What is SLS Printing? | The Ultimate Guide

3D printing is a rapidly evolving method that is making strides in the mainstream plastic scene, and SLS printing is the flagbearer of this change. I’m sharing a highly researched and detailed article on the topic to empower you to make better choices with your prototyping and manufacturing needs.

What is SLS Printing?

SLS printing is one of the most popular and widely used 3D printing methods. It belongs to the powder bed fusion group. Selective laser sintering means a laser is carefully sintering the particles of a material powder, combining them, and building the part layer by layer.

The materials which are used for SLS are thermoplastics used in granules form. SLS is considered a competent method to produce parts within a stringent deadline. It is compatible with low-volume production-grade manufacturing. The layer-by-layer manufacturing technique can produce parts with intricated geometries with less time and title to no waste.

Apart from speed, consistency, and producing parts with great mechanical properties, SLS stands out among other 3D printing methods such as SLA and FDM. However, to utilize all the capabilities offered by selective laser sintering, one must have a detailed knowledge of its benefits and limitations.

SLS Printing Working Process – 

Below is a step-by-step of the Selective later sintering process:

• Printing
• Cooling
• Post-Printing  

#1 Printing:

The powder is evenly spread on the platform’s top inside the build chamber. But before that, the powder bin and bin area must be heated just below the melting temperature. The pre-heating makes it more convenient for the laser to raise the temperature of the powder bed’s specific areas while solidifying the part.

The laser will scan a cross-section of a 3D model, heating the powder to a point unjust below the material’s melting point. The particle will be combined mechanically to create a solid part. The uncombined powder also comes in handy by becoming a support mechanism for the part being printed. When the layer is complete, the build platform moves lower by one layer, and the process repeats itself until the part is produced.

#2 Cooling:

After printing is completed, the build chamber needs to cool down both inside and outside to ensure the ideal quality, mechanical properties, and zero warpings in parts.

#3 Post-Printing 

It is an extremely crucial stage of the method as the parts we removed and separated from the build chamber and cleaned to get rid of excess powder (Which can take up to 10 hours). The parts are cleaned with compressed air and media tumbling. The excess powder is collected and can be reused accordingly.

As the excess powder acts as a support arrangement, the versatility of SLS 3D printing increases significantly. Thus it can produce complex shapes, such as interior features, exterior features, thin walls, and undercuts.

Engaging Read – What is FDM Printing? | The Ultimate Guide

Key Attributes of SLS – 

Printer Criteria:

The machine manufacturer plays a key role in deciding the process criteria of SLS. If a manufacturer’s focus is on small-scale productions, it becomes extremely important to take the essential advantage of the build volume. Although the defined layer height is 100-120 microns, a random height bin will take about the same time to print regardless of the number of parts it accommodates.

The reason behind that is the processing time is decided by the re-coating steps, and the machine will cycle through the same number of layers.

Layer Fixing:

The additional benefit of SLS compared to other 3D printing methods is its excellent bond strength between layers, leading to printed parts with remarkable mechanical properties.

SLS parts also boast good tensile strength and modulus but have a weak elongation at break. That’s because of the internal foraminous of the last part.

Warpage:

Warping is SLS parts are uncommon but not completely absent either. When the newly sintered layer cools, its dimensions contract, and internal strain build up, pushing the central layer upside.

Flat surfaces are often more susceptible to warping, but manufacturers with a good presence of mind adjust the design and size accordingly. The prime causes can differ, but adjusting the part vertically in the build platform should be avoided.

But, what can change production dynamics is the reduction in volume by decreasing the size of the flat areas and adding cutouts to the design; that change will also reduce the production cost as less material is used.

The typical shrinkage in SLS parts is 3-3.5%

Oversintering:

This phenomenon occurs when heat is trapped with unsintered powder around a region. This can readily affect the aesthetics of a part. The wall thickness of the feature mainly triggers Oversintering.

Take into account that slots wider than 0.8 mm and holes greater than 2 mm diameter can be printed in SLS without any complications.

Best Suited SLS Printing Materials – 

The most commonly used material for SLS printing is Polyamide 12, AKA Nylon 12. Polyamide 12 is ideal for intricate joints and assemblies and durable components. Other compatible materials are PEEK and PA 11, but their overall usage is low.

Several additives, such as glass fibers and carbon fibers, are blended with polyamide powder to enhance the mechanical and thermal properties of the sintered component. However, parts made with blended materials might become more brittle.

Here’s a table describing the benefits and limitations of potential materials:

 Engaging Read – What is Ultrasonic Welding | Ultrasonic Welding for Injection Molded Parts | Common Welding Problems and Solutions | Ultrasonic Welding Advantages

Advantages – 

1. SLS parts boast excellent isotropic mechanical properties, making them highly compatible for serval types of functional parts and prototypes.
2. SLS provides phenomenal manufacturing abilities for small-scale to medim0scale manufacturing requirements.
3. Polyamide 12 is the most utilized SLS material; its processing speed becomes significantly faster, even comparable to the SLA printing process. The reason is nylon requires light exposure to laser for sintering. The best part is that speed doesn’t compromise on quality.
4. SLS printed parts have a porous surface, making them inclined to intake moisture and other liquids. That makes coloring the parts post-printing very easy. However, moisture exposes SLS parts must have waterproof finishing to face external damage.
5. It doesn’t need support structures, so designing and producing complex shapes becomes convenient.

