*3.2. Non-Conventional Manufacturing Processes—Electrical Discharge Machining (EDM)*

This review also presents some new insights into a non-conventional process, which is Electrical Discharge Machining (EDM). The process is a non-conventional machining method that allows the production of pieces with complex shapes, and it can be used in materials such as INCONEL® 718 and 625. This particular manufacturing technique removes material from the wrought-stock thanks to melting and vaporising cavities using electrical discharges that come from a scrolling wire [95], as illustrated in Figure 13.

**Figure 13.** Schematic representation of the EDM experiment setup (adapted from [96]).

Table 9 presents the latest experimental challenges and developments in the machining of INCONEL® alloys with EDM.

**Table 9.** Critical challenges and developments in the EDM process of INCONEL®.


#### **Table 9.** *Cont.*


#### *3.3. Tool Wear*

With the tool operation in machining, wear starts to be a key factor in quality and productivity, namely with INCONEL® alloys, such as 718 and 625. To identify a worn milling tool, the ISO 8688-2 [101] standard predicts that a tool presenting either *VB* = 300 μm or *VB*max = 500 μm on the flank is considered a worn tool [69]. For turning tools or inserts, the ISO 3685 standard is the one to consult [102]. Taking into account a novel lubrication method, Bartolomeis et al. [69] observed that the tool wear behaviour mechanisms during EL conditions were abrasion and microchipping on the cutting edge, due to the tendency of INCONEL® 718 to develop BUE.

Figure 14 packs the initial causes of wear, the various wear mechanisms that lead to different types of wear and the final consequences from the tool-wear due to INCONEL® machining. As a complement to Figure 14, Table 10 presents the typical TW mathematical models, used to characterize the numerous TW mechanisms. It is suggested to consult the work of Wang et al. [37] to better understand the additional variables described in Table 10.

**Table 10.** Typical TW mathematical models (adapted from [37]).

