The Effect of Process Parameters in Helical Rolling of Balls on the Quality of Products and the Forming Process

Abstract

This paper presents selected numerical and experimental results of a skew rolling process for producing balls using helical tools. The study investigates the effect of the billet’s initial temperature on the quality of produced balls and the rolling process itself. In addition, the effect of billet diameter on the quality of produced balls is investigated. Experimental tests were performed using a helical rolling mill available at the Lublin University of Technology. The experiments consisted of rolling 40 mm diameter balls with the use of two helical tools. To determine optimal rolling parameters ensuring the highest quality of produced balls, numerical modelling was performed using the finite element method in the Forge software. The numerical analysis involved the determination of metal flow kinematics, temperature and damage criterion distributions, as well as the measurement of variations in the force parameters. The results demonstrate that the highest quality balls are produced from billet preheated to approximately 1000 °C.

Determination of the critical value of damage in a channel-die rotational compression test

“…1 Schematic of the test of rotational compression between channeldies these dents increased with s. As a consequence of this deformation, the thickness of the axial zone of the specimens decreased, which resulted in the formation of a crack along the specimen's axis, running along the entire length of the specimen. A similar phenomenon was observed by Tomczak et al [16] in helical ball-rolling processes when the roll pass was overfilled. In our case, the fact that cracking could be observed on the end faces of specimens facilitated the experiments.…”

“…Earlier versions of specialised software did not make it possible to model the material separation, which is why it was a common practice in simulation studies to leave small connectors (bridges) between workpieces such as balls or stepped shafts [11][12][13][14]. Recently, however, theoretical models of rolling processes for the production of balls [15,16] and ball pins [17] have been developed in which the separation of the material has effectively been simulated. In these models, the Cockcroft -Latham damage criterion was used, with the critical damage value arbitrarily chosen to be in the range of 2-3.…”

Rotational Compression of Cylindrical Specimen As a New Calibrating Test for Damage Criteria

“…The state of stress in the axial area of the sample, occurring in this test, causes the material to crack as a result of the so-called Mannesmann effect. A similar state of stress occurs in numerous industrial processes, such as cross-wedge rolling, helical rolling and punching according to the Mannesmann method [41][42][43][44]. For this reason, the limit values of the damage function obtained using the new test have a significant utilitarian meaning.…”

A rotary compression test for determining the critical value of the Cockcroft–Latham criterion for R260 steel

“…The test material (R260 steel) was selected based on the fact that the rolling process is commonly used to form scrapped railway rails into rods, which can be used to produce, among others, steel grinding mill balls (Pater et al., 2018b). It is quite important to know the critical value of the damage criterion for this steel, because rolling of balls may be hampered by the undesirable process of internal cracking of the material (Tomczak et al., 2018). In addition, the balls must be separated from each other in the rolling process.…”