Best 3D Printing Technology: SLA Vs SLS

At Sculpteo we’re often asked: what is the difference between SLA technology and SLS tech? Today we’d like to share with you the similarities and differences of the 3D Printing technologies and materials, so as to assist you determine what technology you require to your 3D printing endeavor. Knowing not just what they mean but also exactly what you get out of them is even harder and that’s why we would like to offer you a fast but thorough comparison of two of the principal technologies on the industry right now. Following this read, you will learn just why and when you want to use SLS or SLA technologies to your next 3D printed endeavor.
Intro: SLA and SLS technology

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The acronym SLS stands for Selective Laser Sintering that is precisely what goes on at the center of this type of 3D printers. The keyword here is Sintering which is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the stage of liquefaction.
Inside these SLS 3D printers, a thin layer of material powder is applied on top of the surface, all of this, inside a hot chamber with the warmth just under the material’s sintering point. Immediately after that, a powerful laser beam”draws” a 2D segment of the item on that surface, raising the temperature above the sintering temperature onto a tiny area (where it is concentrated ) and hence sintering the powder particles together.
Next, a new layer is deposited on top of the initial one and the process repeats itself until the last 2D section of this object is produced. This SLS procedure is a layer by coating technique. The last step is just uncovering the solid object that’s now buried inside the unsintered powder, clean it and it’s ready to go.

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On the other hand, SLA or SL stands electronics for Stereolithography also it was the first additive manufacturing technology to be theorized and patented back in the 80s. Today we’ve got many slight variations of this initial concept but the main idea remains the same: a near-UV laser beam is focused on a thin layer of liquid photopolymer resin and immediately draws a 2D section of the desired object (equivalently to some other 3D printing technology). The photosensitive resin reacts invisibly and thus forming a single 2D layer of the item thanks to UV light. Applying a fresh layer of resin on top and iterating the procedure for every section of the object results in the complete 3D printed object. The last step is cleansing the last object that’s soaked in liquid resin and much more often than not- removing support structures.
Resolution of these additive manufacturing techniques

Though there is not any intrinsic resolution ascertained for each of these technologies, you will find actual physical constraints that result in each kind of printer that provides a resolution in a particular selection. Both systems use motorized platforms that will need to be able to solve the desired resolution, which is usually not a big technical issue. Leaving that aside, both systems also use focused laser beams to solidify the building material but since they use very different wavelengths (ultraviolet for SLA and infrared for SLS), their focus size could be also very distinct, with the UV focus area being significantly smaller than for an Infrared laser (or IR laser). Having a smaller focus is similar to drawing a shaper pen, you are able to solve more than using a blunt pencil and therefore SLA printers usually achieve higher resolutions both vertically and horizontally!
Note: Keep in mind we are still talking from tens of thousands to a few hundred microns! SLS technology can totally help you create very detailed versions.
Different mechanical properties for SLA and SLS technologies
Another significant difference between items printed with SLS and SLA printers is how they act mechanically. As we mentioned on Resolution, here we can only generalize and describe the most commonly used materials for every tech.
SLS printers may utilize a wide range of substances, constantly powdered materials, but most often they are polyamides (typically, Nylon PA12) which can have additives to alter properties like colour, strength, flexibility, vibration etc.. You may think you don’t know this material but definitely its name will ring a bell: it is just Nylon, an excellent all-rounder that features durability, strength and outstanding abrasion resistance among other characteristics.

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For SLA printers, the manufacturer provides their own resins however there’s a wide selection of third-party options available that are generally more affordable. Broadly speaking, they are usually more rigid and thus fragile compared to Nylon although new substances are being introduced all of the time, with thicker and more flexible features, quite similar to rubber material.
One important difference of resin objects compared to Nylon is that their behaviour under load. Rigid resins have a tendency to fail violently crashing in multiple pieces while Nylon has a broad elastic area under load (where could still return to its initial form ) accompanied by permanent deformation and finally failure. The selection between SLS vs SLA 3D printing will totally depend on the nature of your project
Here it comes one of the most obvious differences in first sight. Using an SLS printer, the sintering process intrinsically creates a porous solid material, as the air that was initially within the powder goes to create microscopic air bubbles onto the sintered material. On the other hand, polymerizing a liquid material creates a solid homogeneous majority of substance.
PreForm Support made by Formlabs to minimize its impact on the printing.
Colorwise, polyamide powder is offering basic option: black and white, for raw material options. A third option could be grey by mixing those two, but you could state that the deal is rather restricted, with no option for translucent or transparent SLS prints. Resins printed using SLA machines allow for different options, while mixed with colour pigments.
Supports through the 3D printing process
For objects that do not have a clear standing position (e.g. a ball) or they are doing but they’ve overhangs (e.g. the color of a desk lamp) support material or structures are needed for almost all 3D printing technologies, together with SLS printers being one of the few exceptions, as a result of the unsintered powder behaving as service material all over the item being printed during SLS process.