Daniel Staupendahl

Innovative Machine Concepts for 3D Bending of Tubes and Profiles

The paper deals with two new processes and developed special machines for profile and tube bending. The first process is a new roll-based machine for three-dimensional bending of profiles with symmetrical and asymmetrical cross-sections that has been developed. Compared to conventional processes like stretch bending, the advantage of Torque Superposed Spatial (TSS) Bending is the kinematic adjustment of the bending contour, leading to higher flexibility and cost efficiency especially in small batch production. The second process is the new process of Incremental Tube Forming (ITF). This process is based on a combination of a spinning process and kinematic free form bending of tubular semi-finished products. It is suitable for bending tubes two- and three-dimensionally to arbitrary contours and for manufacturing tailored tubes. The combined spinning and bending process leads to low bending forces with the possibility of a significant springback reduction.

The Impact of Torsion on the Bending Curve during 3D Bending of Thin-Walled Tubes - A Case Study on Forming Helices

Chassis or cabin designs in the transportation sector are currently manufactured out of several single structural elements. To save handling steps and energy intensive joining processes and furthermore support lightweight design, bending processes can be used that offer the direct production of structural parts that incorporate the functionality of several single elements. In recent years, several processes for the kinematic bending of three-dimensional tubes and profiles have been developed. Additionally, three-roll push bending has gained in importance in manufacturing three-dimensional tubes. In this kinematic process, three-dimensional bending is achieved by continuously changing the bending plane relative to the workpiece during the forming process. Several studies exist that investigate the mechanisms that lead to three-dimensional bending contours. These were, however, based on the generation of empirical models, e.g. characteristic maps. Up until now, no analytical model exists, which describes the process of bending three-dimensional tubes in a comprehensive manner, especially taking into account tube torsion. In the following case study, the tube rotation needed to produce helices is measured and compared to helix radii and helix height. The results were subsequently used to set up an analytical model, which, first of all, describes the tube rotation needed to produce the torsion of the investigated helices and, more importantly, can be generalized to describe the tube rotation needed for the torsion of arbitrary bending curves.

Closed-loop control concept for kinematic 3D-profile bending

Kinematic tube and profile bending processes produce bending contours by the relative movement of single process axes. Tools only need to be adapted to fit the cross-section of the tubular material. While offering a great flexibility in production, kinematic bending processes cause a high part springback and as a result, compensatory methods are needed to achieve target contours. These compensatory methods are generally embedded in bending tables or analytical calculations that in turn are embedded into the process control software. This procedure can cope with known material behavior, as for instance gained through a tensile test of the material batch prior to the bending process. Material variations inside a batch cannot be detected however and cause contour deviations. To counter this error, a closed-loop control system can be used, which can quickly adapt axes’ movements to produce target shapes and thus reduce scrap. In this paper, two methods to apply closed-loop control to 3D profile bending will b...

Torque Superposed Spatial bending

A new roll-based process and machine for three-dimensional bending of beams with symmetrical and asymmetrical cross-sections have been developed. Compared to conventional processes like stretch bending, the advantage of the Torque Superposed Spatial (TSS) bending is the kinematic adjustment of the bending contour, leading to higher flexibility and cost efficiency, especially in small batch production. To define the spatial geometry of the workpiece, a torque is superposed to the bending moment. Process principle, process control and the machine design of the new process are presented.

Development of a procedure for forming assisted thermal joining of tubes

With the demand of lightweight design in the automotive industry, not only the wall-thicknesses of tubular components of the chassis or spaceframe are continuously decreased. Also the thicknesses of exhaust system parts are reduced to save material and mass. However, thinner tubular parts bring about additional challenges in joining. Welding or brazing methods, which are utilized in joining tubes with specific requirements concerning leak tightness, are sensitive to the gap between the joining partners. Furthermore, a large joining area is required to ensure the durability of the joint. The introduction of a forming step in the assembled state prior to thermal joining can define and control the gap for subsequent brazing or welding. The mechanical pre-joint resulting from the previously described calibration step also results in easier handling of the tubes prior to thermal joining. In the presented investigation, a spinning process is utilized to produce force-fit joints of varying lengths and diameter r...

Investigation of the effects of process and geometrical parameters on formability in tube hydroforming using a modular hydroforming tool

Tube hydroforming is one of the most important manufacturing processes for the production of exhaust systems. Tube hydroforming allows generating parts with highly complex geometries with the forming accuracies needed in the automotive sector. This is possible due to the form-closed nature of the production process. One of the main cost drivers is tool manufacturing, which is expensive and time consuming, especially when forming large parts. To cope with the design trend of individuality, which is gaining more and more importance and leads to a high number of product variants, a new flexible tool design was developed. The designed tool offers a high flexibility in manufacturing different shapes and geometries of tubes with just local alterations and relocation of tool segments. The tolerancing problems that segmented tools from the state of the art have are overcome by an innovative and flexible die holder design. The break-even point of this initially more expensive tool design is already overcome when forming more than 4 different tube shapes. Together with an additionally designed rotary hydraulic tube feeding system, a highly adaptable forming setup is generated. To investigate the performance of the developed tool setup, a study on geometrical and process parameters during forming of a spherical dome was done. Austenitic stainless steel (grade 1.4301) tube with a diameter of 40 mm and a thickness of 1.5 mm was used for the investigations. The experimental analyses were supported by finite element simulations and statistical analyses. The results show that the flexible tool setup can efficiently be used to analyze the interaction of the inner pressure, friction, and the location of the spherical dome and demonstrate the high influence of the feeding rate on the formed part.Tube hydroforming is one of the most important manufacturing processes for the production of exhaust systems. Tube hydroforming allows generating parts with highly complex geometries with the forming accuracies needed in the automotive sector. This is possible due to the form-closed nature of the production process. One of the main cost drivers is tool manufacturing, which is expensive and time consuming, especially when forming large parts. To cope with the design trend of individuality, which is gaining more and more importance and leads to a high number of product variants, a new flexible tool design was developed. The designed tool offers a high flexibility in manufacturing different shapes and geometries of tubes with just local alterations and relocation of tool segments. The tolerancing problems that segmented tools from the state of the art have are overcome by an innovative and flexible die holder design. The break-even point of this initially more expensive tool design is already overcome when f...