Key Engineering Materials Vols. 622-623

Abstract: Adapters are a component of the output system in the internally geared hub for a bicycle. Originally, adapter parts were produced by a machining process with low productivity and material usage rate. In this study, the metal powder injection molding (MIM) process has been applied as an alternative manufacturing method to the machining process. Microstructure analysis and mechanical property testing has been conducted in order to select the material for the adapter with changes in the nickel content. The geometrical precision of the adapter is measured by using three-dimensional scanner with various mixing ratios of the powder and the binder. The developed alternative process for the adapter results in increased productivity and material usage rate. Previously, this process was only used for small parts less than 10 mm in diameter. With this development, the MIM process may be used more widely than before.

Abstract: During the last 90 years, a lot of works have been published about rolling theories for the two-roll rolling process (2RP). In the last decades, the three-roll process (3RP) has become a significant technique in the production of wire rod and bars, as it allows to cover a wide range of finished dimensions with one pass design, or to realize very close tolerances, depending on the pass design method used (free size rolling or high precision rolling). Horihata and Motomura [2] made use of the upper bound theorem to construct a method for spread calculation, but up to now, a straightforward mathematical method for calculation of stress distribution, roll forces, torques and forward slip is still missing. The present paper aims at a transfer of the slab method, which is well-known and established for the 2RP, to the 3RP. After the rolling theory for flat passes is introduced, Lendl’s equivalent pass method is transferred to the 3RP, which allows the calculation of section passes. Computational results show, that roll forces, torques and forward slips can be calculated under inclusion of elastic stand feedback and interstand tensions. Therefore the model can be used for roll speed set-up to minimize interstand tensions, which is of great importance for the rolling industry.

Abstract: This work is concerned with rolling of a Teflon-Cu-SPCC steel plate, which has been used as a base material for an oilless bearing or dry bearing. Materials for an oilless bearing require special characteristics such as high wear resistance, low friction, fast heat loss, as well as structural strength. Such superior mechanical properties could be obtained by rolling the multilayer plate composed of a mixture of Teflon-Cu powder and a SPCC steel. The main objective of this research is to investigate the deformation characteristics of a Teflon-Cu-SPCC steel plate during rolling process. Especially, focus is given to the thickness changes of the Teflon-Cu powder mixture layer. An Eulerian finite element method coupled with a contact profile correction algorithm is adopted for the simulation of rolling. Validity of the proposed finite element analysis is given. The important parameters chosen in this work are the reduction ratio, roll size, and the Cu content in a Teflon-Cu mixture. Effects of the above important parameters on the deformation behavior and on the final thickness of a Teflon-Cu mixture layer are carefully studied.

Abstract: Helical-wedge rolling (HWR) is a forming process wherein the wedges are helically wound on the roll face. Developed at the Lublin University of Technology (Poland), the HWR process has been successfully applied to produce balls. The present paper describes an example of application of the HWR process for producing a long stepped shaft. The design of the process is discussed and the tools necessary for its realization are described. The developed rolling concept was positively verified by a numerical simulation. The distributions of effective strains and temperatures in a shaft are given, and the variations in forming forces and torques are presented. Particular emphasis is given to the problem of production accuracy of the shaft.

Abstract: In the seamless pipe rolling process, the pipe wall thickness is largely determined at the mandrel mill or plug mill. It is possible to obtain the target thickness at these mills by defining the gap of a grooved roll and an inside tool such as a plug. However, the thickness of the free deformation part, which is not in contact with the roll and tool, had generally been estimated by experimental techniques. Although a number of analytical studies of mandrel mill rolling had been reported, few reports had examined plug mill rolling. Therefore, in this research, a finite element analysis model for plug mill rolling was developed by extending the rigid plasticity finite element model "Computational Rolling Mill (CORMILL)." Good agreement between the calculated results and experimental results was obtained for the wall thickness, and it was found that the thickness of the flange part decreases with reduction of the wall thickness at the grooved bottom. These results suggested that the wall thickness distribution of rolled pipes can be controlled by using a suitable inside tool and roll shape in each rolling pass, and the necessary shapes can be obtained by using the newly-developed model.

