Fine Detail Plastic Crystallization Formation

Discussion in 'Finishing Techniques' started by Model_Monkey, Dec 5, 2016.

  1. andycarlson
    andycarlson Member
    No worries! I'm based in the UK and most of my modelling has a UK focus although there are a few N scale souvenirs from the other side of the pond in my collection. Clearly I have a namesake who also likes wagons/freight cars.

    I've seen some very promising prints from a friend with a Photon and am also planning to try out a company here in the UK who offers SLA printing for scale models (Form 2 IIRC).

    My own feeling (and it's just that) on printing artefacts is that SLA/DLP tend to smooth over small things (whether you want that or not). I suspect that with FUD/FXD/Fine Detail Plastic the layering artefacts are worse than would be explainable with the layer depth and resolution alone but I don't know why this might be. One of my other prints has 0.2mm holes for wire handles. These work fine with FUD/FXD but I expect they will be lost with an SLA/DLP print.

    Splitting tank barrels is certainly an option but as well as cleanup we also need to be confident of the repeatability and accuracy of the print - any errors (e.g. from sagging) will show up as a registration issue when the parts are joined. Most issues with most printing options are easily solved with a welded tank but with rivets your cleanup and adjustment options are severely limited.

    Regards, Andy
     
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  2. jjschaible
    jjschaible Active Member
    I should have figured it out. 1:152. Eindhoven. UK sunlight. (mis) spelling of "artefacts". My bad.

    Well THAT Andy just got a 20lb bottle of N.... and is also an excellent modeler.

    Back to the topic...
     
  3. stannum
    stannum Well-Known Member
    Yes, resin flows, what is more, it can be partially cured with DLP, creating smoother transitions. FUD/FXD is spitting multiple blobs of resin that must stay in place enough time for the curing, so they can't be as fluid. And IIRC, it gets a shaving pass to level the layers. The others have the flat work zone for free, by means of top or bottom of resin in tank.

    SLA/DLP is decades old, so resins for it must be too. Just like resin for fake teeth isn't new, and it lasts a lot. With SLA/DLP, there should be no bubbles in solid parts, trapping air or uncured resin that later can react with the activated resin, unlike in FUD/FXD. Ironic that it is called Smooth now.
     
  4. Model_Monkey
    Model_Monkey Well-Known Member
    If I may offer some insight regarding the From2, I own one and am very happy with it. Like any machine and process, it has both advantages and disadvantages. It has been my experience that the Form2 complements Shapeways' technology, and therefore having access to both technologies provides a good breadth of capability.

    Some Form2 disadvantage examples first.
    • As you know, the Form2 builds models using structural supports that look kind of like the sprues found in injection-molded plastic toys and kits (see photos below). The Form2 does not use waxy support material. Models with a complex geometry can get smothered in structural supports. Some customers find structural supports objectionable and therefore prefer Shapeways' tech. Removing the supports requires care since cutting does pose some risk to the model. Rushed or ham-fisted support cutting can damage the model.
    • The mechanical printing process makes printing large flat objects more susceptible to warping. Flat objects oriented in the printer horizontally can develop areas that sag between supports spoiling the print. Therefore, object orientation in the printer is critical.
    • Cleanup is done in a large bath that stirs 8.6 liters of at least 91% isopropyl alcohol (IPA) over, around the model. That makes for a large volume of a very flammable liquid. IPA also produces harmful vapors. IPA may be difficult to obtain in some areas.
    • Consumables include the alcohol (which must be replaced as it becomes saturated with liquid resin over time), the resin itself, and the tank that contains the resin. Resin and the resin tank are very expensive. Resin cartridge, IPA and tank disposal require some steps to be taken to ensure any residual resin is fully cured before disposal. The resin in its cured state is safe but in its liquid state is toxic.
    • Printing is excruciatingly slow, a normal characteristic of many 3D printers, as is cleaning, which can be labor-intensive depending on the complexity of the model.
    • A major printer malfunction is likely only reparable by the factory, and thus can be very costly and business crippling with respect to production "down time".

