3D printing is a very capacious definition for a number of technologies that differ from each other in manufacturing processes, the materials that are used, and the type of objects that can be made of them. At the moment, we can distinguish several dozen production methods, which can be described as additive – some of them differ in small technical nuances, others are completely separate manufacturing processes without virtually no common features apart from the name “3D printing”.
In this study, we present the most important additive technologies in the context of their advantages, disadvantages and differences, which we hope will help you understand what 3D printing is, will it be used in the context of your application – and if so, which particular solution should you use?
Let’s start with the basic thing, i.e. the definition of 3D printing:
3D PRINTING – the manufacturing method involving the applying a layer to the layer of some material which is bond selectively. Alternative and equivalent name for 3D printing is additive technology.
Detailed information on 3D printing can be found in the following article:
Types of 3D printing technologies
As mentioned above, as 3D printing we can define at least several dozen different manufacturing techniques. Many manufacturers of 3D printers, when developing a given additive method, often patent its unique part, creating a separate technology from a formal point of view, although, as a rule, it is derived in a straight line from something that has been on the market for several dozen years. For simplicity, we can try to divide them into four main groups by the form in which building material is supplied to the 3D printer of a given type:
- material in the form of a wire
- material in the form of a liquid (light-cured resin)
- powder material
- other (hydrogels and other semi-liquid materials, building or food masses and techniques that have already become obsolete, such as 3D printing from foil or paper).
- FDM – 3D printing with thermoplastic in form of a wire)
- education / home
- amateur / hobby (DIY kits)
- SLA – 3D printing with resins light cured by laser beam
- DLP – 3D printing with resins light cured by DLP projector
- UV LCD – 3D printing with resins light cured by LCD screen (desktop only)
- PolyJet / MJP – 3D printing with resins light cured by UV light (industrial only)
- other photopolymer methods:
- CJP – 3D printing with gypsium powder in full color
- Binder Jetting – 3D printing with sand or metal powder
- SLS – 3D printing with polyamide powder selectively sintered by laser beam
- MJF – 3D printing with polyamide powder selectively glued and welded
- SLM / DMP / DMLS – 3D printing with metal powder selectively melted by laser beam
- EBM – 3D printing with metal powder melted with elctron beam
- LOM – 3D printing with foli or paper
To the “other” category we can include a whole bunch of manufacturing methods, whose creators try to incorporate three-dimensional printing in a rather stretched way. They are e.g.
- bioprinting, derived from bioplotting, i.e. an automated way of applying / instilling biological (or hydrogel) material
- 3D printing with concrete (3D printing of houses), i.e. applying building masses with a technique similar to FDM, which is a de facto automated technique of applying concrete from a pump
- 3D printing of food, where we can apply nutritional masses in a similar way as hydrogels in 3D bioprinting, or building masses thus building objects (unfortunately, so far no one has found any useful application of this method in everyday life).
In this study, we will focus on the most popular, most common and most used 3D printing technologies comparing them to each other and trying to show which is the best from the point of view of a given application.
When to use 3D printing technology?
3D printing is the same manufacturing technology as any other – its goal is to produce things in a certain way, from specific materials. Some applications can be made better on 3D printers than on other types of machines, some will come out worse – we will also find those that cannot be printed or whose 3D printing is economically unjustified. Historically, incremental technologies have been brought to life as an alternative way of making prototypes. The advantage of this method over others was and are primarily:
- short time in model making
- low cost
- the ability to quickly apply changes
- high profitability of creating individual copies and / or low series
- possibility of personalization.
Another advantage is the ability to print very complex geometries that are impossible to do with other manufacturing methods (in particular, techniques using powders).
- 3D printing is the fastest
- 3D printing is the cheapest
- 3D printing has the ability to create the most complex geometries.
- 3D printing has poor surface quality
- 3D printing is inefficient in high volume production (hundreds of thousands – millions of details).
We choose 3D printing technology when we need to produce something relatively quickly, cheaply and in quantities not exceeding several hundred – several thousand pieces, and at the same time we do not care about the quality of the surface such as in injection molding or casting technology.
