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Multi Jet Fusion – Best Practices & Things to Keep in Mind


What is MJF?
Three-dimensional printing of production-useful objects and machine parts is becoming a reality. 3D printing offers the ability to produce—both rapidly and at low cost—short runs or one-of-a-kind parts. HP Multi Jet Fusion (MJF) technology offers high build quality at a much higher speed and at the lowest cost relative to competitive 3D printing solutions in the marketplace today.
HP selected GoProto as a foundation partner to deliver prototype and production parts in North America due to our customer-solutions orientation, production capacity, and decades-long relationship with the HP printing family. As one of the first service bureaus to be selected in the country, we offer leading-edge expertise, and will help you get started with this groundbreaking manufacturing process. Whether you need quick-turn prototypes or more robust production parts, GoProto is your source for all things Multi Jet Fusion.
The resulting parts from MJF manufacturing are extremely strong, highly accurate, and have a surface finish that makes them ideal for mechanical testing and production manufacturing.

How does it work?
HP’s Multi Jet Fusion (MJF) is an industrial 3D Printing technology where parts are built by thermally fusing polymer powder particles layer-by-layer. A thin layer of powder is first spread over the build platform where it is heated to a near-sintering temperature.

A carriage with inkjet nozzles (which are like the nozzles used in desktop 2D printers) passes over the bed, depositing fusing agent on the powder. At the same time a detailing agent that inhibits sintering is printed near the edge of the part to improve resolution and definition.
A high-power IR energy source then passes over the build bed and sinters the areas where the fusing agent was dispensed while leaving the rest of the powder unaltered. The process repeats until all parts are complete.

What are the prime applications?
Prime applications for 3D printing include the functional and aesthetic components of machines, consumer and industrial products that are manufactured in short runs of typically less than 1000 units, highly-customized and high-value products that can be one-of-a-kind, and parts with complex internal and external 3D geometries.

Before 3D printing, parts with complex surfaces, moving elements, and internal fluid passages were assembled from subcomponents that were aligned and assembled with fasteners and/or adhesives. In conventional parts—especially those designed to handle air and liquids—joints and sealing surfaces may be points where mechanical failure and leakage occurs. Because 3D printing builds objects from a stack of thin cross-sections, complex parts can be produced either as a monolithic structure or from many fewer subcomponents. 3D printing has the potential to simplify design and manufacturing processes and to reduce processing time and costs. Parts can be made by 3D printing that cannot be made by other methods, and this creates many new possibilities for innovations in design, form, and function.

What is the Digital Manufacturing Network?
The Digital Manufacturing Network (DMN) is a very select group of production-capable suppliers of Multi Jet Fusion parts, as certified by HP.  HP set a standard of very high quality in printed parts that DMN members must meet for solutions engineering, production capacity, consistency, quality and repeatability of prints.  HP audited all partners to also verify our stability as a company that will be a key partner to our customers.

Digital Manufacturing Network Partner

GoProto was selected as one of the first six partners globally that meets the very high standards of acceptability to be part of the program. Going forward, this means tremendous value to our clients who rely on GoProto for the most effective implementation of MJF into their product development and production manufacturing programs.

General Guidelines

Maximum Build Size
14.96” x 11.15” x 14.96” (380 x 285 x 380mm)

Dimensional Accuracy (measured after sand blasting):
• Up to 100mm: ±0.2 mm
• Greater than 100mm: ±0.2%

Printable Features:

Cantilever: The dimensions of a cantilever are based on the aspect ratio, determined by the length divided by the width. It is advisable to keep the aspect ratio <1.

Text, Graphics and Numbers
Multi Jet Fusion technology excels at very high resolution for letters and drawings.
Minimum printable font size: 6 pt

Minimum Text Height (Emboss and Deboss): 1mm (0.039”)

Text Orientation: The best orientation for embossing letters is to place them upside down in the build chamber, while for debossing letters it is better to place them face up to achieve the best resolution.

Design Concerns & Things To Consider

Long and thin parts have the potential to warp. Generally, any part that has an aspect ratio higher than 10:1 is susceptible to warpage.

What can you do?
• Increase the thickness of the part
• Add ribs in the areas that may be affected
• Replace solid the volume with a lattice structure as in the “Lighter Design” shown here.

• Reduce sharp transitions, as shown in the “Smooth Transition” shown here.

Parts That Assemble
Sometimes a pair of parts need to fit together for the final application.

What can you do?
The recommended minimum gap between the interface areas of the parts is 0.024” (0.6mm) to ensure correct assembly

Parts Printed as Assemblies
One key advantage of additive manufacturing is the ability to print a part as a single assembly.

What can you do?
Assembly parts that are printed together should have a minimum clearance of 0.035” (0.9mm). Parts with very thick walls above 50mm should have a higher gap in order to ensure proper performance.

