In today’s fast paced development cycle, the role of employing a digital design solution cannot be minimized. At almost every design step, from creative rendering to the 3D printed consumer testing prototypes some electronic version of the package geometry is employed.
A growing trend is to validate designs through performance simulations. More and more CAD files are first transferred to simulation software rather than to a CAM software for generating the tool path for mold manufacturing. In this new routing, the CAE simulation software predicts performance by meshing the CAD generated geometry besides applying realistic loads and boundary conditions. The meshing techniques commonly employed breaks up the CAD generated surfaces into many small quadrilateral and triangular elements. For purposes of load propagation, these meshes need to be connected with no open ends for the forces to balance. Elements that are too small or too big or have large aspect ratio typically do not deliver accurate results. This is due to the corners of the element being not equidistant from the centroid. Hence CAD construction that renders small slivers are typically a problem. The typical workaround is to either neglect that small feature using a smearing technique to smoothen the topology or recreate the geometry for that region.
It might be argued that there is no problem constructing the mold with the file. So why the fuss for FEA simulations. The reasons can be that more and more geometry is being analyzed this way. This helps streamline the process improving efficiency and preventing manual intervention to rectify these anomalies. Additionally, the FEA meshing technique would catch any holes or surface mismatches that is the goal of every CAD engineer to avoid. The topology correction can cause unintended interpretation of geometry and lead to inaccurate predictive results. Additionally, most stretch blow molded plastic does not fill geometry with sharp corners and deep and narrow outward ribs. We often encounter under blown or less sharp molded features in reality. The rational thing to do would be perhaps design the CAD exactly how the plastic blows. Not only would this then cause the geometry to be accurate but the simulation as well for replicating the blown geometry well. The greater benefit is a quality CAD part that has now been reviewed by a meshing algorithm and highlighted key areas to be addressed. The end result is a CAD design of higher quality that does not break easily and is future proof.
About the Author
Sumit Mukherjee
Director of CAE and Simulation at Plastic Technologies, Inc. His 23 years of experience includes finite element analysis (FEA) for package performance prediction. Mr. Mukherjee obtained his Bachelor’s degree in Chemical Engineering from the Indian Institute of Technology in India and earned a Master’s degree in Polymer Science and Engineering from the University of Toledo Polymer Institute.