3D Printing Resolution on Multicolor Prints: the complete Q&A

Posted By Arthur Cassaignau on Apr 15, 2015 | 0 comments

Being able to construct an object through 3D printing—directly in color to boot—is a very enticing prospect. To achieve this, some 3D printer manufacturers have developed technologies that allow color to be added directly during the 3D printing process. Objects created through this process serve as mock-ups or are ornamental in nature, owing to their mechanical weaknesses. This is characteristic of this new technology, which is limited in its ability to control for dimensional deviations between the digital model and the final 3D printed product. Matthew, our process engineer, explains why:

•  How many types of multicolor 3D printing are there ?

Among all the 3D printers currently on the market, only a select few are able to print directly in color. They are spread out among three different types of technology : Binder Jetting, Selective Deposition Lamination and a variation of Polyjet technology. Binder Jetting is currently used most often for this kind of printing. And it’s actually the technology used in the Projet 660 printers by 3D Systems that we use at Sculpteo. Across the board, these “full color” technologies hold the advantage against their competitors. They’re relatively inexpensive, can easily produce a large quantity of pieces and also produces pieces of good aesthetic quality. That being said, Binder Jetting also has a couple of drawbacks : less consistent dimensional accuracy than technologies like SLA or SLS and printed pieces with weaker mechanical resistance.

• How do Binder Jetting 3D printers work?

Because this is an additive manufacturing technology, the object is built by the successive layering of raw materials. Like other SLS technologies, it doesn’t just dispense a fixed amount of the building material necessary to creating a “slice” of the object. On the contrary, these machines deposit a thin layer of powder (100μ thick) over the entire surface (the x and y-axis) and interior of the machine, and the printer head applies a liquid binding agent to the surface of the powder, which then solidifies. To obtain results in color, the printer head can also apply color while it applies the liquid binding along the edges. After this, a layer of the object has been created. Following this, the print platform lowers slightly to make room for a new layer of powder. This process is repeated until the 3D printed object is complete.

However, in comparison to other 3D printing technologies, this method requires more post production stages: vacuuming up excess powder, dusting the object with compressed air, and reinforcing the object with a resistant binding agent.

• With this printing technology what factors influence the print resolution ?

Four factors come into play:

• The accuracy of printing along the x, y and z axes. The x and y axes determine the precision of the printer head. The z axis, where the layers are applied, determines how fine they will be.
• The viscosity of the binding agent.
• The accuracy of the color application (depending on the quality of the texture file sent to the printer).
• Treatment of the 3D printed object after it comes out of the machine: pieces need to be reinforced after they’ve been printed with a Binder, a sort of glue.

If we want to elaborate on the accuracy of 3D printing, we need to discuss the different technologies in terms the axes used to produce the object. On the raw production end (the x and y axes) , the application of the binding agent is similar to that of conventional printers . As a result, the Y axis, called the fast axis—which is the axis the printing head runs along—is more accurate than the X axis, the slow axis .

This flaw is also present in traditional printing methods : it is easier to apply ink in one pass than it is in successive passes. But there’s still the Z axis to take into account, which controls the application of the different layers. Given a layer whose thickness is 100 microns, the dimensional tolerance will be weaker than in the blueprint. For comparison, the thickness of a resin layer will about 35μm.

Unlike other technologies, the construction material have little effect on any dimensional deviations of the printed parts. Indeed, the mineral powder used in multicolor 3D printing does not undergo any physical transformation during the process. It is agglomerated, but not transformed as it is with SLS technologies wherein the polymer powder is heated, fused, and then cooled.

• How is dimensional tolerance accounted for in your calibration of the machines?

The calibration of the machines is verified on a daily basis by strictly monitoring the objects produced for each project, the same way we monitor SLS processes.

Color accuracy is also an important factor in multicolor printing—for this we perform colorimetric tests.

Although dimensional inaccuracies are rarely noticed with this technology (since objects are produced as visual mockups), dimensional tolerances can range up to 0.5mm, which allows us to use the parts for numerous options. The look of an object is important—so is getting the physical dimensions right.

• Which tolerance are you assuring at Sculpteo?

The multicolor parts that we are 3D printing have a maximum precision of ± 0.5mm for pieces 99mm or smaller and a global precision of ± 0.5% for pieces 100mm or larger.

•  I have printed an object 2 months ago and I need to reprint one : would it be exactly the same?

Yes and no. As I mentioned there is a big difference between printers using the Binder Jetting process for instance and the one using an SLS technology. While the consistency of the raw material (polymer powder) is a real topic with SLS, it’s a factor that has less impact with Binder Jetting. However, obtaining a color consistency is difficult with this technology. If you’re printing a 3D file today and in two months, it will be very difficult to match the exact same color.  As for SLS, if you plan to have several part printed, consider ordering them in a batch, you will have a better consistency on printing 10 X 1 item in a single job instead of printing 1 item in 10 different jobs.

•  How can I calculate in advance the maximum tolerance that would apply to my design?

Similar to what I did for the SLS print precision, I have created a form that will give you an idea of the maximum and the minimum dimensions of our multicolor printers.

Here you can enter the dimension you want to check (for example 1.234):
mm
Will give you a dimension between:
mm and mm

I recommend to have a look on our design guidelines to prepare your model in any case.

• If I receive an object that doesn’t respect this tolerance, what should I do?

If  you feel that despite our control process, your part is not within the tolerances we’re announcing, you need to send an email to [email protected] with a picture of the part and your order reference. If you can show the measure with a caliber, that quickens our the verification steps! In every case, we will reprint your object right away at no cost to you.

To learn more about multicolor 3D printing technology, check out our page on the subject.