2D meshing for Plastic Component [Bottle Cap]

2D Meshing for Bottle Cap [Plastic Component]

Aim -

• To do a Pre-Processing on a given Bottle Cap model using ANSA Software [Version 19.1.4].

Objective -

• To check the geometrical errors on the Bottle Cap model.
• To extract a mid surface on the component.
• To generate 2D mesh on the component based upon the quality criteria given in the question.
• Set property ID to assign thickness to the respective regions in Bottle Cap Component.

Theoretical Frame Work -

• A bottle cap or bottle top seals the top opening of a bottle.
• A cap is typically colourfully decorated with the logo of the brand of beverage. Plastic caps are used for plastic bottles, while metal with plastic backing is used for glass; plastic caps are commonly made from PE or PP,whilst metal caps are usually either steel or aluminum.
• Plastic caps may have a pour spout. Flip-Top caps like Flapper closures provide controlled dispensing of dry products.
• Caps for plastic bottles are often made of a different type of plastic from the bottle.

 

Figure 1-Bottle Cap.

 

Procedure -

 

 

Figure 2-Procedure.

 

Phase 1-Importing the CAD Model 

• Hence we are importing a given CAD geometry into the ANSA.
• There are file formates like IGES,STEP,Parasolid where we can import these file formats into any CAD,CAE Softwares.
• In ANSA we can import all the CAD Software file formates like 
  

 

Figure 3-Supported File Formats.

• IGES [Initial Graphics Exchange Specification].
• STEP [Standard for the Exchange of Product Model Data].
• Solidworks.
• Catia V5,V6
• Simens NX CAD
• Inventor
• Creo
• Solid Edge
• Rhinoceros 3D
• IGES,STEP,These two are standard file formats which are mostly used in industries.But now a days in industries,they are aslo using parasolid file format.
• Now import the model into ANSA GUI.The Model given to us is in STEP File Format.
• Go to Main Pull Down Menus >> File >> Open.

 

Figure 4-Importing/Opening the Model.

 

 

Figure 5-Model imported into GUI.

 

• Now go to the the model browser by Tool Bar Menu >> Model Browser/Properties.
• To see how many components are availabale in the model.
• Here inly one component is available,Delete the unnecessary models in the model browser.

 

Figure 6-Model Browser.

 

• Simillarly do the same thing in property browser also.
• If there are any unnecessary properties delete that and then proceed.

 

Figure 7-Property Browser.

 

Phase 2-Initial Check

• Before working on the model.We have to check the geometry if there are any errors like
  

1. Damaged Geometry.
2. Free edges in unnecessary areas.
3. Unnecessary points on the lines.
4. Unnecessary Connections and connectivity error.

• By assessing the Bottle Cap model there are no errors in the geometry.
• If there are any unnecessary properties in the property browser,Delete them and then proceed.
• We have to do some geometry clean up on the model,Cause there will be some minimal errors in the model.To solve that we should do some geometry clean up on the model.

 

Phase 3-Geometry Clean Up

• Here we will be doing some geometry checks on the parent component.
• We have to fix the geometrical errors in the parent component,Then only we will be able to extract midsurface.
• To fix the geometry checks go to Tool Bar >> Checks >> Geometry.

Step-1

Figure 8-Checks Manager.

 

• After clicking on the check geometry,The geometric errors will be displayed.
• We can fix that geometric errors by manually or automatically.
• For this hood model,We can fix that errors automatically by auto fix.
• While checking for errors in the geometry make sure to check this options in the checks manager.

Step-2

Figure 9-Check Geometry Options.

 

Terminologies for Geomerty Options -

• Unchecked faces - Faces that failed for the shadow operation. 
• Needle Faces - Degenerated faces are faces that have their opposite CONS coincident. 
• Collapsed Cons - A CONS where it's starting and ending position coincide.
• Triple Cons - Areas where three or more faces have a common boundary.
• Cracks - Red CONS at inner areas.[Holes are excluded].
• Single Bounds - Red CONs at outer areas.[Holes included].

Step-3

Figure 10-ANSA Check Manager.

