PREPROCESSING OF PLASTIC COMPONENT USING ANSA

PREPROCESSING OF PLASTIC COMPONENT USING ANSA

AIM:

To mesh the given Bottle Cap (A Plastic Component) model using Preprocessing Software (ANSA).

OBJECTIVES:

• Clearing geometrical and topological issues in the model.
• Extracting the Mid surface for the given Bottle cap Model using Manual Mid.
• Generating Mesh on the Model.
• Eliminating Tria elements and Rotating Quad Elements of the Mesh.

PROCEDURE:

1.GEOMETRY CLEANUP

Importing the model from other software to ANSA results in some geometrical deviations which needs to be cleared before proceeding to other steps. To perform geometry check Tools-->Checks--> Geometry. In General needle faces and Unchecked faces error occurred which is common while importing the model to ANSA from Modelling software. Images shown below were the geometrical errors showed up in Bottle cap model while performing Geometry Checkup.

To clear these errors ANSA either we can use AUTO FIX option or Fixing the errors manually one by one.

• Auto FIX option by which ANSA detects the deviations and Heals by itself.To Auto Fix the Errors Right Click on the error and click on Fix now the error will be gone.
• To FIX the errors manually you need to find where the errors is occurring to know that Right click on the error and click Show only it will Highlight the error. To get the clear idea on the location of error we can get the neighboring faces using neighbor option or by using AND Boolean Operation.

• Needle faces and Unchecked faces can be cleared using universal delete option once the errors were highlighted.

Now our geometry is clean without any translation issues or geometrical deviations so we can proceed to topological activity.

2.TOPOLOGICAL ACTIVITY

Topology describes how the different faces and features of the geometry connected with each other.

Boundary Cons of the faces and Features were called as feature lines other Cons in the Model were called as Construction Lines which were generated during modelling of the component. Construction lines can be altered as we want to get the better mesh flow. Feature lines should not be disturbed as it will result in Change in geometry however if the cons Length is less than the minimum element size it will result in element failure under such circumstances the feature line can be altered up to some extent without giving up the design feature of the part.

Image below shows the faces were parallel with one of the perimeters is lesser than the other face due to the fillet available in the face and it will result in smaller mid surface which will lower the result accuracy. Therefore, it is fine to remove the fillet to get the exact mid surface of those faces. To remove the fillet Select Faces-->Dach option.

Auxilaries-->Fine option is used to refine the curves for better understanding of the model.

Select Fine and click multiple times on the curves that need to be refined. Image below shows before and after refining the curves makes the model easier to understand

In the topological activity final step will be orienting the faces using FacesàOrient option. Orientation in ANSA indicated by Grey or Yellow surfaces Grey surface usually acts as a positive direction and Yellow acts as a negative direction. Face is said to be inconsistent if one face having both the Grey and Yellow Colours. FacesàOrient option will fix this issue by changing one side of the face to be yellow in colour and other side to be Grey colour. Now the model is consistent.

3.MIDSURFACE GENERATION:

Mid surface is the exact middle layer or surface of the component having uniform thickness over the part.For instance if the component or sheet metal having the thickness of 1mm then the surface at the 0.5mm from any of the face considered to be a midsurface.

In ANSA can generate Mid surface by two ways:

1. By Faces-->Offset option
2. By Faces-->Surface option
3. By Faces-->Middle option

1. Faces-->Offset:

This is manual method to generate the mid surface. Midsurface for te entire component is genetated by is generating the faces one by one by Faces-->Offset command where you have to give the offset distance manually(Usually Thickness/2). In this method we have an option the keep the original face or to delete it. Once the mid surface is generated for the entire model they don’t have the associated with each other. ANSA will indiacte this by using a Single con on the boundaries of all the surfaces. To stitch all the faces with each other Face-->Topo option will be used. Select Faces-->Topo-->Select the faces to want to Stitch-->Middle mouse click, Now the faces were attached with each other indiacting the double con where the two surfaces attached togather. In this method the child surface orientation may differ from the parent surface so it is advisable to perform Faces-->Orient once the Topo performed after Mid surface generation.

Step 1:Select Faces->Offset and select the faces needs to offset.

Step 2: On middle click ANSA shows the direction in which the faces will be offset. As we wanted to shift the direction in opposite side the negative sign is used.

