Getting to Know Additive Manufacturing Technologies

• FDM Strengths: Desktop friendly and accessible. Boutique-style printing means a wide variety of materials and a relatively easy changeover. The alterable infill can make parts more lightweight.

• FDM Trade-offs: Visible layering can be a challenge for strength and cosmetics on thin vertically-grown features, small details, and organic contours.

Material Jetting (PolyJet)

Material jetting is a process where microdroplets of material selectively deposit on a build platform. Similar to a three-dimensional inkjet printing process, material jetting can produce high-detail parts and often boasts the ability to use multiple materials, colors, or both. It performs this by selectively depositing a material pixel-by-pixel.

Material jetting is not to be confused with binder jetting, where the jetted binder holds together a material, layer by layer, typically on a powder bed. Material jetting is depositing the part material directly.

Courtesy: pixel_B/Adobe Stock

PolyJet

PolyJet, a portmanteau of “polymer jetting,” is a material jetting process that selectively deposits a UV-cured liquid resin using ink-jetting. A lamp on the printhead cures the deposited materials in a single motion, hardening the liquid, and the build tray moves away from the print head to build height. Unique to PolyJet is the way to mix and customize materials on a single print. Applications could be for full-color 3D printing, digital overmolds, soft-touch exterior, or multi-material prints that exhibit all of the above and more!

• PolyJet Strengths: One of the best prototyping methods for building concept models with a look and feel of the final product.

• PolyJet Trade-offs: Creating a digital file with color or multiple materials can have a learning curve. Materials typically are not viable beyond prototypes.

Powder Bed Fusion (SLS, HP MJF, DMLS)

Powder Bed Fusion, or PBF, is an additive manufacturing process where plastic or metal parts are formed by selectively melting model features in the powdered raw material. Typically, this process is done layer by layer, fusing parts with a heat source such as a laser. Because PBF creates fully dense parts in real metals and thermoplastics, it is ideal for rapid prototyping and production-viable components.

Selective Laser Sintering

Selective Laser Sintering, widely known as SLS, is a laser powder bed fusion process (LPBF) where a fine layer of nylon powder spreads across a heated chamber, and a laser will fuse cross-sections of the part, building layer by layer. SLS is a powerful way of making plastic parts in bulk due to no support structure requirements. The fusion process, known as sintering, creates solid parts with a matte, sugar-cube-like surface finish. Post-processing can include color dyeing, media tumbling, and vapor smoothing.

Typically SLS parts are made in nylon – most notably nylon 12 (polyamide 12, PA12). The SLS process can also produce parts in nylon 11 (polyamide 11, PA11), TPU, PS, PP, PEKK, PEEK, and others. Some SLS materials have been enhanced and modified with different filler options such as glass beads, mineral, carbon, and flame retardant additives. Variants of nylon 12 and nylon 11 are by far the most commercially available.

• SLS Strengths: Affordable and functional parts can be made readily at industry-low costs. SLS can accommodate more design flexibility because it does not require support.

• SLS Trade-offs: Limited material choices on the market. Post-processing requires specialized environments for powder handling. Part design must consider trapped material removal.

HP Multi Jet Fusion

HP Multi Jet Fusion (MJF) is a PBF process developed by Hewlett Packard. Like SLS, this process starts with a heated powder bed of thermoplastic material. However, HP MJF does not use a laser to fuse parts like SLS. The MJF platform uses an ink-jetted fusing agent, which will precisely deposit on the part cross-sections for that build layer. A second material, called a detailing agent, is also deposited around the edge of the fusing agent to create a defined edge for the part slice. Afterward, a heat bar travels across the entire build area. The heat emitted is not enough to melt the natural material but does cause a melt where the fusing agent is present, creating a solid part feature and fusing to the part layer underneath. Once the heat bar passes, the build area lowers slightly, and a layer of fresh powder is smoothly deposited for the process to repeat.

Like SLS, HP MJF can build parts without support structures as they are suspended in unfused powder during the build. A specific advantage HP MJF has over SLS is the time it takes to fuse each layer. HP MJF has a higher throughput of builds overall versus SLS platforms, making it a strong alternative to SLS. Currently, SLS still has an advantage in build size and material selection.

Because the process is similar to SLS, many of the material options are nylon (polyamide, PA) based. Part properties overall are similar to SLS with slightly higher fatigue resistance. Due to the fusing and detailing agent, HP MJF parts will look matte grey on the exterior and jet black on the interior. HP MJF parts can be dyed black and vapor smoothed.

