Christoph Becker

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.

Development of a tele-operative testing cell as a remote lab for material characterization

Laboratory experiments play a significant role in engineering education. The experience gathered during the labs is one of the most important experiences during studying engineering because there is a strong connection between theory and practical relevance. A tele-operative testing cell for material characterization for forming processes is presented. This testing cell is used as a remote lab so that students can gain their experiences location and time-independent via the internet. In addition, the tele-operative testing cell is also used within the scope of lectures to combine the theory with live experiments in interaction with the students. The main aspects are, on the one hand, the developments in the field of engineering and the implementation of the IT components like iLab and, on the other hand, the integration of the tele-operative testing cell into engineering education.

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.

Basic Investigations in Incremental Profile Forming

Increasing demands in profile manufacturing lead to a constant increase of the geometric complexity of the profile. Especially in times where lightweight design and load adaption are of huge importance, a need for new profile manufacturing technologies exists. In order to cope with this development a new profile forming method was invented, the Incremental Profile Forming (IPF). IPF allows the flexible manufacturing of profiles with varying cross section geometries along the longitudinal profile axis and offers therefore high potential for the manufacturing of lightweight design parts. Due to the high degree of innovation research work regarding the process fundamentals as well as the process limits is necessary. For this reason, the results of the first basic experimental and numerical investigations are presented. While in the experiments the potential of the process is shown in feasibility studies, first analysis of the forming process as well as the influence of diverse process parameters on the process was carried out in numerical investigations. Finally first analytical approaches for predicting the forming behavior are presented.Copyright

Prediction of surface roughness due to spinning in the incremental tube forming process

Incremental tube forming (ITF) is a new process allowing a flexible manufacturing of 2D and 3D bent tubes with load-optimized cross sections by means of the combination of the procedures spinning and bending. The aim of this paper is to acquire an in-depth process understanding concerning the surface roughness. This paper focuses on the spinning process operation of the ITF process. The influence of the spinning roll geometry and the process parameters on the theoretical surface roughness is studied in detail. Crest height h and roughness average parameter Ra are formulated as function of process parameters and spinning roll geometry. Also, a fishbone diagram with the parameters influencing the tube surface characteristics is provided. Experiments are performed to quantify the divergences of the equations. The theoretical approach can be used to understand the incremental tube forming process in more detail.

Numerical Investigation of the Incremental Tube Forming Process

As a response to the recent years’ growing demand for innovation in manufacturing processes towards lightweight design in several industrial sectors, a new process, called Incremental Tube Forming (ITF), and a corresponding machine layout have been developed. ITF is a process to manufacture bent tubes with varying cross-sections. During ITF a tube is clamped in a feeding device, which transports the tube through a spinning tool, where the diameter reduction takes place. This stage is followed by a superposed bending process without suppressing continuous feeding. This combination leads to various advantages such as improved tool life with reduced tool forces and improved product accuracy (e.g. springback behavior), as it is shown in various experimental works. This paper presents a complementary numerical treatment of the process using FEA. For this purpose, a 3D model is constructed using ABAQUS/Explicit, where the tube is modeled with conventional shell elements with uniformly reduced integration to avoid shear and membrane locking (S4R), whereas the spinning rolls are modeled as discrete rigid. With this model, the influences of process parameters, such as diameter reduction ratio and tool geometry, are investigated. This helps not only to gain a deeper understanding of the process but also to interpret already gathered experimental data with better precision and, thus establishing a basis for further improvement and optimization of this fairly new process.

Development of a tele-operative control for the incremental tube forming process and its integration into a learning environment

A deficient access to experimental equipment leads to the usage of remote labs to improve engineering education and open experiments for every student location - and time - independent. The usage of a tele-operative controlled industrial bending process in lecture combines theoretical learning contents with practical experiences. Lecturers can make experiments in interaction with the students, who are able to assist in choosing the process values. The chosen and presented bending process is the incremental tube forming process that uses in contrast to many ordinary bending processes targeted the superposition of stresses. By superposing of stresses, in this process for example a tube bending and a tube spinning process, several fundamental process characteristics can be observed and integrated into lectures to visualize the theoretical fundamentals behind. Incremental tube forming combines the tube spinning process, which affects the diameter of the tube all along the tube and creates a compressive stress, and a bending process. The understanding of superposition of stresses and the process phenomena are ambitious, so that experimental experience is very useful. By using a tele-operative control, the experiment is location- and time-independent available for lecturers and students all over the world. They can interact with the process like stopping it, influencing it during the process or laying it up. The possibilities for a usage in learning environments are described and pointed out.

Development of a cupping test in remote laboratories for engineering education

A remote controlled cupping test for sheet metal as material characterization for forming technology is presented. This formability test is included in a tele-operative testing cell consisting of an additional testing machine, an industrial robot, and other necessary components for the automation and execution of experiments. First, a methodology is introduced explaining how the remote cupping test is realized. Afterwards, the integration of the cupping test in a remote laboratory is presented.

New process for flexible manufacturing of bent parts with variable arbitrary cross section

In accordance to the increasing demands in profile manufacturing the general profile geometries become more and more complex. The complexity is basically characterized by varying cross section geometry along the profile axis as well as a longitudinal curvature. A new process for the flexible manufacturing of curved profiles with variable cross section geometries along the longitudinal axis is introduced. The process is a combination of the incremental profile forming process and a free form bending operation and has a high potential for lightweight construction and energy saving. Beside the description of the process principle and possible machine setups, the potentials of the process are discussed in this article.

Incremental Tube Forming

The incremental tube forming process is an innovative approach to manufacture three-dimensionally bent tubes with varying cross sections. The process combination of a tube bending and a tube spinning process leads to a significantly reduced bending moment as well as to a reduced springback compared to a conventional bending process. Therefore, this innovative process combination is especially suitable for the manufacture of high-strength materials as well as thin-walled tubes. Besides the mentioned process phenomena the process allows the manufacture of tubes with varying cross sections. The diameter as well as the wall thickness of the tube can be varied and, therefore, the cross section can be adapted to the load case applied during the subsequent usage of the bent tubular part.