A Guide to 3D Printing with HP’s Multi Jet Fusion

HP’s Multi Jet Fusion 3D Printing Solution [Source: http://www8.hp.com]

HP’s innovative Multi Jet Fusion technology has made waves in the manufacturing sector since it was first introduced to the market in 2016. And while the technology is still relatively new, it has had a ripple effect across industries, representing new possibilities for the production of industrial-grade functional parts and prototypes on a commercial scale.

As the number of companies using HP’s Multi Jet Fusion machines grows, we’ve put together a comprehensive guide to the technology. In this guide we’ll touch on the system’s printing process, materials, benefits and limitations and final points to consider when deciding on whether to invest in Multi Jet Fusion system. 

The Printing Process

Multi Jet Fusion technology belongs to the powder bed fusion family, although, unlike SLS technology, it does not use lasers. And while Multi Jet Fusion uses the material PA 12 like Selective Laser Sintering, its printing process actually most resembles that of Binder Jetting technology, where a bed of material is selectively fused together through the addition of a binding agent.  

During the Multi Jet Fusion printing process, a layer of powder is fused together with the help of a fusing agent and, after printing, a heat source. The process is then repeated, layer by layer, to create the final part.

A step-by-step guide to the MJF printing process:

1. A layer of powder is evenly distributed on the powder bed, and is then uniformly preheated.
2. The print head selectively ejects a fusing agent onto the layer of powder where the particles need to be melted. A second agent, the detailing agent, prevents sintering and is deposited around the contours of the part to improve its resolution and ensure that the parts sharp edges are printed.
3. Lamps with infrared light then move over the powder bed, heating up the areas with the fusing agent. This ensures that the powders in these areas are melted and fused together.
4. Once one layer is finished, the powder is distributed on top of the previous layer and the process is repeated until the part is complete.
5. Once the part is completed, it is still encapsulated in loose powder, which must be removed. Additionally, the part can be bead blasted and dyed black to achieve an aesthetically pleasing surface. 

   Check out the MFJ in action here:

Material Choices

When the Multi Jet Fusion system was first introduced in 2016, the technology was limited to one material – Polyamide 12 (PA12), also known as Nylon. PA12 is a fine-grained, strong thermoplastic material with a wide range of applications — from parts with complex details and intricate shapes, like connectors, panels and enclosures, to functional parts, such as gears and rotating joints. Nylon parts are characterised by their high mechanical properties, chemical and thermal resistance, and are lightweight.

Today, HP’s has expanded its material portfolio to include a wider range of thermoplastics, such as Polyamide 11 (PA 11), as well as HP 3D High Reusability PA 12 Glass Beads and HP 3D High Reusability Polypropylene (PP). Each allows for the production of low-cost, durable parts ideal for prototyping and as well as industrial applications:

• PA 11

HP’s PA 11 is ideal for creating low-cost, ductile and functional parts, and offers chemical and impact resistance. According to HP, the material is suited to the creation of prostheses, insoles, sports goods and living hinges, among other applications.

• High Reusability PA 12 Glass Beads

The High Reusability PA 12 Glass Beads offers 40% glass bead filled thermoplastic material and is most suited for parts requiring stiffness, such as enclosures, fixtures and tooling, as well as dimensional stability and repeatability.

• Polypropylene

This third new material is said to provide high chemical resistance and flexibility  in addition to being lightweight and watertight, and will be available from mid-2018.

HP’s Open Platform model, which encourages collaboration with material developers, already comprises over 50 companies, including Evonik, DSM and Lubrizol. With this in mind, the launch of further thermoplastics and even materials such as metals, may be just around the corner. 

Benefits of Multi Jet Fusion

As Multi Jet Fusion makes headway in various industrial sectors, the main benefits of the technology that have taken the manufacturing industry by storm have been its speed and high print quality:

• Multi Jet Fusion allows for the printing of parts in ultra-thin layers (80 microns). This results in parts with low porosity, high density and, particularly, high resolution and dimensional accuracy (which is also helped by the detailing agent). This makes MJF ideal for functional prototypes and small batches of end-parts. 
• Multi Jet Fusion offers shorter lead times, particularly when compared with SLS technology. Its printing system also includes a post-processing station that helps speed up the overall product life cycle. 
• The MJF printing process results in highly isotropic parts with incredible strength. 
• Similarly to SLS, parts printed with Multi Jet Fusion technology require no support structures, allowing for several parts to be nested in one printing bed — and so reducing the average print cycle.
  

  
  Limitations of Multi Jet Fusion

Despite the range of benefits that HP’s Multi Jet Fusion technology provides, its relatively new entry to the market means that there are some limitations that should be taken into consideration when deciding whether to invest in the technology.  

• For now, Multi Jet Fusion only offers a limited range of materials, and the raw parts are produced in a grey colour, due the fusing agent being black. Although your parts can be easily dyed black, a full-colour part will require additional coating, which will of course come with an additional cost. If you require a greater range of materials, colours and finishing options, it may well be worth considering a different technology, such as SLS. 
• As a rule parts printed with MJF have good a surface quality; nonetheless it is rougher than the surface finish of parts produced by Stereolithography or Polyjet. While parts can be bead blasted to improve its cosmetic appearance, this, of course, adds time and cost to the overall process.

Final points to consider

• Thanks to its fast printing speed, Multi Jet Fusion is an ideal choice for low to medium batch production that require tight deadlines. 
• If you require parts with great mechanical properties, dimensional accuracy and high resolution, then MJF is an ideal solution. 
• HP has also recently announced the release of its compact Jet Fusion 300/500 series, for full-colour 3D printing. With a price point starting at $50,000, this option may well be worth exploring for small and medium-sized businesses and universities.