From CAD to the plasma cutter-what's involved?

Having a strong interest in boatbuilding and having built some of my own cnc driven tools, I would appreciate it if someone could outline the steps to go from a cad design to toolpaths. What brings the question to mind is, frankly, the cost of having the code developed for a new design. In looking for a design for a 28-30' alloy powercat it was common for this development to cost as much as the original design work. Makes me think I'm most likely not aware of what level of effort is involved.

Here's what my experience has been, granted for much simpler shapes than boat hulls. Draw your widget parts in cad dfx., import file into CAM program which generates g code files from dfx. Edit (in the less sophisticated programs) the toolpaths to be sure your plasma cutter isn't spending too much time in one area (for aluminum cutting), that lead in is okay and not crossing another part, etc. These g-codes are fed into the indexer which sends direction pulses to XYZ axis motor controllers. Since we're essentially talking two axis here for cutting plate, it's much simpler than say, milling a complex 3d part. Most CAM programs have other useful features such as parts nesting and materials optimization but these are fairly automatic.

So, if you've already done a cad drawing of a boat hull, aren't frames and longitudnals located and dimensioned? I can see that plating would be another matter, but it seems like for a hard chine hull that, knowing plating thickness...what am I missing? I've been told that it involves many many hours of tedious effort to do.

Are there any services that specialize in taking a design to code? I greatly appreciate any insights into this.

Regards,

Charles

 

Hi Charles,

The first thing you need to know is if the hull can be reduced down to developable panels. If so the panels must be developed to determine the shape when flat. Then you can write the tool path the way you always do. It is when the hull is not developable then the engineering can get tricky, and is beyond my skills. Some hull shapes are not possible unless the panels are very small. I don’t know if this helps.

Gary

 

Gary,

Ah yes, I'm assuming that the panels are developable, if I have the concept right you mean bent in one plane only, not rolled, stretched or formed? If I understand you, it is necessary to then translate the 3d form into flattened plates. How is this accomplished? I guess I assumed a 3d design program would extrapolate these flat shapes. As you can tell I have no experience with marine design software....

Thanks for the help.

Charles

 

Some software will unroll the panels with the push of a button. Rhino is fairly good at this. Soon there will be a plug in for Rhino to flatten out distorted panels. I doubt if this would be of much use to you. If your hull is developable, it should not be an expensive deal to get the G-code.

Gary

 

Once you've got the G-code, does that mean you can also find it's corresponding spot....?

 

sorry - couldn't help myself....

 

LOL!!

The bottom line here is that once you have a complete 3D model a good deal of the hard work is done. Producing the cut files should be a small percentage of the overall engineering work.

Will, you won’t find THAT spot on this screen.

Gary

 

Well, I guess you could say once you got the G code, you will most definitely find the spot that makes her hot....plasma, baby,the fourth state of matter!

I'm thinking that the designers I've been dealing with most likely don't use a 3-d rendering program for the design phase, I suppose this would only be necessary if you wish to proceed to files for manufacturing or have a need for enhanced graphics. Having looked at some of those modeling programs briefly, let's see Rhino boasts of 600 commands and a 500 page manual, it may make sense to outsource this work. Any ideas or recommendations on this?

Charles

 

Easy peasy

Learning Rhino is the easy part!

If you are thinking abot having someone design it for you then choose your designer wisely.

If you are considering to do the design yourself, you are in for a lot bigger troubles than learning Rhino!

IMHO it's when you want to build a one off it really pays off to have it designed on computer! You get plate development all the framing etc.

Any "modern" designer would have the tools and the knowledge to do it for you. So, as I said before, choose your designer wisely. It makes a lot more sense spending a little bit more on the design, and get the plate development "thrown in" at the same time.

