Seznam abstraktů 2016: SEKCE B - TVÁŘENÍ KOVŮ
Datum: 25.5.2016
The different schemes of resource-saving Thermomechanical Processing (TMP) based on the hot, hot-warm and cold deformation applied to various steels and alloys including sheets, bars and parts production are described. Structural and phase transformations in the course of TMP and their role in formation of structure and mechanical properties in the different cross section shape of billets and parts are presented. The basic physical principles of non-isothermal TMP as a base for developing of new resource-saving technologies of metal products manufacturing and examples of industrial application are demonstrated. Different TMP schemes developed for application to two rolling methods - radial face rolling for producing annular billets including billets with Z-shaped profile and longitudinal rolling for producing cylindrical billets with variable sections of profile, for stepped shafts. Physical simulation, Experimental Planning and FEM application to control structure and mechanical properties of TMP treated products are presented.
This article deals with the design of cooling systems for grooved rolls. The purpose is to extend the life time of rolls by minimizing negative thermal stress during the rolling process. Specifically, the design of a cooling section for a U-caliber roll is presented in this paper. The first part of the article described an experimental stent which was built to obtain the boundary conditions (Heat Transfer Coefficients) on the surface of rolls. The laboratory stand consisted of a rotary cylinder and the cooling section. The cylinder is instrumented by set of thermocouples. HTC are evaluated from the temperature record from the cooling experiments solving a 2D inverse heat conduction problem.
The influence of water pressure and varied geometric configuration to cooling intensity were studied.
The second part of this article deals with the design of optimal cooling configuration to reduce thermal stress in critical points of the grooved roll. The temperature-deformation FEM model was used to express the state of stress inside the roll. HTC obtained from the first part were used as boundary conditions.
The cooling effect of the proposed cooling configuration was verified by an experiment. The stainless steel instrumented sample with U-shaped groove was made for this purpose. The size and dimension of the sample was designed on a real scale of caliber.
Hydraulic descaling plays an important role in the surface quality of hot-rolled steel.
The descaling occurs immediately before hot-rolling in order to eliminate layers of iron oxides on the surface. These oxides are called scales and form stratified layers.
A hydraulic descaler consists of a row of high-pressure flat jet nozzles, i.e. descaling nozzles. Descaling nozzles are composed of several parts, one of which is the flow stabilizer.
The stabilizer is an important part which attempts to minimize the turbulence of the flow within the system and contributes to the optimal performance of the nozzle. Currently, it is possible to choose from a wide variety of stabilizers according to the system operating conditions.
This paper explores the influence of the length of a chosen stabilizer on the impact pressure distribution of the water flow. It was found that a longer stabilizer can significantly improve the performance of descaling nozzles. These findings can increase the performance of the descaler and reduce the production cost of hot-rolled steel.
Surface defects on metals products often have their root cause created during the hot rolling process by oxide scale in cavities and indents becoming embedded from the plastic deformation. The size and aspect ratio of these initial surface features are critical parameters determining whether they will be eliminated or not by the rolling process. The present research investigates the effects of initial defect geometry and the evolution mechanisms in the first hot rolling pass with the substrate being a high-silicon electrical steel. Laboratory hot-rolling experiments were carried out on blocks with open cavities of different geometries machined into the surface. The final geometry of the longitudinal and transversal profiles of the deformed defects were analysed from metallurgical cross-sections. The results were in good agreement with the literature, initial cavity dimensions was found to be crucial to determine whether the defect is eliminated or not after the rolling operation, in this case defects with a depth of 1 mm almost disappeared after the rolling. The results also show that for a given constant initial cavity width, the final defect width shows an inverse relationship with the selected initial depth. It has also been observed that at similar initial depth the wider defects evolve to much shallower surface features. The obtained results indicate that the length of the final defect is only dependent on its initial length along the rolling direction.
