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
Reply to
Nev Williams
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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.
Reply to
ms
Who do you use for "Objet"?
Reply to
JKimmel
Metropolis Design
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are great to work with. Call and ask for Randall Wardle.
Reply to
ms
I have personally worked most with SLS (Selective Laser Sintering), but I also have experience with SLA (Stereo Lithography), FDM, and cast urethane prototypes. Any of these technologies would work well for test fitting and evaluation. There are slight differences in pricing and surface finish, but choosing the best method depends upon your quantity, part size, desired mechanical properties, etc. You can make rapid prototype wax patterns for use in investment casting, but they would not work for test fitting and evaluation. Typically, your test and evaluation prototypes are not used as patterns for investment casting, unless you can utilize a silicon mold process to create wax copies of your pattern and your tolerance requirements are not very tight.
Without learnine more about your project requirements, I can't recommend a particular technology for your test and evaluation prototypes. On the other hand, I highly recommend SLS Castform for casting patterns. This process results in wax patterns that are effectively the same as traditional wax patterns (they burn out in the same manner and don't run the risk of blowing out) and avoid the problems associated with making copies of copies.
Ultimately, rapid prototypes with high dimensional accuracy and good surface finish are possible with all of these technologies if the RP service bureau understands the process well and takes the time to do everything carefully. You might want to avoid using the cheapest approach available to you because many companies cut corners to keep their cost down and remain competitive in the RP industry.
Reply to
John Eric Voltin
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"
Reply to
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.
Reply to
jjs
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
Reply to
MM
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 !!
Reply to
Nev Williams
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"
Reply to
Jerry Steiger
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.
Reply to
Nev Williams
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"
Reply to
Jerry Steiger
I've had good success with Xylex (GE). Some grades are excellent against chemical attack.
Reply to
ms
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
Reply to
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 !
Reply to
Nev Williams
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.
Reply to
Nev Williams
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 Williams wrote:
Reply to
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
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Reply to
John Layne
Airtight - That's impressive. Finish must be real good !
Reply to
Nev Williams

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