Where do I start with CAD?

Hello, I would like to make some things out of plastic. I've done a
lot of 3D modelling work, mainly for animation, which I know is
insufficient when it comes to making actual stuff. I'm guessing that
making a model into real live plastic isn't going to be as easy as
just saving a DXF and sending it somewhere to be, er "made real" (I
don't even know the term for that).

So what I want to know is- what books should I get? I figure start
there rather than ask a bunch of annoying questions. I think I can
handle the software, it's the reality stuff that I don't know. I'm
probably going to need to learn about different types of plastics.
And how much do I need to know about the equipment that actually does
the "realization"? Can you tell I don't know what I'm talking about?

The stuff I want to make is pretty simple- sort of like a frisbee to
start.

thanks very much

 

It is actually as simple as sending the 3D cad data to a manufacturer. Save
the 3D file as IGES or STL, and send it to a stereolithography manufacturer.
Most of them can manufacture from this data in resin or various plastic
materials, and you should get your first-off part in less than a week.

If you're happy with the product and your volumes are high, then you can use
the same model to get tooling made.

You will need dimensioned drawings only for quality control and inspection.

Dave

 

That bit of advise is loaded with issues. For one a sterolith part can be
made with all types of manufacturing issues. Specifically speaking
undercuts. Undercuts are areas in a part with will cause it NOT to release
from a cavity/injection mold. If you're really looking to start with a
frisbee like part take a look in a kitchen and look for a baking tin/mold.
The side walls are drafted ( tapered ) to make it easy for the cake/part to
release from the mold. Tapering walls on injection molds are essential for
manufacturing. I would recommend that you do a google search on the web for
plastic part design. I'm sure there is a ton of materials to bring you up to
speed to make easy parts. One other thing, a part can be drafted many ways.
Leaving draft up to the toolmaker can result in a part that is
non-functional. The best way to get a part produced to your expectations is
to draft all the surfaces. That way there is no surprises or costly charges
to modify the injection mold to your original design intent.

Good Luck

 

One other bit of advice. It sounds like you're wanting to do something
like this on your own. I hope you realize the costs involved. A
prototype part can cost thosands of dollars and really won't work that
well. They're usually more brittle than real molded parts. They're
just to test looks and basically functionality, not to be used by your
potential customers.

If you're looking to injection mold something, you'll need tens of
thousands of dollars to have a tool built. When you're into that kind
of dollar range, and since you have no plastics knowledge, you'd be much
better off hiring an engineering consultant to do this work for you.
Sure it might cost thousands of dollars for their expertise, but you'll
make sure the 50,000 tool you'll be building won't end up as scrap metal.

Cj

 

Awesome, thanks very much. Can you recommend a stereolithography
place? Also I probably still need to learn about plastics- do I ask
the stereolith place to give me samples or should I get a book or
something?

thanks very much

 

Depends on your locality. Do a google search for stereolithography or 'rapid
prototyping'.

See the link for basic principles.

http://www.bath.ac.uk/~en0dpj/Stereolithography.htm

Speak to your local rapid prototyping shop, and they will explain the
process and probably recommend vacuum casting for lowish number batch
production. They will recommend plastics to you based on your application.
The plastics field is complex, and you will not learn it in a few days,
rather leave it up to the experts.

Dave

 

http://computer.howstuffworks.com/stereolith1.htm

TRY THIS

 

For prototype parts try Design Prototyping Technologies (DPT) they are out
of New York. I use them on a weekly basis and I am down in Mississippi so
they don't have to be local. They also have online instant quoting. Parts
like a Frisbee are going to be expensive. It a simple part but there is a
lot of plastic to it. DPT has a 3 day turn around. Works great.
http://www.dpt-fast.com/

As far a adding draft to your part, Since it sounds like you have little
experience with plastic part design. What you can do is meet with a Tool
Shop let them quote a tool. After you have found a tool price you can live
with, the next step usually would be a tool concept review. At this review
the tool shop will recommend where and how much draft is needed, but don't
let them walk all over you. They are out to make the tool as simple as
possible and I know that is what I use to do to people. When you leave the
review you can go work on your part adding the draft that was recommended or
you could let the tool shop modify your part for you if you can afford their
CAD time. Just make sure that you review every surface on the part before
any steel is cut. Another way that you can go is prototype tooling.
Depending on what kind of volume you are planning on, you can make what some
companies refer to a prototype tool. They are good for 100's and in some
cases 1000's of parts before the tool is shot. The price on these tools are
1/4 that of a production tool, but press time when you are actually running
the tool in most cases will be higher. There are some shops out there that
specialize in prototype tooling.

As far as the type of plastic to use. That is a tough one. I don't think
that you will be able to find a book that has enough information in it to
help you chose the plastic to use like Plastics for Dummies. You might be
better off talking about it with your tool shop. They should be able to
help you or at least point you in the right direction.

When it comes to drawings, The tool shop will probably require one for
quoting purposes. Nothing with a lot of dimensions, just the basic size.
Just make sure to add the note that dimensions are controlled by latest 3D
data.

Good Luck
John