For the newly proposed pneumohydraulic drive of workpiece return movement it is researched relations, analysis was carried out and recommendations of selecting values of the initial pressure in the pneumatic chamber, ensuring a rational ratio between the periods of acceleration and deceleration were obtained. The mathematical model and program were created for calculation of the law of motion of the brake rod with floating piston device using the system variable throttling the flow of the working fluid along the movement in the brake chamber. On the basis of the developed model there is made the numerical analysis to assess the impact of the inner surface of the brake axle box on the final rate of the brake piston, as well as the effect of the location and change in the area of additional throttling apertures therein on the trend values of the maximum braking acceleration of moving masses. There is obtained the algorithm of determining the constants and variables control law of motion, minimizing the maximum values of dynamic loads per cycle movement of the workpiece. It is shown that the proposed embodiment of the rod system of the workpiece return movement in the working cage with a floating piston ensures reduce the moving masses and increase the rigidity of the movable rod. It is obtained calculated relations for the definition of effort mobile carriage prop, providing gapless its support with mechanism of feed limit.
In work was done the analysis of changes in the depth of the contact layer of metal during rolling of reinforcing steel in pre-finishing calibers for possible determination of transformation of surface defects. Using the results of comparing the obtained data we can conclude that the most promising form of pre-finishing caliber for rolling-off surface defects during rolling of reinforcing steel is a flat oval with a double concavity, the use of which will allow you to evenly roll out of possible surface defects along the entire length of the workpiece.
The paper presents application of multistage compression test for modelling of hot rolling of various steel products. To carry out these experiments multifunctional deformation simulators Gleeble of different types have been used. It was primary applied to simulate rolling of ribbed bars in slitting passes from steel having high value of yield stress. Next two tests were used to model rolling of flat products in finishing stands from multiphase steel, namely dual phase (DP) and martensitic steel (MS). The test parameters, i.e. temperature of deformed metal, strain, strain rate and idle time between passes were selected to represent as precisely as possible the rolling condition occurring in real processes. Results of this work show that the flow stress data can be obtained for high strain values, much higher than can be acquired in plastometric tests. Thus, conditions of Gleeble tests are more close to industrial condition and data (flow stresses) obtained from Gleeble simulation are more realistic. Apart from that, the multistage compression tests realized in the investigation aimed at identification of grain size evolution and softening behaviour as function of temperature, strain, strain rate and idle time between deformations. Furthermore, obtained data of deformed metal are most often applied in the other investigations, namely computer modelling using FEM. Physical modelling using multistage compression tests provides basics for the designing of hot rolling processes of various products and allows to learn more about metal flow in deformation conditions.
The main disadvantage of using classical (butt) oval roll groove in the oval-round roll pass schedule is relatively small coefficient of elongation. This fact requires a larger number of passes to achieve the final dimension of the bar (or wire). This may be a problem for rolling mill with fewer stands. Coefficient of elongation can be increased by reducing the distance between the rolls. However, we are facing the problems with arising of the flash in second (round) groove. A possible solution is to use an elliptical oval groove in first pass which causing greater elongation in round groove. This paper deals with computer simulation of hot bars rolling in two consecutive passes in the oval-round roll pass schedule by FORGE. The initial and boundary conditions of FE analysis was validated and verified by a laboratory hot rolling of round steel bars on flat and round grooved rolls at different rolling temperatures. We compared the rolling forces and the rolled shapes after the individual passes. In this paper are presented the different settings of butt and elliptical ovals and their impact on the overall coefficient of elongation in both passes. Our results showed that the use of an elliptical groove can greatly improve the overall coefficient of elongation.
The article presents the use of multiscale model to estimate the shape and size of the mixed and liquid zone in the modelling processes with semi-solid core. On a macro level to calculate the heat flow is used three-dimensional thermal model based on the Finite Element Method. While at the micro level it was used a cellular automata combined with the finite element method based on the work of Gandin and Rappaz. Furthermore, the state of the cells influences to the temperature distribution it can be concluded that there is a bidirectional coupling. Each cell changes its state from liquid through mixed to the solid. Thanks to the use of cellular automata it can be possible both a better understanding of the process of creation and estimation the mixed and liquid zone. The paper presents the proof of concept of the original application allows to estimate and visualize the mixed and liquid zone.
