In the UMFO project, the new Flexible Strip Width Reduction Rolling (FBRW) process for rolling variable-width strips is being developed in simulation by the cooperation partner LASSO Ingenieurgesellschaft mbH. The further processing of the semi-finished products into variable-width profiles using flexible roll forming is to be researched at the PtU. To this end, the influence of the material inhomogeneities introduced by the FBRW on the profile defects during flexible roll forming will be investigated using a manufactured prototype.

This new process chain is intended to enable the continuous production of individualised, large-dimensional and variable-width strips for the manufacture of load-adapted beams with cross-sections that vary in the longitudinal direction in a cost-reduced and resource-saving manner. One potential application is the production of longitudinal chassis beams for the construction of trucks and semi-trailers.

Motivation

Flexible profiling processes, such as flexible roll forming, enable a high degree of product customisation while maintaining a continuous production process. Furthermore, they facilitate optimisation of installation space or integration of functions. At the same time, load-adapted beams with cross-sections that vary in the longitudinal direction of the profile are considered a key element of lightweight construction.

The semi-finished product required for this process is a sheet metal blank of variable width, whereby the cutting results in waste. The objective of the FBRW is to eliminate the need for cutting by directly forming variable-width strips, thereby combining lightweight construction and resource efficiency. The new process chain to be developed thus enables flexibility right from the start.

The flexible roll forming of variable-width profiles is currently being utilised to produce chassis side members in semi-trailer construction. A total of around 1.3 million semi-trailers (as of 2021) are manufactured for freight transport worldwide every year [*], which presents a significant opportunity for material savings. However, load-adapted carriers could also be utilised in the construction of railway, ship, and aircraft components as well as in the construction industry, aerospace, racking systems and electricity pylons.

[*] https://www.statista.com/statistics/743480/truck-trailer-production-worldwide/ (Website abgerufen: 20.11.2022)

Approach

The FBRW's innovative approach to the production of lightweight structural components made of steel is shown schematically in figure 1. In the first step, a previously calculated thickness profile is rolled into a billet using a flexible compression stand. The required thickness profile is determined by inverse modelling or simulations based on the desired band width. It is then rolled over several hot and cold rolling stages to form a strip with the required final geometry. The finished strip is coiled in step 2 and delivered to the processing plant. At the processing plant, the strip is directly formed into the finished lightweight structural beam in step 3 using the flexible roll forming process.

A significant challenge will be the further processing of the resulting inhomogeneous properties of the variable-width strips due to the varying degrees of rolling. Consequently, typical profile defects during roll forming, such as springback, twist or dents in the profile base that occur during flexible roll forming, can occur to varying degrees at different points.

At the PtU, the development of a model for flexible roll forming, with particular consideration of material inhomogeneities, as well as the process window, will be investigated and developed on the basis of simulations and experiments. Based on the analysis of the properties of the prototype produced in the laboratory, model validation, model reliability and generalisation for the new forming technology will also be carried out.

Acknowledgement

The presented research project is funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK) on the basis of a decision by the German Bundestag.

We would also like to thank our project partner LASSO Ingenieurgesellschaft mbH for its cooperation in the realisation of the project.

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