For finishing in 5 axis, NX CAM software development is focused on the “Guiding Curves” operation. Our NX CAM customers report guiding curves to be very flexible with the geometries and patterns it handles, yet providing good machine behavior and finish quality. In the future Tech Tips I’ll write more about it, but to give a better perspective about Guiding Curves, let’s start with some explanations about Variable Contour operation using Surface Area and Streamline. Knowing how the system works, helps you guide it to do what you want it to do.
There are many aspects we can cover, but I will concentrate on three important ones:
Coverage and Pattern
Position, Projection and Collision Avoidance
Tool axis policy
The Coverage and Pattern is covered in this NX CAM Tech Tip. The other two as well as detailed description of the Guiding Curves operation will be detailed in separate Tech Tips.
Note: this article is describing the behavior of NX CAM software, but many pieces are common to surface base (NURBS) path generation in other software.
Coverage and Pattern
Generating the pattern on an arbitrary set of faces with variable slopes is pretty challenging. Some of the faces you see on the screen have a parametric representation called U and V. To visualize it you can use the modeling ‘Isoparametric Curve’ tool to draw those:
In Surface area when you select this face as the drive, the system will use this parametric representation to draw the pattern. ‘Zig’ / ‘Zigzag’ / ‘Zigzag with lifts’ will go along U or V. ‘Follow Periphery’ will offset from the outer shape in the parametric field.
Helical will only work if the drive performs a close loop (i.e. - a cylinder).
In case that you want to machine more than one face at a time, three things may happen:
The next face I select has a matching parametrization so the system can merge those to a grid of well behaving U/V: it also can be extended to the next row(s):
The next face has a parametrization that do not match. This will pop up the “Grid Error”:
In this case the curves on the right lower side of the selected face cannot find continous matching curves to the faces already selected.
In a limitted set of cases you can “force” the system to accept an irregular grid like by increasing the chaining Tolerance:
It is a bit experimantal and the results might not be smooth but it is useful to know it and try when needed.
To handle the cases where a well behaving grid cannot be extracted from the cut area geometry we have Streamline. In Modeling there is a tool to create “Through Curves” surface:
Which uses two flow curves to blend a surface in between. As you can see the surface is sometime inside and outside the part. As further the drive deviates from the part – your tool path will stick less to the intent. To get a bit closer you can use Through Curves Mesh.
With proper selection the surface is way closer to the path, yet it is not perfect since we miss some cross curves. In manufacturing the same is available in streamline.
Flow and Cross:
In case you need cross curves but the geometry does not have those and you do not want to streach your modeling skills, NX CAM enables you to generate those on the part:
This will be detailed in another article.
The parametric representation allows you to trim or extend. Because it is parametric – you cannot use a distance value (i.e. extend by 2 mm or 50% Tool), instead you can only use a % value:
The pattern from the drive is later projected to the cut area / part so the real coverage cannot extend beyound the (extended) drive, nor beyond the cut area / part geometry. This topic and other Position, Projection and Collision Avoidance topics and a detailed description of Guiding curves and how it is different will be discussed in my next NX CAM software Tech Tip.
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