What is MJF (HP’s Multi Jet Fusion) 3D Printing?

Multi Jet Fusion (MJF) Defination

Multi Jet Fusion (MJF) is a 3D printing process designed to quickly create prototypes and end-use parts. As a professional IATF16949 and ISO9001 certified manufacturer of 3D printed components with extensive experience, I’m excited to share how MJF works and why it’s such a game-changer.

Multi Jet Fusion 3D printing

Exploring the Versatility of 3D Printing Technologies

Today, designers and engineers have a plethora of options when it comes to 3D printing technologies and materials. In this discussion, we focus on Multi Jet Fusion (MJF), HP’s proprietary 3D printing technology, which is a viable solution for many complex and industrial applications. We will cover how it operates, its benefits, and whether it is the right technology for your needs.

If you’re eager to learn more about the 3D printing technologies available through Protolabs Network, be sure to check out our 3D printing service page.

What is Multi Jet Fusion (MJF) 3D Printing?

Multi Jet Fusion (MJF) is a 3D printing process that produces precise, finely detailed complex parts using powdered thermoplastics at impressive speeds.

Known for delivering parts with high tensile strength, fine feature resolution, and well-defined mechanical properties, MJF 3D printing services have quickly become the preferred additive manufacturing (AM) solution for industrial applications. It is frequently used to create functional prototypes and end-use parts, particularly those requiring consistent isotropic mechanical properties and complex, organic geometries.

For a quick and detailed reference, watch our video all about MJF.

The Development of MJF

Launched in 2016, MJF was developed by HP Additive, leveraging the company’s expertise in inkjet printing technology and precision mechanics. The journey of MJF began much earlier, however, in the 1990s when additive manufacturing was transitioning from research and development to real-world industrial applications.

During this period, speed emerged as a significant hurdle. Compared to injection molding or metal stamping, 3D printing was notably slower. Early adopters attempted to accelerate production by using arrays of multiple machines, but HP opted for a more integrated, automation-focused approach.

In their global AM hub in Barcelona, HP created a system that builds parts layer by layer in a large bed of powder material, with additional machinery for seamless post-processing. This system, akin to Selective Laser Sintering (SLS) and other powder bed fusion designs, evolved into the current MJF technology.

How Does Multi Jet Fusion Work?

MJF utilizes an inkjet array to deposit fusing and detailing agents onto a bed of powder material, which are then fused into a solid layer. The printer distributes more powder on top of the bed, and the process repeats layer by layer.

Here is a step-by-step overview of how MJF builds parts:

  1. The moveable build unit is placed into the printer.
  2. The material recoater carriage deposits a thin layer of the powder material across the build area.
  3. The printing and fusing carriage moves across the build area, preheating the powder to ensure material consistency.
  4. An array of inkjet nozzles applies fusing agents onto the powder bed in areas corresponding to the part’s geometry and properties.
  5. After each layer is finished, the build unit retracts to create space for the next layer of material.
  6. This process continues until the build is complete.

Once the printing process is finished, the build unit contains the printed part and unfused powder. A separate processing station, attached to the moveable build unit, is used to cool and unpack the part, and recover excess powder for future use. Bead blasting removes any remaining powder, allowing for further cosmetic steps if necessary.

MJF additive manufacturing

Materials Used in MJF

MJF materials can be broadly categorized into rigid plastics and flexible plastics. Rigid plastics include Nylon PA11, Nylon PA12, and PP, while flexible plastics include Estane 3D TPU M95A. HP’s system primarily focuses on polyamide materials, developed in collaboration with its partners.

Here is a list of MJF 3D printing materials available on the Protolabs Network platform:

  • HP PA 12 (Nylon 12): A robust thermoplastic with excellent physical properties and chemical resistance, ideal for functional prototypes and end-use applications.
  • Glass-filled HP PA 12: Reinforced with glass bead, this nylon offers higher stiffness and thermal stability compared to standard nylon.

Post-Processing in MJF

Like other manufacturing processes, MJF requires further processing before a part is ready for use. However, post-processing in MJF is relatively minimal compared to other AM technologies.

