3D Printing - which process?

I am just finishing a enclosure for a client that houses an
electronic/pneumatic product. It's made of 3 parts and the next step is
Rapid Prototyping of the model parts. I know there are quite a few here that
have used this process and probably have valuable opinions that they
wouldn't mind sharing.
What sort of finish, structural integrity do the various 3D printers
produce? There are quite a few of these machines around our way now, but
it's difficult to get an objective opinion on pros and cons of each.
Ideally I would be after RP that would take minimal finishing, to use as a
pattern for investment casting and has a reasonable amount of strength. We
would use these initial RP samples to fit internals of device and have the
machine used by a limited number of people to get feedback.
Can this be really be achieved with items produced by rapid prototype. I
know all the advertising blurb says this is possible , but in the real world
is this actually so.
Initially the quantity would be quite low hence investment cast or similar
process. If product starts selling in numbers, material would switch to
plastic and injection molded dies would be required.

Would much appreciate any input from those who have used the process.
Cheers

 

I have had the best success with Objet prototypes. The resolution is great.
And the cost is better than SLA, but not quite as cheap as some of the 3D
printers (FDM). There are several materials to choose from for the Objet
prototypes, but most are similar to acrylic in material properties.

 

Who do you use for "Objet"?

--
J Kimmel

www.metalinnovations.com

"Cuius testiculos habes, habeas cardia et cerebellum." - When you have
their full attention in your grip, their hearts and minds will follow.

 

Metropolis Design http://www.metropolisdesign.com/contact.html
They are great to work with. Call and ask for Randall Wardle.

 

Thanks for an enlightening reply John.
This is new territory for me. Product ultimately could be a consumer product
although at this stage probably a little pricey.

I cannot really divulge to much more other than to say size of 2 halves is
about 315x160x90 and shape has an flattened ellipsoid as the primary
feature. For the prototype we are going to use a silicon rubber mold so
probably go the zinc alloy route. Each half is a shell 4mm thick for initial
prototype. We were advised that anything less than this would be pushing it.
Slightly longer term would be to use aluminum investment cast maybe down to
3mm shell.
Long term a high strength plastic - shell down to 2mm ??
I will be asking more questions about that later !!

I have come into this after some ideas man produced a semblance of a
product in Solidworks. He was not an experienced user. The model was a bit
of a basket case to work with. Whoever created it had major geometry planes
off all sorts of edges and points that can easily dissapear when making
changes to the model. As you can imagine this usually breaks the model when
even a small change is made. Some planes have 4 or 5 children so changing
one makes a mess of alot of other stuff. To make matters worse some
electronic control panel overlays on the outside curvy surface, have already
been tooled and made from this model, so any changes have to be thought
through without these shapes.
Half of my time has been spent trying to improve the robustness of the model
!

Cheers

Neville Williams
Z-Axis Design - NZ
"remove the KNOT to reply"

 

On Fri, 23 Jun 2006 10:31:24 +1200, "Nev Williams"

The first thing Neville is to reduce your client's expectation for
the first off protoypes. Without spending a fortune on modelmakers to
do the finishing and who are worth every penny, the base parts you
recieve in the post will not look like the finished moulded or even
cast item. However you have to decide what you want to use the
prototype for.

If it is an aesthetic model then go for an SLA and spec a good rigid
material. this will give you or your modelmaker the best chance on
sanding and finish thing the surface off to a good styandard and get
the parts together with a good fits.

If you want something you can test for strength and toss around the
office for a few weeks and check physical functions then go for a SLS
as they tend to be tougher and easier for the bodger like me with a
scalpel to cut and tweak till the parts fit together.

As for using the parts as the moulds for investment castings, consult
the Bureau and chose the material and process that suits who ever is
going to do the casting of the first off items.

There is not much difference in cost between SLA and SLS so choose the
one that gives the best blend you need.


Jonathan

PS - Personally I go for SLS as they tend to clearly look like working
prototypes while SLAs can sometimes just look like badly moulded parts
and then some dumb f**ck at the headoffice moans that the the
mouldings on the model really need to be better, and I have to explain
for the millionth time its only a protoype that cost £200 and that if
they wanted a aethetic show model they should have budgeted £2000.

 

Yep,

The Eden is the best I've ever seen for resolution. Lots of different
materials as well.

Were looking at buying the smaller one for in house stuff. Same resolution
as the big one, just a smaller work envelope, and under 60K. Cost of
materials is the big question.


Mark

 

Jonathan

Thanks for the reply
The first one is just for strength and tossing around.
The next 6 will be for a customer.
What I think has happened is someone has said "I want 6 of these", and
basically short circuited the development a bit.
We have both SLS and SLA available.
Am getting an issue now with RP manufacturer saying they cannot open stl
file from Solidworks ??
I'm using the settings Binary & Fine with "Do not translate into Positive
space" left unchecked.
Other outfits I have sent to can open fine. Makes you wonder about the
software some of these guys use !!