 

Step-4

Figure 11-Geometric Errors.

 

• Here in the Checks window all problems are reported with red color.
• Under Description column the kind of problem is explained.
• Focus functions are available in order to isolate geometrical problems and handle them easier.Select to fix all or specific reported problems by pressing right mouse button on the header of the list or one or more highlighted problems.

Step-5

Figure 12-Fixing Errors.

 

Figure 13-Errors Fixed.

 

• [Note: All problems except triple CONS can be fixed by the automatic fixing.]
• [Note: Right mouse clicking on Check Geometry line, performs an action to all listed problems.In case where not all problems are fixed automatically, retry or proceed to fix them manually.For this component no need to fix manually because all the errors have been fixed with auto fix.]

 

• Similarly do the same process for the Outer Extract,Hinge Reinforcement Extract and Latch Reinforcement Extract.
• Here for the Outer Extract we have toggle the lines in the hemming regions because that hemming lines will be failing for minimum length,So we have to toggle that lines while meshing on it.

 

Phase 4-MidSurface Generation

• Before extracting the mid surface for the components we need to give perimeter and macros length on the components while extracting mid surface.
• This makes the component to get a desired shape,So it will be easy to extarct a midsurface without any errors.The possiblities of errors will be less.
• To give perimieters and macros length on the componets,
• Go to Mesh Module >> Perimeters >> Length.

 

Figure 14-Permieter Length Tool.

 

Figure 15-Selecting the CONS to give perimeter length.

 

Figure 16-Enter the Value as 1 according to the component size.

 

• Simillarly do the same thing for the macros also.
• Mesh Module >> Perimeters >> Length.
• This tool defines the element length on selected perimeter segments or macro areas.
• The element length may be explicitly declared or may be declared as a factor to be multiplied by the existing element length.

 

Figure 17-Before giving perimeter length and macros.

 

 

Figure 18-After giving perimeter lenght and macros.

 

• We can Extract Mid Surface by Two Methods called
• Using Skin MidSurface Option in Faces Panel in Topo Module.
• Using Offset Tool in Faces.
• But for this component,We will be extracting midsurface by using offset.
• We can extract midsurface for this component manually because this component is plastic.
• The plastic component will be having varying thickness,So extract midsurface manually.

 

4:1 Why to Extract Mid Surface ? 

• Before extracting the mid surface for every component,We should measure the thickness of the component and then we have to proceed to extract the mid surface.
• If the component thickness is less than 6mm then we will come to know it is a sheet metal or plastic component.
• For sheet metal and plastic components,Mid Surface extraction is must.

4:2 Generate Mid Surface

• To generate a midsurface manually
• Go to Topo Module >> Faces >> Offset >> Select the Face >> Give Offset Value and Direction.
• We will be extracting midsurface manually for the components which have varying thickness.

[Note:While extracting the midsurface,make sure to uncheck delete original faces option.]

Step-1

Figure 19-Inner Circle.

• Here we are extracting misurface for this inner circle.
• Before extracting midsurface for this inner circle.
• Hide that inner circle using not tool in focus tool bar.
• And then retrieve that inner circle using Invert tool in focus tool bar.
• Now extract the mid surface for that using middle in the faces panel.

Step-2

Figure 20-Inner circle surface has been  hidden using not tool.

 

Step-3

Figure 21-Surface Inverted.

 

• Now extract the midsurface using middle in faces panel.
• You can use single or multi option to extract midsurface.It's up to us and it's our choice.
• Go to Topo Module >> Faces >> Middle >> Multi >> Select the appropriate surfaces >> Middle Click.

Step-4

Figure 22-Faces Panel.

 

• This Middel Multi option creates Faces that represent the middle skin of a solid description.
• It is applied on selected or automatically identified groups of Faces.
• The resulting Faces can be automatically connected to the rest of the part.

Step-5

Figure 23-Middle Multi Option.

 

Step-6

  

Figure 24-MidSurface Extracted.

 

• Simillarly do the same process for every regions in the bottle cap model.

 

  

Figure 25-MidSurface Extraction for Top Circular Surface.

