When HP debuted its Jet Fusion 3D Printing Solutions in 2016, it introduced an entirely new industrial additive manufacturing technology. While powder melting, light catalyzed solidification and filament deposition systems have been refined steadily over the last 20 years, the key constraints of speed, cost and resolution remain issues that restrict the adoption of additive as a true production technology.
With a large powder bed designed to hold nested batches of parts, HP Jet Fusion 3D printers, powered by Multi Jet Fusion (MJF) technology can deliver high productivity – making them a serious option for industrial-scale polymer 3D printing. That’s why engineering.com took a closer look at the machines, comparing them not only to other additive techniques but also to traditional manufacturing methods.
Outside of the 3D printing business, HP is a leader in microfluidics (the ability to manage fluids at a microscopic level). It’s this ability to place billions of drops of ink or agents per second with accuracy that enables HP 2D and 3D technology. HP uses this technology in inkjet printers for the consumer, office, commercial and industrial markets as well as for Multi Jet Fusion 3D printing. To learn more about HP Multi Jet Fusion, engineering.com spoke with Vance Stephens, R&D Director of the HP Jet Fusion 500/300 Series 3D Printers.
The Basics of HP Multi Jet Fusion technology
The HP MJF process is similar to a binder jetting or digital light processing (DLP) process, but with a few key differences.
In the removable build unit, the print head jets a fusing agent in one pass onto the PA-12 powder surface in the shape of the two-dimensional layer. Next, infrared lamps heat and fuse the powder. Then, the next layer of powder material is deposited.
The jetting system is highly precise, with 30 million drops deposited per second per inch. In addition to the fusing agent, the jets can deposit other agents such as a detailing agent, which is sprayed onto areas next to the intended fusing area to prevent thermal bleed. This improves performance for features such as sharp corners and raised or recessed lettering. MJF is capable of delivering a layer thickness of 0.08 mm (0.003 inches).
The process differs from selective laser sintering (SLS) by the application of heat to the entire layer at once via infrared lamp, versus an aimed laser which selectively sinters together powder particles bit by bit. It also differs from binder jetting. The difference between a binding agent and a fusing agent is that a binding agent cements particles together without changing the particles’ structure. A fusing agent uses thermal energy to melt and fuse the particles together, resulting in functional parts with high isotropy.
Since the launch of the first HP Jet Fusion 3D Printing Solution in 2016, the portfolio has been steadily growing – now including: the new HP Jet Fusion 5200 for mid-volume production environments, the HP Jet Fusion 4200 for industrial prototyping and final part production, and the smaller HP Jet Fusion 500/300 series, which delivers functional parts and prototypes and is ideal for small/medium-sized product development teams, design firms and universities in applications such as prototyping, assembly aides and short run production. In the HP Jet Fusion 500-series printers, coloring agents can be added.
Additive Manufacturing vs. Traditional Plastics Manufacturing
In plastics manufacturing, injection molding (IM) is the gold standard for mass production parts. For additive manufacturing to be viable for industrial production of resin parts, the technology will need to compete with IM in terms of accuracy, precision, capability and throughput.
“Everybody thinks that injecting molding is perfectly uniform in part strength and process repeatability. But in reality, injection molding has issues in and around how you gate the part, how you cool the tool, the feature sizes as well as failures such as flash, warping and jetting, for example,” explained Stephens. “There are significant design constraints around injection molding. I went through significant training as I started designing for injection molding as an engineer. In all manufacturing processes, limitations exist, but in injection molding they are all very second nature to us.”
When it comes to capability, because molds can be highly polished, IM parts can be produced with high surface finish with minimal post-processing. In contrast, the rough surface of printed parts must be sanded and polished if high surface finish is required.
However, beyond these limitations, the capabilities of additive manufacturing for design features and geometry far outstrip those of injection molding. Fundamentally, every molded part must be designed to be released from the mold, which must be machinable by conventional machine tools. This limits the design features that can be added to molded parts.
Complexity is Free
In contrast, complexity is “free” in 3D printed parts. This simple fact can be paradigm-shifting, as entire subassemblies can be consolidated into one printed part. Functional features such as conformal cooling channels, or features that would usually require multiple operations, can be done in the same print. One simple example of this comes from HP’s use of MJF to print production parts for HP printers.
“We put 40-50 different parts in a single build unit,” said Stephens. “With IM, that would require 40 or 50 different molds. Using a single build unit helped us lower production time compared to working with a mold shop. While the HP Jet Fusion 3D printer can print several parts in one build, a mold shop would need to hang a tool, mold the parts, take the tool out, hang the next tool, mold the next parts, and that kind of process, where I can just create all of those parts for a part of a printer in a single build and operation.”