3D PRINTING TECHNOLOGIES
FDM / FFF: 3D printing from thermoplastics in the form of a wire
One of the most popular and widespread 3D printing technologies. It comes in three dimensions: amateur, desktop and industrial. Although the principle of operation is exactly the same in every case, 3D printers from the amateur sector are not able to print well and accurately from professional-grade materials, which, in turn, do not pose a major challenge for industrial-grade machines (including polyamides, materials reinforced with carbon or glass fiber etc.).
The technology involves creating details by supplying plastic in the form of a line to the print head and warming it to a semi-liquid state. The print head applies material on the work table in XY axes by “drawing” the shape of a single layer. When it finishes, the head either rises up or the work table lowers down by the specified layer height and another layer is applied. Semi-liquid plastic binds under the influence of high temperature and quickly freezes to form a uniform structure. The difference in names (FDM / FFF) is due to the fact that FDM is a registered trade name of the creator of this technology – Stratasys.
FDM / FFF ADVANTAGES:
- the ability to 3D print from a wide spectrum of plastics, including the same materials that are used in injection molding technology; the possibility of 3D printing from composite materials doped, e.g. with carbon or glass fiber
- cheap consumables and operation of 3D printers; easy and quick servicing, which is important in low-volume production
- speed of work – small details with simple geometry are printed in up to several minutes; details of medium sizes, not exceeding a dozen centimeters in XYZ axes are printed within a dozen or so hours, so often during one business day
- post-processing – not counting complicated geometries, where a lot of support structures must be generated, post-processing is simple, and sometimes even on 3D printers you can immediately produce a ready-to-use detail.
FDM / FFF DISADVANTAGES:
- not very high accuracy compared to other manufacturing methods – the height of the printed layer in FDM / FFF technology is standard 0.1 – 0.3 mm (of course you can try to print on a lower or much higher layer depending on your needs); the standard diameter of the print head is 0.4 mm (i.e. the hole from which semi-liquid plastic is extruded);
- material shrinkage problems
- post-processing of complex geometries – some geometries will require the generation of such complex internal support structures that their removal after printing will be either very complicated or impossible.
SLA / UV LCD: 3D printing from light-cured resins
SLA (stereolithography) is a technique of creating details from light-cured resins, hardened by irradiation with a laser beam. The container is filled with resin in which the work table is immersed. It is lowered to the height of the given layer (e.g. 0.05 mm from the bottom of the container), after which the laser beam “draws” the shape of the object in the XY plane, hardening the resin. The resin adheres to the surface of the work table, after which it is raised to the height of the next layer and the process is repeated – this time the new layer adheres to the previously hardened one.
UV LCD is a production process similar to SLA, except that the resin is not cured with a laser beam, but with the light emitted by the LCD screen with UV backlight mounted under the resin container. The advantage of this method is that the entire layer is exposed (cured) simultaneously. The disadvantage is that when curing large surfaces (with a length / width greater than a dozen centimeters), there is a large shrinkage of the resin cured at the same time. The alternative to this method is DLP, where the resin is cured with light emitted by the projector.
SLA / UV LCD ADVANTAGES:
- high precision of 3D printed models – the ability to create details with a layer at 0.025 mm; this guarantees the surface smoothness closest to injection molding or molding
- easy removal of support structures – not counting very complicated geometries, supports made of resin are easily removed, which are created in a completely different way than e.g. in FDM / FFF
- works great in low-volume production of small and very precise details
- the possibility of using biocompatible resins – 3D prints made from such resins can be used in prosthetics and even during surgical operations and have contact with the patient’s tissue.
SLA / UV LCD DISADVANTAGES:
- due to the fact that more precise models are printed, their production time is longer than in the case of FDM / FFF
- while it works great in the production of small objects, large details are problematic, and their correct printing much more expensive than in the case of FDM / FFF
- high price of consumables – ordinary building resins are about 2-3 times more expensive than the thermoplastics used in FDM / FFF and have weaker physical and temperature resistance; the use of more durable resins is much more expensive
- the need for chemical post-processing – the 3D printing process with resins is “dirty” – the prints are immediately removed from the work table covered with a layer of uncured resin, which should be rinsed; this extends production time and increases costs.
MJF: 3D printing from powdered polyamides
Technology developed in the 21st century by the HP group. It consists of scattering a layer of powdered polyamide PA12 (or flexible TPU) on the work table and selective spraying of the binder that bonds individual layers of the detail. At the same time, the material is welded with heat emitted by the lamps, creating a perfectly durable structure of any geometry. After finishing the work, the detail should be extracted from the unsaturated powder and cleaned – this is done in a dedicated, automated post-processing station.
