Radial-axial Ring Rolling Research Articles

Contact geometry estimation and precise radial force prediction for the radial-axial ring rolling process

In the present research work, the modular parametric design plug-in Grasshopper, available in Rhinoceros 5, is utilized as a pre-processor for the estimation of the projection of the contact length between ring and tools in the radial-axial ring rolling process. The estimated lengths, for each round of the process, are then used in a slip line based force model for the precise estimation of the radial forming force. The proposed method allows reducing the inaccuracies of the traditional approaches since it supersedes the concept of common thickness draft on both mandrel and main roll side, allowing a more precise estimation of the projection of the contact arc between ring and tools, considered to have a unique value on both mandrel side and main roll side. The fulfillment of this last assumption ensures the forming force to have the same value regardless it is calculated on the mandrel side or on the main roll side. The model has been validated by cross-comparing the analytical results with those of laboratory experiment and finite element simulation. The developed analytical model has been also applied to three different study cases where the previous literature models for the calculation of the projection of the contact arc have shown inaccuracies, demonstrating that the proposed approach can overcome these limitations. The positive cross comparisons among laboratory experiment, FEM simulations, and analytical estimations prove the reliability of the proposed approach, as well as its good integration with authors’ previous analytical algorithms.

Study on the microstructure evolution during radial-axial ring rolling of IN718 using a unified internal state variable material model

Microstructure control during radial-axial ring rolling (RARR) of IN718 is important for increasing the performance in service of IN718 rings. However, RARR is an extremely complex dynamic rolling process with non-uniform local deformation and non-uniform temperature distribution, making the microstructure control difficult. This paper presented an internal state variable (ISV) material model which enables the unified prediction of flow behavior and microstructure evolution during dynamic and post dynamic regime. Based on user defined subroutine, a multiscale finite element (FE) model with adaptive motion control of rolls was established to study the evolution of dislocation density, recrystallized fraction and grain size during RARR of IN718. RARR experiment was conducted to verify the multiscale FE model. The predicted outer diameter of the ring and the radial rolling force as well as the microstructure distribution on the ring cross section were in good agreement with the measured results. The evolution and distribution of ISVs were discussed, and the effect of mandrel diameter, main roll diameter, initial temperature, and rolling ratio on the microstructure evolution of the ring was analyzed. Sensitivity analysis of rolling parameters was conducted. The initial temperature is the most sensitive parameter and the initial temperature should be as high as possible with the pinning of δ phase particle to promote the recrystallization process. It should be careful to increase the rolling ratio when the rolling ratio is higher than 1.667. Because the refine effect of grain structure decreases and the rolling force may increase dramatically due to the low temperature.

Temperature estimation and slip-line force analytical models for the estimation of the radial forming force in the RARR process of flat rings

In this study, a mathematical model for the prediction of the temperature evolution in the ring during the radial-axial ring rolling process is developed and used, together with the authors’ previous results, to determine analytically the flow stress of the material during process. These results, combined with Hill's slip-line field solution adapted to the RARR process, allow a fast and reasonably precise calculation of the radial forming force, a key parameter at the preliminary stage of the process design. The approach is validated by applying the proposed model to a case available in the literature and comparing the analytical results with those of the laboratory experiment and FEM simulation. Following the successful comparison, the models were applied to a large variety of flat rings, comparing analytical predictions with the results of FEM simulations. The accuracy of the analytical calculation and the reliability of the proposed models, for different ring configuration and process parameters, are presented and discussed.

Investigation for an Automated Avoidance of Ring Climbing in Radial-Axial Ring Rolling

Abstract Radial-axial ring rolling is the most important production process for seamless rings. One of the most occurring process errors is the climbing of a ring in the radial rolling gap. With the conventional sensors of a radial-axial ring rolling machine, it has not yet been possible to detect a ring’s climbing in any way. For this purpose, an image processing system was installed at the radial-axial ring rolling machine of the LPS (Chair of Production Systems) which particularly records the side of a ring in the radial rolling gap. This paper proves the basic measuring capability of this intelligent image processing system in the rather difficult setting and presents different steps and experiments chosen to give reliable information on the system’s measurement accuracy. Furthermore the used algorithm to detect the climbing height of rings is presented and the degree of repeatability gets examined and evaluated. Once it is proven that the system delivers reliable results, this work uses different parameters based on the state of the art to affect the climbing of a ring. The intensity with which these parameters affect a ring’s climbing is tested in a fractional factorial design. This knowledge is used to design rolling strategies which avoid a climbing of the ring. Based on these strategies, this work introduces first experiments with static parameters during the entire rolling process. This paper shows the necessary steps and the ways these are realized to implement an image processing system to determine a ring’s climbing height. This finally serves to implement an automated system to avoid a ring’s climbing at an early stage in radial-axial ring rolling.

