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Description
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The production technology of incremental sheet metal forming (ISF) combines high process flexibility with low component-specific tooling and thus represents a technology of great potential for the ongoing trend towards shorter product cycles and a growing variant diversity. The current state of the art of ISF and its variants indicates that an economic industrial production of components in small batch sizes at high quality standards seem feasible. The process advantages of ISF can only be entirely utilized if the complete process chain including the subsequent finalization operations - such as hole flanging and flanging - can be carried out with a minimum of component-specific tooling. Moreover an individual and flexible modification of mass products by incremental flanging operations seems feasible. The goal of the present thesis is to gain a complete fundamental understanding of flanging operations by ISF to identify the process limits and derive methods for further product improvement. For the investigations on incremental flanging operations, various machiningstrategies are applied to the basic flange types. It is identified that a single-stage strategy is sufficient and effective for the incremental forming of a flange. The application of multi-stage strategies - in contrast to the conventional ISF - does notshow any significant improvements to the general product properties. Furthermore, it is shown that - in contrast to conventional flanging - there is no dependence of the process limits to the flange radius. Solely the flange length represents a sensitive process parameter to the flange geometrical properties. A significant improvement of the geometrical accuracy with a minimum limitation of the process flexibility is achieved by application of a developed adaptive blank holder. The process limits of conventional flanging methods are significantly exceeded. For incremental hole flanging operations multi-stage strategies prove advantageous. The resulting flanging properties can be adjusted by adapting theprocessing strategies. It is shown that a gradual increase in the diameter of the hole flange leads to a reduction in the flange length and a slight increase of conicity but also a significantly high maximum expansion ratio of up to 5.5. Conventional hole flange operations with a punch in comparison achieve a maximum hole expansion ratio of up to approximately 2.5, given similar geometric boundary conditions. A process strategy where the hole flange wall angel is increased stepwise results in an increase of the flange length, a higher final wall angle but also in an increased local sheetthinning and thus in a smaller maximum expansion ratio. Additionally it is presented,that the application of a tool concept with multiple synchronously acting tools can improve the hole flange properties - especially with respect to the geometry. A prior forming step shows no significant influence on the process and the final hole flange properties. In order to increase economic efficiency and therefore the industrial relevance various methods for a process acceleration are derived and evaluated. Two tool concepts are compared, that both gradually increase the diameter of the hole flange by means of rotatively-free forming tools. Within the scope of the experiments conducted a process acceleration could be achieved by a factor of 35. Therefore an application of the incremental hole flanging in combination to conventional production technologies appears realistic. Furthermore, it is presented that the high process flexibility of incremental hole flanging can be used for form-fitting joining. As an example a sheet metal with a prehole diameter of 50 mm could be formed in a first step to a hole flange with a diameter of 98 mm and subsequent formed around the joining partner to a maximum diameter of 130.5 mm to a joint connection. Finally, the technological potentials of incremental flanging and hole flanging operationsare demonstrated
