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How to Design for HP Multi Jet Fusion

Each 3D printing technology has a unique set of design recommendations to ensure the best result. We would like to share the design specifications provided by HP for their HP Multi Jet Fusion 3D printing technology to help you achieve the best results possible. These design guidelines apply to all Multi Jet Fusion materials, including Nylon PA12, Nylon PA12 Glass Bead, Polypropylene, and TPU Flexible Polymer.


What is HP Multi Jet Fusion (MJF)?

Before starting, it helps to understand what HP Multi Jet Fusion (MJF) is and how it differs from other 3D printing technologies.


According to HP, The MJF printing process is a combination of Powder Bed Fusion and binder jetting technologies. Unlike SLS or FDM, which use a point-by-point printing approach, HP MJF technology can print a complete layer at the same time. A layer of powder material is spread on the print bed, then fusing and detailing agents are deposited at voxel-level on top of the powder. These define the regions of the layer that need to be fused or protected from fusion respectively. The bed is heated and the areas where the fusing agent was deposited are fused together.. Once these fused layers cool down, they solidify to form the designed 3D-printed part.

Wall thickness

When you’re creating a 3D design for Multi Jet Fusion, the minimum recommended wall thickness is 0.3mm for short walls oriented in the XY plane, and 0.5mm for short walls oriented on the Z plane. If you design your part to be optimized for a specific orientation, make sure you make this clear to the person or company printing your part.

Minimum Wall Thickness for HP Multi Jet Fusion
Minimum wall thickness

Cantilevers

When printing a cantilever, the minimum wall thickness depends on the aspect ratio, which is the length divided by the width. For a cantilever with a width of less than 1mm, the aspect ratio should be less than 1. There are no specific recommendations for widths of 1mm or larger, but for parts with a high aspect ratio, it is recommended to increase the wall thickness or to add ribs or fillets to reinforce the part.

Cantilever Guidelines for HP Multi Jet Fusion
Designing for cantilevers

Connecting Parts

Sometimes a pair of printed parts need to fit together to form the final application. To ensure correct assembly, a good starting point would be to leave a gap between the interface areas of these parts of 0.4 mm (+/- 0.2 mm for each part).

Connecting Parts - 3D printing with HP Multi Jet Fusion
Minimum Gap between Connecting Parts

Moving Parts

As a general rule, spacing and clearance between faces of parts printed as assemblies should be a minimum of 0.7mm. Parts with walls which are 30mm or thicker should have a larger gap between each side to ensure proper performance. Parts with walls that are thinner than 3mm thatcan have a clearance as low as 0.3mm, but this depends on the design. Testing may be necessary to ensure quality performance.

Minimum gap between moving parts3D printed with HP Multi Jet Fusion
Minimum gap between moving parts

Thin or Long Parts

Thin and long parts are susceptible to non-uniform cooling, which may cause uneven shrinkage along the printed part. This can warp the part from it's original shape. The potential for warpage can be minimized with good design practices.


A general guideline is that any part with an aspect ratio higher than 10:1, an abrupt change in its cross-section, or a predominantly long and thin curved segment is susceptible to warpage. These include thin and long parts; parts with abrupt changes in cross-sections; and thin and curved surfaces.

To minimize the possibility of deformation, there are several guidelines to follow when designing the part. These include:

  • Increase the thickness of long walls to reduce their aspect ratios.

  • Avoid ridges and ribs on large, flat areas.

  • Re-design parts with high potential stress and smoothen their cross-section transitions.

  • Lighten the parts by hollowing them or by adding internal lattices.

Minimizing Warpage with HP Multi Jet Fusion
Minimizing Warpage with HP Multi Jet Fusion

Hollow Parts

Example of a Hollowed Part - HP Multi Jet Fusion

For large or thick parts, it is recommended to minimize the risk of warping by hollowing the part or adding an internal lattice structure. The minimum recommended wall thickness is 2mm, but better mechanical properties are achieved with thicker walls. The optimum choice is dependent upon the application. Hollowing can be easily achieved with professional software such as SolidWorks, Materialise Magics, Autodesk and Netfabb.


Depending on the end-use application, the part can be left solid, or drain holes can be added to remove the powder in the post-processing process. Ensure the drain holes are at least 4 mm wide if there is a single drain hole, or 2+ mm wide for multiple escape holes. When placing the holes ensure they are placed in a way that forced air can be used to effectively clean out trapped powder.


If no escape holes are provided and powder remains within the part, the part will be heavier and stronger than with the fully hollow option. Leaving the powder trapped within a part also saves post-processing time since powder extraction is not required.


Lattice structures

Lattice structures are used in thick or large parts to minimize the chance of warping or for producing lighter parts. Replacing solid materials with a lattice also reduces the cost to 3D print the part.


This design optimization strategy involves hollowing a part and replacing the internal solid mass with a lattice structure that provides mechanical integrity. This re-design can be automated with professional software such as Materialise Magics or nTopology.


Additional Considerations


Material Choice

Each type of material that is 3D printed with HP Multi Jet Fusion has different properties. Select your material based on the properties you desire such as strength, flexibility, biocompatibility, weather resistance, or chemical resistance.


File Resolution

The resolution of your file is an important factor to consider when 3D printing your part. If your file is too low resolution it may lack quality, and if the resolution is too high then the file size may be too large for the printer to read. Keep your file size under 100MB if you can.


HP Multi Jet Fusion 3D Printing with Tempus 3D

For additional advice on how to design for HP Multi Jet Fusion, you can take a look at the guidelines provided by Tempus 3D on our design guidelines page. Here you will find details regarding dimensional tolerances for different design features, guidelines to optimize your print accuracy and aesthetics, and details such as how to design for interlocking parts and hinges.


As an HP Certified Multi Jet Fusion 3D Printing Professional, Tempus 3D has the technology, skills and service to provide you with consistently high-quality parts, quickly and affordably. When you are ready to put your idea into reality, you can access online quotes through Tempus 3D's instant quote page, or learn more about our materials, services, and access case studies and customer success stories through our website at www.tempus3d.com.



note: all photos and design guidelines are provided by HP.


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