The drilling of holes in CFRP/Ti (Carbon Fiber-Reinforced Plastic/Titanium alloy) alloy stacks is one of the frequently used mechanical operations during the manufacturing of fastening assemblies in temporary civil aircraft. A combination of inhomogeneous behavior and poor machinability of CFRP/Ti alloy stacks in one short drilling brought challenges to the manufacturing community. The impact of the drilling temperature and time delay factor under various cutting conditions on hole accuracy when machining CFRP/Ti alloy stacks is poorly studied. In this paper, the drilling temperature, the phenomenon of thermal expansion of the drill tool, and hole accuracy are investigated. An experimental study was carried out using thermocouples, the coordinate measuring machine method, and finite element analysis. The results showed that the time delay factor varied from 5 (s) to 120 (s), influences the thermal-dependent properties of CFRP, and leads to an increase in hole roundness. Additionally, the thermal expansion of the drill significantly contributes to the deviation of the hole diameter in Ti alloy.

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The sound velocity of Sedlec kaolin during heating from 20 • C to 1100 • C was investigated by modulated force thermomechanical analysis (mf-TMA). In the interval from 20 • C to 250 • C, the sound velocity increases which can be explained by liberation of the water molecules from pores and micropores. Dehydroxylation (450 • C to 650 • C) presents itself with a decrease of the sound velocity. After dehydroxylation, a two-step increase of the sound velocity was observed. The first step of the increase of the sound velocity is due to solid-state sintering at low temperatures. The second step starts at 950 • C as a consequence of the collapse of the metakaolinite structure. After the maximum, a steep increase of the sound velocity follows as a result of solid-state sintering.

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In this paper the laser surface texturing (LST) technology as one of the methods of tribological properties modifying of mating steel surfaces is analysed. The area density of dimple-like depression along with the dimple diameter are the only main factors which significantly influence the friction coefficient value, therefore the effect of different values of area density of dimples: 6 %, 11 % and 16 % on the contact coefficient of friction was analysed. Surface textures were manufactured on the planar areas of compression platens (90MnCrV8 tool steel) using a pulsed-beam laser. The values of coefficients of friction were obtained via a ring compression test. Test sample compression was realized in lubrication-free and hydrodynamic regime. A significant improvement of tribological properties in contact steel areas was experimentally observed in both friction regimes. The results of experiments showed that by applying of surface texturing with defined shape and dimensions of dimples and lubricating oil at the same time, the coefficient of friction value can be reduced to about of 75%.