Journal of Mechanical Engineering 57 (2011) 10

 

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Development of a Part-Complexity Evaluation Model for Application in Additive Fabrication Technologies

Authors - Bogdan Valentan ‒ Tomaž Brajlih ‒ Igor Drstvenšek ‒ Jože Balič

Abstract

With the rapid development and expansion of devices for the production of both traditional (cutting) procedures and layered technologies (also known as 3D printers or rapid prototyping/manufacturing), the question arises of how to find the appropriate production technology.
The article describes the basic features of the CAD output file STL. The STL file format is a widelyused file format developed for layered technologies and, as such, a basis for analysing and developing methods when determining the complexity of a model.
For the analyses of basic STL data, and complexity determination, several real-life models are presented. Actual manufacturing procedures suitable for the manufacture of unique products or serial production are presented, with accentuation towards layered technologies.
Technological test models are analysed based on the fundamental properties of manufacturing and certain manufacturing processes are chosen using complexity estimation. The results are comparable with those choices of manufacturing procedures on the basis of experts’ estimates. Complexity evaluation is also used for post-processing time determination for several layered technologies.

Keywords - rapid prototyping, STL, complexity, shape, layered technology, technology selection

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 709-718
DOI:10.5545/sv-jme.2010.057

Development of a Part-Complexity Evaluation Model for Application in Additive Fabrication Technologies (pdf)

 

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Overall Structure Calibration of 3-UCR Parallel Manipulator Based on Quaternion Method

Authors - Gang Cheng ‒ Wei Gu ‒ Jing-li Yu ‒ Ping Tang

Abstract

In this article a simple yet effective approach for the structure calibration of a three degree-offreedom (DOF) parallel manipulator is presented. In this approach, the model of the pose error expressed by the Quaternions Parameters was established, based on complete differential-coefficient theory. This was followed by an investigation into the degree of influences represented as sensitivity percentages, of source errors on the pose accuracy with the aid of a statistical model of sensitivity coefficients. Then, the kinematic calibration model with the successive approximation algorithm was achieved. The simulation has been carried out to verify the effectiveness of the proposed algorithm and the results show that the accuracy of the calibration can be significantly improved.

Keywords - 3-UCR parallel manipulator, complete differential-coefficient theory, Quaternion, least squares method, sensitivity model, kinematic calibration

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 719-729
DOI:10.5545/sv-jme.2010.167

Overall Structure Calibration of 3-UCR Parallel Manipulator Based on Quaternion Method (pdf)

 

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Optimal Control of Workpiece Thermal State in Creep-Feed Grinding Using Inverse Heat Conduction Analysis

Authors - Marin Gostimirović – Milenko Sekulić – Janez Kopač – Pavel Kovač

Abstract

Due to intensive friction between grinding particles and workpiece material, a substantial quantity of thermal energy develops during grinding. Efficient determination of real heat loading in the surface layer of the workpiece material in grinding largely depends on the reliability of basic principles of distribution of heat sources and the character of the temperature field within the cutting zone. Therefore, this paper takes a different approach towards the identification of the thermal state of the creep-feed grinding process by using the inverse problem to approximate heat conduction. Based on a temperature measured at any point within a workpiece, this experimental and analytical method allows the determination of a complete temperature field in the workpiece surface layer as well as the unknown heat flux on the wheel/workpiece interface. In order to solve the inverse heat conduction problem, a numerical method using finite differences in implicit form was used.
When the inverse heat conduction problem is transformed into an extreme case, the optimization of heat flux leads to an allowed heat loading in the surface layer of workpiece material during grinding. Given the state function and quality criterion, the control of workpiece heat loading allows the determination of optimal creep-feed grinding conditions for particular machining conditions.

Keywords - creep-feed grinding, head loading, inverse problem, optimal control

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 730-738
DOI:10.5545/sv-jme.2010.075

Optimal Control of Workpiece Thermal State in Creep-Feed Grinding Using Inverse Heat Conduction Analysis (pdf)

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The Formation of Saw Toothed Chip in a Titanium Alloy: Influence of Constitutive Models

Authors - Roberto Alvarez – Rosario Domingo – Miguel Angel Sebastian

Abstract

This work analyses the effect of eight constitutive models on the saw-toothed chip formation in Ti6Al4V orthogonal cutting, by means of the finite element (FE) simulation and experimental contrast, in dry and with conventional emulsion coolant, mixed with water at 7%. The models are focused in Johnson-Cook equations with four different sets of constant parameters, El-Magd-Treppmann modified and three Zerilli-Armstrong models based on the behavior of different crystal structures (body-centered-cubic – BCC, hexagonal-close-packed – HCP and modified HPC model). The flow stress model of Ti6Al4V at high strain rates and temperatures has been analysed using a 2-D FE model through constitutive equations and three friction coefficients (0.4, 0.6 and 0.8). A critical comparison of outstanding process outputs as cutting force, temperature – on rake face and measurable parameters for segmented chip (the peak tooth height, the valley tooth height and the tooth width, chip compression ratio, and chip deformation) is carried out. The application of different constitutive models has proved a strong influence on the results. Zerilli-Armstrong models, for BCC and HCP structures, have achieved the best fitting in machining with and without coolant respectively, for a friction coefficient of 0.8, getting for cutting force, temperatures, peak tooth height and chip deformation, deviation lower than 2%. The chip compression ratio has reached 4.7% and 7% for BCC and HCP respectively. Only the valley tooth height and the tooth width show some limitations.

