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The paper describes a new method for producing stepped rail axles. The method is based on the skew rolling process. With this method, the product is formed by three tapered rolls located every 120• on the perimeter of the billet. Positioned askew to the centerline of the billet, the rolls rotate in the same direction and with the same velocity. At the same time, they get closer together or go apart depending on the desired cross sectional reduction of an axle step. In addition, the workpiece is shifted lengthwise relative to the rolls by the translational motion of the workpiece-holding chuck. In order to verify the designed method for producing rail axles, a series of numerical simulations were performed using the Simufact.Forming v.12 simulation software. The numerical modeling enabled the determination of maps of the effective strain and temperature in the finished product as well as variations in the loads and torques during rolling. The numerical results unambiguously confirm that the skew rolling method can be applied to form parts of considerable dimensions (the modeled axles had a length of 2146 mm and their maximum diameter was 202 mm).Keywords: Skew rolling, rail axle, FEM W artykule opisano metodę wytwarzania stopniowanej osi wagonowej bazującą na procesie walcowania skośnego. W metodzie tej wyrób kształtowany jest za pomocą trzech rolek stożkowych, rozmieszczonych na obwodzie wsadu co 120• . Rolki te ustawione są skośnie względem osi wsadu, a w trakcie kształtowania obracają się z jednakową prędkością w tę sa-mą stronę oraz jednocześnie zsuwają lub rozsuwają się -w zależności od redukcji przekroju poprzecznego kształtowanego stopnia osi. Dodatkowo, wyrób kształtowany przesuwany jest wzdłużnie względem rolek, w wyniku ruchu postępowego uchwytu utwierdzającego jeden z jego końców. Sprawdzenia poprawności założonej koncepcji kształtowania osi wagonowej dokonano w drodze symulacji numerycznej wykonanej w programie Simufact.Forming v.12. W efekcie wykonanych obliczeń uzyskano mapy intensywności odkształcenia i temperatury w ukształtowanym wyrobie oraz wyznaczono przebiegi sił i momentów w trakcie walcowania. Jednoznacznie potwierdzono możliwość kształtowania wyrobów o dużych gabarytach (długość osi wynosi 2146 mm, a jej średnica maksymalna 202 mm) metodą walcowania skośnego.

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This study relates to an innovative method for forming rail car axles by skew rolling in a CNC 3-roll mill. The rolling mill was constructed at the Lublin University of Technology. The use of this machine makes it possible to produce elongated axisymmetric parts that are up to 55 mm in diameter and up to 1000 mm in length. Experimental rolling tests are performed (in 1:5 scale) using this machine. Two types of axles are analysed: one manufactured in accordance with North American standards (AAR Class E) and one manufactured in compliance with European standards (BA302). Diameters of produced axles have a dimensional accuracy of ± 0.4 mm. Produced axles are free from internal cracks, and their surface defects (shallow helical grooves) can easily be removed by machining. The major shortcoming of the proposed method is the presence of chucking allowance. To eliminate this allowance, it is proposed that the forming process should be performed in two operations: rolling extrusion and skew rolling. Results of a numerical analysis were performed using the Simufact.Forming program confirms that rail car axles can be formed by the proposed method.

The article presents the issue of material fracture during the process of cross-wedge rolling (CWR). The object of the research was the process of forming a harrow tooth preform. In the conducted analysis nine damage criteria were applied. The critical value of damage was determined with a new calibrating test, basing on rotational compression of a sample in a channel. The results of calculations were compared to the results of experimental testing performed in laboratory conditions in Lublin University of Technology. On the basis of the obtained results an assessment of the applied damage criteria and their applicability in the analysis of CWR processes was conducted.