After a print job, you are left with a build unit filled with unfused powder and the printed part buried inside. The main steps in MJF post-processing are:

  • Cooling: This occurs within the build unit. HP offers modules for natural cooling so that the build unit can be reused for a new print without waiting for the powder and part to cool.
  • Recovering Unfused Powder: Once cooled, the build unit is moved to a processing station where the unfused powder is vacuumed into a container for future use.
  • Bead Blasting: Remaining powder is removed through bead blasting, air blasting, or water blasting, either manually or automatically using a tumbler, ultrasonic cleaner, or vibratory finishing machine.

Additional post-processing may be necessary depending on the part, such as machining for specific features, sanding for meeting technical requirements, or further steps required for casting processes.

Advantages of MJF

If you need functional prototypes and small production runs of end-use parts, MJF is an excellent choice. It produces stronger parts than SLS, with tensile strengths of maximum XY and Z 48 MPa/6,960 psi using the ASTM D638 method.

MJF excels in producing mechanical properties uniformly throughout the part’s geometry, making it ideal for complex, multifaceted designs that require robust small features. It also reduces the need for extensive post-production, offering faster lead times and high-quality surfaces with minimal human intervention.

The technology’s speed is enhanced by consistently scanning the surface of the part during printing, even when printing multiple parts at once, leading to quicker build times compared to other technologies.

Why MJF is Ideal for Manufacturing End-Use Parts

MJF stands out from other additive manufacturing processes by producing high volumes of parts with great complexity, detail, and structural integrity. It is a popular choice for manufacturing precise and durable electronic component housings, mechanical assemblies, enclosures, jigs, and fixtures.

Modern MJF machines feature a build unit that is a rolling cart attached to a processing station. Once a part is complete, the powder bed is moved to the processing station to remove excess powder. Post-processing can be done in bulk, often requiring minimal hand finishing, making it well-suited for higher volume production runs.

The powder bed system eliminates the need for supports, allowing parts to be efficiently nested in the build area. Unused powder can be reused for future print runs, enhancing efficiency.

MJF vs. SLS 3D Printing: Key Differences

While similar to MJF, SLS has a few key differences. SLS printers also deposit powder material layer by layer, but use a laser to fuse the powder particles. The laser’s power can be modulated to alter the part’s material properties, though this feature is limited.

In contrast, MJF uses a broad selection of chemical agents, offering more opportunities to alter the properties of each voxel of the part.

MJF vs. Injection Molding: Which is Better?

MJF is a strong alternative to injection molding. Injection molding involves costs for the mold and extensive DFM analysis before production, along with restrictions in part geometry and longer lead times.

MJF offers greater design freedom, significantly reduced lead times, and rapid design changes without relying on a mold. It is ideal for creating high volumes of small to medium-sized parts with complex geometries.

MJF is generally preferred for creating prototypes and small to medium production runs. Prototypes can be printed in a few days, and MJF-printed parts have mechanical properties comparable to injection molding.

MJF 3D printing process

Examples of Multi Jet Fusion in Action

One notable example is CNC Würfel, a manufacturing and process automation specialist. In 2017, CNC Würfel replaced milling machines and lathes with 3D printing for many components, drastically cutting production times and costs.

Another example is HP’s Z 3D Camera. Switching from injection molding to MJF allowed HP to produce the camera more quickly and cost-effectively, optimizing the design and improving the end product’s quality.

Handy Tips and Tricks for MJF

To get the most out of MJF technology, consider the following best practices:

  • Reinforce thin-walled or large, flat surfaces with ribs or gussets.
  • Surround holes with raised bosses when possible.
  • Raised text and cosmetic features smaller than 0.5 mm might not survive secondary post-processing.
  • Part walls should be between 2.5 and 12.7 mm thick to ensure tolerances.
  • Clearly identify cosmetic surfaces to avoid features like stair-stepping on oblique angles.

By following these guidelines, you can maximize the benefits of MJF and achieve the best results for your parts.

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