Selection of milling strategy based on surface integrity investigations of highly deformed Alloy 718 after ceramic and cemented carbide milling

Surface Integrity Investigation to Determine Rough Milling Effects for Assessment of Machining Allowance for Subsequent Finish Milling of Alloy 718

“…Furthermore, it was shown that down-milling resulted in longer tool life compared to up-milling. This agrees with the results shown by the author in prior investigations; the increased deformation and tensile stress state alters in the workpiece material depending on up or down-ward milling [8]. On the topic of tool wear, Hadi et al showed that down milling, on the contrary, resulted in less wear when milling using a tungsten carbide end mill for machining of alloy 718 [27].…”

“…It is also shown that by using this approach, it is possible to study the influence of different subsequent operations in the same profile. In relation to deformation, it has been shown in prior work that deformed grain boundaries could be observed to depths of 40 µm for ceramic milling and 6 µm for cemented carbide milling [8]. This is much less than the assessed impact depth determined based on the residual stresses shown in this work.…”

“…Figure 2 shows, an overview of the ceramic insert after the milling test and the new end-mill before the milling tests. The measurement of the cutting-edge radius was done using the confocal fusion technique using a principle described in prior work [8]. The edge radius was measured at three locations and the presented values are the mean values, including the standard deviations, for the measurements.…”

“…Selection of milling strategy might be crucial since the deformation and residual stresses can vary greatly. On this topic, the author has shown in prior work that the preferable milling strategy changed with tool wear [8]. A new tool shows lower impact for up milling but as the tool wear increases, down milling shows less deformation and lower tensile stresses.…”

“…A framework for how to assess a suitable machining allowance was suggested in the context of manufacturing an Alloy 718 gas turbine component, using milling in prior works by the authors [7,8]. In those works, the machining effects of the individual milling operations were investigated and a large impact from the rough ceramic milling was found as well as effects caused by tool wear, and thus, change of the cutting edge radii.…”