Questionable Surface / Face Features

[REDesigner09]

Hi,

I have a turbine blade and the airfoil concave surfaces or face has a very noticeable questionable vertical surfaces or faces in the middle of it.

This is most noticeable when Shading with Edges is on & of course, when shading without edges is off, this area looks perfect.

My question is that is CAD model is considered a "validated" model, which will be handed over to ANSYS operators & I think CNC operators.

If they inspect or analyze this model, will they also see these questionable surfaces or faces? More importantly, how are these questionable surfaces / faces affect end ANSYS analysis & CNC programming or any other CAD model analysis?

If this is an issue & not just an appearance issues then I need to justify the "risks" or "ramifications" to the Design Engineer & Management that not fixing this area will cause ....???

Thanks

 

[cowski]

...questionable vertical surfaces...

...is considered a "validated" model...

How was the model validated? Do the questionable faces pass the geometry checks (Analysis -> examine geometry)?

The fact that there are 'extra' faces is not necessarily a problem, but long, skinny faces (aka sliver faces or high aspect ratio faces) can lead to meshing problems and/or questionable FEA results.

I have little experience with CAM, so I'm unsure how it would affect CNC programming.

You may want to include these downstream users in the validation process. I've spent a good deal of time passing 'fixed' models back and forth to an ANSYS user who kept finding more and more 'problems'. We didn't have a very good validation process at the time.

 

[REDesigner09]

Hi Cowski,

This particular turbine blade or CAD model was "validated" within Geomagic or Polyworks software. In these applications, it looks for positive or negative surface differences when compared to the nominalized '.stl' that was created through reverse engineering data collection.

In this particular instance, the surfaces differences matched up well or was in tolerance & therefore, did not recognize these questionable surfaces that I see.

From a visual perspective, it does not look good & will show up in the drawing, which would then have to be manually edited out in all views.

Trying to determine if there are ramifications - small or big that would justify the need to fix. Of course, we'll under time constraints & the other engineers believe the model is good to go, but I think it needs more work because there are multiple questionable surfaces or faces or edges.

If I recall correctly, through ANSYS & CNC programming & perhaps some other applications, these surfaces would be picked up, but I don't use these applications.

I just wanted to get others opinions.

Thanks

 

[REDesigner09]

Hi Cowski,

So, you didn't haven't a good validation system either? That's the problem I'm having now with the company I work at. The engineers thought they do or did, but now that more "eyes' are on their work, we definitely need to improve it & slowly in the process of doing so.

Previously, this company did not have a CAD Design Engineer who can critique CAD models to make sure it met dimensional requirements. That's part of what I'm doing, but it's been a while. I do believe that these questionable surfaces, faces or edges I see will cause downstream issues, but just wanted to validate & justify some reasons or ramifications for not fixing from forum members here.

Thanks

 

[JohnRBaker]

Try editing the display tolerance.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.com/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[DaSalo]

The NX CAM module allows you to set toolpath tolerances in much the same way that you can set tolerances for modeling operations. If the face is smaller than the tolerances set the toolpath with often just flow right over it. Every situation is different, however. What do your Zebra stripes look like when you do a face analysis? If you have smooth continuity across that face then you should also get a smooth toolpath across it.

 

[REDesigner09]

Hi John, DaSalo & Others,

It's probably best for me to just show you a picture of my questionable surfaces, faces or edges, rather than me trying to explain them.

So, what you will see is what is considered a "validated" turbine blade & with shading without edges, this turbine blade does look pretty dam good.

Perhaps, my questionable areas isn't that significant of a concern or issue, but I just want to get others opinions to see what their thoughts are, if they see the same things that I'm seeing.

Check out the picture & give me your assessments if this is a low, mid or high concern & if changes aren't corrected, what might be the ramifications.

I'm thinking these will show up in ANSYS analysis & perhaps in the CNC programming, where they use the final CAD models, but I don't use these applications & therefore, not my areas of expertise.

Thanks

 

[cowski]

I can't download/view your file, probably because it has "&" in the file name. Please rename it and re-post.

 

[REDesigner09]

Hmm?


It's a '.jpg' image, but I did change the name of the file to not include any symbols.

Hopefully, this opens.

 

[DaSalo]

Speaking from a CAM perspective here:

1) There is no way to say anything with certainty without analyzing the model in detail. The types of things that tend to cause trouble with CAM paths are small ripples, reversals, gaps, or other small, sudden changes in continuity. The interruption of the contoured surface with a joint or small face as shown in your image is not necessarily a problem. You could have much bigger problems in the surface of the larger contoured faces if they aren't smooth.

2) That said, it all depends on the manufacturing tolerances. If the tolerance on the path can be loosened up safely the software will often smooth out a lot of this type of stuff.

Your concern for the downstream users of your model is admirable. We manufacture turbine components for several large OEMs and are constantly amazed at the poor quality of the models coming out of some the worlds top companies. Some companies do a great job, others provide models full of rippled, twisted, and torn surfaces. We are always able to find a way to use the models we receive to manufacture a quality product. Sometimes we have to rebuild the model or resurface selected areas to get something we can work with.

 

[cowski]

Thanks, that one works.

I wouldn't worry too much about what the top and bottom arrows are pointing at, but that mass of extra faces in the middle might be a problem for FEA (or CFD) meshing and analysis.

You might want to try out the join face, delete face, or replace face commands to see if you can get rid of any of those extras without affecting the overall shape too much.

 

[REDesigner09]

Hi DeSalo & Cowski,

Thanks for the feedback & suggestions. As suspected or appears, it these questionable surfaces "could" cause issues downstream or would require analysis engineers to find work arounds to ignore these surfaces.

Just wanted to reconfirm my perspective of these questionable surfaces.

Thanks again..

 

[Xwheelguy]

Adding to what has already been said.....

I'm not an experienced turbine blade designer, but I have had my fair share of surface analysis - seems to me that you could verify at least the continuity and smoothness (transitional) within NX and possibly get a good "feel" for surface quality - but maybe not to the precise degree to which you may require - without knowing full details, difficult to give a definitive answer.

The Face Analysis tools (Gaussian Radius), once set correctly, can point out obvious flaws in transitional surfaces, such as the middle surface(s) your image is pointing to. Look out for sudden and drastic changes in color rather than gradual and more natural looking transitions from one color to another. You may have to "play" with it to get a feel for it....like throw a cube in there and see what the display looks like with sharp corners, then modify the cube to have edge blends and see how the flat surfaces transition into the rounded corners - you will see what I mean.

Another powerful tool within NX (possibly depending upon the licensing configuration you have) are the Cross Sectional Curvature Combs - the peaks of the combs (again, once set correctly) will point out flaws within surfaces, regardless of how minor they might be.

Interrogating those surfaces as early as possible in the design process is key, especially if those blade surfaces are modeled as sheets and later sewn into a solid body and finishing features (blends, holes, chamfers) added later.

Hope this helps.

Tim Flater
Senior Designer