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18-07-2017 ADVANCED MANUFACTURING PROCESSES A.Y. 2016-2017 Prof. C.A. Biffi Exercise 1 In the industry, in which you are working, you are required to design the cutting process, performed by means of abrasive water -jet machining. You are asked to design the dimension of the primary nozzle and the oil pressure (section ratio equal 5:1) in order to guarantee a maximum power of 80 kW in correspondence of a single intensifier feeding 4 cutting heads. The thickness of the sheets is 5 mm and the kerf width is about 1.2 mm for all the products in order to reduce the removed material. During the production of the components, a constraint on the productivity has to be kept constant and equal to 35 cm 3/min for each cutting head. The coefficient of discharge is evaluated to b e about 0.7 and the efficiency coefficient is equal to 80%. You are also required to evaluate the process speed during the cutting process and the final water stream velocity. Exercise 2 Stainless steel plates of 3 mm in thickness have to be cut with a Co2 laser source (the laser was focused with meniscus lens: kas=0.029; f=120 mm; df=20 mm) with a cutting speed of 6 m/min. It is required to calculate the values of power enough to cut the plates, defining the correct focus position, with BPP = 6 mm∙mrad, as well as the laser spot size. Consider the following data for the material properties: • Density 8030 kg/m3 • Thermal capacity 500 J/kgK • Thermal conductivity 20 W/mK • Latent heat of fusion 300 kJ/kg • Latent heat of evaporation 6500 kJ/kg • Melting temperature 1450 °C • Fraction of the vaporized material 10%