There are common poor-practices in the moulding industry, in this series we will shed light on some.
They often occur due to:
Lack of internal company best-practices; attempting to rush though a project to meet the common compressed deliveries of today’s industry; lack of available tools in competitor software products; lack of awareness by the designer; or sometimes due to lack of training in the functions/tools available to the designer.
In this series we will cover several scenarios where the right feature functions, and the right training, can create a better finished product and more
stable steel conditions.Stable steel conditions allow the mould to stand up to high production volume and eliminate production downtime due to pulling
the mould for repair.Having more of the finished parts being passed through QC inspection, and having less downtime of the mould, both contribute into
a lower life cycle cost of the project.
The scenarios we are going to cover in this series include:
- I)The general Isocline split
- II)The corner contoured split (This entry)
- III)Mechanism lead in and angled Isocline.
What is an Isocline?
For those unfamiliar with the term Isocline, here is the dictionary definition:i-so-cline, noun, a line connecting points of equal gradient or inclination.
Where to find it
The Isocline Feature can be found several ways.If you are familiar with the traditional NX menu you will easily find it under Menu->Insert->Derived Curve->Extract
If you are more comfortable with the NX Ribbon style interface first you will need to have the Advance Role loaded, or your own customized Role where you have already added the Extract Curve to your ribbon. In the Advanced Role you will find it in CURVE->More Gallery->Derived Curve group->Extract Curve
There is always the command finder where you can search the Isocline feature and access it directly.
Use:Part II, The Corner Contoured Split
Note:If unfamiliar with the Isocline feature and its use, please refer to Part I of this series where it is described in more detail.
Here we have a moulded part with a full radius around the periphery of the wall-stock edge.
This is a close-up view of the radius following the outer wall-stock edge with an Isocline generated for the parting-split.
Common Poor Practice of Contour Split Parting-line
The common poor-practice around contoured corners typically manifests as a designer pulling off the parting-line split in the X and Y axis without regard for the shape when looking down from the plan view (die-draw axis).This often leads to poor steel conditions when the plan view has curvature and the profile has depth changes.These steel conditions can become very sharp (knife edge/feather edge) when the parting-line split is done off a ball radius.
Below is a Plan view (die-draw view) of poor-practice parting-split that is seen all too often.
Below is an Iso-View of the poor parting-line split.
Items to note are:the transition point at ‘x’ –which never gets fit cleanly and leaves a little mark on the part at that junction point; and the run-off of the parting-line split in the Y-Axis that is pulled off without regard to the shape of the part—this creates a wedge shape for the cavity steel coming in.This is better illustrated in the Section A-A which accompanies the Iso-View.
Below is another section cut Normal to Z-Axis just to illustrate the knife edge for another perspective.
This type of parting-line split with such a sharp steel condition has a significantly shorter life span than a well generated run-off.This type of steel condition can be difficult to fit during the manufacturing process when spotting the core and cavity halves together.During production this condition tends to get bent over and wears quickly--requiring frequent weld and re-cut / re-spot work.This raises life cycle cost of the mould, and also overtime the match edge of core to cavity tends to drift, causing more rework on the opposing half to keep the match line clean.
Best-practice for Generating a Robust Corner Contour Parting-split.
First generate the Isocline as previously described.We want to create is a parting-line split surface that extends perpendicular to the shape of the trim-edge while maintaining a flat to Z orientation.Creating this type of mould run-off ensures that any sections cut perpendicular to the contour will always be creating a solid steel condition for both the core and cavity based of the Isocline curve.
This type of run-off can’t be built by simple Extrudes since the Extrude needs a fixed axis.The designer could do some Extrudes for areas that are aligned with the X or Y axis and then manually build smooth surfaces to transition around the corner-- connect tangentially to the two Extrudes. Manual operations can be time consuming, so in this case the two best options we have are Law-Extension surface, or Ribbon Builder.Both features can be set to create an almost identical desired output.
Law Extension Method
The Law-Extension Feature can be found several ways.If you are familiar with the traditional NX menu you will easily find it under Menu->Insert->Flange Surface->Law Extension
If you are more comfortable with the NX Ribbon style interface first you will need to have the Advance Role loaded, or if you are in the Essentials Role you will need to first add the Surface Ribbon tab to the top interface by right-clicking and setting the check-mark for Surface.Once your Roles and Ribbon are set you will find it in SURFACE->Law Extension
With the Law Extension dialog box open:
1.Set the Type to Vector method in the drop down option.
2.Select your previously created Isocline curve(s)
3.Set the vector option to be the +Z die-draw axis.
4.With the Length Law-type set to constant, enter a value for how long you want the surface extension to be.
5.With the Angle Law-type set to constant, enter 90° (or -90° if curve direction forces surface to extend the wrong direction.)
Then click OK and a surface is build °90 from the die-draw axis which follows the contour of the part.
Ribbon Builder Method
The Ribbon Builder Feature can be found several ways.If you are familiar with the traditional NX menu you will easily find it under Menu->Insert->Surface ->Ribbon Builder
If you are more comfortable with the NX Ribbon style interface first you will need to have the Advance Role loaded, or if you are in the Essentials Role you will need to first add the Surface Ribbon tab to the top interface by right-clicking the border for the tabs and setting the check-mark for Surface.Once your Roles and Ribbon are set you will find it in SURFACE->Surface Group->More Gallery->Ribbon Builder.
With the Ribbon Builder dialog box open:
1.Select your previously created Isocline curve(s).
2.Set the vector option to be the +Z die-draw axis in the drop down list.
3.Set the ribbon extension length as needed.
4.Set the angle to 0°
Then click the preview option to see if that ribbon is created as desired, click OK if it is, and a surface is built that is 0° Normal to the +Z axis of die-draw.
Using either method shown above to generate a run-off surface from the Isocline results in a split-surface that separates the core and cavity halves at the split of the radius. It also follows the curve path so that the extension/ribbon is created close to perpendicular to the plan view orientation.This ensures the steel condition is consistent and does not exaggerate sharp corners by the designer arbitrarily determining which vector direction to pull the surfaces off of -- as seen in the poor-practice example near the top of this article.
Below is our result, and the pictures following show the superior steel condition created as a result.
Below is an Iso-View and Section view cut perpendicular to the Isocline curve.
Below is an Iso-View and Section View of a section cut through the vertical wall transition
If you would like to learn more about this operation and other advanced operations, you should attend one of our advanced NX CAD courses. To arrange for advanced training please contact your Account Manager, or contact us directly at[email protected].