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.

The article considers the issue of modeling the oscillations of a boring mandrel with vibration damper connected to the mandrel with a viscoelastic coupling. A mathematical model of the boring mandrel oscillations, machine support and inertial body (damper) is developed in the form of a differential equations system. The model is made in the form of a four-mass system of connected bodies. The solution to the differential equations system was found using the finite difference method, as well as the operator method with the use of the Laplace transform. As the simulation result, it was found that the use of vibration damper can significantly reduce the amplitude of the boring mandrel natural vibrations when pulsed, and also significantly reduce the forced vibrations amplitude when exposed to periodic disturbing forces. The developed mathematical model and algorithms for the numerical solution to the differential equations allowed us to choose the optimal parameters of the boring mandrel damping element. The obtained data will be used to create a prototype boring mandrel and conduct field tests.

Rotary ultrasonic machining (RUM) is suitable particularly for machining hard and brittle materials, such as glass and ceramics. This contribution investigates the machining of poly-crystalline cubic boron nitride (PCBN) by using this advanced machining method. In the experiment, a tool for friction stir welding (FSW) was manufactured. Such tool is 1pprox.1 for welding the materials with enhanced mechanical properties. The research was focused on machined surface roughness, because roughness has a significant influence on the welding process, especially on sticking ability. If roughness of the tool is too high, the welded material will stick on the tool and the weld cannot be fabricated. According to the performed experiment, RUM seems to be a proper method to manufacture a FSW tool, owing to the low roughness achieved (Ra 0.24 μm).

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Nitride hard coatings Al25.5Cr21Si3.5N were deposited on WC-Co substrates with a different thickness and a negative substrate bias voltage by the LAteral Rotating Cathodes Arc technology. The nanoindentation tests were performed for analysis of AlCrSiN coatings in order to determine the most promising combination of parameters for subsequent machining. On the basis of results of nanohardness measurement and Ratio H/E*, which represents the resistance to plastic deformation and cracking, deposition conditions were selected for coating of turning cemented carbide inserts. For the evaluation of coating adhesion to substrate, Mercedes adhesion test was used. Chip forming tests and long-term tool life tests were performed for determination of cutting parameters (cutting speed, feed rate and depth of cut) for AlCrSiN coated cemented carbide inserts when machining austenitic stainless steel material.