Christian Magnus

Incremental Sheet Metal Forming with Direct Resistance Heating Using Two Moving Tools

This paper describes new developments in an incremental, robot-based sheet metal forming process (‘Roboforming’) for the production of sheet metal components in small batch sizes. The dieless kinematic-based generation of a shape is implemented by means of two industrial robots which are interconnected to a cooperating robot system. Compared to other incremental sheet metal forming machines, this system offers high geometrical form flexibility without the need of any part-dependent tools. The industrial application of incremental sheet metal forming is still limited by certain constraints, e.g. the low geometrical accuracy and number of formable alloys. One approach to overcome the stated constraints is to use the advantages of metal forming at elevated temperatures. For the temperature input into the sheet metal, there are different approaches like heating with warm fluids, a laser beam or using direct resistance heating. This paper presents results of the research project ‘Local heating in robot-based incremental forming’, funded by the German Research Foundation (DFG), where the heating of the current forming zone by means of direct resistance heating is examined as a variation of the Roboforming process. In order to achieve a local limitation of the heating on the current forming zone, the electric current flows into the sheet at the electric contact of the forming tool and the sheet metal. Thus the forming tool is part of the electric circuit. In current literature Authors report about results from experiments using single-point incremental forming, where the forming tool and the clamping frame of the sheet are connected to the power source. In order to further limit the heating on the forming zone, a new approach will be presented in this paper, where a second tool is used to support the forming and heating process, as both tools can be connected to the power source, making a current flow through the rest of the sheet and the clamping frame unnecessary. With the use of two tools the current flow and thus the heated zone of the sheet can be manipulated. Additionally the advantages of the supporting tool, already shown in forming at room temperature, such as increased geometrical accuracy and maximum draw angle can be used. Starting with a description of the new process setup for steel forming at about 600 °C, results of experiments evaluating the influence of the supporting tool on the forming process at elevated temperatures and the resulting geometrical accuracy will be presented in this paper. Therefore, different process parameters as forming temperature, cooling and relative positioning of the both tools have been varied.

Robot-Based Incremental Sheet Metal Forming – Increasing the Geometrical Accuracy of Complex Parts

This paper describes new developments in an incremental, robot-based sheet metal forming process (Roboforming) for the cost-effective production of sheet metal components for limited-lot productions and prototypes. The paper presents strategies in robot based incremental sheet metal forming for the force controlled forming of complex parts. These parts can consist of features such as steep flanks or convex/concave alternating surfaces and they are mostly formed with a local support tool which substitutes a full die. The strategies were developed in a cooperative project funded by the German Federal Ministry of Education and Research and the German Research Foundation. Approaches to increase the part accuracy of complex parts are presented. One approach concentrates on a servo loop, consisting of sensors and a programming system. It guarantees higher part accuracies by measuring the deviations between a formed part and its target geometry. These deviations are used to derive corrected tool paths. The abdication of a partial or full die leads to a larger influence of the free compliant sheet area surrounding the formed part. Because of that the geometry shifts away from the forming tool and it cannot be formed completely. Another approach to increase the part accuracy by reinforcing this free sheet area is also presented.

Tool Concepts and Materials for Incremental Sheet Metal Forming with Direct Resistance Heating

ncremental sheet metal forming with direct resistance heating is used for flexible sheet metal forming at elevated temperature, where electric current is conducted through the forming tool (s) into the forming zone. The electrical and mechanical contact combined with a high temperature of up to 600°C in steel forming results in complex tool requirements and a high wear of the tooltip. Starting with a description of a new process setup, both studies concerning existing and new tool concepts and materials will be presented in this paper. Therefore, the wear of different materials for tooltips and its dependence on lubrication has been investigated in forming experiments and will be thoroughly discussed.

Robot-Based Incremental Sheet Metal Forming – Increasing the Geometrical Complexity and Accuracy

The industrial application of incremental sheet metal forming is still limited by certain constraints, e.g. low geometrical accuracy and geometrical complexity. In order to overcome these constraints, this paper presents two approaches which have been carried out within the research project Development of a robot-based dieless incremental sheet metal forming process funded by the German Research Foundation (DFG). The first approach increases the geometrical accuracy by adding an addendum stabilization surface. As neither a partial nor a full die is used in this universal concept, there is a larger influence of the free compliant sheet area surrounding the formed part of the geometry. Thus the sheet shifts away from the forming tool more easily, which often results in a less accurate forming. The addendum stabilization surface reinforces this free sheet area. Experiments have proven this to be as good as a partial die. Especially the subsequent deformation resulting from the interaction of differently shaped elements causes geometrical deviations which are limiting the scope of formable parts. The second approach is based on the subsequent forming of elements belonging to the original geometry, which helps to increase the geometrical accuracy as well as the geometrical complexity. Thus the basic geometry is formed in a first step. Afterwards, further elements are formed subsequently, while the adjacent areas are supported by a peripheral supporting tool which prevents their deformation.

Flexible Production of Small Lot Sizes by Incremental Sheet Metal Forming with Two Moving Tools

Incremental sheet metal forming processes have a high potential for flexible and cost efficient production of prototypes and parts in small lot sizes. Recent developments in this field bring incremental sheet metal forming one step closer to industrial application. Amongst these are improvements concerning geometrical accuracy, part complexity and surface quality. Also solutions for forming of advanced materials as magnesium or titanium alloys are being developed, which shows a high potential for the production of lightweight sheet metal parts, as used in aerospace industry.

CAM-Solution for Two Robots Based Incremental Sheet Metal Forming

Robot based incremental sheet metal forming (Roboforming)is a new dieless forming process, which is suitable for cost-effective manufacture of prototype parts and small batch sizes.The principle of Roboforming is based on flexible shaping through a freely programmable path-synchronous movement of two industrial robots. These two robots, which are connected to a cooperating robot system, hold respectively a forming and a supporting tool. Similar to other incremental forming methods, the final shape is produced bythe movement of the forming toolalongthe lateral direction and its gradual infeed in the depth direction. In Roboforming, there are twodifferent strategies for the synchronous movement of the supporting tool, eitheralong the outer contour onbacksideof the sheet or directly opposed to the forming tool building a forming gap.The second strategy can be combined with a force controlled method to increase the surface quality and geometricaccuracy. MThe most existing CAM systems used in numerous incremental forming approaches are only applicable for milling machines. In this paper, with the use of self-programmed postprocessors and an Application Programming Interface (API) in a CAM system, movement programs for two cooperating robots can be generated for both forming strategies to produce sheet metal parts with different sizes and complex freeform structures. This CAM-solution for Roboforming is validated bythe forming experiments.

Design of CAM-Interfaces for Two Robots Based Incremental Sheet Metal Forming

Robot based incremental sheet metal forming (Roboforming) is an innovative die less forming process, which is developed by the Chair of Production Systems at Ruhr-University Bochum. Suitable for rapid prototyping and manufacture of small batch sizes with low costs, this forming process is based on flexible shaping through the synchronous movement of two tools hold by two industrial robots. Since there is no existing solution to quickly and accurately generate two synchronized tool paths according to the will of users, the research of this method should first be focused on the tool path generation. In this paper, different forming strategies and their algorithms of generating synchronized path points are explained at first. Based on these established algorithms, three approaches to create CAM-interfaces for the generation of robot programs are introduced thereafter. Depending on different users, they are individually based on postprocessors, Application Program Interface (API) and a stand-alone program. Each introduced approach for Roboforming is validated by forming experiments and they also give a good reference to the third-party development of a CAD/CAM-system.