 

  

Figure 26-MidSurface Extraction for Top Surface.

 

Extracting Midsurface for outer ribs-

 

• Here we can extract midsurface by three methods called

1) Creating a curves over the ribs and fill the surfcace.

2) Using middle single option to extract.

3) Using middle multi option to extract.

• Here I'm using method one to extract midsurface for outer ribs.
• First create a curves using middle option in curves panel.

Figure 27-Curves Panel.

 

 

Figure 28-Curves Created.

 

• Now create a surface using new in faces tool.
• Go to Topo Module >> Faces >> New >> Fitted >> Create.

 

Figure 29-Surface Created.

 

• After Creating the surface extend the surface to the mid surface extrcated for the outer circle.
• Simillarly do the same process for every rib and do the same thing for the inner ribs also.

 

Figure 30-Project the cons to the midsurface.

 

Figure 31-Projected the CONS to the MidSurface.

 

Figure 32-Fill the Surface.

 

Figure 33-MidSurface Extracted in Every Region.

 

Figure 34-In Transparency Mode.

 

Another Method of MidSurface Extraction-

• In this method,I'm spitting the model.Like I'm deleting the surfaces which are symmetric in the parent component.
• After deleting the symmetric surfaces,Extrcact the midsurface for the surfaces which are symmetric.
• Don't extract the midsurface for the surfaces which are not symmetric.After reflecting the symmetric surfaces we can extract the midsurface for the surfaces which are not symmetric.

 

Figure 35-Deleted One Portion of Symmetric Surfaces.

 

Figure 36-Mid Surface Extracted.

 

• Now reflect one side of symmetric surfaces to the other side by using transform tool.
• Go to Utlities Panel >> Transform >> Copy >> Entities >> Select the Entities to reflect >> Symmetry >> Use Default Symmetry Plane >> Apply >> Finish.

 

Figure 37-Symmetric Surfaces has been Reflected.

 

• After reflecting bring back the deleted parent other half using undeleted tool in faces tool.
• Here every surfaces will be come back when you use undleted tool.
• It will be difficult to to bring back like this.
• So try to eschew deleting the surfaces in the middle.

 

Figure 38-Surfaces has been highlighted by using undelete tool.

 

• Now select the surfaces which we have deleted.
• It will be little difficult.After bringing back the surfaces,Topo the surfaces by dragging square box on the surfaces to get connectivity.
• After topo,Triple cons may occur,To eliminate triple cons,try to hide the surfaces and delete the surfaces which are extra in the parent component.

 

Figure 39-Selecting the appropriate surfaces to bring back.

 

Figure 40-Triple CONS in the parent component has been fixed.

 

Figure 41-Final MidSurface by Method 2.

 

• We can also bring back the parent component by merging the file into the exsisting one.
• I have attched the video link down here,how to bring back the parent component in another method.

https://screenrec.com/share/dfQB8xv6Lk

 

Phase 5-2D Meshing

• Once geometry cleanup is completed (e.g. surfaces are stitched together — no unwanted free surface edges inside the geometry), meshing is next.

Some rules of thumb when meshing:

• The mesh should look rather smooth and regular (keep in mind that the analysis is based on your mesh and the mesh quality is key.
• Use the simplest element type suited for the problem.
• Start with a coarse mesh and understand the modeling results; then use a finer mesh if needed.
• Try to keep mesh related uncertainties to a minimum if possible. Keep it simple as it can get more complicated on its own.

 

Figure 42-2D Element Shapes.

 

• Different Element Type Options for Shell Meshing:

Figure 43-Element Types.

 

5:1 Enter the Parameter quality criteria what they given for the Hood Model

• Select and set the respective quality criteria for the corresponding elements to perform the Quality Checks (Hidden Mode). Also set the general presentation settings concerning the ANSA workspace
• Use the F11 key to open the Quality Criteria and Presentation Parameters management window (F11 Menu).
• Tool Bar >> Quality Criteria (F11) >> Enter the Values.
• Tool Bar >> Parameter >> Enter the Values.

