Effects of cutting strategy in the contour milling of open pocket AISI H13 with a low ratio thin-walled feature

Abstract

In the pocket machining of hard material with a thin-walled structure, the selection of cutting strategy and conditions significantly influences the process, machined part, and tool condition outputs. Variations in cutting engagement variables, including cutting speed, feed rate, and depth of cut, could either significantly improve or deteriorate the cutting time components, machined part quality, and tool conditions to certain levels. This research combined the roughing and finishing operations in the pocket milling of hardened AISI H13 tool steel. Two consecutive cutting processes, with different contour tool paths, were integrated into a single operation (run) made for two distinct features of open pocket lateral wall and low-ratio thin-walled feature.

The organisation of the research was made into two consecutive parts. The first part was carried out entirely through the conduct of virtual machining for the development of tool path and the investigation of simulated machining time, while the second part was focused on the actual machining to collect experimental data for the characterisation of the process, workpiece and tool wear. Supersaturated response surface methods: Definitive screening design (DSD) was used as the experimental design where eleven independent variables were employed for the virtual machining, and six independent variables were employed for the actual cutting processes.

The simulated feeding time and rapid time results indicated that the axial and radial depth of cuts, the incremental distance of feeding and rapid planes, as well as the fixed components and rapid traverse speed overrides were among the variables that contributed to the tool path length; hence, increasing the machining time. In terms of actual machining, the significant variables for the open pocket wall machining were (1) cutting speed vc(OP), (2) feed rate vf(OP), (3) and depth-of-cut for finishing operation DOCf, and for the thin-walled feature machining were (1) the depth-of-cut for roughing operation DOCr, (2) cutting speed vc(TW), (3) and feed rate vf(TW). The observations on cutting temperature suggested that the two cutting processes of open pocket wall and thin-walled feature differed due to the different radial depth of cut. The maximum observable cutting temperature for the machining of the open pocket wall was 278.1 ˚C, while the thin-walled feature was 107.9 ˚C. The surface roughness was ranged from 0.09 to 0.27 μm for the pocket floor, 0.35 to 2.03 µm for the lateral pocket wall, and 0.15 to 1.58 μm for the thin-walled feature. Furthermore, the observations on mechanical surface alterations showed the presence of built-up edge, burr, and feed marks in almost all experimental runs.

The findings of this research were expected to be useful for other researchers and industrial practitioners by providing valuable multiple data that could act as a point of reference in carrying out similar processes. In this case, the research parameters can be further adapted for the production of parts with certain desired outputs, particularly in terms of machined part tolerances, allowances, and surface roughness. Furthermore, the data from tool damage observations can also be adopted to further develop the tool life estimation from the application of a similar tool class.