Keywords - machining, orthogonal cutting, Ti6Al4V, FEM, chip morphology, constitutive models

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 739-749
DOI:10.5545/sv-jme.2011.106

The Formation of Saw Toothed Chip in a Titanium Alloy: Influence of Constitutive Models (pdf)

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The Influence of Airflow Inlet Region Modifications on the Local Efficiency of Natural Draft Cooling Tower Operation

Authors - Matjaž Dvoršek ‒ Marko Hočevar ‒ Brane Širok ‒ Nikola Holeček ‒ Božin Donevski

Abstract

We present the influence of the cooling tower airflow inlet region modifications at the Šoštanj 4 thermal power plant on cooling tower local efficiency. Local efficiency change was estimated based on temperature fields of drift eliminators before and after the reconstruction of the cooling tower. Temperature fields were measured with thermal vision method. The local reduction of cooling tower efficiency was analyzed based on phenomenological relations of heat transfer obtained from the selected vertical segment of the cooling tower. The characteristic influence that the reconstruction had on the temperature field was detected on the circumference of the cooling tower. The efficiency reduction was the highest on the periphery of the cooling tower and in particular section it peaked at 2%, while in most part of the area it was below 0.5%. The presented measurement and analysis method enables the estimation of changes in the local efficiency of heat transfer in cooling towers.

Keywords - cooling tower, modifications, local efficiency

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 750-759
DOI:10.5545/sv-jme.2010.208

The Influence of Airflow Inlet Region Modifications on the Local Efficiency of Natural Draft Cooling Tower Operation (pdf)

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Global Optimization of Lateral Performance for Two-Post ROPS Based on the Kriging Model and Genetic Algorithm

Authors - Wang Jixin ‒ Yao Mingyao ‒ Yang Yonghai

Abstract

To improve their energy-absorption capacity, the current study provides a global optimization design method for two-post rollover protective structures (ROPS) that utilizes the Latin hypercube method to determine sample point values, the Kriging model as an alternative to traditional second-order polynomial response surfaces for constructing global approximations, and the genetic algorithm to yield optimized results. Through optimization, a satisfactory variation tendency of object function in the lateral loading analysis is obtained, and the load-carrying capability, deformation, and energy absorption are found to match each other well. The matching rationality between energy absorption and lateral loadcarrying capability effectively improves the energy-absorption capacity of the ROPS.

Keywords - engineering vehicle, rollover protective structure (ROPS), global optimization, Kriging, genetic algorithm, energy absorption

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 760-767
DOI:10.5545/sv-jme.2010.246

Global Optimization of Lateral Performance for Two-Post ROPS Based on the Kriging Model and Genetic Algorithm (pdf)

 

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Development of Prosthetic Knee for Alpine Skiing

Authors - Ivan Demšar ‒ Matej Supej ‒ Zmago Vidrih ‒ Jožef Duhovnik

Abstract
Above-knee amputation significantly reduces the amputee’s mobility and physical condition that can be built up through training or other sports activities. Alpine skiing is one of them. This paper deals with an above-knee prosthesis, which provides better kinematics of the leg structure. Imitating the kinematics of the human body, we looked for the kinematics of a system that comes closest to imitating natural movement and replace the missing limb to the highest possible degree. Based on the analysis of human leg kinematics and entire human mass system dynamics, a prototype for a special multi-axis prosthetic knee was developed. Measurements of leg movement during skiing were performed, which served as a basis for the concept. The concept was verified by kinematics, dynamics and strength analysis, and a complete geometric model was made. The concept was then verified on a working prototype, tested on a ski slope.

Keywords - alpine skiing, above-knee amputation, prosthesis kinematics, skiing dynamics, research, development, testing, product adoption

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 768-777
DOI:10.5545/sv-jme.2011.017

Development of Prosthetic Knee for Alpine Skiing (pdf)

 

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Application of Promethee-Gaia Methodology in the Choice of Systems for Drying Paltry-Seeds and Powder Materials

Authors - Slavica Prvulovic − Dragisa Tolmac − Ljiljana Radovanovic

Abstract
This work deals with the application of Promethee-Gaia methodology and the choice of three systems for drying paltry-seeds and powder materials pneumatic driers, spiral driers and rotation driers with a drum with regard to five different criteria. The analysis is based on the Promethee I method, the Promethee II method and the Promethee-Gaia method, which withal shows a complex figure of the relation between alternatives and criteria in the Gaia plane. In this work the application of Decision Lab program is shown, which was the basis in analysing results and ranking alternatives.
The paper analyzes three different systems for drying. When choosing the system of drying the comparative analysis of five influential parameters, such as: the coefficient of heat transfer, price, drying energy, thermal usefulness, specific use of energy. Based on the analysis, the application of a pneumatic dryer is the cheapest, given the significant savings in cost, ie. investment cost and energy efficient. Next in order of the spiral dryer, and third in the rotation with a drum dryer, in terms of benefits administration.

Keywords - method Promethee-Gaia, multi-criteria, systems for drying, Decision Lab program

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)10, 778-784
DOI:10.5545/sv-jme.2008.068

Application of Promethee-Gaia Methodology in the Choice of Systems for Drying Paltry-Seeds and Powder Materials (pdf)

 

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