Solid Modelling - Modelling for machining

Starboxx

Hi guys !

I make carbon fiber parts, mostly for cars. Up until now, i have made my molds by hand, either copying/modifying some existing parts, or sculpting some models out of foam. But recently, i decided it was time to stop doing the molds by hand, and have them milled, for a question of speed and quality over price.

I don't know if anyone here is "fluent" at modelling stuff for machining, or with softwares like Solidworks or Fusion360, but the machinist i contacted required that i provide some models from Solidworks or some "Solid" models.

After having played around evaluation versions of Solidworks and Fusion, i realised how hard it is to model complex shapes with this type of 3D. I have always been used to polygon modelling, since i've been playing around 3D since around 2005, but i find it extremely tedious and complicated to model with CAD softwares.

So, i was wondering if any of you guys have some tips to model some shapes like vehicle bodywork based on photogrammetry scans, or if there are ways to convert/remodel some subdivision polygon modelling? I wish i could just model my molds in standard 3D packages but it is not the case, as the machines need some sort of "mathematical models" to be able to understand the 3D.

Anyhow, if any of you is familiar with modelling for machining and/or CAD softwares, i would greatly appreciate some tips on modelling workflows to create complex shapes a bit less "parametric".

Thank-you !

Andy_3d

What about Rhino? I know it has tools for detailed modelling/ designing and there are users who use it to prepare models for 3d printers.

jaker3278

Hi , can you explain the "mathematical models" needed for the machines to understand the data. I come from a 3d printing background and i use polygon modeling for it. All i need to do is export as an .STL file and the machine translates this into the necessary gcode. Thats all that most of these machines are working with is gcode, a very simple code that can be read in notepad. Its just a list of x,y,z commands that the stepper motors on the machines are reading. 

I would recommend finding out what file formats are needed. You might find you can still use polygon modeling. 

Starboxx

Thank's for the answer guys !

After further investigation, i found out that i just need to use nurbs, wich is kind of the equivalent (as far as i understand) as surface models in CAD softwares. I sent a polygonal subdivision model converted to nurbs in Maya to my machinist, and apparently it opened as a surface model in Solidworks. The only thing he told me is to "tune up" the resolution (probably the steps of curves of the nurbs).

He requested either *.STEP or *.x_t formats, wich i have been able to export from Maya.

About Rhinoceros, yes, i have heard of it, just didnt tried it beceause i can't find an evaluation version and i don't feel like purchasing a 1k software without trying it.

The problem with polygon model itself, is the "resolution" of it, if i can say. CAD programs don't have subdivision options, and for the sizes of parts i intend to do (example a bumper of a car), the polygons edges will be marked and visible on the machined mold. If you are using some 20M faces models for 3D printing of a 20cm figure, this is negligable, but when your bumper is 140cm large, this is something else (plus the fact the machinist will hate me for sending him so huge files for his machining software wich is probably not optimised for this).

Now i am just trying to figure out the best workflow to have good resolution from photogrammetry scans with realitycapture and to remodel it as precisely and smoothly as possible (might need some sub milimeter precision on some parts).

It'll be either :

- Polygon subdivision model converted to nurbs
- Modelling nurbs directly
- Give a try to Rhino wich apparently is a nurbs modelling software.

kanga

Polygon models are faceted, always. You just dont see the blocks. Polygon modeling is always an approximation of a form. Poly modeling is fine if the translation of curves is approximated for rendering either for realtime or precooked animation/presentation. Im not sure about 3D printing, might be handy too look into that. Solidworks is a friendlier program then CAD, and there are others out there that deal with real world measurements. By the nature of poly modeling I think you are stuck with splines for now.

welbot

You could try modeling it in whatever package you normally work with, then importing to Fusion 360, and converting it to a T-Spline model. 
If the mesh is heavily triangulated, it may have issues, but results may vary between file formats and the complexity of the mesh. 
I've often used 3d studio max to get models in to Fusion, and if I have any problems converting the mesh inside Fusion, generally quadrifying it will help. There are scripts for max to assist with that though, so it may depend on the software you're using. 
There's a video showing how to convert a 3dsmax model to a solid body in Fusion here if it helps.
https://knowledge.autodesk.com/support/fusion-360/learn-explore/caas/screencast/Main/Details/7d2b6c16-60c4-48c4-9c9d-49245456ed9a.html

janoshx

I have done 3D modeling for CNC milling for quite long time. I highly recommend to use Fusion 360 or Rhino. Fusion 360 has good construction history so you can alter dimensions and values while working. Rhino is good as well but I am not sure if it has, today,  a construction history like fusion has. Moi 3D i also quite good but more simple than rhino.

When using fusion make sure that you measure everything and fix the location of all parts by measurements. You don't want to accidentally move or change anything.

In office i use a software called Catia which is like fusion 360 but with steroids. Fusion is still amazing compared to catia. It lets to pretty much everything you normally need to do in catia.

With fusion you can program CNC mills as well, not 100% sure about 5-axis but at least 3-axis. Milling strategies in Fusion are pretty clever as well. If you need better option for routing I would recommend Powermill by Delcam.