Contents of Journal of Mechanical Engineering 55, 2 (2004) 


 

PANDA, D. K., BHOI, R. K.: Study of crater geometry and size
in electro-discharge machining                                             61 

YEH, L. J., CHANG, Y. CH., CHIU, M. CH., LAY, G. J.:
GA optimization on muffler with side inlet/outlet under space
constraints                                                                77 

SKOPECEK, T., HOFMANN, P.: Tool life under high speed and 
hard cutting                                                               90 

STAVA, P., ZAPOMEL, J., WAGNEROVA, R., ZUBIK, P.: 
Investigation of instabilities during transition from laminar 
to turbulent flow in the gap between two concentric discs, 
one rotating, by methods of nonlinear dynamics                            100

Abstracts



Study of crater geometry and size in electro-discharge machining

DEEPAK KUMAR PANDA, RAJAT KUMAR BHOI

Various researchers have predicted the crater geometry and crater size under single spark by considering the thermal erosion theory. Theoretical models have been developed by solving the transient heat conduction equation considering suitable assumptions with appropriate initial and boundary conditions. For the sake of close-form solution, too many assumptions and simplified initial conditions resulted in a solution, which is far from reality. In actual machining, the growth of plasma channel, energy sharing between electrodes, vaporization of workpiece, formation of recast layer, temperature sensitivity of thermal properties of material are few physical phenomena encountered, which have not yet been considered mathematically. Therefore, the theoretical results show wide differences from the experimental results. In the present paper, the growth of the plasma channel is considered in the mathematical model to predict the crater geometry and size under the condition that plasma channel radius grows during pulse duration and at the end of the pulse it becomes equal to the crater radius formed on the surface of the work-electrode in electro-discharge machining.

GA optimization on muffler with side inlet/outlet under space constraints

LONG-JYI YEH, YING-CHUN CHANG, MIN-CHIE CHIU, GAUNG-JER LAY

Considering the prerequisite of operation and maintenance in an existing machine room, the available space of muffler is then occasionally limited.

The issue to maximize the acoustic performance in muffler by using shape optimization method is presented. To overwhelm prohibitive numerical complexity of the problem, we have applied here a genetic algorithm (GA). A numerical case dealing with the elimination of pure tone noise is introduced. Before GA optimization, one example is tested for accuracy check of the mathematical model. Consequently, the result shows that the predicted sound transmission loss (STL) is maximized exactly at desired frequency.

Tool life under high speed and hard cutting

TOMAS SKOPECEK, PETR HOFMANN

This report is mainly concentrated on finding a dependency of tool life upon cutting conditions under high speed and hard cutting. Thereby a complete process characterization under HSC-conditions is to carry out. The research was made in the field of HSC milling of high-strength and extra-hard materials (DIN 1.2342, AISI H13, 56 HRC), where the application of this technology is at the very beginning. Effects of selected parameters of machining process (cutting speed, feed rate, axial and radial depths cut) on tool life magnitudes are characterized in this work. The results of experimental measurement are particularly included here. The measurement, carried out during HSC milling, was made in order to support and confirm fundamental assumptions for economic optimization. Synthesis of the results forms conclusion of the report.

Investigation of instabilities during transition from laminar to turbulent flow in the gap between two concentric discs, one rotating, by methods of nonlinear dynamics

PAVEL STAVA, JAROSLAV ZAPOMEL, RENATA WAGNEROVA, PAVEL ZUBIK

Visualization results of a viscous incompressible isothermal fluid flow in a gap between the rotating and stationary axisymmetric discs are presented in this work. The flow was realized for a wide as well as for a narrow gap. The boundary is set by the ratio h/R = 1. 10-3. Visualization of an L-T transition flow gives the data regarding development of the instabilities when Reynolds number Re is rising. There are four types of instabilities in a narrow gap. They start from concentric circles through two types of spirals and end up as rollers. In the case of a wide gap there is gradual development similar to Taylor vortices of spirals which are oriented in the opposite direction as the ones for a narrow gap. A basic wavy regime and wavy turbulent regime can be identified for a wide gap. It is relatively difficult to identify the beginning of a fully developed turbulent flow. Linear methods for the time sequences development investigation can be used for this purpose. Especially velocity vectors monitored by some of anemometer methods, for instance LDA, are of main interest. It is possible to search them according to Ruelle-Takens scenario which is used for Taylor vortices not only for two independent bifurcation frequencies but also for a characteristic of the strange attractor, which evaluates the degree of chaos.