 

Target/Average Length- 1 Unit

Sl. No.	Quality Criteria	Function / Definition	Value
1	Aspect Ratio Ratio	Ratio of Max. Length by Min. Length	3
2	Skewness	Deviation from the ideal shape	45
3	Warping	Angle between the 2 planes of the same element(Quad)	15
4	Jacobian	Transformation of Coordinate System.	0.7
5	Min. Length	Shortest length of any given element	0.5
6	Max. Length	Longest length of any given element	3
7	Min angle Quad	Minimum angle in any given Quad element	45
8	Max angle Quad	Maximum angle in any given Quad element	135
9	Min angle Tria	Minimum angle in any given Tria element	30
10	Max angle Tria	Maximum angle in any given Tria element	120
11	Tria %	Percentage of Tria on any meshed surface	15

 

 

Figure 43-Quality Criteria Panel.

 

Figure 44-Mesh Parameters

 

[Note : Save the Mesh Parameter and Criteria file for that component and save it in any other drives,Cause whenever we open that component,we can open the Element Criteria file and Parameter file,So criteria and mesh paremeters will be applied habitually instead of entering again.]

 

1) Aspect Ratio

• This is the ratio of the longest edge of an element to either its shortest edge or the shortest distance from a corner node to the
  opposing edge ("height to closest node").

 

Figure 45-Aspect Ratio Calculation.

 

2) Skewness

• Skew of triangular elements is calculated by finding the minimum angle between the vector from each node to the opposing
  mid-side, and the vector between the two adjacent mid-sides at each node of the element. 
• For Skewness: Ideal=0,But < 45 is acceptable.

 

 

Figure 46-Skew Angle.

 

3) Warping

• This is the amount by which an element (or in the case of solid elements, an element face) deviates from being planar. Since
  three points define a plane, this check only applies to quads. The quad is divided into two trias along its diagonal, and the angle
  between the trias’ normals is measured.

Figure 47-Warp Angle.

 

4) Taper

• Taper ratio for the quadrilateral element is defined by first finding the area of the triangle formed at each corner grid point.These
  areas are then compared to one half of the area of the quadrilateral.                                          

 

 

Figure 48-Taper Angle.

 

5) Minimum and Maximum Length

• The shortest distance from a corner node to its opposing edge (or face, in the case of tetra elements) referred to as height to
  closest node. 

 

5:2 Conditions to be followed while meshing

• Feature Capturing
  

• Feature capturing is must while meshing.All the nodes must be connected to the shared edges.

• Tria Management
  

• Avoig higher number of trias.
  
  

• Important Parameter's in tria management
  

1. No trias in corner's or edge's.
2. No opposite trias.
3. No back to back trias.
4. No trias in fillets or hemmings(We can have minimum but anyhow try to avoid).
5. No rotational quads.
6. No trias should share a boundary with feature line.
7. Connectivity between elements.
8. Split and perform the mesh.
9. Use mixed type mesh for irregular shaped surfaces and quads only for rectangular/square surfaces(Opposite sides should be parallel and equal).

5:3 Begin meshing the surfaces

• Start meshing from the centre regions or from least free edges.You will get proper mesh density and proper mesh flow.

Why Meshing is Needed ?

• Finite Element Method reduces the degrees of freedom from infinite to finite with the help of discretization or meshing (nodes and elements). One of the purposes of meshing is to actually make the problem solvable using Finite Element. By meshing, you break up the domain into pieces, each piece representing an element.

How to Begin Mesh ?

• Start meshing form the least free edges,Like start meshing from the center.
• It will be easy to get proper mesh flow and we will get uniform mesh density.
• Don't mesh form the edges,It will be difficult and you will get many error,So start meshing from the center.
• Choose the element type while meshing.
• For this component we will be using mixed element type and working on it.
• We can also quads element type.This type can be used when we have rectangular surface.
• We can use Tria Element type.This type can be used for 3d tetra meshing.

