Week 12 - Project-1

MESHING THE PLASTIC COMPONENT OF A CAR SIDE DOOR USING HYPERMESH

Aim: To extract the mid surface of the given plastic component and mesh the model according to the given quality criteria and apply thickness.

Tools used to perform the above objective are:

• Quick edit:The Quick Edit tools can be utilized with the option to force the immediate re-meshing of surfaces after a topology change (set in the Meshing Options panel accessible from the Preferences menu's, Meshing Options sub-menu; the setting is labeled topology revision on that panel.
• Auto clean up:Use the Autocleanup panel to perform automatic geometry cleanup and prepare your model for meshing based on the parameters set in the Batchmesher criteria file.
• mid surfacing:Use the Midsurface panel to extract the midsurface representation of a solid part or to generate a finite element shell representation of a solid geometry.
• Auto mesh:Use the Automesh panel to generate a mesh of plate elements using surface geometry or existing shell elements to define the mesh area.
• Element clean up:Use the Element Cleanup panel to perform automatic cleanup of 2D elements based on the element quality criteria from the Quality Index panel or a separate criteria file.
• Quality index:Use the Quality Index panel to calculate a single value to represent the quality of the displayed shell (2D) model.
• Smooth:Smooth panel to improve element quality in a surface-based mesh or a mesh of solid elements using one or more algorithms that adjust node positions to moderate sharp variations in size or quality in adjacent elements.
• Rebuild:Use the Rebuild Mesh panel to streamline the process of remeshing existing meshes to generate a new mesh with good quality and flow.
• Split:Use the Split panel to split plates or solid elements. In addition, hexa elements can also be split using a technique that moves progressively through a row of elements in the model.
• Edit element:Use the Edit Element panel to hand build, combine, split, or modify elements.
• Replace:Use the Replace panel to relocate one node to the position of another or manually equivalence two nodes.

Procedure:In order to accomplish the above objective we need to follow following steps:

1. Import the CAD model into hypermesh.
2. Geometry clean up of the model.
3. Extraction of mid surface using various techniques.
4. Perform the 2d-mesh on the mid surface.
5. Eliminate the elemental failure as per the quality criteria.
6. Apply the thickness and convert the shell elements into solid elements.

Step 1: Import the CAD model into Hypermesh:

We import the CAD file into the hypermesh and radioos as profile,using import geometry in the menu bar.

Step 2: Geometry clean up for the given model:

In order to extract the midsurface we make sure that the cad model imported is free from topology errors i.e any deformation occurs while importing the file into hypermesh or any errors present in the cad file itself or any overlapping of surfaces.If any such errors are present we eliminate those errors.In this model we delete the surfaces which are not useful and also fixed some gaps present between the surfaces.

Step 3: Extraction of mid surface using various techniques:

Now the given plastic component is free from topological errors,now we can proceed to extract the mid surface of the component.We first extract the midsurface using auto extraction method.

Due to extraction of midsurface using auto extraction method there are some surfaces gets overlapped and some surfaces gets distorted due to the complexity of the model.

so we delete those surfaces created by auto mid-surface and we extract those surfaces using manual surface extraction method i.e we first duplicate the required surface and then we offset the duplicate surface to the required dimension based on the surface thickness.

We also carried out several geometry edit in order to obtain good quality mesh.We toggle the unwanted topology edges.Some surfaces are extended and trimmed some fillets are eliminated which makes the mesh fails in quality checks.Now the midsurface is extracted properly as shown in the figure.

Step 4: Perform the 2d-mesh on the mid surface:

• In order to mesh the midsurface we make sure that the extracted mid surface geometry is clean.
• We mesh components using automesh in 2d mesh pannel.

• We mesh the midsurface by assigning the element size as 4mm and element shape as mixed.
• We mesh the complex surfaces first in order to maintain the proper mesh flow and make meshing easier.
• While meshing the midsurface we make sure that the we maintain the trias percentage as low as possible.
• While meshing curved or complex surfaces if the mesh doesn't properly catch the surface properly then we increase or decrease the node count so that mesh attaches the surface properly.
• We use the rebuild or smooth option while meshing in order to maintain the proper mesh flow.

Step 5:Eliminate the elemental failure as per the quality criteria:

• After meshing the midsurface by assigning the target length as 4mm and shape as mixed i.e(quad and tria).
• We make sure the mesh we generated on the midsurface pass the given quality criteria.

S.N	Quality Criteria	Value
1	Aspect Ratio	5
2	Skewness	45
3	Warping	15
4	Taper	0.5
5	Min. Length	2mm
6	Max. Length	6mm
7	Min angle Quad	45
8	Max angle Quad	135
9	Min angle Tria	20
10	Max angle Tria	120
10	Tria %	10

• This is performed in 2d>quality index>check elements.
• We use various options like rebuild,smooth,split elements,create elements,move node,drag trias etc in order to eliminate the errors caused due to the violation of quality criteria.
• We eliminate the rotating quads and the trias present near the topology edges.
• We also reduce the trias concentration by dragging the trias to the free ends or combing the opposite trias by dragging them near to each other.

Step 6: Apply the thickness and convert the shell elements into solid elements:

• After completion of meshing the midsurface,we now assigning the thickness to the midsurfaces.
• For assigning the thickness we create the property and in property we add the thickness value to the property and then we assign the property to the required surfaces in the midsurfaces compnent.
• Due to the given CAD model is plastic component,the thickness was not same for all the surfaces so we need to create the different thickness required for the different surfaces.
• The thickness we assign for the different surfaces are as shown below;

Conclusion: The given plastic component is meshed by extracting its mid surface and we assigned the thickness as required.

The mesh that is generated also passes the quality checks.