December 12, 2023
Manufacturing industries are in the throes of change. As dynamic markets, sophisticated customer demands, and cost pressure force manufacturers to question established business practices, they are seeing merit in embracing a globalised, digitised environment. Additive manufacturing, commonly called 3D printing, is considered a building block of digital transformation in the manufacturing industry.
One of the latest technologies to enter the 3D domain is Multi Jet Fusion (MJF) printing. Developed by US multinational Hewlett-Packard (HP) in 2016, MJF quickly gained acceptance in the ecosystem. It’s ideal for rapid prototyping and building customised, complex end-use parts while maintaining surface quality and consistent build time.
Once the 3D model is prepared and sliced into thin cross-sectional layers using software, the printer gets into the act.
Printing: MJF is a powder-based technology that prints layer by layer. At first, a powder recoater lays down a thin layer of the material on the printing bed. This is followed by an array of inkjet printers moving across the bed and depositing fusing/binding droplets and detailing agents in specific areas, as per the 3D design of the part. An infrared heating unit also moves across the bed. The fusing agents absorb the thermal energy causing the underlying layers to melt together. At the same time, the detailing agents (applied on the edges) evaporate in this heat and the areas exposed to them experience a sharp drop in temperature. This results in fused parts with distinct, precise edges that prevent a melt pool from forming into the loose powder.
Then the bed goes down slightly, typically 80 microns, and the powder recoater spreads a thin layer of powder onto the previous layer. This goes on till the part/parts are complete. Since the unfused powder acts as a support for the fused material, MJF technology allows for the fabrication of intricate shapes without additional support structures.
While printing multiple parts, each and every part is evaluated for optimum print orientation. The parts are put inside the build envelope whose maximum size is 500 x 500 x 400 mm. One should maintain the height and packed density to avoid sudden changes in the print surface area.
Once the build unit is packed, it is inserted into the processing station to be filled with powder, as per the desired ratio of new and recycled building material. Usually, the mixed ratio is 80% recycled material and 20% new. MJF uses the highest percentage of recycled material compared to any 3D printing technology.
Once filled, the build unit is inserted into the printer and printing is initiated.
Post-processing: MJF parts have to go through a series of finishing steps to become customer-ready. It includes cooling, unpacking and cleaning.
Cooling could happen either the natural way or in an accelerated manner
Natural cooling involves naturally bringing the temperature down, which could take up to 48 hours. The powder and the builds are automatically shifted to the natural cooling unit en bloc to avoid thermal shocks to the individual parts. Experts say natural cooling is the best way to retain the mechanical and structural integrity of the parts.
Fast Cooling, which takes about 4-6 hours, entails bringing the contents back to room temperature through forced ventilation. While it shortens production time, it could lead to stress and warpage of the parts due to uneven cooling.
After adequate cooling, the build is subjected to unpacking. The powder can be removed manually like an archaeological excavation; or, automatically, by a device that uses compressed air and vibrations to wipe off the unmelted dust from the pieces, and suck it up for reuse later.
Post unpacking, some finishing processes such as bead blasting, air blasting, water blasting, and vapour smoothing are performed on the products to remove a fine layer of powder and improve their appearance and quality.
Vapour smoothing: A chemical vapour seals the outer surface of the part, smoothens the rough surface, and provides a shiny finish. It is also known to enhance mechanical properties.
Bead blasting: High pressure compressed air containing minute glass beads is used to remove any remaining powder.
Air blasting: After bead blasting, compressed air is used to remove any further unattached powder on the surface.
Water blasting: It requires jetting a mixture of compressed air and water to clean up the parts.
A few post-processing activities contributing to the aesthetic appeal of the parts are graphite blasting, dyeing, painting and electroplating.
MJF uses engineered thermoplastic nylon and polypropylene powders. Depending on the end-use, the common materials are:
Polypropylene (PP): Chemical resistant and lightweight, this thermoplastic is also tough and ductile.
Polyamide 12 (PA12): Also known as Nylon 12, an engineering grade material, it's widely used for its strength, rigidity, and high dimensional accuracy, low moisture absorption, weldable and bondable properties.
PA12-glassbean: Brings out some of the finest details in MJF printing, it is stiff, stable, good at heat deflection, and greatly reduces warping problems.
Thermoplastic polyurethane (TPU): A thermoplastic elastomer, it has the strength of plastic and elasticity of rubber.
Other lesser-known materials for MJF are PA11 and Thermoplastic Amides (TPA), which are used for their flexibility.
In just 7 years, MJF has become the go-to technology for rapid prototyping and on-demand manufacturing of fully functional, large-scale components at high resolution, with multiple colour and surface finishing options. Its popularity can be attributed to the following reasons.
