Effect of different contact formulations used in commercial FEM software packages on the results of hot forging simulations

Commercial FEM-software packages are widely used in the industry to predict material flow, temperaturedistribution and die load during the forging process. Contact in conjunction with plastic material behaviour,which is typical for forging simulations, leads to highly nonlinear equations in the FEM algorithms, whichmay cause problems in numerical convergence. Some FEM software providers handle this problem byautomatic contact damping or similar algorithms. However, the user has mostly no detailed information aboutadjustments and prediction accuracy. The only possibility for the user to have an impact on the contactbehaviour is to set a friction factor and to choose a friction model (e.g. Coloumb or Shear) appropriate to theinvestigated process. Friction factors are often measured by standard tests like the ring compression test whichshould be valid for all used software packages. In this paper a benchmark between three software programs isperformed based on a model for ring compression tests under typical hot forging conditions. The commercialFEM-software programs Deform2D, Forge2007 and Abaqus are compared by generating a nomogram for eachsoftware package. For all simulations identical physical (temperature, flow curves etc.) as well as numericalinfluence parameters are used. The simulations show a significant divergence in the results depending on theused FEM-software. This leads to the conclusion that a friction coefficient which is true for one softwarepackage can not be transferred directly into another one

Reproduce diameter reduction process of a powder filled tube in finite element analysis

Aim of the present work is to improve the production of laserwelded flux cored wires with the help of Finite Element Analysis in Abaqus. This flux cored wires are used as welding consumables. To simulate the whole production process for every variety of input parameters is far too time-consuming particularly with regard to the filling. The production process is as following: after roll forming of a strip to a U-shape it is filled continuously with flux. This powder consists of up to 20 different substances. Afterwards the profile is closed to a tube and the edge is laserwelded. At last the diameter of the tube is reduced to 1.2 mm. The reduction step is investigated and subject of the present work. Observations have shown the most abrasion of the working dies in reduction steps where it is not expected due to the calculated true strain sequence. Therefore, the influence of the filling on the roll drawing process has to be taken into account. This is not easy because the process starts with loose multicomponent powder and ends with high compaction. It is hard to cover these demands with a single model for powder behaviour. So a phenomenological approach is established to solve the problem. The influence of the powder is described as a load which only appears in the projected contact area. Consequently, it becomes possible to study parameters on the reduction like different quantities of the multicomponent powder, the reduction sequence of the roll drawing process and the geometry of the rolls

Forgiatura La Metallurgia Italiana -n

INTRODUCTION Friction is a major factor in determining the characteristics of metals as they are formed. In forging, friction is a key factor in the pattern of metal flow and die wear. In general, excessive friction has a negative influence on die wear, product quality, product cost, and productivity. It is therefore common to use various lubricants to reduce friction during metal forming operations. Major factors affecting friction include the normal stress along the die-material interface, the lubrication condition, the relative velocity, the temperature, the roughness and the mechanical properties of the material and/or the die. A detailed investigation of these factors is not easy because the die-material interface in metal forming is under high pressure and temperature. Thus, friction in this area is still somewhat of a mystery even though many researchers have performed detailed studies in various ways for a long tim

Experimental Characterization and Modeling of Residual Stress Gradients across Straight and Bent Seamless Steel Tubes

Residual stress gradients across the wall of seamless steel tubes influence decisively the mechanical stability and reliability of automotive and industrial constructions. Irreversible bending moments imposed on the tubes induce gradual and asymmetric elasto-plastic deformation across the tube cross-sections which result in very complex residual stress distributions. The aim of this contribution is to present a novel methodology as well as complementary modeling approach to assess the three-dimensional distribution of triaxial residual stresses in bent steel tubes. The stress characterization was performed using high energy X-ray diffraction at the HEMS beamline of PETRA III synchrotron source in Hamburg as well as using laboratory hole drilling. For the complementary modeling of the stress distribution, a FEM software package DEFORM HT wasused. The results reveal that the stress gradients across the tube wall are primarily influenced by themartensite profile predetermined by the parameters for thermo-mechanical treatment of the tubes. The tube bending causes the formation of continually varying compressive and tensile stresses across the tube circumference whereas the stress magnitude across the wall thickness scales againwith the martensite appearance. Finally the results document the importance of the water cooling process control and the influence of the applied bending radius on the resulting stress distributions as well as related mechanical parameters like fracture toughness and fatigue behaviour