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This paper presents a FE-analysis and experimental results of a hot forging method for fabrication of large copper canister lids with a low forging load. The forging sequence is carried out in two ...

Forging of large copper lids for cylindrical canisters meant for nuclear waste is treated. Based on recent full-scale experiments, an alternative way of forming is proposed. In the experiments, a p ...

The work is focussed on the start of void formation close to a hypothetical single macro-inclusion in the hot rolling of steel slabs. The inclusion is chosen to be either three times harder or thre ...

The aim of the work is to increase the material yield in closed-die forging of a front axle beam meant for heavy trucks. The amount of flash obtained in production constituted 35% of the total work ...

In order to avoid pores in heavy rings, a new forming concept is presented. The proposed manufacturing route is based on an analysis regarding the current manufacturing of a ring associated with serious pore closure problems. It is concluded that the present method results in small strains close to the outer surface of the ring. Thus, the likelihood for remaining pores in this region is considered to be high. This apprehension was confirmed both by ultrasonic testing and metallographic analysis. The forming route starts with heavy upsetting of a cylindrical billet followed by piercing in a closed die. The penetrating punch is furnished with an upper flat part that is used for upsetting at the end of the process, forcing the material to fill the cavity between the die and the upper tool. The remaining bottom disk is then sheared off in a separate tool. The new concept starts with a lighter upsetting, resulting in a higher “pan cake” of smaller diameter. This workpiece is then moved to a closed die of the same diameter as that of the material. The diameter of the piercing punch is not changed. Because of the small die diameter, the workpiece is, after piercing, considerably higher than in today’s production. The so-obtained workpiece is placed into a die equal to the original one with the exception of a bottom hole. A new mandrel, with a flat upper part and a lower part meant for shearing off the thin bottom disk, will be inserted to fit the recently generated cylindrical hole. At the beginning of the operation, the bottom disk is cut away as the punch moves through the bottom hole and after that, during the same stroke, the high ring will be heavily upset to its final geometry. During the upsetting the ring is supported by the mandrel. If the ring is too high during upsetting, there is a risk for the material to loose contact with the punch, which might result in instability and a fold. Applying the new concept, the strains close to the envelope surface became approximately 160% larger. The present analysis is carried out with an FE-code Q-form making it possible to trace different material elements of the initial billet throughout the different manufacturing steps. The results are presented in form of hydrostatic pressure as a function of the effective strain. Theoretically determined workpiece shapes, based on the conditions of today’s production are in good agreement with those obtained from full-scale experiments. The present work also includes comparisons with another analysis of similar character, published by the authors. In that work, the manufacturing of two other types of rings were analysed, one with pore closure problems and one without.

The behaviour of transversal cracks in reverse rolling of steel slabs is analysed. For this purpose a commercial FE-program, LS-Dyna3D has been utilised. Process parameters from an industrial rolli ...

The behaviour of a longitudinal V-shaped crack, on the surface of a continuously cast steel slab, is studied during hot rolling. The analysis is carried out by means of the commercial FE-code LS-DY ...

Two wear models are compared. The first model constitutes the classical model which assumes that wear is proportional to die pressure and sliding length, while the second model assumes that wear is proportional to the energy dissipated on the tool/workpiece contact interface. The models are applied to the counter-blow hammer forging of a pinion. The upper die cavity is furnished with a bottleneck. Five blows are needed for forging the component. The process is analysed by full-scale experiments and a commercial FE-code, FORM2D. In order to evaluate the two models for different positions of the upper cavity, each blow is divided into a number of incremental time steps. For each of them, the sliding velocity, the contact pressure and the contact shear stress is determined. In this way it is possible to predict which part of the upper die is exposed to the most serious conditions. Both models show satisfactory agreement with the results of full-scale experiments. However, the model based on energy dissipation indicates the location of the wear-sensitive parts of the tool more distinctively.

