Multidisciplinary framework for Laser Assisted Direct Joining Analysis of AISI304 and polycarbonate

During Laser Assisted Metals and Plastic joining (LAMP), the metal sheet is heated by means of a laser source; thus, heat is conducted to the polymer (that is forced against the metal sheet) causing softening and melting. The presence of small bubbles that develop at the interface forces the molten plastic to adhere to the metal surface. As a result, van der Waals forces produce the interaction force between the sheets. Two main phenomena may occur during the process, including: insufficient heating of the polymer that leads to weak or absence of adhesion, or excessive heating, which may lead to the polymer degradation, with consequent material loss, formation of fumes and excessive increase of the bubbles size at the interface. These cause a reduction of the effective adhesion area and, then, a reduction of the joint strength. A number of investigations have been conducted until now by means of a pure experimental or modelling approaches. Both these approaches suffer of some limitations, e.g. difficulty to experimentally determine the thermal field during the process, difficulty to characterize the polymer degradation by means of very fast thermal cycles (hundred Celsius degrees per second), high inhomogeneity of the bonds produced. On the contrary, numerical modeling of the process (once correctly validated) enables the prediction of the thermal field at the interface, but does not provide any information about the strength of the joint, local dimension of the bubbles, and information concerning the degradation of the polymer. The present investigation concerns the development of a multidisciplinary framework for the analysis of LAMP process. Since adhesion of the substrates depends on the thermal field developing during the process, a FE model was adopted to estimate the temperature field. Thus, experimental tests of LAMP were conducted on AISI 304 stainless steel and polycarbonate sheets to determine how laser beam power and scanning speed affect the strength and the morphology of the joints. Finally, the local strength of the joint was related to the temperature field to build a strength-temperature function that enables the estimation of the overall strength of the joint. Although the study is still under development stage, early tests cases confirmed the effectiveness of the developed framework.