The ability to print a three-dimensional object from a spool of plastic filament, a vat of liquid resin, or a bed of metal powder is a concept that seems straight out of science-fiction. Yet, this is a ‘now’ technology. Yes, it is still in its early stages, but this fact actually makes it even more remarkable. Already we have access to household 3D printers, and domestic, research, and industrial 3D printing is capable of producing functional parts, not just prototypes, and models.
3D printing is the layer-by-layer construction of three-dimensional objects according to digital computer-aided design files. Each new layer is fused to the preceding one using light, heat, or a binding agent, depending on the printing process. Materials are powders, filaments, wires, liquids, or sheets.
3D printing is a fascinating and very broad topic. In this article, you will learn about what 3D printing is, the different stages of 3D printing, what materials can be used, the main 3D printing processes, the pros and cons of 3D printing, and its applications.
What Is 3D Printing?
3D printing is the layer-by-layer production of a three-dimensional object, item, or part. Each new layer is fused to the preceding layer as the print progresses. The build follows the specifications of computer-aided design (CAD) data and is thus digitally controlled.
The layer-by-layer construction technique has resulted in 3D printing also being referred to as Additive Manufacturing. It has arisen as an alternative to the more traditional and subtractive production techniques.
The Three Stages Of 3D Printing
There are many different 3D printing techniques, which will be discussed in a later section, but all 3D printing can be divided into three stages:
- Pre-processing
- Processing
- Post-processing
The Pre-Processing Stage Of 3D Printing
Pre-processing involves setting up the CAD for the print job and preparing the machine.
When you set up your CAD, you have to consider the type of 3D printing process or processes you have access to and choose the one most suited to your project.
The material you use needs to be compatible with the printing process and also needs to match the desired criteria of the final item, object, or part.
You have to use the correct CAD software and file resolution. If the file resolution is too low, it can result in a poor or coarse finish. If the CAD file resolution is too high, the printer may be incapable of printing it.
Additionally, you will need to take into account the physical limitations of your build, which may not seem problematic in the digital design. Things like overhangs (printing on ‘nothing’), wall thickness, build supports, warping potential, intricacy, etc.
All of these things can affect the success of the build, the time it takes, the cost, the amount of post-processing required, and the quality of the final product.
Preparing the machine involves inputting the CAD file, calibrating and adjusting the machines appropriately, and loading the materials into the printer.
The Processing Stage Of 3D Printing
The processing stage requires minimal work by the printer’s operator. The machine is busy printing the part, and the operator just needs to monitor it.
The Post-Processing Stage Of 3D Printing
During the post-processing stage of 3D printing, the printed item has to be carefully and safely removed from the machine. Furthermore, builds seldom come out of the printer ready to be used. There are certain finishing touches that are required.
Firstly, any supports need to be removed. The supports are the structures that were printed to act as scaffolds for the main body of the item but which are not part of the design.
Secondly, there is the tooling. Some parts need to be sanded, polished, painted, etc. There may even be a level of assembly required if pieces are printed apart.
What Materials Can You 3D Print With?
3D printing materials can come in many forms, including powders, sheets, liquids, filaments, and wires.
Thermoplastic and high-performance plastic polymers, resins, metal alloys, and ceramics are the three most common 3D printing materials. However, there are many different kinds of plastics, metals, and ceramics. Furthermore, there are also hybrid materials that combine these materials with each other or with materials that could not be 3D printed alone.
Thermoplastic And High-Performance Plastic Polymers
Thermoplastic polymers will become soft and formable when heated and then solidify again once cooled. Below is a list of just some of the thermoplastics used in 3D printing.
- Acrylonitrile Butadiene Styrene (ABS). This is a hard, tough, and heat-resistant plastic. It can be difficult to print with because it requires such high temperatures and needs a heated printing bed in order to stick. It also produces unpleasant fumes.
- Polylactic Acid (PLA) plastic is a biodegradable plastic, less durable than ABS, but it comes in a variety of colors, and it is relatively easy to work with.
- Polyvinyl Alcohol (PVA) is used as support material because it readily dissolves in water. This solubility makes it highly unsuitable for anything other than supports.
