Cross Wedge Rolling Process Research Articles

Numerical and experimental study for process improvement of cross-wedge rolling of bearing steel balls

The uniaxial compression experiments were conducted on GCr15 bearing steel to obtain the flow stress curves under hot deformation conditions. Based on the results of uniaxial compression experiments, finite element modeling was conducted on the cross wedge rolling (CWR) of GCr15 bearing steel balls, and numerical simulation was conducted using Simufact Forming 16.0. The results show that the distribution of effective strain of existing CWR steel balls is uneven, which may lead to uneven quality of steel balls. In addition, the three principal stresses at the center of the steel balls are all tensile stresses, and the effective stress at the center of the middle ball is relatively large, which can easily induce central defects. Moreover, different diameter billets were used for steel balls rolling experiments. It can be seen that when the die cavity is underfilled with billet, the rolled steel balls have no central defects. When the die cavity is fulfilled with billet, there is central piercing appearing at the middle ball, while the side balls have no obvious central defects. Finally, the paper proposes the method of even numbered ball rolling (ENBR) which starts from the middle connector to improve the CWR process of steel balls.

Modified hybrid damage criterion for the cross wedge rolling process

This paper considers the problem of material fracture in the cross wedge rolling (CWR) process. A modification of the hybrid damage criterion dedicated to crack prediction in CWR was proposed. The aim of the modification was to make the limits of the new criterion independent of the implementation temperature of the calibration tests. A rotary compression test was carried out to obtain specimens in which cracking is initiated. Based on the analysis of the FE results of the rotary compression test simulation, the final version of the modified hybrid damage criterion (MHDC) was presented. Using the results of experimental tests and FE simulations, the MHDC limit values were determined. The MHDC limits for the three different temperatures were obtained at similar levels, indicating that the MHDC limits can be made independent of the rotary compression test execution temperature. The MHDC was verified on the example of the cross wedge rolling of a railway axle forging. The verification carried out confirmed the possibility of predicting cracks in CWR-rolled forgings using MHDC. The research results obtained are of an applied nature. In particular, the criterion developed can be helpful in the design of cross wedge rolling technology.

Multi-Variant Analysis of the Cross Wedge Rolling Process for Producing Railcar Axles

Multi-Variant Analysis of the Cross Wedge Rolling Process for Producing Railcar Axles

A novel method for ball forming by cross wedge rolling

In this paper, a novel method for ball forming by cross wedge rolling (CWR) was proposed, and the finite element (FE) simulation and experimental verification were carried out with the 26 mm diameter steel ball as an example. First of all, the die parameters including spreading angle β and forming angle α were selected and the 3D models of the die and guide plate were designed. Then, the FE model was established and preliminary simulation was carried out using the Simufact 16.0 software. The preliminary simulation results showed that the pushing empty defect occurred in the process due to lack of transition from spreading stage to sizing stage and conical die section. Modifying the die design by adopting the method of adding transition spreading angle θ and forming angle α´ increasing with the increase of rolling depth to, the defect could be eliminated and the full filling can be obtained. In addition, the simulation analysis after modified also included effective strain and stress distribution, the kinematic analysis of metal flow, the damage distribution based on the Cockcroft-Latham criterion, the temperature evolution and force parameters in the CWR process. Finally, the rolling experiments and radial rolling force testing experiments were carried out to verify the numerical results. The results indicated that the FE simulation results were consistent with the experimental results through quantitative analysis, which proved that the novel method for ball forming by CWR was feasible simultaneously.

Mechanism and Control Scheme of Central Defects in Cross Wedge Rolling of Railway Vehicle Axles

Faced with a great demand for railway axles, the cross wedge rolling (CWR) process has the advantages of high efficiency and material saving, and good forming quality of axles is significant for railway transportation safety. The stress inside the railway axle of CWR was analyzed by the finite element method. It was found that the center of the rolled piece is subjected to tensile stress in transverse and axial directions and compressive stress in radial direction, making it more prone to defects. By simulating the evolution of micro voids in the center of the CWR piece, it was found that the presence of voids makes the strain around them significantly large and concentrated and the material between the voids deforms intensely. When voids expand relative to the rolled piece and the internal necking between voids is significant, void coalescence is easy to occur, and central defects are formed. The influence of process parameters on void evolution was analyzed. The scheme of detaching die was proposed to avoid central defects of the CWR piece and the optimal parameter conditions of CWR of railway axles were determined, which proved that the quality of railway axles formed with optimized parameters meets the technical requirements of railway vehicle axles.

