Week 3 - 2D meshing for sheet metal

2D MESHING FOR SHEET METAL

Aim:

Creating the mid surface for all the components of the given CAD model after checking the geometrical errors and meshing the mid surface with the given element 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.

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	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
10	Tria Percentage	15

METHODOLOGIES ADOPTED:

1. Geometry Cleanup
2. Mid-Surface extraction
3. Mesh creation, Quality check & assigning thickness

PROCEDURE:

Import the cad model and start the 1st operation 'Geometry Cleanup'.

• Check if there are any errors in the given model using Check manager(Checks>Geometry>Execute). If errors are found, it is to be corrected & in this model there were several errors like thriple cons, needle faces etc. These errors are removed.
• To remove the errors certain commands are used such as:
  • Autofi
  • Cut
  • Topo
  • Creating new surfaces if necessary
  • Delete hot points at unnecessary places
  
• Then Check the thickness for each component by measuring option. This operation is very important for the purpose of creating Mid Surface.

• Measuring thickness and orienting the geometry

  • After measuring the thickness and storing the thickness extract the mid surface by using offset option. For extracting the mid surface, the entire geometry has to be oriented accordingly which results in easy extraction of the mid surface.
  • To orient the geometry go to Faces>Orient>then select the geometry (Grey is positive & yellow is negative)

Next is the 2nd operation 'Mid Surfacing'.

• For extracting mid surface go to Faces>Offset>Select the entities>Enter the offset value(Half of the thickness).
• To select faces for extracting, there two methods:
  1. We can select manually by clicking on the cross lines on one side of the surface.
  2. Other method by using the feature caption option set an angle and select any of the cross line this will select the whole one side of the surface.
• Now the mid surface is extracted, given below is an example:
• Repeat this procedure for the rest of the all components.
• In the hemming region(in the Outer panel’s bend region), Elements will fail for the Min length error due to the very small surface to capture the curved surface.In order to solve this Min length error, 'Defeaturing' operation is to be performed. Toggle (suppress) the top and bottom double cons at the fillet region of a mid surface.
• Then MIDs are checked for verifying there are no existing errors.

3rd operation 'Mesh Creation, Quality check & Assigning Thickness'.

• Before starting meshing operation the properties are to be created. As there are 5 components here 5 different properties according to their thickness is created.(Lists>Properties>right click>new>PSHELL)
• Then Change all perimeter element and macro elements distance to 5mm
• Confirm whether perimeter element distances are in acceptable range
• Make sure hole edges are parallel to adjacent edges.
• Half portion of the symmetrical components are deleted, which reduce time and effort to perform the operation.
• 1st check for symmetricity(Topo>Faces>Rm.Dbl) and after identifying them, hide unsymmetrical portions and delete the required half (Topo>Faces>Project cut>Cut along the required points>>Utilities>Delete>Select the portion).

• Input all the given Quality criterias (shortkey - F11)
• Then each components are meshed seperately

• Next is Meshing operation. 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 gaining the suitable mesh remove unneccessary cons(Topo>Faces>Cut>right click on cons).
  • For meshing 'Best mesh' & 'Batch mesh' (In mesh genereation)are used which gives a mesh within the quality criteria.
  • If in some region mesh is violating quality criteria, it is to be rectified. For this purpose 'Reconstruct', 'Smooth' (In Shell mesh) tools are used.
  • Formation of trais in the mesh is acceptable only under certain conditions. Trais not satisfying these conditions are to be corrected. For correcting those, 'Split', 'Join', 'Swap' (In Elements) tools are used.
• After meshing the symmetrical halves are to be mirrored accordingly. For this go to, Transform>Copy>Select entities>Symmetry tab>Select 'Default Symmetry plane>ok>finish.

• Finally we have to input the thickness values to corresponding components PIDs. (Shortcut - Cntrl+P)

Learning outcomes :

At the end of this challenge, I am 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. Also came across various tools that can be used in the future projects.

Conclusion:

Hence midsurfacing / meshing / and assigning thickness is done successfully

To conclude

1.Manual mid surfaces gives more accurate results

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

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

Link for the ANSA model is given below:

https://drive.google.com/file/d/1DhwB3_5L_zq8ce2y8Q-BirqFtfE_KF95/view?usp=sharing