Recent development of ring rolling theory and technique

Rings are basic mechanical components. Ring rolling is a well-known advanced plastic forming technique to manufacture high-performance seamless rings. Since the 21st century, the fast development of global manufacturing has raised an urgent request to high-performance rings, thus, comprehensive and in-depth studies on ring rolling technique were carried out. Based on long-term investigations and attentions on ring rolling, important developments of ring rolling theory and technique in recent 15 years were simply summarised, including the traditional radial ring rolling and radial-axial ring rolling, as well as the novel combined ring rolling. It is expected to give a valuable reference to the research and application of ring rolling.

Recent development of ring rolling theory and technique

Rings are basic mechanical components. Ring rolling is a well-known advanced plastic forming technique to manufacture high-performance seamless rings. Since the 21st century, the fast development of global manufacturing has raised an urgent request to high-performance rings, thus, comprehensive and in-depth studies on ring rolling technique were carried out. Based on long-term investigations and attentions on ring rolling, important developments of ring rolling theory and technique in recent 15 years were simply summarised, including the traditional radial ring rolling and radial-axial ring rolling, as well as the novel combined ring rolling. It is expected to give a valuable reference to the research and application of ring rolling.

Improvement of the dishing process in ring rolling using conical guide rolls

Ring rolling is an incremental bulk forming process for producing seamless rings, which are suited for high loads. For seamless dish shaped rings, there are applications in different areas such as offshore, aeronautics and the mining industry. At the moment, dish shaped rings are produced by machining of rings with rectangular cross section, by (open die) hollow forging on a conical mandrel, by using a shaped main roll and mandrel in ring rolling or by casting. These ways of manufacturing have different disadvantages, such as high material waste, long process time, geometrical limitations or a cast structure with poor mechanical properties. If dish shaped rings can be produced on conventional radial-axial ring rolling mills, the range of products for ring producers could be expanded without the disadvantages of the current manufacturing processes. In prior studies dish shaped rings were successfully generated by ring rolling. However, a problem was the achieved poor form accuracy and reproducibility of the process. Thus, the goal of this investigation is to improve the geometrical accuracy of dish shaped rings produced on conventional radial-axial ring rolling mills by replacing the lower cylindrical part of the guide rolls by a conical module. Using this improved rolling strategy, the dishing angle deviation was reduced from 5° to 1°. In addition to the experiments, the influence of the most important numerical and process related parameters on the final geometry and the climbing height was investigated by finite element-simulations.

Modeling and application of ring stiffness condition for radial-axial ring rolling

Radial-axial ring rolling (RARR) is an advanced incremental metal-forming technology for manufacturing various seamless rings, especially for large scale rings. A primary problem for RARR is to facilitate rolling process stable and form a ring with good dimension and performance. However, RARR is an extremely complex dynamic rolling process with high flexibility. To reasonably control guide roll is an important approach to keep rolling process stable during RARR. In this paper, a mathematical model of ring stiffness condition for RARR was established based on the force method. Then the influence factors to ring stiffness were discussed, especially the section bending moment factor. To verify the ring stiffness model, finite element (FE) simulation was adopted. In addition, a comparison of different ring stiffness models was made. It can be found the proposed stiffness model has a high accuracy. Furthermore, a control method of the pressure in the hydraulic cylinder to adjust the guiding force based on the stiffness model was proposed. By FE simulation of RARR, an appropriate adjustment coefficient to determine the guiding force was obtained. Finally, an experiment of RARR for a large ring was carried out. The rolling process was very smooth and steady, and a super-large ring with diameter more than 9m was manufactured successfully.

Determination of Influencing Factors on Ring Climbing in Radial-Axial Ring Rolling via Design of Experiments

Seamless rings are applied in several industrial sectors and are mainly produced by radial-axial ring rolling. Ring climbing is one of the most occurring process errors leading to a distortion of the ring’s cross section. This paper presents the determination of the influencing factors and their impact and correlations on the process error of ring climbing via Design of Experiment. The highest impact on the climbing height of a ring has the adjustment of the rolling table and the guide rolls. Relatively low but still noticeable is the influence of the process parameters of the rings displacement and the unequal axial rolling speeds. With this knowledge it will be possible to develop, test and implement a rolling strategy that may reduce or avoid ring climbing successfully.