Abstract: This study investigated the effect of grain size on the cross wedge rolling of micro copper rod. Annealing techniques and equal channel angular extrusion were employed to refine the grains of copper, after which the treated copper was machined to prepare the cylindrical billets with 1 mm diameter for conducting experiments. The billets were rolled between a pair of the dies fixed in a developed cross wedge rolling system to form micro copper rods. The results show that the developed system was able to successfully produced micro copper rods. The grain refinement led to a higher hardness and thus a greater forming load. The rod with fine grans had a larger concave curvature radius of the end face. The grain size clearly influences the material flow in the cross wedge rolling processes of the micro copper rod.

Abstract: Severe plastic deformation is now recognized the most efficient way of producing ultrafine grained metals and alloys. At the present time a lot of severe plastic deformation methods have been proposed and developed. They differ in the deformation schemes. Unlike such severe plastic deformation methods as high pressure torsion and equal-channel angular pressing, rolling with the velocity asymmetry is a continuous process. It helps to solve the problem of the limited length of manufactured bars with semi ultrafine structure. Rolling process with roll velocity asymmetry generates high shear strain necessary for obtaining ultrafine structures of the processed material. A new process of asymmetric rolling of profiles in multi-roll passes has been developed. This process can be used for production of high-strength profiles such as circles, hexagons, wire rods, etc. Compression of the bar in multi-roll passes can be done not only from two, as usual, but from three or four sides. In case of a multi-crimped bar, a uniform compression scheme with large hydrostatic pressure is created in the deformation zone. It enhances the ductility of the material and allows increasing the strain intensity. Simulation in DEFORM 3D^TM proved that the process of asymmetric rolling in multi-roll calibers allows to obtain higher values of shear strain and strain effective.

Abstract: The importance of coil cooling conditions on mechanical properties uniformity of HSLA and AHSS steel grades is discussed. It is namely shown that hot rolled coil under conventional industrial production can be cooled non-uniformly. That is why to predict correctly the final steel microstructure and mechanical properties of hot-rolled products an accurate description of not only run-out table condition but also of coil cooling should be done. Two solutions to provide accurate description of coil cooling were tested. First one is to use 2D finite element (FE) thermal model. When coupled with the ArcelorMittal metallurgical model to predict hot-rolled microstructure and properties (TACSI) it matches well the industrial data within +/-15-20MPa both for the tensile and yield strength. However, this approach is recognized to be heavy and time consuming. A second solution, a new 2D coil cooling simplified model incorporated in TACSI model, proved to be quite efficient, as it leads to performances similar to the more detailed first solution. Moreover, it is able to compute the coupling between the thermal evolution of the hot band and the kinetics of phase transformation during coil coiling and cooling, and will enable a better evaluation of the final mechanical properties especially for the grades for which the phase transformation is not completed before hot band coiling.

Abstract: Materials with ultrafine grain structure and unique physical and mechanical properties can be obtained by methods of severe plastic deformation, which include asymmetric rolling processes. Asymmetric rolling is a very effective way to create ultrafine grain structures in metals and alloys. Since the asymmetric rolling is a continuous process, it has great potential for industrial production of ultrafine grain structure sheets. Basic principles of asymmetric rolling are described in detail in scientific literature. Focus in the well-known works is on the possibility to control the structure of metal sheets. However the systematic data on the influence of the process parameters (e.g., ratio of rolls velocity mismatch, reduction per pass, friction and diameter of rolls), and the shear strain rate required to achieve a significant grain refinement in asymmetric rolling are lacking. The influence of ratio of rolls velocity mismatch, reduction per pass, friction and the rolls diameter on the distribution of shear strain through the sheet thickness in asymmetric rolling has been studied in DEFORM 2D. The results of the study will be useful for the research of evolution of ultrafine grain structure in asymmetric rolling.

Abstract: Roll bending is a useful technology for manufacturing a wide variety of products in small quantities. However, the roll bending of structural channels, which have a complicated sectional shape, causes irregular deformation. On the other hand, there are fewer reports on the bending of structural channels compared to those on the roll bending of sheet-metals. The purpose of this study is to clarify the deformation behavior in the roll bending of structural channels. The present paper reports on the results from a finite element analysis of the effects of the roller shape on the deformation behavior in the roll bending of structural channels.