Roll Forming and Flow Splitting

Roll Forming and Flow Splitting

Research in the field of roll forming has been one of the core topics at the PtU since the 1970s. Today, two roll forming lines with over 30 stands are available to the institute. In addition to conventional roll forming stands, a variety of new developments has been integrated successfully, such as automated calibration stands, linear flow and bend splitting processes as well as stands with additional degrees of freedom for the manufacturing of profiles with varying cross sections. Current research focuses on four areas: flexibilization, improved methods of process design and dimensioning, the use of roll forming process to introduce additional functionality into the part and continuous splitting processes.

Flexibilisation

A significant part of roll formed products is used as structural components and therefore subject of lightweight design. Load adapted cross-sections are an effective tool of realizing the lightweight idea. However, cross-sections of typical roll formed parts don’t change along the longitudinal direction. Instead, they are designed to withstand the maximum loads at critical points. Oversizing and material waste are the result of this. Flexible roll forming solves this problem by adding additional rotational and translational degrees of freedom to the roll forming stands. In doing so, roller positions may follow changes of the desired cross-section. A similar approach allows for the roll forming of blanks with variable thickness in the longitudinal direction, the so-called Tailor Rolled Blanks (TRB).

Methods of process design and dimensioning

Incremental forming processes enable for an increased flexibility in forming, low forces and the processing of materials which are usually hard to form. By incremental forming technology, technically demanding parts with optimized material properties can by realized. Main focuses in the department process development are spinning, flow turning and rotary swaging. Also the advancement of simulation methods is regarded. Furthermore, the integration of actuators in structures by incremental forming is investigated.

Methods of process design and dimensioning

One of the basics of all bending process design is a determination of the required bend allowance. A variety of scientific and industrial methods are state of the art. However, in calculating the unfolded length of profiles different approaches provide (at times heavily) differing results. The objective of one of our projects is to derive an unified and improved method for bend allowance calculation on the basis of extensive experimental investigations on roll forming, folding and die bending. Another important goal is a reduction of set up times for roll forming machinery. An in-line measurement of the roller imprint on the workpiece provides data directly relatable to roller positioning errors. Current researches investigate how this relation may be exploited to shorten set up times. Another highlight project is targeted on an acceleration of finite element roll forming simulations. The developed algorithms make use of similarities within the forming process and so far were able to reduce computational time for the simulation of simple roll forming processes by 50 %.

Splitting processes

Linear flow splitting and bend splitting are two process developments of the PtU. They are used for manufacturing metal sheets with integrally bifurcated cross-sections at room temperature. Bifurcations can be created at the band edge (linear flow splitting) or somewhere else on the sheet (bend splitting). In contrast to roll forming, these continuous bulk forming operations avoid double layers of material. Combined with conventional roll forming stringer profiles and multi-chamber profiles made of high strength steel can be manufactured from the coil. Current projects targets are dedicated to the development of flexible flow splitting. By analogy to flexible roll forming this process allows bifurcated cross-sections changing along the longitudinal direction.

Integration of functionality

Due to their sequential arrangement roll forming installations are easily integrated with other manufacturing operations. Using a forming operation not only to shape a part but also to introduce further functionality is an idea that leads to profiles with integrated electrical conductors. Following this idea metal conductors are introduced to roll forming work pieces before or during the forming process. Sheets and conductors are then formed simultaneously to profiles with closed cross-sections and built in electrical circuits.

Current research projects