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

379

4

a

b

Fig. 2. Multi-materials used in the drilling process: (a) type I plate; (b) type II plate. A universal machining centre (DMG Mori DMU 60 eVo) was employed in all drilling experiments, alongside a clamping system fixed to the machining centre table, for a proper multi-material back support. The cutting load and torque were measured through a spindle-mounted Kistler type 9170A rotating dynamometer and data acquisition system. The dynamometer consists of two parts, the stator and the rotor, being positioned directly on the spindle. The stator is then coupled with a Kistler type 5238B signal conditioner, which is coupled with a Kistler type 5697 data acquisition system, allowing the connection with the Kistler DynoWare software for results analysis. Regarding the drilled holes analysis, for delamination damage assessment, the surface of the drilled holes was examined through a DinoLite AM-4031MZTL digital USB microscope, connected to the DinoCapture 2.0 software, for image collection and visualization , which was also used for the tools’ wear analysis. To infer on eventual intra or inter delamination, an X-ray analysis was carried out. For this to happen, the specimens were immersed for 30 minutes in an Analar Normapur Diiodomethane solution, followed by drying and posterior X-ray subjection in a Satelec X Mind X-ray emitter and a Kodak RVG 5100 digital sensor, positioned beneath the hole for photo taking. Afterwards, the pictures were treated using a Matlab script developed by (Marques et al., 2022), for image correction and delamination factor evaluation. For roughness analysis, a band saw machine cut through the holes meant to be measured and a mechanical roughness meter was used. Additionally, s ome holes’ 3D surfaces were generated using the Alicona Infinity Focus SL microscope, for supplementary data. 3. Results and discussion The experimental drilling tests began with the multi-material type I. Several combinations of different parameters were used in an iterative process at first, intended to assess the influence that each parameter had on the composite surface delamination. A set of low, medium and high level parameters were used, namely feeds of 0.05, 0.1 and 0.15 mm/rev. and cutting speeds of 50, 100 and 150 m/min., and from that inspection, the next tests were followed. Afterwards, the cutting speed was increased to 300 m/min., which revealed to be a good parameter value. A 0.3 mm/rev. feed was also tested, but severe delamination was registered, so this was an issue to be solved, reason why later the feed was decreased once more to 0.05 mm/rev., keeping the cutting speed at a high level, as observable in Table 1. The tests performed with drill 1 intended to assess the defects which arose in the multi-material, whereas in the case of drill 2 a much higher number of holes was produced, so as to evaluate the tool wear. For the multi-material type II, the same parameters as the first set were used, but it was quickly found that this configuration supported a higher feed, namely of 0.2 mm/rev., but the cutting speed had to be lowered again to 150 m/min. for compensation. Nevertheless, this last combination was the one with the higher material removal rate (MRR) and, thus, more preferable for the industry, since it takes less time to drill, resulting in higher process efficiency and cost reduction. Table 1. Combination of parameters and respective features used in the main drilling campaign.

Multi-material

Drilling tool

Feed (mm/rev.)

Cutting speed (m/min.)

MRR (cm 3 /min.)

Number of holes

Drill 1 (N-type) Drill 2 (W-type)

0.05 0.05

300 300

22.5

45

Type I (CFRP/Al/CFRP)

24

345

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