A Complete Selective Laser Sintering 3D Printing Guide

SLS is Selective laser sintering, one of the most widely used additive technologies.

The principle of operation of SLS is the point sintering of plastic powders with different components by a laser beam.

Some machines sinter powdered metal – this 3D metal printing technology is outdated, but still used. Beam power in production 3D printers varies from 30 to 200 watts.

The method was created in the mid-1980s at the University of Texas at Austin by Carl Deckard and Joe Beeman.

In 1989, the invention was patented by Deckard-founded DTM Corporation, which was subsequently acquired by 3D Systems. In the bowels of the latter, another fundamental additive technology was created – this is laser stereolithography (SLA printing).

So, in this article below, let’s know all about SLS parts, SLS process, SLS Materials, and other additive manufacturing technologies using SLS process parameters.

What Is Selective Laser Sintering (SLS)?

SLS technology involves the point sintering of a powder mixture based on durable plastic parts and other components using a high-power laser. Previously, this method was applied to metals.

It was first created in the mid-1980s by Carl Deckard and Joe Beeman at the University of Texas. In 1989, it was patented by DTM Corporation, which later became part of the 3D Systems brand.

The power of the equipment varies from 30 to 1000 watts. Initially, the polymer powder is heated and then subjected to short laser exposure.

As a result, it sinters with the hardened particles of the lower layer. So, layer by layer and get a 3D workpiece, the same as the original sample loaded into the program.

By adjusting the machine settings and functional parts, you can achieve the required porosity and density of the product.

Unlike Stereolithography (SLA) or Fused Deposition Modeling (FDM) 3D printing methods, it delivers parts with great and also consistent mechanical properties using additive materials.


How Does SLS 3D Printing Work?

All parameters of workflow in the SLS 3D printing method are determined by the manufacturer of the printer. So, this’s how the Selective Laser Sintering (SLS) works:

Printing

The SLS 3D printing machine utilizes a laser as an energy source that selectively melts plastic material of coated powders in a thin layer, fusing them into a fine 3D printed piece.

This method is a part of the Laser Powder Bed Fusion (in short LPBF), among the most reliable and advanced systems in the field of 3D printing or additive manufacturing.

Utilizing a 3D build platform from a CAD software model, the laser melts the bulk material precisely at the predefined parts in the powder bed of the 3D printing or additive manufacturing technique.

After the melting temperature is reached and a solid structure is made using the SLS system, the low volume production, and also a new layer deposition of powdered material are added.

This printing process keeps on repeating layers until the solid-state sintering is completed. It can be used with different binding mechanisms.


Cooling

After the completion of printing with desired layer thickness, the build section needs to cool down slightly inside the print section and then also outside the printer.

This will make sure the best mechanical powder properties and also help you avoid bending in parts. This will also support the material used in the procedure.


Post-processing Methods

The completed parts have to be taken out from the machine’s build chamber and clean of the item of extra powder after being separated.

The SLS powder’s influence can be reclaimed and the 3D printed components can be post-processed further by media tumbling or media blasting.

Since the unfused powder in the method supports the parts while printing, there is no need for reliable support structures.

It makes SLS perfect for complicated geometries, consisting of undercuts, interior features, negative features, and thin walls. Parts built with an SLS machine have superior mechanical features, with strength corresponding to injection-molded components.


Different Kinds Of SLS 3D Machines For Printing

All 3D printers using the SLS method work on the principle described above. They differ in the size of the working chamber, the type and power of the laser, and some design features.

Industrial Models

For many years Selective Laser Sintering has been the working technology of manufacturing. In addition to high cost, devices have several requirements for organizing the workflow.

To prevent oxidation and destruction of the material by the laser, an inert environment is required, respectively, special equipment.

It is also necessary to supply industrial power, air conditioning, ventilation, heating systems, and an area to adjust equipment of at least 10 square meters.

In case we add to all the above requirements the price of industrial machines, starting from $ 100,000, it becomes clear why the equipment was available to a narrow circle of companies.

SLS printers for industrial use are widely applied. They are in demand in many areas, from automotive, engineering, and space industry, and end with small-scale production and medicine.

There are overall systems that can print models whose length exceeds 1m. Industrial printers generally operate on one or more carbon dioxide lasers. It’s quite logical that the larger the assembly volume, the more complex the system will be involved.

