With the development of high-performance CNC machine tools, milling has been established as one of the main means of machining thin-walled parts. Thus, the selection of process parameters for milling operations is an important issue in end milling of thin-walled parts to assure product quality and increase productivity. The current study explores three machining parameters, namely wall thickness, feed, and machining strategies, that influence dimensional and form errors, surface roughness, and machining time milling of 7075-T6 aluminum alloy thin-walled parts. The effects of machining parameters on each of the response variables were analyzed using graphs of the main effects and three-dimensional surface plots. Analysis of the results show that the most influential factor for wall thickness deviation, dimensions deviation, perpendicularity deviation, flatness deviation, surface roughness of inner walls, surface roughness of outer walls, and surface roughness of reference plane was machining strategy, while feed is the most influential parameter affecting the machined time, followed by the machining strategy. The desirability concept has been used for simultaneous optimization in terms of machining parameters of the thin-walled parts machining process. Finally, a confirmation test with the optimal parameter settings was carried out to validate the results.
Research of the human body vibrations, carried out under controlled laboratory conditions, shows that human body is the most sensitive to vibrations in the frequency range that matches the biomechanical resonance. In the vertical direction, the resonance of the body is approximately 5 Hz, while in the horizontal direction the resonance occurs at frequencies less than 2 Hz. The vibrations of the vehicle have been transferred to the driver and passengers over the seats, which have the ability to attenuate or to amplify vibrations which human body is exposed to while driving. One way to determine the vibration behaviour of the seat is to measure the SEAT (seat effective amplitude transmissibility) factor, which represents the ratio between the vibrations measured on the seat and vibration measured directly on the floor under the seat. Measurement of vibrations in these two positions must be performed simultaneously. If the value of SEAT is less than 1, a seat attenuates vibrations and meets vibrational comfort, the value of SEAT greater than 1 indicates that a seat amplifies vibration, reducing vibration comfort. This paper gives results of SEAT factor investigation done on a hybrid vehicle, for different types of road surface and different modes of driving (electric power and internal combustion engine).
The aim of this paper is to examine the metrological characteristics of some of the most commonly used coordinate measurement systems in industry in a case study of the flatness error. The accuracy and measurement uncertainty of the coordinate measuring machine with contact probe, point by point mode and scanning mode, and with non -contact probe, then performance measuring arm, optical scanner and finally industrial computed tomography were analyzed. In order to exclude factors that affect the accuracy of measurement and measurement uncertainty, and are not part of the hardware structure of the CMS, the experiment was conducted on a reference workpiece and an independent software solution was used to estimate the error of flatness. The accuracy of measuring systems was determined as the difference between the reference value and the mean value of repeated measurements and the measurement uncertainty was determined according to the instructions for estimating the measurement uncertainty GUM. The results of the research showed high metrological performance of the coordinate measuring machine and the optical scanner for this measuring task. Also, it was found that industrial computed tomography gives a very large measurement error and that the measurement uncertainty is very difficult to determine.
The challenge that will be posed to researchers for an even longer period is the development of a predictable model for describing mechanical connections, their variable stiffness and dissipative contact interaction processes. The main challenge to this goal lies in the lack of understanding of how friction behaves on a small scale. Coulomb friction, a large heuristic model is not predictable and has actually been proven to be untrue in many modes. Expecting a universal law of friction for all types of materials and therefore contact interactions is not very realistic. Instead, the goal of the international research community is to develop a predictable model for a limited range of cases. So far, the metal-metal contact is most often tested, respectively the contact interaction behaviour of aluminium and steel elements of different quality. We also know that in the application those two metals are most often found in making mechanical connections. The aim of this paper is to make a brief overview of some of the previous tests and approaches to the study of contact interaction in mechanical connections and the role of friction in energy dissipation.
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