Contact Temperature Measurements on Hybrid Aluminum–Steel Workpieces in a Cross-Wedge Rolling Process

The Collaborative Research Center 1153 is investigating a novel process chain for manufacturing high-performance hybrid components. The combination of aluminum and steel can reduce the weight of components and lead to lower fuel consumption. During the welding of aluminum and steel, a brittle intermetallic phase is formed that reduces the service life of the component. After welding, the workpiece is heated inhomogeneously and hot-formed in a cross-wedge rolling process. Since the intermetallic phase grows depending on the temperature during hot forming, temperature control is of great importance. In this paper, the possibility of process-integrated contact temperature measurement with thin-film sensors is investigated. For this purpose, the initial temperature distribution after induction heating of the workpiece is determined. Subsequently, cross-wedge rolling is carried out, and the data of the thin-film sensors are compared to the temperature measurements after heating. It is shown that thin-film sensors inserted into the tool are capable of measuring surface temperatures even at a contact time of 0.041 s. The new process monitoring of the temperature makes it possible to develop a better understanding of the process as well as to further optimize the temperature distribution. In the long term, knowledge of the temperatures in the different materials also makes it possible to derive quality characteristics as well as insights into the causes of possible process errors (e.g., fracture of the joining zone).

Feasibility study for the manufacturing of hybrid pinion shafts with the cross-wedge rolling process

The Collaborative Research Center 1153 is investigating an innovative process chain for the production of hybrid components. The hybrid workpieces are first joined and then formed by cross-wedge rolling. Pinion shafts were manufactured to investigate the behavior of the joining zone under increased complexity of the forming process. For this purpose, six types of workpieces produced by three types of joining processes were formed into pinion shafts. The reference process provides a shaft with a smooth bearing seat. It was found that the increased complexity did not present any challenges compared to the reference processes. A near-net shape geometry was achieved for the pinions made of steel.

The Application of Finite Element Method for Analysis of Cross-Wedge Rolling Processes-A Review.

The aim of this article is to review the application of the finite element method (FEM) to cross-wedge rolling (CWR) modeling. CWR is a manufacturing process which is used to produce stepped axles and shafts as well as forged parts for further processing on forging presses. Although the concept of CWR was developed 140 years ago, it was not used in industry until after World War 2. This was due to the limitations connected with wedge tool design and the high costs of their construction. As a result, until the end of the twentieth century, CWR tools were constructed by rolling mill manufacturers as they employed engineers with the most considerable experience in CWR process design. The situation has only changed recently when FEM became widely used in CWR analysis. A vast number of theoretical studies have been carried out in recent years, and their findings are described in this overview article. This paper describes nine research areas in which FEM is effectively applied, namely: the states of stress and strain; force parameters; failure modes in CWR; material fracture; microstructure modeling; the formation of concavities on the workpiece ends; CWR formation of hollow parts; CWR formation of parts made of non-ferrous materials; and new CWR methods. Finally, to show the potential of FEM on CWR modeling, a CWR process for manufacturing a stepped shaft used in car gearboxes is simulated numerically. This numerical simulation example shows that FEM can be used to model very complex cases of CWR, which should lead to a growing interest in this advanced manufacturing technique in the future.

Simulation of Cross Wedge Rolling and Hot Extrusion-Combined Forming Process for Axle Sleeve

In this paper, an axle sleeve is formed through a combined cross wedge rolling (CWR) and hot extrusion process, and the combined forming process is simulated via finite element analysis software Deform-3D. The forming mechanism is revealed by analyzing the stress and strain distribution, the temperature variation and the metal flow law of the workpiece during CWR and hot extrusion. Combined with CWR and hot extrusion forming experiments, the feasibility of a combined rolling and extrusion process to produce an axle sleeve is verified. It has been proven that the outer steps of the axle sleeve produced through the rolling extrusion composite process are well formed, the flange extrusion cavity is full, the metal streamline is continuous, the axis of the inner hole does not easily deviate, the product quality is good and the production efficiency is high.

Interface phenomena and bonding mechanism in the new method of cross wedge rolling bimetallic shaft

Since the drive shaft mainly relies on the outer metals to transmit torque, its inner materials are the dead weight. Therefore, a new method of cross wedge rolling (CWR) bimetallic shaft by using bimetallic billet to directly roll-bond laminated shaft was proposed. In this work, we conducted experimental studies including rolling trial, element diffusion, microhardness, fracture morphology and microstructural evolution to investigate the new method. In the rolling trial, the assembled billet with a tolerance of H7/p6 have significantly reduced the ellipse of outer sleeves. The defects such as spiral grooves, knifing grooves, necking, and cracking appeared on the rolled shafts, which are the typical defects of CWR process and can be avoided by optimizing parameters. The TEM observations demonstrate that the 42CrMo/Q235 interfaces can be metallurgically bonded without large cracks and obvious oxides, which agree with the detection results of element diffusion, fracture morphology and microhardness. As the elements diffuse with each other, the interface microhardness was gradually transited, and small dimples appeared on the tensile fracture. Based on experimental results, the bonding mechanism was discussed. The rolling interface is compressed in the radial direction and stretched in tangential direction because of Mannesmann effect. Due to the radial compressive stress is greater than tangential tensile stress, the bimetallic shaft can be roll-bonded eventually. Under the hot CWR deformation, the microstructure of the bimetallic shaft experiences dislocation pile-up, interface bending, grain nucleation and growth, thus realizing metallurgical bonding at micro scale. This new CWR process is efficient and high-performance, which can be extended to have industrial applications in high-end equipments with an economical way.

