19 02 19

Pagina 1

Course of ADVANCED MANUFACTURING PROCESSES Proff. Michele Monno – Barbara Previtali – Matteo Strano SURNAME NAME PERSONAL ID Exam - February 19th 2019 Exercise n. 2 – technological problem A famous automotive company needs to evaluate the capabilities of laser marking for several car pieces. As application engineer of a laser laboratory you are requested to determine process parameters and evaluate the productivity of the proposed application with the facilities of the lab. To start, you decide to perform some tests on a AISI 304 metal sheet. To have marking, the surface has to reach a temperature of 450°C. You use a marking unit composed by a pulsed laser source and a scanner head; further specifications are reported in Table 1. Due to the high beam intensity, the beam focal position is placed 2mm above the surface. Finally, the pulse shape is assumed to be rectangular. 1. Calculate the spot diameter and the absorbed heat flux. 𝒅𝒘𝒂𝒊𝒔𝒕 [µm] 𝒅𝒔𝒑𝒐𝒕 [µm] 𝒒𝟎, abs [MW/m2] Table 1 Processing data Symbol Value Unit Pulsed laser source specification Laser power 𝑃 5 W Laser type - Fiber - Beam quality factor 𝑀/ 1.7 - Collimated diameter 𝐷123 5.9 mm Focusing lens 𝑓521 200 mm Process paramters Material - AISI 304 - Heat conductivity 𝜅 16.2 W/mK Thermal diffusivity 𝛼 3.68 x 10-6 m2/s Treatment temperature 𝑇9:;< 450 °C Ambient temperature 𝑇= 25 °C Surface absorptivity 𝐴= 0.7 - Pulse duty cycle 𝛿 20 % Pulse repetition rate 𝑃𝑅𝑅 80 kHz 2. Assuming that the process can be modelled using the Extended 1D heat laser source, calculate the number of pulses required to reach the treatment temperature. Neglect the effect of the previous pulse on the current one (consider each pulse independent from the others). 𝚫𝑻𝒔𝒕𝒆𝒑 [K] 𝚫𝑻𝒇𝒊𝒏𝒂𝒍 [K] 𝑵𝒑 [-] 3. Assuming the diameter of the spot diameter as…