Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cutting depth and tool radius nose) on the cutting forces (cutting force, feed rate cutting force and penetration cutting force) as well as on the residual stresses, in conical bearings made of steel DIN 100 CrMn6 hardened (62 HRc), searching correlations between the residual stresses and the cutting forces。73800

Design/methodology/approach: A complete factorial planning was used to establish the correlations。 At the same time, the cutting parameters influence in the microstructure of the material and it’s correlation with the residual stress was studied。 A turning center machine and CBN inserts was employed for the tests。 To the cutting force measurements was carried out using a piezoelectric dynamometer。 The residual stresses measurements were carried out by X-ray diffractometry。

Findings: The penetration cutting force was the most important factor in the residual stress generation, and it was influenced by the feed rate and the cutting depth。 A correlation between the cutting depth and the residual stresses was established。 The results do not showed any changes in the microstructure of the material, even when the greater cutting parameters were used。

Research limitations/implications: The residual stress is one of the major causes of failures in bearings by contact fatigue, keeping this on mind, this work helps the developer to select correct cutting parameters in order to increase the machined workpiece life in service。

Originality/value: This work were based on the real components (conical bearings), real cutting conditions and with these results were possible to make greater improvements in the manufacturing and in the quality of the studied parts。

Keywords: Machining; Turning; Hard turning; Residual stress

Unlike the conventional process, the hard steel turning introduces compressive residual stresses in surface and in the subsurface of the work piece, increasing with this its fatigue resistance [1], what is particularly beneficial to the applications in rotational elements under external loads, as the bearings。 The reference [2] affirms that the high temperatures and the fast cooling in the cutting area can introduce a temper treatment in surface material, generating a fine layer of tempered martensite well-known as white layer [3-6]。 As a consequence of this transformation, below this layer, another one can be formed, the black layer, of lower hardness and under tension stress state。 According to references [6-8], one of the main factors of this structure generation in the surface and in the sub-surface of the machined steel, is the tool wear, which is a critical factor in the increase of the temperature in the cutting area。 Regarding the influence on the components of the cutting forces, in agreement with reference [10-12] the high-speed turning process  of hardened materials differs of the conventional process, once in the first, the cutting force penetration is the bigger one, while in the second, it’s the cutting force。

The machining also introduces residual stresses on the material surfaces, and it’s an important factor to be analyzed specially on the recurrent solicitations where it has greater importance。 Depending of its value, the life of a bearing can be increased in more than 30 % [12]。 So many studies have been conducted in this area, some of then recent [13-24]。

This work, tried to investigate the existence of a relationship between the cutting forces, particularly by penetration force, with the residual stresses introduced in the surface of one machined piece (internal ring of a conical bearing), of steel DIN 100CrMn6 and with hardness between 60 and 64 HRc。

The tests were planned by a statistical analysis according to the DOE (Design of experiments) methodology, reducing with that, the costs and the expended execution time of the tests [29]。 The analysis was made being taken in consideration the influence of the cutting parameters effects (cutting speed, feed rate, cutting depth and tool nose radius), on the introduced residual stresses and the cutting force。