Papers by Author: Joachim Zettler

Abstract: In the aerospace industry lightweight design in combination with fast and reliable manufacturing processes are key components to defend the leading position in the worldwide competition. In this frame it is an overall goal to reduce the number of process steps in order to produce parts for an aircraft to its minimum. Integral design is one way to cope with this goal but on the other hand raises a lot of problems that may occur in manufacturing or final assembly. To be able to predict potential bottlenecks or drawbacks in certain designs, finite element simulation can be helpful. Especially if it’s an early design phase and new material concepts are taking into account, the virtual manufacturing, done by finite element simulations is the only way to predict real life behavior. In this paper we will focus on the use and benefit of finite element simulations in the early design phase of very huge integral parts of a next generation aircraft. The parts do belong to the nose fuselage structure and will be manufactured from a 100-150mm thick AlMgSc plate. Two different manufacturing routes will be covered by simulation. 1. Hot forming the plates at around 300°C and machining 2. Explosive forming of the plates and machining For both routes, a complete simulation chain from forming over springback to final machining is developed and presented in detail. Special care is taken on a fully automated workflow from one step to the other to allow an easy adaptation to other part geometries in the future. To ensure a high quality of the simulation results all process steps of the hot forming route are simulated with ABAQUS implicit and approved constitutive laws. The explosive forming manufacturing route is simulated using an Eulerian-Lagrange approach taken into account the various possibilities of detonation loading. To validate the simulation results to real measurements, a scaled down version of one of the parts is manufactured in reality and each process step is compared with the simulation result.

Abstract: Asymmetric Incremental Sheet Forming (AISF) is a process for the flexible production of sheet metal parts. In AISF, a part is obtained as the sum of localized plastic deformations produced by a simple forming tool that, in most configurations, moves under CNC control. Flexible processes with low tooling effort like AISF are suitable for sectors with small lot sizes but premium products, e.g. for the aviation and the automotive sector. Four main process limits restrict the range of application of AISF and its take-up in industry. These are: (i) material thinning, (ii) limited geometrical accuracy, (iii) the process duration and (iv) the calculation time and accuracy of process modelling. Moreover, the material spectrum of AISF for structural parts is mostly restricted to cold workable materials like steel and aluminum. This paper presents some new investigations of incremental sheet forming combined with laser heating or stretch forming as possible hybrid approaches to overcome the above mentioned limitations of AISF. These hybrid incremental sheet forming processes can increase the technological and economical potentials of AISF. A possible application is the fabrication of lightweight sheet metal parts as individual parts or small batches, e.g. for the aerospace industry. The present study provides a short overview of the state of the art of AISF, introduces the new hybrid process variations of AISF and compares the capabilities of the hybrid processes and the standard AISF process. Finally, two examples for applications are presented: (i) the production of a part used in an airplane for which the manufacturing steps consist of die manufacture, sheet metal forming by means of stretch forming combined with AISF and a final trimming operation using a single hybrid machine set-up; (ii) laser-assisted AISF for magnesium alloys.

Abstract: Nowadays many industrial sectors use forming processes in order to produce sheet metal components. The most widely used processes are stamping and deep drawing, which are based on big, costly dies and presses. These processes require large initial investment and specific dies for each part, which makes them inflexible and only profitable for large batches. A possible approach to small series production is based on the incremental sheet forming technique (ISF), which consists of a gradual plastic deformation of flat sheet metal by the action of a CNC controlled tool. Equipment such as a 3-axis milling machine can be used for ISF, such that the initial investment costs in ISF are around 5-10% of those required to set up a production line for conventional stamping. In its current stage of development, dedicated dies are often used as support tools in ISF. However, due to the fact that the forming forces are low in ISF, the dies can be made out of cheap materials like resin or wood. Although this is an additional advantage over stamping, the need to use additional tools still reduces the flexibility of the process. The present paper details the concept of a truly “dieless” incremental forming process. In the framework of the SCULPTOR EU project, the authors are working on an innovative concept of incremental sheet metal forming which is based on the replacement of the commonly used dies by a second forming tool which moves in a coordinated way with the first forming tool, thus creating a flexible die system, which does not depend on the specific geometry of the part to be formed. The present work summarizes the results obtained up to now in two fields: (i) the development of a prototype for the flexible die system to be included both in milling machines or combined with robots and (ii) process modelling to improve the understanding of the process.