Mold Tutorial

A Mold In 8 Hours

Here is my second tutorial, aimed at moldmakers.
There are specialized tools to do the same job, often an integrated software that will have all the functions used here (with mold-industry specific terminology but its the same functions anyway) such as UG MoldWizard, Cimatron, Vero Visi, MoldMaker... but most cost a lot more than the combination of Rhino and one of the dozen middle-range parametric modeler such as SolidWorks or Solid Edge and are a lot more difficult to master.

You can click on most images to open a bigger version in a new window. You can leave this new window open and the subsequent images you click on will show in this window, letting you read the main page at the same time.

You can download a PDF version of this tutorial if you want to print it.

A Mold In 8 Hours Here is my second tutorial, aimed at moldmakers. There are specialized tools to do the same job, often an integrated software that will have all the functions used here (with mold-industry specific terminology but its the same functions anyway) such as UG MoldWizard, Cimatron, Vero Visi, MoldMaker... but most cost a lot more than the combination of Rhino and one of the dozen middle-range parametric modeler such as SolidWorks or Solid Edge and are a lot more difficult to master. You can click on most images to open a bigger version in a new window. You can leave this new window open and the subsequent images you click on will show in this window, letting you read the main page at the same time. You can download a PDF version of this tutorial if you want to print it.
	First of all I set the tolerance in Rhino to be extremely loose like 10 units...
...so when I import the IGES file, a dialog box will ask me if I want to proceed with the import even if the tolerances are not matching, telling me at the same time what units and tolerance were used in the file. I answer No to cancel the import...
	...and set the units and tolerances to match the file's properties and import again.
I then carefully check the imported model, spending as much time as needed to understand it completely (here we have a suspension part for a snowmobile, modeled in Euclid). I then join the surfaces one by one, checking for bad objects and naked edges often; after about 5 surfaces have been joined. Most of the time, some repairs like re-triming or recreating some surfaces, are needed. The final result should be a closed solid from which the volume can be calculated and confirmed to the client.
	Now it's time for one of our favorite tool; DraftAngleAnalysis. With an active CPlane that is normal to the mold movement (parallel to the press' plates, in this case the World Top CPlane), this command shows us what part of the object is at an angle equal or greater than the one specified, relative to the vertical. In this image what we see in blue will be in the fixed part of the mold, what we see in red will be in the moving part. What we see in green has no draft so we'll have to do something about that in the next step. If there was a of blue area surrounded by red, or a red area surrounded by blue, it would mean an undercut. That means modifying the part or designing the mold with moving systems such as lifters, slides or drawers. These greatly increase the mold's cost so the part designer should try to avoid them.
The big hole with vertical walls will be machined after the part is molded, so I just extract and delete these vertical surfaces and fill the two holes left with two planar surfaces, then join these with the object, getting a closed solid again. In the next pictures you'll see that I chose another method that works when the hole is totally enclosed in one surface; I simply untrimmed these edges. It makes a simpler object.
	The VolumeCentroid command creates a point at the object's centroid, a good start point for the scale command to take the material's shrinkage into account. Here I scaled the object by 1.03 because the material specs says the material will shrink by 3%.
The Silhouette command is not perfect but it creates curves from which it's usually quite easy to obtain the parting line of the object (the line that defines the separation between the two mold halves). Don't forget to have the right CPlane active (the one perpendicular to the mold's opening direction) when calling this command, in this case the Top CPlane as when we used the DraftAngle Analysis command.