Papers by Author: Henry Valberg

Abstract: It is common to use scaled down laboratory extrusion processes in order to physicalmodel the industrial big-sized aluminum profile extrusion process. In industrial extrusion use ofbillets with a diameter size of ~210 mm, or above, is common. In the scaled-down laboratoryprocesses half this size is often used, and in mini-extrusion also 1/7th of this size. An investigationhas been undertaken in order to study what are the thermo-mechanical conditions in extrusionprocesses of such different sizes of processes, and to what extent a small-sized process is able tophysical model accurately the conditions in an industrial large sized process.

Abstract: It is a common understanding that hot forging will improve the properties of a steel part in relation to when the same part is made by casting solely. A study has been performed where two crank pin disks of a particular steel alloy, one hot forged and the other cast, both in quenched and annealed condition, have been tested using a new innovative “eye”-specimen bending test. The used test procedure is described, and it is shown that the forged and the cast material will collapse and beak down in very different way in this test.

Abstract: The velocity and strain rate fields in the primary deformation zone ahead of the extrusion die opening are investigated by theory and FE-simulation for direct and indirect Al extrusion. The metal flow obtained in the FEM-models of extrusion is compared with the flow recorded in previous experiments and it is shown that the FE-analysis mimics real metal flow with good accuracy. The velocity and the strain rate fields computed by FEA (using DEFORM^® 2D) are described and comparison is made with the idealized spherical velocity field of Avitzur, to see if there is good agreement between the results from theory and FEA, and the correlation between the results from the two is discussed. Moreover, a clear difference in metal flow is confirmed between the two processes direct (FwE) and indirect extrusion (BwE).

Abstract: Finite element analysis (FEA) is applied to study metal flow in an asymmetric porthole die with two ports where one port is bigger than the other. It is shown how FEA predicts the velocity differences between the two ports to depend on applied extrusion velocity, i.e., the ram speed, and in addition, how increasing size difference between the ports changes the flow balance between the ports. Two of the simulations have been validated by experiments in previous work, so the trends shown by FEA have also been confirmed experimentally. In long billet extrusion metal flow through the two die channels is predicted stable throughout the major part of the extrusion stroke. However, in the end stage of the process, there is predicted a shift in metal flow. Now the velocity in the small channel is speeded up on the expense of that in the big channel. In short billet extrusion the same shift in metal flow is also confirmed towards end of extrusion. An explanation is given why the metal flow in the small channel speeds up towards end of extrusion. In the article it is also quantified (in a diagram) how big the shift in flow balance between the two ports is as the size difference between the ports increases.

Abstract: Metal flow inside the container and in the metal behind a butt-ended die bridge in idealized aluminum extrusion welding has been investigated by FEA and experiment with respect to the deformation of the material flowing around the bridge and into the layers close the extrusion seam weld. Along the mid-axis of the extrusion process the effective strain subjected to the extrusion material can be determined in three different ways. One way is to determine the strains from grid pattern experiments that reveal the real deformations. When it comes to FEA there are two options; the strains can be determined from the initial and final positions of a number of material points distributed along the mid-axis of the material, where after traditional theoretical strain-equations can be used to calculate the effective strain distribution along the axis. Another possibility is to use the post-processor of the software to calculate the strain distribution. In this work the effective strain distribution along the mid-axis of the billet inside the container volume were determined by all these three methods. The effective strain in the thin layer of the squeeze zone ahead of the dead zone in front of the die bridge determined from the experiments was found to be much larger than the strains elsewhere along this axis. The same was the case when effective strain was determined by FEA from the computed position of the points, but this strain value was predicted approximately 10% lower than the corresponding value from the experiments in the layer with the heaviest strains. However, when this effective strain distribution was calculated by the post-processor of the software the high-strain layer in the squeeze zone was not revealed at all, instead the effective strains were predicted rather even over the whole length of the mid-axis. Corresponding effective strain distributions were determined along the mid-axis of the extrusion material in the weld chamber also, and after outflow of this material into the extrusion seam weld of the resulting profile where no experimental information is available. When this effective strain distribution was computed by FEA, based on initial and final position of points, very different strain values were obtained as compared to when same strains were collected directly from the post-processor. It is believed that the first results, i.e., the effective strains computed from the points are quite accurate, while those values calculated by the post-processor are less reliable.

Abstract: This study investigates the velocity fields that are descriptive for the forward, backward and friction assisted extrusion of axisymmetric rods. The Avitzur theory was used to calculate the velocity field and strain rate in extrusion of Al alloys. Several simulations have also been performed by using finite element analysis (FEA) with DEFORM 2D, in order to find the admissible velocity field for different conditions of friction including high and low friction. The results from FEA and theory of axisymmetric extrusion are compared to see if there is good agreement. The correlation between the data obtained by theory and FEA is discussed.

Abstract: In extrusion of hollow Al-profiles two kinds of pressure welds are present inside the extrusion. One is called the charge weld (CW) and forms across the boundary interface between two billets extruded in sequence. The other is the seam weld (SW) which extends longitudinally along the extruded profile and the extrusion metal behind each die bridge. It is considered to form because of the splitting of the extrusion metal over the die bridge into metal streams which flow past the bridge and rejoin as they encounter behind the bridge. Over the time attempts have been made to explain the mechanics of extrusion welding for both the CW and the SW. Still there is lack of understanding of how these welds form, the main reasons for this is that the deformation conditions around a die bridge are complex and difficult to investigate. Because of the recent advancement of two technological fields, experimental grid pattern analysis and simulation of metal flow by FEA; new tools for analysis of the mechanics of formation of the SW and the CW are now available. The simplest possible case of 2D-extrusion seam welding is considered here and an attempt is made to describe the fundamental deformation mechanisms present when this weld forms behind a butt-ended die bridge.

Abstract: Forward two-hole extrusion of Al has been investigated with the purpose of studying how metal flow inside the billet is influenced by the location of the holes in the dies, i.e. whether they are position near to or far apart from each other. The study has been conducted by means of finite element analysis (FEA) using the software DEFORM 3D® and validation of simulation results are done by comparison with grid pattern experiments performed long time ago by one of the authors. The analysis shows that the experimental conditions are well reproduced by FEA. New insight into the metal flow phenomena in two-hole extrusion is also gained thanks to the analysis. It is shown, for instance, that moving the holes far apart from each other brings about a distinct shift in the metal flow. The deformations subjected to the peripheral outer shear zones of the billet material then become much more localized than when the two holes are close.

Abstract: In this study the cold extrusion of Al alloys will be investigated by finite element analysis (FEA) using DEFORM 2D. Besides, theoretical calculations to find the required extrusion force will be done. Several FE-simulations have been performed for two different extrusion geometries and for different conditions of friction including high and low friction, to quantify the influence of friction on the extrusion force. The results from FEA and theory for cold extrusion are compared to see if there is good agreement. The correlation between the data obtained by theory and FEA is discussed.