WGP Congress 2016

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Authors: Bastian Zimmermann, Marion Merklein
Abstract: Different tests to determine friction factors for cold forging processes are given in the literature. The double cup extrusion test, the ring compression test and the T-shape compression test are three of the common tests, which are compared in this investigation. From former investigations it is known that there is an influence of the work-hardening of the test sample on the friction factor, which is determined by the test. At this study, the influence of the work-hardening of the material on the three named tests is investigated by using a wire drawing process. In addition, the drawn wire from the originally thermo mechanical rolled wire is also annealed to have a second material state without any work-hardening. The used material and its numerical modelling as well as the analyzed tribological conditions of the real specimens are described. Afterwards the three test setups are explained for the numerical as well as for the real experiments. In the end, the influence of the drawing respectively the work-hardening for the three tests is presented and discussed.
Authors: Martin Barthau, Mathias Liewald
Abstract: The production of irregularly shaped deep drawing parts with high quality requirements, which are common in today’s automotive body shell production, consistently challenge production processes. This challenge results from the high design requirements and automotive lightweight design, and hence the necessary use of high strength steels. Metal forming technology deals with these challenges using highly sophisticated methods to control the material flow. Several control loop methods have existed already in order to control the material flow in deep drawing processes, but only methods with a control intervention between two strokes. However, this kind of control method merely allows control intervention on measurements on the previous part or on measurements of material properties before the actual process. The method developed at the Institute for Metal Forming Technology in Stuttgart makes a control intervention possible during the deep drawing stroke. The used reference variable is the part wall stress and the control variable is the blankholder force, which is manipulated by using the segment elastic blankholder as an actuator. In this paper the experimental setup, the control methods, and the control loop itself will be presented. Furthermore, the developments of the new method will be described.
Authors: Lennard Lippold, Mohammad Kazhai, Anas Bouguecha, Milan Vucetic, Christoph Hübsch, Kai Möhwald
Abstract: In this paper a high loaded hot forging die, which is oriented towards an industrial forging process, is developed with assistance of finite element analysis. In serial hot forging tests and process accompanying analysis methods the designed die geometry gets investigated concerning occurring wear mechanisms. Within the investigation it could be shown, that calculated results of the wear condition are corresponding to the experiments. Abrasion, plastic deformation and mechanical cracking could be detected. The variety of occurring wear mechanisms on the designed die allows a promising approach of further investigations on the valuation of different wear reducing strategies.
Authors: Franziska Neubauer, Konstantin Hofmann, Kolja Andreas, Marion Merklein
Abstract: Over the last few years, hot stamping has been established as a suitable manufacturing process to produce high-strength structural parts. A tensile strength up to 1500 MPa and a high shape accuracy of the hot stamping parts are achievable. The hot forming tools are thereby stressed by varying thermo-mechanical loads resulting in increased surface wear. In order to reduce expensive and time consuming rework of the forming tools, an analysis of the tribological conditions is required. Purpose of this work is to increase the wear resistance of the tool surface and to investigate the wear behavior. In this regard, a laser alloying process is developed to influence the properties of the base material. Firstly, the alloying elements are selected and the element concentration is determined. Results for the composition of NiCrMo90 are presented, which is added by a wire fed laser alloying process unlike the previously used and already researched methods of powder bed fusion. This wire fed method is engineered to ensure a higher material utilization and to simplify the material feeding. After the alloying process the wear behavior of the alloyed surfaces are examined and compared to a not alloyed control group of pins under similar thermo-mechanical conditions.
Authors: Sven Stockert, Matthias Wehr, Johannes Lohmar, Gerhard Hirt, Dirk Abel
Abstract: Almost all metal strips with thicknesses of < 2 mm are produced by cold rolling. Thickness variations of cold rolled strips are caused by various factors like fluctuation in strength of the material, the eccentricity of the rolls or thickness variation of the incoming strip. As the demands concerning the thickness variation are ever increasing the Institute of Automatic Control and the Institute of Metal Forming aim at reducing the thickness tolerance of thin, cold-rolled steel and copper strips to 1 μm. As high frequency disturbances are expected, it is assumed that this goal can only be achieved by using a predictive controller in combination with a high precision strip thickness gauge and, for roll adjustment, a piezoelectric actuator in addition to the existing electromechanical actuator. The objective of this work is the constructive implementation and the testing of a thickness gauge based on laser triangulation. The gauge includes guide rollers to prevent strip vibration, a C-frame to allow an inline calibration and mechanical adjustment of the measuring range so that even flexible strip thicknesses can be measured. The designed gauge showed a high repeat accuracy of 0.4 μm for two different metal strips. Furthermore the gauge was used to investigate the dynamics of the thickness change of a steel strip at maximum rolling speed of 5 m/s using a Fourier transformation. This frequency analysis supports the need for a piezoelectric actuator that can also subsequently be dimensioned based on the obtained frequency data.