 

At that size, you're probably better off with 2.5 mm or possibly even 3 mm,
depending on your material. (When you say high strength, what do you mean?
Do you also want high stiffness?) You can go down to 2, or maybe even
thinner, if you do a very careful thin-wall design with the right materials
and more expensive tool design (multiple valve gates, for example). GE can
tell you more about thin-wall design, as they were pushing it a few years
ago for notebook PCs and the like.


Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

Jerry,

Yeah, I was thinking of 3mm client was saying 2mm, but sounded to delicate
for my liking.
It has uses in sports and medical industries, so for strength product will
have to take a few knocks - falling off table onto hard floor, type of
abuse.
Stiffness is not such a high priority as there are no items within that have
to remain exactly aligned.
Housing is more of a cover to package and protect inner workings.
Any suggestions as to material ? Fairly smooth shiny surface required.

 

You would be amazed how much damage can happen in a fall from a table! From
you size, your product is liable to be pretty heavy (a kg or more). There
will be lots of movement of the pieces. Parts that are normally trapped
between other parts can be found floating free after a drop.

Polycarbonate is a very high impact material with good appearance, but it
doesn't flow all that well, so you may have to go to 2.5 or 3 mm walls. When
you say medical, will the product have to be sterilized? That can severely
limit the materials that you can work with. Even more "normal" cleaning can
cause problems with Polycarbonate, as it isn't much good at chemical
resistance.

ABS might be a good choice provided you don't need to survive too long at
too high a temperature. It flows better than PC and is not quite as easily
attacked by chemicals. PC/ABS is often a nice compromise.

These amorphous materials are my favorites because they have low and fairly
uniform shrinkage, so tolerances and warpage are good. I have never used
Noryl (modified PPO), but it falls into the same class. Semi-crystalline
materials will give you better chemical resistance, but have much higher
shrinkage, worse tolerances, and more warp. Another compromise would be
PC/PET or PC/PBT that would give you better chemical resistance but worse
warp and tolerances.


Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

I've had good success with Xylex (GE). Some grades are excellent against
chemical attack.

 

Neville, the newer resins for SLA allow very tough and somewhat
flexible resins to be used to approximate ABS to Polypropylene range of
parts, where earlier SLA resins tended to be very brittle. Accura 25
from 3D Systems, maker of SLA machines, is one I've used for the tough
semi-flexible parts to allow stresses on the RP part yet not crack
during all the handling and testing. I've even used it for snap fits
successfully.

Bo

 

When I say medical, it will not be used in an operating theatre environment,
so does not have to conform to these more rigorous requirements.
Product primarily used in sports performance for athletes, but has uses that
give very real medical benefits for some chronic conditions - asthma is one.
The PC/ABS material looks interesting - will definitely look into this more.
We are due to get a SLA prototype today.
It's always interesting to have the actual article in your hand !

 

Bo,
The machine we are using for RP is a 3D Systems model - Viper si2 SLA
We chose it for that very reason you mention.
Model has to reasonably tough as it will be used as a working demo
I've seen output from it and is very good finish.

SLS was also very good and was first choice, but it came down to the company
who we felt was more responsive and helpful to us.

 

Nev you are in good hands with the SLA.

I have also use the harder Somos branded grades for a tougher more ABS
like function and have even succeded in making small amounts of snap
fits work with those parts.

What has been amazing to me is that I have ordered these ABS like parts
and then did a very slight polish up on interference fit-snap fit parts
that rotated in a valve, and the valve worked and was air tight on the
very first parts made with the 3D Systems SLA. Those guys are real
good at getting their parts right (my vendor I use is Scicon in
Valencia near 3D Systems).

Bo

 

Nev

Are you getting your RPs done in house or are you using a bureau, if you
getting them done outside what company do you use?

John Layne
www.solidengineering.co.nz

 

Brien OBrien at Plastic Design Technologies in Silverdale.
www.pdt.co.nz
Very helpful and informative.

 

Airtight - That's impressive.
Finish must be real good !

 

Not knowing the size or shape of you product I will offer a few
suggestions. You mention castings. Depending on your part and the
amount you plan to make, Urethane castings may work well. My
suggestion is to go to www.protocam.com. Out of 4 sources for this
they are the least expensive and do the best quality work. Ask for
Faye. She will get you to where you need to go. As for objet that
people speak of, your system is an enclosure right? If you have any
heat in that enclosure you need to be careful because the Objet melt
point is very low. Like 110-120 degrees F. I use C-Ideas for this
www.prototype3d.com. They also have FDM and SLA machines as well and
will be happy to give you all their wisdom. Ask for Dan. Those two
sources are the best I have and they know all. Call and pick their
brain. Thats the best advice I can give.

Ken M
Muderlak Design