Papers by Keyword: Bulk Forming

Abstract: Currently, common inefficient trial-and-error procedures are used in designing bulk forming dies. Numerous iterations, consisting of numerical simulations and subsequent real tests, are needed to achieve accurate parts. During the compensation cycles, manual redesign in CAD environments is necessary to transform discrete data into parametric descriptions causing approximation errors. Automation of these surface reconstruction processes is barely possible. To address these issues, different data-driven numerical strategies have been deduced based on either displacement or force. In this work, a material point tracking method in forming simulation between die and part geometry is presented. Based on this, enhanced displacement-based and stress-based methods for compensation of bulk forming parts are compared. The convergence behavior of both methods is analyzed with respect to the compensation factor. Finally, the material point tracking approach is validated and verified by compensating a two-dimensional bulk-formed component.

Abstract: The aim is to realize a Q&P (Quenching and Partitioning) process for a hot forged component made of low-alloyed advanced high-strength steel (AHSS) 42MnSiCr. One advantage of this steel is the low alloy concept which is cost-effective. After forging, the component is cooled down to room temperature with a subsequent heat treatment to achieve the characteristic microstructure with martensite and retained austenite. The material is annealed and then quenched to just above the martensite finish temperature (M_F-temperature). Hence, in the martensitic matrix about 10 to 15% retained austenite is included. Finally, the Q&Ped material is artificially aged at 250 °C to support the diffusion process of carbon from the over-saturated martensite into the austenite. Thereby, mechanical properties of 2000 MPa for tensile strength with fracture strains of 10% can be achieved. This paper provides details of the process and material behavior for a reduction of the process chain. The goal is to develop a technology for the quenching and partitioning treatment of forged components by using the thermal energy from forging. Ideally, the quenching step should be performed in the forming dies just above the M_F-temperature with additional holding on the temperature level. The majority of forged parts have different cross sections. Therefore, the cooling conditions are inhomogeneous in each cross section of the components. This cooling behavior was analyzed in laboratory tests with a forged part. Furthermore, the heat transfer coefficients were determined for different cooling media (water, air). The cooling technology was experimentally and numerically simulated in a first step for the conventional process chain (forging, cooling to room temperature, austenitisation, quenching, artificial ageing) and correlated with the microstructural evolution in combination with the component’s mechanical properties.

Abstract: Inner cavities in cast ingots have to be closed by means of open-die forging to guarantee the integrity of the forged components during usage. In the paper a differentiation is made between the macroscopic and the microscopic closing of natural inner cavities. Special attention is paid to the dendritic structure of the surfaces of inner cavities and their impact on the microscopic closing behavior. Additionally, investigation showed that a closing on the microscopic scale is only possible if the cavities do not come in contact to the atmosphere during hot forming. For the analysis of the cavity closing, ingots of a heat-treatable, hot-working and a cold-working steel were used. The ingots were cast, forged and the surface of the inner voids was analyzed with the help of light-microscopy, SEM and EDS for the microstructure and by using tensile tests on macroscopic scale. Also, numerical investigations were a part of the work, whereby the parameters void size, void shape and anvil-shape were varied. As a result of the numerical investigation, a so called closing function was formed. This function enables the user to calculate the necessary height-reduction for closing of inner cavities of the regarded ingot format.

Abstract: Many fasteners used in electromechanical systems are micro metal parts which should be manufactured with high accuracy and reliability and in large quantities. Micro forming is promising to fulfill these demands. This research focuses on investigating a gripping unit in a multi stage former, as the positioning unit was discussed earlier. The parameters which play important roles in the gripping unit will be discussed and the precision and reproducibility evaluated to show the performance of the unit. This includes two different tests. The first test will show how accurately the unit can locate the parts and the second one is intended to depict how the unit transfers the parts with different diameters with respect to the front profile of the fingers. The experiments showed that the manipulator can handle the parts with 7 µm accuracy, 2 µm reproducibility and 9µm uncertainty for a 20mm distance between two adjacent stations.