SLS vs. SLA and Their Differences

SLS (selective laser sintering) is a 3D printing technique that uses a laser to fuse together small particles of plastic, metal, glass, or ceramic powder into a solid object. SLA (stereolithography) uses an ultraviolet (UV) laser to cure (harden) photosensitive resin into the desired shape. Both technologies employ a laser as part of their build process, but they differ in terms of build speed, precision, price, and processing. A full understanding of the choice between SLS vs. SLA requires more background information. 

A major advantage SLS has over SLA is in the time it takes to manufacture a part. It has a shorter lead time. Therefore, more such parts can be produced per day. However, if precision details are important, SLS becomes the best choice because it produces parts with tighter tolerances.

In this article, we will compare and contrast these two types of 3D printers. We will also take a cursory look at other alternatives that can serve as replacements for either one of them.

SLS was created in the 1980s at the University of Texas in Austin by Dr. Carl Deckard and Dr. Joe Beaman. SLS is a 3D printing technology that uses a powerful laser to selectively fuse layers of powdered particles. Most such machines use nylon-based or polymer-based build materials, though more advanced versions have been created to fuse materials with higher melting temperatures. 

Each print begins with a digital version of the part, built into a computer. The SLS machine turns that into a physical object by tracing out the geometry of each successive 2D slice of the object, fusing powder at the necessary points. After one layer is finished, another fine layer of powder is applied and the process repeats. SLS produces parts with good mechanical properties making them suitable for end-users. This is not the case for SLA, the products of which are not as tough as those of SLS. The diagram below shows how an SLS printer works:

To learn more, see our article on What is SLS.

The Advantages and Disadvantages of SLS Compared to SLA

There are advantages to using SLS vs. SLA. Some are listed below: 

1. SLS parts need no support structures during production while SLA parts do. The surrounding powder serves to support overhanging components during the building process. SLA parts need to be designed with supporting structures or built in such a way that makes the parts self-supporting.
2. The SLS production process is faster than SLA. That makes it handy for rapid prototyping activities.
3. The parts produced via SLS are tougher than those of SLA, so they’re more often used as functional parts.

Though SLS is very capable, it still has its disadvantages. These include:

1. SLS machines are more expensive than SLA machines.
2. The SLS laser demands a lot of electricity. This means the print needs to be completely enclosed and shielded. The laser beam in SLA uses less power; users can view the print while it is enclosed behind plastic or tinted glass. 
3. SLS machines are bulkier. They typically fill an entire laboratory workbench. In contrast, SLA machines are often designed as desktop devices.

The Advantages and Disadvantages of SLA Compared to SLS

SLA’s advantages compared to SLS are:

1. SLA systems provide greater resolution than their SLS counterparts.
2. SLA produces parts with better surface finishes than SLS. Its parts are comparable to injection-molded parts.
3. SLA machines are less bulky than SLS. For this reason, they can serve as desktop devices.

Listed below are the disadvantages of SLS compared to SLS:

1. SLA cannot print parts as large as those of SLS.
2. The resin in SLA is not environmentally friendly. It produces unpleasant fumes and requires gloves when handled. On the other hand, SLS uses polymer powder such as nylon, which is not particularly harmful except to people with specific allergies. 
3. SLA produces weaker parts compared to SLS. They are best used as proofs of concept or for experimental use.

The polymer resin used in SLA is sensitive to UV light. As such, it should be kept away from sunlight or any other source of light that contains UV radiation. SLS products do not have this shortcoming, and nor do they need supporting structures during manufacturing. The unfused powder particles are sufficient to provide support.

Technology Comparison: The high-powered laser in SLS is completely enclosed, giving operators no view of the print. SLA laser output is significantly lower in power and requires only tinted glass or a plastic enclosure to prevent the UV light from escaping.

Material Comparison: The polymer powder in SLS is easy to handle but users must wear gloves while handling SLA parts. The resin used in the production process is slightly harmful. Some commercially available production materials used in SLS include: polyaryletherketones, thermoplastic elastomers, polystyrenes, and nylon. SLA materials include but are not limited to: epoxy photopolymer, acrylic photopolymer, and some others with polypropylene-like and ABS-like properties.

Product Applications Comparison: SLS produces parts that are tougher than those of SLA. This makes them better options for mechanical or end-use applications.

Print Volume Comparison: Thanks to its size and the sintering time, SLS prints faster than SLA both on large- and small-scale models. In addition to this, SLS requires no supporting structures during the building process.

Cost Comparison: SLS devices are generally more expensive than SLA devices. In both cases, the cost is compounded over time since materials such as resin or powder have to be purchased regularly. SLS machines can be purchased for as little as $10,000 or as much as $650,000. The cost depends on the maximum build volume, minimum layer thickness, print speed, laser type, and the build materials it can accept. SLA machines, on the other hand, usually fall in the range of $3,750 to $5,000, depending on the size. They can be classified into four different types: DIY, advanced hobbyist, professional and performance, and business and industrial.