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The use of continuously cast round blooms as a substitute for cast ingots has attracted wide interest because it can improve yields and reduce operating costs through continuous operation. However, central voids and segregations, which are the most common internal defects in continuously cast round blooms, must be eliminated through the cogging process to ensure adequate mechanical properties. In general, because the diameter of a round bloom is not large owing to the limited facility capacity, the permissible amount of forging reduction may be insufficient to completely close the internal defects. Accordingly, it is necessary to apply a more efficient cogging method to eliminate internal defects, particularly central voids, in a round bloom. Therefore, an innovative square cogging process using a square-shaped billet was implemented in this study to concentrate deformations within the central region of a Ø 1000 mm round bloom. A comparison of shop-floor operations between round and square cogging processes for the manufacture of main shafts shows that the square cogging operation noticeably increases the void closure efficiency with a reduced number of forging blows. Furthermore, the square-cogged products show improved mechanical properties as a result of the enhanced forging effect. Finite element simulations of the square cogging process also confirm the experimental results and validate the feasibility of the square cogging process. [ABSTRACT FROM AUTHOR]

Based on the crack phenomena observed in an actual cogging experiment of the new as-cast GH4151 alloy, the mechanism of crack generation and propagation during cogging was studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results reveal that there were massive and spherical precipitates at the original grain boundary, large-scale holes at the edge of the precipitates and other areas, tiny pores near the grain boundary, and secondary microcracks along the grain boundary. These phenomena all promoted the generation and propagation of cracks. The fracture surface of the crack was determined as intergranular fracture, and local cleavage fracture was found to occur at the grain intersection. Moreover, the strain energy concentration at the grain boundary was evident, and the deformation of billets was found to primarily depend on grain boundary slip and grain rotation. [ABSTRACT FROM AUTHOR]

This article defines process reserves for improving the efficiency of producing milling balls by the example of AO EVRAZ ZSMK and also defines the regulatory parameters of their production on ball-rolling mills. [ABSTRACT FROM AUTHOR]

Calculation time of some material forming processes is tremendously expensive which makes reducing computational time one of the most urgent challenges in this domain. Among strategies that have been developed to speed-up calculations, one of the most flexible solutions is to utilize enhanced linear solvers such as Multi-Grid algorithm. It consists in using several levels of meshes of the same domain in order to more efficiently solve the systems of equations derived from the discretized problem. The speed-up results from the efficiency of coarse meshes in computing the low frequencies of the residual while fine meshes are more efficient in reducing the high frequencies of the residual. The method is integrated in the commercial software Forge® and applied to the industrial cogging process. The obtained results show that the speed-up depends on the number of nodes; for an industrial scale mesh of 50,000 nodes, the multigrid technique allows dividing the computational time by a factor of two. [ABSTRACT FROM AUTHOR]

This work addresses the systematic modeling of a linear feed drive based on a linear synchronous motor, a helpful step in control design for precise machine tools using linear motors. The model considers the electrical dynamics, ripple, cogging effects, and friction. For ripple and cogging, periodic and aperiodic behaviors are analyzed, and simple models are proposed to reflect the observed behavior. Friction is represented by the generalized Maxwell-slip model Al-Bender (IEEE Trans Autom Control 50:1883-1887, ), and the particular manner in which pre-rolling parameters and Stribeck curve were determined for the current system is shown here for completeness. Finally, the model shows a good performance both in simulation and feedforward control. [ABSTRACT FROM AUTHOR]

A Multi-Mesh Multi-Physics (MMMP) method is developed to reduce the very long computational time required for simulating incremental forming processes such as cogging or ring rolling. It consists in using several finite element meshes on the same domain to solve the different physics of the problem. A reference mesh is used to accurately store the results and history variables, while the different computational meshes are optimized to solve each physic of the problem. The MMMP algorithm consists in two main key-steps: the generation of the different unstructured meshes and the data transfer between the meshes. The accuracy of the method is supported by using meshes that are embedded by nodes. The method is applied to the simulation of the cogging metal forming process for which it shows as accurate and more than ten times faster than the standard method with a single mesh. [ABSTRACT FROM AUTHOR]

In order to reduce the very long computational time required for the simulation of incremental processes such as cogging or ring rolling, a Bimesh method is proposed. It consists in using different finite element meshes for the resolution of the different physical problems: a main fine mesh to store the results and to carry out the thermal computations, and an intermediate coarser mesh for the mechanical calculations. It makes it possible to take advantage of the localised deformations that characterize incremental processes to coarsen the mechanical mesh and consequently reduce the computational time. After presenting the main components of these Bimesh method, the building of the embedded meshes and the data transfer between the meshes, its extension for parallel calculations are discussed, before analysing the obtained speed-ups for several cogging applications, both in sequential and in parallel. [ABSTRACT FROM AUTHOR]

For the calculation of torque in synchronous motors a local method is analysed, based on the Maxwell stress theory and the filtered contributions due to the harmonics of the magnetic vector potential in the motor air-gap. By considering the space fundamental field only, the method can efficiently estimate the average synchronous torque for a variety or motor topologies, including concentrated winding designs. This approach employs an analytical filter for the Maxwell stress tensor and `frozen permeability' technique. The proposed method is validated by comparison with FE results for several synchronous motor types: interior permanent magnet motors, wound field motor, synchronous reluctance motor. [ABSTRACT FROM AUTHOR]

The phenomenon of strain-induced porosity (SIP) in extra-low interstitial (ELI) grade Ti-6Al-4V with a transformed β starting microstructure is investigated to understand its origin during α-β cogging. For this purpose, the constitutive behavior of the material is coupled with finite-element method (FEM) simulations of the cogging process. Two distinct types of SIP relevant to cogging speeds and temperatures, viz., shear cracking and void nucleation, are identified. While the former occurs at the prior β grain boundaries below 825 °C, the latter occurs at the prior colony boundaries when the deformation temperature is close to the β transus. The FEM simulations have shown that deformation conditions existing in the midregion of the billet are favorable for void nucleation. The mechanism of void growth in the presence of tensile residual stress and temperature during resoaking is modeled using the Cocks-Ashby coupled growth model. Repeated cogging and resoaking steps cause multiplication of void population in large numbers. To avoid both types of defects in any region of the billet, a practical solution has been developed by introducing a differential temperature profile from the surface to the center, and the validity of the proposed scheme is verified with FEM heat-transfer simulations. [ABSTRACT FROM AUTHOR]