PSI - Issue 53

Bruno Sousa et al. / Procedia Structural Integrity 53 (2024) 291–298 Author name / Structural Integrity Procedia 00 (2023) 000–000

293

3

2. Materials and methods

2.1. Workpiece material and machining experimental testing

The chosen workpiece material is a representative tooling steel (AISI 420 modified, commercial name Uddeholm Stavax ESR), typically employed in moulding inserts given its excellent machinability and polishability allied to corrosion and wear resistance. Originally supplied in 60 mm diameter rods (in a soft annealed state), the workpiece material was quenched up to a hardness of 49 HRC (representative of insert moulds) and machined into small individual samples, as illustrated in figure 1d. These samples were placed on a 5 axis CNC machine (MAZAK CV5-500, figure 1a) and were machined using a ball nose end mill as the cutting tool (as depicted in figure 1b), a WC-Co coated 6 mm diameter with two flutes and AlCrN coating, produced by High Power Impulse Magnetron Sputtering (HiPIMS), shown in figure 1c. Figure 1e represents the workpiece material’s microstructure which was etched with Kalling’s reagent and then observed through optical microscopy (Olympus PMG3). An uniform dispersion of grain boundary carbides on a martensitic matrix is exhibited. Moreover, the material’s chemical composition was measured using spark emission spectroscopy (SPECTROMAXx). The obtained results (in table 1) allow for compliance confirmation of the processed materials with the chemical composition standard. A total of 9 parameter sets were selected to machine the samples (full factorial combination) as shown in table 2, using a cutting speed of 200m / min. Regarding milling toolpath, it can be observed in figure 1d.

Fig. 1. Workpiece material and experimental milling setup: (a) 5 axis milling machine MAZAK CV5-500; (b) illustration of sample clamping setup and milling strategy; (c) ball nose end mill; (d) scheme of milling sample evidencing toolpath strategy; (e) microstructure of the AISI 420 workpiece material, obtained by optical microscopy.

Table 1. Chemical composition of the Uddeholm Stavax ESR steel. Element C Si

Mn

Cr

V

wt.%

0.37

0.63

0.50

13.55

0.25

Table 2. Parameter levels using in the machining experimental testing, for a cutting speed ( V c ) of 200m / min. Test Reference: A1 A2 A3 A4 A5 A6 A7

A8

A9

Axial depth of cut, a p ( µ m) Radial depth of cut, a e ( µ m) Feed per tooth, f z ( µ m / tooth)

80 80 80

80

80

120

120 160 100

120 240 120

160

160 160 100

160 240 120

160 100

240 120

80 80

80 80