Issue 46

C. Bellini et alii, Frattura ed Integrità Strutturale, 46 (2018) 319-331; DOI: 10.3221/IGF-ESIS.46.29 322 defined on the mould drawing. As reported in Fig. 5a, the first machining phase, precisely that of rough milling, was done with a 20 mm diameter cylindrical tool; in this way the rough shape of the mould was obtained, without the groove for rib stratification and with a surface still to be finished. For the second machining phase, that consisted in the surface finishing, a tool change was necessary, since a ball nose tool with a diameter of 10 mm was used, as visible in Fig. 5b. Figure 2 : Length of the thickness variation zone. Figure 3 : Spline curves for groove intersections . Figure 4 : Circumferential groove depth variation following a plane surface. The third machining phase, reported in Fig. 5c, consisted in the milling of the stratification groove, made with a 5 mm cylindrical tool to obtain the groove width as defined in the design. These grooves also had a variable depth for the reasons extensively described above. At first the right-handed and left-handed helical grooves were machined and then the circumferential ones. For each groove there was a constant feed speed, changing only the z-axis in the points of interest,