- Acrylic Styrene Acrylonitrile (ASA) is similar to ABS, but it has a much greater resistance to UV rays, making it a great option for outdoor applications. As with ABS, printing is made more challenging by the high-temperature requirements, and it produces unpleasant fumes.
- Polyethylene Terephthalate (PET) is a recyclable plastic that is safe to use for items that will come into contact with food and drink. The main drawback of PET is that it is brittle. PETG is a version of this plastic but with a glycol modifier to reduce brittleness. Items made from PETG are susceptible to wear.
- PEEK is one of a new range of plastics known as high-performance plastics, and it has properties similar to metals. PEEK requires high printing temperatures and a closed printing chamber, which not all 3D printers can provide.
- Polypropylene is a lightweight, semi-flexible plastic with good impact resistance. However, Polypropylene has low heat- and UV-resistance.
- Nylon, also called polyamide, is a durable, abrasion-resistant, and semi-flexible plastic. The integrity of nylon is compromised by humidity, and warping can be a print issue.
- Thermoplastic Polyurethane (TPU) is a flexible plastic. This is an excellent property for many items, objects, or parts, but it does make printing with it challenging.
Resins
Resins are also synthetic polymers, but they are photosensitive and in liquid form. Below is a list of some of the kinds of resins available for 3D printing.
- Standard resins have similar properties to ABS plastic, including the production of unpleasant odors and fumes during printing.
- Rapid resins cure quickly, shortening the post-print time and reducing the chance of the part becoming deformed once printed. However, the rapid curing means that you have to work quickly.
- Flexible resins are similar to TPU.
- Tough resins. As the name suggests, these are strong and durable.
Metals And Metal Alloys
Metal alloys are excellent 3D printing materials. They can be used to achieve high degrees of geometric complexity. They are also ductile, malleable, strong, lightweight, and even biocompatible. The main disadvantage of using metals in 3D printing is the cost; the feedstock is expensive. Metal alloys used in 3D printing include:
- Aluminum alloys.
- Titanium alloys.
- Titanium.
- Stainless steel (iron-based).
- Inconel (nickel-based).
- Tungsten.
- Silver.
- Brass.
Ceramics
It is possible to 3D print with ceramic materials (sand, silicon, etc.). However, the item, object, or part will have to go through post-processing to be made durable.
Hybrid Materials
Thermoplastic filaments can be mixed with wood particles, stone particles, metal particles, carbon fibers, fiberglass, etc., to provide different finishes and properties. There are also composite materials like Alumide, which is a Nylon base containing aluminum powder.
What Are The Main Types Of 3D Printing Processes?
All 3D printing techniques fall into one of the seven main types of 3D printing processes.
1. Binder Jetting
Binder jetting involves spreading a layer of powdered material onto a printing bed and then selectively depositing a liquid binding agent onto the powder according to the design, much like an inkjet nozzle deposits ink onto paper.
Once the first layer has been printed, the print bed is lowered fractionally to accommodate a new layer of powder, which is spread over it. The liquid is deposited again according to the design specifications of the next layer. In this way, an item, object, or part is printed.
Once the print is complete, the final product will be surrounded by the unused powder from each layer. It is left in this powder bed to harden or cure fully before being removed, the excess powders cleaned off, and the part subjected to the required post-processing.
Powdered metals and sand can be used in binder jetting, and binder jetting and metal binder jetting are the two main techniques of this process.
| Pros of binder jetting | Cons of binder jetting |
| The binder jetting printing speed is comparably fast. | Without post-processing, the final part produced by binder jetting remains porous and brittle. |
| Printing can be done at lower temperatures because the powder is bound with the binding liquid as opposed to heat. | Metal binder jetting produces parts that require sintering or infiltration to be durable and suitable for functional parts. |
| The low-temperature requirements mean that warping is unlikely. | Post-processing can take longer than the actual print. |
| Binder jetting has a large build volume. | |
| No support structures are required for parts printed with binder jetting because the build is supported by the unbound powder until fully cured and removed. | |
| The materials can be colored while being printed. |
Sand binder jetting is often used to produce casting cores and molds because of the large build volumes and print speed. Even the fact that the printed part is brittle is useful for this purpose because it makes breaking the cast or mold easier when removing the casted component.
