3D Printing Technology Classification, and Non-Mainstream Technology Introduction

Additive manufacturing (Additive Manufacturing; AM) refers to the process of manufacturing parts or physical objects by means of material stacking based on 3D model data. Three-dimensional printing (3D printing) refers to the use of print heads, nozzles or other printing technology, through the accumulation of materials to create parts or physical process, the term is often used as a synonym for additive manufacturing, therefore, also known as "3D printing".

It is a form of manufacturing in which components are generally built in the form of layer-by-layer deposition. At the same time, there are seven different types of additive manufacturing technologies that are internationally recognized by ISO/ASTM

1. light curing - UV light selectively cures liquid resins through point-by-point or layer-by-layer illumination.
2. powder bed fusion (PBF) - the use of an energy source (usually a laser or electron beam) to fuse powdered metals or polymers together.

3, binder jetting - the binder deposited on the metal powder or sand forms the geometry; for metals, sintering is usually also required after printing to melt the powder.

4. material jetting - droplets of material are deposited precisely to create a geometry
5. sheet lamination - sheets of material are stacked and laminated together by ultrasonic welding, brazing, adhesives or chemical means
6. material extrusion - where materials such as polymer filaments or pellets are heated and extruded through a nozzle.

7, Directed Energy Deposition (DED) - metal powder or wire is fed into a molten pool generated by a laser or electron beam in a process similar to welding.

In addition, "hybrid manufacturing" describes a process that combines additive manufacturing with traditional subtractive technologies. For example, a CNC machine can be equipped with a DED print head, allowing the same machine to both 3D print materials and mill them.

At the same time, NJC needs to highlight that each of these seven families has a different 3D printing subcategory. For example, Directed Energy Deposition (DED) can use powder or wire for making metal parts. Light curing, on the other hand, includes categories such as stereolithography (SLA) and digital light processing (DLP), with SLA being point scanning and DLP curing one layer at a time.

Machine manufacturers may also have proprietary processes or use different terminology for the following types of special technologies in addition to these seven categories of 3D printing processes.

Digital Light Synthesis (DLS)

Digital Light Synthesis (DLS) is a proprietary resin-based 3D printing process developed by Carbon.

How does DLS work?

Digital Light Synthesis is based on stereolithography. Both processes use UV-curable resins. However, unlike stereolithography, Carbon's process does not pause after each layer. The resin continuously flows through a "dead zone" above the oxygen permeable film, representing a cross-section of the part, and is projected onto the oxygen permeable window to cure the resin. The part is inverted as the build platform is lifted from the resin drum.

What materials can be used?

Carbon offers DLS resins including elastomers, flexible, rigid and medical grade polyurethanes, silicones, cyanates, epoxies, urethane methacrylates and dental materials.

What post-processing is required?

After printing, the part is removed from the build plate and all supports are removed. Some materials also need to be heat cured in an oven, which can take anywhere from 4 to 13 hours to complete. The heat triggers a secondary chemical reaction that strengthens the part, and no further post-processing is required after cleaning and curing.

Why use DLS?

The continuity of Carbon's DLS 3D printing process avoids the creation of layer lines in the part, thus providing a surface finish comparable to injection molded parts. DLS parts are also said to be waterproof and isotropic, with the same strength in all directions. In addition to providing a method for manufacturing prototypes, it can also be used as an alternative to manufacturing production parts.

1. Nanoparticle Jetting (NPJ)

NanoParticle Jetting (NPJ) is a 3D printing process developed by XJet. It is a material jetting technique that uses a suspension of powdered materials to build parts.

How does NPJ work?

NPJ jets a liquid containing suspended nanoparticles of a metal or ceramic material to build the part, while jetting a support material. The forming process takes place in a heated bed at 250°C, allowing the liquid to evaporate as it is injected, so that the particles adhere in all directions and only a small amount of adhesive is present in the body and support of the printed 3D object.

What materials can be used?

Xjet supports nanoparticle jetting using 316L stainless steel and two ceramic materials (zirconia and alumina). The materials are mounted in the machine through the cartridge and do not require processing or handling.

What post-processing is required?

After printing, the NPJ part retains a small amount of adhesive and may have a support structure. The carrier material is water soluble and can be dissolved in a water bath. If desired, it can be machined or polished at this stage.

Why use nanoparticle jetting?

This process enables the manufacture of many small parts at once. According to XJet, the material injection process can be controlled drop by drop, within ±25 microns for small parts and ±50 microns for larger MIM/CIM parts. The minimum feature size is 100 microns and the layer height can be 8 to 10 microns, allowing for fine detailing.

Because NPJ uses suspended materials, there is no need for sieving and other steps required for powder processes. The material can be printed in normal atmosphere without special gases, vacuum or pressure, and is easily recoverable.

