Comparison of Metal 3D Printing — Part Three: Inkjet

Metal 3D printing is a burgeoning area at the moment. Many companies are investing in metal 3D printing systems and the market is growing quickly. There are a number of different metal 3D printing technologies out there. You can find the previous parts of this series comparing metal 3D printing technologies here, covering powder bed fusion and directed energy deposition technologies. In this part we will be looking at inkjet.

Inkjet

Inkjet metal? Welcome to the future, kids. Inkjet is a very versatile technology that can deposit a wide array of things. Inkjet is currently being used in several ways to 3D print metal parts. Also called, rather boringly, binder jetting, this process works differently depending on how the OEM implemented the technology. MIT also patented the core inkjet 3D printing patents. The University gave different companies different licenses so this also sometimes leads to different implementations as well. The MIT patent form of 3D printing was the one actually called 3D printing before journalists took this one technology name and used it for a whole host of different technologies as the collective name 3D printing.

The binder jetting technologies tend to work very differently hence their relative merits vis a vis the other metal 3D printing technologies differ. Typically however they all benefit from huge advancements in inkjet 2D printing. Better inkjet heads are advances upon which 3D printing companies can piggyback. On the other hand these tend to be multi-step processes which include a series of machines, process steps or production steps. In some cases these processes can make a single metal 3D print take a few days to make. The mechanical qualities of parts made with inkjet are often lacking as well (depending on the process). Typically however these processes are comparatively low cost. Inkjet metal 3D printing processes make some of the most production ready parts in the world. Whereas Direct Metal Laser Sintering/Selective Laser Melting/Powder Bed Fusion is used primarily in dental, implants and aerospace, inkjet metal processes have a wide application area.

voxeljet

Take a stroll inside your voxeljet 3D printer.

Voxeljet is a quickly expanding German company that makes high throughput inkjet based 3D printing systems. The company makes some of the largest 3D printers in existence and has made innovations in continuous 3D printing as well. Voxeljet focuses largely on prototyping and production of small series, rather than manufacturing. The technology’s sweet spot is for large complex timely items for industry, frequently working in cooperation with the foundry industry, for which the technology was initially developed. In this sense it competes often with Prometal below. Voxeljet uses binder with an inkjet head to harden PMMA and sand powders. The company sees applicable use in the automotive and aerospace sector, where development cycles are extremely short.

The company has a room-filling VX 4000 3D printer that can make 4 x 2 x 1 meter molds as well as a smaller VX1000 that can for example make investment casting molds out of PMMA. The voxeljet process is not a direct metal 3D printing process but instead is a part of a chain of steps resulting in 3D printed parts. The voxeljet process results in relatively economical metal parts with very high tolerances. The company has over 280 employees and over $22m in revenue.

Prometal ExOne

ExOne’s binder jetting inkjet nozzles.

ExOne is an American company that also specializes in making metal parts for end-use applications. With tolerances of the final parts not as tight as voxeljet the ExOne processes can be used to make lots of relatively small low-cost metal 3D printed parts. This means that ExOne could be very suitable for things such as door handles, customized metal parts and any kind of new consumer application. ExOne makes sand printers with a comparable accuracy to voxeljet systems while the latter have larger build volumes and higher throughput. The ExOne metal printing process works by depositing binder on a metal powder. This fragile model is then put in an oven where it is sintered while being infused by another metal. It is a multi-step process and after this parts need post processing as well. However the parts made in this way are low cost and can be used for all sorts of applications. The video below explains how this process works.

Xjet

The Xjet machine.

Xjet is an Israeli startup that uses nano particle jetting. A suspension of metal nanoparticles in a liquid is deposited using an inkjet head. The liquid is then evaporated by the heat of the 3D printer’s build chamber. Xjet and the Höganäs technology below both have extremely high levels of detail on the 3D printed parts. Xjet itself may be a completely revolutionary technology that could greatly expand the application area for metal 3D printing. The startup is relatively new however and will have to prove itself against much more established technologies.

Höganäs

A Hoganas Digital Metal 3D printed part.

Digital Metal was developed by a small team before being acquired by Höganäs. Höganäs is a large metal powder company which specializes in high-value and often custom metal powders. The Digital Metal process sees powder being spread out over a print bed and being selectively hardened by a binder from an inkjet head. The parts are then taken to a sintering oven and sintered. Digital Metal’s build volumes are very small. The surface quality, level of detail and accuracy make it a very mature process for printing out tiny metal parts for industry. Not yet suitable for the most demanding industrial applications Digital Metal is sure to find a niche making relatively low-cost highly detailed tiny metal items in industry.

Desktop Metal

Desktop Metal’s office and production 3D printers.

Desktop Metal is a $200m funded start up which brings together a lot of very talented 3D printing and materials people. The company’s Single Pass Jetting technology spreads metal powder, compacts it and spreads binder over it in one pass. Additionally it deposits “anti sintering agents” to inhibit sintering, this means that post processing will be easier and cheaper. The assembly with the print heads on it then reverses itself and produces a new layer. The build chamber is lowered and then later removed and the parts are sintered in a microwave furnace. Generally all of this means that the printer is printing most of the time not spending two-thirds of its time recoating for example. The company is also able (and willing) to use regular injection molding metals which means that a wider variety of metal powders will be on offer for customers. Desktop Metal is a very exciting technology. The level of funding and candle powder the team has should let them achieve great things. The team will have to get their machines in customers’ hands however and these will have to validate performance.

Conclusion

Inkjet is probably the most exciting area in metal 3D printing at the moment. There are new companies and new technologies being commercialized. Inkjet could very well give us the low-cost metal 3D printed parts that we dream of. It is unclear however if there are to be some patent issues with some of these players. ExOne and voxeljet should have solid access to the relevant core patents, it is unclear if some of the newer companies can say the same. As has happened with stereolithography (SLA, SL, vat polymerization) and SLS  (powder bed fusion) there could be patent conflicts that could inhibit development of these firms. Some of the players in SLS and SLA nearly killed each other rather than survive and the patent battles fundamentally affected the industry. At the same time the newer technologies promise much but can they deliver? Several very promising 3D printing technologies and companies were very good at promising. These firms failed on the workshop floor by not delivering on things such as throughput or repeatability. You can’t eat hype. 3D printing is becoming a manufacturing technology. In that scenario part cost, reliability and things such as customer service and machine quality will play an ever greater role. The inkjet technologies by and large are the challenger technologies bringing lower-cost parts to market. These companies seem to be burgeoning but will they follow through and dominate their niches in the years to come?

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