2. Directed Energy Deposition
Other terms used to describe directed energy deposition include laser engineered net shaping (LENS), direct metal deposition (DMD), directed light fabrication (DLF), laser deposition welding (LDW), and electron beam additive manufacturing (EBAM). But even though there are many names for this 3D printing process, the methodology is the same.
Directed energy deposition involves the extrusion of the feedstock material from an extruder nozzle onto a build platform. While it is being deposited, a thermal heat source, such as an electron beam, laser, or plasma arc, melts the material and fuses each subsequent layer to the previous one.
Each layer solidifies on the build platform once deposited into the correct pattern. The build platform moves down as the item, object, or part is built up.
Most often, the directed heat source and the extruder are mounted onto movable arms that follow the CAD-driven pattern. However, it is possible for the arm to remain in a fixed position while the build platform moves.
Directed energy deposition can be used with wire, filament, metal powder, or ceramic powder, but metals are the most commonly and successfully used materials for this 3D printing process.
| Pros of directed energy deposition | Cons of directed energy deposition |
| The control achievable by directed energy deposition means it can be used to repair high-quality functional parts. | The level of finish depends on the material used. Some materials will require more post-processing. |
| Directed energy deposition can be used to print relatively large items, objects, or parts. | Compared to some other 3D printing processes, directed energy deposition has a limited range of materials that can be used. |
| Minimal tooling is required on large-printed items. | The parts produced by directed energy deposition are comparable to those produced by traditional manufacturing. This means that the 3D printing of these parts needs to be more cost or time-effective than conventional manufacturing, which is not always the case. |
| Hybrid structures can be printed using different materials. |
Directed energy deposition can be used to build new items, objects, or parts. However, one of its primary functions is in the repair or modification of existing parts, such as turbine blades.
3. Material Extrusion
Material extrusion is only used for thermoplastic filament materials (these may be composite plastics). A motor feeds the plastic filament through a hot printer extruder nozzle, and the molten plastic is deposited onto a printing platform where it solidifies. The extruder nozzle can move along the x-axis, following the CAD data.
The platform is lowered incrementally with each successive layer as the item, object, or part is built up. The layers are fused using heat or chemical binding agents.
One particular material extrusion technology, known as fused filament fabrication (FFF) or fused deposition modeling (FDM), is the primary 3D printing technique used in desktop or household 3D printers.
| Pros of material extrusion | Cons of material extrusion |
| Material extrusion 3D printing machines can be inexpensive. | Can only use thermoplastic filament materials. |
| Material extrusion is capable of producing a really good surface finish, which limits the required post-processing. | The final items, objects, or parts tend to be brittle (although this may vary depending on the thermoplastic used). |
| Material extrusion 3D printing machines are widely available. | Extruder nozzles can become blocked as the melted material is extruded. |
| Materials are typically inexpensive and freely available. | Material extrusion has a comparably low printing speed. |
In the industrial sector, material extrusion is used mainly in the production of prototypes, but it is commonly used to produce hobbyist 3D printed items (household FDM machines).
4. Material Jetting
In material jetting, 3D printing material is selectively deposited in droplet form onto the build platform according to the CAD specifications. Each layer is then exposed to UV light, which cures or hardens it in the deposited design.
The print head moves along the x-axis, and the droplets are formed through the oscillation of the deposition nozzle. The build platform is lowered with each successive layer.
Material jetting follows a line-wise method of deposition. Whereas other 3D printing processes deposit material in one point at a time, the droplet nozzle of a material jetting machine deposits multiple droplets alone a line at the same time.
One type of material jetting technique is called drop on demand (DOD), and it involves the use of two different nozzles. One deposits the build material; the other deposits the support material.
| Pros of material jetting | Cons of material jetting |
| Different materials can be used in a single build with material jetting. | Material jetting can only be used with materials that can be formed into droplets, such as viscous polymers or wax. |
| Material jetting is capable of a high degree of print accuracy. | The item, object, or part requires support materials during the build. |
| Even though the builds require support structures, the ability to change materials within a build makes printing the support structures relatively easy. | Supports have to be removed during post-processing. |
| Material jetting produces an excellent surface finish. | The final build is brittle, so material jetting is not a suitable 3D printing process for mechanical parts. |
| The line-wise method of material deposition in material jetting can significantly reduce the print time. |
Material jetting is used to produce various prototypes, molds, and models.
