28 06 18

Pagina 1

Exercise n. 2 – technological problem Your Company is asked to manufacture a steel spring for automation technology applications (Figure 1). Figure 1. The spring to be cut. The sliding guide (highlighted) walls must be manufactured with higher surface quality. The component is made of stainless steel, starting from a 4 mm thick plate. Small geometrical defects are allowed in general, but tight tolerances must be accomplished on the walls of a sliding guide that will house a moving pin (as reported in Table 1). Your Company uses a µAWJ cutting centre equipped with Ø 0.30 mm and Ø 0.20 mm jets and fine abrasives (performances described in Table 2), with optional finishing by grinding (if needed and only for this first case), and a Wire-EDM cutting centre (performances described in Table 3, where Ra must be calculated according to the reported equations). Table 1 Geometrical defects and tolerances Symbol Value Unit GENERAL (length to be cut: 1250 mm) Maximum wall taper T_maxG 0.2 deg Maximum wall roughness Ra_maxG 2.0 µm SLIDING GUIDE (length to be cut: 215 mm) Maximum wall taper T_maxS 0.0 deg Maximum wall roughness Ra_maxS 0.8 µm Table 2 µAWJ performances, based on the set quality level (Q3 to Q5) Jet diameter [mm] vf [mm/min] Wall taper [deg] Ra [µm] 0.30 Q3 78 0.38 1.31 0.30 Q4 54 0.18 1.24 0.30 Q5 42 0.10 1.56 0.20 Q3 24 0.07 1.31 0.20 Q4 15 -0.02 1.22 0.20 Q5 12 -0.09 1.13 Table 3 Wire-EDM performances, based on the set quality level (Q3 to Q5) Configuration vf [mm/min] Wall taper [deg] Ra [µm] Roughing (Q3r) 68.4 negligible 0.0001vf2 + 0.0076vf + 2.6316 Roughing (Q4r) 37.6 Roughing (Q5r) 17.6 Semi finishing (Q3s) 10.4 -0.0017vf2 + 0.1069vf + 0.2056 Semi finishing (Q4s) 5.6 Semi finishing (Q5s) 3.2 Finishing (Q3f) 7.1 0.0113vf2 - 0.0021vf + 0.26 Finishing (Q4f) 4.8…