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

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

Correlative cross-sectional characterization of nitrided, carburized and shot-peened steels: synchrotron micro-X-ray diffraction analysis of stress, microstructure and phase gradients

Mechanical properties of case modified steels depend decisively on the near-surface gradientsof residual stresses, microstructures, phases and chemical composition, which aregenerated by the empirically well-established case-hardening techniques. Currently,however, to obtain the correlation between near-surface structureeproperty gradients,applied hardening process parameters and steels’ overall performance is a very challengingtask. In this work, high-energy synchrotron cross-sectional X-ray diffraction(CSmicroXRD) using a pencil beam cross-section of 20 500 mm2 and complementaryanalytical techniques are used to characterize the surface-to-bulk gradient of (i) a plasmanitrided steel W300, (ii) a carburized case hardening steel (grade 18CrNiMo7-6) and (iii) ashot-peened high strength steel, type 300M. CSmicroXRD analysis reveals complex gradientsof martensite and austenite phases, residual stresses in both phases, crystallographictexture and the evolution of diffraction peak broadening with a spatial resolution of~20 mm. These parameters are correlated with the gradients of hardness, morphologymicrostructureand with the changes in N and C concentrations and/or retainedaustenite formation/depletion in all three model samples. Finally, the correlative microanalyticsapproach indicates the complexity of near surface structure-property relationshipsas well as the importance of innovative cross-sectional characterization, whichallows for assessing gradual near-surface physical and/or chemical changes accompanyingthermo-chemical and mechanical surface treatment