Robustness is an important success factor for production networks in which the operation of enterprises is subjected to an uncertain environment. In this paper, the robustness of networks is studied as a function of network size. The study is performed through a simulation experiment in which the uncertain environment is modelled by introducing perturbations in demand. The decision-making model mimics the behaviour of socially connected human subjects. The results show how robustness and production rate are affected by system size and social network structure, and how this is relevant for the design and operation of future manufacturing systems.
COBISS.SI-ID: 13971739
We report on a concept of a fiber MOPA based quasi-CW laser working at high modulation bandwidths up to 40 MHz capable of producing arbitrary pulse durations at arbitrary repetition rates. An output power of over 100 W was achieved and an on-off contrast of 25 dB. The laser features a dual-channel (dual-wavelength) seed source, a double stage YDF amplifier and a volume-Bragg-grating-based signal de-multiplexer. Minimization of transients was conducted through experiment and model analysis.
COBISS.SI-ID: 14385947
The effects of laser shock processing without protective coating on high-cycle fatigue crack growth and fracture toughness were investigated. Laser shock peening treatment was performed on compact tension specimens from both sides perpendicular to the crack growth direction, followed by subsequent grinding. Fatigue crack growth tests were performed at frequencies between 116 and 146 Hz, at R = 0.1 and a constant stress intensity range during the fatigue crack initiation phase and K-decreasing test. A lower number of cycles was required to initiate a fatigue precrack, and faster fatigue crack growth was found in tensile residual stress field of LSP-treated specimens. The crack growth threshold decreased by 60% after LSP treatment. The fracture toughness decreased by 28-33% after LSP treatment. The fatigue-to-ductile transition boundary on fractographic surfaces show linear fatigue crack fronts in non-treated specimens and curves after LSP treatment.
COBISS.SI-ID: 14539035
Radio frequency welding is a material joining process based on the dielectric loss principle which is well suited to join plastic materials used in biomedical applications such as drainage and solution bags. For these kind of applications it is very important that welds are of good quality due to the sterility and biological hazard concerns. This usually means that welds must have a certain predetermined strength. In production environment destructive testing of sample products is commonly used method of quality control. This is however time consuming and the results obtained on sample testing can by no means be fully relied upon for all the products within a batch. Therefore a decision was made to design an artificial intelligence monitoring system which could determine the quality of each weld based on the measurements performed in real time. The main signal being measured is the displacement of the upper electrode. Various parameters of displacement curve were found out to be in relation with the weld strength. Due to disturbances in air supply which result in variable welding force a force sensor was added as well. The measurements obtained from both the sensors were used to form the input vector for linear vector quantization (LVQ) neural network. This type of network is suitable to put the input vectors in different classes. In our case this means if a certain measurement corresponds to a good quality weld or a bad quality weld. The experiments have shown that the proposed neural network performs really well and could be of great value in a production environment.
COBISS.SI-ID: 14382619
In this paper thermal cycling of tungsten alloy WNi28Fe15 used as a filler material for cladding of the surfaces on the high pressure die casting tools is presented. Gas tungsten arc welding was used for deposition of the tungsten alloy in a form of a welding rod on the cylindrical specimens made of AISI H13 hot work tool steel. High frequency generator working with 20 kHz was used for thermal cycling of the 40 mm high specimens with the diameter of 30 mm. Water with a temperature of 8 °C was flowing through the internal hole of the specimen. Each thermal cycle consisted of 5 s long heating section and 30 s long cooling section. The temperature of the surface during thermal cycling was measured using infrared camera. The resulting clad was studied by means of microstructural analysis. The results have shown superior thermal fatigue resistance of cladded layer compared to reference heat treated hot work tool steel AISI H13. Surface hardness of the specimens cladded with tungsten alloy is approximately 100 HV0.5 higher compared to heat treated AISI H13 steel at the end of thermal cycling. Additionally coefficient of the linear thermal expansion was measured for WNi28Fe15 alloy in the range from room temperature to 1100 °C.
COBISS.SI-ID: 14404123