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Introduction
Rapid Manufacturing (Baking) allow the production of finished parts in a short process (less time but also less steps). A 3D file contains all the informations to drive the machines to create a final product. But for the process to be smooth and the result to be satisfying a fair amount of informations have to be known beforehand. Trying directly your first 3Dprint is also a way to learn, but reading the lines under could save you working time, and being a Maker is knowing this kind of stuff.

 

Check our easier guide to 3D Printing basics.


3D PRINTING / RAPID MANUFACTURING CONCEPT
3D printing or Additive manufacturing is a process of making a three-dimensional solid object of virtually any shape from a digital model. An .STL (Standard tesselation language) file is sliced horizontally into 2D shapes that are solidified one on top of another to recreate the initial volume. .STL files only contain vertices and faces in order to be readable by any 3D printer. As every 3D software uses its own way to describe geometric object, a standard format is needed, such as .STL.
         

3D PRINTING PROCESSES
SLS
-File exportation
When exporting the file, great attention should be taken to ensure that the export parameters are correct. In order to verify it is strongly adviced to re-import the .STL file into your software to be sure that the geometry hasn't been altered.
-File preparation
The 3D file containing all the informations describing the part to be produced has to be checked and corrected in order to be accepted and processed by the 3D printer.
-3Dprinting
The 3D file is slicesd into 2D shapes which are solidified one on top of another to recreate the volume. It is called the additive manufacturing process.
-Cleaning
The part is taken out of the .cake., extra powder is pushed away by sand blasting the part with at a pressure of 9 Bars. At the scale of a model it is like a hurricane, small features without enough structural links would go away at this stage.
-Polishing
Polishing is made in a hi-energy vibratory tumbler with ceramic beads and polishing soap. It softens the surface while keeping the edges sharp. Objects larger than 12x12x16 cannot fit in the polishing tank, therefore cannot be polished.
-Dyeing
The part is dipped into boiling water with acid dyes (the ones used for whool), and then rised and dryed.


LOST WAX INVESTMENT CASTING
-Wax infiltration
The part 3D printed in polystyrene is diped into hot wax, in order to get a better surface finish.
-Plaster casting
Under decompressed atmosphere, very fine grain plaster is cast all around the part placed in a container. Hollow parts would explode under decompression at this stage, they have to be avoided.
-Lost wax process
The plaster container is put in a kiln for several hours to let the wax impregnated polystyrene completely burn away, creating the void of the mold.
-Metal casting
In the gap left by the burnt polystyrene, molted metal is pourred. It goes by gravity by the sprue and should reach every part os the piece. We design the sprues so the metal flows well and cast is even.
-Plaster removal
The plaster investment (mold) is broken and sand blasted away.
-Polishing
Metal polishing is done with a buffing wheel, the wheel thickness is about 3cm, and its diameter about 30cm. Therefore, recessed elements, holes and negative geometries cannot be polished, only outside, reachable by the wheel, surfaces will be polished.
-Metal coating (plating)
Thanks to electrolyse, a extremly thin layer of metal (gold or silver) is applied to the part
-Surface finish
We have two additional finishes, brown and green patinas. Soon, we'll have an antique patina for silver plated parts.
-Surface protecting
We apply a light coating of lacker to the parts before shipping them to you.

GENERAL DESIGN GUIDELINES
-Objects must be closed
The 3D printing industry like to call this being 'watertight'. If there are missing faces, finding where is the inside and the outside in a geometry becomes a difficult task for a computer.
 

-Objects must be manifold
A mesh will become non-manifold if it has edges that are shared between more than two faces. Being manifold means you could unfold you volume on one flat piece of paper. A T-mesh cannot unfold, and cannot be 3Dprinted.

-Normal should be oriented towards the outside of object
All surfaces of your model should have their normals pointing in the correct direction. When your model contains inverted normals our printers cannot determine the inside or outside of your mesh or model.

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The three points above can be checked and corrected with the free software: Netfabb Studio Basic.

-Objects should observe the minimum wall thikness and features sizes
The thicknesses to be observed depend on material and process, they can be found in the Design Guidelines specific to each material.


-Unsintered powder should be able to escape from the geometry
If you print a house, doors and windows should be opened so the loose powder could be removed when the sintering process is finished.

Our pricing strategy is by Containing Volume, therefore cutting and packing your volume would save you expenses. If your model is above 10% density (ratio void/solid) you can be sure that our services are the less expensive worldwide.