Industrial systems, in particular SLS 3D printers, need the use of an inert medium. We are talking about filling the chamber with gas. Most often it is nitrogen or another inert gas.

This is done to prevent oxidation and subsequent decomposition of the powder material used. For this reason, industrial applications include compressed air handling equipment.

Since the systems are powerful, they also require industrial-grade power. And any industrial printer is large. Even the smallest system requires a room with an area of ​​at least 10 sq.m.


Revolutionary Fuse 1

In recent years, manufacturers have begun offering more affordable SLS 3D printers. However, they were imperfect: the quality of products suffered, and there were no ready-made solutions for simple post-processing.

Formlabs has succeeded in developing and launching an innovative product – the Fuse 1 model. The printer is small in size, much cheaper than previous industrial machines, and prints high-quality models.

The model uses 1 laser, the material heats up faster, so gas supply to the chamber and professional ventilation aren’t needed. The printer can be powered by a standard power outlet at the cost of less power than previous generation industrial designs.

The developers have created a unique Surface Armor technology, which is currently in the process of obtaining a patent.

Its advantage is the creation of a semi-sintered shell, the task of which is to maintain uniform heating of the area around the printed objects to form a high-quality surface and better mechanical properties.

Fuse 1’s working volume is slightly inferior to traditional SLS printers, but the device wins in price, compactness, and ease of use.


How Did Selective Laser Sintering Process Come About?

Doctors of Sciences Joe Beeman and Carl Deckard invented the technology of laser sintering of plastic powder in the mid-80s of the 20th century. We can say that this technology was one of the first 3D printing methods to see the light of day.

So far, there have been many innovations, and this additive manufacturing technique has been adapted to different materials. We are talking about glass, plastics, metals, ceramics, and various composites.

Now powder laser sintering technology is available in two variations. In the first case, the laser sinters the plastic powder – this is the SLS technology.

In the second case, metal powder is sintered – these are DMLS and SLM technologies. The principle behind the work of all these 3D printers is the same – the laser sinters or fuses the material.

The difference lies only in the power of the laser used, and also in the fact that metals are oxidized when heated under the action of oxygen, therefore, a special environment (inert gas, vacuum) is required to prevent this oxidation and, accordingly, a decrease in strength characteristics.

All of the above technologies were very expensive not so long ago, which greatly limited their use in printing expensive and non-standard products. To a greater extent, they were used in the medical industry and aerospace. Now everything has changed dramatically.

SLS technology has become popular, available, and in-demand along with other plastic printing technologies (SLA, DLP, FDM). In addition, compact desktop printing systems appeared, which also made SLS more popular.

So, the technology appeared in the eighties of the last century in America. The authors were University of Texas doctors Carl Deckard and Joe Beeman. Since the invention of the method, the range of working materials has gradually expanded.

Now, with the help of SLS-3D printing, ceramic, plastic, glass, and metal products with a different set of mechanical characteristics are created.

The method has two varieties:

• Based on plastic powder – Selective Laser Sintering (SLS)
• Based on metal powder – Direct Metal Laser Sintering (DMLS)

A few years ago, such printing was available only to a narrow circle of enterprises. However, today, thanks to modern developments, SLS production is becoming no less accessible than the usual additive methods, such as SLA and FDM.


Advantages & Features Of Selective Laser Sintering

As for the features, selective laser sintering should be immediately separated from another similar 3D printing technology – selective laser melting (SLM).

The difference between them is that SLS provides only partial melting of the powder, which is only required to combine it into a single element. SLM, on the other hand, melts the particles completely, sintering the powder into a monolithic product.

See how the SLS technology uses elastomeric and thermoplastic materials to build parts with great mechanical properties.

Absolute parts can be utilized to test forthcoming injection molded parts or as end-use, functional components. As for the advantages, the following advantages can be distinguished.

Large build area in 3D printers.

Industrial equipment for SLS 3D printing is usually equipped with a large build area, which allows you to create not only large parts but also small-scale production.

High-quality 3D printing

This technique allows you to almost completely avoid visible layering on the model, and the absence of supports also has a beneficial effect on the quality of products.

Lasers are much more powerful and more precise than the working elements of devices in other types of printers, such as FDM. SLS is the fastest method for additive manufacturing of prototypes and functional products. It allows you to print several products in one cycle.

The software helps to place the models as close as possible on the platform. D-printed nylon products are more durable than plastic, injection-molded, or other 3D printing technologies.

