The enhanced normalized normal constraint approach to multi-objective robust optimization in helical milling process of AISI H13 hardened with crossed array

Helical milling is an alternative to conventional drilling which, applied to the molds and dies industry, greatly impacts its competitiveness once it guarantees high levels of surface and geometrical quality. Excellent surface quality and the ability to drill holes with just one tool are some of the advantages of this process. Concerning the machining of hardened materials, its low machinability is another aspect that compromises the competitiveness of the mold segment. Faced with the challenges of hard machining, the present research aims the robust multi-objective optimization of AISI H13 hardened steel at high speeds to achieve competitive levels of surface quality and increase the productivity of the helical milling process. Experimental planning, robust parameter design with a focus on the crossed array, response surface methodology, and enhanced normalized normal constraint method were employed in the conduction of experiments, analysis, modeling, and optimization of the responses of interest. The responses evaluated were the mean roughness R_a, the total circularity Ron_t, and the material removal rate MRR. The control variables used were the axial feed per tooth f_za, the tangential feed per tooth f_zt, and the cutting speed v_c. For the robust parameter design, the tool overhang length l_to and borehole depth l_b were considered as noise variables. The possibility of increasing the productivity of helical milling in a hardened material, maintaining the quality of the holes, was concluded. It was verified to the total circularity robustness about the two noise variables, and the average of the confirmation runs is equal to the mean model.