A Comparison of Two-Roll and Three-Roll Cross Wedge Rolling Processes

A Comparison of Two-Roll and Three-Roll Cross Wedge Rolling Processes

Criteria for opening an axial cavity in cross-wedge rolling

The application of empirical, phenomenological deformation and energy theories of metal fracture in relation to the process of cross-wedge rolling is considered. A distinctive feature of cross-wedge rolling in comparison with other metal pressure treatment processes is the complex stress-strain state in the deformation focus and the possibility of opening the axial cavity. The existing empirical criteria of destruction are given. The scheme of a new calibration test based on crosswedge rolling and the fracture criterion proposed by Zbigniew Pater are considered. It is shown that the Zbigniew Pater’s empirical criterion for the destruction of Zbigniew Pater provides a correct determination of the moment of opening the cavity during cross-wedge rolling. The improved phenomenological deformation theory is based on the theory of fracture developed by V. L. Kolmogorov. It is proposed to evaluate the plasticity of the metal depending on the stress state in the form of two independent invariants of the stress tensor: the average stress and the parameter of the third invariant of the stress tensor. The dependence of the limit value of accumulated deformation, at which destruction occurs, on the stress state is constructed in the form of a plasticity surface. The phenomenological deformation criterion of metal destruction during plastic deformations allows us to determine the moment of opening the cavity during cross-wedge rolling and the plasticity resource of the metal.

Central defects control of Ti-6Al-4V alloy with heavy section reduction during flat cross wedge rolling

Cross wedge rolling (CWR) process is expected as an efficient and innovative preforming process for the forged aero-engine blades. But it is still a grand challenge to control the process defects and the performance of the rolled parts. According to the requirements of an aero-engine Ti-6Al-4V (TC4) blade billet with heavy section reduction up to 83%, flat CWR tools were designed and optimized by the thermal-mechanical coupling finite element (FE) method. The metal flow, damage evolution, and the distribution of stress and strain during the forming process were analysed. Then, the CWR experiments were carried out on IM500 flat CWR mill under different technological conditions. The obtained rolled parts were subjected to non-destructive testing (NDT), tension tests and microstructure analysis. The results showed that the central defects, such as micropores and voids, which seriously reduce mechanical properties, occurred in some of the rolled parts more or less. The volume of central defects was closely related to the initial rolling temperature of the billets. When the heated temperature of the TC4 billet was higher than 850°C, the target rolled part without central defects can be obtained. This research work can be a reference for the single-wedge CWR forming of titanium alloy with heavy section reduction, promoting the application of CWR in the aero-engine blade preforming process.

Analysis of the use of variable angular parameter tools in cross-wedge rolling

This paper proposes novel tools for cross-wedge rolling (CWR). Previously used standard tools have a flat forming surface described by two angles, i.e. the forming angle α and the wedge spreading angle β. In this study, the authors investigated whether the use of tools with modified forming surface due to the use of variable angles α and β would have a positive effect on the CWR process. Numerical modelling was employed to determine the impact of the tools with variable angles β and α on CWR. The focus was put on assessing the effect of the changed forming surface of the wedge tools on the radial and forming loads, effective strains, and damage functions determined by fracture criteria developed by Argon et al., Oyane et al. and Pater et al. Numerical results were used to design a novel wedge tool shape that would ensure a reduction of rolling forces and energy consumption as well as a reduced risk of internal cracking in the axial zone of the workpiece. Experiments were conducted using both standard and novel tools of the same size. Experimental results confirmed that the use of the proposed novel tools had a positive effect on the CWR process.

Assessment of the Susceptibility to Material Fracture in the Cross-Wedge Rolling Process with Concave Tools.