Authors: Amer Almohallami, Michael Rusch, Milan Vucetic, Anas Bouguecha, Markus Bambach, Bernd Arno Behrens
Abstract: Due to the limitations of other processes in joining different types of material, mechanical joining methods can be alternatively used. Joining by upset bulging can be employed for joining tubes with other structures such as sheets, plates, tubes or profiles as well as for joining different materials. In spite of successful industrial applications of this joining process, material damage is still a challenge. This damage affects the resistance of the created joint to service loads. Thus, in this paper, a local heating is studied, which aims at avoiding pre-damage or failure of the joint. A parametric FE model is developed to analyse the influence of local heating on the bulging process. It is found that the process window set by the bulge length suitable for joining is widened, but only to a minor extent. The marginal influence of local heating on the bulge geometry allows designing the process in the same way as room temperature processes. Metallographic investigations confirm the damage-free bulging of tubes by forming at elevated temperatures. Another important result is that tubes can be equipped with predefined bulge zones by local heating zones to 700 °C for 15 seconds for example. This enables bulging of tubes during joining by applying an axial load only, without using tools to define the location of the bulge or its length, thus enabling joining operations with limited access.
Authors: Joerg Volpp, Jennifer Srowig, Frank Vollertsen
Abstract: The energy efficient, high-speed laser deep penetration welding process is a technology which is increasingly used for industrial applications. In order to guarantee weld seams of high quality a stable process needs to be established. Especially when welding aluminium alloys the weld quality is reduced due to occurring spatters which entails a loss of material. Solidified spatters remain on the surface of the specimen after welding and need to be cleaned for further processing steps. One method to change the process behaviour is beam shaping. In this work, a bifocal optic is used to produce two foci along the beam axis in order to manipulate the energy input into the keyhole. Bead-on-plate welds are produced in aluminium alloy EN AW-6082 and mild steel S235. For comparison, welding is conducted using standard optics. The spatter occurrence is compared when using these different beam shapes. While a reduced number of spatters per time are observed the spatter size increases when using the bifocal optic in this study.
Authors: Peter Arrabiyeh, Vandeet Raval, Benjamin Kirsch, Martin Bohley, Jan Christian Aurich
Abstract: Micro grinding is a promising process to produce small scale structures in hard and brittle materials. Just like macro grinding processes, a high number of abrasive grits embedded on the grinding tools, are applied. This high number of grits results in low cutting forces on individuall grits and very small chip thicknesses, thus generating surfaces with a high quality. The manufacturing of the tools needed to produce such small structures is very challenging. In this paper, a method for the coating of micro pencil grinding tools (MPGTs) is proposed. MPGTs utilize coated superabrasive grits for micro machining hard and hardened materials. The MPGTs developed in the research presented here consist of a base body made of cemented carbide, abrasive grits made of cBN and a nickel bond. The experimental setup and the coating parameters needed to produce a 50-55 μm MPGT with 5-10 μm cBN grits nominal diameter is outlined. In addition, the tools are validated by machining a 500 μm long groove on a hardened 16MnCr5 workpiece.
Authors: Florian Hübner, Christoph Löpenhaus, Fritz Klocke, Christian Brecher
Abstract: Generally, hard finishing is the final step in manufacturing cylindrical gears. The most established processes for hard finishing are continuous generation grinding and discontinuous profile grinding [1]. Despite the wide industrial application of the continuous generation grinding process, only few scientific investigations exist. One possible reason for this are the complex contact conditions between tool and gear flank. Modelling the complex contact conditions between grinding worm and gear to calculate cutting forces, characteristic values as well as micro- and macroscopic gear geometry are the topics of this paper. The approaches are introduced and results for validation are presented and discussed.
Authors: Marco Kampka, Christoph Löpenhaus, Fritz Klocke
Abstract: In order to improve load carrying capacity and noise behaviour, case hardened gears are usually hard finished. One possible process for hard finishing of gears is generating gear grinding, which has replaced other grinding processes in batch production of small and middle sized gears due to high process efficiency. Especially generating gear grinding of large module gears with a module higher than mn > 8 mm can be challenging due to high process forces and the resulting excitation, which can influence gear quality negatively. TÜRICH suggested applying a pitch diameter shift during generating gear grinding to equal out the number of contact points between the left and right flanks of the gear with the grinding tool [1]. This qualitative approach is not sufficient to predict the process behaviour because it does not take the changing radii of the curvature of the involute into account and, therefore, the changing contact conditions along the gear profile. In this paper a methodology to quantify the influence of pitch diameter shift on the generating gear grinding process using a manufacturing simulation is introduced. Additionally this methodology is validated for one manufacturing test case.

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