Mathematical definition of the 3D strain field of the ring in the radial-axial ring rolling process

The paper focuses on the radial-axial ring rolling process and details a new mathematical approach for the determination of the evolution of the ring geometry during the deformation process, taking into account separately the sequence of incremental deformations occurring when the ring passes through the mandrel-main roll gap and through the axial rolls gap. Based on the determined geometry of the ring, the three strain components of the strain tensor are estimated and the equivalent plastic strain is computed. The proposed approach, taking into account a third strain in each deformation gap, allows an estimation of the equivalent plastic strain, which is a required parameter for the analytical estimation of the flow stress of the material, needed to compute the forming force. Since a direct validation of the strain components is not possible in the industrial RARR process, authors’ models for the determination of geometry and strain, together with preliminary authors’ models for the estimation of strain rate and temperature drop along the process, have been applied to a literature case for the estimation of the radial forming force in order to obtain a validation of the proposed models. Prediction of radial forming force utilizes a literature model based on slip line theory adapted to the ring rolling process. To extend the validation of the approach and to explore the quality of its predictions to other process configurations, different geometry of the ring have been considered and compared with FEM predictions. These comparisons resulted in good agreement between analytical and FEM results as concerns ring geometry evolution, strain tensor prediction and effective strain estimation.

Optimization on cooperative feed strategy for radial–axial ring rolling process of Inco718 alloy by RSM and FEM

During radial–axial ring rolling process, cooperative strategy of the radial–axial feed is critical for dimensional accuracy and thermo mechanical parameters distribution of the formed ring. In order to improve the comprehensive quality of the ring parts, response surface method (RSM) is employed for the first time to optimize the cooperative feed strategy for radial–axial ring rolling process by combining it with an improved and verified 3D coupled thermo-mechanical finite element model. The feed trajectory is put forward to describe cooperative relationship of the radial–axial feed and three variables are designed based on the feed trajectory. In order to achieve multi-objective optimization, four responses including thermo mechanical parameters distribution and rolling force are proposed. Based on the FEM results, RSM is used to establish a response model to depict the function relationship between the objective response and design variables. Through this approximate model, effects of different variables on ring rolling process are analyzed connectedly and optimal feed strategy is obtained by resorting to the optimal chart specific to a constraint condition.

Curvature control in radial-axial ring rolling

Abstract: Radial-axial ring rolling (RARR) is an industrial forging process that produces seamless metal rings with uniform cross-section using one radial and one axial rolling stage. Conventionally, the ring products are circular and the process is tightly constrained using guide rolls for stability, and to ensure the circularity and uniformity of the ring. Recent work has shown that when guide rolls are omitted, stability can be maintained using differential speed control of the roll pairs. However, achieving uniform curvature in this unconstrained configuration was not always possible when the controller only centred the ring within the rolling mill. In addition to the regulation of constant curvature in circular rings, differential speed control in unconstrained rolling offers an opportunity to bend the ring about the mandrel to create shapes with nonuniform curvature, for example: squares, hexagons, rings with flat sections, etc. We describe a control technique for creating non-circular rings using the rolling hardware of a conventional RARR mill, machine-vision sensing and differential speed control of the rolling stages. The technique has been validated for an industrial material in numerical simulations using the finite element method and also demonstrated on a desktop-scale RARR mill using modelling clay to simulate metal at elevated process temperatures.

Investigation of a composite ring rolling process by FEM and experiment

Roll bonding is a well-known process to produce composite sheet metals. Transferring this principle to ring rolling would allow to produce seamless radial composite rings, which combine the advantages of different material properties. This process is studied, both experimentally and using FEM-simulation. For the FEM an explicit model is applied including the kinematic control algorithms of the radial-axial ring rolling machine. In the used model the occurrence of unexpected asymmetrical joints can be reproduced, which are observed during the rolling experiments. By varying the influencing parameters on the asymmetric joint in the FEM a plausible reason was found.

Measurement of Rings via Image Processing during and after Radial-Axial Ring Rolling

Seamless rings are used in several industrial sectors and are mainly produced by radial-axial ring rolling. To be able to detect process or form errors, which nowadays cannot be detected reliably by the conventional sensor technology of a radial-axial rolling machine, an image pro­cessing device has been mounted above the table of the ring rolling machine. This paper introduces the possibilities for measurements via image processing during and after radial-axial rolling of rings.

Thermography in incremental forming processes at elevated temperatures

Temperature measurement is essential for several forming processes at elevated temperatures. It serves to determine and control the workpiece temperature. Thermography as a non-contact-based technology offers the possibility to capture thermograms of complete workpieces without any time-offset. However, the application of thermography requires the knowledge of the fundamentals of radiation thermometry, in particular the emissivity. This paper presents the results of the application of thermography in incremental sheet forming (ISF) with Joule heating and radial–axial ring rolling as a bulk forming process. Using thermography for the determination of the temperature of the forming zone allows for a real-time closed loop control in ISF with Joule heating. Additionally, the results of the temperature measurement of the surface temperature of radial–axial rolled rings are presented, which can be used as a starting point to make a forecast of the rings’ dimensions in cold state.

