I have chosen to combine these two technologies into one article today since the principles are very similar with how the objects get created.
The only major difference is the projection method, but more on that as we get into it later.
Stereolithography known as SLA is the oldest printing technology and is the first method developed for AM by Charles Hull in 1986 when he patented the technology. He later was one of the co-founders of 3D Systems. Inc.     He designed a machine called a stereograph to convert liquid plastic resins into solid objects using ultraviolet lasers.
Now Digital Light Processing or rather DLP was created and patented just one year later in 1987 by Larry Hornbeck of Texas Instruments. What he did differently is that he did not use Ultraviolet lasers but rather use a series digital micro mirrors laid out on a semiconductor chip. The technology is applicable for movie projectors, cell phones and 3D printing, this is what is now days used in almost all Displays and projectors.
Both process start off the same as all the other processes we have already covered, with a 3D CAD File that has been converted to a .stl file and “sliced” according to the layer thickness required. That is where this technology holds its own, I mean if it’s the oldest 3D printing technology surely it is outdated and is no longer practical? That would be wrong, yes it is the oldest technology but there are still very few other technologies that can even come close to the print quality and layer resolution that these printers can achieve.
The reason will become evident as soon as I start explaining the process to you.
Both these technologies use a photopolymer as a source material to build the objects from, in SLA each layer gets scanned over by the Laser until the material of that layer has hardened, where with DLP the entire layer gets projected at once until it has hardened. The build platform with part on, then moves out of the way to allow new unhardened resin to flow in place then the build platform returns to start curing the next layer on the previous one.
With both these technologies you can achieve a much smaller layer thickness and the surface finish is amazing.
After the printing has completed the parts get removed from the build platform and are rinsed in a solvent and then placed in an ultraviolet oven to finish the hardening process. The fact that you are using a Liquid resin as a base material and it is allowed to ‘Flow” you get the unmatched surface finish.
Please feel free to leave any comments and questions below.

In the 1980s this techniques was developed by Joe Beaman and one of his students Carl Deckard from the University of Texas.
What lets SLS stand out from some of the other 3D printing techniques like Stereolithography and FDM is the fact that with SLS there is no need to use Support structures on overhangs since with SLS the “Un-sintered” material serves as its support.
In same way as all other Printing methods the process starts with the 3D CAD Model that needs to be designed on a computer CAD Program and then converted to a .stl format for printing.
Some of the materials that one could print with using this technology include the following, Nylon (the most common), some ceramics and even steels and Aluminium’s.
The drawback of this technology is the fact that it is considerably more expensive than FDM and as a result of this it is more often found in larger companies and not so much amongst Enthusiasts and Hobbyists, It is however starting to become more and more accessible as more and more 3D Printing bureaus start coming into the marketplace.
It is very often used for Prototyping and Product development, and I have even seen a strong growth in low volume production runs where the quantities are too low for other methods but to high to justify the costs of an Injection moulding tool.
Next time we will have a closer look at SLA and DPL together since these two are so different but are so closely used.