Unlike machining – which consists of starting from a block of raw material and removing material until the desired part or shape is obtained, 3D printing will start from scratch and add material per layer until you obtain the desired object, without going through a mold or other process beforehand.
Below are seven major families of additive manufacturing processes, each with distinct characteristics.
This process consists of depositing material (in the liquid or semi-liquid state) via a nozzle. The material will convert to a solid state once deposited. We build an object by superimposing several layers of solidified lines.
This process is the most widespread. This is because it is relatively safe even in an office environment, and the raw material is inexpensive and varied; allowing us to print large objects having good mechanical properties. On the other hand, the process remains one of the slowest, with a rough surface finish and below average tolerances.
This makes hardware extrusion an ideal candidate for hobbyists, schools such as FabLabs, and also companies that want to use it for prototyping, mock-ups or tooling at low cost.
This process combines Stereolithography (SLA), Digital Light Processing (DLP) and Continuous Liquid Interface Production (CLIP). The principle is to use a resin contained in a basin, and a light source to solidify the resin.
This process is the second most common. The process uses extrusion, can be used in an office environment, and is relatively affordable. Using light over an entire surface ensures excellent accuracy, a smooth surface finish with tight tolerances, lower time spent in post-processing, and a reduction in print time. However, the raw material is highly toxic and the size of a given object is quite limited – hence, it is vital to follow safety protocol while using this technology. In addition, post-processing operations must be performed to prevent the part from being degraded.
Light curing is, therefore, a prime candidate in the dental industry, for art objects (jewelry, figurines, etc.) or for prototypes or replacement parts that require a high level of precision.
Powder bed fusion
This process starts with a powder bath, which will be melted selectively using a beam of energy such as laser or electron.
The process makes it possible to obtain very high precision parts, both metal, and plastic, with good tolerance and with excellent mechanical properties, but at a high cost. The powder used in this process must be very fine, and the particles must be similar in shape and size, making the raw material and the printer itself very expensive. Titanium powder can sell for $ 800 per kg, for example. Powder also poses a risk to human health and parts must be carefully cleaned before they can be used.
Powder bath melting, however, remains the most mature process for metal. This makes it the process of choice for the aeronautical or medical sectors, which can afford to have expensive parts.
This process uses two materials: a powder bath and a binder. A thin layer of powder is deposited in a layer and selectively bonded by a binder jet (similar to an inkjet printer). The binder may be heated in some cases to improve adhesion or baked in a post-treatment phase.
This process is one of the fastest and allows to obtain parts with good tolerances and good mechanical properties. The finish, however, remains rough and post-treatment may be required some cases.
The principle of these printers is the same as that of inkjet printers. The difference is that we will selectively project a jet of resin (or other manufacturing equipment) that will potentially immediately solidify through light for example.
The jet of material makes it possible to obtain objects with a good finish and good tolerances. This also makes it easy to vary the colors or even the materials within the same object. However, printers are expensive and resins can pose a risk to human health.
Directed Energy Deposition
This process is like welding. The raw material is deposited in the solid state and a beam of energy (laser, electron) is used to melt it as it is deposited. This process makes it possible, among other things, to repair metal objects (eg turbine blades).
The process makes it possible to manufacture or repair very large format metal objects. However, the machines are very expensive and not as widely available as powder bath melting.
This process consists of superimposing sheets and joining them together (by ultrasound in the case of metal or binding in the case of cardboard or plastic). As soon as a sheet is linked, it is cut out to represent the 3D shape. We end up forming an object in 3D by superimposing these sheets on each other.
This process, however, is fairly new and not as widely used as some of the other 3D printing options.
Each process comes with its peculiarities, strengths, weaknesses. In addition, each printer that uses the same process can have variability in tolerance, volume, speed, and cost depending on the application.
The following table summarizes the characteristics of some commercially available printers:
* The cost of the golf ball is the cost of a quote to a professional printing service to print a golf ball with the given printer.
The price, therefore, reflects the cost of the raw material, the cost of labor and post-processing and the depreciation of the printer as well as the profit margin for the service.
All submissions were made with 316L stainless steel in the case of metal, nylon for plastics (enriched with carbon fiber in the case of Markforged ©) and polyurethane for resins.
By dissociating itself from the constraints of tools or demolding, it becomes possible to manufacture virtually any object with 3D printing. This is one of the greatest strengths of the process. 3D manufacturing is recognized for its ability to produce low-cost objects, tailor-made, locally, on demand and without human interaction.
The process also comes with its weaknesses. Although the implementation time is almost zero, the actual manufacturing remains long. It may also be expected that the post-processing would be as long or even longer than the impression itself.
Moreover, since 3D printing is still relatively new, it can be difficult to find qualified people to operate printers or design parts that take advantage of the benefits of this technology. This trend is bound to change, as we see that many countries are starting to integrate 3D printing into their academic curriculum.
The process does not offer any quantity gains: the time and price will be the same per object, whether it is one or ten miles. The available materials are also a constraint: not all materials can be printed in 3D, and the price is sometimes significantly high, especially for metals. Finally, it is sometimes difficult to characterize the mechanical properties of printed objects.
3D printing is not, by any means, meant to replace all other manufacturing processes. It is, instead, a new tool accessible to the factories that meet certain specific needs. Like any tool, you need to know when to use it and when another tool is better suited to a particular need. If used well, additive manufacturing can provide benefits in terms of cost reduction, time reduction or quality improvement.
Also published on Medium.