Reduced Lead Time
Possibly the most significant difference between IM and AM is the lead time.
“In injection molding, you must prototype, test, tool, test and then produce. So, you've got all that lead time, said Stephens. “With 3D printing, I can prototype and print production parts in the same process.” This difference is what gives MJF a cost-per-part advantage over conventional manufacturing techniques.
“3D printing creates several degrees of freedom that clearly do not exist in injection molding, but it also comes with its sets of constraints and design guidelines. It can do many things that injection molding can’t do, and injection molding can still do things where 3D printing is in its infancy,” said Stephens. “My view is that MJF can definitely meet the needs of injection molded parts in a variety of applications and even exceed the needs of injection molded parts in some applications. But in other areas, injection molding is still a clear choice.”
HP has recently released the MJF Handbook, which includes comprehensive design and material selection guidelines for MJF.
Voxel-Level Control
One example of the breadth of capability available with AM compared to IM is MJF’s volumetric pixel (voxel)-level control of physical and mechanical properties. In molding, liquid material is flowed into the mold, producing a homogeneous part. When different mechanical properties are needed throughout the part, manufacturers may need to consider overmolding or insert molding, for example.
With AM, parts are built up voxel by voxel, allowing fine control of the color, strength, elasticity, and other properties of each voxel of the part. “Some of this is implemented today and some of it is still R&D work in progress, but the power of Multi Jet Fusion is that we can combine the chemistry of agents with the physical properties of powder and work to create new solutions,” explained Stephens.
Reliability of Industrial AM
In order to make industrial additive competitive with established processes like IM and machining, AM also needs to be highly reliable. To address this, HP has built redundancy into the system. For example, during development of the new 5200 series printer, HP decided to include a backup lamp module. The machines also employ in-process monitoring to gather data before and during each print cycle.
“We have several monitoring devices that are monitoring the process and the capabilities, so that we can get indications of things that may be failing ahead of time, that are helping to ensure adjustments in real time, and compensating for things that may not be occurring during the process. We also have a series of processes that validate the health of the machine and make any needed compensations for that prior to the actual building process,” said Stephens.
HP Multi Jet Fusion vs. Other 3D Printing Methods
There are two common approaches to printing large numbers of parts in an industrial setting. One is to use a system like MJF or SLS with a large build volume and nest several parts into each build. The other is what’s sometimes called a printer farm, where several smaller printers, typically FFF or SLA systems, are stacked up and actively tended as they fire off one or two parts per build. But which approach is better?
The approach which uses a fleet of small printers can make sense at the small scale, as it doesn’t require as large a capital investment up-front. However, according to Stephens, these print farms are difficult to scale for production simply due to the number of failure points and maintenance issues that arise from a large number of complex print heads is greater than the number of failure points of one larger machine. This lowers the overall reliability of production.
Compared especially to fabrication techniques such as stamping, AM is a slower process. However, among the variety of AM processes available, there are significant differences in throughput that must be considered. In processes such as FFF, SLA and SLS, the print head or laser is directed along a path, typically using G-code, to gradually complete each layer before beginning the next layer. MJF and DLP use the entire 2D image of the layer slice, instead of a meandering path. This can save significant time per layer.
Next Steps: Supporting Adoption of Industrial AM
Manufacturing engineers who have seen or experienced what’s possible with AM are eager to apply it in production, but the manufacturing industry tends to move slowly. To start realizing the potential of AM on the factory floor, AM OEMs, including HP, must find inroads to prove its viability. One of the ways HP has tackled this problem is by expanding the MJF product line from the 4200 printer to the 300 and 500 series printers, which are smaller, more affordable and designed for the design office, rather than the factory floor.
“The earlier that AM-thinking is integrated into the product development cycle, the greater the potential benefits and value creation, which is why it’s extremely important for HP to democratize the complete workflow of Multi Jet Fusion,” explained Stephens. “The best way to drive adoption for the production space is to introduce and enable designers, creators and those that create the parts that need to be printed and create access so that they can easily prototype. And then, with the same technology, they can migrate those prototype designs into production. That way we work across that complete workflow of concept to part generation.”
HP’s system is in use with major manufacturers – including those like SmileDirectClub who are disrupting their market using 3D printing– across a variety of industries. As HP adds new materials options to the portfolio, more applications are expected. The combination of large parts, many parts and a fast build make the Multi Jet Fusion process a serious competitor in a crowded field.
If you’re interested in exploring the applications of AM in your manufacturing operation, check out www.hp.com/go/3DPrint.
HP has sponsored this post. All opinions are mine. --Isaac Maw