Research on the Possibility of Lowering the Manufacturing Accuracy of Cycloid Transmission Wheels with Intermediate Rolling Elements and a Free Cage

Purpose: In the present work, different combinations of fits and accuracies, in relation to the profiles of mating parts, have been analysed in order to assess the degree of the engagement of transmissions that contain intermediate rolling elements. The aim of this work is to determine which fits have decreased accuracy, but nevertheless provide a minimum manufacturing clearance for the transmission engagement in order to reduce the cost of parts production. Methods and materials: Considering the normal probabilistic distribution law in relation to the obtained dimensions of the manufacturing equipment, a combination of fits were selected using the incomplete interchangeability method, taking into account the peculiarities of the cycloid engagement in transmissions with intermediate rolling elements (IRE). Results: Having studied various combinations of fits of parts that are engaged in transmissions with intermediate rolling elements and a free cage (IREFC), a combination of fits for a “ring, rolling-element cam” were determined, in which a technological clearance of 3 µm is formed in the engagement. At the same time, cycloid disk profiles are manufactured according to the 9th tolerance grade, which reduces the laboriousness and cost of the production. Discussion. When reducing the manufacturing accuracy of cycloid disks, it is possible to obtain both very ample clearances and significant negative allowances. For example, having manufactured a ring with the H9 fit, rolling elements with h6 and a cam with js9, the maximum manufacturing clearance can reach 0.086 mm, while the clearance limits vary from 0.025 mm to 0.061 mm. Additionally, if mating parts are manufactured using a combination of K9-h6-js9 fits, a negative allowance varying from 0.014 mm to 0.026 mm will emerge in the engagement. Both described cases are unacceptable because both ample clearances and large negative allowances will negatively influence the working capacity of the mechanism. However, it is possible to select a combination of fits using the 9th tolerance grade of the basic parts, by which the parts will contact in the range from a small negative allowance of 1 µm to a clearance of 3–4 µm. Furthermore, if this is considered, taking into account the machine settings, it is possible to obtain parts according to the 9th accuracy tolerance grade and, at the same time, provide a clearance in the engagement that is almost equal to zero. Moreover, such a combination of fits is relevant for any transmission with IRE. This is a positive result because it reduces the laboriousness when manufacturing parts and, at the same time, provides high accuracy of the mechanism. Conclusions: It has been established that when lowering the accuracy of manufacturing transmission parts with IRE, both clearances and negative allowances may occur in the engagement, depending on the combination of fits. At the same time, it is possible to select such a combination of fits, by which the parts manufactured according to the 9th tolerance grade, will provide almost zero clearance of the engagement of the transmission. In this way, it is possible to reduce the cost of manufacturing the parts for gears with intermediate rolling elements and, at the same time, maintain a high accuracy of the transmission mechanism.

Establishment of Thermal Ductile Fracture Criterion for As-Cast 42CrMo Steel and Its Application in Hot Ring Rolling Process

The casting-rolling compound forming process of ring parts is an advanced plastic forming technology that has been developed due to the merits of high efficiency and energy and material saving. However, cracks often occur during the hot ring rolling process, especially at the edges of the ring parts, which severely affects the forming quality. To predict and try to avoid the occurrence of cracks in the casting-rolling compound forming process of ring parts, the high-temperature fracture behaviors of as-cast 42CrMo steel were investigated by thermodynamic experiment method. The high-temperature tensile tests were carried out using the Gleeble-3500D thermomechanical simulator at various temperatures and strain rates. Stress-strain curves and fracture morphology were examined, through which the sensitivity of stress to temperature and strain rate and the effect of dynamic recrystallization and cavity evolution on fracture were found. The law of critical fracture strains was analyzed, and the model of critical fracture strain as a function of temperature and strain rate was established. Based on Oyane criterion, the thermal ductile fracture criterion was established in conjunction with the model of critical fracture strain. By embedding this thermal damage model into the finite element (FE) model for hot ring rolling of an as-cast 42CrMo ring, the damage prediction for this process was realized, and the thermal ductile fracture criterion was proved to be reliable. From the FE results for hot ring rolling, mechanism of damage and fracture in the hot ring rolling process was analyzed. The damage threshold C f is small, and the damage ratio D is large at the top and bottom edges of the inner surface area of the ring, which have the greatest propensity to cracking in the course of hot ring rolling. This is of great significance in terms of improving the forming quality of ring parts in the casting-rolling compound forming process.

Improving quality prediction in radial-axial ring rolling using a semi-supervised approach and generative adversarial networks for synthetic data generation

As artificial intelligence and especially machine learning gained a lot of attention during the last few years, methods and models have been improving and are becoming easily applicable. This possibility was used to develop a quality prediction system using supervised machine learning methods in form of time series classification models to predict ovality in radial-axial ring rolling. Different preprocessing steps and model implementations have been used to improve quality prediction. A semi-supervised approach is used to improve the prediction and analyze, to what extend it can improve current research in machine learning for quality prediciton. Moreover, first research steps are taken towards a synthetic data generation within the radial-axial ring rolling domain using generative adversarial networks.

