Materials 2021, 14, 5697. https://doi.org/10.3390/ma14195697 www.mdpi.com/journal/materials Article Experimental Investigation on Dry Routing of CFRP Composite: Temperature, Forces, Tool Wear, and Fine Dust Emission Tarek Elgnemi 1 , Victor Songmene 1, *, Jules Kouam 1 , Martin B.G. Jun 2 and Agnes Marie Samuel 1 1 Department of Mechanical Engineering, École de Technologie Supérieure (ÉTS), Montreal, QC H3C-1K3, Canada; tarek-shaban-mohamed.elgnemi.1@ens.etsmtl.ca (T.E.); jules.kouam@etsmtl.ca (J.K.); agnesmsamuel@gmail.com (A.M.S.) 2 Department of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA; mbgjun@purdue.edu * Correspondence: victor.songmene@etsmtl.ca Abstract: This article presents the influence of machining conditions on typical process performance indicators, namely cutting force, specific cutting energy, cutting temperature, tool wear, and fine dust emission during dry milling of CFRPs. The main goal is to determine the machining process window for obtaining quality parts with acceptable tool performance and limited dust emission. For achieving this, the cutting temperature was examined using analytical and empirical models, and systematic cutting experiments were conducted to assess the reliability of the theoretical predictions. A full factorial design was used for the experimental design. The experiments were conducted on a CNC milling machine with cutting speeds of 10,000, 15,000, and 20,000 rpm and feed rates of 2, 4, and 6 µm/tooth. Based on the results, it was ascertained that spindle speed significantly affects the cutting temperature and fine particle emission while cutting force, specific cutting energy, and tool wear are influenced by the feed rate. The optimal conditions for cutting force and tool wear were observed at a cutting speed of 10,000 rpm. The cutting temperature did not exceed the glass transition temperature for the cutting speeds tested and feed rates used. The fine particles emitted ranged from 0.5 to 10 µm aerodynamic diameters with a maximum concentration of 2776.6 particles for those of 0.5 µm diameters. Finally, results of the experimental optimization are presented, and the model is validated. The results obtained may be used to better understand specific phenomena associated with the milling of CFRPs and provide the means to select effective milling parameters to improve the technology and economics of the process. Keywords: CFRP; machining; temperature; cutting forces; dust emission; tool wear 1. Introduction The use of a carbon fiber reinforced polymer (CFRP) has considerably increased in the last few years. The aerospace and automotive industries especially are concerned about these materials, due to the fact that (i) CFRPs are relatively easy to manufacture using several automated lamination techniques; (ii) they feature excellent unique mechanical properties as well as good chemical and dimensional stability; and (iii) their corrosion and heat resistance are also outstanding [1–3]. The main attraction of these materials is the low density compared to the traditional engineering materials such as steel or aluminum [4]. These characteristics allow for a reduction in costs [5,6], which is an important requirement in any kind of industry. However, due to the multiphase and inhomogeneous nature of the material, various types of damage, e.g., fiber breakage and pullout, fuzzing, delamination, resin degradation, etc., are easily induced [7,8]. In addition, the highly abrasive nature of the carbon fibers and the low thermal conductivity Citation: Elgnemi, T.; Songmene, V.; Kouam, J.; Jun, M.B.G.; Samuel, A.M. Experimental Investigation on Dry Routing of CFRP Composite: Temperature, Forces, Tool Wear, and Fine Dust Emission. Materials 2021, 14, 5697. https://doi.org/10.3390/ma14195697 Academic Editor: Karim Benzarti Received: 3 August 2021 Accepted: 22 September 2021 Published: 30 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses /by/4.0/).