Finite Element Analysis in Roll Forming Applications

This white paper gives a brief overview of the roll forming process and then describes how FEA can positively affect roll-forming manufacturing applications by reducing development and testing time, which will enhance productivity and profitability for manufacturers and their clients alike.

Finite Element Analysis (FEA) is a computer-driven modeling method used to evaluate the quality and performance of products and processes prior to actual production. When applied to the roll forming process, FEA qualifies the design of the roll tooling prior to its manufacturing.

Roll forming is a manufacturing process in which a continuous strip of metal (typically coiled) passes through consecutive sets of rolls, or “forming stands”. Each forming stand gradually forms the strip into the desired cross sectional shape. Unlike other common metal forming methods, roll forming’s flexibility allows secondary processes to be integrated into a single production process.

Holes, slots, or other features are easily added by combining prenotching, midnotching, or postnotching to the roll forming process. Roll forming excels in applications that require high-volume production runs of metal parts with tight tolerances and consistent, complex cross sections. The process can accommodate material gauges typically ranging from .010 in to .375 in thick and is an effective alternative to extrusion, press brake and stamping processes.

WHAT IS FEA?
Finite Element Analysis (FEA) is a mathematical modeling method. A wide range of studies can be performed by applying FEA – heat transfer, fluid dynamics, and structural analysis to name a few. It is also used for product design and structural analysis under both static and dynamic loading. RFC uses FEA for these traditional means, but what separates us is the use of FEA for analyzing the roll forming process. Therefore, this white paper is only discussing the topic of how FEA is applied to roll forming.

In the early years, FEA programs were based off the “linear” or elastic region of the stress-strain curve. Failure would occur once the structure exceeded the yield point of the curve. Today, because of advancements in software and computer technologies, FEA programs use both the elastic or “linear” and plastic or “non-linear” regions of the stress-strain curve. These advancements have provided the engineer with a tool that will allow the analysis of “deformation” or how a body will deform under various loading conditions.

This ability to study deformations is what makes FEA a great tool for analyzing the roll forming process. The material strip deforms as it contacts the forming passes. If modeled correctly one can see the effects on the forming of the rolled shape. These effects show up as residual strains and deformations in the part as it exists in its “free state” or unloaded position.

The FEA model is broken down into a mesh of small elements. Results needed from the study dictate the required density of the mesh. Typically, a higher mesh density in the area of study is used. The intersection points of the mesh represent nodes. The FEA program solves the calculations necessary to establish equilibrium at each node. Inputs to the model include the mechanical properties of the material. One can study the effects of different materials on the model by changing these properties. The results from the FEA study can be depicted in the nodes with each node having its own displacement and state of strain or stress. These values are graphically displayed on the computer screen and can be quantified for the engineer to analyze.

Today, FEA is a computer-driven tool used by engineers to conduct virtual research and development evaluations to test new product designs or to refine existing product specifications before prototype production – allowing engineers to more cost-effectively manage product design, development, and fabrication.

FEA IN ROLL FORMING
When applying FEA to the roll forming process the material strip is considered a deformable body. The roll tooling is defined as a “rigid body” or fixed in position. One is studying the effects of the roll tooling geometry on the material strip. The strip is broken down into elements and the mechanical properties are defined for the strip. As the strip feeds through the roll forming mill it makes contact with the surfaces of the roll tooling (see Figure 1).