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Roll forming of a high strength aluminum tube
The presented paper provides a modelling strategy for roll forming of a high strength aluminum alloy tube. Roll forming allows the cost-effective production of large quantities of long profiles. Forming of high strength aluminum brings challenges like high springback and poor formability due to the low Young’s modulus, low ductility and high yield strength. Forming processes with high strength aluminum, such as the AA7075 alloy, therefore require a detailed process design. Three different forming strategies, one double radius strategy and two W-forming strategies are discussed in the paper. The paper addresses the question whether common roll forming strategies are appropriate for the challenge of roll forming of a high strength aluminum micro channel tube. For this purpose, different forming strategies are investigated numerically regarding buckling, longitudinal strain distribution and final geometry. While geometry is quite the same for all strategies, buckling and strain distribution differ with every strategy. The result of the numerical investigation is an open tube that can be welded into a closed tube in a subsequent step. Finally, roll forming experiments are conducted and compared with the numerical results.Current research in production technology focuses primarily on increasing resource efficiency and thus follows the approach of fundamental sustainability of processes and products. High strength aluminum alloys (e.g. AA7075) are commonly used in aerospace applications in spite of their high cost of about 5 €/kg and poor formability [1]. Due to ambitious legal requirements, such as the CO2 target in automotive engineering, new lightweight construction concepts are still needed [2]. An excellent basis is offered by the production of high strength AA7075 thin walled tubes as semi-finished products by roll forming. These can be further processed in subsequent customized processes such as welding, stamping, cutting or rotary swaging.
According to DIN 8586, roll forming is a bending technology with rotating tool motion to produce open and closed profiles [3]. Several pairs of forming rolls are aligned one behind the other for the forming process. The friction between the rotating forming rolls and the sheet metal causes a forward movement of the sheet. Simultaneously the sheet is formed in and between the stations. For the production of large quantities, roll forming is a cost-effective manufacturing process, compared to tube extrusion or tube drawing. Roll forming can also be competitive for smaller quantities, if the number of forming passes is small enough [4]. The incremental nature of the roll forming process also allows forming of high strength materials, such as ultra high strength steel (UHSS) [5].
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