Positive draft and negative draft

[zhengrong]

Hello all,
I just want to ask a basic question. How dose NX define whether a face is positive or negative draft when doing the draft analysis or in the check regions( molded part validation)command? Can we say that if the face is invisible when see from the die draw direction, it is negative draft. Otherwise, it is positive draft.
Thank you.

 

[Xwheelguy]

First off, I cannot answer for Molded Part Validation - never used it.

From my experience, negative draft means that the molded part will get stuck in the mold (AKA die lock) based on the draw direction and the angle will usually open opposite from your draw direction. Positive draft means the part won't get stuck in the mold when pulled in the draw direction and the angle opens in the same direction as your draw direction. I'm others might have a different description of that.

Draft Analysis is based upon your selection(s). If your Selection Intent is set to Single Face, then the invisible faces you're seeing aren't being analyzed. If you want to analyze all faces of a solid, change your Selection Intent to Body Faces and it will select all faces in the body you've selected. Over on the right side of the screen, you will see a graphical scale based upon your inputs (you'll have to specify a limit angle which is typically the minimum angle you'll allow on your mold to avoid die lock).

In the attached image, I created a cylinder for my mold "base" and subtracted a square from it and added 4 different draft angles to each of the 4 walls. The yellow wall you see is 2.5° draft (from +Z) and going clockwise the walls are 5°, 10° and 0°. You can see in the dialog that my limit angle (minimum angle OK for molding) is 5°. Anything that is blue or red is, to me, going to be considered negative draft. Positive draft technically would be green or yellow based on all of my inputs (draw direction and limit angle). The scale on the right gives you what is positive and negative. Now, the yellow area is an area of concern because it doesn't meet the 5° limit I set - and that could be considered negative draft but only in the sense that it isn't meeting our minimum requirement. The angle for that wall is yellow because it falls between 0° and 4.99999999° (it's 2.5°) I'll need to go back to the model and revise that angle until it turns green and passes my (fictional) requirements to avoid die lock.

Hope this helps.

draft.png


Tim Flater
NX Designer
NX 9.0.3.4 Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

 

[zhengrong]

Hi, Thank you for your help. I am more clear now.