Over the past several decades, aluminum foam (Al-foam) has found increasing popularity in industrial applications due to its unique material properties. Unfortunately, till date Al-foam can only be affordably manufactured in flat panels, and it becomes necessary to bend the foam to the final shape that is required in engineering applications. Past studies have shown that thin cell walls crack and collapse when conventional mechanical bending methods are used. Laser forming, on the other hand, was shown to be able to bend the material without causing fractures and cell collapse. This study was focused on the thermal aspects of laser forming of closed-cell Al-foam. An infrared camera was used to measure the transient temperature response of Al-foam to stationary and moving laser sources. Moreover, three different numerical models were developed to determine how much geometrical accuracy is needed to obtain a good agreement with experimental data. Different levels of geometrical complexity were used, including a simple solid geometry, a Kelvin-cell based geometry, and a highly accurate porous geometry that was based on an X-ray computed tomography (CT) scan. The numerical results were validated with the experimental data, and the performances of the numerical models were compared.

To date, metal foam products have rarely made it past the prototype stage. The reason is that few methods exist to manufacture metal foam into the shapes required in engineering applications. Laser forming is currently the only method with a high geometrical flexibility that is able to shape arbitrarily sized parts. However, the process is still poorly understood when used on metal foam, and many issues regarding the foam's mechanical response have not yet been addressed. In this study, the mechanical behavior of metal foam during laser forming was characterized by measuring its strain response via digital image correlation (DIC). The resulting data were used to verify whether the temperature gradient mechanism (TGM), well established in solid sheet metal forming, is valid for metal foam, as has always been assumed without experimental proof. Additionally, the behavior of metal foam at large bending angles was studied, and the impact of laser-induced imperfections on its mechanical performance was investigated. The mechanical response was numerically simulated using models with different levels of geometrical approximation. It was shown that bending is primarily caused by compression-induced shortening, achieved via cell crushing near the laser irradiated surface. Since this mechanism differs from the traditional TGM, where bending is caused by plastic compressive strains near the laser irradiated surface, a modified temperature gradient mechanism (MTGM) was proposed. The densification occurring in MTGM locally alters the material properties of the metal foam, limiting the maximum achievable bending angle, without significantly impacting its mechanical performance.

Aluminum foams are generally very attractive because of their ability of combining different properties such as strength, light weight, thermal, and acoustic insulation. These materials, however, are typically brittle under mechanical forming, and this severely limits their use. Recent studies have shown that laser forming is an effective way for foam panel forming. In this paper, the laser formability of Al–Si closed-cell foam through experiments and numerical simulations was investigated. The bending angle as a function of the number of passes at different laser power and scan velocity values was investigated for large- and small-pore foams. In the finite element analysis, both effective-property and cellular models were considered for the closed-cell foam. Multiscan laser forming was also carried out and simulated to study the accumulative effect on the final bending angle and stress states. The maximum von Mises stress in the scanning section was on the order of 0.8 MPa, which was lower than the yield strength of the closed-cell foam material. This paper further discussed the reasonableness and applicability of the two models.

To date, the industrial production of metal foam components has remained challenging, since few methods exist to manufacture metal foam into the shapes required in engineering applications. Laser forming is currently the only method with a high geometrical flexibility that is able to shape arbitrarily sized parts. What prevents the industrial implementation of the method, however, is that no detailed experimental analysis has been done of the metal foam strain response during laser forming, and hence the existing numerical models have been insufficiently validated. Moreover, current understanding of the laser forming process is poor, and it has been assumed, without experimental proof, that the temperature gradient mechanism (TGM) from sheet metal forming is the governing mechanism for metal foam. In this study, these issues were addressed by using digital image correlation (DIC) to obtain in-process and post-process strain data that was then used to validate a numerical model. Additionally, metal foam laser forming was compared with metal foam 4-point bending and sheet metal laser forming to explain why metal foam can be bent despite its high bending stiffness, and to evaluate whether TGM is valid for metal foam. The strain measurements revealed that tensile stretching is only a small contributor to foam bending, with the major contributor being compression-induced shortening. Unlike in sheet metal laser forming, this shortening is achieved through cell wall bending, as opposed to plastic compressive strains. Based on this important difference with traditional TGM, a modified temperature gradient mechanism (MTGM) was proposed.

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