M. Golle

Innovative Tools and Tool Steels for the Blanking of Press-Hardened Ultra High-Strength Manganese-Boron Steels

One substantial goal of modern vehicle construction is to reduce weight at a high level of crash safety. When steel is used in lightweight construction, the process of press hardening of boron-alloyed steels can be of great importance. The heat treatment during hot forming process increases the material’s tensile strength to a level of approximately 1500 MPa. The increased tensile strength needs to be considered in subsequent manufacturing processes, such as punching operations. At present, laser cutting is a common method to cut press hardened sheet metal, a process which is more cost-intensive and time-consuming as conventional tools and tool steels cannot be produced with a profitable output. One aim of the present project has been the investigation of tool steels as well as the different damage mechanisms occurring during the blanking of press-hardened sheet metal. A new tool concept has therefore been realized, which comprises the entire expertise of the Institute. Thus, the tool developed is a very good basis for assessing tool steels and their damage behaviour. Tool life and damage mechanisms have been analyzed.

Automatic Process Control in Press Shops

The manufacturing of automotive body components in press lines is a sensitive process. The quality characteristics of body components vary. These fluctuations are rooted in the fact that the factors influencing the component quality are varying, e.g., fluctuations of batches regarding material quality, abrasion or heating of the tool during the production cycle. If a certain quality characteristic exceeds a predefined range an intervention in the process is necessary. This intervention is based upon the subjective know-how of the machine operator. Objective information about the state of the process, like tool temperature or the material quality of the semi-finished product is not available. Therefore, a lack of knowledge emerges in the interrelations between the tuning parameters of the system press-tool and the component quality during different stages of the process (material quality, temperature…). In this paper a complete concept for an automatic process control in press shops is described. The concept will be realized in a pilot plant for mass production in the press shop of AUDI AG. The mechanisms of occurrence of quality defects are shown in the paper, as well as the essential factors influencing the quality during the mass production of body components in the automotive industry and their variation. A sensor-system for continuous measurement of influencing variables during the mass production is presented. The key element of the concept is the non-destructive identification of material-properties for every single blank. By associating the sensor-data with the respective quality, a knowledge-based process control can be realized. The purpose is to create a failure prediction algorithm and make optimal adjustments for each stroke of the moulding press, respectively. The potential of existing actuators in modern press lines as well as new, tool integrated proposals for actuators are highlighted.

Geometrical Modeling of the Sheet Metal Parts in the Incremental Shrinking Process

Shrinking is an incremental forming process and can be carried out using a driving machine, so called “Kraftformer”. It needs an upper and a lower shrinking tool, each of which has two moveable jaws as contact and force transform units. During every forming operation the tools clamp the metal sheet, so that the vertical forces from the upper tool are switched by the leverages inside the tools into the horizontal directions. The moveable jaws are practiced by the horizontal forces to compress the metal sheet. The shrinking of the metal sheet brings out the different three-dimensional forms. As a traditional manual forming method, economical productions can’t be reached for individualized sheet metal parts to achieve the customer’s demands. Hence, it is proposed to automate this forming process to reduce the manual work. The production strategies are to be deduced from the manual shrinking process. A direct way to get them is to simulate the forming process in a FEM-software environment. But within such a FEM-simulation it can take about even one hour only just to finish one forming step. Furthermore, an analytical modeling of the shrinking can’t be realized because of its complex procedures such as variation of contact conditions, material hardening. However, a pure geometric model can be established to demonstrate the change of the 3D-forms of the sheet metal parts. The respective forming parameters can be identified through the experiments. The simulation can take place only in a few seconds. This paper provides general information about the application of the manufacturing method and with it the qualification of shrinking as a manufacturing concept for the production of individualized sheet metal products.

The Innovative Control Technology for a New Hydroforming Press Concept

The company Schnupp GmbH + Co. Hydraulik KG, Bogen, has developed a new type of press for sheet metal hydroforming. The advantages of this machine are derived from its new cinematic characteristics, with spacers inserted between the machine frame and press ram during the forming process. These spacers transmit the high forces to the press frame via positive engagement. The nominal press force is generated by 100 short-stroke cylinder which are located underneath the table plate. These short-stroke cylinders, which can be switched on or off individually, are divided into six independent control circuits. Thus it is possible to influence the blankholder force locally during the forming process. A system of this kind has already found its successful application at AUDI AG, Ingolstadt, for the sheet metal hydroforming.

