Wrinkling study in flexible roll forming of high strength automotive components

Researcher: Sadegh Ghanei

Aim:

The main target of this project is to develop a fundamental understanding of the wrinkling shape error in the flexible roll forming (FRF) of high and ultra-high strength steels (HSS and UHSS). This knowledge is implemented to manufacture a wrinkle-free profile having a cross-section which is variable in depth or width.

 

Background:

HSS and UHSS have limited formability, therefore, their lower formability is a great challenge for implementing them in the vehicles. In the last decades, the hot stamping process has developed for manufacturing automotive components from the HSS and UHSS. Taking into account their achievements in the automotive industry, high tool wear, crack formation during the forming of high strength components, costly and complexity of the process design are some of the most considerable drawbacks of this attractive forming process. Thinking of a substitute, the FRF offers higher flexibility in the production line because of a computationally controlled forming system. It implements the rolls which can move by translation or rotation, producing a profile with a variable cross-section. Therefore, a wide range of different components can be created without a need to change the tooling, which makes it a cost-effective substitute for conventional stamping. Due to the implementation of a stepwise forming concept, it can be a good substitute for the stamping process when forming of HSS and UHSS considering their limited formability. Some common shape errors are occurring during the FRF. Web warping as the deviation of height in the web area of the profile and wrinkling in the flange, are two most critical shape errors. Both increase with material strength. Thus, those shape errors will be the most critical issues to be considered during the FRF of high strength steels.

 

Methodology:

Below approaches has been proposed to address the research challenges related to the fundamental wrinkling study:

• Constructing accurate finite element analysis (FEA) models of the FRF (according to experimental trials) to investigate wrinkling. Using the FEA models to study the shape and stress evolutions in FRF.
• Examine if the forming condition in Deakin’s 3D forming facility produces the same forming condition as the conventional FRF. Find the differences between both approaches in terms of dominant shape error mode.
• Find a measure to determine the severity of a wrinkle. Determine the wrinkle initiation based on a valid criterion which is in agreement with the shape evolutions. Distinguish a buckle from a wrinkle. Find out the differences between buckle and wrinkle in elastic or plastic modes.
• Determine the efficiency of the hat forming process in avoiding or compensating wrinkling. Apply findings to optimise a hat forming process.
• List all the valid geometrical and material parameters which affect the wrinkling initiation. Divide them into two categories: first, parameters with a direct effect on the critical level and second, parameters with the only influence on stress or strain measurements.
• Try to solve the complex problem of wrinkle initiation prediction. An analytical method is followed to predict wrinkling. Optimise the geometry to find a wrinkle-free sample based on the proposed analytical calculations.
• Try to find out effective compensation routines. Optimise the hat characteristics to reduce more the severity of wrinkling.