Plastic Cap Midsurfacing and 2D meshing in ANSA

AIM

2D Mesh the given plastic component wih the given quality criteria.

OBJECTIVE

To mesh the given platice component we need to take the midsurface of the component.But since the component is plastic and having varying thickness across the geometry,we need to go for manual midsurfacing and then we need mesh the midsurface with shell elements and at the end we will be applying diifferant properties of different thickness applied to the respective components.

PROCEDURE

The cad model needs to be imported into the ANSA GUI.This is done by File>Open>select the CAD File>open.Then the cad file will be opened in the ANSA.Since the platforms are different for CAD and CAE there will be so many translational issues in the model imported,So we need to first topologically cleaned up the component.To topological clean up of the model we need to stay in TOPO Module and use the necessary options in the TOPO Module.Before that check the topological errors occurred due to the platform change by the use of check manager in ANSA.For that go to Check Manager>Geometry >Execute.It will show up the topological issues in the Model.We can go to each part and rectify the issues.The options used are

CUT : This is used to make the lines in the model which will divide the entire model.Face>New>Fitted>select the cons of the geometry to be created.

Fig 1 Geometry cleaned up

Taking the midsurface of the plastic componenet is a hectic task and there where we spend most of the time in meshing.Before extracting the midsurface we need to check the thickness of the bottle cap at everyplace.And from measuring we can see that the thickness is varying across sections and also it is varying in the features as well.We can start taking the midsurface from bottom the bottle cap using the FACE> MIDDLE > Select the surfaces we need to take the middle of>Middle click confirmation, this will give us the middle surface of the selected faces.in this way we can extract the middle surface of the majority of the portions including the ribs features.And in some places we need to create the middle curve using the cons of the features and later we will be joining the middle curve for extraction of midsurfsce of features like threads.For taking Midsurface we can use Curves>Middle>select one con >middle click >select second con.Middle click>This will gave us the middle curve of the sleected cons.Most of the features in the model like ribs and trapzoidal wedges and all are symmetric and arranges at a particular angular offset in the model,so we can extract midsurface on of the feature and we can use the Rotate option to arranged the midsurface at exact place it will be if we extract midsurface of each manually.For that we need to extract the midsurface of the feature >Select the transform>Copy>Select the extracted midsurface of the feature>Choose the option Rotate>Assign the Angle correctly>Choose a normal axis using two points>choos middle click or pree OK>This willl give us the misurface of similar features arranged at its correct place in the model.To extract points at centre we can make use of COG option in points.POINTS>COG>CIRCLE> choose a circle >then this will produce a point at the exact centre of the circle.

Fig 2 Wireframe view after the roation of feature midsurface

After we took the midsurface of every sufaces we can see the midsurface have connectivity issues.Needless to say that the intersecting points will be producing a Cyan coloured cone.To make connectivity between the surfaces, we need to make us of extend option.For that we can select the extend option in FACES >EXTEND>SELECT THE CON OF THE FACE WE NEED TO EXTEND>SELECT THE SURAFCE TO WHICH WE NEED TO EXTEND THE SELECTED CONE>MIDDLE CLICK.This will accurately produce the cyan con at the intersection if we select the surfaces correctly to which we need to extend while using extend option.Otherwise the surface may be protruding out of the surface to which we need to extend.In that case we need to use the intersect option in Faces.FACES>INTERSECT>SELECT THE SURFACE WHICH ARE INTERSECTING>,MIDDLE CLICK> THIS WILL SPLIT UP THE SURFACE AT THE INTERSECTION.So we can manually the delete the protruding surface.

Fig 3 Extend option applied in ribs

After midsurfcing we can start with meshing.First set the quality criteria in Quality.Then we can make some cuts in geometry so that meshing algorithm can gave us the most appropriate mesh flow.This can be done using cuts in the mesh module.Then we can set the hotpoints in the model at 1 mm apart.This can be done using the length option in perimeters in mesh module.Set the length as 1 and select the entire midsurface and press middle click.Then we can start meshing surface by surface.The algorithm BEST in MESH GENERATION TAB.And incase we are not satisfied by the mesh we can always make use of the RECONSTRUCT option in shell mesh tab.And after the reconstruction we can make use of smoothing option to smooth the mesh flow.Since the model is having intersection surfaces very near to each other at some places we cannot always make sure the quality of elements are passing at those regions. And while smoothing always make sure the elements are alligned with the geometric boundary because while we do smoothing, the elements try to extend out of boundary to acheive good mesh because of the algorithm.In any case such deviation happens we can use Grids>Allign option to revert the nodes back to the boundary.After the meshing gets completed we need to create the properties with the required thickness and we need to apply the correct property to the correct surfaces.And we can use the MVFREE option to moves nodes to get pass the failed elements for quality.

Fig 4 Completely meshed model in entity mode

RESULTS

Fig 5 Meshed model in property ID View

Fig 6 Model after draw shell as solid option switched on

CONCLUSION

The plastic model mostly have some reinforcemenets in the form of ribs and wedge features so, that produce adjacent lines in the midsurface which makes the elements fail for quality at those regions.In those regions we need to compromise for quality because if we try to maintain quality using MV FREE option it will distort the allignment of element nodes with the geometric lines.

Link for the Files

https://drive.google.com/file/d/1ukNNd845vIRxrBvblq3p_kZ2O_1wSyYC/view?usp=sharing