Nowadays, traditional sheet metal and bulk metal forming processes are often reaching their limits, particularly in the automotive sector, if closely-tolerated complex functional components are required. In this paper, an approach for the direct forming of high-precision shapes starting from blanks will be presented and fundamentally analyzed. Aim of this new process-class, named "sheet-bulk metal forming", is the direct forming of functional components with variants out of the sheet. In a first step, the complex interactions between regions of high and low strains, which are characteristic for sheet-bulk metal forming, have been investigated by simulations. Based on the identified process characteristic, new tool geometries and forming strategies for extrusion and deep-drawing processes have been developed to fine-control the local material flow for a defined filling of the target regions. A further enhancement of the mold filling can be achieved by a predistribution of material using tailored blanks with a defined varying thickness where material is transferred to its target regions to adjust special local mechanical properties. In the paper it will be also exemplified, that the desired process behaviour can be supported by local increased friction provided by tailored surfaces.
This paper is focused on a combined deep drawing and extrusion process dedicated to the new process class of sheet bulk metal forming (SBMF). Exemplified by the forming of gearings, combined sheet and bulk forming operations are applied to sheet metal in order to form local functional features through an intended and controlled change of the sheet thickness. For investigations on the form filling and the identification of significant influencing factors on the material flow, a EE simulation model has been built. The EE model is validated by the results of manufacturing experiments using DC04 with a thickness of 2.0 mm as blank material. Due to the fact that the workpiece is in extensive contact to the tool surface and that the pressure reaches locally up to 2500 MPa, the tribological conditions are a detet mining factor of the process. Thus, their influence is discussed in detail in this paper. In the first instance, different frictional zones having a distinct effect on the resulting material flow are identified and their effect on improved form filling is demonstrated. Subsequently, a more comprehensive methodology is developed to define tribological zones of forming tools. Eor this, a system analysis of the digital mock-up of the forming process is performed. Besides friction, other relevant aspects of forming tool tribotogy like contact pressure, sliding velocity, and surface magnification are considered. The gathered information is employed to partition the tools into tribological zones. This is done by systematically intersecting and re-merging zones identified for each of the criterion. The so-called load-scanning test allows the investigation of the friction coefficient in dependence of the contact pressure and possible loading limits of tribological pairings. It provides an appropriate tribological model test to evaluate tribological measures like coatings, surface textures and lubricants with respect to their targeted application in particular zones. The obtained results can be employed in the layout of further forming processes to reach the desired process behavior. This can be, for example, an improved form filling, less abrasive wear and adhesive damage or lower forming forces, respectively tool load for an improved durability of the die.
Innovative trends like increasing component functionality, the demand for automotive lightweight constructions and the economic issue to optimize existing process chains, require new ways in manufacturing. Today, the traditional sheet metal and bulk metal forming processes are often reaching their limits if closely-tolerated complex functional components with variants have to be produced. A promising approach is the direct forming of high-precision shapes starting from blanks. Thus, classic sheet metal forming operations, such as deep drawing, are combined with bulk metal forming operations like extrusion of complex variants as for example teeth. This combination of sheet and bulk metal forming operations leads to a side by side situation of different tribological conditions according to the locally varying load situations within the same forming process. This new class of forming processes is defined as sheet-bulk metal forming (SBMF). The tribological conditions in sheet-bulk metal forming processes are of major importance for the process realization, its stability and for the quality of the produced part. The objective of this paper is the investigation of material flow in SBMF in general and the attempt to improve the material flow by local adapted tribological conditions. First the material flow was analyzed by FE-simulation of a model geometry that is typical for SBMF. The investigations with FE-simulation have shown, locally adapted tribological conditions are leading to an improvement in material flow and thus to an increased mould filling. As frictional conditions are directly connected to the topography of workpiece and tool, the modification of the workpiece topography is leading to an alteration in friction values. For the modification of workpiece topography grit blasting was used. The increase in friction of grit blasted surface towards untreated surface was investigates by using the laboratory friction tests. To manufacture specimens with locally adapted topographies for forming tests a masking technique has been developed. The masks are designed after the preliminary findings determined by FE-simulation.
To encounter new challenges regarding the economic an ecological aspects of the forming of functional components, sheet bulk metal forming has been introduced as a new approach. An important aspect for the successful use of such processes is the control of the complex material flow. At the moment there is knowledge on the material flow in uniform arranged cavities, as well as on possibilities which enable its control. However there is no data on the behavior of the material flow in non-uniform arranged cavities and on the usefulness of established flow control methods. The simulated experiments in this paper, which are based on a validated model, reveal that there are significant and interactive effects of combination and type of the chosen geometry of the cavities. Furthermore, a local modification of friction factor shows a significant influence on the form filling which however differs in part from previous findings.
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