Showing papers by "Gerhard Hirt published in 2012"

Tailored Profiles Made of Tailor Rolled Strips by Roll Forming – Part 1 of 2

Abstract: To fully exploit the potential of sheet and profiles, various technologies to produce tailored blanks and profiles have been developed [1,2]. In earlier work [3] it has been shown that Strip Profile Rolling (SPR) can be used to produce metal strips with a predefined thickness distribution across the width of the strip. Building upon this knowledge, in two subsequent papers the extended goal of the project is presented. Therein is demonstrated that Strip Profile Rolling can be applied very effectively using a combination of roll forming (part 1) as well as further processing by roll forming (see part 2) to allow for the production of profiles with varying wall thickness in their cross section. To achieve the goal of part 1, a numerical model describing SPR was developed and used to study the influencing process parameters on spread and bulge formation. As a result of this parametric study, an optimized roll design and rolling sequence was developed to produce a demonstrator strip on a 12 stand roll forming mill manufactured by the company Dreistern [4]. Starting with a conventional strip out of DC01 steel (width 170 mm, thickness 2.5 mm), 29 rolling passes were necessary to achieve the desired geometry (width 186 mm, thickness 2.5 mm with a longitudinal groove being 64 mm wide where the thickness is reduced to 1.5 mm). In the second part of the process chain the coils produced by Strip Profile Rolling were successfully roll formed into a circular tube of 60 mm.

Herstellung frei geformter, selbst tragender Faltstrukturen aus Stahlblech mit der inkrementellen Blechumformung (IBU)

Abstract: Blechumformung ist traditionell ein hochaufwendiger Prozess, der teurer Werkzeuge und Formen wie Gesenke oder Patrizen und zugehoriger Stempel bedarf, die erst bei hohen produzierten Stuckzahlen rentabel werden. Aus diesem Grund beschrankt sich im Bauwesen der Einsatz umgeformter Stahlprodukte bisher auf die Verwendung von Halbzeugen wie z. B. Walzprofilen. Die inkrementelle Blechumformung (IBU), ein neuartiges Umformverfahren, arbeitet auf ganz andere Weise. Statt eines einstufigen Pressvorgangs, bei dem das Blech in Form gebracht wird, fahrt ein Umformwerkzeug die Bauteilkontur in einem sequenziell ablaufenden Prozess mit lokaler Verformung ab, der sich mit einfachen Mitteln an die individuell herzustellenden Blechformen anpassen lasst. Die IBU stellt insofern einen hochflexiblen Prozess dar, der es moglich macht, Serien von geometrisch unterschiedlichen Bauteilen bei hoher Effizienz zu fertigen. Sie verspricht ein ideales produktionstechnisches Mittel fur die Umsetzung des Leichtbauprinzips von Raumfaltwerken und mehrlagigen Faltungen zu sein, auf dessen Basis selbsttragende Hull- und Fassadenkonstruktionen aus Feinblech fur die Architektur und den Ingenieurbau gebaut werden konnen. Die tatsachlichen Eigenschaften und Bedingungen der konstruktiven und praktischen Umsetzung einer mit Hilfe der IBU hergestellten, frei geformten zweilagigen Hullflache wurde im Rahmen eines Forschungsprojekts zwischen dem Lehrstuhl fur Tragkonstruktionen (TRAKO) und dem Institut fur Bildsame Formgebung (IBF) an der RWTH Aachen untersucht. Free-formed, self-supporting folding structure made of metal sheets using the incremental sheet forming (ISF). Sheet forming is traditionally a costly process that requires expensive tools as well as forms such as winds or dies with customized punches, which are only profitable when producing high quantities. However, the incremental sheet forming (ISF), a novel forming technique, works highly differential. In contrast to the common single-stage jacking process, the incremental metal forming is a sequential process in which a forming instrument circumscribes the part contour and warps the sheet repeatedly. This process can easily be adjusted to a variety of individual thin sheet forms. In view of this fact, the ISF is a highly flexible process that allows to craft series of geometrically different components efficiently. ISF appears to be an ideal production-related instrument to realize the principle of lightweight constructions in space folding structures and multilayer folding structures that form the basis of self-supporting building envelopes or facades made of thin sheet. The actual characteristics and conditions of the constructive realization of a free-shaped, two-layered envelope formed with the incremental metal forming procedure has been analyzed during a research project between the Chair of Structures and Structural Design (Lehrstuhl fur Tragkonstruktionen – TRAKO) and the Institute of Metal Forming (Institut fur Bildsame Formgebung – IBF) of the RWTH Aachen University.

Sensitivity Analysis of a Force and Microstructure Model for Plate Rolling

Abstract: Consistent modelling of multipass hot rolling processes has to account for numerous interdependencies within the process. With a growing number of passes, the sensitivity of the model output with respect to variations in the input parameters plays a vital role for assessing the accuracy and stability of the computation. This study details a new concept of using Automatic Differentiation (AD) to obtain exact derivatives of the output values of the numerical model for plate rolling. It is shown that the sensitivities of the roll force with respect to selected material and process parameters can be computed through AD technology. As use case the rolling of a plain C-Mn steel plate is analysed. The results show substantial differences in the influence characteristics of particular input parameters.

Hybrid Production Systems

Abstract: While virtual product development allows great freedom in terms of design, actual development processes are rather restricted. Those boundary conditions are at best hardly possible to exert influence on. Therefore, future research has to focus both on the realisation of the concept of one-piece-flow while simultaneously increasing flexibility and productivity and on the technological advancement. Hence, hybridisation of manufacturing processes is a promising approach, which often allows tapping potentials in all the aforementioned dimensions.

A New Tool Concept for Rotary Peen Forming with Defined Impact Positions

Abstract: Rotary peen forming (RPF) has been developed as a new peen forming process in which the shot is held by a flexible connection and moved on a circular trajectory (see Fig. 1 below). The main advantage compared to a traditional shot peen forming (SPF) processes is that RPF does not need refeed of shot particles. Hence, RPF offers a compact machine design and a flexible use. The RPF process causes localized plastic deformation just as in traditional shot peen forming but involves tangential components which can create shear deformation in the plastic layer. These tangential components depend on the connection used for the setup. Compared to traditional shot peen forming, RPF shows different process characteristics in terms of coverage and the shape of indentations created on the surface of the workpiece. In this paper, a new tool concept for rotary peen forming is evaluated using experiments and numerical investigations of the process. The set-up uses a spring-attenuator system, which leads to more deterministic impact positions than previously used wire-based impactor concepts.