanical strength is subsequently removed by the cutting tool [3,4]. Although, this approach reduces the grinding forces, the effects of phase transformation and thermal cracks may remain on the ground surface of the workpiece [5]. Additionally, the laser scanner needs to be installed inside the machine and the laser beam should radiate close to the grinding area. These factors limit this approach to dry grinding. In recent researches, laser beam was applied to create thermal shocks and grow thermal cracks in the workpiece instead of thermal softening of the material. Afterwards, the cracked surface was removed by the cutting tool from the workpiece and the chipping process was carried out with less cutting forces compared to the conventional grinding (CG) because of the elevation of density of the thermal cracks on the workpiece surface [6,7]. Unlike previous LAG methods, wet grinding could be performed. However, due to utilisation of continues or pulsed laser (pulse duration 1 ms) an uncontrollable heat affected zone (HAZ) could be induced at the surface of the workpiece. Hence, the thermal cracks or phase transformations may remain on the final ground surface [8–10] and damage the quality of the finished workpiece [6,7]. In this study, short pulse laser (SPL) and ultra-short pulse laser (USPL) have been applied with an innovative concept to structure the surface of the workpiece with a specific geometry. The structured surface is removed by the subsequent grinding process. The thermal cracks induced by the laser ablation, along with the specific form of the produced micro structure on the workpiece surface weaken the material strength. Furthermore, the laser structuring removes material from the workpiece surface and reduces the volume of the material which should be removed by the subsequent grinding process. As a result, the grinding forces and energy will be reduced. The depth of induced HAZ could be significantly reduced by SPL and especially USPL compared to other laser types. Therefore, a ground surface without remained thermal cracks and phase transformation is achievable [11]. 2. Laser structuring Prior to the grinding, the workpiece surface (Si 3 N 4 , CeramTec- SL200 BG) was structured with two different lasers; a USPL with laser light intensity, I L = 2.49  10 11 W/cm 2 and pulse duration, t pulse = 10 ps and a SPL with I L = 9.9  10 7 W/cm 2 and t pulse = 100 ns. Both lasers are solid state pulse lasers with the wavelength of v L = 1030 nm. Laser wavelength and light intensity are parameters that determine laser–material interaction mechanism. Average pulse intensity is defined as [8]: I L ¼ E p t pulse  A f oc ð1Þ E p : laser pulse energy, A foc : laser irradiation area. In USPL, the pulses are so short, that the electron temperature and lattice temperature of the workpiece are different and far from CIRP Annals - Manufacturing Technology xxx (2018) xxx–xxx A R T I C L E I N F O Keywords: Laser assisted grinding Silicon nitride Specific grinding energy Ultra-short pulsed laser Laser energy Single grain cutting A B S T R A C T A novel laser assisted grinding process is developed to increase the material removal rates in grinding Si 3 N 4 . Micro structuring of the workpiece surface by nano- and pico-second laser radiations prior to the grinding led to a reduction of up to 55% in the specific grinding energy while simultaneously a slightly improved ground surface quality could be achieved. Ablation mechanism of nano- and pico-second lasers and surface integrity of the ground samples are studied. The results of single grain scratch tests suggest that the reduced specific grinding energy through laser structuring of workpiece is mainly due to the induced lateral cracks. © 2018 Published by Elsevier Ltd on behalf of CIRP. * Corresponding author. E-mail address: aza@hs-furtwangen.de (B. Azarhoushang). G Model CIRP-1817; No. of Pages 4 Please cite this article in press as: Azarhoushang B, et al. Study of the effects of laser micro structuring on grinding of silicon nitride ceramics. CIRP Annals - Manufacturing Technology (2018), https://doi.org/10.1016/j.cirp.2018.04.084 Contents lists available at ScienceDirect CIRP Annals - Manufacturing Technology journal homepage: http://ees.elsevier.com/cirp/default.asp https://doi.org/10.1016/j.cirp.2018.04.084 0007-8506/© 2018 Published by Elsevier Ltd on behalf of CIRP.