3D surface milling defects

[SKaplanZW7T5]

I can't seem to get rid of these surface milling defects. They show up in both the stock simulation and the finished machined part. I've tried using various toolpaths (mostly parallel or 3D contour) on numerous molds that I've machined over the past few years. Playing with tolerance/smoothing parameters does have an effect but has not eliminated the surface defects. The images below show an example and the corresponding tolerance parameters. 

Any ideas?

 

A few keywords to help with future searchability: kellering mold cavity faceting linearization tolerance finish gouging surfacing 

[seth.madore]

If it's a 3 axis move, Parallel may or may not apply smoothing. Can you share your file, or a redacted file that still has that feature and toolpath in it?

What does it look like when you select the "Show Points" option in Simulation or just general toolpath viewing:

 

[SKaplanZW7T5]

Thanks for the response. Here's the points view and file attached.

 

[seth.madore]

A few comments; 

1) The surface model that you're working with is inverted (it's inside out). I took some steps to flip the faces as well as patched and stitched it into a solid mode.

2) I think there's some less-than-ideal curvature going on, which will contribute to a poorer surface quality in the machined part

3) Really cranking up the Surface Triangulation Tolerance (in compare and edit) seemed to have a net-positive impact.

Before:

 After:

What machine are you using, what's the control and what's your post processor?

One last; Steep and Shallow seems to do a slightly better job on the "Steep" portion of the part:

 

 

[SKaplanZW7T5]

Seth, I greatly appreciate your input but I don't think any of those things helped with my issue. Here are my comments to your notes:

1) Thanks for pointing that out. That was a customer-provided STEP model imported from another CAD package.

2) I can't edit the geometry since I was just the "CNC Guy" for the sample model provided.

 

3) Comparing your surface triangulation and smoothing values (.0000075" & .0005") to mine (.0001" & .0001") made the toolpath "points" view look cleaner but the stock simulation shows much larger gouging with your parameters. Screenshot:

4) I am using a generic Haas NGC mill post processor with the G187 property turned on. I most frequently machine molds on a 2013 Haas VF4SS (pre-NGC) and a 2020 Haas VM-3 (NGC) both with HSM option enabled. Since these defects show up on the part exactly as they appear in the stock simulation, the errors must be CAM induced.

5) The sample file has undercut geometry. I've only been able to get the 3D Contour toolpath to reach under-cut features. Aside from that, the Steep & Shallow toolpath you made still has substantial surface defects (stock simulation screenshot below). So, I don't think the toolpath points is a good indicator of what the finished part will look like. 

 

As I said, I appreciate your support and don't want to come off as ungrateful! Just trying to be straightforward, as I would really like to get to the bottom of this issue. These artifacts show up 100% of the time in both the stock simulation and the machined mold cavities regardless of model type (surface vs solid), post processor, CNC control, feeds/speeds. I'm sure other folks have encountered this problem too. Any other ideas?

[seth.madore]

Not to worry, you don't sound ungrateful at all! So, I'm still rather certain this has to do with the curvature of the model and how Fusion is calculating the toolpaths against it. For a toolpath such as 3D Contour, it creates a mesh (STL) of the model and applies toolpaths against it. However, Blend, Flow, Swarf, Flat, some parts of Steep and Shallow (Slope boundary computation), all use the Brep for some/all of their calculation. 

I think your best approach is going to be to use a combination of the toolpaths to machine this part. You mention "Undercuts". Those aren't present on the sample file you shared, so I'm unsure of how large or deep they are.

As a quick test, I tossed a "Flow"(Preview) toolpath onto the part (remember, this calculates directly against the Model, not the STL mesh). The results, in my opinion, were much cleaner, although the file size is rather large (as it's a 3D move, arcs are not fitted to the toolpath):

The new "Flow (Preview)" toolpath is available in Preferences > Preview Features.

 

[SKaplanZW7T5]

Seth,

I agree that this issue has to do with how Fusion is calculating toolpaths against model geometry. However, I encounter these surface defects with all of Fusion's 3D milling toolpaths in all applications, regardless of model curvature, model type (surface vs solid), etc. This model we've been looking at does in fact have negative draft or "undercuts" (hence the lollipop ball mill) as do many of the 3D molds I machine. To my knowledge, 3D contour is the only Fusion toolpath which can reach these features. Here's a screenshot of the draft analysis (red/blue being undercut features)

I've attached a new sample file which I created just for this troubleshooting process. It's a good example of a female mold cavity which I would often machine, although it has no negative draft. It's a solid model lofted from 2 sketches, nothing abnormal. I quickly created a couple toolpaths which show the persistent defects in stock simulation. I did zero fine-tuning so there is a lot of room for improvement. That said, I would like to see if you (or anybody) can eliminate the defects and get a high quality smooth surface. I am willing to machine the part out of aluminum to confirm that we've got it all figured out. Here are some screenshots:

 

 

I'm a big Fusion advocate and I would really like to find a solution here. I have machined many molds over the past 15 years using various CAM packages and Fusion is the only software in which I have been unable to achieve high quality mold surfaces. Looking forward to seeing what you can come up with. Thanks.

[seth.madore]

@SKaplanZW7T5 thanks for the opportunity for the challenge! One quick, slightly related question; what do you have for machining equipment, workholding and tooling? High speed machining, massive look-ahead?

I'll be poking away at your file over the next few days as time allows. I certainly see some of the defects you've raised, and will be interested to get the view of the developers on them and see what we can do to improve it.

Some initial comments;

Of all the toolpaths, the only ones that have a prayer of producing a beautiful finish on this part are:
Blend

New Blend

Flow

New Flow

Of these, it appears that New Flow has a gouge that's being created, so let's scratch that off the list for now.

We also want to be machining "along" the wall and not "across".

Give me a couple days to poke around and I'll post back when I have something more concrete

[SKaplanZW7T5]

Alright thanks for looking at it! I have a 2020 Haas VM-3 (NGC control) and a 2013 Haas VF-4SS (pre-NGC).  Both machines have a CAT40 12K inline spindle, high speed machining, TSC, expanded memory, probing, 4th & 5th axis etc. Lots of tooling and work holding options here at the shop.