Selective Laser Sintering

Since there is advancement in the machinery, software, and materials, many businesses can access SLS printing. Several companies can now use tools that were a preserve for various high-tech industries.

So, what is selective laser sintering? It is an additive manufacturing process that involves adding up materials layer upon layer to make a 3D object. The SLS 3D printing is an outstanding choice for various designers over several decades.

In this selective laser sintering guide, we will give you some more insights into the selective laser sintering process. You will also get to know multiple machines and materials that re available in the market.

In the end, you will still be in the picture of when to apply selective laser sintering over the traditional manufacturing method.

Selective Laser Sintering

An Overview of Selective Laser Sintering

SLS is a process of additive manufacturing that came into being in mid-1980. This method will work with various materials like ceramics, plastics, metal, and certain composite powders. We now categorize this technology as powder bed fusion.

Typically, the most available bed fusion systems are either powder or metal-based. We refer to the plastic option as SLS and the metal-based as selective laser melting SLM. However, the two methods are expensive and sophisticated.

Most of the manufacturers use them to make parts in small quantities, which are of great value. A perfect example is the making of medical devices and aerospace parts.

How does Selective Laser Sintering Work? 

The process will begin as a Computer-Aided Design file (CAD). The computer will convert the CAD file into STL format for better interpretation by the 3D printing apparatus.

The most commonly used materials are plastic. The SLS 3D printers utilize a high power laser to fuse small particles of the polymer powder. This powder goes through a thin layer within the build chamber. At this point, the printer will preheat the powder to the right temperature.

The temperature will be less than the material’s melting point. The design assists the laser beam in the rising temperature of particular regions of powder, which traces the model to cause solidification.

The laser will scan a cross-section of your 3D model while heating the powder at the correct material’s melting point. The process will fuse the particles to be mechanically intact, thus creating a solid object.

The unfused powder has a vital role in supporting the part while printing. It will eliminate the requirement for dedicated support structures. The build platform will be lower by a single layer within the build chamber, between 50 and 200 microns. Later, the laser will begin to scan the successive cross-section of the build.

The process will repeat for every layer until the required part becomes complete. The finished product will now cool within the printer gradually.

When the cooling process is over, the operator will remove the build chamber for your printer and takes it to the cleaning station to remove the excess powder.

Post Processing Options

There are various post-processing options while performing selective laser sintering applications. The post-process of selective laser sintering will need minimal labor and time. It will result in consistent results to restore many batches of particular parts.

You will manually clean the finished part by using a media plaster or compressed air. The cleaning is necessary since the SLS parts will have a rough and grainy surface when out of the printer.

When using nylon material, it will prompt you to undergo various post-processing actions like dyeing, stove enameling, tumbling, and powder coating.

You can still recover the materials by filtering excess powder to remove larger particles and recycle them. The unfused dust will degrade when exposed to extremely high temperatures. You can refresh it with new materials for any subsequent print jobs.

Recycling of the materials minimizes wastes and costs.

Let’s discuss them in full detail.

1. Dyeing

The great way to add color to a Selective Laser Sintering object is by dyeing. The process mimics the one people you to dye fabrics. You begin by dipping the part in a hot dye for at least 30 minutes to ensure the exterior’s uniformity.

It is noteworthy that only the outer layer will absorb the dye. Any cracks, deep scratches, holes, or threads that penetrate the outer membrane after the dyeing process may reveal the original white color beneath the layers.

2. Sanding

You can perform the sanding process to achieve a smoother layer on SLS nylon parts. Sanding is a process that will favor parts that have larger flat areas. However, it may be challenging to handle parts with intricate contours. You will require more effort while doing sanding.

3. Media Tumbling

The nylon parts that come out of the Selective Laser Sintering printer will require cleaning. The purpose of cleanup is to eliminate any unsintered powder on the surface. Later, the pieces will exhibit a bumpy surface due to the nature of nylon materials on the power bed.

You can achieve a smoother surface on nylon oriented parts by using media tumbling. The process may remove peaks but not upgrade it to a wholly glossy and smooth part. Still, you can remove the small and fragile parts. Square shaped pieces may attain a round shape.

4. Plating

It is an electroplating process that helps in giving the parts a metallic look finish. You can perform this process to the parts that are lightweight and rigid. The method of plating and building SLS parts is quicker and more economical than milling parts from aluminum.

We use a bright nickel during the plating process. The thickness may vary depending on the purpose.

The standard thickness may range from 0.002 to 0.006 inches. You can employ plating to achieve an EMI shielding.

What gets made? 

The SLS machines will are ideal for printing objects using various materials like glass, plastics, and metal. The process can make both final products and prototypes. The SLS is useful for specific industries that require small quantities of printed objects featuring high-end materials. The aerospace industry is the greatest beneficiary of this technology.

