PSI - Issue 10

E.L. Papazoglou et al. / Procedia Structural Integrity 10 (2018) 235–242 E.L. Papazoglou et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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they concluded that the thickness of the WL increases as the pulse energy is raised, while the magnitude of the pulse current has little effect on the WL thickness. Also, the density of surface cracks correlates with the thickness of the recast layer. Furthermore, Ra is related with the pulse current and the discharge energy. Rebelo et al. (1998) studied the SR, the metallurgical structure, the residual stress state and the surface crack network of the near surface layers after EDM for steels. Finally, there is an increasing interest in novel application of EDM process, not only to remove material from a workpiece, but at the same time to use it as a surface treatment method and/or as an additive process. Although the field of surface modification using EDM process is still at early stages, it has added a new dimension of capabilities to this technology (Kumar et al. (2009)). The current paper presents an experimental procedure for die sinking EDM, a reproductive shaping process in which the form of the working electrode is mirrored in the workpiece, for AISI O1 work steel as workpiece material and discharge energy higher than 2 mJ. The MRR is calculated, the Ra and Rt are measured and correlated with the machining parameters I P and T on . Finally, through microscopic observation, the WL quality and morphology are estimated for different discharge energies. The main aim of the current experimental procedure is to confirm the existence and the type of relation between machining parameters and machining performances and express them through semi empirical equations. Additionally, the white layer, which is formed on the machined surface, is studied and its quality and morphology variation, depending on the discharge energy, is investigated.

2. Experimental procedure and calculations

The experiments were carried out using an ANGIE EMT 1.10 die sinking machine, as shown in Fig. 1a, with a maximum current capacity of approximately 27 A and manual operating settings. The workpieces were rectangular blocks of AISI O1 work steel and in each block three experiments in successive positions were performed. A copper electrode tool with rectangular geometry and dimensions of 38x23 mm was used; it was cleaned of deposits between every experiment (Fig. 1b). The dielectric fluid was highly purified synthetic hydrocarbon oil.

Fig. 1. (a) AGIETRON EMT 1.10 EDM machine; (b) working electrode and experimental specimens

A series of 12 experiments were carried out, with the following machining conditions: straight polarity, voltage 100 V, pulse current I P from 12 A to 27 A, and pulse-on time from 75 to 500 μ s, see Table 1. The workpiece weight before and after machining, the average pulse current Ī P , machining efficiency (f eff ) and time (t m ) were transcribed for subsequent calculations, evaluation and analysis. The periodic movement of the servo head during machining (jumping cycles) was taken into consideration, in order to calculate the actual machining time. Furthermore, the maximum and average surface roughness Ra and Rt, respectively, as the mean from measurements made at five points on each machined surface, were measured. At the end, four specimens were grinded, polished and chemically attacked with Nital (10%) for evaluation of the recast layer quality and morphology through microscope observation.

Table 1. EDM experimental parameters # 1 2 3 4

5

6

7

8

9

10 15

11 12

12

I P [A] 8 T on [ μs ] 100 100 100 100 300 300 300 300 500 500 500 75 27 24 21 18 27 18 15 12 21