Key Engineering Materials Vols. 622-623

Abstract: A novel microforming process - Micro Cross Wedge Rolling (MCWR) has been developed. It is a very promising technology in the field of microforming due to its advantages such as high product rate and minimised material consumption. How to control geometrical accuracy of the produced micro parts is one of the major challenges in the development of microforming technology. Geometrical accuracy was still concentrated in term of springback. When the wedge tools loads are removed after forming step, a portion of the deformation recovers, which causes a change in the shape of micro parts. In other word, springback happens, which should be determined and controlled especially in microforming technology. A series of MCWR experiments of pure copper and aluminium have been carried out using the machine designed by authors in this study. Cylindrical workpieces were deformed into stepped shafts with cross-sectional area reductions of 35, 52.73 and 75%. Corresponding finite element simulation has also been conducted in consideration of the size effect on the material flow. The springback was proposed to account for the geometrical error of micro products. The effect of grained heterogeneity on the height of surface asperity after rolling was assessed quantitatively. Keywords: Micro cross wedge rolling, Size effect, Dimensional accuracy, Springback

Abstract: Internal stresses or residual stresses remain in almost every part after manufacturing and/or further processing. Even if the entire stress state inside a system is in an equilibrium, single stresses due to their direction and strength may have positive or negative influences to the properties of a body. Especially in big parts, the residual stress state is relatively unknown, because it can only be determined by destructive methods as sectioning or slitting. The possibility of the use of non destructive measuring methods is only given for surface near regions or thin parts and not useful for the specification of the entire residual stress state inside a large compound work roll. This paper outlines an approach for the determination of residual stresses in centrifugal casted work rolls with an indefinite chill double poured or high speed steel shell. In several steps, different measurement techniques are tested and the results are to be presented. Beside the residual stress state, which is caused by manufacturing or heat treatment, these work rolls with different shell and core material differ in their thermophysical and elastic properties. These parameters in combination with the residual stress state and the thermal and load stresses, which arise during the hot rolling process, are causing a complex stress field that is presented by a combined model for work and backup rolls in operation.

Abstract: Ring Rolling is a complex hot forming process used for the production of shaped rings, seamless and axis symmetrical workpieces. The main advantage of workpieces produced by ring rolling, compared to other technological processes, is given by the size and orientation of grains, especially on the worked surface which give to the final product excellent mechanical properties. In this process different rolls (Idle, Axial, Guide and Driver) are involved in generating the desired ring shape. Since each roll is characterized by a speed law that can be set independently by the speed law imposed to the other rolls, an optimization is more critical compared with other deformation processes. Usually, in industrial environment, a milling curve is introduced in order to correlate the Idle and Axial roll displacement, however it must be underlined that different milling curves lead to different loads and energy for ring realization. In this work an industrial case study was modeled by a numerical approach: different milling curves characterized by different Idle and Axial roll speed laws (linearly decreasing, constant, linearly increasing) were designed and simulated. The results were compared in order to identify the best milling curve that guarantees a good quality ring (higher diameter, lower fishtail) with lower loads and energy required for manufacturing.

Abstract: A novel microforming process - Micro Cross Wedge Rolling (MCWR) has been developed, which is promising for fabricating micro stepped components used in micro electro-mechanical systems. Numerical simulations have been established and the effect of geometrical and process parameters such as forming angle α, stretching angle β and reduction ΔA have been studied. Micro stepped components have been fabricated successfully on a MCWR testing rig by adopting flat wedge tools. The effects of initial surface roughness of tool, grain size and cross section area reduction on surface morphology have been assessed quantitatively.

Abstract: Ring rolling is a versatile incremental bulk forming process. Due to the incremental character of the process, it consists of a large number of deformation and dwell steps. Finite element (FE) simulations of bulk forming processes are capable of predicting loads, stresses and material flow. In recent years, the finite element analysis of ring rolling processes has become feasible both in terms of calculation time as well as regarding the closed loop control of the kinematic degrees of freedom [1]. Accordingly, the focus of interest now includes the prediction of the microstructure evolution. The accuracy of such numerical simulations strongly depends on the models characterizing the material behavior and boundary conditions. In this paper, a finite element based simulation study was conducted, in order to evaluate the impact of boundary conditions such as transfer time, radiation, heat transfer and friction on the target values of the ring rolling process. The results of the simulation study were compared to ring rolling experiments on an industrial size ring rolling device. A good accordance regarding the evolution of the outer diameter and radial force was observed. Strong contingencies of transfer time on the forces throughout the process were detected and considered in the simulation study. In a post processing step, the evolution of the microstructure considering the dynamic and static recrystallization as well as the grain growth was calculated using the FE results. The calculated grain sizes show good accordance with the experimentally observed microstructure of the ring before and after the rolling. Furthermore, the impact of process parameters on the evolution of the grain size was investigated.

