MJF vs SLS: Plastic Powder Bed Fusion 3D Printers Comparison

Powder bed fusion 3D printing technology, though not a recent invention, is one of the largest and fastest growing subdivisions of the 3D printing industry. For plastic-based powder 3D printing, the two most popular methods are selective laser sintering (SLS) and multi-jet fusion (MJF) technology.

Through innovations in hardware, software, and materials, 3D printer manufacturers are broadening the scope of possible applications for both SLS and MJF 3D printers, such as low volume production of end-use parts, functional prototyping, manufacturing aids, and replacement parts. Both of these forms of powder bed fusion technology have their specific advantages and disadvantages, and factors such as cost, footprint, intended application, and volume capacity should be considered when choosing between technologies.

In this guide, we’ll discuss how each technology works, the merits and drawbacks of each, and the different applications in which they can be utilized optimally.

Powder bed fusion printers are typically larger than the more ubiquitous fused deposition modeling (FDM) or stereolithography (SLA) technologies, and are therefore more capable of producing many parts in each build. The build chamber and self-supporting nature of the powder bed allows for parts to be stacked vertically and even nested together. This feature enables operators of SLS or MJF 3D printers to maximize the utility of the space and pack the entire chamber as fully as possible. The lack of support structures also means that post-processing parts is easier and less labor-intensive, enabling parts to be produced consistently at a larger scale.

For example, Formlabs’ Fuse Series SLS 3D printers automate this feature through an optimized packing algorithm, which orients the parts so that every possible centimeter is filled. Fully packing the build chamber also aligns the packing density with refresh rate, so that all unsintered powder can be reused for a zero-waste printing workflow. 

In summary, powder bed fusion 3D printing with a fully packed build chamber brings down cost per part by:

• Producing more parts with fewer builds, increasing overall efficiency and reducing labor time.

• Optimizing the amount of unsintered powder to minimize or even completely cut waste.

The main material group used in SLS and MJF printing is nylon, a highly capable engineering thermoplastic for both functional prototyping and end-use production, used for a wide range of modern day industrial and consumer products. Nylon is resistant to UV, light, heat, moisture, solvents, temperature, and water. 3D printed nylon parts can also be biocompatible and not sensitizing, which means that they are suitable for skin contact and safe to use in many contexts.

Though many businesses who outsource parts to a contract manufacturer or service bureau might not understand the differences between SLS and MJF technologies, they are familiar with the material, which means adopting powder 3D printing technologies is easier than most other processes.

SLS 3D printing was the first powder bed 3D printing technology, and has been a popular choice for engineers and manufacturers for decades. Invented in 1982 by a group of researchers at the University of Texas at Austin, SLS refers to technology in which a high powered laser sinters a thin layer of powder from above to form a solid cross section of the desired geometry. After each layer, the printer spreads another thin layer of powder across the top of the build chamber as the print platform drops down and the next layer is built. This method of laser powder bed fusion is attractive to manufacturers, engineers, and product designers because of its low cost per part, high volume capacity, and material familiarity.

Industrial SLS printers have been available for decades, and have been utilized as another piece of heavy machinery or manufacturing equipment—excellent at the job for which they’ve been designed, but only possible for large institutions with space, funding, and dedicated operators. 

Manufacturers like EOS or 3D Systems design these systems with very specific customers in mind. Their customers are spending hundreds of thousands, if not millions, on machinery, service, and upkeep each year, and have warehouses and infrastructure to support them. Their customers are not start-ups, small businesses, or individuals, simply because they’ve been priced out of powder 3D printing solutions. 

In recent years there have been efforts to make smaller scale, less expensive SLS 3D printing solutions, something that is not available with MJF technology, which only offers large-format options. 

The Formlabs Fuse 1 printer was the first benchtop sized SLS 3D printer capable of producing industrial quality parts of comparable quality to those produced by expensive options like traditional SLS systems. With a footprint less than half the size of an EOS entry-level machine, a streamlined workflow, and an affordable price point, the Fuse 1 ($18,999) and new Fuse 1+ 30W ($27,999) have enabled hundreds of small to medium manufacturers to bring SLS in-house, while allowing large manufacturers to add machine capacity and decentralize aspects of their production.

Multi Jet Fusion 3D printing is a powder bed fusion additive manufacturing process that produces similar parts to SLS, using a slightly different process. To form parts, the printer dispenses a liquid binding agent from many small nozzles onto the powder bed, bringing the powders to a semi-solid state before finishing the process with heat. The infrared heat source then cures the semi-solid cross-shape before another layer of powder is deposited and the process repeats. The process was invented in 2016 by Hewlett Packard (HP), and remains patented under that brand.

Multi jet fusion printers are often viewed as interchangeable with SLS 3D printers, especially when businesses are outsourcing 3D printed parts to service bureaus. These service bureaus will offer many types of 3D printing technologies, but often make no distinction between the two separate types of powder bed fusion printed parts, as the properties of the final parts are largely similar.

As with SLS 3D printers, MJF parts do not need supports, and therefore offer more design freedom and do not have the complicated post-processing steps that are necessary with some other 3D printing processes. The liquid binding agent and heat combination creates parts with almost identical mechanical properties as with laser sintering, and the parts are similarly mostly isotropic.

HP still holds a patent on MJF 3D printing technology, and so the only MJF printers on the market belong to HP’s line—the Multi Jet Fusion 3D Series. HP also controls the proprietary software needed to operate the printers. With prices ranging from about $340,000 to more than $500,000, the HP 3D printers deliver highly accurate parts, but require a larger investment in terms of cost, time, ongoing maintenance, and infrastructure, similar to traditional SLS 3D printing solutions. HP MJF 3D printers are most often used by service bureaus, large in-house additive manufacturing labs for Fortune 500 companies, and because of their multi-color capabilities, are frequently part of healthcare centers’ advanced manufacturing initiatives. HP used to offer a smaller format MJF 3D printer aimed at designers and product development teams, but it was recently discontinued.

