This work investigates the influence of the process parameters on the welding strength in hybrid polypropylene composites manufactured by injection overmolding. A hybrid T‐joint specimen was designed to evaluate the global performance of the welding by means of tensile tests. The effects of the process parameters were evaluated in accordance the design of experiments approach and the maximum strength (UTS) was assumed as response variable. The effects of melt temperature and holding pressure, combined to a variothermal mold‐control system, were investigated. The residual stresses induced by the process were considered by means of coupled thermo‐fluid dynamic/structural finite‐element analysis. Moreover, the topography of the laminate‐side surface was characterized and the process‐induced surface modification was related to the performance of the welding. Results show that the melt temperature contributes to increase the welding strength; conversely, the mold temperature counteracts this effect by increasing the residual stress at the interface. POLYM. ENG. SCI., 58:592–600, 2018. © 2017 Society of Plastics Engineers

Reducing vehicle weight to decrease energy consumption and engine emissions is one of the major objectives of the automotive industry today. This goal is mainly achieved by developing new manufacturing technologies for structural lightweight components, such as the hybrid injection molding/composite forming process, which involves preforming a thermoplastic composite laminate and overmolding it to add ribs, attachment points and other features. High part lightness, short cycle times and high degree of automation have recently made this technology an effective solution for the manufacturing of automotive interiors, including door side-impact beams and front ends. In this paper a model of the adhesion bonding mechanism between the overmolded reinforced thermoplastic and the formed composite sheet is proposed, and its dependence on the main process parameters is investigated. The model has been developed conducting experimental tests and eventually validated by means of a significant case study.

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