Notes
Aluminium foams are one of the materials, which are gaining popularity in modern engineering. They are used where lightweight structures are required to carry mechanical and thermal loads or have the capacity to absorb impact energy. Aluminium foam elements generally have a porous core surrounded by a thin, non-porous outer layer. This layer significantly affects the mechanical properties of the element and has the function of protecting against internal corrosion. Mechanical processing by cutting deforms non-porous layer, which leads to a reduction in strength properties and exposure to internal corrosion. The dissertation describes the mechanical processing of different types of closed-cell aluminium foam. In the first part, mechanical processes such as turning, milling, drilling, and single-point incremental forming of samples foamed in moulds were performed. These samples had a porous core and a thin layer of an outer non-porous surface. Better results were obtained using the single-point incremental forming process. With this process, simple shapes such as grooves, slots, etc. could be produced without collapsing the homogeneity of the surface. In the second part, incremental forming and friction rolling studies were conducted on four different aluminium foam samples, with porous outer surfaces. The samples specimens, which differed in density, cell size, and metallurgical composition, were fabricated using a band saw with minimal surface deformation. A carbide tool was used for the forming process. Each sample was machined with the front and side of the tool using well-defined machining parameters (deformation depth, feed rate, and spindle speed). The treated surface was stained for better contrast between the porous and non-porous parts of the surface. High-resolution digital photographs of the treated surfaces were taken and analysed using image segmentation with multispectral thresholding algorithms. The change in surface porosity was calculated for each sample and the influence of the selected machining parameters was determined using the surface response methodology. From the test results, it was found that spindle speed had the greatest effect and the feed rate had the least effect on the reduction of surface porosity. Then, the machining forces and the thickness of the deformed surface were measured and evaluated. Quasi-static compression tests were performed on the treated samples, and the influence of the treated surface on the constant compressive strength in ?-? diagram, was determined. It was found that the thickness of the deformed surface depends on the deformability properties of the aluminium foam. Samples with a higher purity of aluminium, the deformed layer was thicker, which, as the tests showed, meant a higher compressive strength. During the study, it was found that the compressive strength of elements produced with material removal processes, can be significantly increased by subsequent forming processes, such as incremental forming and friction rolling. The use of such a combination of machining processes, carried out on the same CNC machine is useful in small-batch production, where semi-finished products such as blocks, bars and sheets of aluminium foam can be used.