Start Meshing

• To begin mesh,Switch form topo module to the mesh module.
• Before Meshing set the perimeter and macro length to the component.
• Here set the perimeter and macro length as target element size.
• It will split according to the target element size,So it will be easy for us to mesh.
• To Mesh >> Go to Mesh Module >> Mesh Generation >> Best Mesh >> Select the area.
• While Meshing Switch from shaded mode to the hidden mode,Then only we will be able to see the visibility  element quality.

Figure 49-Drawing Styles Panel.

 

• Here for this component,I have used different mesh algorithms like

1) Best Mesh

• This type of mesh automatically meshes Macro Areas using all alternative meshing algorithms and keeps only the mesh of highest quality according to QCHECK.
• The Best function may be applied to selected unmeshed Macros, or to all visible Macros according to the chosen option (Selected or Visible respectively).

2) Batch Mesh 

• This type of mesh automatically meshes Macro Areas and FE shell areas using the Batch meshing method, but with taking into account the global defined meshing parameters.
• The meshing algorithm may be applied to selected or visible unmeshed or meshed Macros or FE shell elements, according to the chosen option (Selected or Visible respectively).

3) Spot Mesh

• This Mesh Generation>Spot-Mesh algorithm generates more elements than the Free algorithm and brings better results to Macro Areas that have Weld or Connecting Spots on them.

4) Free Mesh

• This type of Mesh [Generation>Free algorithm] generates as few elements as possible, trying to maintain the best quality possible.

5) Advance Front Algorithm

• This type of mesh automatically meshes Macro areas and FE shell mesh areas using the Advancing Front meshing method, taking into account the element type already selected.
• The Advancing Front meshing method generates elements beginning from the boundaries of a Macro-Area, taking into account the shell element distortion and minimum length.
• The resulting shell elements are of first or second order shell elements according to the status of the 2nd Ord flag.

 

Figure 50-Elements failing for the min length.

 

• Here in this chamfer regions,elements will be failing for the minimum length,So we can't do anything here,So accept it and proceed.

 

Figure 51-Meshed in Every Region.

 

Figure 52-Meshed Component.

 

5:4 Assign Thickness to the Components 

• Go and assign thickness to the components.
• Go to properties browser and double click on the component which you want to assign the thickness,A new window will pop on the GUI.Give thickness value there.
• Simillarly do the same process for every component.

 

Figure 53-Property Browser.

 

Figure 54-Thickness Assigned to one particular surface.

 

• Simillarly assign the thickness for the every region which have varying thickness.

Phase 6-Final Check

• After Assigning Thickness,Check whether the thickness have been appplied or not.
• To check Go to Utilities >> Quality Criteria >> Presentation Parameters >> Draw Shell as Solid.

 

Figure 55-Quality Criteria Panel.

 

Figure 56-Thickness Assigned.

 

• Now check whether there is a proper mesh flow in every region.
• Check whether the elements have captured the feature lines properly.
• And check whether there are trias touching each other.
• To check this Go to Utilities >> Quality Criteria >> Edit Criteria Visibilty >> Check Triangles Per Node >> Apply.

 

Figure 57-Check Triangles Per Node.

 

Figure 58-Shell Elements Panel.

 

• 49 Trias are touching each other,We cannot drag them in the chamfer regions.
• Every trias are touching each other in the chamfer region.
• This is because of triple points in the chamfer region.
• If we try to eliminate that trias in the chamfer regions,The elements will be failing for jacobian,warping,So accept that trais and proceed.

 

Figure 59-Trias Touching Each Other in these regions.

 

Final CAD Model Images - 

 

Figure 60-Final CAD Model Image 1.

 

Figure 61-Final CAD Model Image 1:1.

 

Result -

• Hence the mid surface has been extracted to the parent component.
• Hence there are no surface deformations in the geometry.
• A well connectivity has been established between the surfaces.
• The features have been captured properly.
• A good mesh flow have been achieved with the 15 elements failing for quality
• Hence tria percentage with 2.3 % have been achieved.

Learning Outcome -

• In this Week 4 Bottle Cap Challenge,I came to know
• How to extract the mid surface Manually for the plastic components.
• How to clean the geometry .
• How to generate a proper mesh flow with low tria percentage.
• How to assign thickness to the components which have varying thickness.