There are new additive manufacturing techniques being developed all the time. Some are best for consumer applications and others for industrial environments, but not all of them are suited for rapid prototyping. Let’s take a look at the top 7 methods for 3D prototyping and their strengths and weaknesses so that you can decide what might be best for your next project.
Stereolithography was the first successful commercial 3D printing method. A bath of photosensitive liquid is solidified one layer at a time using a UV light controlled by a computer. These layers are derived from two-dimensional cross sections of the 3D CAD model and controlled with a software file format called .stl.
This is noteworthy because, being the first, .stl has become the default computer language used by most modern 3D printers, regardless of the printing technology employed.
Stereolithography is best for prototypes and to make master patterns for vacuum casting. SLA is fast and inexpensive and the finished product is strong with a good surface finish. Supports may or may not be needed depending on the machine.
Selective Laser Sintering (SLS)
This is a form of powder bed fusion. Parts are formed on a build plate one layer at a time, using a laser to sinter the powder media. Because the support is surrounded on all sides be the powder medium, it is self-supporting and additional structures are not needed.
SLS can work for either plastic or metal prototypes. Like many other 3D printing processes, the great advantage here is that parts can be made with complex geometries like internal lattice structures that would be difficult or impossible to do any other way.
However, the surface finish is usually rough and may require secondary work to complete it, especially if it’s used as a master pattern for later casting. The strength is also not as good as SLA printed parts.
Fused Deposition Modeling (FDM)
This is the kind of 3D plastic printing often found in desktop machines in a home or small shop. It uses a spool of plastic filament that is melted inside the barrel of a printing nozzle. This hot liquid resin is then laid down layer-by-layer, again controlled by an .stl cutting program.
FDM printing is inexpensive, easy-to-use, and can accomodate different types and colors of plastic combined in a single build. It’s also safe enough that even children can use it in a classroom. FDM printed parts have poor resolution and finish quality compared to industrial techniques, and the parts are not very strong. However it can be ideal for making prototypes and models during the development stage.
Selective Laser Melting (SLM)
Another form of powder bed fusion, SLM is an industrial process that requires carefully controlled conditions. Very fine metal powder of a uniform size and shape is fully welded onto a build plate using a high-powered laser inside of a sealed chamber. Common metal powders may include titanium, stainless steel, maraging steel and cobalt chrome.
SLM is the preferred technique for making sophisticated parts of the highest strength, durability and complexity and this is what we use at Star Rapid for our DMLM service.
The process can be expensive and must be controlled by a skilled engineer, but the results are ideal for the most demanding applications in aerospace, automotive, defense and medical parts.
Laminated Object Manufacturing
Here a series of thin laminates are laid out on a build platform. The laminates can be paper, plastic sheet or metal foil. With each layer, a computer controlled laser or other cutting device traces out the pattern. The platform then drops by the thickness of one layer, a new laminate is glued on top and the process continues.
This stacking process makes a finished part which is less sophisticated than a SLS or SLM equivalent, but it is cheaper and does not require specially controlled working conditions. Also, if paper is used as the laminate the finished part will be similar to solid wood and can be worked accordingly.
Digital Light Processing
Another variation on the polymerization of a curable resin, this process is very similar to SLA printing. It cures the resin with a more conventional light source, but it also requires support structures and post-build curing.
The process is generally faster and a more shallow reservoir of photoresin can be used which also saves on cost. Like with SLA, the finished part has excellent dimensional tolerances and surface finish.
An interesting variation of this process is called CLIP (Continuous Liquid Interface Production). Here the part is pulled from the vat in a continuous motion – there are no layers, it is an uninterrupted process. As the part is withdrawn it crosses a light barrier that is programmed to alter its configuration to produce the requisite cross-sectional pattern on the plastic.
A relatively new 3D process, this has the potential to be a true high-volume mass production technique. Over a horizontal print bed covered in metal powder, hundreds of nozzles spray micro-fine droplets of a liquid binder to form a single layer. This layer is then compacted with a roller, re-coated with powder, and then sprayed for the next layer.
When semi-finished parts are removed from the build chamber, they must still be cured in an oven to burn off the binding resin and fuse the metal powder together into a solid.
The advantage here is that many parts can be printed at one time, and the full volume of the chamber used. Such parts are not as strong as fully-welded SLS parts but they can work as mechanical fittings. This technology is still under development but it may be up to 100x more cost-effective than previous techniques.
Which one is right for you?
Each of these 3D printing techniques has trade-offs in terms of speed, cost, strength and available materials. Want to know more? Contact us today for a free quote and our technical specialists can give advice based on your schedule, design and budget.