The internal cracking of forgings during the cross-wedge rolling (CWR) process is a serious limitation that prevents the correct implementation of this process. The phenomenon of material cracking in the CWR process reduces the technological and application possibilities of this highly efficient process, which can produce forgings with high geometric accuracy. This article presents the results of rolling forgings at different temperatures. An analysis of the results showed that the size of the resulting material fracture in the CWR process is related to the size of the ovalisation of the cross-section of the forging formed during rolling. On the basis of the observations made, it was proposed to realise the cross-wedge rolling process with concave tools. The use of tools with a concave geometry is intended to reduce the excessive flow of material in the rolling direction, which restrains the formation of the ovalisation of the cross-section of the forging. Numerical simulations were carried out comparing the rolling with flat tools and concave tools with different radii of the curvature. The results show that the use of concave tools reduces the ovality of the cross-section of the forging during rolling and reduces the value of the normalised Cockcroft–Latham (CL) fracture criterion.

Internal crack formation in cross wedge rolling: Fundamentals and rolling methods

Material fracture is a serious problem in cross wedge rolling (CWR). Finding new solutions for material fracture prevention in CWR processes presents a technological challenge for researchers these days. This paper presents a new approach to the problem of material fracture, which investigates a not previously undertaken aspect concerning the influence of the cross wedge rolling method on the development of internal cracks. CWR rolling methods in which two tools are used (two flat wedges, two roll wedges, roll wedge-concave segment, two concave wedges) were analysed. In addition, the effect of the number of moving tools on material fracture in CWR is investigated. Material fracture is predicted by a novel hybrid fracture criterion. In this paper, FE simulations were used to determine the value of the hybrid fracture criterion. Experimental studies were used to validate the built numerical model. The conducted research has shown that with the increase in the ovalization of the cross-section of the rolled forging, which depends on the rolling method and the number of moving tools, the degree of damage to the forging increases. The highest degree of damage occurs during the flat wedge rolling method, in which only one wedge is moving. The lowest degree of damage occurs when rolling with two moving concave wedges. The most important conclusion of the study is that changing the rolling scheme from the least favourable to the most favourable one allows to reduce the degree of forgings damage twice.

Study of Cross Wedge Rolling Process of BA3002-Type Railway Axle

Study of Cross Wedge Rolling Process of BA3002-Type Railway Axle

Numerical and experimental study on microstructure evolution of Ti-6Al-4 V alloy shaft preform in cross-wedge rolling process

Numerical and experimental study on microstructure evolution of Ti-6Al-4 V alloy shaft preform in cross-wedge rolling process

Numerical Analysis and Parameter Optimization of Wear Characteristics of Titanium Alloy Cross Wedge Rolling Die

Cross wedge rolling has the advantages of high production efficiency, good product quality, high material utilization, environmental protection, and low cost. It is one of the best processing methods for producing shaft blanks. In this paper, a cross wedge rolling die of TC4 titanium alloy is studied. Based on the Archard wear model, a modified model suitable for cross wedge rolling die wear analysis is derived through finite element simulation. Then, the modified Archard wear model is imported into Deform-3D software for finite element analysis. Orthogonal experimental design is used to combine and analyze different process parameters. Finally, the beetle antennae search (BAS)-genetic algorithm (GA)-back propagation neural network (BPNN) algorithm is used to predict the degree of die wear and to optimize the simulation parameters, which can acquire the process parameters that have the least impact on die wear. The results show that the wear distributions of cross wedge rolling tools is uneven. In general, the most serious areas are basically concentrated in the wedge-shaped inclined plane and rectangular edge lines. The reason is that the tangential force and radial force received by the die are relatively large, which leads to increased wear. Moreover, the temperature change is most severe on the wedge-shaped ridge line. When in contact with the workpiece, the temperature rises sharply, which makes the local temperature rise, the mold hardness decrease, and the wear accelerate. Through response surface method (RSM) analysis, it is concluded that the deformation temperature is the main factor affecting wear depth, followed by the forming angle, and that there is an interaction between the two factors. Finally, the feasibility of the BAS-GA-BP algorithm for optimizing the wear behavior of dies is verified, which provides a new process parameter optimization method for the problem of die wear in the cross wedge rolling process.

Ductile Fracture Prediction in Cross-Wedge Rolling of Rail Axles.

In the process of cross-wedge rolling, axial-symmetric forgings are formed using wedge tools. These tools may be flat- or roll-shaped. This article presents two methods of cross-wedge rolling of rail axles, traditional and multi-wedge, as well as their advantages and disadvantages. Two cross-wedge rolling processes are modelled numerically using Simufact Forming. Numerical results are then verified by experiments performed on a flat wedge rolling mill. Results obtained with the two rolling methods are compared in terms of material fracture, force parameters, effective strain and thermal conditions during rolling. Results show that material fracture poses a serious problem in these rolling processes. It is found that the Cockcroft–Latham ductile fracture criterion does not predict material fracture correctly. Results demonstrate that the fracture of railway axles in cross-wedge rolling can be best predicted by the fracture criteria developed by Ayada, Brozzo, Ko, Rice and Tracey.