Measurement of Radial-Axial Rolled Rings by Using Image Processing and Thermography

Radial-axial ring rolling is a hot forming technology to produce seamless rings, which are used in several industrial sectors, such as gear manufacturing, aviation and aerospace as well as transportation and energy. The use of allowances in the industrial production of these rings via radial-axial ring rolling is still very common to ensure that the rings’ final dimensions are reliably inside the given tolerances. Rolling a ring with allowances causes a lot of additional costs, for example purchasing and processing of the extra material.To enable ring manufacturers to reduce allowances for periodical ring errands, a rating of rings directly after the rolling process is benefical. In this paper the approach using image processing and thermography to detect the outer diameter and the surface temperature of the rolled ring to allow for a rating will be presented.

A new approach in modeling of guide and conical rolls in the ring rolling process

One of the modest methods in producing seamless rings is the radial-axial rolling process. Modeling the guide and conical rolls and calculating their respective forces are essential in the simulation of the radial-axial rolling process. The main objective of the present study is to propose a novel approach in the modeling of guide and conical rolls used in the radial-axial ring rolling process. The parts dedicated to the simulation of the process are two complicate formed rings made of Ti-6Al-4 V alloy. To validate the results obtained via the simulation, practical experiments were carried out in which a simple ring made of aluminum alloy was rolled, and practical results were compared with simulation results. Comparing the results shows a proper agreement between simulation and practical results. Consequently, the obtained radial and axial forces and moments from the simulated process can be used to select proper machine tools for the purpose of mainly producing two complicate formed rings.

Precision ring rolling technique and application in high-performance bearing manufacturing

High-performance bearing has significant application in many important industry fields, like automobile, precision machine tool, wind power, etc. Precision ring rolling is an advanced rotary forming technique to manufacture high-performance seamless bearing ring thus can improve the working life of bearing. In this paper, three kinds of precision ring rolling techniques adapt to different dimensional ranges of bearings are introduced, which are cold ring rolling for small-scale bearing, hot radial ring rolling for medium-scale bearing and hot radial-axial ring rolling for large-scale bearing. The forming principles, technological features and forming equipments for three kinds of precision ring rolling techniques are summarized, the technological development and industrial application in China are introduced, and the main technological development trend is described.

Blank size dependence of microstructure in radial-axial ring rolling of TA15 titanium alloy by macro-micro FE simulation

The blank size, determining the deformation degree and the ratio of axial to radial feed amount of the radial-axial ring rolling process for TA15 titanium alloy, has a strong effect on the grain size and volume fraction of primary α phase, which determine the mechanical properties of the rolled ring. In this paper, a macro-micro 3D-FE model of the radial-axial ring rolling of TA15 titanium alloy has been developed under ABAQUS software. The ring blank transferring from heating furnace to rolling mill, rolling and cooling after rolling during the whole process are considered in the FE model. And multiple blanks with different rolling ratios and ratios of axial to radial feed amount are designed for a desired TA15 titanium alloy ring. Then, the effects of the blank size on the grain size and volume fraction of primary α phase in the rolled ring are investigated by comprehensive FE simulations. Finally, the optimum blank sizes are obtained by evaluating both the volume fraction of primary α phase and the distribution uniformities of grain size and volume fraction of primary α phase.

3D thermomechanically coupled FEM analysis of large disk rolling process and trial production

Recently, rolling technique used to manufacture rings with various dimensions, shapes, and materials is innovated to a revolutionary technique for the fabrication of large disks. In this paper, in order to study the forming capability of this novel method, its principle was introduced, and the 3D thermomechanically coupled FE model was established using the dynamic explicit code ABAQUS/Explicit. Considering the adaptive treatment of boundary conditions, the user subroutines of ABAQUS were explored based on the movement law of the guide rolls and profiled axial rolls, and contacts between these rolls and the disk component. And the reliability of the FE model was verified theoretically and experimentally. Furthermore, the extending rule of plastic deformation zone and the effect of feed speed on the size of both the outer and inner diameters were investigated. The main results show that (1) the smallest equivalent plastic strain (PEEQ) occurs at the hub of the disk and the junction of the rim and the web, and the larger PEEQ appears on the outer surface of the rim and the web of disk. (2) Both the outer and inner diameters of the disk increase gradually at the beginning stage and more and more rapidly at a later stage. With the increase of the feed rate, the increase rate of both the outer diameter and inner diameter will decrease and the lateral spread rate will increase. And trial production of the large disk based on the analysis had been carried out successfully on the revamped Wagner RAW500/400 radial-axial ring rolling mill.