The molded parts are worth the top dollar as they will remain long-lasting. The SLS process can also print customized products like dental retainers, prosthetics, and hearing aid. It is a manufacturing method that can create delicate or highly intricate objects.

Several selective laser sintering companies around the world print certain parts for their clients. They equally make prototypes and finished products.

SLS at Home

The SLS process will require the involvement of high-powered lasers. As a result, it is potentially expensive to use it while at home. Interestingly, rapid inventors are coming out with simplified desktop SLS printer versions.

The focus of the latest technology is to ensure SLS printing is possible in the comfort of the home.

Types of SLS Systems

All selective laser sintering systems will operate on a similar principle, as described above. The only difference comes in the build volume size and the type of the laser.

Also, different systems use various temperature controls, layer deposition, and powder dispensing. The SLS process needs a high level of precision with tight control. You can control the temperature of the powder during preheating, sintering as well as storing.

As such, you will minimize stresses, warping, and heat-induced distortions. Here are the types of SLS systems:

Benchtop SLS Printers

You can use the benchmark that is only comparable to industrial systems. The products will be more manageable and in a compact form. This system uses fiber or a diode laser instead of carbon dioxide lasers to provide equal beam quality.

The benchtop machine has a smaller area that needs less heating. It will expose the powder to higher temperatures within a limited period. It may not require inert gases and any special air handling device.

This benchtop machine will consume less energy that runs on a standard power AC powder. Beyond that, the machine uses a slower speed and has slightly reduced build volume.

Industrial SLS Printers

Industrial SLS Printers

Industrial Selective Laser Sintering printer is a multipurpose machine that makes various applications. The largest systems can produce parts that are as long as one meter. This system will use high-power carbon dioxide lasers. The more complex system will create a large build volume.

The industrial SLS needs an inert environment like nitrogen or other gasses to prevent the powder’s oxidization or degradation. Furthermore, the system will require a specialized air handling device. Most importantly, it will need adequate power.

Features of an SLS Machine

The selective laser sintering technology ensures the accurate creation of parts. The SLS machines are both thermally and mechanically stable during the building process. Here are some of the critical components of the SLS machine:

a) Material Feeds

The role of a material feed is to provide the new material that will get deposited for sintering. It can be both a piston-driven and gravity-fed system.

The material feed may still have thermal controls that can warm up the powder as it accesses the build chamber. But the success depends on the type of the SLS machine.

b) Recoater

A blade or a roller receives the materials for a particular feed and spreads it across the part piston evenly. The recoater is a crucial component during SLS build. Any irregularity that it may have on the depositing powder will reflect on the final parts.

c) Piston Part

The piston part happens to be an effective build area for the machine. It has a rectangular container featuring a flat and movable piston base. The piston will be at the uppermost level when the build begins.

When the machine deposits a layer, the piston will slightly move downwards. The design will allow the recoater to deposit another new material for sintering.

During the process, the piston part gets heated to handle any part distortion resulting from cooling. The temperature will go down once the build becomes complete.

The piston part can be an exchange frame which you can remove and add another frame for the subsequent build.

d) Laser

Its position is above the piston, where you direct the laser through mirrors. You will not need higher wattage for sintering. The Selective Laser Sintering machines of higher wattage (-70-100W) will sinter three times faster than the low wattage option.

e) Overflow Bins 

You can collect the left material after completing the recoating in the flow bins. You can refresh the unsintered and overflow materials with the new powder and later reuse them.

f) The Build Chamber

Others refer to it as the process chamber, which houses the piston part, laser window, and the recoater. This process chamber has several heaters and thermal sensors to ensure the stability of the powder temperature.

g) Peripherals Components

The Selective Laser Sintering machines will require an inert surround. As a result, nitrogen will eliminate oxygen from the chamber. The nitrogen tanks come along with SLS machines. Most importantly, there is post-processing equipment that has a vibratory sifting station.

Common Application of SLS 

Iterative Design 

The SLS can produce quick and affordable prototypes. About that, it reduces the resources that one will need for prototyping phase design. It will leave other resources that you can channel in the improvement of functionality and quality.

Rapid Prototypes

You can use a cost-effective method like SLS to make functional prototypes with moving parts. Most of the users utilize it when performing a concept demonstration. The machines are versatile with high speed.

Fit Checks

The designers will print models and test if they will mechanically fit well. If they pass that level, then the manufacturer will begin a high-level production. The accuracy of SLS if +/- 0.005 inches. It will mimic various plastic depending on the nylon used.

Artistic Creations 

It is a detailed avenue to show off the jewelry and sculptural designs to make it a great artistic tool.

