Metal droplets are basic elements of many droplet based innovative manufacturing technologies which nowadays are highly demanded in different industrial applications. In the presented laser droplet generation process an annular laser beam pulse is used to melt the wire-end of the vertically fed metal wire. Due to the interplay of surface tension, gravity force, and light-metal interaction, undulating pendant droplet is formed from the molten wire-end. The critical phase of the laser droplet generation process, that essentially influences the process dynamics, is pendant droplet detachment from the solid part of the wire-end. In the paper, different possible detachment scenarios, related nonlinear phenomena, dynamics and process instabilities observed in the forced drop-on-demand and continuous droplet generation process are presented. A nonlinear model of continuous mass spring like resonant detachment regime is described, results of which are in good agreement with the experiments. The results are of high importance for understanding of pendant droplet detachment physics from theoretical and from application point of view. Based on this, process stabilization, and reliable and repeatable detachment of pendant droplets has been achieved, which is necessary for further development of metal droplet based technologies. The results have been presented at the Japanese Waseda symposium to the nonlinear and complex sciences experts and at the GA CIRP to experts from the field of additive manufacturing technologies. The latter led to the establishment of contacts and further research collaboration on annular laser beam based direct deposition of metals and 3D metal printing technology with Japanese company DMG MORI.
B.04 Guest lecture
COBISS.SI-ID: 14026523Vibration-based condition monitoring and fault detection approach for compressors built in refrigeration appliances is proposed. The method combines feature extraction and principal component analysis (PCA), and compares unsupervised k-means clustering and discriminant analysis (DA). The method is demonstrated on a case study based on a large dataset of 10.000 industrially acquired vibration measurements of compressors during the production of refrigeration appliances. The initial step of the proposed method is feature extraction, based on statistics, statistical moments, and spectral analysis. A selected single feature was applied for statistical detection of initial compressor faults, based on which the initial compressor classes were defined as 'normal', 'noisy', and 'inactive'. In the next step, extracted features were transformed by PCA and only the first two principal components, contributing over 90% of variability, were retained for subsequent analysis. Three initial classes were applied to initialize DA. The results of linear DA revealed many additional 'noisy' and 'inactive' samples that were not evident from a single extracted feature. Furthermore, an additional cluster defining new class 'unstable' was detected, indicating a new type of defect characterized by high vibration transients. Results of DA reveal decision boundaries between all classes, and confirm the efficiency of the proposed method. Finally, the results are compared also with an unsupervised k-means clustering which shows that unsupervised clustering doesn't provide appropriate decision boundaries. The proposed DA-based approach detects compressors with defects and has the potential to detect novel classes of unusual or faulty operation. The method can be effectively applied for industrial condition monitoring of compressors. The achievement is important for the industry of household appliances and contributes the potential effects of improved monitoring and diagnostic of product quality. Achievement was presented in the context of a scientific conference and applied in the context of cooperation with company Gorenje.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 14815259Results of applied short-term forecasting for the Slovenian natural gas market are presented. A case study for one of the major Slovenian natural gas distribution companies is considered, with forecasting results in hourly resolution in the forecasting horizon from 1 to 48 hours. The development of a forecasting strategy is presented, which includes daily data acquisition from various sources, development of customized forecasting models, and deployment of a forecasting solution. The forecasting models are based on stepwise regression method in order to design model structures with reliable and robust operation. Forecasting results of several years of online forecasting operation are presented. Obtained accuracy of forecasting results is considered as very successful and beneficially contributes to the managing policy of the distribution company. The achievement is important for coordinating the energy markets and to optimize the management of distribution companies. Achievement contributes the potential effects of improved accuracy of forecasting future energy consumption. Achievement was presented in the context of the scientific conference and applied in the context of cooperation with the company Energetika Ljubljana.
F.16 Improvements to an existing information system/databases
COBISS.SI-ID: 14690331In the paper a novel annular "ring shaped" laser beam cladding head and related cladding process are presented. In the cladding head a laser beam is shaped into an annular ring and guided coaxially with the powder tube disposing the powder jet in the centre of the focused annular laser beam ring. An experimental process feasibility analysis was performed using a Nd:YAG pulsed laser system with a maximal average power 250 W. Beside the known influencing parameters of laser cladding process, the important parameters related to the annular laser beam caustics were defined. The process feasibility and influence of the process parameters on powder catchment efficiency was analysed based on the cladding experiments of SS 316L powder on SS 304 workpiece material. Innovative concept of employing an annular laser beam and powder feeding along the beam axis is an important contribution to the laser direct powder deposition technology where the widely used standard configuration employs a central laser beam and sidewise powder feeding. More uniform depth of the melt pool due to the annular shape of the laser beam potentially leads to better metallographic properties of the coating, while the geometrical configuration of the powder jet enclosed within the annular laser beam potentially leads to higher powder catchment efficiency. Higher powder catchment efficiency means reduced loss of powder material and reduced contamination of the working area with a potentially explosive metal dust. Based on the results of the study, a patent application (MP2015/157WO: 9150766WO01) was filed with the Japanese industrial partner DMG MORI Co., Ltd. The paper was presented to the interested public as a lecture at the 9th International Conference of Photonic Technologies LANE 2016 19th-22nd Sep. 2016 in Fuerth, Germany, and in the journal Physics Procedia.
F.09 Development of a new technological process or technology
COBISS.SI-ID: 14887195Since it is known that there is a relative shortage of doctors in family medicine, it is important to know how the decision to choose a career in this field is made. Since this decision is closely linked to students’ attitudes towards family medicine, we were interested in identifying those attitudes that predict intended career choice in family medicine. A cross-sectional study was performed among 316 final-year medical students of the Ljubljana Medical Faculty in Slovenia. The students filled out a 164-item questionnaire, developed based on the European definition of family medicine and the EURACT Educational Agenda, using a seven-point Likert scale containing attitudes towards family medicine. The students also recorded their interest in family medicine on a five-point Likert scale. Attitudes were selected using a feature selection procedure with artificial neural networks that best differentiated between students who are likely and students who are unlikely to become family physicians. Thirty-one out of 164 attitudes predict a career in family medicine, with a classification accuracy of at least 85%. Predictors of intended career choice in family medicine are related to three categories: understanding of the discipline, working in a coherent health care system and person-centredness. The most important predictor is an appreciation of a long-term doctor–patient relationship. Students whose intended career choice is family medicine differ from other students in having more positive attitudes towards family physicians’ competences and towards characteristics of family medicine and primary care. Prediction of career choice in family medicine is very important due to a shortage of family doctors. This is the case not only in Slovenia, but also in many other countries in the world. Based on the knowledge of those characteristics of students that have a significant impact on this choice, it is possible already during the educational process to influence to some extent the decision of choosing family medicine as a career choice. The paper was published in the European Journal of General Practice (vol. 21, no. 1, 2015), which is one of the most prominent journals in the field of family medicine.
F.15 Development of a new information system/databases
COBISS.SI-ID: 3380965