No Need to Build Supports

Selective laser sintering allows you to create products of complex geometry without the need to build support structures. This not only expands the printing possibilities but also has a good effect on the surface quality of the product.

High speed & performance

Because the material does not melt completely, SLS 3D printers work much faster than their other powder counterparts. Higher print speed – higher production productivity;

Design Freedom

Maximum additive manufacturing techniques, like stereolithography (in short SLA) & fused deposition modeling (in short FDM), need technical support structures to simulate designs with some overhanging features.

SLS doesn’t need support structures since unsintered powder covers the parts throughout the printing process.

Selective Laser Sintering printing can build previously unimaginable complex figures, like moving or interlocking parts, items with interior channels or components, and other favorably complex designs.

Generally, engineers design items with the abilities of the ultimate manufacturing method in mind which is called design for manufacturing (in short DFM).

As soon as additive manufacturing is utilized for prototyping alone, it’s restricted to designs and parts that conventional manufacturing devices can finally reproduce throughout production.

As SLS becomes a possible rapid manufacturing process for a rising number of end-use applications, this can discharge new prospects for engineering and design.

Selective Laser Sintering 3D printers can make complex figures that are prohibitively costly or impossible to make with traditional procedures.

SLS even empowers developers to reduce complex masses that would typically need multiple components into a single piece. This helps ease weak joints as well as cuts down the total assembly time.

SLS can take productive design to its maximum potential by allowing lightweight patterns that employ intricate lattice structures unbelievable to manufacture with conventional processes.

Uses Nylon Material Properties

The nylon used in SLS printers can be an excellent alternative to injection molded plastics. It can be used in applications where plastic parts are required, as well as where standard plastics can become decrepit and break.

Proven, End-Use Materials

The key to the versatility and functionality of Selective Laser Sintering 3D printing is the additive materials. Materials like Nylon and also its composites are high-quality, proven thermoplastics.

Nylon functional parts have nearly 100% density with some mechanical properties similar to multiple parts made with conventional SLS printer manufacturing processes such as injection molding for interior components.

Traditional manufacturing using SLS nylon material is a great alternative to common injection-molded plastic materials to make complex geometries. It offers exceptional snap fits, living hinges, and also other mechanical joints than any other additive manufacturing technology.

It’s perfect for functional applications needing plastic parts that’ll last where parts made with other additive manufacturing technologies would spoil and become breakable over time.


What Are The Disadvantages of SLS 3D printing Additive Manufacturing Technologies?

• The time for cool-down is 50% of the total print time. This means around 12 hours of waiting. Thus, it can cause a longer time for production.

• Very costly. The SLS machines can sometimes cost $250,000, or even more. Moreover, the materials generally cost $50 to $60 per kg. Additionally, the SLS machines needed a skilled person to run the machine properly.

• SLS parts produced from the SLS methods come with a coarse surface, thus to fix that, post-processing is needed.


What Materials Are Used For SLS 3D Printing?

The most commonly used SLS material is the Polyamide 12 (in short PA 12), also called Nylon 12. The PA 12 powder price per kg is approximate $50 to $60. Other plastics like PEEK and PA 11 are also obtainable, but these aren’t as commonly used as PA 12.

Polyamide powder for SLS parts can be supplied with different additives to enhance the thermal and mechanical behavior of the created SLS parts.

Instances of additives consist of carbon fibers, aluminum, or glass fibers. Materials loaded with additives are typically more brittle as well as can have favorably anisotropic behavior.

Polyamide 12 Or PA 12 Material

Pros
• Great chemical resistance
• Great mechanical properties

Cons
• Rough, matte surface finish

Polyamide 11 or PA 11 Material

Pros
• High elasticity
• Fully isotropic manners

Glass-filled nylon Or PA-GF Material

Pros
• High wear as well as temperature resistance
• High stiffness

Cons
• Anisotropic manners

Aluminum-filled nylon Or Alumide Material

Pros
• High stiffness
• Metallic appearance

Carbon-fiber-filled nylon or PA-FR Material

Pros
• Superb stiffness
• Increased weight-strength percentage

Cons
• Highly anisotropic


Stages of SLS-3D Printing

Designing & Preparing the Project File

To start a project, you need to use any CAD software file available by scanning. Every software on which the SLS 3D printing machines work makes it likely to cut the item into layers, calculate the printing period, organize objects in a provided order, and also configure the print settings.

