Michael Clemons

Overflow grooves - rubber molds

Discussion created by Michael Clemons on Jul 9, 2019

Hello all,


I have struggled time and time again to create what we call in the rubber industry an overflow groove or flash groove with complex parting lines.  Today I finally found how to do it well and I thought I would share.  Typically you want to run a ball mill around the perimeter of the cavity so there is a slight land at the parting line and then there is a groove that extra rubber can flow into.  What I did is this:

1) Above the parting surface create a plane that is perpendicular to the pull when the mold separates.

2) Start a sketch and offset the entities that make up the perimeter of the cavity.  This will be the center of the guide curve for the solid sweep, so adjust the offset appropriately so your ball mill cuts where you want.  Make sure that all your entities join each other with tangent relations.  Use the sketch fillet tool to fix any square corners.

3) All the surfaces that will receive the projected curve must also be tangent.  Add fillets on your parting line surfaces so they are smooth transitions.  Use the fillet size that will be correct when you ball mill the mold in the CNC machine.

4) Select the sketch you made in step 2 and Insert > Curve > Projected...  Select all the faces that will have the overflow grooves to make a continuous curve around the entire perimeter of the cavity.

5) Start a sketch on a plane that intersects this curve.  Draw the profile of the ball mill that you will use and make sure there is a pierce relation between a point on the axis of revolution and the projected curve.  Make a revolved boss from this sketch and uncheck "merge result" in the dialog (this is required for the solid sweep).

6) Insert > Cut > Sweep, choose solid profile and choose your revolved boss and then your projected curve.  If all goes well, you should get your expected overflow groove.


Note: For some reason when you are selecting your profile for the solid sweep, you cannot select the feature in the tree, you must click on the feature in the graphics area.  This is the case for 2019SP3, but has been a problem for many years.