Gerhard Hirt

Asymmetric single point incremental forming of sheet metal

The use of computers in manufacturing has enabled the development of several new sheet metal forming processes, which are based upon older technologies. This paper describes modifications that have been made to traditional forming methods such as conventional spinning and shear forming, forming processes in which deformation is localized. Recent advances have enabled this localized deformation to be accurately controlled and studied. Current developments have been focused on forming asymmetric parts using CNC technology, without the need for costly dies. Asymmetric Incremental Sheet Forming has the potential to revolutionize sheet metal forming, making it accessible to all levels of manufacturing. This paper describes the genesis and current state-of-the-art of Asymmetric Incremental Sheet Forming.

Forming strategies and Process Modelling for CNC Incremental Sheet Forming

Abstract Incremental Sheet Forming (ISF) is a process capable of producing complex sheet components by the CNC movement of a simple tool in combination with simplified dies. Earlier work revealed two major process limits, namely the limitation on the maximum achievable wall angle, and the occurrence of geometric deviations. The work detailed in this paper focuses on forming strategies to overcome these process limits, including the processing of tailor rolled blanks. Additionally, finite element modelling of the process is presented and discussed with respect to the prediction of the forming limits of ISF.

Strategies to improve the geometric accuracy in asymmetric single point incremental forming

Asymmetric incremental sheet forming (AISF) is a manufacturing process for the small batch production of sheet metal parts. In AISF, a sheet metal part is formed by a forming tool that moves under CNC control. AISF currently has two dominant process limits: sheet thinning and a limited geometric accuracy. This paper focuses on the latter limit. It is shown with a pyramidal part that multi-stage forming can yield an increased accuracy compared to single-stage forming. However, due to residual stresses induced during forming, the accuracy of the as-formed part can be lost if the part is trimmed after forming. A case study with a car fender section shows that the geometric accuracy of the final part can be improved compared to single-stage forming by a combination of multi-stage forming and stress-relief annealing before trimming.

Laser-assisted asymmetric incremental sheet forming of titanium sheet metal parts

Asymmetric Incremental Sheet Forming (AISF) is a relatively new manufacturing process. In AISF, a CNC driven forming tool imposes a localized plastic deformation as it moves along the contour of the desired part. Thus, the final shape is obtained by a sequence of localized plastic deformations. AISF is suitable for small series production of sheet metal parts as needed in aeronautical and medical applications. Two main process limits restrict the range of application of AISF in these fields. These are the low geometrical accuracy of parts made from titanium alloys or high strength steels and, for titanium alloys, the limited formability at room temperature. In this paper a new concept for laser-assisted AISF is introduced including the required components. Furthermore, the CAX tools used for programming the NC path for the forming tool and the laser spot are illustrated. First experimental results show that the formability of the alloy Ti Grade 5 (TiAl6V4), which is usually used in aeronautic applications, can be increased.

Large area rolling of functional metallic micro structures

The reliable fabrication of functional surface structures has become an important factor in modern production processes. With regard to the field of large area micro patterning, particular applications demand for economical manufacturing processes to gain advantageous surfaces. The process-integrated rolling of these structures is a promising approach if suitable roll geometries can be manufactured. This paper focuses on the large area rolling of so called riblet structures. Both experimental test series and related numerical forming simulations are taken into account. Furthermore, demands and potentials from the roll manufacturing point of view are highlighted. Above all, the feasibility of a new winding concept for the continuous patterning of rolls with small negative riblet structures is pointed out. By this means, challenging requirements in connection with riblet rolls—the realization of finest structures with sharp ground radii—can be matched.

Semi Solid Casting and Forging of Steel

The semi solid forming of steel has the potential of an innovative technology, which could open a new possibility of metal components production. Earlier research works in the 1990s have already shown the principal feasibility of the process but also revealed the various kinds of technical problems. Since then, research works on steel processing have been continuously made in several locations in Japan, USA and Europe. Currently, the focus of these research activities is the development of suitable tool material and the achievement of high part quality, which is the key point for the success of the process. This paper gives an overview of the previous research works and the current state of the research with an outlook on future tasks for this challenge.

Homogenization Strategy and Material Characterization of High-Manganese TRIP and TWIP Steels

In this work a hot forming strategy, consisting of forging and hot rolling, to homogenize casted blocks of high-manganese steels with 0.3 % carbon and 22 % manganese is introduced. The resulting distribution of carbon and manganese is evaluated by microprobe scans. The micro-segregation of manganese could be reduced from 7 weight percent to 2. To create the obtained hot forming strategy hot compression tests have been carried out. The deformation behavior has been characterized for two steels with 22 % manganese and between 0.3 and 0.7 % carbon content in the temperature range between 700 and 1200°C and strain rates between 0.1 and 10 s-1.

Semi-Solid Forging of 100Cr6 and X210CrW12 Steel

Semi-solid forging of the steel grades 100Cr6 and X210CrW12 reveals advantages compared to conventional manufacturing process technologies like casting and forging. These advantages result from the thixotropic flow behaviour prevailing when the material condition is varied. Two different strategies to generate a semi-solid precursor material are investigated. With the first strategy conventional rod material is inductively heated into the desired state and subsequently forged. For this purpose a fully automated semi-solid forging plant has been developed. The second strategy consists of producing the semi-solid precursor material directly from a slightly overheated melt with subsequent forced nucleation by means of a cooling slope. The results of the experimental work are presented and an outlook to both process variants is given.

Modeling of Optimization Strategies in the Incremental CNC Sheet Metal Forming Process

Incremental CNC sheet forming (ISF) is a relatively new sheet metal forming process for small batch production and prototyping. In ISF, a blank is shaped by the CNC movements of a simple tool in combination with a simplified die. The standard forming strategies in ISF entail two major drawbacks: (i) the inherent forming kinematics set limits on the maximum wall angle that can be formed with ISF. (ii) since elastic parts of the imposed deformation can currently not be accounted for in CNC code generation, the standard strategies can lead to undesired deviations between the target and the sample geometry.Several enhancements have recently been put forward to overcome the above limitations, among them a multistage forming strategy to manufacture steep flanges, and a correction algorithm to improve the geometric accuracy. Both strategies have been successful in improving the forming of simple parts. However, the high experimental effort to empirically optimize the tool paths motivates the use of process model...

Investigation of flow behaviour and microstructure on X210CrW12 steel in semi-solid state

This paper describes the basic investigation on material behaviour of cold working steel X210CrW12 in semi-solid state concerning the semi-solid forging. It includes a study of flow behaviour and microstructure by means of a high temperature isothermal upsetting test applying a special cylinder sample with a shell, which is designed to avoid collapsing of samples during the compression. The flow curve of the semi-solid steel is determined by an inverse modelling via FEM using the obtained load curve of the samples and the separately obtained flow stress of the shell material. An extensive microstructure study of the compressed samples provides a comprehensive understanding on the flow mechanism of the semi-solid steel. At the end of the paper some general restrictions and remarks for the semi-solid forging process are given based on the gained results.