As soon as ready, the software transmits commands to the 3D printer through a wireless connection or cable.

Preparing the 3D Printer

Preparations differ based on the model of the 3D printer. Previous generation devices need special skills for maintenance and operation. The manufactories of the Fuse 1 device have made the SLS printing way easier than before.

Print The Product

After the initial work, you can start the process. The complexness of the task defines the printing term: from a few hours to many days.

After finishing printing with good mechanical properties, the model should be left in a cooling compartment to avoid shape loss and to improve the mechanical parts. For the following work cycle, you even can use an exchangeable build chamber for the cooling process.

Recovery & Post-Processing

The ultimate procedures take time as the SLS 3D technology doesn’t involve the usage of supports, therefore the time is devoured at their disposal.

The cooled items are taken out from the chamber as well as cleaned of all residual powder on the product.

The polymer powder is then filtered and also processed for additional usage. Material properties are negligibly decreased, so a blend of new & old powder beds is utilized for the following printing cycles.

The raw materials are a significant benefit of the SLS 3D technology. Thus, different devices are utilized to reconstitute, store, and blend the powder bed fusion.

Extra Post-Processing Of SLS 3D Printing

Cleaned items can be immediately used. But for various projects, extra processing of items may be needed.

For instance, to remove coarseness from the surface of the SLS parts, the manufacturer suggests blasting or tumbling.

In case you need to adjust other parameters, like water resistance, color, and also electrical conductivity, items can be covered with numerous compositions.


The Main Benefits of The Procedure

• High quality
• Performance
• Development of engineering abilities
• Reliable materials
• Design convenience

3D printing depending on SLS doesn’t need the formation of supports, unlike several other printing methods, for example, SLA and FDM.

Thus, Selective Laser Sintering SLS printers make it potential to produce parts of complex configurations, with internal holes, protruding elements, and also other features.


Prospects For The Development Of Technology

SLS technology was originally used for rapid prototyping, but gradually its scope expanded. Selective laser sintering has shown excellent results in small-scale production of finished products, master patterns for casting, etc.

Not so long ago, another interesting area of ​​application of selective laser sintering was the manufacture of art objects.

The technology continues to develop: new materials are being introduced, the power of laser radiation is increasing, and developments are being made to use several materials in one technological process.

SLS printers are becoming more productive, smaller, and easier to use, while desktop models aimed at-home use have already appeared on the market.

The potential of selective laser sintering is enormous because this method opens up the scope for the implementation of the most promising technical and creative ideas.


Application Industries

Selective laser sintering has been widely used in various industries:

• Mechanical engineering
• Aerospace industry
• Foundry
• Construction
• Engineering design
• Architecture, art design

It’s essential in the production of pipe hoses, functional prototypes, gaskets, insulating washers, art objects, elements of power plants, etc. Especially high efficiency of the technology in small-scale production.

Originally, it was utilized for rapid prototyping, but slowly the scope has largely expanded. The possibility of the technology is quite large and hasn’t yet been completely explored.


FAQ Selective Laser Sintering 3D Printing Guide

Following are common questions on selective laser sintering 3D printing.

What Does It Mean By Additive Manufacturing Technologies Used In SLS?

Selective Laser Sintering (SLS) is a powder-based 3D printing or additive manufacturing technology that utilizes energy equipped with the laser to melt as well as fuse the powders. Then stack one layer after another to create a printed part depending on 3D model info.

What Is Direct Metal Laser Sintering or DMLS?

The 2 most standard powder bed fusion methods today are plastic-based and metal-based. And the metal-based is known as the Direct Metal Laser Sintering or in short DMLS, or even known as selective laser melting (in short SLM).


BOTTOM LINE

SLS process printing equipment is equipped with large build chambers (up to 750 mm), which allows you to produce large products or entire batches of small objects in one printing session using traditional manufacturing methods.

It thus offers excellent mechanical properties of the finished product: high strength, the accuracy of construction, and high-quality surfaces. No backing material required: The process is virtually waste-free and unused material can be reused for printing.

High performance: SLS printers do not need to completely melt the material particles, which allows them to work much faster than other powder 3D printers.

Multiple thermoplastic polyurethane (in short TPU) and nylon-based product materials are obtainable, which make highly stable final SLS parts that require heat resistance, flexibility, chemical resistance, or dimensional stability.

 

Resources

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