As with any additive manufacturing system, Multi Jet Fusion has its own set of limitations and considerations when designing for the build process. In many ways designing for Multi Jet Fusion is similar to designing for other powder bed fusion processes, however the process is unique in the following ways:
–Fine feature resolution – Multi Jet Fusion parts have a fine feature resolution of 0.02 in. Anything smaller will print, but it may not be fully dense or meet specified material properties.
–Materials –HP offers HP 3D High Reusability PA 12, HP 3D High Reusability PA 12 Glass Beads, and HP 3D High Reusability PA 11, with others under development.
–Color – HP recently introduced the Jet Fusion 300 / 500 series of 3D printers that now print parts in full color. The original Multi Jet Fusion system prints in a grey color palette.
–Surface finish – The average surface finish of Multi Jet Fusion parts is 125 to 250 microinches RA. Surfaces can also be hand-sanded or tumbled for a smoother finish.
–Part size – The build envelope for the Multi Jet Fusion machine is 16 in. x 12 in. x 16 in. It is recommended that a part should be a maximum size of 14.96 in. x 11.25 in. x 14.96 in. to add a buffer around parts for the printing agents.
Beyond the differences between Multi Jet Fusion technology and other powder bed fusion processes, there are three main design and mechanical limitations to keep in mind when designing for a powder bed process.
–Wall thickness – Nylons, like any thermoplastic, shrink as they solidify. Very thick walls can accumulate heat and cause spot shrinkage in dense areas with an accumulation of material, resulting in geometric deformations. Therefore, walls should be at least 0.02 in. to 0.12 in. (0.5 to 3.0 mm). Thinner walls are possible, but at the risk of inaccuracies and deformation due to non-uniform in-process shrinkage. For parts with high aspect ratio, either increase the wall thickness or add ribs or fillets to reinforce the part.
–Orientation – Parts built with Multi Jet Fusion are nearly as strong in the Z orientation as they are in the XY orientation. However, there are a few orientation adjustments to make when the application requires a part with a high level of detail, accuracy or strength. If your application requires a smooth surface finish, place visible features in the XY plane rather than the Z direction to avoid a stair-stepping effect. Also, place parts face down toward the build platform for a smoother surface finish on that side. Lastly, position pins and clips horizontally whenever possible.
–Dimensional accuracy and minimum feature size – Typical tolerances for Multi Jet Fusion parts are ± 0.010 in. (0.25 mm) or ± 0.001 in./in. (0.025 mm/25.4 mm), whichever is greater. The minimum practical feature size for Multi Jet Fusion is also 0.02 in. (0.5 mm), including hole diameters, shaft diameters and feature clearances. The minimum printable font size for embossed or debossed lettering is 6-point.