Károly Gyáni

Environmentally Friendly Precision Machining

ABSTRACT Material removal processing has been investigated both theoretically and experimentally to a certain extent. The demands for environmentally friendly processes impose new parameters such as the use of minimal quantity or even the complete omission of cutting fluids. Therefore, the related processes need to be newly studied in order to be optimized for specific cutting conditions. Cutting fluids are used in material removal processes mainly for lubrication, reduction of the temperature in the cutting region, and increase of tool life. However, cutting fluids are associated with skin and breathing problems of the machine operators. Furthermore, after their disposal and if, as in most cases, recycling is not possible, they may become polluting agents in soil and water when inappropriately handled. In this paper the case of hard cutting, a process that can be performed without the use of a cutting fluid, is investigated. A discussion on the technological parameters involved is given and experimental data are presented in order to point out the environmental as well as the economical benefits emerging from the use of such a technology.

Thermotechnical modelling of hard turning: A computational fluid dynamics approach

Abstract During hard turning the original hardness of the surface layer changes, as does its texture structure and stress state. Even cracks and other defects may appear if the heat effect is too intense. As experimental investigations into heat effects are difficult and expensive, simulation investigation methods based on modelling are of great significance. In this paper an example of heat modelling of hard turning is presented. The layer thickness on the workpiece surface that reaches high temperature is determined. In that layer different modifications can occur due to heat. It was found that the thickness of the layer affected by heat depends primarily on the feed and only secondarily on other cutting parameters. The cooling gradient of the layer was determined, allowing conclusions to be drawn on the re-tempering of the heated layer. The computational fluid dynamics method and a commercial software was used for the modelling and proved to be suitable for the simulation analysis of the hard turning process.

Analysis of lead twist in modern high-performance grinding methods

According to quality requirements of road vehicles shafts, which bear dynamic seals, twisted-pattern micro-geometrical topography is not allowed. It is a question whether newer modern grinding methods - such as quick-point grinding and peel grinding - could provide twist- free topography. According to industrial experience, twist-free surfaces can be made, however with certain settings, same twist occurs. In this paper it is proved by detailed chip-geometrical analysis that the topography generated by the new procedures is theoretically twist-patterned because of the feeding motion of the CBN tool. The presented investigation was carried out by a single-grain wheel model and computer simulation.

THE SIGNIFICANCE OF CONTINUOUS DRESSING IN PRECISION GRINDING OF HARD AND BRITTLE MATERIALS

The precision grinding of hard cemented carbides and brittle ceramics using diamond wheels with continuous electrochemical dressing is considered. A novel grinding apparatus, the electrochemical dressing Miskolc (ECDM), was developed and used. Higher grinding efficiency was observed as compared to grinding using mechanically dressed wheels.

Machining performance of CBN cutting tools for hard turning of 100Cr6 bearing steel

This article presents the examination of cutting performance of a low CBN content cutting tool in the case of hard turning of 100Cr6 hardened bearing steel. One of the indicators of cutting performance is the wear rate, which can be calculated as a ratio of a measurable geometric parameter of a wear form and some technological parameters (cutting time, cutting length or removed material volume). The wear of CBN cutting tools is characterized by the extent of flank wear hence the wear rates related to cutting time and removed material volume are calculated based on the measured flank wear during the cutting experiments. The alteration of wear rates as a function of flank wear and cutting speed was examined.

On the Surface Integrity of Precision-Ground Steel Cylindrical Parts

Abstract The effects of traditional corundum and boron-nitride (CBN) wheels on the surface integrity of internally and externally ground steel parts has been investigated in respect to microhardness, residual stresses, and change of texture. The microhardness and residual stress components of the surface layer of HSS tools ground with CBN wheels have been measured and texture has been also investigated. Case-hardened steels have been ground with mainly traditional wheels. The change of microhardness, residual stresses, and texture depends to a large extend not only on grinding parameters but also on the grade of sharpness of the wheel. The difference between grinding with sharp and worn wheels is significant. These facts prove the importance of different continuous wheel dressing processes. The effect of the coolant on the surface quality has also been examined.