RATIONAL FOR REHEATING IN THE AUTOMATED LINE FOR RING BLANKS PRODUCTION

Features and requirements to the use of reheating of ring blanks in the conditions of production on the automated line are considered. An assessment is given for a technological temperature state of ring blanks at various stages of production under conditions of the automated line. For assessment of rational for reheating at production of ring blanks, a classification of ring manufacturing technology is proposed with the production of a pressed non-core blank in an open die, with the production of a pressed profile blank in a closed die, with the production of a pressed profile blank in a stamp with reverse extrusion. The technology of ring rolling with the production of a pressed non-core blank in an open die is the most economical and does not require the use of reheating in the manufacture of rings made of medium-alloy steels. The technology of ring rolling of a profile blank obtained in a closed die does not require the use of additional heating after pressing, in the case of manufacturing rings with a simplified profile on the outer or inner diameters of the ring. In the manufacture of rings with a more complex profile on the outer and inner diameters of the ring, as well as rings made of high-alloy steels, the final decision on the need for additional heating is made depending on the temperature of the end of intensive plastic deformation for the selected steel grade of the ring. The technology of ring rolling with the production of a pressed profile blank in a die with reverse extrusion requires the use of reheating after the pressing operation before the ring rolling operation, and is recommended for the manufacture of rings from medium- and high-alloy steels with a complex profile section on the outer and inner diameters, wall thicknesses, with a ratio of wall thickness to outer diameter D within h / D = 0.011...0.016 and with a ratio of wall thickness to ring height L within h / L = 0.020...0.041. The proposed recommendations are intended for use in the development of technological support for the operation of the automated ring-rolling complex at OJSC “BELAZ”.

Grain evolution during hot ring rolling of as-cast 42CrMo ring billets

During hot ring rolling and subsequent air-cooling processes, the as-cast metal alloy undergoes a complicated microstructural evolution. In this paper, the grain refinement of as-cast 42CrMo ring billet during hot ring rolling and air-cooling was conducted by FEM simulation and tests. Moreover, the grain refinement mechanism of as-cast 42CrMo was also studied by comparison of single-pass deformation and multi-pass deformation with short pass interval time, with the purpose of studying the influence of the deformation process on grain refinement supported by the results of FEM simulation. As a result, effective strain and average grain size of the ring show zonal distribution characteristics The effective strain on the inner and outer layers of the ring is large, contributing to fine and homogeneous grains. In contrast, the cumulated effective strain on the interlayer of the ring is small, resulting in inhomogeneous and mixed grains and large average grain size. Grain growth occurs during subsequent air-cooling. The microstructural distribution of the hot rolled ring was confirmed by a hot ring rolling test.

Data based model predictive control for ring rolling

Thermomechanical ring rolling is an evolution of the process where deformation and heat treatment are combined to obtain a product with both the desired geometry and hardness or microstructure in a single step. However, the high sensitivity of the process to the initial condition and to various disturbances limits its repeatability and accuracy. In this paper, the authors implement a concept for hardness control of ring rolling in virtual experiments. A concept based on soft sensors and model predictive control is implemented on a digital twin. The operation of the different models needed for this control loop are detailed and the controller itself is illustrated.

TASKS OF TECHNOLOGICAL SUPPORT OF THE AUTOMATED RING ROLLING COMPLEX

The physical foundations and advantages of ring rolling are described. The materials science and technological processes of manufacture of products with its use are generalized. An analysis of the equipment of an automated ring rolling line was carried out, which showed that it is a complex and expensive technical solution. Moreover, the organization of the line with maximum load and efficiency is not included in the supplier’s tasks. The requirements for the maximum load of the line and its efficient operation have been determined. It is shown that the use of the experience of creating automated production of railway wheels when creating an automated production of ring blanks is impossible due to the need to ensure the production of rings of different structural shapes from different steel grades with different temperature ranges of plastic deformation and with different (from a hundred to several thousands) annual production programs. This requires the use of a different ratio of the radial and axial forces of the ring rolling, different technological equipment, taking into account different stiffness of the rings and their tendency to deformations during processing, transportation and cooling, a special development of mechanization means for readjustments. It is impossible to work out in advance all the technological options for the production of rings of different standard sizes on an automated line. In this regard, for the effective work of the complex, it is necessary to develop technological support and software for the manufacturing processes of each ring, to provide for the possibility of adjusting technological processes directly on the automated line with the participation of operators. On this basis, the tasks of technological support for the operation of the automated ring rolling complex at the OJSC “BELAZ” were formulated.