Metal 3D Printing: Laser Sintering vs. Bulk Sintering in a Furnace – Pros and Cons

November 13, 2017 by Matt Sand 3D Printing Business Metal 3D Printing Science & Technology

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Powder bed fusion (PBF) is by far the most widely used metal 3D printing process today. For evidence of how popular PBF has become, look no further than GE’s massive $1.4 billion investment last year into Concept Laser and Arcam. PBF includes both laser sintering and electron beam melting, but for this article we will focus on the more widely used laser sintering.

There is plenty to like about laser sintering, but the technology does have its limitations. Newer technologies are being developed to fill the void in the market where laser sintering just can’t compete as a technology. The unaddressed opportunities are typically higher volume applications that require lower price points than can be achieved through very expensive laser sintering technology. Most of these new, low-cost technologies separate shaping the part and sintering the metal powder, resulting in green parts that are bulk sintered in a separate furnace.

Let’s explore the pros and cons of the two approaches to understand which technology best fits a given use case.

Laser Sintering

Laser sintering begins with a layer of metal powder being rolled onto the build tray, and then an energy source (laser or electron beam) fusing or melting the powder into deliberate 2D designs. These thin 2D layers are fused on top of each other to create the 3D object.

Powder Bed Fusion Process [Image courtesy of 3DEO]

The sintering temperature of stainless steel can approach 2,500 degrees Fahrenheit. It requires a lot of energy to get metal that hot – expensive energy. When each individual machine needs an energy source capable of reaching these temperatures, there is a large increase in the cost of that machine. What makes laser sintering worth the cost is the larger build size of parts. This high cost typically makes sense in just a few situations – with extremely complex internal channels that can only be done with laser sintering, to create very large parts, and for high-end parts, such as jet engine fuel nozzles and satellite components.

Bulk Sintering

There are various 3D printing technologies that are gaining popularity which do not contain the sintering source within the machine itself. Most new technologies – being commercialized by companies like 3DEO, Markforged, and Desktop Metal – received their inspiration from metal injection molding (MIM), a mature technology that has existed for over 30 years and is widely used across many industries. MIM begins with metal powder being compounded together with a binding agent (i.e., glue), which is in turn injected under pressure into an existing mold to create a “green” part. After many of these green parts are created, they are bulk sintered in a high-heat furnace. Much like MIM, 3D printing technologies such as binder jetting, material jetting, and other bind and sinter processes create green parts that require sintering in a furnace to attain full density.

Binder Jetting Process [Image courtesy of 3DEO]

By separating sintering from the part printing process, there is a massive drop in cost per machine. The result is a fleet of machines working in parallel to create large numbers of green parts, which are subsequently bulk sintered en masse. Lower cost machines also mean part cost is dramatically reduced, since much less of the machine cost is being passed through to each part. Lower cost parts in high volumes has long been the goal of metal 3D printing, and bulk sintering technologies are rapidly gaining attention in this regard. The current limitation of bulk sintered 3D printing revolves around how big the parts can be – early binder jetting technology used bronze infiltration to reduce the associated shrinkage and sintering issues, but this changed the material properties of the metal and proved to not be a viable solution for production parts. Newer binder jetting technologies are coming to market hoping to address the build size issue while reaping the benefits of low-cost parts and high throughput.

3DEO’s Intelligent Layering is one of the newest bulk sintering approaches that combines traditional manufacturing technology with novel, additive processes. The process uses a precision CNC operation to machine layers while they are still in the green state. Forgoing the complexity of an inkjet head used in binder jetting, they instead use an off-the-shelf spray technology to bind whole layers of powder which are then machined. The bound green parts are then bulk sintered. The result is low cost metal 3D printed parts in high volumes.

Bind and Sinter — 3DEO’s Intelligent Layering Process [Image courtesy of 3DEO]

A Future with Many 3D Printing Technologies

What seems to be clear is that the future has room for many different metal 3D printing technologies. Each is beginning to find its niche applications, and none appear to be a silver bullet for every use case. It will be important moving forward for manufacturers to stay up-to-date on the latest technologies and how they fit into the additive manufacturing landscape. They will need to continue thinking about each part with respect to size, material required, lead time, cost, etc.

Laser sintering certainly has its place secured for the foreseeable future due its larger build size and strong material properties, while new and existing bulk sintering processes are showing much more promise to fill in the gap for lower cost parts in higher volumes.

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Matt Sand, President of 3DEO, and Lance Kallman, Vice President of Business Development, discuss sintering processes used in metal additive manufacturing.