Contents of Journal of Mechanical Engineering 56, 4 (2005) 




SINGH, S., MAHESHWARI, S., DEY, A., PANDEY, P. C.: Experimental
investigations into die-sinking electric discharge machining of
hardened AISI 6150 tool steel using different electrode materials        197

POCHYLÝ, F., FIALOVÁ, S., HABÁN, V.: Flow with large deformation
of boundaries                                                            211

SRINATH, A., RAO, A. C.: Evaluation of planar parallel  manipulator
structures  for errors of positioning                                    221

GUŽELA, Š., PECIAR, M.: The evaluation of the force of granular
material acting on a moving blade                                        235

JANKURA, N., PALENČÁR, R.: The calibration experiment design
and evaluating of measuring instruments calibration model                249

Abstracts



Experimental investigations into die-sinking electric discharge machining of hardened AISI 6150 tool steel using different electrode materials

SHANKAR SINGH, SACHIN MAHESHWARI, ALOKE DEY, POORN CHANDRA PANDEY

Electric Discharge Machining (EDM), a non-conventional machining process, is being vastly used for manufacturing tools, dies, moulds etc. Tool steels have proved to be extremely difficult-to-machine using conventional machining processes, due to heavy tool wear, incapability to produce complex shapes having better surface finish and low machining rate. Better performance of any machining process can be achieved by faster rate of metal removal, better surface finish with a reduced tool wear. The use of medium carbon chrome-vanadium alloy steel as material for trimming dies, heavy duty punches, press tools and plastic molds is becoming an increasing demand in the tooling industry due to its high strength, impact and fatigue strength at moderate hardness.

The paper presents details and results of an experimental investigation into the machinability of AISI 6150 tool steel (IS Designation: T 50 Cr 1 V23, En-47), hardened and tempered to 55 HRc, using die-sinking EDM process with varying pulsed current and four different electrode materials. The process performance characteristics were studied under different machining conditions and electrode materials. Investigations indicate that the performance measures of EDM increase with the increase in pulsed current and the best machining rates are achieved by copper-tungsten electrode.

Flow with large deformation of boundaries

FRANTIŠEK POCHYLÝ, SIMONA FIALOVÁ, VLADIMÍR HABÁN

This method is based on Bézier body principle, which is generalized from Bézier surface to the 3D body. The solution is performed in curvilinear coordinates that are expressed by Bézier body parameters. The main principle of solution is that the body shape and the solution approximation are described by Bézier body equation.

The boundary movement is uniquely determined by the prescription of time dependent function for the position vectors determining the Bézier body boundary.

This way we are able to obtain in every moment the velocity and pressure fields of the liquid as a function of boundary deformation. The advantage of this method is that the computational mesh, which determines the new shape of the computational area, need not be regenerated in every time step.

The article contains derivation of the relations that determine the solution algorithm and as the example, the flow of the liquid with large deformations of the boundaries in time and other FSI problems.

The presented theory is also applicable for the solution of more complicated problem, as unsteady movement of a body in a liquid where large vibrations of a body are assumed.

In the future we want to improve this theory for the description of a heart function.

Evaluation of planar parallel manipulator structures for errors of positioning

ADUSUMILLI SRINATH, ATLURI CHAKRADHARA RAO

For a total evaluation of manipulators many factors should be considered. These factors include size of work space, accuracy of positioning, load capacity, speed, reliability, cost, safety, ease of operation and settling time etc. Accuracy of positioning is the aspect studied in this work. Accuracy of positioning depends upon structural rigidity and joint clearances of the manipulator. Structural rigidity depends upon both the topology and link dimensions. Since the rigidity of the same structure varies with the dimensions it is not possible to compare a huge number of distinct structures with all possible combinations of dimensions. Hence evaluation of the topology of structures for inherent rigidity in a comparative sense and sensitivity of the structures for joint clearances is investigated. The method developed in this paper is applicable only for planar manipulator structures in which singularities do not occur.

The evaluation of the force of granular material acting on a moving blade

ŠTEFAN GUŽELA, MARIÁN PECIAR

Mixing elements (blades) of various size and forms are forced through a layer of a particulate material in various machines and equipment for processing of the granular materials which evolves a resistance against the blade motion. Knowledge of interactions between the granular material and moving element through the granular material bed is needed for regular design and computation of main dimensions of the functional parts of such machines and equipment. The paper deals with exact determination of the force effects of mixed material on the submerged blade moving in the granular material. The solution comes out from the tensions yield equilibrium of the particulate material described by theory of Mohr`s circle. Rectangular box was used in the experiments which enables a uniform rectilinear motion of the simple shaped blending elements. Dimensionless dependences of a force necessary for a movement of the mixing element through the granular material layer were acquired by correlation of the experimental data.

The calibration experiment design and evaluating of measuring instruments calibration model

NORBERT JANKURA, RUDOLF PALENČÁR

In practice, in the calibration experiment different situations may arise with respect to the significance of uncertainties and covariances of both the standard and calibrated measuring devices. The purpose of the article is to show possible designs of evaluation models of experimental instruments calibration in which we are able to evaluate the calibration experiment. A different approach to the evaluation is needed in different situations. It is shown in the article, how to classify individual situations with respect to the evaluation conditions of calibration experiment.