ANSA Week 4 Challenge - Meshing a bottle cap

OBJECTIVE

To extract the manual midsurface of the given bottle cap, mesh the component using the given quality parameters and assign thickness.

QUALITY CRITERIA

 
CAD MODEL IMAGE



PROCEDURE

1. Firstly, before we begin any kind of work on the model, we can go ahead and carry out the geometry cleanup. That is done via Checks > Geometry where we can execute checks of certain defects that can be selected from the menu and the algorithm looks for said defects. After detection, we can select all the defects and right-click > fix to fix them.

2. After that, we can go ahead and change the cons resolution by accessing the mesh module and selecting 'length' in the perimeter section. We will then need to select the whole model and assign a 1 mm length. This improves the resolution of the model as a whole and at the same time, cater to the target element length requirement for meshing, which we will be doing later.

3. To make it easier, we can break down the model into different views with the help of the NOT, OR, AND commands to hide certain surfaces.

Then using the 'store lock' feature, we can save views with surfaces masked. This helps with ensuring we cater to the complexities of the model. Surfaces are hidden using the 'NOT' feature and the remaining part of the component can be locked and saved, by clicking the lock option on the bottom toolbar and then the arrow > 'store lock'.

The store lock option is especially useful in helping us focus on certain regions without any obstructions that may be caused by other regions on the component.

4. Now that we have prepared ourselves to work on the model, we can go ahead and generate the midsurfaces. There are multiple ways to do this. We shall be using the 'middle' and the 'offset' tools for this challenge. The middle tool is especially useful for generating midsurfaces for the various ribs in this model. It can be accessed by going to Faces > Middle. After that, we just need to select either side of the rib and that generates the middle surface.

If there are multiple, separated surfaces to the rib, we can go ahead and use middle > multi to select the opposing faces for the algorithm to form a satisfactory midsurface. The different surfaces of the particular region to be midsurfaces are required to be denoted using the colours red, green and blue as shown below.

In other cases, such as the cylindrical regions, we can use the auto-midsurface option via the Faces > Mid.Surface tool or we can use the manual offset method. I used the offset method to ensure the generated midsurface has no defects since there are chances of that happening in an automatically generated midsurface. The thickness of the surface can be measured using the measure tool on the top toolbar.

Then, selecting the offset tool (Faces > Offset), it will ask us to select the surfaces to offset. We can select the surfaces on one side of the component. After that, we can assign the offset value (half the thickness). The offset tool will show the direction of the offset in the form of an arrow. If it is in the opposite direction of the required offset, the offset value needs to be in negatives. If we proceed, the surface will be offset and we will have the option of keeping the parent surfaces.

As a sidenot, it is best to create properties for each of these midsurfaces as soon as you create them. Just as in the stored lock views, properties can also be helpful in facilitating your workflow and helps focus on a certain region. The procedure to create properties has been elaborated later.

5. The offset/middle option cannot be used for the threads inside the bottle cap model. For that, we can make use of the curves > middle option to generate a middle curve on both the top and bottom surfaces of the threads.


Using these newly created curves (spanning the entire length of the thread), we can create a surface between the curves to form a midsurface through the entire thread. This is done by selecting the curves and creating the midsurface through the Faces > New tool.

6.


In cases such as these, where the ribs/teeth have multiple copies going around the component surface, we can make use of the transform > copy > rotate option. Before doing that, we can extract the midsurface of one of the ribs/teeth as a precursor. After that, we need to create an axis using two points at different heights. This is done using the Points > COG tool. Using that, we just need to select two circular regions that share the same axis as the rotational plane of the ribs/teeth.

After that, it is just a matter of using the rotate option to select the rib/tooth to copy, then going to the rotate section and selecting the two points of the axis. The number of steps is then specified (number of copies required). Proceeding gives us the midsurfaces of the remaining ribs/teeth.

7. After extracting all the midsurfaces, we can go ahead and extend them to each other to join them with their adjacent counterparts. That is done by using the Faces > Extend tool and selecting 'target'. This option helps extend edges of surfaces to target faces.

In the following case, the adjacent midsurfaces are extended to a common region using Faces > Extend > Pairs option. Both edges are selected here.

8. In other regions such as the following, excess surfaces require deletion. The intersect tool makes it easy for us as it does the job of both extending surfaces to each other and deleting regions that aren't required. The algorithm asks us to select the surfaces that need to be intersected, creates the cuts and it then asks us which surfaces are to be deleted. Intersect tool can be accessed via Faces > Intersect.



9. After extending, some modifications needed to be carried out in the teeth region. Some teeth were extended/reduced in size to coincide with a triple con formed as a result of a midsurface on the other end of the surface. This was done to prevent minimal length failure.

We can extend by creating a surface as seen here (using curves):

And in the other case, the excess surface can be removed by simply making a cut using a con and deleting it.

10. With the midsurfaces generated for every surface, we can go ahead and assign the thickness property for each of them using the properties too. To create a property, go to properties from the upper toolbar and right-click the list. Then go to New > PSHELL > PSHELL to create a new property ID. 

This opens a new window where we have the option to edit many of the particular property's attributes. In this case, we are to assign a thickness (T). We can go ahead and assign the thicknesses. The process will be repeated for each of the components' midsurfaces. We can do the same and assign properties for the main components. The intention is to view the midsurfaces (and their mesh) and parent surfaces separately.

11. Now, having generated midsurfaces for the entire component, we can proceed with meshing. Before meshing, we need to set the target length. This was already taken care of when we made the cons resolution finer (through perimeter > length). With that taken care of, we can assign the other parameters. This is done by accessing mesh parameters and quality criteria from the top toolbar.

12. We can then start meshing the entire component (using Mesh Generation > Best from the Mesh module) starting from one region and spreading out. It is ideal to start from a region with more single cons surrounding it. One of the outer ribs, for example. Since most surfaces have straight cuts, the mesh is less likely to have a large number of trias.

13. Nevertheless, we can make use of the reconstruct tool (Shell Mesh > Reconstruct) to generate a better mesh if the initial mesh is not satisfactory.

14. Sometimes, the reconstruct tool doesn't work in getting rid of some trias. Trias are okay but certain types of trias need to be avoided - like opposite trias or trias touching feature lines. Trias can be worked on using the swap, split, join and smooth tools. The first three are available in the 'Elements' section and the smooth tool is available in the 'Shell Mesh' section. The following example shows the tools in action:

15. We can simultaneously switch to hidden mode (from the bottom toolbar) to check mesh quality and work on improving the mesh. The cycle of meshing, reconstruction and tria removal + smoothing is carried out throughout the entire component.

16. Finally, after we finish meshing the entire component, as required, draw shell as solid needs to be activated. This can be done by going to Quality Parameters and accessing the Presentation Parameters tab. In that section, the 'Draw Shell as Solid' box needs to be checked.

FINAL MESHED COMPONENT IMAGES

No quality issues.

With 'draw shell as solid' activated:

LEARNING OUTCOMES

1. Learnt to make use of the middle tool - a third alternative to midsurface creation.

2. Also learnt the transform > rotate option, to form copies of the same surface around an axis.

3. Was able to familiarize with the intersect, extend and project tools which were required for this component.

4. Also learnt to make use of curves to generate surfaces, be it through manually created curves as well as curves generated with the help of cons.

RESULT

The given bottle cap component was meshed as per required quality criteria, after having carried out topology cleanup and generated midsurfaces for each of its surfaces and thickness was assigned to each of them.