3D printing is perceived as a very inexpensive and fast manufacturing method. Why is that? After all, producing a single unit of a product is often more expensive and time-consuming compared to other technologies. In this article, I will try to explain this phenomenon. I will also outline why and when additive manufacturing technologies are competitive with other production methods.
A Few Words About Additive Technologies
These methods, also referred to as additive processes, involve depositing successive layers of material. The most popular of them is FDM technology, which is based on layer-by-layer material deposition. The material is extruded through a nozzle heated to the appropriate temperature. It is the only method used in the production of large-scale components. Next are technologies based on the layer-by-layer curing of liquid material (SLA, DLP, and PolyJet technologies). They provide the best surface smoothness and the highest level of detail reproduction; however, 3d printing large parts is problematic with these methods. There is also selective powder sintering technology (SLS and MJF), which involves bonding finely ground polyamide powder using a laser beam or thermal energy.
It should be remembered that none of the above methods is universal. It is worth carefully selecting the technology for a given application in order to avoid generating unnecessary costs.
3D Printing vs Injection Molding
The most common comparison for 3D printing technology is injection molding. The fundamental difference lies in the strength of the prints, which is approximately 30% of the mechanical strength of a part made from the same material using injection molding. The main advantage is the lack of need for production preparation—specifically, the manufacture of an expensive steel injection mold. Aside from the much longer time required to produce a part, even the raw material used for printing is more costly. A simple example is filament used in FDM technology. It is a material in the form of a spool of wire with a precisely controlled diameter, and it is on average 20 to 100 times more expensive than the raw material used in the injection molding process.
This does not change the fact that producing an injection mold for a small production series is not economically justified. The situation is even worse when a mold is made to produce a single part. Regardless of the size of the component, it will certainly be a solution many times more expensive than additive manufacturing or machining. In summary, 3D printing is an alternative to injection molding for small and medium production volumes. The greatest savings in the case of series production can be seen with small-sized components.
3D Printing or CNC Machining?
Other technologies that 3D printing is compared with are subtractive manufacturing methods—mainly milling, electrical discharge machining, and turning. In conventional machining, also referred to as subtractive machining, parts are produced by removing material. The material is cut away using a tool until the desired geometry is achieved.
Subtractive technologies often require the use of specialized tooling, especially for more complex geometries. They also demand carefully planned material fixturing and precise positioning of the tool relative to the workpiece. These limitations of conventional methods contribute to higher initial costs. For this reason, 3D printing of plastic components is often a much more cost-effective solution.
Even greater cost differences arise when a part has a complex geometry. Especially if it requires the use of machines with more than three axes. The best example is holes oriented along axes perpendicular to each other. In three-axis machining, the tool is always in the same position. Subtractive manufacturing technologies also do not allow for the production of internal structures (e.g., channels) that can be manufactured using additive technologies.
In summary, 3D printing can be an alternative to CNC milling. However, much depends on the production volume, geometry, and the required dimensional accuracy.
Accuracies below 0.1 mm are still reserved for subtractive machining.
When Is 3D Printing Not Worth Using?
3D printing is certainly not cost-effective for flat components. Flat components are those that can be fully defined by their outline shape and thickness. A much cheaper manufacturing method in such cases is cutting, usually waterjet cutting or laser cutting. These technologies, in their common forms, allow for the production of 2D parts. They are not a direct competition to additive manufacturing technologies; however, they should not be overlooked.
These are very fast manufacturing methods, with lead times and costs that are not comparable to additive technologies. Producing flat parts using 3D printing is not economically justified. Generally speaking, 3D printing makes sense when the part would otherwise require the removal of a large amount of material.