Extra-Large Parts
When parts are larger than the maximum build size, we can work with you to print the parts in multiple pieces and then join them together. It is recommended to design interlocking features, such as shown here, as a guide to position the parts and help them bond together. GoProto is happy to help with this process every step of the way.

“Elephant Skin”
“Elephant Skin” is a phenomenon where the nylon material on a part shrinks and is cured unevenly resulting in surfaces that are uneven and “pocked”. Anything thicker than 0.8” can get “Elephant Skin”.

What can you do?
To decrease wall thickness, it is recommended to hollow out your parts or introduce internal lattice structures. The ideal wall thickness is 0.125~0.250”.


Nylon PA12
PA 12 is a strong, multi-purpose thermoplastic for functional prototyping and final parts. It is optimized for the MJF platform to deliver high-density parts with balanced property profiles. It is ideal for complex assemblies, housings, enclosures and connectors, and optimal for post finishing processes. PA 12 also has excellent chemical resistance to oils, greases, aliphatic hydrocarbons and alkalis.

Nylon PA12 with Glass Beads
Glass Beads are added to Nylon PA 12 to produce stiff, functional parts. This material provides dimensional stability along with repeatability. It is ideal for applications requiring high stiffness like enclosures and houses, fixtures and tooling.

Nylon PA11
Nylon PA11 is a material with excellent performance characteristics that mitigates many of the negatives inherent to other materials. With excellent impact and chemical resistance and an eco-friendly and bio-friendly profile, here are six reasons to consider Nylon PA11 for your project.

Impact Resistant – With a Shore Hardness of 80 and a high elongation at break of 50%, Nylon PA11 has excellent impact resistance over a wide range of temperatures. It is highly ductile and its performance in impact tests is twice as strong as Nylon PA12.

Chemical Resistant – Nylon PA11 has excellent chemical resistance to hydrocarbons including aliphatic hydrocarbons and aromatic hydrocarbons. It is also resistant to grease and has been tested against substances such as motor oils, gasoline, toluene and brake fluid. And it is also resistant to bases and salts including chlorine salts, concentrated alkaline, alcohol and esters.

High Heat Deflection – Nylon PA11 has been used in devices and cases under harsh weather conditions and prolonged use. It has an HDT of 350° F and will hold its mechanical properties under extreme environments.

Strength and Flexibility – With its excellent mechanical properties, Nylon PA11 is used within consumer goods markets for cases and containers as well as within the sports and aerospace industry. But it is also finding a particularly useful space within the medical industry as well. It is ideal for prosthetics, insoles, snap fits and living hinges.

Biocompatible – Nylon PA11 is biocompatible and meets the requirements of USP Class I-VI and US FDA guidance for intact skin surfaces for in-vitro cytotoxicity, muscle implantation, skin irritation and systemic toxicity.

Eco-Friendly – Nylon PA11 is 100% biocompatible and is plant based and made from castor oil. It is also highly reusable within 3D printing systems with up to 70% reusability resulting in less waste.

Which Nylon Should I Use?

(Thermoplastic Polyurethane)
3D Printed elastomer parts can be used in place of traditionally molded rubber for just about any 3D printed application. And, now, with this specially optimized TPU (Thermoplastic Polyurethane) elastomeric powder, designed for HP’s Multi Jet Fusion (MJF) technology, we can further accelerate the already fast processing times of MJF printers.

TPU is valued by engineers for its:
• High Precision & Resolution
• Flexibility → High Elongation at Break
• Well-Balanced Strength Profile
• Good Shock Absorption
• High Wear and Chemical Resistance
• High Thermal Stability
• High Oil & Grease Resistance

Parts created from TPU offer excellent accuracy, unlimited design possibilities, high flexibility and shock absorption, and a well-balanced strength profile. And, with our in-house BLAST vapor smoothing technology, we can manufacture parts that are more flexible, stronger, water resistant, and with a surface finish more like that of injection molding.

Ideal Applications for 3D Printed TPU
• Gaskets, Seals, Connectors & Hoses
• Robotics
• Automotive Instrument Panels, Shock Absorption
• Bellows & Ducting
• Isolation Dampers
• Harnesses & Fasteners
• Lattice Design Structures
• Functional Prototypes
• Footwear & Sporting Goods
• Medical Components
• Machine Tool Arm End Effectors

Figure x: TPU parts printed with MJF printer.

Finishing / Post-Processing

BLAST Vapor Smoothing
One of the most exciting secondary finishing techniques GoProto employs on our Multi Jet Fusion parts is BLAST Vapor Smoothing.  This process uses the AMT PostPro3D smoothing machine to expose parts to a vaporized solvent gas, which reorders the surface molecules to smooth the part without dramatically affecting the dimensions ( itreduces the part dimensions by roughly .4%).

Figure x: BLAST vapor smoothing of MJF parts, before (sand blast only) and after (sand blasted, dyed and smoothed).

