Journal of Mechanical Engineering 53 (2007) 9

 

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A Model-Based System for the Dynamic Adjustment of Cutting Parameters during a Milling Process

Corresponding author - Franci Čuš

Authors - Uroš Župerl - Edvard Kiker

Abstract

This paper presents a model-based mechanism of control ensuring the constant quality of the surface finish by controlling the cutting forces during the end-milling process. Using the dynamic adaptation of feeding and speed the system controls the surface roughness and the cutting forces on the milling cutter. The purpose of developing such a mechanism is to find the limitations of this type of control, which maintains a constant cutting force by adapting the cutting parameters. This model-based system of control was developed by the evolutionary method of genetic programming (GP). A drawing of experiments was made in order to determine the empirical correlations between the quality of the surface finish and the cutting force. With the depth of cutting defined in advance the influence of the workpiece material and cutting parameters (feeding, cutting depth) on the abovementioned correlation has been experimentally researched. The evolution genetic programming method (GP) was applied to derive an empirical relationship for the surface finish and the cutting force values for steel materials. These relationships were applied to develop the proposed evolution simulation model in which the cutting force is adjusted to improve the required surface quality for the end-milling process. The results provide a means for greater efficiency by improving the surface quality, minimizing the effect of the process variability and reducing the error cost during finishing operations.

Keywords - end-milling, cutting parameters, genetic programming, model-based control

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)9, 524-540
UDC 621.914

A Model-Based System for the Dynamic Adjustment of Cutting Parameters during a Milling Process (pdf)

 

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Process and Apparatus Developments in Dry-Machining Applications

Corresponding author - Mustafa Kemal Kulekci

Abstract

In this study a recent development in the dry-machining process is discussed. Dry machining eliminates the problems of cutting-fluid contamination, disposal, filtrations and the risk of health problems. The suitability of the workpiece for dry machining depends on the material's properties. The performance of the cutting tool for the dry-machining process depends on the properties of the coating. The process also has a restriction that must be taken into consideration: the rapid, repetitive fluctuations of the temperature lead to expansion, contraction and an increased risk of thermal cracking of the cutting edge. The presence of the coolant exacerbates the thermal cracking problem. Dry machining keeps the tool hot and tougher. During the dry-machining process the coating takes the place of the coolant in protecting the cutting edges from wear and ensures reliable chip evacuation. Additional studies are needed on the dry-drilling and taping process for long chipping materials.

Keywords - dry machining, coatings, cutting inserts, tool life

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)9, 541-547
UDC 621.91

Process and Apparatus Developments in Dry-Machining Applications (pdf)

 

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The Thermo-Economic Optimization of Hot-Water Piping Systems: A Parametric Study of the Effect of the System Conditions

Corresponding author - Hasan Karabay

Abstract

A thermo-economic optimization method for a hot-water distribution pipe is presented.   The method is based on the second law of thermodynamics. Both the optimum pipe diameter and the insulation thickness are determined simultaneously, considering exergy destruction due to friction and exergy loss due to heat losses as the operation cost, while the piping and insulation costs are considered as an investment.  The effect of mass flow rate, annual operation time, depreciation period and water temperature on the optimum pipe diameter and insulation thickness are presented with a parametric investigation.  The results show that the mass flow rate dominates the optimum pipe diameter. The annual operation time, depreciation period and water temperature are the decision parameters for the optimum insulation thickness.

Keywords - hot water networks, optimizations, exergy destruction, exergy loss

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)9, 548-555
UDC 697.44

The Thermo-Economic Optimization of Hot-Water Piping Systems: A Parametric Study of the Effect of the System Conditions (pdf)

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A parametrical Analysis of a Biomass Stirling Cogeneration Unit for Use in Housing

Corresponding author - Uroš Stritih

Authors - Gregor Zupan - Vincenc Butala

Abstract

This paper presents a combined heat and power (CHP) unit using wood biomass to provide an energy supply for housing. The Stirling engine is used as a CHP-producing technology for which a thermodynamic analysis was carried out. The thermodynamic values were mathematically calculated and a computer program for the CHP simulation was written. A parametrical analysis of different combinations of thermodynamic values with respect to the efficiency of the Stirling engine was made. The power of the engine can be changed by the quantity of the working gas, which requires a reservoir. We concluded that if all the isochoric heat were regenerated, the electrical efficiency would be equal to Carnot's efficiency, since it depends only on the upper and lower temperatures in the engine.

Keywords - Stirling engines, biomass, parametrical analysis, efficiency

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)9, 556-568
UDC 620.92:621.412

A parametrical Analysis of a Biomass Stirling Cogeneration Unit for Use in Housing (pdf)

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Analysis of the Knowledge and the Use of Investment Project Evaluation Methods in the Field of Mechanical Engineering

Corresponding author - Igor Pšunder

Authors - Nadja Ferlan

Abstract

Research done in the USA and the UK has shown that, with the increased use of computers and electronic spreadsheets, the use of these investment project evaluation methods that are based on discounted cash flow has increased. However, theoretical findings about these methods show that they have numerous limitations, and ignorance of these limitations can lead to false results as well as false conclusions about investments and investment projects. This paper shows the research results acquired from project managers of Slovene companies. Their personal opinions about investment project evaluation methods and knowledge of the methods' faults were studied in the research. Methods based on discounted cash flow as well as single-period methods of investment evaluation and investment projects were used. During the analysis of the results the situation in the field of mechanical engineering was treated separately and compared with other technical and non-technical sciences. Research has shown that experts dealing with investment project evaluation who have a degree in the field of mechanical engineering more often use discounted cash-flow methods for investment project evaluation than do experts of other technical sciences, but approximately as often as experts in economics and similar sciences. We were able to conclude that experts with education in mechanical engineering are more than usually familiar with the flaws in investment project evaluation methods, but at the same time, only half of them know the multiple internal rate of return, which is the most commonly mentioned fault of the internal rate of return method. Only one-third of experts are familiar with result deformation due to a disregard for the time component of payments in the payback period method.

Keywords - mechanical engineering, investment projects, evaluation, cash flow

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)9, 569-581
UDC 330.322:621

Analysis of the Knowledge and the Use of Investment Project Evaluation Methods in the Field of Mechanical Engineering (pdf)

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The Use of Moving Least Squares for a Smooth Approximation of Sampled Data

Corresponding author - Igor Grešovnik

Abstract

The use of the moving least-squares approximation for the smoothing of data and the approximation of noisy response functions is presented. The approximation properties are treated with respect to the level of noise, the sampling density and the effective range of the sample. The applicability of the method is demonstrated by smoothing experimental measurement data and solving an optimization problem with a noisy response by the successive response approximation technique. The results indicate that the moving least-squares approximation is applicable to a wide variety of problems due to its smoothness, its accurate approximation over arbitrarily large domains using low-order basis functions, its ability to deal with an irregular arrangement of sampling points and to adapt to different modes of the approximation function in different regions.

Keywords - sample data, function approximation, moving least squares methods, smoothing, optimization

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)9, 582-598
UDC 517.518.8:519.243

The Use of Moving Least Squares for a Smooth Approximation of Sampled Data (pdf)

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