Sheet Metal 2007

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Authors: Wilko C. Emmens
Abstract: This paper describes the process of shaping fully formed beer & beverage cans with a rotating high-pressure water jet. In detail the paper discusses situations where forming is restricted to a limited area by using a special mould. This causes the strain to shift to biaxial causing quite different properties. The process is compared to ‘normal’ incremental forming showing many similarities that are discussed in more general terms and can be summarized into four propositions.
Authors: Hideo Iseki, Tomoyuki Nara
Abstract: As a result of the trend of consumer demand for many stamped sheet metal products, the study of flexible and incremental sheet metal forming and the small-scale production of stamped goods has received considerable attention. In the previous study, Iseki has developed the incremental sheet metal bulging method using water jet for the clean forming without the need for lubricating material. Though he succeeded in shaping wide range of complex shapes of an annealed aluminum sheet (thickness 0.3 mm, tensile strength 100 MPa ), for example, pyramidal shells, shells of pyramid frustums, shallow pans and embossed panels, he was completely unsuccessful in forming shells of a stainless steel sheet (thickness 0.3 mm, tensile strength 640 MPa ). In the present paper, an incremental bulging method of sheet metal using water jet and shots has been proposed to form shells of a stainless steel sheet, and the characteristics of deformation, strain distributions and the forming limit were experimentally studied.
Authors: M. Skjoedt, M.H. Hancock, N. Bay
Abstract: Single point incremental forming (SPIF) is a relatively new sheet forming process. A sheet is clamped in a rig and formed incrementally using a rotating single point tool in the form of a rod with a spherical end. The process is often performed on a CNC milling machine and the tool movement is programed using CAM software intended for surface milling. Often the function called profile milling or contour milling is applied. Using this milling function the tool only has a continuous feed rate in two directions X and Y, which is the plane of the undeformed sheet. The feed in the vertical Z direction is done in the same angular position in the XY plane along a line down the side of the work piece. This causes a scarring of the side and also results in a peak in the axial force when the tool is moved down. The present paper offers a solution to this problem. A dedicated program uses the coordinates from the profile milling code and converts them into a helical tool path with continuous feed in all three directions. Using the helical tool path the scarring is removed, the part is otherwise unchanged and a major disadvantage of using milling software for SPIF is removed. The solution is demonstrated by SPIF of three different geometries: a pyramid, a cone and a complex part.
Authors: K.P. Jackson, J.M. Allwood, M. Landert
Abstract: This paper presents a first investigation of the applicability of incremental sheet forming (ISF) to sandwich panels. Two initial tests on various sandwich panel designs established that sandwich panels which are ductile and incompressible are the most suitable for the process. Further tests on a sandwich panel with mild steel face plates and a continuous polypropylene core demonstrated that patterns of deformation and tool forces followed similar trends to a sheet metal. It is concluded that, where mechanically feasible, ISF can be applied to sandwich panels using existing knowledge of sheet metals with the expectation of achieving similar economic benefits. Potentially this will increase the range of applications for which sandwich panels are viable.
Authors: Horst Meier, V. Smukala, O. Dewald, Jian Zhang
Abstract: This paper describes a new development of an incremental, robot based sheet metal forming process for the production of sheet metal components for limited-lot productions and prototypes. The kinematic based generation of the 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 a high geometrical form flexibility without the need of any workpiece dependent tools. The principle of the procedure is based on flexible shaping by means of a freely programmable path-synchronous movement of two robots. So far, the final shape is produced by the incremental infeed of the forming tool in depth direction and its movement along the contour in lateral direction on each level. The counter tool, with its simple geometry, was used to support the sheet metal on the backside by moving synchronously along the outer contour, constantly on the same level. This corresponds to a fixed backplate used in other incremental sheet metal forming processes. Due to the use of a new robot system with extended control algorithms for cooperating robots, it will be possible to release the counter tool from its constant path on the outer contour and support the forming tool right on the opposite side of the sheet to generate a predefined gap between the two hemispherical tools. This way at each moment a small part of a full die, as it is used in other processes, is simulated without the need of producing a workpiece dependent die. The extended payload of the new robot system gives the opportunity to form steel blanks, for the first time.
Authors: E. Maidagan, Joachim Zettler, Markus Bambach, P.P. Rodríguez, Gerhard Hirt
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.
Authors: A. Hadoush, A.H. van den Boogaard, J. Huétink
Abstract: This paper presents the effect of combined stretching and bending on the achieved strain in incremental sheet forming ISF. A simple two dimensional model of strip undergoing stretching and travelling three point bending in cyclic form is used. The numerical model presents the effect of the ratio of stretching velocity to roll-set speed on the achieved strain and its distribution.
Authors: J.M. Allwood, D.R. Shouler, A. Erman Tekkaya
Abstract: Incremental sheet forming is known to give higher forming limits than conventional sheet forming processes, but investigation of this effect has been impeded by the computational cost of process models which include detailed predictions of through thickness behaviour. Here, a simplified process is used to gain insight into the mechanics of a broad class of incremental forming processes. The simplified process is described and shown to give increases in forming limits compared to a conventional process with the same geometry. A model of the process is set up with a commercial finite element package, validated, and used to trace the history of a ‘pin’ inserted perpendicularly into the workpiece. The history of the deformation of the ‘pin’ demonstrates significant through thickness shear occurring in the direction parallel to tool motion. This insight is used to modify an existing analysis used to predict forming limit curves. The analysis shows that for a sheet with uniform proportional loading, the forming limit is increased when through thickness shear is present, and this is proposed as an explanation for the increased forming limits of incremental sheet forming processes.
Authors: M. Ham, J. Jeswiet
Abstract: Single Point Incremental Forming (SPIF) is a new method of forming sheet metal for which not all forming limits and forming parameters are yet completely understood. In this paper, a Box-Behnken design of experiment (DOE) is used to execute an experimental study used to determine the forming limits in Single Point Incremental Forming (SPIF). The Box-Behnken allows for good accuracy in defining a surface response for a relatively low number of experimental runs – hence its usefulness in experimental work. The Box-Behnken used in this paper solved five factors at three levels in forty six runs. The five factors analyzed are based on the most critical factors effecting SPIF; they are material type, material thickness, formed shape, tool size and incremental step size (depth of each step in form). The data resulting from the Box-Behnken progressed into graphical response surfaces; the response surfaces allow designers to determine what factors they need to select in order to successfully form a part using SPIF.
Authors: Gerd Sebastiani, Alexander Brosius, Werner Homberg, Matthias Kleiner
Abstract: Sheet Metal Spinning is a flexible manufacturing process for axially-symmetric hollow components. While the process itself is already known for centuries, process planning is still based on undocumented expertise, thus requiring specialized craftsmen for new process layouts. Current process descriptions indicate a vast scope of different dynamic influences while the underlying mechanical model uses a simple static approach. Thus, a 3D Finite Element Model of the process has been set up at IUL in order to analyze the process in detail, providing online as well as cross sectional data of the specimen formed. Within the scope of this article, the results of the above mentioned Finite Element Analysis (FEA) are presented and discussed with respect to the qualitative stress distributions introduced in the existing theoretical models. Main emphasis of this paper is set on a discussion of the qualitative stress distribution, which is, to the current state, only known in theory.

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