Detecting the key geometrical features and grades of carbide inserts for the turning of nickel-based alloys concerning surface integrity

Machining science is aimed at defining both cutting tools and machining conditions based on economic performance and to maintain workpiece surface integrity. Currently, machinists face a wide offer of turning, milling, drilling, and threading tools. Tools present a lot of similarities and light differences between them, being the latter the concealed reasons for a better or worse performance on difficult-to-cut alloys machining. However machinists had not useful methods for detecting which key tool aspects implies the best performance. The classic and expensive 'test-trial' method results non-viable due to the market exponential increase, both in size and specialization. This paper brings up an indirect method for seeking common features in the group of those tools with the best performance on machining Inconel 718. The method is divided into five stages, namely: (a) raw testing of a basic operation with a lot of commercial solutions for the same operation; (b) filtering of results to reduce the feasible solutions to a few ones, studying the common features of successful cases; (c) testing of these feasible solutions aimed at choosing the best insert or tool (d); and finally (e) full testing concerning all workpiece surface integrity issues. The proposed method provides knowledge based on the distilling of results, identifying carbide grades, chipbreakers shapes, and other features for having the best tool performance. All surface integrity effects are checked for the best solution. This new point of view is the only way for improving the difficult-to-cut alloys machining, reaching technical conclusions with industrial interest. This paper shows the method applied on Inconel 718 turning, resulting in a carbide grade with 10% cobalt, submicron grain size (0.5-0.8 mu m) and hardness around 1760 HV, coating TiAIN monolayer with 3.5 mu m thickness, chipbreaker giving 19 degrees of rake angle that becomes 13 degrees real one after insert is clamped on toolholder. Cutting edge radius after coating was 48 mu m approximately. Cutting speed was 70 m/min higher in comparison with that recommended in handbooks.