The manufacturing of two types of heavy rings has been analysed with respect to pore closure. The forming routes differ significantly from a principal point of view. One ring is associated with problems regarding remaining pores whilst the other is not. The objective of the present work is to explain this feature by studying the effective strain and hydrostatic pressure distribution in the workpieces throughout the processes using a commercial FEM-code, FORM2D. It is assumed that large strains and high pressures are favourable. The forming route resulting in a ring, which is free from pores, starts with a heavy reduction in the upsetting of a cylindrical billet, followed by piercing in closed dies. After that a thin circular bottom disc is cut away in another closed die at the same time as an outer flange is formed. The other route starts with a light reduction in upsetting, followed by open die piercing and shearing away a thick bottom plate. Finally the upper part of the ring is flattened by a small reduction in height between plane and parallel dies. The theoretically determined shapes of the workpieces, after different forming steps, are compared with the results of full scale experiments, good agreement being obtained. The final ring rolling of the two ring types is not included in the analysis. Regarding the ring that is formed in closed dies, it is concluded that the final accumulated effective strains are found at high levels for large areas of the axial symmetry plane compared to the other ring. For both rings the strains decrease from the inner towards the outer surface. Characteristic for the ring of a pore closure problem, is that the effective strain decreases along the inner surface, from the cutting region towards the flattened part of the ring. As expected the main part of the forming operation takes place under a higher hydrostatic pressure for the ring formed in closed dies. Predictions regarding pore closure are compared with ultrasonic tests and are found to be in good agreement.

In many metal-forming processes the material flow is complex and cannot be treated accurately by two-dimensional analysis. In the present work a three-dimensional UBET model meant for simulating the material flow in the forging of long components is proposed. Three-dimensional brick-shaped elements are utilized to partition the workpieces according to the geometry of the dies. The analysis incorporates non-uniform strain-rates inside the elements. A detailed formulation of the model is presented. The model has been applied to simulate the deformation of a block in forging between flat dies and grooved dies of simple geometry. The results show satisfactory agreement with the results of model-material experiments.

Physical modelling is an important tool for analyzing material flow and strain distributions in metal-forming processes. A common technique, utilized for plane-strain conditions, is to make use of a grid network which is printed or etched on a visible cross-section of the original workpiece. During the process the distortion of the network is studied. In this work, a PC-based system has been developed to facilitate the evaluation of the mesh and to improve the accuracy of the results. An ordinary video camera is used to record the continuous distortion of the grid. A frame-grabber, which is installed in a PC as an add-on board, is utilized to digitize the video signals. The coordinates of the network-nodes are determined automatically by a newly developed software based on image-processing techniques. By means of the so-established coordinates, the material flow and strain distributions can be followed through the whole process. Special algorithms are proposed to treat mesh images of low quality. Several methods for strain calculations are incorporated in the system, this having been done to make it possible for the user to choose the theory that is considered proper for the actual application. In order to clarify how the system works, the evaluations of two forging experiments are described in detail.

Cold-rolled copper foils in thicknesses between 10 μm–100 μm have many ranges of applications, as for example in the electronic industries for flexible printed circuits boards (PCB) and for cable wrapping and shielding. A good flatness of the foils is important, especially for the PCB-foils which are surfaced after rolling. Normal shape defects, such as centre buckles and long edges, are today detected efficiently by commercial shape meters. Flatness is controlled by, for example, work-roll bending and thermal crowning of the rolls. However, in the rolling of copper foils a special kind of out-of-flatness occurs, which is impossible to detect and control by normal systems for shape control. This kind of defect is characterized by an evenly distributed pattern of small buckles. In the present work it is supposed that this phenomenon is related to a variation in forward slip along the barrel of the roll. This in turn is due to various friction conditions at different locations along the contact between the rolls and the foil. According to a theoretical model advanced by the authors, the variation in forward slip can be decreased for certain combinations of entry- and exit-tensions. The applicability of the model that has been developed for improving the flatness has been confirmed in industrial production.

Uniaxial compaction of powders is studied theoretically for plane-strain conditions, the analysis being focused upon the material flow into the holes between the powder particles. The original powder material is assumed to be built up of close packed cylinders of equal size. With this configuration, it is found sufficient to analyze the deformation of one elementary cell. The investigation is carried out by means of step-wise calculations, starting with a pore volume fraction of 16% and finishing at approximately 1.6%. The investigation is based upon a finite-element approach. After each step the deformed elementary cell is remeshed in accordance with its new shape. The agreement between the material flow as determined from plasticine experiments and that from the finite-element analysis, which latter incorporates the plasticine constitutive equation, is good. Theory and experiment are in acceptable agreement also in respect of the step-wise change of shape of the boundary surfaces defining the holes. Encouraged by this agreement, theoretical results are presented also for a linear viscoplastic material and hot, pure aluminum. It is concluded that the material flow is very sensitive to the mechanical properties of the material, such as the flow stress and its dependence of the strain rate.