Step 3: Middle click after entering the values ASNA asks wheather to keep the original faces or to delete it.Clicking YES will delete the original faces.

II.Faces-->Mid.Surface:

This is auto mid generation option by which Mid Surface is generated by deleting the original faces. To generate the mid surface Select Faces-->Mid.Surface now select the faces for which you want to generate the mid surface then middle mouse click now ANSA will highlight One side of the Face Red in Colour and other face in Green Colour and the faces in thickness region in Blue colour now Middle click Now the original faces will be deleted automatically leaving the Mid surface on the work space. It is mandatory that Red and Green faces shouldn’t be neighbouring surfaces

In this model Faces-->Mid.Surface is not used to generate the mid surface as the component having various thickness values at every surfaces. Therefore in this model Auto mid option cannot be used.

III.Faces-->Middle option:

Middle option in ANSA will be a semi automatic mid surface generation by which the mid surfaces will be generated automatically when the faces were selected. Middle function has two methods:

• Faces->Middle->Single.
• Faces->Middle->Multi.

1. Faces->Middle->Single:

Faces->Middle is selected. Then select the Faces for which the mid surface to be generated. ANSA will create a new face once you have selected the 2^nd face as shown below

ii.Faces->Middle->Multi:

In this method multiple faces can be selected to generate a mid surface. As shown below.

Middle Surface is created by using the options shown above

Some of the Mid surfaces which were created will not be contact with the other face. Stays away from the object.

Image shows the faces were seperated apart after generating the mid surface. To make them contact with the faces two commands were used in major.

• Faces->Extend
• Faces->Intersect

i)Faces->Extend:

The Unwanted faces is deleted by the Faces->Delete option.

The Entire Mid surface of the model is generated by using the commands said above is Shown below.

4. DEFINING MESH PARAMETERS AND QUALITY CRITERIA:

Quality of the mesh is user defined one as it varies for different applications. Quality of mesh will be defined by Mesh parameters and Quality Criteria. Mesh parameters option is available in the Utilities Bar.In that window average element Size, Minimum Element Size, Maximum Element Size and order of Mesh will be defined as shown below

Mesh Quality criteria also need to be defined from the Utilities bar.

Our quality criteria inputs for the mesh were

1. Average Element Length - 1 mm .
2. Minimum Length - 0.50 mm
3. Maximum Length - 3 mm
4. Aspect ratio - 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

• Aspect Ratio: Ratio between Longest side and Shortest side of the element
• Warpness:Angle between normals of two planes of a quad element.
• Min angle and Max angles were Angles included in the particular type of element.
• Jacobian: Transformation of elements to one form to another form. If the transformation can be done without any deviation then Jacobian will be 1. We should not have jacobian less than 0.6
• Skewness:

Skewness for the Element 2>Element 1.

5.MESHING GENERATION:

Mesh generation is process of discreting the entire model into smaller elements.In ANSA mesh generation is done by set of algorithms available for meshing.Image shows options available for meshing. However BEST MESH is used in preprocessing of this model as it gives best mesh eliminating maximum number of elements not conforms to the quality criteria.

2D mesh has two types of elements:

• Quadrilateral or Quad Elements
• Triangular or tria Elements

Quadrilateral Elements:

Quad elements were the elements having four nodes. Square is considered to be an ideal quad element and the deviations were calculated in comparison with the square element. Quad elements were structured elements. They have short processing time and also have highier accuracy. Therefore Quad elements were preferred over the tria elements.

Triangular Elements:

Tria elements consists of three nodes. Equilateral Triangle is Ideal Tria element and deviations were compared with the Equilateral Tria Element. Tria element is said to be unstructured mesh. Stiffness of the Tria element is high which results in highier processing time and also have low accurate results. Therefore we should try to avoid the maximum possible number of triangular elements.

Rotating Quadrilateral Elements:

Rotating quad elements were formed when any one corner of the 5 quad elements meet at a point to form a Star like structure. Even thought they were quad elements they should be avoided in the model as they act like the tria elements.

Meshing:

Step 1:Mesh GenerationàBest selected from the Mesh Module and selecting the face that needs to be meshed.

Step 2:Now Middle Clicking will generate the mesh

Mesh is generated for the entire model by following above said steps.

