István Deszpoth

Some Aspects of the Hard Machining of Bore Holes

The machining of hardened surfaces can be done even fulfilling the ever stricter accuracy and quality prescriptions, besides the economic efficiency. Decisively, hard machining is highlightedly important in finish processes because the components must meet increased functional demands. Therefore the number and/or the hardness of the hard surfaces on the components is continuously increasing. In practice the demand for such components is high since they are more wear resistant and their tool life may be higher. Today there are several possibilities for finish machining of components having hard surfaces. We have done experiments for hard machining of inner cylindrical surfaces. The examined procedures were as follows: grinding, hard turning, combined machining. The first two procedures (hard turning, grinding) have got different procedure-specific advantages and disadvantages. Combining these two procedures, using-up the advantages of them, the efficiency of the production can be increased. This paper outlines these procedures of hard machining, their applicability, the increase of their efficiency, and the possibilities provided by the combination of the procedures.

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.

Analysis of machining time and material removal performance as factors influencing efficiency and profitability

In the automotive industry, the machining of hardened surfaces has become a serious topic in terms of its manufacturing and economic efficiency in recent decades. The reasons for this are the machining difficulty of hardened components and the need for machining that results in increased accuracy and surface quality. In addition to grinding as the conventional fine finishing procedure substituting procedures such as hard turning have appeared. They can be applied to reach surface quality and accuracy values equal to those of grinding. This paper analyzes different machining procedures (conventional bore grinding, hard turning and combined procedure) on hardened internal cylindrical surfaces, compared them in terms of time parameters of machining and the practical material removal rate as an efficiency parameter of material removal. While the practical parameter of material removal rate allows efficiency-based comparison of identical or different procedures (machining with abrasive or single-point tools), while the time parameters of machining (mainly the operation time) aim at direct comparability of costs of the procedures. The cost-related relationships of the procedures are also analyzed.

Effect of Cutting Feed and Chip Size Ratio on Cutting Force

In producing parts, besides increasing accuracy and maintaining/improving the cut surface quality, the main effort of the manufacturers is to improve the productivity/profit. In face milling this aim can be achieved first of all by increasing cutting speed and feed. The importance of feed impact analysis is justified by the general effort to prefabricate parts near net shape, if possible by one pass material removal. If the manufacturing is done by one pass, the surface rate (Aw, mm2/min) can be increased by the increase of feed. It fz feed is increased, the feed per tooth (keeping ap at constant value) ap/fz ratio is changed and as a consequence also the load on cutting edges and the character of chip deformation. The increase in the feed and the change in the chip cross section shape influence the cutting forces and the efficiency. In this paper, the changes in the cutting force components with different feed rates are demonstrated, while the value of the feed is increased 16-fold.