Institute of metal forming

Aachen, Germany

Institute of metal forming

Aachen, Germany
SEARCH FILTERS
Time filter
Source Type

Guk S.,Institute of Metal Forming | Hoppach D.,Institute of Metal Forming | Kawalla R.,Institute of Metal Forming
Key Engineering Materials | Year: 2017

In the present study an investigation has been carried out for spheroidization of 100Cr6 bearing steel used in forging industry. Three different spheroidization processes were considered. The first one was the annealing of normalized steel under Ac1 temperature for a long time. The second one was the annealing of normalized steel above Ar1 temperature after heating between Ac1 and Acm for one hour. The third one was the annealing of hardened steel under Ac1 temperature for a long time. For evaluation of cold workability with different spheroidization annealing periods, the yield strength and percentage of reduction in area in uniaxial tension were recorded. The present results indicate that low alloyed carbon bearing steels can be easily processed to achieve unique microstructures and properties. © 2017 Trans Tech Publications, Switzerland.


Guk S.,Institute of Metal Forming | Preiss M.,Institute of Metal Forming | Kawalla R.,Institute of Metal Forming
Key Engineering Materials | Year: 2017

A commercially available laser marking system based on diode-pumped Nd:YVO4 laser was used for creating grid patterns for forming strain analysis of three different multiphase steels. The aim was to determine and analyze the influence of laser working parameters on the formability of the investigated sheet materials by means of an in-depth characterization of this induced microstructural and geometric inhomogeneity. The electrochemical etching served as the reference method without the negative effect of generating inhomogeneity. The formability was evaluated using the cupping test according to Erichsen. While the quantification of geometric inhomogeneity was based on the determination of the notch factor, microhardness measurement was used for the evaluation of micro-structural inhomogeneity. The results showed that multiphase steels exhibit similar values of the mark depth under the same creating parameters by means of laser. Furthermore, only the induced geometric inhomogeneity had a marked influence on the material formability. Finally, a method for the prediction of the optimal values of the grid pattern mark depth was developed from the perspective of its good visual recognizability and associated with the microstructure based material sensitivity to stress concentrators. © 2017 Trans Tech Publications, Switzerland.


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.


Xiong W.,Institute of metal forming | Lohmar J.,Institute of metal forming | Bambach M.,Institute of metal forming | Hirt G.,Institute of metal forming
International Journal of Material Forming | Year: 2015

Reliable isothermal flow curve data are often needed for the process simulations in metal forming technology. As a rule of thumb, at strain rates above 10−3s−1 even isothermal compression tests are affected by deformation heating, such that the flow stress data should be corrected for stress decrease due to the temperature increase in the specimen. However, if the temperature increase during testing is larger than the interval of the nominal testing temperatures foreseen for individual tests, the compensated flow curves may show undesired kinks. When it comes to high strength materials, this phenomenon will be even more pronounced. The occurrence of kinks in compensated flow curves can be attributed to the interpolation methods used in the existing temperature compensation methods. As a remedy, an alternative strategy based on Thin Plate Spline interpolation is proposed on the example of two high strength materials. It is shown that this new strategy can be generally adopted to derive reliable isothermal flow curves over a wide range of temperatures and strain rates, especially for high strength materials. © 2013, Springer-Verlag France.


Puchhala S.,Institute of Metal Forming | Franzke M.,Institute of Metal Forming | Hirt G.,Institute of Metal Forming
WIT Transactions on the Built Environment | Year: 2010

The elastic behaviour of the forming tools has a significant influence on the quality of the end components. For example, in the case of the flat rolling process, the strip quality criteria, i.e., strip flatness and thickness profile are highly influenced by the elastic deformation of the working rolls. The Finite Element (FE) Method is the standard approach for the computation of such forming processes. Considering the elastic effects of the tolls in a single FE model using a traditional approach (standard in the case of commercial FE programs) will lead to large FE models (as very fine descretization of work piece as well as tool at the contact regions is necessary). As a result, the computation requires tremendous amount of time and resources. This paper presents a recently developed concept, which meets the above mentioned demands very efficiently. Within this concept, the computation of the tool elastic effects is separated from the process simulation. The advantages of this concept include, easy handling of the contact situations, reduced FE model size as the tool is modelled as the rigid body and good convergence of the computation. On the other hand, for the validation of the concept, optical measuring techniques were used to validate the numerical simulations. The experimental results of the flat rolling process were compared. To show the portability of the developed concept, qualitative results of the forging process were also given. © 2010 WIT Press.


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.


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.


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.


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.

Loading Institute of metal forming collaborators
Loading Institute of metal forming collaborators