# Analysis of the Chip Geometry in Dry Machining of Aeronautical Aluminum Alloys
## 1 Introduction  
Light alloys, especially aluminum alloys, have been traditionally used in the aircraft industry, mainly in the manufacturing of aircraft structural components [1; 2]. However, in the last few decades, new materials, such as Carbon Fiber Reinforced Polymers (CFRP), are being used in the manufacturing of these parts [3]. Frequently, these new materials are utilized in combination with light alloys, to form Fiber Metal Laminates (FML) structures (CFRP/Al) [4]. Notwithstanding, most of the aeronautical projects for commercial aircraft usually have a lifetime of about 15-20 years [5]. So, these alloys are still used in the manufacturing of parts such as wing tension members, shear webs, and ribs, where critical requirements include high compressive strength, tension loading, or fatigue [6]. Consequently, their probability of failure must be reduced. As a result, their manufacturing must be carried out with narrow margins of deviation from design specifications [7]. Among the different forming processes used in the manufacture of these parts, machining is one of the most common (mostly turning, drilling, and milling operations) [8; 9]. Although aluminum alloys have, in general, good machinability [10], when they are hybridized with CFRP, several problems arise, which remain mostly unresolved [11; 12]. One of the critical factors influencing these processes is the need to complete machining in dry conditions. There are various reasons that lead to such machining under these conditions. On the one hand, CFRP do not exhibit good behaviour under cutting fluids [13]. On the other hand, the mixture of aluminum chips, CFRP, and cutting fluid presents difficulties when it comes to recycling [14]. In addition, the new environmental laws call for the use ofsustainable manufacturing technologies [15; 16]. This requires minimizing or eliminating toxic and/or environmentally harmful substances, such as cutting fluids [17; 18]. Under these dry conditions, the chip evacuation becomes an especially relevant factor, either when machining aluminum alloys as an isotropic material, or during hybridization with composites. High temperatures in the cutting area result in material adhesion phenomena of the cutting tool, which hampers the chip evacuation. In addition, the chip morphology can be related to the tool wear and the surface integrity of the machined part [19; 20; 21]. Therefore, it influences the dimensional accuracy of the part, and the continuity and stability of the process [22]. Because of this, the control and monitoring of the chip formation are important to consider during the performance improvement of machining processes [23]. The chip morphology depends on cutting parameters (cutting speed, feed, and cutting depth), tool geometry, the relative position of the tool-workpiece, and work material properties [24]. In the literature, many research works on the impact of cutting conditions on the chip formation process and the mechanism of chip formation, can be found [25; 26; 27; 28; 29; 30]. So, in the case of dry machining aeronautical aluminum alloys, most of the studies are devoted to characterizing the chip arrangement and morphology under different values of cutting parameters, in order to obtain information about the machinability of a particular alloy [31]. However, there are a lack of studies dedicated to obtaining the relationship between cutting parameters, and geometric and dimensional chip parameters, especially in dry machining. In this regard, there are few studies devoted to obtaining parametric relationships, which allow one to predict the chip morphology and its geometric parameter values, as a function of the cutting parameters [7; 32]. In this work, a study of the feed influence on chip morphology in dry machining of UNS A97075 (Al-Zn) and UNS A92024 (Al-Cu) alloys has been performed. Different geometric parameters of the chip morphology have been obtained and their evolution with feed has been analysed.