13 09 18

Pagina 1

Course of ADVANCED MANUFACTURING PROCESSES Proff. Michele Monno – Barbara Previtali – Matteo Strano SURNAME NAME PERSONAL ID Exam - September 13rd 2018 Exercise n. 2 – technological problem Your company is equipped with an abrasive water jet (AWJ) machine and a laser cutting center both able to cut 10 mm thick plate (h) of stainless steel. You are required to compare these two technology in terms of feasibility and cost in order to determine the best solution to cut a perimeter of 400 mm on this material. Regarding the AWJ solution you can refer to table 1, while table 2 is referred to laser cutting center. Table 1 AWJ DATA Symbol Value Unit CUTTING HEAD Primary orifice diameter do 0.30 mm Overall discharge coefficient Cd 0.70 - Focusing (mixing) tube diameter dm 0.90 mm PROCESS PARAMETERS Water density ρw 1000 kg/m3 Water pressure P 350 MPa Abrasive mass flow rate ma 6 g/s Feed (traverse) rate u 80-100 mm/min Material erosion strength σf 35000 psi Abrasive-solid friction coefficient µ 60 - Abrasive particle velocity in the jet va 620 m/s Maximum trail back accepted tb_max 1 mm Trail back (M. Hashish, 2016) (empiric formula - use radians) 𝑡"=𝑙𝑛&𝑠𝑒𝑐*ℎ∙𝑢𝑣/0∙1𝑣𝑢2 mm Coefficient for trail back calculation (empiric formula) 𝑣= 𝜇∙𝑚6∙𝑣67𝜎9∙𝑑; - MANAGEMENT AND COSTING Machine cost Cm_w 200,000.00 € Amortization period Ay 5 years Purified water cost Cw_w 8.00 €/m3 Abrasive cost Ca_w 420.00 €/ton Energy cost Ce 0.08 €/kWh Cutting hours per day t 7 h/d Working days per year d 200 d/y Electric power absorbed from the network Pe_w 42 kW 1. The AWJ CAM software suggests two feed rate levels (80 and 100 mm/min). Verify if also the constraint on trail back is matched. 2. Calculate the expense for AWJ cutting. Calculate the expense for a 400 mm long cutting at the feed rate level…