Wyniki wyszukiwania - Biblioteka Nauki

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The tribological state test in metal forming processes using experiment and modelling

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Jurkovic M. , Jurkovic Z. , Buljan S.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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tom Vol. 18, nr 1-2

383--386

EN

Purpose: of this paper is test of the tribological state in metal forming processes with main aims the determination of state on the tool contact surface (contact stresses and friction coefficient) friction coefficient modelling and simulation and to present the original method of defining contact stresses tf and pn and coefficient of contact friction m. Design/methodology/approach: of this research is review of contact stresses determination methods, general principles of stochastic modelling, experimental friction test and modelling, examples tribological state test and simulaton by deep drawing and drawing processes. Main achievement are: original experimental identification of contact stresses, original experimental of tools for measurement of contact stresses, mathematical model for defining the tribological state. Application methods of this research are: experimental, tribological state test in forming processes by means of experiment and modelling, statistical and direct contact stresses determining method. Findings: experimental and stochastic modelling of tribological parameters of the forming processes and verification of mathematical model. The tribological state test is performed on the basis of experimental investigations and stochastic modelling. Research limitations/implications: modelling and optimization of tool geometry and selection of optimal lubricators, development experimental methods in the determination of contact stresses, etc. Practical implications: Results of investigations in processing conditions show that the desired effects can be achieved: increased durability of tools 20-40%, reduced stagnation time in the machining process 20-30%, increase on the productivity of the forming process 15-30% and less energy consumption up to 15%. Originality/value: of this paper is obtained original mathematical model for defining coefficient contact friction and contact temperature on the contact surface of tool. Also, is obtained original experimental tool for measurement of contact stresses.

2

Optimization of extrusion force prediction model using different techniques

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Jurkovic Z. , Jurkovic M. , Buljan S.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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tom Vol. 17, nr 1-2

353--356

EN

Purpose: This research is determination of the optimal cold forward extrusion parameters with objective the minimization of tool load. Design/methodology/approach: This paper deals with the different optimization approaches relating to determine optimal values of logarithmic strain, die angle and coefficient of friction with the purpose to find minimal tool loading obtained by cold forward extrusion process. To achieve this, it has been carried out two experimental plans based on factorial design of experiment and orthogonal array. By using these plans it was performed classical optimization, according to response model of extrusion forming force, and the Taguchi approach, respectively. Findings: Experimental verification of optimal forming parameters with their influences on the forming forces was done. The experimental results showed an improvement in minimization of tool loading. It was compared results of optimal forming parameters obtained with different optimization approaches and based on that the analysis of the characteristics (features and limitations) of both techniques. Research limitations/implications: Suggestion for future research it will be application of evolutionary algorithms namely model prediction of the process by genetic programming and optimization of extrusion parameters by genetic algorithm. Practical implications: a practical (industrial) implication on the smallest energy consumption, longer tool life, better formability of the work material and the quality of the finished product. Originality/value: This paper is obtained original extrusion force model for experimental domain of forming parameters and identification of parameters influence in that model

3

Analytical study of different approaches to determine optimal cutting force model

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Krizek Z. , Jurkovic Z. , Brezocnik M.

Archives of Materials Science

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2007

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tom Vol. 28, nr 1-4

69-74

EN

Determination of optimal machining parameters is an engineering task with aim to reduce the production cost and achieve desired product quality. Such exercise can be tackled on many different ways. The goal of this work is to present some of the possible approaches and to benchmark them among each other. These principles are analyzed: response surface methodology (RSM), evolutionary algorithms (GA & GP), support vector regression (SVR) and artificial neural networks (ANN). All methods implement completely different data handling philosophies with the same goal, to build the model which is able to predict cutting force in satisfying manner. Those aspects are chosen to be evaluated and compared: average percentage deviation of all data, ability to find generalized model and minimize the risk of over fitting and at least the runtime of each single model determination. Average percentage deviation is one of the best indicators of the quality of model. The ability to find generalized model is good indicator of the flexibility of model, and shows how model deals with unknown data. The runtime is important in a real time environment or in scenarios where conditions change frequently. Cutting force data used in this benchmark comes from experimental research of longitudinal turning process.