Rapid Prototyping – SLA vs. DLP

Rapid prototyping is the process of going through the CAD processes to create something realistic on a smaller scale within a budget and timeframe. Hence the term. The prototypes can either be in regards to the scale, by creating something 1/10th of the actual product for visual inspection purposes, or it can be in regards to structure, for example, a replica that is hollow on the inside, lacking functionality but complete on the outside again for visual and physical inspection. The whole process revolves around being able to save money and time in pre-development phase and can offer new insight into a product and it’s subsequent strategy.

Today, we talk about the most important things we need to consider when we practice rapid prototyping. In specific, we will see how you can create such prototypes for the later printing purposes using SLA or DLP printers. Read on for more.


Charles Hull

Rapid PrototypingBefore the advent of additive manufacturing (manufacturing by adding material to develop a product), the industry used what is known as subtractive manufacturing (carving the finished product out of a block of material). Mr. Charles Hull was the first to create the STL filing format that allowed computers to aid with the process of manufacturing. Both SLA and DLP are light-based printing techniques. He is also the first person to have used the term “Rapid Prototyping”.

Stereolithography – SLA

This process involves the use of a laser that is guided over a pool of resin. The resin, being a photosensitive polymer solidifies where the laser touches, and the continued pointing of the laser quite literally solidifies the liquid resin creating a solid object out of liquid. For this purpose, this technique can be pretty fast in printing although printing sizes are limited because of the fact that this technique is mostly used for personal printers. Commercial printers use SLA lesser because of the single laser nature printing as well as the printing costs. Because of the SLA technique, the laser precision ensures detailed prints and finer imprints when printing smaller parts. That is why for rapid prototyping, SLA is the preferred technique in the industry.

Rapid Prototyping for SLA

Rapid Prototyping SLAWhen prototyping, the model will probably be smaller or hollow, or even both. For that purpose, the added scaffolding can be quite an issue. Many software packages will handle this for you but the final output needs to be checked as the automated scaffolding will be according to a set of criteria, you can’t alter. Creating that scaffolding yourself will be the best way to go forward. On top of that, if the prototype is smaller than the original, then it may have enough sturdiness to withstand some shock. Hollow models, in particular those that are taller or lengthier will provide issues when trying to clean them up. Getting the rest of the polymer to dry off is not always a good idea, cleaning it may help.

Lastly, creating water-tight models is another great way to ensure that your prototype is appropriate for physical inspection. In the case, you believe that your model may get printed in a manner that may trap resin inside, holes should not be created below (as with FDM – Fused Disposition Modelling) but instead the top assembly or part should be made to be removable. The sealed off enclosure will surely be more supportive.

Digital Light Processing – DLP

Rapid Prototyping DLPAnother way to use light as a means of manufacturing in the DLP technique. This basically uses a projector to project an entire cross section of the model as opposed to the point to point movement of the laser. The whole cross-section gets printed in the resin and hardens it layer by layer. This technique offers its own advantages, such as exquisite surface finishes and faster printing times than non-light methods. DLP is essentially used for printing and not for rapid prototyping unless a great level of detail is required. A variation is CLIP (Continuous Liquid Interface Production) where the model is “pulled” from the pool of resin, a sort-of up-side-down version of DLP. This makes the process eliminate the layered methodology and creates an uninterrupted process.

Rapid Prototyping for DLP (and CLIP)

For CLIP, scaffolding doesn’t much matter. For DLP, the scaffolding is just as important as is for SLA. The resin, however, being of completely different composition needs to cleared off, mostly with a chemical bath. Since the process will be for prototyping the best time to use this is when you need real-model like details and resolutions of prints. This is very comfortably covered with the way the LP projector works hence this technique should be used only when needed for rapid prototyping purposes.


Conclusion

With over 7 different type of additive manufacturing techniques, this comparison is only the tip of the iceberg. With sintering or multi jet molding, we have other problems to worry about. In the case you have the option, sintering won’t give you much choice of resolution unless you have industrial grade printers. Molding of all sorts will be slow, turtle slow compared to the light based techniques. Hence whether it is prototyping or the actual production of the finished product, your choice of technique will definitely be limited by the available 3D printing technology you have available.