Erik

 

CAD/CAM

Most shipyard professionals use software that takes data from a hull definition program like Rhino or Fastship and does the loft functions needed to get from a 3D shape to pieceparts, and to manage them, nest them and convert them to torch code automatically.
One professional level program that is very widely used is "ShipConstructor", www.shipconstructor.com
The plates also do not need to be developable. Double curving plate is not terrifically hard, and professional level software provides "expansion" routines as well as "development" routines, and also provides the sight templates needed to determine the shape of the double curved plates.
In steel, the plates can be line heated to form into double curves, (which only requires a torch and a water hose) and aluminum can be "wheeled", using a device that essentially makes very small thickness reductions along a line by squashing the plate between two wheels. Since the wheels are small, relatively little force is required, so such machines can be home made.

 

I've been designing welded aluminum boats for about 14 years, and at this point virtually all of my designs include NC cutting files. Generally, the hulls are designed in ProSurf (New Wave Systems) or SurfaceWorks Marine (Aero Hydro). From there the parts detailing and construction plans are done in AutoCad. If you are interested in either a complete design or a NC cutting files and construction plans for an existing design, feel free to e-mail me at wal@responsemarine.com.

Bill

 

CAD Design Stream for NC Cutting

For a designer's view of the process, please check out what I've posted on the CAD Design Stream at:

http://www.kastenmarine.com/design_stream.htm

You could substitute other CAD software systems for those that I use and get similar results. This page mainly describes the process, from design to cutting...

Best regards,
Michael Kasten
Kasten Marine Design, Inc.

 

Here are some additional resources:

http://www.pilot3d.com/surface_development.htm
See also the articles called
1. Plate Development and Expansion
2. Developed Trimmed Surface Example

http://www.pilot3d.com/2DPatterns.htm
See also the article called
1. Tutorial for Creating a Parabolic Dome Awning

http://www.pilot3d.com/5axis.htm
for an article called:
CNC Milling for Plugs, Molds, and Tooling

Generally, the steps you need to do are:

1. Create the 3D geometry of the object.
2. Derive (cut, unwrap, flatten, expand, etc.) the 2D shapes from the 3D geometry. Note that the process of getting the simple, closed-loop 2D shape of each "part" from the 3D shape can be very difficult, if not impossible. And, if you have hundreds or thousands of parts, well, can you say "tedious"?
3. Increase the size of each part by the half-thickness of the cutting head of the CNC machine. Ideally, the CNC cutting software will do this for you automatically. This has to be accounted for in the nesting.
4. Orient (nest) the 2D parts onto the image of the sheet of flat material you are cutting. Some people use a 2D CAD program for nesting and some use a specialized nesting program. If you are using specialized nesting software, then it could do this for you automatically. However, if you have hundreds or thousands of parts, then you have to worry about what parts are on what sheets of material. To do one job of the construction, you don't want your worker to have to get parts from sheet 2, 15, 27, 42, 43, etc. Often, parts are not cut out completely from the sheets - they remain connected by very small tabs. Then, what about labeling of the parts. Perhaps you want the nesting software to print sticky labels that you can put on the cut parts.
5. Generate the G-code. This should be the easy part, but you want some way to verify the G-code before you begin cutting the expensive piece of aluminum. I have heard stories...
6. Use the G-code to drive the machine.

Cost? The cost of producing the final G-code instructions for a large AL yacht can cost tens of thousands of dollars. It seems to me that the high cost comes from the tedious nature of generating all of the detailed 2D part shapes from an unknown form of 3D geometry. In addition, the 3D geometry was most likely created without any thought to creating all of the required 2D part shapes.

It's unlikely that one piece of software will do everything for you. I would recommend starting by cutting simple 2D shapes. Then, you can worry about generating 2D part shapes from your (or someone else's) 3D geometry. If you are dealing with compound curvature (not exactly developable) surfaces, then watch out. Some programs do just simple triangularization type unwrapping or plate layouts that can cause problems very quickly, especially if you are CNC cutting the frames and the plates out exactly. Some programs, however, use a stress/strain approach to flatten out double curvature surfaces. These programs work better for larger number of shapes, but at some point, you just cannot stretch or twist a 2D plate into the proper 3D shape.

Steve Hollister