5. Powder Bed Fusion
Powder bed fusion is the 3D printing process whereby a layer of powdered feedstock is spread over the build platform and a thermal energy source, such as a laser, selectively fuses the powder particles together according to the CAD data.
The build platform is incrementally lowered, and a new layer of powered feedstock is then spread over the first by a powder roller. The next layer is selectively fused together and to the previous layer with the thermal energy source. Thus, the final item, object, or part is built up and surrounded by the unused powder.
The powdered feedstock is most commonly made from thermoplastic polymers or metal alloys.
Powder bed fusion with polymers is known as selective laser sintering (SLS). The powder bed is preheated to just below the melting point, a layer is spread over the build platform, and a CO2 laser beam fuses the powder particles together.
Powder bed fusion with metals can be done with a direct metal laser sintering (DMLS) technique or a selective laser melting (SLM) technique. DMLS is used for metal alloy powders, and SLM is used for single-element metals.
| Pros of powder bed fusion | Cons of powder bed fusion |
| To a certain extent, the unused powder acts as a support for the printing item, object, or part. | Powder bed fusion is definitely one of the slower 3D printing processes. |
| When metal powders are printed at high temperatures in powder bed fusion, the particles can fuse fully, producing an item, object, or part with high density and low porosity. | The metal feedstock powders are quite expensive. |
| Powder bed fusion is excellent for printing geometrically intricate parts. | There are build size limitations to the items, objects, and parts produced with powder bed fusion. |
| Powder bed fusion with plastic polymers is relatively inexpensive. | The surface finish of the final powder bed fusion build is not always good. |
Powder bed fusion is used to produce functional parts and hollow parts, such as ducting.
6. Sheet Lamination
In sheet lamination, a layer of material is laid on the build platform and cut into the correct shape (as determined by CAD data) with a knife or laser. The next sheet is layered over and fused to the first. This second layer is then also cut into the correct shape.
The sheets can be made of metal, cut with a laser, and fused using ultrasonic welding. This sheet lamination technique is known as ultrasonic additive manufacturing (UAM). Alternatively, the sheets can be made of paper, cut with a knife, and fused using an adhesive. This sheet lamination technique is known as laminated object manufacturing.
| Pros of sheet lamination | Cons of sheet lamination |
| Sheet lamination is a low-temperature and low-energy 3D printing option. | The materials that can be used in sheet lamination are limited. |
| Multiple materials can be used in the same build. | For paper sheet lamination, the strength of the part is dependent on the quality of the adhesive. |
| Sheet lamination 3D printing has a short print time. |
Sheet lamination can be used for a range of visual models and lightweight, functional parts.
7. Vat Polymerization
In vat polymerization, a vat of photosensitive resin polymer is selectively exposed to a light source. The portion of the resin that is exposed to the light becomes hardened or cured.
With each successive layer, the build platform is lowered further into the vat of liquid, allowing the previous layer to be covered with more photopolymer. This next layer is then also selectively exposed to the light source and cured.
The final build is immersed in the excess liquid, which is drained before the part is removed.
Another technique places the light source beneath the vat of photopolymer. The item, object, or part is adhered to the build platform from the first layer, and with each successive layer, the platform is raised, incrementally pulling the in-progress build out of the vat.
Stereolithography printing (SLA) is a particular type of vat polymerization technique. It was the very first 3D printing technique, and it is now the second most common 3D printing technique available to and used by 3D printing hobbyists. SLA uses mirrors on the x- and y-axes to direct the light beam onto the resin.
Digital light processing is a vat polymerization technique that uses flashes of light to fuse each layer all at once. Needless to say, this is technique is much faster than SLA.
| Pros of vat polymerization | Cons of vat polymerization |
| Vat polymerization produces items, objects, and parts with a smooth finish. | Vat polymerization is relatively costly. |
| Vat polymerization is capable of producing detailed parts. | There are limited materials available for use in vat polymerization. |
| The parts need to be subjected to post-processing to ensure durability. |
Vat polymerization is used to create medical models, hearing aids, prototypes, jewelry, and castings.
