Week - 4 - 2D meshing for Plastic components

Meshing of a Bottle Cap using ANSA

Aim: - For the given Bottle cap (plastic component) model, we have to clear the geometrical errors that are present in the model, we have to extract the Mid-surface of all the components and have to mesh the mid surface by fulfilling the quality criteria given in the problem statement, and have to assign different PID’s to various Thickness regions to enable shell as solid command with the help of ANSA.

Procedure: -

• Basic checks of geometry
• Geometry cleanup
• Mid surface Extraction
• Meshing the Mid surface
• Applying Different PID’s to various thickness regions
• Applying “Draw shell as solid” command

Step 1: -

Basic checks of Geometry: -

• First, we will import the CAD Geometry to ANSA and will check whether the CAD model format is in supportable format or not. Supportable formats are

STEP (*. STEP/ *.step/*.stp/*.STP)

IGES (*.IGES/*.iges/*.IGS/*.igs)

STL (*.stl)

• Second, we have to ensure that the dimensions of all parts in the model, importing in ANSA must be same, and it is recommended to be in mm.
• Most important thing is graphics check. Here we have to ensure that the Hot points and CONS are clearly visible and no problem should be there in visibility. If problem is there, we can put this command “-performance_mode 3”, in the popup box while opening ANSA to get good Graphics.

TIP: - If we need to get Good Resolution of the hot points, do the following

Click F11 >> Go to Presentation parameters >> scroll the bar of “all details” to left >> click on apply

Step 2: -

Geometry cleanup: -

• First, we have to assign the material to the given model without letting any problem to arise further. Here, assigning means nothing but just ticking the box of the created material in MID tab.
• Now, we have to perform checks on the geometry using “checks” Geometry checks are, checking for Single cons, triple cons, cracks, needle faces, collapsed CONS, unchecked faces.

Go to checks >> Geometry >> select checks to be performed >> Execute

• Before Geometry cleanup:
• Errors in Geomentry:

• The above error can be cleared in two ways. Either by going to error by error and dealing with it, or by using the inbuilt ANSA “fix” option for removing all errors at once. I used the “fix” option, as it is easy to use when there are lot of errors and doing manually consumes so much time.

• Select all the errors using “CTRL+A” >> right mouse click >> click on FIX

• Sometimes the ANSA might show some errors after some time even after using FIX option, then we have to clear the errors manually. This is the drawback of FIX

• Manually, most of errors can be cleared using basic release CONS & Hot points, TOPO, paste options etc.

• After removing Errors In Geomentry:

• 

• Another Geomentry Hiccup:

• After removing the Geomentry Hiccup:

At neccessary places , we have to adjust our fillets using DACH function to form a flat faces.

Fillet Before DACH: Fillet After DACH:

• Now, we have to do visual check, which means the outer surface or positive surface should be “Grey” and the inner surface or negative surface should be “yellow”.

  Using Orient >> visible, we can orient the surfaces.

• we also have to check the entire model, if there are any thickness changes. So, here we will go to feature by feature, surface by surface and randomly measure the thickness.
• Finally, we will check whether the features are correctly placed or not. How we will check?

  Go to Auxiliaries >> Fine >> click on the features

  Here we will know the true shape and placement of the feature.

Step 3: -

Mid surface Generation:

• Before mid-surface Generation, we have to ensure that we have created different locks for components based on their PID’s. It will be easy for us further, while doing mid surface generation and meshing, component by component.
• We can generate the mid surface in 3 types, either by using “Faces >> offset” or “mid surface >> skin” or "Faces >> Middle ".
• I used all the options together to generate the Mid surface, as it is a Plastic component.
• Mid surface Generation

Faces >> Middle Multi >> Select Multiple faces >> middle click >> ALL(after clicking all we see generated Mid surface)

and

Faces >> Offset >> Give offset value

Mid surface Generated:

Now, we will assign Different PID's to various features according to their thickness using PSHELL Card.

PID's Created and Thickness assigned:

Mid Surface After PID Assignment:

Step 4: -

Meshing: -

• After generating the mid surface and before meshing also, we have to check for the geometrical errors and has to do basic things such as, performing Geometry check, surface orientation. Only after having zero errors, we have to proceed for meshing.
• We will perform meshing on the extracted mid surface components one by one, which already stored in locks.
• Now, before meshing, we have to perform some operations such as creating and removing construction lines on the component, defeaturing of some features, to create a good mesh flow and to avoid the Tria’s in the component.
• We have to follow the Quality criteria given in the question,

Quality Criteria	value
Target / Average Length	1
Minimum length	0.5
Maximum length	3
Aspect ratio	3
Warpage	15
Skewness	45
Jacobian	0.7
Min Quad Angle	45
Max Quad Angle	135
Min Tria Angle	30
Max Tria Angle	120
Tria percentage	15

• And after set Quality parameters such as, average length, min length, max length, first order, mixed type, etc.,
• Don’t forget to activate the “element %” in quality criteria >> Performance parameters.
• Now, we can start doing meshing. For meshing,

Go to perimeter >> Length >> select entire component >> set element length to 5

and do the same for macros also.

• Now, Go to Meshing >> Mesh Generation >> Best mesh >> select entire component >> middle click.
• To achieve the good element quality, we can use options such as Reconstruction, split, paste, swap, join, cut, edge2perimeter, Num +/-, Mv surface etc.,

Meshed Model:

• Now, we have to apply the " Draw shell as solid " command to the meshed model to know, whether the thickness is applied accordingly or not.

Click on F11 >> Goto Presentation Parameters >> Tick the " Draw shell as solid " command box.

Model with " Draw shell as solid " command :

Learning outcomes: -

• Knowing the ANSA GUI and its tips for Better visualization.
• To practice all the commands in TOPO and Mesh Module.
• To know, how to handle the errors in geomentry, both manually and automatically.
• Mid surface extraction of plastic components using different options and some tricks.
• How to obtain a good mesh flow by adjusting construction lines and some defeaturing with lower percentage of traingles.
• Managing the Element quality using different commands in Mesh module.
• Assigning different PID's to different features according to their thicknesses.

Conclusion:

• Proper extraction of Mid surface.
• Generated Good Mesh flow.
• Tria's near Holes and Free edges are eliminated.