    Like Smooth Fine Detail plastic, post-curing (exposure to UV light after the model has been printed) is still required, which is done in a UV light booth available from the printer's manufacturer. Post-curing is necessary because, like many 3D printers, the printer is deliberately set to under-cure each layer during printing. This is done so that once each layer has been printed, there is enough uncured resin present in that layer so that the next layer can bond to it. If a layer was perfectly cured during the print cycle for that layer, the next layer printed could not bond to it, and the model would de-laminate. Post-curing ensures all the resin has fully cured and that all the layers are completely bound to each other.

    The biggest Form2 advantage is that it produces very smooth surfaces right out of the printer. Since supports are structural, not wax, there is is no wax to clean up. There is no surface roughness caused by hot wax contact with the resin during printing. Therefore, the Form2 does a great job printing objects with a boxy geometry and with curved surfaces. I have observed no crystallization issues with FormLab's gray resin nor am I aware of any reports of crystallization experienced by others. Cured gray resin does accept more kinds of hobby paints without any paint-curing issues, including enamels and metallic paints (Alclad 2).

    A comment regarding resolution: surfaces are generally very smooth, even though the best resolution the Form2 can print is 25 microns, and that only in the Z axis. Otherwise, its best is 50 microns in the X and Y axes. But even at 50 microns, surfaces are generally smoother than achieved with Smooth Fine Detail at 29 microns. And fine detail features are just as crisp as Smooth Fine Detail. So, resolution selection may be less important with the Form2 than it is with Smooth Fine Detail plastic options ("Smooth" and "Smoothest").

    Here are a couple objects created with the Form2 as they appear right out of the printer. Both models were printed at 50 micron resolution in standard gray resin. The first model is about 2 inches long, the second about 3 inches or so. Notice how smooth the surfaces are and the structural supports:

    Model Monkey 1-18 P-51 Mustang Exhausts a.jpg
    Model Monkey 1-350 Gneisenau Hangar 1942 a.jpg

    The resin I have been using is FormLabs "standard gray", which is just one resin among many available for that printer. Standard gray works very well for the objects I create. It is an acrylic plastic and may be similar chemically to Smooth Fine Detail plastic. It is more brittle than polystyrene. The manufacturer does offer a stronger form of the resin, one that contains fibers which provide additional strength. That resin is quite a bit more expensive than standard gray.

    As you can see, an object with a very complex geometry could get smothered in these supports. Physical supports are not suitable for many of my designs which means those designs can only be offered by Shapeways using their wax-support tech.

    Shapeways can print larger objects than the Form2 can because the Form2 has a comparatively smaller work-space than the printers Shapeways is using. For those models that would tend to get smothered in structural supports, Shapeways' wax support process may be the better option. Shapeways' prints may be better when it comes to removing physical supports when cutting may pose too much risk of damage.

    Shapeways having more than one factory may also be an advantage with respect to shipping costs to some locations. Shapeways' use of 3rd party printers world-wide may also help keep shipping costs reasonable for some customers. For example, a vendor printing in the US and shipping to customers in the EU may have to charge more to ship than Shapeways charges. An object weighing 8 ounces or less will cost about $13.30 USD to ship from the US to most EU countries. Shapeways can ship to many EU nations for less than half that. [edit: Shapeways can ship to a few EU countries for a bit more than half that cost.] Especially for a small object or small orders, shipping cost can be the deciding factor.

    Just my 2 cents.
     
    Last edited: Jan 23, 2019
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  5. stannum
    stannum Well-Known Member
    5 countries for more than half that, 6.99. Soon it could be only 4. Everyone else (28 - 5 = 23) minimum 13.99. All prices excluding VAT.
     
  6. Model_Monkey
    Model_Monkey Well-Known Member
    I stand corrected.
     
  7. southernnscale
    southernnscale Well-Known Member
    Here is another photo of the crystalizing! these have been sitting for a year!The only thing is you have to move the part around to see the sparkling. The white areas are cover more!
    This was the FUD!
    IMG_9079.JPG