Modelling of an automotive instrument panel substrate using ANSA

Problem Statement:

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

Write a detailed report on your meshing process and also mention which method you used to extract the mid-surface along with the reason.

Theory-

The given component is an automobile's dashboard part called the instrument panel substrate. It is the underlying part that houses and provides mountings and support to all the other components of the instrument panel. The part is usually is an intricate geometry made out of plastics such as acrylonitrile-butadiene-styrene (ABS).

The complete external surface of the IP substrate has a uniform thickness. Most variations in thickness and form are found in the gussets that provide strength and locator pins that help in the assembly of the part.

Procedure -

1.) After importing the part, the CONS resolution is increased so that most minute parts are resolved.

2.) A topology is run for the complete part for surface definition and connections.

3.) It is quite likely that translational errors might have occurred while importing a geometry that had been created in different CAD software or they can also occur when the topology is run and improper connections are created between surfaces. To identify such issues, a geometrical check is run and tools under the topology module are used to resolve any and all issues. Following issues occurred in the model -

Triple Cons - These connections are formed where three surfaces meet and this is an error for such a part since as per its manufacturing process, such an occurrence is not possible. Hence these false connections need to be released, cleaned, and converted into double and single cons before moving forward. Triple Cons are shown as 'blue lines'.

Needle Faces - These are very tiny cross-section surfaces formed as translation errors when a part is imported from different software.

Unchecked Faces - Occurs when unnecessary CONS (connections) form near the edges of a surface and when the topology is run they convert into faces having no actual connection.

Overlapping Faces - As the name suggests when two faces overlap and improper connections form. Hence these false connections need to be released, cleaned, and converted into double and single cons before moving forward.

Crack between CONS - Sometimes a connection doesn't form automatically between two surfaces and single CONS are formed. This has to be repaired by making a connection manually.

4.) Once the geometry is clean, it can be prepared for meshing. Since it is majorly a uniform thickness part with most regions having a thickness below 6mm, the part will be converted into a shell to which thickness will be assigned. This shell is obtained by the process of the mid surfacing. The topology module provides multiple functions to obtain the mid surface of various elements of the part as shown below -

a.) Auto-Mid Surface (Skin) - The function automatically recognizes the top and bottom surface and the thickness of the part. Once the user confirms the automated selection, a mid surface is generated.

b.) Manual Offset - Here the user has to firstly measure the thickness of each part after which each surface has to be manually selected and offset by the distance that is half of the given surface's thickness.

c.) Faces -> Middle - The method can be used for elements of a part that have uniform top and bottom surfaces with neither having features on the surfaces.

d.) Curves converted to faces - For features of cylindrical nature like the locator pins of our model which are mainly to provide connection data, we represent them as 2D surfaces that capture the diameter and length of the part.

Although most surfaces of the part have a uniform thickness, due to the gussets and the locator pins on the bottom surface of the substrate the software is unable to distinguish between the various surfaces and produce a mid surface using the auto mid surface and middle function. To accomplish mid surfacing, we'll be using 'Curves converted to faces' for the locator pins and manual offset for the rest of the part.

5.) Parts like the gussets and the locator pins have to be joined to the substrate's shell using the extend function.

6.) Once all parts are captured as shells, we run another geometry check.

7.) Before moving onto meshing, thickness has to be assigned using the property manager to all the parts.

8.) The shell is ready and we move to the mesh module. Here we set the mesh and quality parameters as per the given criteria -

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

9.) Meshing

a) Now that we are all set for meshing, we firstly select an area to start from. A good practice would be to move from the middle of the part towards the outer edges. This leaves some flexibility for rearrangements while in the other case, the area becomes constrained by the surrounding mesh.

b) Once the area is selected, if quite large it has to be further divided into smaller regions to define the flow of mesh that you desire. This can be done using the 'Cut' and 'Project Cut' functions under 'Macros'.

c) Next, we generate a mesh for the given area using one of the automatic algorithms that suit our purpose under the mesh generation tab. In this case, I have used the 'Best' function. This function automatically meshes Macro Areas using all alternative meshing algorithms and keeps only the mesh of the highest quality according to quality check.

d) Although the algorithm generates the best mesh possible, there are still some best practices to be taken into account before moving onto the next area. Since most areas are not perfect rectangles, the mesh is a mix of tria and quad elements. Since trias do not deform as well as quads, they are avoided in structural analysis near sensitive regions such as fillets and bends. Also opposing trias and rotating quads can form which need to be removed. In some cases, quality issues might remain unresolved even though the 'Best' function is used. In all such cases, elements can be iterated to achieve the desired quality using the functions shown in the image below,

Some functions majorly used in this model are -

Reconstruct - It examines a given mesh and performs re-meshing to correct problematic areas and optimize the overall quality of the mesh according to the mesh parameters.

Smooth - This function automatically applies Smoothing attributes so as to 'relax' the mesh on already meshed Macro Areas or on FE-model shell mesh.

Split - This function splits quadrilateral and triangular shell elements into smaller ones. Element splitting is performed between selected nodes and/or inserted nodes along selected element edges. The function can be applied to individual or groups of shell elements in order to improve the mesh orientation, reduce the number of triangles, or refine locally or globally the mesh of a part.

Swap - The Swap function rotates the shell edge picked by the user, inside the two shells which have that edge as common.

10.) Once meshing of the part is complete, a solid version of the part can be visualized by ticking the 'Draw shells as solid option' under the quality parameters tab. This can be overlaid on the actual part and checked for any inconsistencies.

Output -

Learning Outcome -

1) Geometry cleanup and performing topology.

2) Generating mid surface

3) Assigning mesh parameters, quality parameters, and properties.

4) Mesh Generation using different algorithms and fine-tuning the mesh using various functions.

5) Converting shell mesh to solid.

Conclusion -

Firstly, uniform thickness parts can be meshed using 2D elements. This is done to save processing power and time. Secondly, off elements, rotating quads and trias, more importantly, the ones face each other and the ones near open edges, features, fillets, and bends should be avoided at all costs. And lastly, mesh flow is very important for the proper transfer of information along the complete part.

Google drive link -

https://drive.google.com/file/d/16-MgnSn28Q52528ggQDtB8nfu4e0o0nm/view?usp=sharing