David Bailly

Flexible Manufacturing of Double-Curved Sheet Metal Panels for the Realization of Self-Supporting Freeform Structures

Product development is complex due to the manifold requirements resulting from various perspectives, such as design, production, safety and sales. A concurrent engineering (CE) approach permits to respect all perspectives in the early development stage. However, in the architecture and construction sector for example, CE is particularly difficult to realize, because the central steering for this collaboration process is missing. Thus, the application of CE in the research sector can promote technical progress and cost reduction. In the specific field of freeform architecture, in most cases an individual shape of single components is unavoidable and the use of standard components impossible. Due to missing universal and mature construction concepts for freeform buildings, they are mostly realized with customized solutions often including material-consuming substructures, while the visible skin has only limited structural and functional properties.In this context the present paper proposes a novel universal panel system made of double-curved sheet metal layers enabling the assembly of self-supporting lightweight structures for the realization of freeform surfaces. The panel system has been developed in cooperation of architects, construction and production engineers, successfully applying an interdisciplinary CE approach. As a result, the concept allows for material and cost efficient solutions applicable for a wide range of freeform applications. The detailed development of the panel system is still in progress.Besides the general panel concept, the paper presents in particular the corresponding manufacturing chain and the tooling concept. Accounting for the varying part geometries in this application a flexible manufacturing chain based on the combination of stretch forming and incremental sheet forming has been developed. The entire production process is implemented in a single machine setup and successfully tested on a small-scale prototype.

Analysis into Differences between the Buckling in Single-Point and Two-Point Incremental Sheet Forming of Components for Self-Supporting Sheet Metal Structures

In the architecture and construction sector the trend for individualization is often expressed in complex-shaped freeform buildings. Due to missing universal and mature construction methods for freeform buildings, they are usually realized with customized solutions that often include massive, material-consuming substructures, while the visible skin has neither structural nor functional properties. In this context a new concept for self-supporting lightweight structures for the realization of free-form surfaces and the production of the corresponding components has recently been proposed. Taking into account the large part dimensions and the varying part geometries in this application a flexible production chain based on incremental sheet forming has been developed and optimized. It has been validated by producing six-sided large-scale pyramids in 140 similar variants which were assembled to a self-supporting free-form demonstrator. Two-point incremental sheet forming (TPIF) was used with a universal partial supporting tool with the goal to produce all variants without dedicated tooling. Although the majority of pyramids was produced successfully with the applied TPIF strategy, there was a small number of parts with a very asymmetric shape that showed severe buckling in the side walls. For a detailed analysis of this observation the asymmetry was quantified using a wall angle ratio. Subsequently, a single-point incremental sheet forming (SPIF) strategy was successfully applied as an approach to avoid buckling. The results confirm the assumption that the circumferential expansion in SPIF suppresses buckling due to tensile stresses in the side walls, whereas the circumferential compression in TPIF triggers buckling due to the compressive stresses in the side walls.

Multi-technology Platforms (MTPs)

The growing demand for individualized commodities requires new solutions for a highly flexible yet cost-efficient production. Hence, the research results described in this chapter address the question of how different manufacturing technologies could be combined and employed efficiently in industrial practice. Reaching across the whole field of Multi-Technology Platforms (MTPs) a generalized design methodology was examined. The resulting template-based procedure, combining function structure and technology chains, is introduced in the first section. Consecutively, the next section advances this approach by illustrating the incorporation of metrology into machine tools and MTPs. For technological validation, all newly-developed scientific approaches were successfully integrated into four demonstrator test beds located at the RWTH Aachen University: a Multi-Technology Machining Center, a Hybrid Sheet Metal Processing Center, a Conductive Friction Stir Welding Center and a laser-enhanced hybrid lathe. The economic efficiency of manufacturing technology integration is reviewed before a profitability assessment based on the aforementioned demonstrator test beds is performed. The chapter concludes with an outlook on future research topics.

Homogenisation of the strain distribution in stretch formed parts to improve part properties

Inhomogeneous strain and sheet thickness distributions can be observed in complex sheet metal parts manufactured by stretch forming. In literature, this problem is solved by flexible clampings adapted to the part geometry. In this paper, an approach, which does not rely on extensive tooling, is presented. The strain distribution in the sheet is influenced by means of hole patterns. Holes are introduced into the sheet area between clamping and part next to areas where high strains are expected. When deforming the sheet, high strains are shifted out of the part area. In a local area around the holes, high strains concentrate perpendicular to the drawing direction. Thus, high strains in the part area are reduced and the strain distribution is homogenised. To verify this approach, an FE-model of a stretch forming process of a conical part is implemented in LS-Dyna. The model is validated by corresponding experiments. In the first step, the positioning of the holes is applied manually based on the numerically determined strain distribution and experience. In order to automate the positioning of the holes, an optimisation method is applied in a second step. The presented approach implemented in LS-OPT uses the response surface method to identify the positioning and radius of the holes homogenising the strain in a defined area of the sheet. Due to nonlinear increase of computational complexity with increasing number of holes, the maximum number of holes is set to three. With both, the manual and the automated method, hole patterns were found which allow for a relative reduction of maximum strains and for a homogenisation of the strain distribution. Comparing the manual and automated positioning of holes, the pattern determined by automated optimisation shows better results in terms of homogenising the strain distribution.Inhomogeneous strain and sheet thickness distributions can be observed in complex sheet metal parts manufactured by stretch forming. In literature, this problem is solved by flexible clampings adapted to the part geometry. In this paper, an approach, which does not rely on extensive tooling, is presented. The strain distribution in the sheet is influenced by means of hole patterns. Holes are introduced into the sheet area between clamping and part next to areas where high strains are expected. When deforming the sheet, high strains are shifted out of the part area. In a local area around the holes, high strains concentrate perpendicular to the drawing direction. Thus, high strains in the part area are reduced and the strain distribution is homogenised. To verify this approach, an FE-model of a stretch forming process of a conical part is implemented in LS-Dyna. The model is validated by corresponding experiments. In the first step, the positioning of the holes is applied manually based on the numerically ...

Hybrid Sheet Metal Processing Center

Incremental Sheet Forming (ISF) is a flexible sheet forming process suitable for single part and small series production. To form a component, a CNC controlled generic forming tool is moved along the contours of the desired shape and locally induces plastic deformations. Hence, the final shape of the component is obtained stepwise as a sum of all localized plastic deformations. However, the basic process shows several process limits, such as long process time, material thinning and limited geometrical accuracy. Here, a Hybrid Sheet Metal Processing Center is presented that addresses these process limits. It allows for combining stretch forming with ISF, performing laser assisted ISF as well as pre- and post-processing in one concerted machine setup.