Not only does this process improve the surface finish of the parts, but tests have shown that the parts are also made more tough, elongation is improved, resistance to liquids is improved, and the part is sealed better, which provides for better surface adhesion for gasketing and suction and provides an excellent base for adding paint, Cerakote, hydrographics or clear coat.  For more details on these tests, please reach out to GoProto directly for the corresponding white paper.

Hydrographics are a cosmetic finish we apply to Multi Jet Fusion parts using graphics that are printed on a soluble sheet substrate.  When the sheet is placed in water, and activator is applied, the substrate dissolves and the graphics are left on the surface of the water.  The MJF part is dipped through the graphics which transfer them onto the part in a “wrap” fashion. 

Figure x: Hydrographics on MJF parts.

The graphic is relatively durable, but further improved by a clear topcoat that can be either glossy or matte.  There is a huge range of graphics available including wood grains, carbon fiber, diamond plate, camo, metallic, leather, etc. Hydrographics add very minimal thickness, with the clear topcoat adding just 0.005”. 
Careful consideration needs to be taken to avoid a “stretching” effect with grained patterns such as carbon fiber, leather or even wood grain.  Also, the graphic film may not reach some pocket or “deep draw” features since the graphic becomes too thin as it stretches. However, we at GoProto have utilized this technique extensively on MJF parts and are happy to help determine the best hydrographic for your specific design.

Cerakote is a name brand protective coating we apply to Multi Jet Fusion parts.  It is applied as a paint which is then post-baked to cure the coating onto the parts.  It is extremely durable, scratch resistant, chemical resistant, heat resistant, liquid resistant and UV resistant.  It also is extremely thin at about .002”. 

Figure x: Cerakote on MJF parts, various colors.

It is possible to add a primer to the part prior to application of the Cerakote which fills in some surface roughness to give the parts a more even and “satin” appearance.  Cerakote is applied while the parts are hung in commercial racks so the hanging of the parts may leave a cosmetic blemish.  This requires consideration of where to hold onto the parts to minimize this effect while giving maximum line of site to the features of the part so the Cerakote can reach all surfaces. 

Multi Jet Fusion parts are durable enough to be able to be plated with metal finishes.  GoProto employs two types of metallization. 
The first is cosmetic “metal” which is chrome finish to make the parts shiny and reflective.  This process involves spray application of a chrome effect metal finish that is applied like paint.  It is line of site and can be masked to leave areas unfinished for assembly or fit reasons.  The chrome is as durable as standard paint.  This process requires extensive finishing of the MJF part to make it as smooth as possible prior to applying the finish.  Design Considerations with the chrome finish are very similar to paint in that not all surfaces can be reached completely if they are deep pockets, back sides of parts or undercut.  The surface finish of MJF has a light texture inherent in the process.  Smoothing surfaces completely is not possible, so it is critical to work with our shop to specify the cosmetic surfaces required to be highly cosmetic.

Figure x and x: Chromed MJF parts.

Figure x: Electroplated MJF part.

The second is functional metal which is done with electroplating.  MJF electroplates very well by using copper and nickel.  Plating MJF parts can make them very effective EMI/RFI shields, conductive pieces or very stiff mechanical parts.  The process is not intended for highly cosmetic chrome effects.  It is a functional plating meant to make the parts conductive, so they are functional for your application.  Like other coating processes the parts must be held while the finish is applied.  This results in visible blemish areas on the parts, so it is critical to work with our team to specify where it is acceptable to locate these blemishes on the parts.

Dyeing, Painting, Clear-Coat
After printing, Multi Jet Fusion parts are a matte gray color with a light grain texture.  The gray can be mottled from light to darker in color. To create an even appearance, these parts are often dyed black. This is done at an elevated temperature for a fixed period to bond the dye to the part. The parts are then rinsed and dried. GoProto can dye your parts with black dye, or other dark colors such as dark red, dark green and dark blue. 

Figure x: MJF parts dyed and painted various colors and sheens.

Multi Jet Fusion parts accept paint well.  The light grain texture on the surface gives a mechanical bond to the primer that is applied to the parts. After primer the parts can be painted with a huge variety of colors and sheen levels from matte to gloss. However, it is important to note that gloss sheen will show the light grain texture on the printed parts. 
To add durability to painted parts we often add clear coat as a final finishing coat.  Clear coat can add different sheen, UV stability, impact and scratch resistance. Talk to us about what finishing steps are best for your parts.

Who Is GoProto?

GoProto is a full-service manufacturing partner, with a focus on customer service across the country. We are organized unlike any other rapid manufacturing solutions provider, with dedicated work groups in 14 territories across the US. Each territory is staffed with an expert Business Development Manager living and working in that region, matched up with dedicated project manager experts to offer consistent and amazing service from initial consultation through production. 
People matter, relationships matter, and consistent expertise is critical to help you achieve your goals of speed, cost-effectiveness and the best possible process to meet your project needs.  We know you like to win.  We do too.  We’ll work together to make “it” happen.