The control of texture and microstructure can be achieved by an appropriate thermomechanical treatment in industrial production. The effects of finish rolling temperature, cold reduction and annealing temperature on texture development and microstructure in Brass sheet were investigated. The role of deformation inhomogeneities on texture evolution has been considered. The formation of transition bands during hot rolling enforced the intensity of cube components. Shear bands increased the intensities of S and Cu components after cold rolling and at higher cold reductions. Transition from Cu to Y and Y to Bs was completed better because of mechanical twinning. Thermal twins annihilated the rolling texture components during final annealing at high temperature.
Hot rolling of an alloy Al Mg3 was physically simulated by anisothermal uniaxial compression tests performed on the Hot Deformation Simulator HDS-20. The main aim of the research was to define the effect of the finish rolling temperature (in range from 250 to 350 °C) on the structural and mechanical properties of the investigated alloy. The ten height passes with the uniform size of ca 10.4 % lead to samples-upsetting from the initial height of 15 mm to the nominal height of 5 mm, which corresponds to the total height deformation of 67 %. Strain rates were chosen uniformly as the 3 s-1. Two simulations even at the strain rate of 13 s-1 were performed to supplementary assessment an influence of strain rate on the properties of the investigated alloy. Metallographic analyses demonstrated an intensive forming of the structure in the central area of the samples, which results in strong flattening of the individual grains. It can be assumed on the basis of the obtained results, that significant suppression of recrystallization occurred in most cases and the resultant microstructure was mainly influenced by the strengthening cumulating from partial passes without significant effect of softening processes. Lower finish rolling temperatures clearly lead to a gradual increase of the hardness HV10 by tens of percent.
Datum: 26.5.2016
This contribution delivers theoretical analysis of process and relevant findings related to mentioned process. Design solutions on used metal sheets holders for forming are being presented in this article. In the experimental part the laboratory tests were conducted on sheet metal samples. Contribution is complemented with discussion of presented problem.
Ecological and economic reasons are forcing industry to improve efficiency and to save energy and resources. Especially for the automotive and transport industry – but also for all other industrial branches dealing with accelerated masses – lightweight design is a key issue for achieving this goal.Higher process stability, improved material exploitations and general shortening of process chains are the most important aims of Fraunhofer IWU. The requirements of the future car ask for lightweight construction concepts, in which materials, design and manufacturing process harmonize optimally. The usage of lightweight materials is only reasonable when their mechanical characteristics such as stability, stiffness and temperature resistance are better than those of classic steel. The same is true for the material and production costs. Therefore, Fraunhofer IWU researches on forming and joining technologies in order to achieve the optimum usage of high-strength steels, aluminium, magnesium, and fiber composite materials. New forming technologies as press hardening or electromagnetic forming (EMF) bring positive effects by resource efficiency and energy save. By developing new materials, it is important to design the whole process chain according to the specific material properties. Press hardening offers an effective method of forming high strength steels. EMF is a high-speed forming technology applicable for shaping, joining and cutting electrically conductive sheet metal or hollow profile components. A target-oriented design helps to save the weight by using of structures.
The prediction of a fracture in forming processes was analyzed strongly in recent years. A number of material tests for determining a fracture criterion were carried out. This study examines a fracture criterion on the basis of tension and torsion tests. The correct value of the fracture criterion is influenced by forces and fracture areas. Normalized Cockcroft-Latham and Oyane fracture criteria were used for comparison of a simulation and an experiment. Obtained values of the fracture criteria were consequently used in a simulation of the plate shearing. The description of the whole process of the plate shearing covers not only the initiation of a fracture but also the growth of the fracture until the material parts are separated. This issue was solved by means of two numerical methods, the softening and the element deletion. The simulations were performed using DEFORM software based on the finite element method.
