Thermo-mechanical analysis of additively manufactured hybrid extrusion dies with conformal cooling channels

Profile overheating and surface defects during hot aluminum extrusion can occur when seeking higher productivity rates at increased ram speed velocities. The incorporation of cooling channels in the die-design allows overcoming this process limitation by keeping the profile temperature below the melting point of the alloy used [1]. Selective laser melting (SLM) of conformal cooling channels provides, in contrast to conventional manufacturing techniques, the opportunity to place the cooling circuit inside the mandrel of a porthole-die in a well-defined position to the critical bearing region [2]. In the framework of this study, a preliminary numerical investigation on the extrusion process under the assumption of liquid nitrogen cooling is analysed. The results show, that by combining conformal cooling channels with liquid nitrogen as a cooling media high cooling rates, which are well beyond the state of the art of conventional dies, can be achieved. In a hybrid extrusion die set-up, a part of the mandrel, that is additively manufactured, is either joined [3] or directly selective leaser melted onto the conventionally manufactured parts [4]. For a proper implementation in the extrusion process, material testing of the welded joint are needed. Thus, in the current study, tensile tests performed at room temperature for hybrid specimens, partially consisting of conventionally processed tool steel 1.2343 and partially additively manufactured 1.2709, will be presented. Moreover, four different heat treatment sequences of the hybrid specimens will be discussed. In addition, for each configuration, micro-structural images are taken to investigate failure at the bonding region. Finally, an optimal manufacturing sequence for a hybrid die with the described material combination is proposed

Observability of quality features of sheet metal parts based on metamodels

Deep drawn sheet metal parts are increasingly designed to the feasibility limit, thus achieving a robust process is often challenging. The fluctuation of process and material properties often leads to robustness problems. Especially skid impact lines can cause visible changes of the surface fine structure even after painting. Numerical simulations are used to detect critical regions and the influences on the skid impact lines. To enhance the agreement with the real process conditions, the measured material data and the force distribution are taken into account. The simulation metamodel contains the virtual knowledge of a particular forming process, which is determined based on a series of finite element simulations with variable input parameters. Based on these metamodels, innovative process windows can be displayed to determine the influences on the critical regions and on skid impact lines. By measuring the draw-in of the part, sensor positions can be identified. Each sensor observes the accordant quality criterion and is hence able to quantify potential splits, insufficient stretching, wrinkles or skid impact lines. Furthermore the virtual draw-in sensors and quality criteria are particularly useful for the assessment of the process observation of a subsequent process control

Temperature dependent friction modeling for sheet metal forming

Stainless steel in sheet metal forming processes show a hardening behavior, which can be described only in dependency of the deformation and temperature history. Because of the temperature influence to the material properties, the temperature dependence of the friction in the process has to be taken into account. Friction tests using different temperatures showed a change of the friction regime. From the experimental observation the temperature and velocity dependence of the friction was modeled and integrated in a finite element code for metal forming. On the macroscopic scale the temperature and velocity dependent friction was integrated in a FEM code of metal forming. The FEM simulation has been applied to the biaxial stretching test and compared with the experiment. The numerical results showed a good agreement with the failure behavior of the stainless stee

Modified maximum force criterion, a model for the theoretical prediction of forming limit curves

In order to perform the theoretical evaluation of Forming Limit Curves (FLC), the Modified Maximum Force Criterion (MMFC) has been proposed. This paper investigates the mechanism of the fracture of ductile sheet metals and introduces the MMFC model. The evaluation process and the simplified formulations are presented. The influences of hardening behavior and the yield loci are discussed as well. Comparisons with the experimental data of different materials showed generally satisfactory agreemen

Modelling of Dynamic Strain Aging with a Dislocation-Based Isotropic Hardening Model and Investigation of Orthogonal Loading

Based on experimental results, a dislocation material model describing the dynamic strain aging\ud effect at different temperatures is presented. One and two stage loading tests were performed in\ud order to investigate the influence of the loading direction as well as the temperature influence due\ud to the hardening mechanism. Bergström’s theory of work hardening was used as a basis for the\ud model development regarding the thermal isotropic behavior as well as the Chaboche model to\ud describe the kinematic hardening. Both models were implemented in an in-house FE-Code in\ud order to simulate the real processes. The present paper discusses two hardening mechanisms,\ud where the first part deals with the pure isotropic hardening including dynamic strain aging and the\ud second part involves the influence of the loading direction regarding combined (isotropic and\ud kinematic) hardening behavior