POLYAMIDE DESIGN GUIDELINES


-Minimal thickness
Minimum details and wall-thickness depend on the production method (material) that you are planning to use. For SLS: Minimum fully vertical wall thickness is 0.5mm, non-vertical non-horizontal: 1mm, fully horizontal: 0.4mm. Detailing can reach 0.1 mm on the vertical axis and 0.4 mm on the horizontal.


We would never recommend that you make large portions of your model 1mm thick. This would lead it to be impossibly fragile and this might make the model so weak that we couldn't even get the support material out without breaking it, for bridges crossing more than 50mm a minimum thickness of 1.5 mm is highly recommended.


-Smallest feature
The laser beam that solidifies (sinters) the polyamide powder has a diameter of a bit more than 0.4mm; smaller features on X and Y will be printed at 0.4mm.
The smallest features 3Dprintable are the horizontal ones of a thickness superior or equal to one layer thickness (0.1mm) on Z.

However, due to the sand blasting cleaning process, it is not safe to try anything under those two recommendations:
a-self standing unsupported structures: Length should be less than four times the thickness, and thickness cannot be less than 0.8mm.


b-Supported structures (on both ends), length cannot be more than 6 times the thickness and no thickness can be less than 0.6mm.

-Visible layers / Printing orientation
Additive manufacturing works with layers, depending on the orientation during the print, those layers will show more or less. On surfaces facing up, with an angle inferior to 15 degrees with the horizontal, layers will show the most.

When you 3D print a bolt, nut or screw, you need to orient it vertically in order to benefit from the 0.1 mm layer thickness precision, and avoid the X,Y 0.4mm laser beam diameter rounding.



-Escape holes
The powder that has not been hardened by the laser in the process has to be removed, therefore, if you modeled a sphere, you have to leave two opposite escape holes so that we can take the powder out. The holes should not be smaller than 10mm.


-Moving joints
If you want to 3Dprint moving assemblies (gears, joints, etc.), you should always leave a minimum gap of 0.4mm between the two parts. If the parts are massive you will have to increase that distance, because powder between parts will heat more during the process and risks of adhesion will increase.

-Fragile structures and temporary supports
If you have to create very fragile structures, you will have to create temporary connections, that you will cut out after the 3Dprint, in order to support the weak shapes and preserve the integrity of the part during the process.


-Polishing
Hi-energy polishing, in water, with ceramic beads, gives a very nice and smooth surface with soft gloss, but is challenging for unsupported features, we recommend to not put any geometry under 1mm thickness to polish.
-Dyeing
The part will react to the dyeing process depending on its thickness. Thin parts tend to get more color, and thick parts to be lighter. If you want a very even color, you have to design your part so the thickness is continous throughout.


METAL DESIGN GUIDELINES


-Absolute and relative thicknesses in the same 3Dprint
For Investment Casting (steel, brass and silver): the recommended minimum thickness in any direction is 0.8mm
Because the temperature of the cast is defined by the thickness of the piece, you cannot cast without risk of bubbles a part which would have its maximum thickness superior to twice its mimnimum thickness.

-Geometry / castability
As the shape will be immerged into plaster to create the lost wax investment mold, it is important that no air bubble could be created while plaster is cast (otherwise the bublle will be filled with metal). You should think of escapes for air in enclosed corners and create escapes at the extrimties of enclosed shapes.

-Constraints inherent to manual polishing
Metal is mainly polished (buffing) by hand. The buffing wheel is large (about 30cm dimater) and thick (about 3cm). This means only reachable surfaces will be polished. Inner spaces, depth, crevaces, recessed letters, will remain unpolished (and usually, it's a cool contrast). If you want a part to be fully polished, it has to be designed so it can actually be so.

Polishing and buffing tend to round corners and kill sharp edges. As much as possible, we are trying to preserve the intend in the shape. For a knife, it is easy to polish the surfaces separately and keep the edge very sharp, but in many shapes it has to be a compromise between a good polishing and some rounded edges. For most of jewelry, rounding edges is a positive thing as it avoid people wearing the part to hurt themselves or anyone with the metal.

If you do a chain or interlocked parts, you need to model as well the sprue and casting tree to hold the parts afar from another during the casting. We'll cut the sprues to allow for the polishing. Chain elements are not counted as separate parts, one chain has one handling fee.

The STL file format is the industry standard for 3D printing. It is quite common to have minor geometry issues in these files, so they need to be corrected before quoting or printing.