Stereolithography

[Guest Tim E.]

Never heard of it? It is an interesting (to me at least) technique for making parts layer-by-layer. In my eyes this might be a way to make obsolete and unobtainable parts for our antique vehicles. So far it has been mostly basic research aimed at prototypes; but stereolithography is close, it appears to me, to being able to make one-off parts.

However, a computer drawing (CAD) file is required. This is a very serious problem, since CAD files for our parts simply don't exist--we're lucky to have draftsman drawings or blueprints. Which brings me to my question: Does anyone know of a method of producing a CAD file from the physical part?

[Steve Braverman]

That's easy, have a draftsman create the drawing using a CAD program from the part. Most of the stereolithography machines I have seen only work in plastic though.

[Friartuck]

Tim,

Does a program like Solidworks allow you to import picture(s) that has a high contrast, and thus be able to make both 2D and 3D graphics. If at least a program allowed this and only needed 20 percent to "clean up the part", that would be better than starting a drawing from scratch. If this lithography method can be used for plastics that might work. Plastics can make good patterns for the casting process.

[avantey]

Friartuck-

Having worked with various CAD packages in the past 20 years I can say that this is a goal more than a reality for CAD. I know UG NX has the ability to "wrap" a 2D image around a 3D part once it is created but that is the closest I have seen to the idea of converting a 2D image into a 3D object on the fly.

There are various systems out there that do 3D scanning of a part, convert it to a file and that can then be manipulated to program a printer type machine to produce a very close likeness. There are many issues with this however:

The first is a simple idea- the new part is only as good as the original when it comes to wear, finish, weakness, etc. IF you start with a bad sample (especially wear in our car parts case)you only get a similar (worn out) copy.

Materials are also seriously lacking but are coming along very quickly. There is even sintered metal technology which prints and bakes metal powder into a real metal part. But they do not have anywhere near the characteristics of a good engineered material. Some of the STL materials may be very good replacements for the early plastics like Bakelite in some applications like knobs or dash pieces but research it VERY thoroughly before making parts. Using these STL parts for patterns may be the best use they will ever have

As for reverse engineering a part into a CAD file it is time consuming, expensive and like any other human involved process open to error, interpretation, etc. when measuring and modeling the part.

Not sure this is helpful but I have spent a lot of work time in R&D doing engineering concept design and working with engineering model shops on rapid prototyping of new product models.

[Guest Tim E.]

Bill--Avantey

Sounds like we can say "we are almost there."

Your 2nd paragraph indicates 3D scanning may be promising, but a while until it is fully ready for us. If your pattern (borrowed part of whatever) is poor due to wear, strength, etc, can the 3D file be "manipulated" to make improvements--like to allow a bit of extra material for machining bearing and joining surfaces, etc?

I have seen an article, in Machine Design I think, that they had printed a battery; so I expect that improvement in materials availability will follow.

Time consuming is expected I guess, but perhaps worth it for non-available parts.

Thanks for replying.

[Guest bkazmer]

I worked a little on this a while back. Stereolithography normally sinters a powder using a computer- directed laser. The resulting part is dimensionally correct but rarely close to the mechanical properties. The result is more an accurate 1:1 model than a duplicate part

[avantey]

At the place where I spent most of my working life we had a very good and extensive engineering model shop that tried many rapid proto (RP) systems. We made parts from cornstarch and resin, special thermowax, epoxy and urethane resins and powdered metals. Different results with each in terms of finish, precision, etc. and very different costs.

STL is probably the most expensive but has the highest precision, the best variety of resins available, and can get results very close to injection molded parts made from engineering plastics with very little cleanup (on the parts). However it is the most expensive with up front machine costs, time of build and cost of materials.

The future of RP is very exciting and RAPIDLY changing, almost monthly in the trade magazines so your dreams may not be as far off as you think.

- Bill

[avantey]

At the place where I spent most of my working life we had a very good and extensive engineering model shop that tried many rapid proto (RP) systems. We made parts from cornstarch and resin, special thermowax, epoxy and urethane resins and powdered metals. Different results with each in terms of finish, precision, etc. and very different costs.

STL is probably the most expensive but has the highest precision, the best variety of resins available, and can get results very close to injection molded parts made from engineering plastics with very little cleanup (on the parts). However it is the most expensive with up front machine costs, time of build and cost of materials.

The future of RP is very exciting and RAPIDLY changing, almost monthly in the trade magazines so your dreams may not be as far off as you think.

- Bill

[Guest bkazmer]

I remember first seeing the process about 20 years ago. As you say , it offers the highest precision but highest operating cost. However, since no mold needs to be built, it's best at small runs, like we usually need.