In MJF technology (as in SLS) it is not necessary to use support structures, because their form is fulfilled by unsolidified powder. This enables details to be printed with geometries that cannot be achieved using other traditional manufacturing techniques. Another advantage of the MJF system is high production efficiency – HP 3D printers are adapted to the production of low production series and are in this respect incomparably more efficient than 3D printers working in FDM / FFF technology as well as SLA and UV LCD.
Another important feature of MJF technology is the possibility of 3D printing of details in full color using PA12 plastic.
- the ability to 3D print objects from very durable and resilient or flexible materials
- the ability to 3D print objects with complex geometries – due to the fact that it is a powder technology, powder that is not sintered creates a natural support structure, which after printing is easily removed (although there are situations where the supports are still advisable)
- much higher precision and accuracy than in FDM / FFF technology
technology dedicated to mass production (possibility of stacking printouts)
- the ability to print details of a final nature
- possibility of using full color.
- to the production time you should add the second amount for post-processing (e.g. 1 day of 3D printing = 1 day for processing details)
- full color prints are very expensive; the default color of the details is graphite
- the specificity of the technological process makes the technology cost-effective primarily for lower production series or large facilities with complex geometry; small and simple things are more profitable to print in other additive techniques.
DMP: metal 3D printing
3D printing from metal is one of the most desirable and also the most difficult to use additive technologies. It consists in even distribution of successive layers of powdered metal alloys and their selective melting by means of a laser beam. 3D metal printers are industrial grade machines, using, among others protective gas atmosphere. Many popular metal alloys, including stainless steel, titanium or aluminum, can be used at work.
DMP (direct metal printing) technology is the original additive method of 3D Systems. At the same time, there are many varieties on the market that, in principle, work and rely on the same, but differ in technological nuances – and hence the name. Techniques called SLM (selective laser melting), DMLS (direct metal laser sintering) and others describe the same manufacturing process.
- the ability to 3D print details from metal alloys
- the ability to 3D print objects with complex geometries
- the ability to 3D print very precise details with 0.2 mm thick walls (or lower – depends on the model)
- technology dedicated to mass production
- possibility of 3D printing final details for aviation, automotive etc.
- the ability to 3D print medical implants (titanium).
- high costs (expensive machines + expensive materials + expensive operation)
- complicated and thus long post-processing
- very complicated preparation of models for 3D printing.
Which technology should you choose?
Each of the above incremental methods has a number of advantages and disadvantages. To choose the right one we need to know the specifics and expectations of the created application. The factors we consider in comparison are:
- accuracy of mapping details and dimensions
- degree of complexity of geometry
- resistance to mechanical factors (impacts, abrasion, compression and stretching)
- temperature resistance
- chemical resistance
- number of details produced vs. time of production
- production cost.
FDM / FFF technology will be used where large 3D prints are involved and the low price is important. It works well in low-volume production. Depending on the material used, prints can be either very durable (PC, PCABS, PA6) or cheap (PLA). This is not the best method when it comes to high quality surface details or the print geometry will be extremely complicated.
SLA technology is excellent in applications where surface quality and precision of 3D prints are important. Unfortunately, it is not very effective in low-volume production and is definitely dedicated to the production of individual parts.
UV LCD technology is slightly inferior to SLA in terms of accuracy and the differences in this area are really small. It is better for low-series production of small components, because in this respect it is much faster than SLA. Prints will also be slightly cheaper. In principle, however, UV LCD and SLA are very similar manufacturing methods, differing in small nuances.
MJF technology is perfect for practically any type of application, and its only disadvantage may be the price in the production of unit elements with simple geometry, where the advantage of FDM / FFF will be significant. It is an ideal manufacturing method for the rapid implementation of production series of several dozen / several hundred / and even several thousand pieces of detail. The low quality rating is quite unfair here, because in fact the quality of the prints is many times higher than that offered by FDM / FFF.
DMP technology has one key advantage over all others, and it is possible to print metal details. This type of material determines all other comparative factors. One thing to consider is price – 3D printing from metals is expensive.