In many industrial metal-forming processes, bulging of free workpiece surfaces occures. At the same time these surfaces may fold over and come into contact with the dies. These kind of phenomena are often neglected in metal-forming analyses. The present work deals with the problem of bulging and folding over in plane-strain upset forging. It is a basic work which is meant for a deeper understanding of the problem, and for future utilisation in more complicated simulations such as that of filling of die cavities in the closed-die forging of long components. A computer program has been developed by means of which it is possible to study the influence of workpiece geometry and friction. The analysis is carried out with the upper-bound method for a rigid-perfectly plastic material. A flexible velocity field is utilised and a rigid region of variable shape is supposed to be in contact with the dies. By minimizing the total rate of energy dissipation the best velocity field is obtained. The shape and extension of the dead region is found to be influenced heavily by friction. Theoretically and experimentally obtained fold-overs, free surface shapes and grid network distortions are in satisfactory agreement.

The demand from industry for metal-forming simulation models has increased during the last ten years. Such models are found to be valuable tools considering process optimization and the development of new processes. The application of simulation models makes it possible to reduce the number of time-consuming experiments. The present work concentrates on the cylindrical mandrel drawing of tubes. If the total reduction is small, i.e., if not more than one drawing pass is necessary, this process is characterized by high productivity: compared to pilger rolling the process has been estimated to be about eight times faster. Tubes which have been manufactured by means of cylindrical mandrel drawing are distinguished by close tolerance and good surface smoothness. The tubes are often delivered in the cold-drawn, strain-hardened condition, i.e., without a subsequent annealing. Because the customer often orders a product of minimum yield stress, it is of great importance to be able to predict the strains of the tube material. The theoretical part of this study comprises the development of a simulation model based on the matrix method, the model being utilized for prediction of strains. In the experimental part a high precision investigation considering one workpiece is presented. This sample was furnished with a square network in the axial plane of symmetry. Strain distributions from theory and experiment are found to be in good agreement.

The work which is presented here concentrates upon the compaction which takes place within the container in the extrusion of powder materials. By the use of a model-material technique the material flow in compaction is studied. This information is utilized for the proposing of velocity fields which are used as the starting point for an upper-bound analysis. The proposed velocity fields are optimized by minimizing the rate of energy dissipation considering the location of characteristic coordinates defining the upper-bound solution. The compaction is followed incrementally until a coherent material is obtained. The pressure necessary for each incremental step is calculated. The compaction model has been checked by the results of experiments using lead-shot and encapsulated aluminium powder, the densification predicted from the model being found to be in satisfactory agreement with the experimental results. The compaction model is finally linked up with the extrusion process. Thus the pore volume fraction for the material which is located in the extrusion chamber, as influenced by specific process parameters such as reduction, semi-die angle and friction, is derived.

The centres of ingots often contain voids or even a central longitudinal hole. If the ingots are hot-rolled to semi-manufactured artickes such as blooms or billets intended for the closed-die forging of components for the automobile industry, it is of utmost importance that these kinds of defect are eliminated during hot rolling. If they are not, pores might be found in the material after finishing forging, which is not acceptable considering that many components constitute so-called “safety-details” such as crankshafts, steering spindles and connecting rods. Under some circumstances the problem of pore closure is especially pronounced. If, for example, the production in a workshop is to be changed from light forgings to heavy forgings, it might be necessary to close the holes during only a small reduction in rolling. If a heavy rolling mill with large rolls is not available and sub-contract rolling is not possible from the economical point of view, it is then necessary to search for other solutions to the problem. In the present work the influence of cooling of the hot workpiece surface is studied. For this purpose full-scale hot-rolling experiments in steel were carried out. The results indicate that a temperature gradient in the stock, obtained by water cooling and especially by means of interrupted water cooling, improves the possibility of eliminating a central longitudinal hole.