The Pros And Cons Of 3D Printing When Compared To Traditional Manufacturing
Although 3D printing has not yet wholly replaced traditional manufacturing, its benefits are generating significant interest and research, but as with every technology, there are also certain disadvantages attached to 3D printing.
Pros Of 3D Printing
Increased capability of geometrically intricate designs. In traditional manufacturing, the complexity of design is limited by what can be cut out or removed. With 3D printing, the item, object, or part is being built up, layer upon layer, thus adding detail to the design is much easier.
Increased customization potential. Ease of design means that customization is more accessible. Customization in traditional manufacturing would involve, for example, the production of new molds and machine reprogramming, whereas 3D printing simply requires a digital adjustment to a CAD file.
Furthermore, the increased complexity and customization do not come with a like increase in cost. In traditional manufacturing, customization has to be done during production. With 3D printing, it is done beforehand using CAD, which lowers the cost of creating unique pieces.
Minimized waste production. 3D printing typically only utilizes the amount of material required to build the item, object, or part and the supports. Furthermore, the left-over feedstock can often be reused. In this way, 3D printing produces less waste than traditional, subtractive manufacturing techniques.
Cons Of 3D Printing
The overall cost of 3D printing is higher than that of traditional manufacturing. The cost is mainly in the printing machines and the raw materials
The build size is limited to the size of the printer’s build chamber.
Currently, 3D printing is unsuitable for the mass production of items, objects, and parts.
3D printing is relatively new. As such, there is still much work to be done with regard to the standardization of materials and procedures.
Additional research is needed in order to understand the full extent of the health and safety risks associated with 3D printing.
The introduction of 3D printing introduces the potential for copyright infringement as people can counterfeit patented parts, items, and objects much more easily than before.
Applications For 3D Printing
The customizable, geometrically intricate, lightweight, and durable properties that 3D printing can achieve in the printed item, object, or part makes it an ideal technology for industries such as the aerospace, automotive, and biomedical fields.
Certain 3D printing materials such as titanium alloys and stainless steel have the further advantage of being biocompatible. This means that they can be used to print customized and fully functional internal implants for dentistry and joint replacement.
Yet another medical application is the production of customized and fully functional prostheses.
The original name for 3D printing was rapid prototyping because it was used to improve the prototyping technique in product design. 3D printing is still being used in a number of fields to produce prototypes and models.
3D printing may not be able to match its conventional subtractive counterpart for mass manufacturing, but it is a viable option for small-scale intricate and customized manufacturing.
3D printing techniques are also used in art and jewelry-making.
One branch of 3D printing is hobbyist printing. 3D printers for your home are accessible and not as costly as you might imagine. The materials (mostly FDM thermoplastic filaments and SLA resins) are available in many physical stores as well as on Amazon. Then getting a printing file is also easy because of the hobbyist communities on sites like Thingiverse and My Mini Factory.
Conclusion
3D printing technology is growing in popularity and potential application. Already, it is used in many industrial and research fields, including the aerospace, biomedicine, and automotive fields, as well as prototyping, models, and castings. There is also a branch of hobbyist 3D printing, which uses desktop 3D printers.
3D printing is the process of building an item, object, or part layer by layer, as per the specifications of CAD data. The successive layers are fused together using heat, light, or chemical bonding agents.
3D printing has multiple applications thanks to the range of materials that can be used, including thermoplastics, other plastic polymers, resins, metal alloys, ceramics, and hybrid or composite materials.
Furthermore, there are seven different 3D printing processes, each of which has one or more different techniques. The seven 3D printing processes are binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, and VAT polymerization.
The overall cost, limited build size, unsuitability for mass production, lack of standardization and health research, and the potential for copyright infringement are some of the major drawbacks of 3D printing.
However, the advantages, such as geometric intricacy, customizability, and reduced waste, show that this form of manufacturing has great potential and should be researched further.