Force Reduction During Blanking Operations of AHSS Sheet Materials

Within the manufacturing process of sheet metals, blanking represents an essential process operation. As the industrial application of high-strength multi-phase steels grows, the blanking process must consider high blanking and shear forces, which are characteristic for processing these materials. This paper presents options for reducing these forces. Experiments were performed utilizing a novel tool concept, which can correlate necessary blanking forces to the punch stroke in three dimensions and in the direct force path. Results from three different AHSS materials are presented showing the variation of decisive blanking parameters such as die clearance, shearing angle and sheet positioning angle.

Experimental and numerical investigation of forming and springback behavior and the resulting effects on industrial application on a structural part in mass production

Springback prediction and compensation is nowadays a widely recommended discipline in finite element modeling. Many researches have shown an improvement of the accuracy in prediction of springback using advanced modeling techniques, e.g. by including the Bauschinger effect. In this work different models were investigated in the commercial simulation program AutoForm for a large series production part, manufactured from the dual phase steel HC340XD. The work shows the differences between numerical drawbead models and geometrically modeled drawbeads. Furthermore, a sensitivity analysis was made for a reduced kinematic hardening model, implemented in the finite element program AutoForm.

Beschneiden von pressgehärteten Blechen

Kurzfassung Zur Gewichtseinsparung und Erhöhung der Crashsicherheit von Fahrzeugen kommt zunehmend Blechwerkstoff der Güte 22MnB5 zur Anwendung. Dieser Werkstoff wird auf Rekristallisationstemperatur erhitzt und während der Umformung im Werkzeug gezielt abgekühlt, sodass Martensitbildung einsetzt. Dabei erreichen die Bauteile Zugfestigkeiten um 1500 MPa. Derzeit werden Blechdicken über 1,5 mm durch das zeit- und kostenintensive Laserschneidverfahren beschnitten, da auf Grund geringer Werkzeugstandzeiten ein Scherschneidprozess noch nicht wirtschaftlich erscheint. Ziele des Forschungsprojekts sind die Untersuchung verschiedener Werkzeugstähle beim Schneiden von pressgehärteten Blechen und die Beschreibung der Verschleißmechanismen. Dafür wurde ein neuartiges Versuchswerkzeug entwickelt, bei dem verschiedene Maßnahmen ergriffen wurden, um die hohen Prozesskräfte aufzunehmen. Somit konnten die Werkzeugeinflüsse bei den Versuchen mit verschiedenen Werkzeugstählen auf ein Minimum reduziert werden.

Automated Bead Design Considering Production Constraints

For design of stiff and lightweight sheet metal parts different construction methods are practicable. One important is weight neutral stiffness increasing using beads. Mostly empiric guidelines are used for designing bead structures until now. Alternatively rudiment simulation based methods for optimizing bead structures exist. But they do not consider production constraints such as formability or forming history. Users have to interpret optimizing results and have to transfer them into forming tools. Thus stiffness properties can be easily changed in a wrong way. Within the framework of a research project funded by the Deutsche Forschungsgemeinschaft a new method for automated design of bead structures considering production constraints, defined as ManuBeadOpt (Manufacturing based Bead Optimization), is developed. The methods substantial goal is linking forming simulation (based on inverse approach) and bead optimization to generate iteratively an optimal production-oriented bead structure. Therefore a forming tool based on the Nakazima-experiment for determining forming limit curves has been developed where punch is scaled on 400 mm diameter. Depending on this punch diameter a selected preformed area on pole of test pieces will be used for bead punching. Thereby specific strain allocations are possible, which accordingly affect the final test piece geometry. Afterwards the beaded area will be blanked and tested concerning stiffness behavior depending on bending, torsion and shear load cases. So relations between forming history, bead geometry, bead depth, stiffness, tool parameters, etc. will be identified. This knowledge is integrated in ManuBeadOpt for automatic evaluation of manufacturing. Tool, experimental and simulation results as well as the optimization method ManuBeadOpt will be shown.