Abstract: The article presents assumptions and the process of construction of an ontology for the knowledge base that concerns industrial processes of metal sheets rolling including heat treatment operations. Creating of an ontology enables to build a knowledge base, which can be understood by both computers and engineers. Such a knowledge base can be used afterwards by intelligent computer techniques helping in solving of encountered problems during production process. The built ontology should be relevant to the nature of the rolling process – it has to take into account sequence of roll passes of the whole rolling process including all control parameters for each pass (e.g. the thickness before and after the pass, time of pass, temperature). Presented process of the construction of the ontology follows an ontology development cycle that should ensure relevance for industrial use of the ontology. The built ontology in the domain of industrial rolling should enable building knowledge base that concerns considered industrial process. One of possibilities is using of the elaborated ontology at construction of an advisory system that supports design of rolling process for a new product, which can be similar to some products made in the past. Other possibilities of utilization of the ontology can be seen in production scheduling or estimation of production costs.

Abstract: Gear rolling is a new gear manufacturing process which can partly replace traditional gear milling processes. High gear wheels with modules of 4mm up to 6mm are of interest to truck manufacturing. The process is of interest since it involves no material removal and since it has the potential to give good performance of the gear wheels. The process must be adopted for the large plastic deformations which occur for gear rolling with large modules. In this paper special emphasis will be put to loads and torques during the gear rolling process of gear wheels with large modulus. The FE method will be used to model the plastic deformation process to fully form a gear wheel with the gear rolling method. The radial and axial loads and the torques in this process are predicted. The loads of the process are high compared to the situation for small gear wheels so simulation of load level is essential for the design of rolling machines for high gears.

Abstract: In consideration of the zone between rolls and deformed area where friction at roll-sheet interface is lower than predetermined value of Coulomb friction in rolling process of ultrathin strip steel, fully integrated with equipment and process features of cold tandem mills, after a large number of field experiments and theoretical studies, on the basis of the improvement of ultrathin strip steel rolling force model, with the allowable rolling pressure and production efficiency as constraint condition, a new calculated theory about the minimum rolled thickness was put forward. What’s more, the theory will be used in the productive practice of 1220 five-rack cold tandem mills of China. The technique has the value to be further popularized.

Abstract: Distribution of residual stress through the thickness of a cold-rolled aluminum sheet is analyzed by the elastic-plastic finite element method under plane strain condition. Single-pass rolling of 2mm-thick aluminum sheet is considered. Influences of roll diameter D, reduction in thickness r, and friction coefficient μ are investigated. When the friction is low (μ = 0.1 and 0.2), and the case with smaller rolls (D = 130 mm) and low reduction (r = 5%), the residual stress in the rolling direction is compressive at surface and tensile around the layer quarter deep from the surface. While in the case with larger rolls (D = 310 mm) and high reduction (r = 30%), the stress is tensile at surface and the stress decreases to compressive with increasing depth from surface. In other words, with low friction, the residual stress distribution strongly depends on the aspect ratio (contact length / mean thickness) of the roll bite. On the other hand, when the friction coefficient is high (μ = 0.4), the residual stress is compressive at surface regardless of roll diameter and reduction. It means that the friction makes the residual stress at surface more compressive. It is found that the relationship between the residual stress at surface and the aspect ratio is almost linear, and that the slope depends on the friction coefficient.

Abstract: The aim of this study is to suggest the die design method for single-profile ring rolling in the production of a large scale welding neck flange, based on the modified uniform volume distribution element technique (UVDET). UVDET is presented as the ratio of volume change of ring blanks to that of undeformed rings per unit height. A welding neck flange has only one–side contour without a symmetry plane and the highly different volume distribution. To manufacture this type of ring, the blank preforming is recommended before a single–stage profile ring rolling process. FE simulations were performed to test the validity of proposed die design method, under Forge software environment.