PSI - Issue 53

R.D.F.S. Costa et al. / Procedia Structural Integrity 53 (2024) 376–385 Costa, R. D. F. S./ Structural Integrity Procedia 00 (2023) 000 – 000

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in multi-material type I and drill 1, lower forces and torques are obtained for the same feed when the cutting speed is increased. On the other hand, when the cutting speed is equal, but the feed increases, both forces and torques increase greatly, meaning that a higher feed gives rise to a worse result in the material. Finally, multi-material type II also generates higher values for the two variables in analysis, as the tool begins to drill in the aluminium layer, which can withstand higher loads due to its ductility, being subjected to plastic deformation. Since this type of multi-material has more aluminium layers, the forces are higher, corroborating the conclusions in the last paragraph. Additionally, a Taguchi scheme was developed and an analysis of variance (ANOVA) was performed to the data from the first set of experiments with multi-material type I and drill 1, since it was the one where the evaluation of the parameters influence was made, in order to show the contribution of each parameter to the results, as well as their statistical significance. Furthermore, an L4 experiment was carried out, just with the tests where a full factorial was developed, i.e., with feeds of 0.15 and 0.3 mm/rev. and cutting speeds of 150 and 300 m/min., using the respective maximum thrust force and drilling torque obtained from the data acquisition. From this statistical approach, Figure 4 shows the Taguchi analysis of the L4 scheme considering the thrust force (a) and drilling torque (b) maximum values obtained from the holes drilled. The two graphs are similar, which means the results are in accordance with each other, and allow to conclude that the feed has a much higher influence on these two outcomes than the cutting speed. Moreover, the optimum set of parameters, the one which generates lower forces and torques, is for lower feeds and higher cutting speeds. From the ANOVA (Table 2), although no parameter has statistical significance, i.e., has a P-value lower than 0.05 (since 5% is the typical statistical significance level), the feed considering the torque is clearly the parameter which has a better significance, being close to the limit, fact which corroborates the graphs analysis of Figure 4. Statistical approaches are more and more chosen by authors in the literature to complement and support their findings, such is the case of Kuo et al. (Kuo et al., 2017), who employed the Taguchi method in their CFRP/Al laminates drilling. Sridhar et al. (Sridhar, Bolar, & Padmaraj, 2022) conducted an ANOVA, observing that feed had a considerable impact on the thrust force, being more significative than spindle speed, which is in agreement with the present study. Additionally, in their work, aiming to investigate the effect of drilling parameters on thrust force while drilling carbon fibre reinforced aluminium laminates, they concluded that when the axial feed rate was increased, higher thrust forces were originated.

a

b

Fig. 4. Taguchi analysis of the L4 scheme experimental drilling tests considering the thrust force (a) and drilling torque (b) maximum values.

Table 2. Analysis of variance of the L4 scheme experimental drilling tests considering the thrust force and drilling torque maximum values.

Factors

Source

GL

SQ (Adj.)

QM (Adj.)

F value

P-value

Feed

1 1 1 3

167809 10699

167809 10699

34.15

0.108 0.379

Thrust force

Cutting speed

2.18

Error Total

4913

4913

183421