• HP MJF Strengths: Affordable and functional parts can be made readily at industry-low costs. Production is viable for smaller parts. HP MJF can accommodate more design flexibility because it does not require support.

• HP MJF Trade-offs: MJF has limited material choices on the market. Part design must consider trapped material removal.

Direct Metal Laser Sintering

Direct Metal Laser Sintering (DMLS) is a metal additive manufacturing process where powdered material is fused by a laser on a layer-by-layer basis creating a dense metal object. Other names for DMLS are Direct Metal Laser Melting (DMLM), Direct Metal Printing (DMP), or Selective Laser Melting (SLM). The most common 3D printed metal alloys are aluminum, steel, stainless steel, nickel-alloy, and titanium. Unlike plastic PBF technologies, such as selective laser sintering, DMLS requires the first layer to be fused with the build plate and sacrificial support structures to be generated due to intense stresses created when melting and cooling metal. This means that 3D-printed metal parts in DMLS can be nested beside each other but not above each other like plastic powder bed technologies. Metal 3D-printed parts via DMLS will have a matte grain finish, similar to cast parts.

• DMLS Strengths: Complex and organic designs can be built out of genuine metal alloys. Metal is fully dense and more robust than cast components.

• DMLS Trade-offs: Throughput and the part size are limited to the platform size, which is often under 9”. Metal 3D prints can require significant post-processing to achieve a finished result.

Vat Photopolymerisation (SLA)

Vat Photopolymerisation is one of the longest-established additive manufacturing processes in the industry. The process consists of a chamber with a liquid material that is selectively cured using ultraviolet (UV) light. Vat Photopolymerization processes, like stereolithography (SLA), are known for achieving incredibly high detail in the prints and smoother surfaces versus other processes like SLS or FDM.

Courtesy: Josef/Adobe Stock

Stereolithography (SLA)

Stereolithography, commonly referred to as SLA, is a 3D-printing process using vat photopolymerization to create objects. SLA parts are formed by ultraviolet (UV) light selectively curing cross-section profiles, layer-by-layer, from the bottom to the top. The UV light is typically from a UV laser but can also be generated from a digital light projector (DLP) for added speed. SLA’s natural print surface is smoother than other 3D printing methods. This makes SLA materials ideal for cosmetic prototypes, model making, and fit check engineering models.

SLA materials are typically engineered to act like traditional thermoplastics but are thermoset polymers. After printing, SLA materials undergo a UV cure in a specialized light chamber to ensure all material is fully hardened. Sacrificial support structures are used in the SLA process to enable overhanging features. These supports are manually removed and residual features can be easily sanded.

• SLA Strengths: Fine and intricate details can be achieved with a smooth surface. Prints easily can be post-processed for an enhanced finish, such as increased gloss or clarity on translucent materials.

• SLA Trade-offs: SLA materials are not as robust as thermoplastics and have limited use cases for long-term installations.

Binder Jetting

Binder jetting is a multi-step additive manufacturing process that begins with a powder bed of material being selectively sprayed with an inkjet-style print head. The print head has a liquid binder, gluing the material together successively over multiple layers. After this first stage, binder jet parts are in a “green” state that requires secondary processing to harden, solidify, or sinter.

Metal Binder Jetting

Metal Binder Jetting is a process that uses an ink binder and a metal powder build bed to create net shapes of parts. The process can accommodate multiple parts in a single print over a build area. After the green stage, parts undergo a furnace step. This stage will melt and sinter the parts with significant shrinkage for single alloy parts, often around 20% smaller than the green stage. In some cases, a secondary metal is infiltrated to replace the binder, such as bronze, where the parts only shrink a percentage point or two. Metal binder jetting does not require supports for the infiltrated parts but will require wicks to allow the flow of the secondary material into the part body. Metal binder jet parts are matte in their appearance and can be post-processed.

• Metal Binder Jet Strengths: Can be used for scalable production of small intricate parts as an alternative to die casting or metal injection molding.

• Metal Binder Jet Trade-offs: The multi-stage process is design-sensitive and typically requires multiple iterations to tune.

3D Printing Resources

Building a digital file for 3D printing helps produce successful outcomes, regardless of the process chosen. Onshape’s tech guide to successful 3D printing is a great starting point for design principles. For getting parts made, Xometry.com or the Xometry app for Onshape provides instant pricing and simple checkout for over a dozen manufacturing processes from 3D printing to CNC machining and beyond. Powered by an AI-drive Instant Quoting Engine, Xometry is where big ideas are built.