Disadvantages – 

1. The biggest setback one might face setting up SLS printing is its cost. It’s costly for beginners and even for long-time manufacturers. A basic desktop-scale SLS printer set will cost you about $5000. Even the Sintratec Kit, a basic model SLS 3D printer, costs a little above $5300, capable of 100 mm x 100 mm x 100 mm build volume. Not everyone is capable or willing to pay that amount of money, which is why SLS printing hasn’t evolved as a mainstream manufacturing method.
2. Selective later sintering printing parts are often grainy on the surface area with internal porosity. To tackle that, post-processing is required for smooth surface finish and water tightness.
3. Small holes and late surface surfaces are prone to warping.

Applications – 

Architecture: Although it’s still in its early stages, some promising developments have been made in the architectural space, such as designs of furniture, estates, villages, buildings, layouts, offices, parks, etc.

Fashion: SLS is being accepted as an integral, time and raw material-saving tool in the fashion industry. Take an example f clothing that is made without stitches and cuts. The precise type of clothing can also be made depending on the consumer’s preference without any wastage of material as the specifications are defined.

Art: The process is used by certain art enthusiasts preferring odd and unconventional art pieces like sculptures and monuments.

Anatomical Models: Often used in healthcare and retail industries for producing dummies, mannequins, pre-operative planning models, and training aids.

Rapid Prototyping included functional prototyping, proof of concepts, and early concept physical models.

Prosthetics: SLS is considered ideal for producing prosthetics and orthodontic parts.

Living Hinges: It is often used for riding living hinges using materials like polyethylene(PE) and polypropylene(PP).

On-Demand Manufacturing: SLS or any other 3D printing method is considered ideal for rapid manufacturing, known as “parts on-demand.” This can result in a good profit for many businesses that aren’t keen on holding a lot of inventory at a time.

Fascinating Read – What is SLA Printing? | The Finest Guide

Types of SLS 3D Printers – 

Traditional Industrial SLS 3D Printers:

Traditional Industrial SLS 3D Printers utilize single or multiple lasers. The printing mechanism needs a dormant nitrogen environment to prevent the powder from oxidizing and degrading, making air handling equipment necessary.

These machines are bulky, consume a lot of energy, and take about ten m² of space. With a starting price of well over $100,000, industrial SLS 3D printers have become highly expensive for almost all businesses.

Fuse 1: The First Benchtop Industrial SLS 3D Printer:

Source - Formlabs

Fuse 1 is the first benchtop industrial SLSL printer invented by FormLabs It is a recent development in the SLS printing space, offering lower-cost compact SLS systems.

It works on a single laser and smaller build chamber, which needs less heating—no requirement for inert gases and specialized sir handling equipment.

Fuse 1 consumes significantly less energy than bulky industrial 3D printers and can thus run efficiently at low energy.

History of SLS 3D Printing – 

I deliberately decided to talk about SLS history at the end; it was invented in the 1980s by Dr. Carl Deckard and Dr. Joe Beaman at the University of Texas at Austin. The initial prototype evolved drastically and developed to work with various materials such as plastics, metals, ceramics, glass, and various composites and blends.

Collectively processing all the above materials is called the bed fusion method. There are two main bed fusion methods- SLS and DMLS (direct metal laser sintering).

Mega Comparision: FDM Vs. SLS Vs. SLA –

Interesting Read – What is PET Plastic | PET Characteristics | PET Copolymers | How is PET Made | Advantages & Disadvantages

FAQs – 

1. Is SLS printing a reliable method in terms of accuracy?

Ans. Selective laser sintering is a particularly accurate and reliable process and is often used for making products with complex geometries. SLS printing has a dimensional tolerance of ± 0.3% and a lower limit of ± 0.3 mm, which is more than FDM printing. However, there are still good chances that Although this process is more accurate than FDM, there is still a chance that the layers will not cool at the same rates.

2. Which is stronger? FDM or SLS?

Ans. If we’re talking about tensile strength, then FDM parts are stronger. If you test both FDM and SLS parts, the tensile strength difference between the two orientations was 10MPa, occurring at -60°C. The FDM parts tested at -60°C show a difference in tensile strength 30MPa greater than SLS.

3. Is SLS faster than FDM?

Ans. Lead time for SLS 3D printing ar typically shorter compared to FDM. The printing speed of an SLS printer is generally about 48 mm/h, while FDM can print up from 50 to 150 mm/h depending on the printer. DLP printing is the fastest of the three when it comes to speed.

4. Which are the top 5 3D printing companies in the world?

Ans. The top 5 3D Printing companies are:

1. 3D Systems Corp. (DDD)
2. Proto Labs Inc. (PRLB)
3. FARO Technologies Inc. (FARO)
4. Materialize NV (MTLS)
5. The ExOne Co. (XONE)

5. What are the common shortcomings of practicing while 3D printing?

Ans. Below are the common shortcomings faced while practicing 3D printing in general:

1. Under-Extrusion
2. Over-Extrusion
3. Over-heating
4. Gaps in the top layers
5. Not sticking to the bed
6. Layer shifting
7. The printer is extruding the plastic at the beginning of the print.

Suggested Read – 

• How to Cut Polycarbonate | A Complete Analysis
• ABS Vs PVC | The Complete Guide
• What is Polycarbonate? | Polycarbonate Properties | Types of Polycarbonates | PC Manufacturing | Applications | Advantages & Disadvantages
• What is UHMW Plastic Material? | The Definitive Guide
• What is TPV Material? | A Simple and Detailed Guide
• How to Choose the Right Lubricants For Plastic Parts?
• What is LDPE? | Low-Density Polyethylene | The Complete Guide
• When Was Plastic Invented? | The History of Plastics
• Plastic Abbreviations and Their Salient Features | The Ultimate Guide

The Takeaway – 

So that was it, guys. My best effort was to share all the necessary information about SLS printing. The method makes parts with high mechanical properties and aesthetics. It can be extremely beneficial for both manufacturers and consumers if used correctly.

Have a lovely week ahead.

Peace Out