Week - 4 - 2D meshing for Plastic components

AIM

• To extract the midsurface of the given plastic component & to carry out necessary geometry cleanup operations.
• To mesh the extracted midsurface and to validate the FE model based on the given quality criteria.
• To assign the appropriate thickness to the FE model.

PROCEDURE

• Since the given component is a plastic, using the 'Midsurface' tool to extract the midsurface won't be a feasible option. Hence each feature of the component should be offsetted to the neutral plane by assigning appropriate offset distance based on the thickness of each feature.
• First it is necessary to extract the midsurface of the base of the component as shown below.

• The regions with geometric discontinuities are filled using the 'New' tool under the 'Faces' panel as shown below.

• Now the midsurfaces of the various features such as teeth, threads and ribs are offsetted based on their thickness.
• In the figure shown below it is seen that for extracting the midsurface of the circular thread, a midline is created on the thread using the 'Middle' tool under the 'Curves' panel. This midline is projected on to the base surface.

• Finally a face is created between the two lines, hence creating the midsurface of the circular thread as shown in the images below.

• Similarly the midsurface for the teeth is extracted as shown in the images below.

• Now in order to replicate the rest of the teeth along the circumference of the base surface, the 'Copy' tool under the 'Transform' panel is used. Within the 'Copy' tool the 'Rotate' option is selected. Two COG points have to be created beforehand inorder to establish an axis of rotation. Also the number of steps and the angle between each tooth is provided. On confirming the operation, the tooth gets replicated as shown in the image below.

• As shown in the image below, for each feature a property is created based on its thickness using the 'Set PID' tool under the 'Faces' panel.

• After extracting the midsurface, it is made sure that there are no irregularities in the geometry using the 'Geometry Check' tool. The next process is meshing, before which it is necessary to set the quality criteria as shown below.

• Also the shell element size is preset to 1 unit using the 'Length' tool present under the 'Perimeters' panel of 'Mesh' module as shown below.

• While meshing the midsurface, each surface of the component is meshed seperately using the 'Best' tool present under the 'Mesh Generation' panel of 'Mesh' module. The regions where the the mesh is not refined are remeshed using the 'Reconstruct' tool.

• Since we are preparing this model for crash and safety simulations, we have to avoid rotating quads at any cost. The tria elements are acceptable but should not conflict with each other ie. adjacent trias and trias facing opposite to each other should be avoided.
• The conflicting trias can be rectified using the 'Spilt', 'Join' & 'Paste' tools. Finally the 'Smooth' tool is used to improve the uniformity of the generated mesh.

• Finally in order to visualise the shell element as a solid, 'Draw shell as solid' checkbox under the 'Presentation Parameters' panel of the 'Quality Criteria' tool is selected.

LEARNING OUTCOME

• The various tools concerned with geometry cleanup, midsurface extraction, & mesh generation were learnt during the course of this project.

CONCLUSION

• The plastic model of the bottle cap provided has been meshed as per the given quality criteria and the appropriate thickness has been assigned to visualise the shell element as a solid.