Project 1 - 2D meshing on the instrumental Panel

 2D-Meshing of IP-Substrate of the car

Aim: For the given component, check for the geometrical errors and mesh with the given element Quality criteria. After meshing the component, thickness has to be assigned.

S.No	Quality Criteria	Value
1	Target/Average length	4
2	Minimum Length	2
3	Maximum Length	6
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum  Tria Angle	30
11	Maximum Tria Angle	120
10	Tria Percentage	15

Note:

• Dog house in this model should be captured as "Cross pattern" in Mid surface since dog houses are solid (Hollow from inside) and is not having any thickness.

Objectives:

• Generating the mid-surface from the parent component
• Performing a meshing operation on a middle surface as per element quality criteria
• Checking the element quality by comparing with given quality parameters and criteria and improve the quality by various options
• Assigning the material and proper thickness to it

Theory:

Why we do Geometrical cleanup?

While we importing any geometry data it generally come up with little errors, some geometrical issues are

Surfaces are not stitched together.ie. (there is a gap present between the surfaces)

Very small surfaces are squeezed between the surfaces.

Sometimes duplicate surfaces are present

The junction between the two surfaces also contains the gaps, overlaps and misalignments.

In order to remove that issues and errors we do geometry cleanup.

Mid-Surfacing:

Why we create the Mid-surface?

While doing 2D meshing we extract the mid-surface from the model. Mid-Surface means the surface between the two surfaces. 2D meshing is carried out on the mid-surface, because mathematically element thickness we assigned half in +Z axis (element top) and half in -Z axis (element bottom). Hence for appropriate representation of geometry via 2-d mesh it is necessary to extract the mid-surface & generate nodes and elements on the mid-surface. We try to create the shell elements (one dimension i.e. thickness is significantly smaller than the other dimensions) which is 2D representation of 3D elements. Mid-Surface meshing is used when the geometry thickness is very small as compare to its length and width, so we are generally used in most of industries where structure is made up of sheet metals and plastic etc. In that case, we use 2D elements instead of 3D elements, hence by adopting Mid-Meshing number of nodes are decreases and also computational time decreases.

We can extract mid-surface in two ways

• Manual mid-surfacing
• Automatic mid-surfacing

Here for above component, we choose manual mid-surfacing because the given model is of plastic / casted one, so thickness is not constant throughout, if we use automatic mid-surfacing and meshing it will not give us accurate result, user have to do lot changes in model to repair, so that’s why we choose manual mid-surfacing, in manual mid-surfacing we use offset option to create middle surface

During meshing we have to take care about

• Feature should be capture properly
• No back to back trias
• There should be element connectivity between the elements
• No opposite trias
• No rotational quads
• Quality check to ensure that all element are within good quality

Note: During meshing make sure to check for free edge option at regular interval. It will help us to show that where there is no element connectivity in the mesh

Plastic Meshing:

• Plastic meshing is a type of shell meshing where the thickness of the component will vary
• Mid-Surface extraction plays a major role in plastic meshing
• The mid-surface extraction is somewhat tricky when compared to sheet metal meshing

 Best practice to be followed while meshing a plastic component

• Check if the component is symmetric or not
• If it is symmetric, extract the mid-surface only for half portion
• If component is not symmetric, extract the mid-surface for whole component
• We have to check the auto mid-surface for the component, if it is not giving the better result then, we have to jump to other methods
• Split the component into simple parts and try to extract the auto mid-surface
• The distorted surface can be deleted and by using offset and extend command we can stich the surface
• If auto mid-surfacing is not doing well, then we have to do the whole component
• While extracting the whole mid-surface manually we have to be more-clear about the base surface, since base surface should not having varying thickness in the most cases
• After creating the base mid-surface, we have to take a look at the ribs attached to mid-surface (we can use surface pair to generate the middle surface and extend the and extend the rib to base mid-surface
• If ribs are within same dimensions, we can use the translate rotate and position option in order to create them again.
• After that the mid-surface of critical parts like dog houses snap fits, mounting clips etc can be extracted by surface pair and offset option.
• Check the rib surface are connected properly to the base. There should be a T-Connection between the base mid-surface and ribs surface
•  Meshing the surface from the complicated region and moving toward free edges

Model:

IP-Substrate

• Using Topo-option to stich the surface

• After that we have to check the geometry quality by using the check option in ANSA

Checking geometrical errors

• After finding all the error, the next step is to be removing all the error from the geometry and make the geometry clean

Geometry is cleaned properly

• After cleaning the geometry, the next step is to taking a mid-surface from the geometry, here it is a plastic component, so thickness of component may vary, so we have to use the manual approach to take the mid-surface of the component. So, we are using offset option to make a middle surface of the parent component.

Extraction of middle-surface by using Offset option

Mid-surface extraction of rib

Note: After extracting the mid-surface, make sure to extend the mid-surface to base geometry to make a connection

Rib is extended to the Base-Surface

Extracted Mid-Surface

• Along with creating a mid-surface we are creating properties and assigning a thickness to each and every component that having different thickness.

• After creating the mid-surface, now we can start the mesh, but before mesh we have to set Quality criteria and mesh parameter

Quality Parameter

Mesh Parameter

Meshed model of Ip-Substrate

• To check the thickness, go to presentation parameter and check the option Draw shell as a solid to visualize the thickness

Thickness is assigned properly to rib 

Final meshed model:

Learning outcomes:

• Understanding about plastic meshing
• Understanding about manual method of mid-surface extraction
• Understanding the difference between plastic meshing and sheet metal meshing