Week - 4 - 2D meshing for Plastic components

2D meshing for Plastic components [Bottle Cap]

AIM

• Import the CAD geometry of cap model.
• Clean up the geometry until no topological error is found
• Extract Mid surface for the geometry
• Mesh Geometry with target average length

In this project a cap model is taken and midsurface is generated and then meshed according to the above mentioned quality criteria .This cap model consists of diffrent feature like spiral teeth, ribs with varying thickness

METHODOLOGY

• Import the CAD geometry and do geometry cleanup with no topological error
• Assign the Property ID (PID) and assign diffrent PID for each surface
• Generate midsurface
• Setup Quality Criteria
• Meshing and improvement of the mesh

PRODECURE

• Geometry Clean Up

After importing the geometry into ANSA there will be many topological errors. In order to prevent this we do a geometry clean up which is the check manager

After all the error are rectified if you check the geometry the exceution will be 100% then you can move forward

• ASSIGN PROPERTY ID (PID)

Every part in the geometry has its own property .We can assign PID using Ansa .We have to select the part and click apply then we have to select the whole part using window selection to apply PID .One can also assign diffrent thickness for diffrent parts in the PID manager

PID PID IMAGE OF CAP

GENERATE MIDSURFACE

We have to know why we are generating the midsurface .If you take any geometry half of the thickness will be above the midsurface and the other half will be below .So in order to represent the geometry we have to create midsurface .There are two ways to extract midsurface

• Using Offset we can either create midsurface individually for each part we can select the whole geometry using feature selection.Then give half the thickness for each surface selected.

MIDSURFACE AFTER OFFSETTING

• Auto midsurface generation

If the geometry is closed one we can use this option .But it will delete the parent geometry after midsurface generation .This option is available under the midsurface tab .We have to select the whole geometry and confirm the midlocation .A red line indicates the generation of midsurface which is shown.We can also use multi mid where one surface is selected with red one with green and the thickness with blue.

MIDSURFACE GENERATION

Using all these options create midsurface for all the features and connect them.If there is any connectivity missing with some surfaces we can join them by creating new surface. This cap model there are lot features connected with same surfaces as a result more triple cons canbe formed.

QUALITY CRITERIA

• Aspect Ratio It is defined as the ratio of maximum element edge length to the minimum element edge length.The ideal value is 1 but less than 5 is acceptable.
• Minimum /Maximum length It is very important to check this error as it used for crash analysis check
• Jacobian It is scale factor used in the transformation of coordinated system.The ideal value is 1 but not greater than 0.6 acceptable.
• Skewness If the quad element is not a square and has deformation skewness is defined as 90 minus the minimum angle between two lines joining the opposite midsides of the element and similarly for the traingular element it is 90 minus the line between the each node of the opposing midside .The ideal value is less than zero but 45 degrees is acceptable.
• Target element length It is the size of the element which we get should be nearer to the value compared to experimental value.

QUALITY CRITERIA

• MESHING AND IMPROVEMENT OF THE MESH

Now after assigning all the quality criteria and mesh parameters we can start 2D shell meshing

Number of Nodes

• The quad elements are usually better than traingular elements
• For better merge transition we use tria elements at some places .It also provides good mesh flow
• Trias at the edges and construction lines should be avoided for the better mesh flow.
• We can recreate better mesh using reconstruction option which is in the shell mesh

TOP VIEW BOTTOM VIEW

TEETH SPIRAL

MESH GENERATION FOR TEETH AND RIB

BOTTOM TOP

As there are more triple cons of diffrent features associated with same surfaces there will be some off elements in some areas .The length between each will be less in these situations

TRIPLE CON AND DOUBLE CON OFF ELEMENTS FORM

In this element is converted into 9335 elements in total

Quad elements 9106 which is 97.55%

Tria elements 229 which is 2.45%

CONCLUSION

From this I can conclude method of generating mesh for any geometry is very similar in case of the shell meshing .I followed all the prodecure mentioned in the grading poicy .Practiced all the command in ansa .Generated midsurface for different features with varying thickness .Able to defeature and do line adjustment in some areas able to mesh them successfully without any off elements. The majority of the elements must be kept to target length.

OUTCOME

• Able to do topological clean up with no errors.
• Assigned separate PID for diffrent surfaces
• Able to generate midsurface for complex geometry with varying thickness
• Understood about mesh generation and implemented mesh generation for complex geometry
• Learnt how to improve mesh flow and remove trias to achieve better mesh flow.