Sheet Metal 2005

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Authors: Joost R. Duflou, Alexander Szekeres, P. Vanherck
Abstract: In this paper an experimental platform capable of measuring forces in process during an incremental forming procedure is described and the results garnered from it are presented. Some of the earliest measurements of forces in incremental forming and the changes induced on the measured load are reported. Using a table type force dynamometer with incremental forming fixture mounted on top, three components of force were measured throughout the forming process. They were found to vary as the parts were made. The reported experimental test program was focused on the influence of three different process parameters on the forming forces: the vertical step size between consecutive contours, the diameter of the tool and the steepness of the part’s wall. For the tested material, analytical results demonstrating the relationship between the respective process parameters and the induced forces are presented in this paper.
Authors: J. Jeswiet, Joost R. Duflou, Alexander Szekeres
Abstract: Forces have been measured in Two Point Incremental Forming and Single Point Incremental Forming of Sheet Metal. It is necessary to know the magnitude of these forces when trying to determine if the equipment available is capable of Forming Sheet Metal by either one of the two foregoing processes. The magnitude of forces is also needed when developing appropriate models for the Incremental Sheet Forming. The forces measured in forming cones and truncated pyramids from AA 3003-0 are described.
Authors: L. Lamminen
Abstract: Incremental sheet forming (ISF) has been a subject of research for many research groups before. However, all of the published results so far have been related to either commercial ISF machines or ISF forming with NC mills or similar. The research reported in this paper concentrates on incremental sheet forming with an industrial robot. The test equipment is based on a strong arm robot and a moving forming table, where a sheet metal blank is attached. The tool slides on the surface of the sheet and forms it incrementally to the desired shape. The robot is capable of 5-axis forming, which enables forming of inwards curved forms. In this paper the forming limit diagram (FLD) for ISF with the robot is presented and it is compared with conventional forming limit diagrams. It will be shown that the conventional FLD does not apply to incremental forming process. Geometrical accuracy of sample pieces is also studied. Cones of different shapes are formed with the robot equipment and their correspondence with the 3D CAD model is evaluated. The results are compared with other results of accuracy of incremental sheet forming, reported earlier by other researchers. The third issue covered in this article is a product development point of view to incremental sheet forming. In addition to fast prototyping and low volume production of sheet metal parts, ISF brings new possibilities to sheet metal component design and manufacturing. These possibilities can only be exploited if design rules, that will take the possibilities and limitations of the method into account are created for ISF.
Authors: Horst Meier, O. Dewald, Jian Zhang
Abstract: This paper describes a new 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 a new forming machine comprising of two industrial robots. Compared to conventional sheet metal forming machines this newly developed sheet metal forming process offers a high geometrical form flexibility and also shows comparatively small deformation forces for high deformation degrees. The principle of the procedure is based on flexible shaping by means of a freely programmable path-synchronous movement of the two robots. The sheet metal components manufactured in first attempts are simple geometries like truncated pyramids and cones as well as spherical cups. Among other things the forming results could be improved by an adjustment of the movement strategy, a variation of individual process parameters and geometric modifications of the tools. Apart from a measurement of the form deviations of the sheet metal with a Coordinate Measurement Machine rasterised and deformed sheet metals were used for deformation analyses. In order to be able to use the potential of this process, a goal-oriented process design is as necessary as specific process knowledge. In order to achieve process stability and safety the essential process parameters and the process boundaries have to be determined.
Authors: J.M. Allwood, N.E. Houghton, K.P. Jackson
Abstract: A new incremental sheet forming machine has been built in Cambridge and was commissioned in October 2004. The basis for the machine design is described, including estimates of tool forces, the need for access to the reverse side of the workpiece, and the need to cope with high horizontal loads at the tool tip. The tool-mounting has been designed to rotate freely but passively, and to allow for simple exchange of tool tips. The workpiece is mounted on a set of load cells providing a six degree of freedom constraint without moment loading of the cells. The initial operation of the machine is briefly described.