Applications for nanoparticle jetting include hearing aids, surgical tools, crowns, bridges, and drill guides for the medical industry; high-temperature and friction-resistant parts for aerospace and automotive; and sensors for the electrical industry.

Ultrasonic Additive Manufacturing (UAM)

This process, developed by Fabrisonic, manufactures metal workpieces by fusing and stacking metal strips. The work is done on a hybrid machine that is capable of CNC milling the part as the additive manufacturing progresses. Building by stacking metal strips allows for fast build speeds, which makes large parts practical.

How does UAM work?

In UAM, the material does not melt, but is joined by ultrasonic welding. This welding uses high frequency vibrations to join surfaces while the metal remains solid. By welding layer by layer in this manner, strong parts are constructed.

Under high-frequency ultrasonic vibration and constant pressure, the ultrasonic motion breaks down the oxide by friction, bringing the metal into direct contact with the metal.

This process is repeated until a solid part is constructed. CNC contour milling can then be used to obtain the required tolerances and the best surface finish for the part.

Why use ultrasonic additive manufacturing?

Hard metal outer surfaces can be built on structures made of lighter metals to provide durability and lighter weight parts. Or, two very different metals - such as titanium and aluminum - can be combined into a hybrid layer to form a structure that mixes both properties.

This technology combines the practicalities of additive and subtractive manufacturing, allowing the fabrication of parts with complex geometries and internal channels. The fine dimensional accuracy and smooth surfaces of parts fabricated using UAM and machining demonstrate the possibility of hybrid manufacturing.

Selective Thermoplastic Electrophotographic Process (STEP)

Developed by Evolve Additive Solutions, the Selective Thermoplastic Electrophotographic Process (STEP) technology combines 2D imaging with proprietary IP to precisely align afferent layers and bond them into a fully dense final part with isotropic properties said to equal or exceed injection molding.

What materials can be used?

The company says that STEP's candidate materials are the same polymers that can be used for injection molding. However, offering the material as a toner requires Evolve's proprietary materials engineering technology.

STEP machines have multiple print heads, which can allow for multiple colors in the part, but another possibility is the possibility of multiple materials. The variety of different polymers applied on a voxel-by-voxel level allows for a combination of properties that cannot be obtained in any single material alone.

Why use STEP?

STEP offers a way to get thousands of plastic parts in a matter of days, while waiting for mold processing that can take weeks for delivery. And because there is no tooling, the new technology has a lower cost per part than molding at this volume level.

This process can produce parts without lamination, and STEP fits heated layers to heated parts, producing a more complete fusion than processes such as FDM.

1. Multi-Jet Fusion (MJF)

This process is a powder bed 3D printing process developed by Hewlett-Packard (HP) that bonds reagents and powders together in a process similar to adhesive jetting. Unlike point-to-point laser-based powder bed fusion systems, MJF selectively distributes the fusing and refining agents across the powder bed and uses infrared light to fuse the layers together.

The Multi Jet Fusion system consists of interchangeable build units that can be moved between the MJF 3D printer and a separate post-processing station for rapid cooling and powder removal. This modular system allows the printer and post-processing station to run continuously while the build unit cycles through, resulting in faster part production.

What post-processing is required?

After the build is complete, the build unit (the entire powder bed with encapsulated parts) is removed from the printer and placed into the post-processing unit for rapid cooling. The build unit is then moved to a processing station where the loose powder is removed by vacuum.

Compared to laser-based powder bed processes such as selective laser sintering (SLS), the final part is said to have a high-quality surface finish, fine feature resolution and more consistent mechanical properties. Also, because the heating is done layer by layer and the powder is filled underneath the part, the warpage incidence is lower in MJF than in SLS.

To improve surface finish, parts can be sandblasted and then primed or painted. If the application requires, the printed part can be dyed or further treated.

What materials can be used?

Multi Jet Fusion is compatible with HP's range of thermoplastics, including High Reusability (HR) PA 12 nylon, HR PA 12 GB (glass bead reinforced nylon) and HR PA 11.

HP also supports 3D material certification programs and works with polymer 3D printing material suppliers to develop new materials. Material partners include Arkema, BASF, Dressler Group, Evonik, Henkel, Lehmann & Voss & Co., Lubrizol and Sigma Design.

Why use Multi Jet Fusion

This process can quickly produce functional prototypes and end-use production parts in less than a day. A single MJF printer can run almost continuously if the build unit is swapped out for post-processing at the end of each print run. Used powder can be reused by recycling.

MJF's layer-by-layer fusion is faster than point-by-point 3D printing systems and is said to take the same amount of time to fuse each layer, regardless of complexity. With MJF, parts can be nested vertically and horizontally, filling the entire build volume with separate individual parts. Multi Jet Fusion does not require mold investment or minimum order quantities; these factors, combined with its speed, make the process competitive with injection molding in volume production.