End-use Applications

The materials’ properties, build tolerances, and appearance details have a significant role for end-use. The selective laser sintering printing allows for more accurate products for particular end-user parts. For instance, some of the objects printed in nylon may have an accuracy of +/- 0.005 inches.

Buyers guide for SLS Machine 

The process of selecting the right SLS machine may be tougher than many people would imagine. Several models in the market may be confusing; hence you need to gauge them with specific parameters.

You need to learn the benefits and limitations of each feature for you to decide appropriately. A straightforward way of understanding the machine is by joining the online community and familiarize yourself with clients’ feedback. You will find the right idea that will influence your choices.

However, you are just a beginner; then you can consider doing the following:

Type of the SLS machine

a) Type of the SLS machine 

3D printing involves more than ten processes that will produce high-end products. However, the quality of the print may differ according to the SLS machine. Some of the parts that you generate by FMD may require smoothening to give it a better finish.

On the contrary, parts that you produce by SLS are of high quality than those of FDM. Also, parts produced by SLS are isotropic since they come from powdered materials. You should select the right SLS 3D printer machine if you need high precision models that come in intricate designs.

b) Speed of the Printer

An excellent 3D printer should have a moderate speed. It your priorities and expectations matter a lot about how you want the final product to look like. If you wish to higher turnaround time, you go for the printer that prints fast.

It should also capture finer details in the process. You may also need to be patient since some parts may take hours to several weeks to get the right finish.

Large and complicated pieces will require more time. The printing speed may only matter if the 3D printer produces the right output.

c) Printing Materials

The selective laser sintering machines will support different materials. The most common content is nylon, which is durable with high chemical resistance. You can still put some more fills.

By adding 50% of excellent glass fill, the material will become more rigid. The glass fill will appear whitish. Still, you can add some aluminum fill to make the materials stiffer. The aluminum filled materials will have a metallic grain gray color. Since the aluminum fills are not conductive, they will remain suspended in the nylon.

You can also perform a carbon filling to add strength. The carbon fill is rigid and will favor contoured designs.

It is ideal for UAV housing and automotive ducting. The carbon-filled parts are dark gray.

Lastly, there may want a mineral fill, which is a perfect additive to stiffen the parts. They have natural beige color with slight specks.

d) Print Bed Options

The print bed can be either non-heated or heated. You can select the ideal option depending on the materials that you will want to use.

For instance, the heated bed will favor ABS materials. The non-heated bed will accommodate adhesives or PLA materials adequately.

You can maintain the quality by keeping the first layer, which is possible in preheating options. You should decide on the kind of bed that will favor your work.

e) Your Goals 

It is all about specifying your 3D printing needs. For instance, is you want to buy a selective laser sintering 3D printer, determine if you will keep it in the house. If it fits in the house, then consider the safety features.

You should also consider the size since it will determine the maintenance costs. In case it is for business use, then settle for a larger size.

f) The Print Resolution

The print speed and the resolution will dictate the quality of the 3D print. The print resolution will define the level and clarity of finer details. You can measure the resolution in microns. If you opt for lower microns, you will get a higher resolution.

You can determine the quality of the printer is to see how it prints. Some companies will share the print sample when you request for them. By doing so, you will know what you should expect from such a printer.

g) Inbuilt Slicing Software

The selective laser sintering 3D printer should have a slicing software. You will need it to divide the STL file into horizontal layers. The process is among the last steps towards feeding your digital image to your 3D printer.

Alternatively, you can perform such a task yourself. It grants you the option to decide how you will want to slice that particular digital file.

h) Customer Feedback

You should look for reviews from other customers. You will learn from what other clients are saying about that particular 3D model that you intent to buy. You are likely to encounter certain views that will influence your resolutions.

You should indeed perform thorough research before deciding to buy your ideal printer. Analyze all the perspectives before reaching the final resolution.

Pros of SLS machines

  • They have a sintered bed that is self-supporting to enable complex geometries.
  • The produced parts will be stiff with high strength
  • It enables various finishes like coating, metallization or stove enameling
  • It is the fastest additive manufacturing process that produces durable and functional parts.
  • The parts have excellent chemical resistance

Cons

  • The parts have a porous surface that you must seal by various post-processing methods.

In Conclusion 

You should always embrace new technology since it comes to upgrade the preexisting models. The features of the latest technology will make your work to be cost-effective and sufficient.

Selective laser sintering is a modern approach towards realizing improved parts and designs. You can achieve intricate design effortlessly. However, you must be ready to follow all the procedures for you to get the right results.

As you apply the SLS techniques, you will have an edge in production and quality. Decide now and improve your products. You will eventually get the right products.