Shell Meshing Of A Bottle Cap

Shell Meshing Of A Bottle Cap

Aim: To create the shell (2-D) meshing for a Bottle Cap model by eliminating geometrical errors and considering the given element quality criteria using ANSA.

Element Quality Criteria:

S.No	Quality Criteria	Value
1	Target/Average length	1
2	Minimum Length	0.5
3	Maximum Length	3
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
12	Tria Percentage	15

Procedure:

The meshing is done by following steps

1. Import Bottle cap.IGS in to the ANSA

2. CAD Geometry clean up and topology

3. Mid-surface extraction

4. Setting the PID

5. Defeaturing

6. Shell meshing

1. Import Bottle cap.IGS in to the ANSA: Import the given Bottle cap.IGS in to the ANSA Shown in the fig.1.1. Make orientation of all visual faces and change the element length on perimeter to 1 in both perimeters and macros (MESH>Perimeters>Length) show in fig.1.2.

Fig.1.1: Imported File Bottle Cap.IGS

Fig.1.2: Bottle Cap

Here we can observe the given model is not uniform thickness so that we need take care of while taking the mid-surface.

2. CAD Geometry clean up and topology: In this step the given model undergo geometry check (Tools>Checks>Geometry) where ANSA check for any geometrical errors such as collapsed faces, cracks, single con, triple con etc. those errors are shown in fig. 2.1.

Geometrical errors are cleared by using release triple cons and topo, deleting the overlapped faces and creating new faces. Here all geometrical errors auto fixed. Fig.2.2 shows the fixed all Geometrical errors.

Fig.2.1: Geometry Errors

Fig.2.2: Geometry Clean Up

Before going to the Mid-surface check geometrical errors for all individual.

3. Mid-surface extraction: The given model is plastic component and before going to the Mid surface extraction check for uniform thickness entities and measure (Utilities>Measure).

Mid-surface extraction done by manually. Because in auto mid-surface not able to get proper mid-surface. And so many quality criteria errors shown in fig.3.1.

Fig.3.1: Auto Mid-Surface

While extracting the mid-surface by Offset method it will ask for the offset distance along with direction. With respect to direction input the value. The value may be +ve or -ve depending on direction.

Mid-Surface extraction done by Middle (TOPO>Faces>Middle>Single) shown in the fig.3.2. Make sure that selected surfaces by middle must have same cuts. if not means we have to project the cons to other surfaces before using Middle option.

Fig.3.2: Mid-Surface By Middle

For circular features mid-surf done by exacting middle curve (TOPO>Curves>Middle) and revolve protrusion using Revolute (TOPO>Surfaces>Extrude) shown in the fig3.3. It will ask for the angles for start and end. Enter the starting angle Tmin 0° and ending angle Tmax 360°.

Fig.3.3: Mid-Surface By Revolute

Similarly Mid-surface extracted for different features on given model.

4. Setting the PID: setting PID (Property ID) for each mid surface done by using Set PID (Topo>Faces>Set PID). ANSA asked to select faces after conforming the faces Property Help window will pop up, in that window create new PID by right clicking mouse button and select New>PSHELL. Another PSHELL window will popup there we can assign the Name, MID (material ID) and thickness. We can modify the colors of each PID. But in this case we have different thickness at different region so we need to set PID according to the thickness after mesh and for initially we are going to set PID for reference purpose shown in the fig.5.1.

5) Defeaturing: Update the element length as per given element Quality Criteria (Mesh>Perimeters>Length) which is Target/Average length 1. Removing all unnecessary edges, fillet radiuses etc. also maintain distance between two cons or nodes not less than Minimum Length of 0.5. Shown in the Fig.5.1.

Fig.5.1: Defeaturing

6. Shell Meshing: Assign given element Quality criteria in to the ANSA (Utilities>Quality criteria) and Mesh Parameters (Utilities>Mesh Parameters) shown in Fig.6.1. Here we are going to Generate Shell Mesh which is preferred for 2D mesh.

Fig.6.1: Quality Criteria & Mesh Parameters

Start meshing Process by Best Mesh (MESH>Mesh Generation>Best).

Modify mesh flow using Reconstruct (MESH>Shell Mesh>Reconstruct), Smooth (MESH>Shell Mesh>Smooth) and Split (MESH>Elements>Split). Make sure that while doing mesh all the element Quality criteria mush satisfied. Avid maximum opposite trais and quad elements.

In fig.6.2 show the mesh flow.

Fig.6.2: Mesh Flow

Thickness assigned to the parts by selecting Draw Shell As Solid (Utilities>Quality criteria>Presentation Parameters) and shown on the fig.6.3.

Fig.6.3: Thickness Assigned

Assigning separate PIDs for different thickness region. If we have varying thickness (taper).Then divide that region with respect mesh flow and assign thickness value from maximum to minimum with equal intervals shown in the fig 6.4.

Fig.6.3: Thickness Assigned for taper Region

Learning Outcome:

1. Learnt user inter face of ANSA.
2. Learnt CAD geometry clean up, topology, Mid-surface extraction And Defeaturing for plastic components.
3. Learnt shell meshing and making good mesh flow with considering the Quality criteria for plastic components.
4. Learnt how to give Thickness for non-uniform and varying width.

Conclusion

Shell mesh is done successfully for a Bottle Cap model by eliminating geometrical errors and considering the given element quality criteria using ANSA.

(Find the attached file of Bottle cap_updated_MESH_Release.IGS).