2D meshing of a backdoor of a hatchback car

AIM: To create a 2D mesh in the backdoor of a Hatchback car according to the given quality criteria.

PROCEDURE

The given component is a backdoor model of a hatchback car . This part is a sheet metal part and so that thickness is very low. So instead of going for 3D meshing, We can go for 2D meshing. For that we need to extract the mid surface. This model is having three components and they are the inner panel,outer upper panel and a lower outer panel.

Fig 1 Outer upper panel

Fig 2 Outer lower panel

Fig 3 Inner panel

First step in 2D meshing is to open the hyper works software and in the interface it will ask for to select a solver, Here we select RADIOS as solver .Then we need to import the IGES file which is the CAD file of backdoor of a hatchback car.

For that select IMPORT file icon > Then choose the Backdoor.iges from the directory > Then click on import. Then the hatchback geometry will be appeared in the screen.

Then we need to take the mid surface of the model. Since this is having Third dimension which is very very less magnitude. We can take the midsurface and mesh it in 2D and then we can add thickness to the mesh which is exactly same as the model. Since this model is having 3 different components, we need to take midsurface of the each components in different collectors.

TO take the midsurface, Go to GEOMETRY tab click on MIDSURFACE, then select the surface for which we need to take the midsurface. Then place the radio button in extraction option and select OFFSEt+SWEPS+PLANES.Then choose auto extraction and click on CREATE.But here this method is failed becuse of the complexity of the model.Hypermesh fails to properly midsurface the components.

Fig 4 problem with the automidsurfacing (missing surfaces)

So the only option left with us to go for manual midsurfacing.For that first check the thickness of the components.It can be found out using the distance option by pressing F4 and then place the radio button in two points and select the two points at the extremums and that will give us the thickness of the model.Then for manual midsurfacing we can use the OFFSET option in SURFACES EDIT By pressing SHIFT+F9.Place the radio button in OFFSET and select the outer surfaces of the component and duplicate it to the current component and type the distance as half of the thickness and check the normal using vector normal option and if the vector is not in the required direction then reverse it by using the reverse normal option and hit OFFSET.That will give us the required midsurface.

This file is the Cad model so the file imported may not be proper and some surfaces may get distorted in the process of importing. That will be reflected in midsurface as well.So we need to do the clean up the geometry. Some free surfaces may be presented in the imported model, some surface duplication may be seen, some glitches in the surface etc… will be presented. For to remove all these issues before the process of meshing we need to do the topology clean up. We can use visualization option to see the free edges and surface duplications. For that uncheck the green lines which is of shared edges in visualization option and then switch the model into the wireframe mode. Then we can see the duplication of surfaces and free edges. If there is free edges in the geometry exept at holes and outer boundary, Then that is the indication of missing surfaces and improper connectivity. And if there is no T connection and still there are yellow lines present ,Then it is the indication that thee are duplication of surfaces. So we need to delete the duplicate surfaces and for removing the free edges which are red lines ,if present we can use EQUIVALANCE option in edge edit ,TOGGLE option in quick edit can also be used, If these two cant solve the problem we can make use of spline and ruled surface options in SURFACE panel. Also, we can use the replace point option in quick edit tab.

Fig 5 example for the error in surface(presence of free edges)

Then we need to do the geometry check or clean up .in that process we need to pay attention of our target element size, minimum element size and maximum element size. We need to defeature the fillets which having possibility of elements failing for minimum size. Ask to CAD Design engineers for the importance of those fillets. If those fillets are not that important then it is permitted to defeature those fillets. For defeature go to geometry tab > defeature> surface fillets> select te fillets we need to defeature>remove. If fillets are between 0.1 mm to 5 mm radius, Then we can remove those fillets. And is there is holes present in the surface and the holes id having radius below 3 mm , then it is called a pinhole. We can remove or fill the pinholes for better meshing. To remove PINHOLES Go to geometry tab>DEAFEATURE>PINHOLES>select the pinholes> REMOVE. Then the pinholes will be removed.

Provide WASHERS to the holes above 5 MM radius . Washer can be given by Go to QUICK EDIT> provide offset >click on WASHER SPLIT >click on the edge of the hole, then we can see the washer split is appeared over the hole. Since there is possibility of stress concentration near the holes, we need to mesh those areas with only quad elements.That ‘s why we provide washer in those regions. Other critical areas can be find out by run the analysis an observe the results .The red colored areas are of high stress areas and they are critical areas. We should mesh those areas with small element size for proper capturing of surface and with quad only elements.

Then we can start meshing the midsurface. there we can use auto mesh option in 2d panel to mesh the surface.Go to 2D PANEL> AUTOMESH>Select the surfaces needed to mesh>give the element size AS 5 MM > HIT MESH

Then the whole surfaces got meshed. with the radio button in density we can clean change the nodal densities at various locations so as to get a smooth mesh with lower number of trias. Before accepting the mesh we should change the densities in such a way that the maximum tria removal is possible. Then accept the mesh.Reduce the maximum number of trias in the model with proper remeshing technique.

Then we need to check for quality criteria. The quality requirements are given below.

Fig 6 Quality Criteria

After meshing some of the elements violates the quality criteria . This can be checked by Press F10 which is the check element tab. This can also be entered with Tool>check elements>type the quality in relevant boxes. Then click on the respective options to check whether tab elements fail or not. So we should make them follow the quality criteria .For that the tools used are:

1)replace node option. For that PRESS F3 the replace the nodes with each other .

2)Go to QUALITY INDEX then use ELEMENT OPTIMISE ,this is used to optimize the elements based on the criteria we typed in the criteria file settings in the preferences option in menu bar. Go to PREFERANCES> criteria file setting> edit the Table as the quality criteria> then use element optimize and click on near the element we need to optimize.

Yellow color elements means the element is failed. But the red colour element means the element is worst. Touching near the failed element with element optimize will optimize the element.

3)Also we can use place node option in clean up tools in quality index. We can move the node along the surface /Normal to surface to optimize the element.

4)Also smooth tool in TOOL panel also can be used .

5)in case if element need to split ,Then we can make of split element feauture.For that press F6 place the radio button in split and select the elements we need to split, then click the points through which we need to split the elements. Then click split. Then the elements will get split.

6) PRESS F5 which is the mask option so we can save the elements from check elements tab and then we can retrieve those elements using mask option, And we can work on those failed elements without disturbing the other quality elements.

Since the inner panel, outer lower panel and outer upper panel is having symmetry in the model, we can make use of reflect feature. For this first mesh the half of the geometry, Then Go to TOOL panel> REFLECT>Select the displayed elements>Duplicate those elements into the current component>Choose the axis over which reflection is needed>choose the base node> Hit reflect.

After the reflecton,we need to EQUIVALENCE the elements at the middle.Since the proper connectivity between the exact middle is not proper after reflection.For this Go to TOOL panel>FIND >choose FIND EDGES>PREVIEW EQUIVALENCE>EQUIVALENCE.This will ensure there are no free edges in between elements.

Fig 7 Free edges check in Inner panel

RESULT

Fig 8 Inner panel mesh

Fig 9 outer upper panel

Fig 10 Outer lower panel

CONCLUSION

The process of automidsurfacing cannot be trusted everytime we midsurfacing.So in such a case we need to go fot manual midsurfacing,which gives us the perfect midsurface of the component.As the quality criteria gets stringent and the model gets complex ,number of trias at certain locations gets increased.This project helps me to understand better the 2D meshing process in sheet metal componenets.

Link for the files

https://drive.google.com/drive/folders/1LJLS_upEoV2BmU2Nttog-Oo1G5EAMzes?usp=sharing