The production of seamless steel multi-rifled tubes (i.e. tubes with multiple inner grooving) by means of cold drawing ranks among the most advanced cold forming production technologies. For this particular technology a hot rolled seamless steel tube serves as a feedstock for multiple cold drawing operations with a smooth plug. Then, the final drawing operation takes place, producing the grooving pattern on inner surface of the tube by means of a multi-rifled plug. In this paper, experimental validation of a numerical model of multi-rifled tube drawing is being presented. The model setup was prepared in DEFORM 3D simulation software with final tube dimensions of Ø28.6 × 6.27 mm. The final tube dimensions from the experiment were obtained via optical 3D scanning technology. Comparing the measured quantities with the simulated ones, there was a very good agreement between the simulation and the experiment. Such a validated numerical model can serve as an efficient tool in further optimization of multi-rifled seamless tube production technology, bringing the producer a vital technological innovation into the traditional cold drawing production process.
The main purpose of this work is to meet the need of society ENICAB on the breaking of the wire aluminum AGS alloy, and also answer the question of the misfit properties prescribed by the provider to the final properties of the wire drawn.
In this study we tried to follow the evolution of the properties of wire alloy during drawing. On INODAL designation, it was found that the wire properties were very close to that recommended by the provider. However, the designation MIDAL wire, for which the problem of rupture appeared, it was found that the differences were consistent between the properties of drawn wire and data prescribed by the supplier; these differences may vary from one arrival to another.
Micrographic analysis by optical microscope revealed that there is no difference between the microstructure of the two wires; both have the same microstructure and acquire an elongated grain microstructure along the axis of the deformation during drawing. It should be noted that there was still a slight difference between a grain size of both initials wires. The measurement of the microhardness showed a greater hardening of the wire INODAL compared to MIDAL wire, during drawing. However, the electrical resistivity of MIDAL wire is greater than the INODAL wire.
The experimental material was a drawn and patented wire of 3.4 mm diameter of C78DP steel. The wire was drawn from the diameter of 3.4 mm to 1.5 mm using straight-through single-block KOCH KGT 25 – E wire drawing machine. Two pass schedules were used with different one-pass reduction. Metallographic analysis was conducted on scanning electron micrographs (SEM) of the wire axis area. True interlamellar spacing (IS) was determined for all individual passes by statistical analysis of measured apparent IS. Histograms constructed using true measured data were compared with each other passes for both pass schedules. Both tensile test and torsion test were conducted. Measured mechanical properties (ultimate tensile strength, elongation to the fracture and shears strain to the fracture) evolution was compared with evolution of true IS. We confirmed that there is a strong correlation between true IS and tensile strength or elongation to the fracture. We also discovered that low cycle toughness represented by shears strain to the fracture reach the maximum value before the deformation of cementite lamellae starts. From this viewpoint we also mutually compared both pass schedules.
In the article was produced a study of the advanced variant of combined process "rolling – pressing" using computer simulation in DEFORM-3D program. The key feature of this variant of the process is the new design matrix in which the direction of metal flow changes in three dimensions. During study have investigated such parameters as accumulated strain, deformation of the front end of the workpiece to determine the degree of change in the utilization rate of the metal and deformation force. The simulation results show that the proposed scheme of deformation gives the opportunity to develop in the metal the higher level of strain, thereby reducing the required number of cycles of deformation to achieve a given level of treatment of the metal.
Microstructure changes and strength of low alloy steels were investigated after nanostructuring using different conditions of severe plastic deformation (SPD) with "warm" (at 300 ° C ... 500 ° C) and "cold" (at room temperature) equal-channel angular pressing (ECAP), which provide technically significant improvement in mechanical properties of materials. The conditions of SPD and heat treatment (HT) of low alloy steels on modes of warm and cold ECAP led to the formation of the structure with ultrafine grained ferrite matrix strengthened by nanosized carbide particles. The features of deformation and fracture microprocesses of the samples with nanograined/ultrafine-grained (NG/UFG) structure were revealed. It is established that refinement of structural components creates conditions for strain-stimulated self-organization of structure during subsequent loading. As a result the structure strain localization occurs at later stages compared with the materials in coarse-grained state. The change of base destruction micromechanism by quasi-cleavage to more energy-intensive micromechanism of fracture – the viscous patching separation and disperse quasi-cleavage was observed.