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Before you begin designing for 3D printing, you’ll need to learn certain tried and tested principles and practices to help you create the best possible 3D printable model and get the result from the 3D printer you’re looking for.
As every 3D printing technology or process has its own set of design guidelines and rules, it’s vital to make sure you have a deep understanding of the capabilities of the 3D printing technology you’ve chosen.
You should also be familiar with the materials you’re using to make sure the end product is as you conceived it. This will also involve familiarizing yourself with post-processing techniques.
In this article, we’ll introduce you to the design principles you will work with when it comes to any kind of design and modeling for 3D printing. We will also share the basic principles of designing a model for 3D printing using an HP Jet Fusion industrial 3D printer, including recommended file formats and resolutions.
Minimum wall thickness
Establishing the minimum wall thickness to be achieved depends on the purpose of the 3D printed product itself, its functionality, and its look and feel.
Minimum wall thickness is the lowest thickness the structure of a 3D printed product can have and still fulfill the purpose for which it was designed without compromising its structural integrity. This is impacted by factors such as constant physical forces like gravity and the load or stress that the 3D printed product will need to be able to withstand.
You will also need to be familiar with the characteristics of the 3D printing process and the technology you’re working with. 3D printer manufacturers such as HP will provide you with a design guide covering wall thickness according to tests carried out on the 3D printer you purchase. Good 3D printing service providers will do the same.
Learn about minimum wall thickness for HP Multi Jet Fusion 3D printing technology in our “How to design a 3D print model” article.
Support structures and overhangs
You will need to work with support structures or overhangs when working with certain 3D printing processes, such as Fused Deposition Modeling (FDM) 3D printing technology (also known as Fused Filament Fabrication (FFF), Digital Light Processing (DLP), Liquid Crystal Display (LCD), Stereolithography (SLA) and Material Jetting (MJ).
FDM works by depositing layers of melted filament material over a build platform until a part is completed. Each layer is supported by the one beneath it. So, if you have an overhang, you have no choice but to use a support structure.
As you’d imagine, support structures increase the cost of materials and, because you have to remove them, the time and cost involved in post-processing. If you don’t use them carefully, they can also damage the surface of a model. But they are vital for models where an overhang of more than 45 degrees is unavoidable or if your design includes bridge features.
An overhang is where the material being extruded hangs over the previous layer to the point where it can’t be supported. If you design an overhang less than 45 degrees from the vertical, you may be able to print the 3D object without using support structures.
Horizontal bridges
When you’re 3D printing a bridge, the maximum span you can print without support is usually around 5mm. As it’s highly likely you’ll have no choice but to use support material to help make sure your bridge is printed without any errors, raising your per part cost, the trick is to design, so you use fewer supports.
With bridges, this can be challenging. Apart from 3D printing bridges that are 5mm or less, a useful tip is to slow your printer down. This can enable layers to join together better while creating a stronger bridge with a smoother finish.
In terms of technology, the only way to build a 3D model of a bridge without having to use support is with Powder Bed Fusion (PBF) technology such as HP Multi Jet Fusion or binder jetting technologies that don’t require support structures at all.
Embossed and engraved details
When you’re embossing or engraving features such as patterns, textures, or text raised above a model’s surface or indented – for example, consumer products or packaging - you’ll design for a minimum height, depth, and line thickness. This will be determined by the 3D printing technology you’re working with.
Data courtesy 1
- Minimum feature width
- Minimum clearance or gap between two connecting or moving parts
- Minimum diameter for holes or minimum gap in lattice structures for cleaning
- Minimum pin or shaft diameter
- Minimum diameter for holes for assembly
Additive manufacturing technology vendors such as HP will advise you of the minimum measurements your 3D printing equipment can work with.
Designing a model for 3D printing for an HP Jet Fusion industrial 3D printer
In our “How to design a 3D print model” article we covered a number of essential CAD design tips for 3D printing with HP Multi Jet Fusion technology, including wall thickness, cantilevers, connecting parts, and much more.
We will now focus on the essentials you should be familiar with when it comes to converting a design file into a file format at the right resolution for an HP Jet Fusion industrial 3D printer.
Recommended file formats and resolutions for HP Multi Jet Fusion
The most commonly used file extension in 3D printing is STL (Standard Triangle Language or Standard Tessellation Language), despite the fact that it lacks even basic 3D model information such as color or the identification of distance units.
For this reason, HP and other 3D printing thought leaders formed the 3MF Consortium and developed a file extension that supports the real requirements of current and future 3D printing applications, services, and devices. This is called a 3D Manufacturing Format (3MF) extension file.
Now becoming more widely used by 3D design programs, a 3MF file contains a 3D model, material, and property information that has been compressed using the same method as a Zip archive. A 3MF file has a much lower weight than an STL file for a specific 3D model and resolution.
Tessellation
To convert a 3D model into a 3D printing file, it is necessary to tessellate the model, which means converting its geometry into linked triangles to convey its surface.
A normal file size for a 3D model is between 1 and 30 MB, but the size depends on the type of software that created it, the number of triangles, and the amount and level of details. A higher resolution means a greater number of triangles, which will result in heavier file size.
Once the 3D model has been tessellated, it is imported into slicer software, which slices the 3D model into layers and prepares it to be sent to the printer. If this is not done correctly, it can cause problems such as geometric inaccuracies or slow processing, so it’s essential to get it right.
Exporting a CAD model for 3D printing
Although each version of CAD software uses a different method to export a 3D model to an STL or 3MF file, it’s often necessary to manually enter some exporting parameters, such as deviation chord height and angle tolerance, which define the resolution and the size of the STL or 3MF file by altering the tolerance in CAD software.
Deviation chord height
The deviation chord height is the maximum distance between the geometry of the 3D model and the surface of the STL or 3MF file. The recommended value for the chord height is 0.05mm. A smaller deviation chord height will result in a more accurate surface.
Angle tolerance
The angle tolerance is the maximum angle between the normal vectors of adjacent triangles. The recommended value for the angle tolerance is 1°.
Exporting errors
Unexpected results such as surface inaccuracy—unforeseen holes, unjoined triangles, overlapped triangles, tiny shells, flipped-direction triangles—or poor resolution are common errors that may occur when an STL or 3MF file is inadequately exported.
Too many or too few triangles
Although a mesh with more triangles tends to be more accurate, too many triangles are difficult to process; and when a certain size is reached, the additional triangles do not provide enhanced accuracy. For this reason, an excess number of triangles could increase processing time with no benefit.
Similarly, too few triangles can lead to poor resolution results. Triangulation of a surface causes faceting of the 3D model. The exporting parameters used to output an STL or 3MF file affect how much faceting occurs.
Repairing STL files
Common errors can normally be fixed by properly designing and exporting the 3D model using CAD software or another appropriate repair software. The most common software for repairing STL or 3MF files are the following:
- Materialise Magics with Materialise Build Processor
- Autodesk® Netfabb® Engine
- HP SmartStream 3D Build Manager
Dimensions in 3D printer resolution
The minimum controllable printable volume when 3D printing with HP Multi Jet Fusion technology is known as a voxel, which defines the resolution.
The HP Multi Jet Fusion voxel resolution in the Z axis is 80 microns. It is vital to align critical dimensions to an integral number of voxels: it’s possible to obtain a 3D-printed block of 160 microns or 240 microns, but not one of 168.5 microns.
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Footnotes and disclaimers
- Data courtesy of Hoffmann + Krippner GmbH.