The workflow for SLS and MJF printers is very similar; powder must be maintained in a controlled environment, post-processed using accessory hardware and tools, and for most printers, can be recycled back into new prints. 

Traditional SLS printers and HP’s MJF 3D printer both require intensive, multi-day training for the initial set-up, so that a company technician can instruct the user in the necessary workflow and maintenance steps. Both traditional industrial SLS and MJF printers require ongoing maintenance steps in between each print, so all operators must be trained on the specific machine. For most large businesses, who have their 3D printers in a manufacturing environment with several other advanced machines, this isn’t an additional cost. For healthcare environments, small businesses, and educational institutions, this trained and available operator is an additional incurred cost. 

In contrast, Fuse Series SLS printers are ‘plug and play,’ and require a simple set-up of one to two hours before starting the first print, or a virtual training if preferred. Small to medium businesses can add the Fuse Series printers without a full time technician or operator because of the streamlined nature of post-processing, intuitive pre-print setup in PreForm, the lack of daily maintenance tasks, and the small footprint. A product designer can start a print and post-process it each day while maintaining his or her normal workflow.

Though HP’s printers have slightly better refresh rates on paper—requiring around 20% of fresh powder, compared to 30% with most SLS printers—their possible packing density is much lower, around 10%. Low packing density leads to a higher volume of unused powder that then needs to be recycled. Even with a very good refresh rate, like 20%, there is still more unusable powder leftover than there is with an SLS printer capable of high packing densities. 

SLS printers are capable of zero waste printing workflows, where all purchased powder is used during a print when utilizing optimal packing densities, and creating the optimal printing environment. With HP Jet Fusion Series printers, users have to discard almost as much powder as they’re using to make parts.

SLS and MJF 3D printers are touted as production machines, capable of high speed and large build volumes that can produce hundreds of parts with each production run. Both MJF printers from HP and traditional SLS systems have large build volumes, but the HP Multi Jet Fusion printers are able to print faster than SLS printers—the dispensing of binding agent and infrared heat exposure takes less time per layer than the scanning speed of lasers used in SLS 3D printers. 

However, the high temperature sustained during SLS and MJF printing requires a longer cooldown process for large printers, up to 48 hours. HP offers a refrigeration feature for build chambers that quickens cooldown time, but also comes with an extended footprint and higher cost. Overall, this means that MJF printers are generally capable of a higher throughput than large SLS printers. More compact SLS printers, like the Fuse 1+ 30W have smaller build volume, which results in a shorter cooldown time of only 14 hours for a full build, empowering users to complete finished parts faster than both MJF and large SLS customers.

Scalability is also an important aspect—a business can purchase eight complete Fuse 1+ 30W printer solutions for the same price as a single HP Jet Fusion 4200, leading to comparable throughput. The improved print speed of the Fuse 1+ 30W also allows for double the production of the previous generation model. Most manufacturers do not have products made of only one material, and therefore the ability to print with multiple materials should be taken into account as well when considering throughput.

Traditional SLS and MJF printers require a three product set-up: the build chamber, which slots into the printer, and the post-processing station. Together, these three parts cover substantial footage and require multiple power sources. Compact SLS printers, like the Fuse Series, enable an efficient, streamlined workflow with the inclusion of the Fuse Sift, and all-in-one powder reclamation, cleaning, and recycling station. Fuse Series printers do not require specialized wiring either and can run on a typical AC power outlet. 

MJF printers present a big advantage in one area — color 3D printing without a post-print processing step. The binding agent dispensed by jets can include a color, or multiple colors. While SLS users have to paint, dye, or plate their parts to achieve a colored finish, MJF users can plug their color scheme directly into the software. In the healthcare industry, full color parts present a large value, as medical professionals value the ability to achieve a multi-colored anatomical model without additional labor involved. 

However, producing full color parts is only possible on the more expensive systems—most of HP’s printers produce parts that are a light grey in color, and require the same painting and dyeing steps that SLS parts do. Full color printing also offers limited finish options. As a result, customers of powder 3D printers most often choose to finish parts and then paint them according to the requirements of the final parts.

When requesting parts from a service bureau, the end-product, whether produced by an SLS or MJF printer, can be virtually identical. For one-off parts, or for new businesses getting their first product realized, service bureaus are excellent options, and the differences between SLS and MJF printers are not important. At a certain volume however, bringing a powder bed fusion 3D printer in-house is more cost-effective. 

Before comparing technical specifications (materials, infrastructure requirements) every user has to first think about initial investment cost. SLS and MJF printers use slightly different technologies, have different sizes, and enable different material libraries, but the biggest difference, by far, is purchase price. 

Most small to medium size businesses cannot afford the $340,000 initial investment into MJF printing, not to mention ongoing cost of operation and service contracts, limiting the target market of these machines to large manufacturers and service bureaus with predictable, high-volume 3D printing needs.

There are more options for SLS than MJF, and because the print quality between industrial systems is so comparable, more businesses will find more SLS options which fall within their operation budgets. Factors such as color printing, material availability, workflow, and footprint start to play a more important role once the budget has been established. A more compact SLS printer, such as the Fuse 1+ 30W, is appropriate for a more modest budget. When compared to the costs of outsourcing, it takes most businesses only a couple of months to pay off the initial purchase price. 

To determine if the Fuse Series printers are right for your application, you can request a free sample in our four high performance materials, or speak with an SLS expert today.