Tech Tip: Combine vs Split Body in Ansys SpaceClaim and Ansys Discovery

Whenever I teach Ansys SpaceClaim and Ansys Discovery classes, I always describe the differences between Combine tool and Split Body tool. So, I thought I would do that for you today.  Along the way I also found out something about the Split Body tool that makes life easier.

Say we had a body like this one, and we wanted to mesh it with hex elements in ANSYS Meshing. 

The easiest thing is probably to split it up and let it hex mesh. The two tools that we can use in Ansys Discovery or Ansys SpaceClaim to do this are the Combine Tool, and the Split Body tool.  Essentially, the Combine tool will merge bodies, but also allow you to split a group of bodies using a group of cutters that are made previously to intersect the body, while the Spit Body tool will split a body using a single cutter that is extended to intersect the body.

Let’s Use Combine and Split Body to See the Differences

First, a look at  the combine tool. With the Combine tool, when you pick on a , you  have to have something to use as a cutter.

So in order to do this, we would have to make a plane or a surface large enough to intersect the entire body. After creating a plane, now we can use the combine tool and select the plane to do the split. So now we have each of these separate pieces. Splitting it this way lets each of these bodies be hex meshed in the Y-direction, but then also allows the vertical piece on the left to be hex meshed through the thickness in the in the Z direction, in this case.

But let’s look at some easier ways to do that. If we use the Split body command, you can see that the resulting body is now split.

If you pick the body and then hover over the same surface, you can see it automatically extends through the whole body to save the plane creation step.  So now I have all these separate bodies.

Now let’s say we want this same whole pattern to go through all the fins.
We can do this with the Split Body command.
As we pick a body, and then we pick a cutter. the cylinder gets extended to slice the other body. It then goes into the “Select Regions to Remove” mode to let you select the piece to delete if needed.

To delete the inner piece and then go to the next hole. This works great for the cylinders, but not so well for the square holes. As soon as you pick a a cutting surface, it extends in all directions and slices though the whole body, which is not what we want in this case.

In cases like this, I have always used the combine tool, but we need to have the cutters created first. So normally I would select all the edges along of the features and use the Pull tool to extend them through the bodies. You can use the Power Selection tab to select all the edges of the same size, but I just used the box select to select all of them.

The first tip I’ll give you is that you can put all your cutter surfaces into a component.

Then when you use the Combine tool, you can select on a body and select the cutter component to make all the cuts at one time. You can also box select to select multiple bodies to cut at one time.

It will go through and process all those cuts at one time, which can take a while, depending on how many bodies you’re trying to split and how many cutters you have.
You can also use the box selection in the deletion mode to let you pick all those small bodies.

At this point in the blog creation process, I learned something new about the Split Body tool that will change my “go-to” process.  In the Split Body tool, you can box select around the bodies to be cut, and also around cutter surfaces. When you do this, the surfaces of the square holes are not each extended separately in a way that they would slice through each other. They are only extended in the Y-direction in this case. You can also box select around the newly created bodies to be deleted.  So, we can create all the holes in all the bodies with just one Split Body command, using three box selections.

Hopefully I have explained the difference between the Combine and Split Body tools, helped you understand better when to use each, and found a new way to use the Split Body to make a thousand cuts with one command to save you some time. (That really is always my point. )

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