6.MESH FLOW AND MESH QUALITY IMPROVEMENT:

In ANSA mesh can be generated easily but the mesh will have lot of elements will be generated such that they fail to fulfill the Mesh Quality criteria an also the mesh will have the Triangular elements which needs to be eliminated. Mesh Flow and Mesh quality improvement is the most important steps in order to achieve good mesh quality and Good Mesh Flow. To improve the mesh Quality there are many options available in ANSA. Lets discuss them in detail and how they used to achieve good mesh for the model.

1. Reconstruct
2. Smooth
3. Split, Swap, Join
4. Changing Nodal numbers
5. Edge2Perimeter

1. Reconstruct:

This option is similar to Mesh generation but key difference is that Mesh Generation option will generate the mesh only once but reconstuct option will try to give all possible arrangements of the mesh either by altering nodal numbers, altering the type of element or altering the element size within the allowable limit and also eliminates maximum number of errors.Below steps to perform reconstruct option.

Step 1: Select Shell Mesh-->Reconstruct. Select the Area to reconstruct.

Step 2: Select the Edges and the click OK Now ANSA will show the preview of the reconstructed mesh model if the rearrangement.

Now comparison can be made between new and old mesh and the better one can be selected.

2.Changing Nodal Numbers:

When the perimeter is having odd number of it will for a tria element which is not easy to eliminate. So, if the perimeter has odd number of nodes leaving a tria element after reconstructing it is good to change it to even number of nodes using Perimeter-->Num+/- option in mesh module. The image below shows how nodal number helps in eliminating tria elements.

3.Split, Join Swap:

• Split option is used to split the cells into two parts.
• Join is used to Join the two Tria elements sharing same edges then the edge is removed to form a quad element using join option.
• Swap option is used only on tria elements to swap the edge from one node to another node which is available.

Above said commands can be used in Split command itself.

Left Click acts as Split command, Right click acts as a Swap command if there is only one Tria element and Acts as a Join command if two tria Sharing a vertex.

Step 1: Split is made along the length by clicking on the element edges one by one or by selecting the element totally by drag selection. It will create a split as shown in the Image.

Step 2: Now when you middle click the split previews (violet colored lines) turn into Elements

Step 3: Right click on the sides shared by two tria elements will join the trias to make a single quad element.

3.Smooth:

This option used to improve the mesh quality along with the mesh flow. It improves the quality of the element by adjusting the nodes slightly and makes the elememts equi spaced.

5.Edge2Perimeter:

This option is used to make a cut on the meshed face parallel to the edges of the nodes without altering the existing elements arrangement. It is done by selecting option from the Perimeters tab.

Now select the nodal edges on which the cut needs to be done. Now when you middle click the cut is made on the face along the edges of the elements selected.

This option is used if you wanted to reconstruct one small area of the large surface. Image below shows how the cut is made using this option.

Step 1: Selecting the edges.

Step 2: Middle click after selecting the edges convert the edges into cuts. Shown in Double con (Green coloured line).

Once the perimeter is created the mesh is erased and reconstructed again to get smooth mesh flow. Image below shows the smooth mesh flow

Mesh is generated and the Mesh quality and the Mesh flow is improved using the above said options for the entire model

7.SET PID:

PID is property identification number. We have to assign thickness for the all the faces and the material to the model. To set PID Face-->Set PID is used.Select the faces and Middle click.

Now the properties window opens up. Now Right Click on the window New-->PSHELL now as shown in fig.

Now the PSHELL dialog box opens up (as shown below) where you will enter the thickness and click OK.Now thickness is assigned to the mid surface.

To assign the material create the material using Lists-->Material or Ctrl+M. Materials Dialog box opens. To create a new material Right Click-->New-->MAT1.

A dialog box opens as shown above Enter the properties of materials like Youngs modulus, Poisson Ratio and Density values. Click Ok now material will be added to materials list. To apply that to the our PID. Right click on the material-->Apply. Now the property help dialog box opens up click on the part’s PID now ANSA will highlight the parts in which that materials property will be applied. Click Ok. Now the material and thickness property is applied to the particular model.

To check wheather the PID is applied to the model or not, switch to PID mode from ENT mode in Drawing styles bar. The model will change into same colour as the colour of the particular property is identified in Properties window.

ENTIRE MESHED MODEL

LEARNING OUTCOMES:

• Understood how to handle a plastic component for preprocessing.
• Learned how to create a manual mid surface.
• Learned how to applying thickness to every faces separately.