# Analysis of the Chip Geometry in Dry Machining of Aeronautical Aluminum Alloys
## 2 Materials and Methods  
Several machining tests were carried out with test bars of two aeronautical aluminum alloys, UNS A92024-T3 (Al-Cu) alloy and UNS A97075-T6 (Al-Zn) alloy, both of which are widely used in the manufacturing of aircraft structural components. The composition of tested alloys, presented as a percentage of weight, is shown in Table 1.  
The machining operation selected to perform the tests was parallel horizontal turning, because it minimizes the geometric variables of the process and allows the cutting speed to remain constant. Cylindrical test bars (150 mm long and diameters between 40 mm and 60 mm) were used. Turning tests were carried out in a horizontal lathe, using the model Pinacho SP285R (seen in Figure 1a). All of the tests were conducted with a constant axial machining length, \(L\) = 100 mm, seen in Figure 1b. The tools used were neutral WC-Co uncoated turning inserts, with ISO DCMT 11T308F2 identification. Tool geometry is indicated in Figure 2. In order to ensure the same initial conditions, a new insert was used in each test. A configuration of cutting angles was used, shown in Table 2. Machining tests were carried out using techniques with low environmental impacts, so all of them were performed in dry conditions. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Alloy** & **Zn** & **Mg** & **Cu** & **Cr** & **Si** & **Mn** & **Al** \\ \hline UNS A92024 & 0.12 & 1.25 & 4.85 & 0.01 & 0.15 & 0.54 & Rest \\ UNS A97075 & 6.03 & 2.62 & 1.87 & 0.19 & 0.09 & 0.07 & Rest \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of machined alloys (mass%). In order to evaluate the influence of the cutting parameters on the chip geometry, different combinations of cutting speed (\(v_{c}\)), feed (\(f\)), and depth of cut (\(a_{p}\)) values were applied, as presented in Table 3. In this regard, previous researches have shown a higher influence of feed on the chip morphology of these alloys, whereas the influence of cutting speed and depth of cut were lower [32]. Accordingly, machining tests were carried out with a fixed \(v_{c}\) and \(a_{p}\). It should be pointed out that, although a low cutting speed is not recommended for machining aluminum alloys, these alloys are often hybridized with other materials, in which low cutting speed are required. The cutting process was monitored by using a SONY DCR-DVD92E Digital Camera, in order to record the chip generation process, as well as detect any machining issues. In addition, the generated chip was collected, photographed, and stored for further observations. With the aim of evaluating the evolution of the chip geometry along the axial machining length, the chip collection was conducted in three phases: at the beginning, the middle, and the end of machining. Subsequently, chip samples were  
Figure 1: (a) Horizontal lathe used in turning tests; (b) Cylindrical test bars. \begin{table}
\begin{tabular}{c c} \hline
**Cutting Angles** & **Value** \\ \hline Relief angle (\(\alpha\)) & 7\({}^{\circ}\) \\ Cutting edge angle (\(\beta\)) & 66\({}^{\circ}\) \\ Rake angle (\(\gamma\)) & 17\({}^{\circ}\) \\ Major cutting edge angle (\(\kappa_{\mathrm{r}}\)) & 62.5\({}^{\circ}\) \\ Insert included angle (\(\epsilon\)) & 55\({}^{\circ}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Cutting angles setup. Figure 2: Tool geometry and dimensions. prepared for observation by Stereoscopic Optical Microscopy (SOM). To complete this, metallographic techniques were used. Firstly, the samples were embedded in resin (STRUERS CLAROFAST) by using CITOPRESS-1 STRUERS equipment, Figure 3a. Later, they were polished using TEGRAPOL-11 STRUERS equipment, Figure 3b. Finally, a chemical etching was performed on the samples, in order to facilitate the observation of the chip geometry parameters. For this purpose, a KELLER reagent was used (95% H\({}_{2}\)O, 2.5% HNO\({}_{3}\), 1.5% HCl, 1% HF). Chip specimens (Figure 3c) were observed using an inverted metallurgical microscope, EPIPHOT 280 NIKON (Figure 3d).