Speed: MJF is 10 times faster than other competing processes, claims HP, adding that it can print up to 12000 voxels per linear inch per layer. (Voxel is 3D pixel – a basic unit for a 3D image). Like a laser printer, MJF scans the entire surface of a build layer consistently at each pass, instead of focusing on each individual detail. The high speed translates into faster production as MJF can print dozens of parts simultaneously. The detachable and moveable build units allow for the quick reloading of the printer without affecting post-processing operations.
Design freedom, precision, and aesthetic appeal: MJF printers can produce highly accurate parts with intricate details and aesthetics, in a single piece or sub-components, without sacrificing speed. By incorporating multiple part iterations within a single build, designers/engineers can promptly test the part and choose the best iteration. The printheads deposit the fusing and detailing agents with high precision leading to tighter tolerances of parts. Due to the powder bed system, there is hardly any need for support structures. This has opened up tremendous design possibilities for designers, engineers, and manufacturers. Thanks to the latest technology, 70-100 different kinds of parts can be fitted into the build unit, depending on their size. The end-use parts display quality surface finishes, low porosity, and fine feature resolution.
Strength: MJF parts are up to 98 per cent isotropic. It means they are mechanically consistent along all directions of the part’s geometry. This is especially helpful in the case of complex designs where strength and reliability must be achieved throughout the part. MJF products owe their superior mechanical properties to the way the thermal energy is applied during printing, allowing for the fusing of two successive layers.
Environment-friendly and cost-effective: MJF technology releases less GHG than SLS. A great deal of the powder (80%) can be recycled, which is a big boost to sustainability. MJF also does away with the need for tooling, thus saving costs. It can deliver mass-produced objects and prototypes at competitive prices.
Despite its many advantages, the technology comes with its own set of challenges.
Few materials to work on: HP MJF printers mainly use proprietary materials – the variants of nylon and polypropylene. Currently, the range is restricted. Ceramic materials are yet to be available commercially.
High upfront costs: MJF printers are commercial grade, industry-level machines, requiring an initial investment in the range of $340,000 to more than $500,000, which is beyond the scope of most small and medium enterprises.
Warping: Large parts and thin features could suffer from warping
Surface finish and colouring: Though MJF parts can boast of good surface quality, they could require, depending on their end use, post-processing such as blasting, vapour smoothing, and dyeing to improve the look and feel. This adds to time and costs.
While MJF machines are expensive, and there are fixed (EMI repayment, rent for the space where the printer is installed) and running costs (raw materials, electricity, and machine wear and tear) involved, here are a few ways to optimise productivity and costs.
MJF is beginning to have a transformative effect across industries, inspiring innovation and new possibilities in additive manufacturing. Automotive, healthcare, aerospace, consumer goods, housing and architecture are a few of the sectors where MJF parts have become indispensable.
Automotive: The transport sector uses MJF for lightweight, robust, complex parts. These include interior components like dashboard panels, door handles, air vents as well as ducts, brackets and connectors.
German auto major BMW uses HP MJF to print attractive keycaps of its MINIs. French auto giant Peugeot uses the technology to print car accessories like a sunglasses holder, a can holder and a phone/cardholder.
Oechsler, a global supplier to the auto industry, teamed up with TECHART, an automotive company, to develop a lightweight, performance-oriented car seat printed with HP Multi Jet Fusion (MJF). The seat offers enhanced ventilation and breathability, while also providing the ideal damping properties needed for racetracks.
Healthcare: MJF is considered a game changer in the medical sector due to its ability to produce biocompatible customised one-off parts at speed. Its impact is most palpable in bespoke orthotics and prosthetics as the technology can create detailed lattices that can be matched to the user’s body shape and skin tone. MJF products are also strong, durable and economically viable.
MJF’s coloured 3D models help doctors differentiate between tiny veins and arteries while practising procedures before complex surgeries.
Aerospace: It utilises this technology for fabricating lightweight, high-strength components.
Consumer goods: MJF has entered the footwear space with sport brand Decathlon and luxury brand Botter. HP is pushing the envelope in the sporting goods and eyewear industry. Using MJF, Oakley, a sport performance brand, has been able to cut down on the product development stages of its eyewear. selection and athletic equipment.
Architecture: MJF applications in architecture and construction sectors can be seen in the intricate scale models and prototypes of buildings that enable better visualization and planning.
MJF is an evolving technology with tantalising possibilities that could radically transform 3D printing, culminating in wider adoption of additive manufacturing techniques. HP plans to use its proprietary technology to revolutionize part design and manufacturing with streamlined workflows and new capabilities for its MJF printers.
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