Mold Split

kristoffer_falk

I am trying to make a mold split to a mold, that has already been splited. But it's not really working.

Is it not possible or am I making a mistake here?

It's the middle part, which I would like to split in half using Surface 1 as a split line.

I have also tried the normal split function without result.

romeograham

The problem is that the tire tread creates "non-manifold geometry" when you split with the Front and Top planes:
You can see that the corners of the treads are coincident with the split plane. Once you make the cavity tooling, those areas can't be split.


A simple solution could be to add fillets to your existing treads, so the corners are no longer coincident with the split plane:


Here's a document showing this in action: https://cad.onshape.com/documents/c86cb25c34b7a77dcd7dccfe/w/1d6dc4efcb1cae5df0a9ebda/e/d706e67e264f0ba172c1a0b3

There's also a slightly different approach to part studios: you may find value in separating the Part modelling from the Mold modelling.
Hope this helps!

EvanReese

It's tough to say without access to your model. Maybe you could just use the right plane as the splitting tool?

romeograham

The 4 Mold Custom Features are kind of specific to a limited set of operations, and are looking for specific bodies to do the work (often created by the previous instances of the Mold features. It's likely that the Mold Split custom feature you're using for this feature isn't set up for using Surface 1 as the parting surface (in fact, it's looking for a single surface body that includes half of the cavity, and extends out to the outer faces of the Mold block).

It would probably be best to use the regular Split feature from the toolbar for this feature and use the Right Plane as @Evan_Reese suggested above.

Use the Mold tools at the beginning of your feature list (and probably only once per Part Studio), and use regular features after that. There is good documentation for the Mold tools, but they are a tough to get working in some difficult situations.

kristoffer_falk

Thanks for the feedback.

I got to know about the Mold Stock and Mold Split in a webinar featuring Neil Cooke, and he used a surface to split the mold, and I also split the mold twice using a surface.
I have also used the regular Split feature with a plane as parting surface. Also no luck.

I have split the part using 3d part studio in Windows - that us usable, but I would like to work more on the parted parts in Onshape. It's still a work in progress....

romeograham

@kristoffer_falk
If you can share a public link to your model, we can have a look and see if we can help.

EvanReese

If the normal split tool with a plane isn't working I suspect the split would create "zero thickness geometry". Rotating the position of the wheel a degree or so at the top of the feature list might fix it. A shared model would definitely help though.

kristoffer_falk

Sorry for the long wait.

Here is a link to my model. It is the part B which I would like to split. And ideally in 4 parts using the Front and Top plane as split lines.

https://cad.onshape.com/documents/a1ec71c942c235a8a585444f/w/d09780828fd5d7e4f9b9f4cd/e/b0e40daad5f47a96b1cd0c4c

romeograham

The problem is that the tire tread creates "non-manifold geometry" when you split with the Front and Top planes:
You can see that the corners of the treads are coincident with the split plane. Once you make the cavity tooling, those areas can't be split.


A simple solution could be to add fillets to your existing treads, so the corners are no longer coincident with the split plane:


Here's a document showing this in action: https://cad.onshape.com/documents/c86cb25c34b7a77dcd7dccfe/w/1d6dc4efcb1cae5df0a9ebda/e/d706e67e264f0ba172c1a0b3

There's also a slightly different approach to part studios: you may find value in separating the Part modelling from the Mold modelling.
Hope this helps!

kristoffer_falk

Thank you @romeograham!

A simple solution to a complicated (for me) problem.

I have replicated your design changes in my model without problems.

romeograham

One other note @kristoffer_falk the split tooling components can be successfuly made (in CAD) with this method, but there are very (very!) small features in the resulting tools...so if this is anything more than a CAD learning excercise, you'll need to evaluate the tooling components carefully. I think the easiest solution might be to rotate the part (Tire) inside the mold just a bit so that the treads don't interfere with the mold split faces.

kristoffer_falk

Yes I spotted the line when moving the B-parts away from each other.

I plan to try and print the mold and use it to cast the tires.

Your point about rotating the tire makes good sense. This is the result after a 3 degree rotation. 

Now the split line is free of the thread pattern. If it makes any problems in the casting, then I can adjust the number of thread patterns to increase the distance between them.

matthew_stacy

@kristoffer_falk, the alignment pins between center mold quadrants may prove challenging because they are orthogonal to one another.  What is the direction of pull?

Presumably you want to pull a mold quadrant at 45 degrees to extract the tire.  Perhaps you could mate ribs to slots rather than using dowel pins.

kristoffer_falk

Good point @matthew_stacy.

Thanks for the input.