Authors: Giuseppina Ambrogio, Luigino Filice, Francesco Gagliardi, Fabrizio Micari
Abstract: Incremental forming processes are characterized by a well known and particular feature: any deformation across the sheet plane determines sheet thinning, since the blank is fully clamped by means of a proper equipment. As a consequence, the availability of effective and reliable CAE tools capable to supply an accurate prediction of sheet thinning as a function of process parameters, represents a strong requirement for a wider practical application of incremental forming. The already available theoretical models (i.e. the sine law) do not provide, on the other hand, satisfactory results. Therefore in the paper a couple of numerical analysis strategies was applied to simulate simple incremental forming processes, as well as a proper experimental equipment was developed to verify the accuracy of the numerical predictions.
Authors: J. Jeswiet, Joost R. Duflou, Alexander Szekeres, P. Lefebvre
Abstract: Single Point Incremental Forming is a new process, which has been developed to make both Rapid Prototyped products and low volume product batches from Sheet Metal. This paper presents a case study of the manufacture of a solar cooker cavity for developing country applications. In the first instance the request was for a rapid prototype, which quickly evolved into a request for low volume production of solar cookers for the developing country market. The paper describes the manufacture of the solar cooker cavity, and shows how the possibility of manufacturing part of the solar cooker, by Single Point Incremental Forming, gives rise to the possibility of manufacturing other parts for the solar cooker less expensively.
Authors: R. Göbel, Matthias Kleiner, N. Henkenjohann
Abstract: Due to the high complexity and the large number of possible geometries to be formed, a systematic design of the sheet metal spinning process is, up to now, difficult and time consuming. Sustainable models of the spinning process do not exist so far. Due to this, a new approach for the systematic design and optimization of the spinning process has been developed. In a first step of the planning sequence, a prediction of initial parameter settings is given by a case-based-reasoning approach. A first adaptation of the pre-selected parameters is then realized on a fuzzy-based model. In the next step, a model based optimization using statistical design of experiments is performed. For this, a new statistical approach has been developed being optimized regarding the requirements of the spinning process. In this paper, the methods used and the implementation of the approach in a process planning software are described. The approach is verified by the example of setting up a process to manufacture a cylindrical model workpiece.
Authors: Claudio Giardini, Elisabetta Ceretti, Aldo Attanasio
Abstract: Sheet Incremental Forming (SIF) is a modern technique that deforms the sheet on a positive or negative die using a simple punch mounted on a general purpose CNC machine. Several working parameters (tool path, spiral width and tool depth) have been studied in previous papers [1, 2] analyzing their influence on a simple part when working AISI 304 or Cu DHP sheets. The main problem was to study the process feasibility, that is, the possibility of correctly deforming the pieces without breaking them. The research reported here has been focused mainly on other two important variables, studying their influence on the final part quality: the punch diameter and its velocity when deforming the sheet. Surface roughness and minimum thickness of the deformed sheet have been chosen as parameters for analyzing and evaluating the process efficiency. In FEM analysis, a simulation model was developed and implemented considering Cu DHP sheet. The comparison with experimental results was used to validate the simulation model and to identify the most suitable simulation parameter values (friction coefficient between various elements and blank holder force). The developed and validated model can be used for studying the process optimization. The results obtained in this paper can also be used as guidelines for the correct design of Sheet Incremental Forming process.
Authors: M. Bambach, Gerhard Hirt, J. Ames
Abstract: The present paper focuses on a new methodology to quantitatively evaluate finite element calculations on incremental sheet forming (ISF). ISF is a new manufacturing process for prototypes and small lot sizes. In ISF, a part is manufactured by the CNC-driven movement of a simple tool, giving rise to very challenging problems concerning the efficient modeling of the alternating contact conditions and the material's response to the cyclic deformation. The quantitative validation of the finite element analysis is achieved by an optical deformation measurement system which has been enhanced by a new calibration procedure, yielding a precisely defined local coordinate system for deformation measurements during forming. In combination with mapping algorithms for large point sets, this allows for a quantitative validation of process simulations and material input data.

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