Week 3 - 2D meshing for sheet metal

AIM: for given hood model , take out mid surfaces for all the components in the model,

mesh these midsurfaces with given quality criteria ,and assign the thickness

GIVEN DATA:

Here given data provide are

1.Quality criteria -

Every product which has been produced will go through the set of quality check .

if the quality check is fail other steps like boundary condition & applying loads

will not be feasible ,

The criteria provided is mention below in the table

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

2.CAD Model -

the provided CAD is of Hood Panel of car consisting of five components

1. Latch
2. Left hinge
3. Right hinge
4. External extrude panel
5. Internal extrude panel

Steps involve

1. To check all the geometry error and rectify them
2. To check the thickness of all the components in the model
3. To extract the mid surface from the geometry
4. To generate mesh with good flow in the given quality criteria

PROCEDURE :

1) Check For Undefined Material:

< PROPERTIES > Here we can observe how many components are there in the geometry

according to how many property ID's are present

< MATERIALS > Here how many material properties are available and are they defined or not.

if not we have to ONN the mark sign to defined or undefined it.

Then check for undefined materials in checks manager .

2) Check The Geometry:

Here we have to check geometry issue with CAD before going to mesh it.

it is an important stage.

<< CHECKS MANAGER > GEOMETRY >>

Latch , L Hinge, R Hinge , External Extract panel

On checking these PID's for geometry . We didn't get any geometrical issues .

Inner Extract Panel :

Here it was failed for 51 issues on first check

On auto fix all 51 of them get resolved , if they were not we have to do some operations to get

them resolve such as releasing cones, deleting unnecessary hot point / cones , inserting hot point

if required doing Topo .these operations had to be done in accordance of problem in hand.

3) CHECK THICKNESS EACH COMPONENTS

Here we have to check the thickness of each component in order to assign it in properties .

The thickness we get on checking is as follows :

1. Latch =1.2
2. L hinge =1.2
3. R hinge =1.2
4. External extract panel =0.75
5. Inner extract panel =0.75

4) MIDSURFACING

There are two methods by which mid surfaces can be extracted 1. auto mid , 2 .manual method

for this project we only gonna use manual mid surfacing for that << FACES >OFCET >> and select the region

where mid surface is to be extracted.

Picture below shows the mids of the.

• Latch
• L hinge
• R hinge

For

• External extract panel
• Inner extract panel

we use << FEATURE AREA COMMAND >> as there are multiple regions to select .

Feature area command gives single click selection of our region of interest . Thus

reduces region selection time.

<< FACE >OFSET > FEATURE AREA AT 40 DEGREE (IT WILL ONLY SELECT THOSE

AREA WHOSE ANGLE IS LESS THAN 40 DEGREE ) >>

5) Set New PID'S To MID'S

Here we set new PID's to dIfferent component and refine the geometry to better

understand it's feature.

Assigning these PID's as follows.

• Latch
• L hinge
• R hinge
• External panel
• Inner panel

6) Checking Mid Surface Geometry

Check the geometry again for mid surface.

Here latch , l hinge , r hinge , external panel has pass the check

For this check Inner panel was failed for multiple issues.

To fix this we do the auto fix.

7) Sizing Perimeter, Defeaturing & Mesh Preparations :

• Change all perimeter element distance to 5mm
• Confirm whether perimeter element distances are in acceptable range

Here in latch hole some elements having un uniform distance between perimeter element

By removing unnecessary HOT POINT and again resizing perimeter elements distance

we can bring distance to acceptable range

Make sure hole edges are parallel to adjacent edges . Like here in the hinge

Here region is too small & it might fail in minimum length criteria so we have to

DEFEATURE it.

Make sure that every hole's perimeter is even.

To get better mesh flow make appropriate changes in construction line .it is

recommended to divide the region into rectangular or square form.

Here in inner extract panel the geometry is bit complex so we check for symmetricity

for that we use << topo>face>{Rm Dbl} >>.

Doing Symmetry reduces much time and efforts.

The blue and green colour indicate symmetrical portion in the selected component,

in here except latch all other portion are symmetrical .

After identifying .

Hide unsymmetrical portion and delete half symmetrical portion

8) Defining Quality Criteria & Meshing Parameters

Input all the given QUALITY PARAMETERS.

10) Meshing

Definition - A mesh is a network that is formed of the cells & points . It can have almost

any shape in any size & is used to solve partial differential equations each cell of the mesh

represent an individual solution of equation which , when combined for the whole network

result in a solution for entire mesh.

For good mesh quality divide the domain into appropriate sections by using

<< CUT / JOIN COMMAND >>.

To apply mesh use << BEST MESH < MESH GENERATION>> and to remove the mesh use

<< ERASE < MESH GENERATION >>.

Clear the mesh quality by the combination of

<< RECONSTRUCT/ SMOOTH < SHELL MESH >> (for automatic alternate mesh

suggestions / pattern smoothing effect ), << SPLIT /SWAP / JOIN <ELEMENT >> (to

remove the trias and manipulate them ) ,<< MV surf < GRIDS >>(to adjust the element

within surface ), << CUT /JOIN /EDGE2PERIMETER < MACROS >> (Defining the region

to mesh )

Rules to be kept in mind :

. Trias should be less but should be kept where it is necessary

. Trias should always move/point towards diverging sections

. Rotational pattern should be avoided

. Uniform perimeter element number should be ensure before meshing

. Unnecessary hot points should be removed

. Feature area and fillet region should be given more care

. Element should not be fail in any quality criteria

1.Latch

2.L Hinge

3.R Hinge

4.External Extract Panel

As external panel is symmetrical we use symmetry method to do mesh in which we

have to do mesh on half part and other half will generate on doing symmetry.

5.Inner Extract Panel

Do mesh on half symmetrical panel

After meshing on half side do symmetry and then unhide latch which was not symmetrical

And do the mesh on latch portion as well thus completing mesh on inner panel

10) Assigning thickness:

Finally we have to input the thickness values in << T < properties manager >>

which we have measured earlier for respective PID's.

Learning outcomes :

• At the end of this challenge , i can able to
• Perform geometry clean up for any complex sheet metal components
• Generate midsurface / skin for any complex sheet metal components.
• Generate the shell mesh meeting the given quality criteria for any complex sheet metal components
• Identify the quality failure and resolve the failure & improve the mesh quality
• Working with ANSA

Conclusion:

Hence midsurfacing / meshing / and assigning thickness is done successfully

To conclude

. Manual mid surfaces gives more accurate results

. Cut/ construction line to divide critical region for meshing, helps in better mesh flow

. Changes in feature line should be only done when elements are failing