Stainless steel (SS316) plates within brazed plate heat exchangers are pivotal for guiding two fluids and facilitating heat transfer. Sheet metal forming simulation enables the prediction of defects like spring back and thinning. By adjusting the forming process parameters, these issues could be minimized. Leveraging the LS Dyna finite element software in this project, the forming simulation results, validated against experimental data, exhibited an error of less than 10% in calculating spring back and thinning.
Research Highlights
- The forming process simulation of the SS316 sheet was performed and utilized the three-parameter Hill 1948 Yield Criterion in the LS Dyna finite element software.
- To ascertain the plastic behavior and mechanical properties of the SS316 sheets, a specific tension test was conducted at three different angles relative to the rolling direction.
Challenges
Common challenges in forming plates for heat exchangers include geometric deviations from the Computer Aided Design (CAD) due to spring-back phenomena and sheet thinning in vulnerable areas. These challenges can result in reduced heat exchanger efficiency and potential fluid flow leakage.
Our solution
Metal plates within plate heat exchangers play a crucial role in facilitating heat exchange between two fluids. Typically shaped through a deep drawing process, these sheets ensure the correct formation of fluid channels, meeting the necessary heat transfer requirements. Accurate shaping of the fluid path geometry during the forming process is paramount, influenced by the mechanical properties of the sheet and forming conditions. Over time, operational wear can lead to the risk of hole formation in low thickness areas, increase potential fluid mixing, and leakage in such heat exchangers.
Numerous studies have explored the behavior of sheet metals in the forming process and their resulting geometry through the application of the Finite Element Method (FEM). Ensuring accurate inputs of mechanical properties into the software and determining the yield strength based on the actual conditions of sheet behavior are critical factors influencing the outcomes of this method.
To precisely characterize the physical properties and behavior of sheets in the plastic region, we conducted tensile tests in three directions—0, 45, and 90 degrees to the rolling direction of SS316 sheet (see Figure 2). These tests facilitated the determination of anisotropy coefficients, the work-hardening graph of the material, and various other mechanical properties essential for accurate representation.
Results from the tensile tests were input into the LS Dyna software for simulation, utilizing Hill’s yield criterion and employing 140,000 shell elements. The explicit solver was chosen to address large strain changes, non-linearity, and the dynamic nature of the problem’s conditions. To optimize computation time and considering the symmetry of the problem, only half of the forming process was simulated, and the results were extrapolated for the remaining half (see Figure 3).
To validate the simulation’s accuracy, we conducted a point cloud scan on the formed sheet from the experimental test and compared it with the simulation results. This comparative analysis revealed that the average deviations of the simulated model, when compared to the experimental sample, fall within the range of -0.12 to +0.14 mm.
Outcomes
- Simulation played a crucial role in anticipating potential tear areas in the metal sheet due to thinning during the forming process.
- Accurate predictions were made through simulation regarding the extent of deformation the metal sheet would undergo post-forming, considering the spring-back phenomenon.
Related Publications
Simulation of the forming process and the spring back effect of the spacer piece in mist eliminators using the finite element method
A. Shouri, S. M. H. Mousavi, P. Oliazadeh, Mohammad H. Farshidianfar
19th National Conference of Manufacturing Engineering (ICME 2023)