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Aachen, Germany

Guk S.,Institute of metal forming
Key Engineering Materials | Year: 2016

The evaluation of formability for sheet metals by means of different tests such as holeexpansion and forming limit tests is widely used in industry. The experimental efforts for these tests and the scatter of the results are much higher than those for the identification of the mechanical properties of various material charges for the same material grade in tensile test. Difficulties in accurate formability evaluation for new steel grades, such as AHSS, have necessitated a review of the existing prediction methods. Consequently, a new formability criterion was developed from the statistical relations of parameters for approximately fifty steel grades in various thickness ranges. The criterion considers the combination of mechanical properties from the tensile testing as the yield strength, tensile strength and total elongation and plastic deformation energy in a single value. The quality ranking of different charges and coils was made by using of the criterion as well as, for comparison, other well-known criteria which are currently used in the industry. The results obtained involving the new formability criterion seems to be accurate for a wide range of material grades and thicknesses, from the viewpoint of automotive design requirements. © 2016 Trans Tech Publications, Switzerland. Source


Milenin A.,AGH University of Science and Technology | Rec T.,AGH University of Science and Technology | Walczyk W.,Institute of metal forming | Pietrzyk M.,AGH University of Science and Technology
Steel Research International | Year: 2016

The manufacturing process of forging of large crankshafts is affected by bending of the shaft during heat treatment, as well as at the forging step. For this reason, analysis of the curvature of the shaft at various stages of the technology is needed. This paper deals with the modeling of elastic-plastic bending of crankshafts during heat treatment after forging. Present work is dedicated to heat treatment after forging. The aim of the paper is to develop a model and finite element (FE) software to simulate the elastic-plastic deformation of the shaft due to thermal expansion and dilatometric effect caused by phase transformations. Shaft material model is developed and the elastic-plastic characteristics are implemented in the FE code. Heat exchange with the cooling medium, dependence of thermal properties on temperature, and heat of phase transformations are accounted for in a solution of the thermal problem. Dilatometric tests are performed to supply data for identification of the phase transformation model. The method of estimation of the curvature of the shaft with one design variable is proposed. This allows to perform optimization of heat treatment in order to reduce the curvature of the shaft. The calculations are performed for several modes of the heat treatment. It is shown that in the presence of phase transformations, cooling process is accompanied by a three-time changing of stress sign and the direction of bending of the crankshaft, which is due to the nonlinearity of thermal deformation during the phase transformations. The manufacturing process of forging of large crankshafts is affected by bending of the shaft during heat treatment, as well as at the forging step. Shaft material model is developed and the elastic-plastic characteristics are implemented in the FE code. Heat exchange with the cooling medium, dependence of thermal properties on temperature and heat of phase transformations are accounted for in a solution of the thermal problem. The calculations are performed for several modes of the heat treatment. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Guk S.,Institute of metal forming | Milisova D.,TU Chemnitz | Pranke K.,Institute of metal forming
Key Engineering Materials | Year: 2016

The present technical work reports on the formability and related behaviour of components during hot rolling of metal matrix composites (MMC) produced from powder. A new metal matrix composite based on TRIP (Transformation Induced Plasticity) austenitic steel AISI304 with varying amounts (10% and 20%) of homogeneously embedded zirconium dioxide (partially stabilized with Mg (Mg-PSZ)) was investigated by means of compression tests and rolling of wedge shaped samples at temperature of 900°C and 1100°C. Two different particle size distributions of Mg-PSZ powder were investigated: fine and coarse. Based on the experimental results, the deformation behaviour (arc of contact length, roll gap ratio, strain, strain rate), the microstructure evaluation (pore amount and their cross sectional area) and the formability (equivalent fracture strain) under different stress state conditions had been analyzed. © 2016 Trans Tech Publications, Switzerland. Source


Pranke K.,Institute of metal forming | Guk S.,Institute of metal forming
Key Engineering Materials | Year: 2016

The material flow in particle reinforced metal-matrix-composites (MMC) had been investigated. The composite consisted of TRIP steel and magnesium stabilized ZrO2 particles (Mg-PSZ) in volume fractions of 0 %, 5 % and 20 %. The basic materials were produced by hotpressing and showed a very homogeneous particle distribution and a almost full density. Then the samples were cut to wedge shape and hot-rolled with a constant roll gap. Caused by the shape, the true strain increased over the length and reached a maximum of true strain of 0.6. The strain rate was set to be higher than 0.1 and lower than 10/ s. After rolling, it was possible to combine rolling force, true strain and the material flow due to the grid on the surface. With an increase in volume fraction of Mg-PSZ the rolling force increases as well. Metallographic examinations were performed to determine and document the flow of particles within the composite due to true strain conditions. It was found that the particles flow with the base material and turn parallel to the rolling direction. This effect was measured using the degree of orientation of partially oriented linear structure elements ω12, according to ASTM E 1268-01. The index was increasing with increasing true strain value. Further microscopic examination showed debonding of the interface between particles and matrix-material. For MMC's having a volume fraction of 20 % Mg-PSZ a true strain at fracture of 0.5 to 0.6 was determined. © 2016 Trans Tech Publications, Switzerland. Source


Russig C.,Institute of metal forming | Bambach M.,Institute of metal forming | Hirt G.,Institute of metal forming
Key Engineering Materials | Year: 2013

Rotary Peen Forming (RPF) is a new peen forming process, comparable to Shot Peen Forming (SPF), in which the shot is held by a flexible connection and moved on a circular trajectory. Hence, RPF uses less machine components and therefore offers a compact machine design and a more flexible use than SPF. Just as conventional Shot Peen Forming the RPF process causes localized plastic deformation but involves tangential components which can create shear deformation in the plastic layer. In this paper, three different RPF tool concepts are compared and the applicability of Rotary Peen Forming for the production of slightly curved parts is analyzed. The first design offers a stochastic impact distribution, the second design leads to deterministic impacts. The third one is a further enhancement of the previous designs and combines the advantages of both. In contrast to previous tests a new, stiffer testing setup was used which offers good comparability of the tool concepts. Particularly the forming potential in terms of the realization of high curvatures and the surface quality are investigated. Depending on the tool concept the surface quality differs significantly, but generally RPF allows the forming of curvatures that are commonly used for aerospace structural parts. © (2013) Trans Tech Publications. Source

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