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Guide to Stereolithography: What is SLA 3D Printing?

Introduction

Sculpteo offers an SLA printing service to help you manufacture smooth and detailed parts. To help you understand the full potential of this 3D printing technology, we prepared this complete Stereolithography guide.

How does it work? Which 3D printing material could you use to manufacture your SLA project? What are the advantages of 3D printing your parts with SLA? Follow the guide. 

What is stereolithography 3D printing technology?

Stereolithography (SLA) is one of the oldest 3D printing techniques ever developed. This additive manufacturing process uses a photochemical process to 3D print resin material.

The liquid photopolymer resin used in this SLA 3D printing technology is cured in a vat. The liquid polymer is exposed to light when the build plate is incrementally moved, and the UV laser uses this exposure to create a cross-section. This is a layer-by-layer process that is repeated until a model is produced. Pulling the thing out of the resin (bottom-up) makes room for the liquid, uncured resin at the bottom of the container, which can then be used to construct the object’s next layer.

Since the photopolymerization process is irreversible, it is impossible to return SLA components to their liquid state. These SLA components won’t melt when heated; instead, they’ll burn! This is because, in contrast to fused deposition modeling (FDM), which uses thermoplastics, materials generated with SLA are formed of thermoset polymers. 

SLA

A little bit of history about stereolithography

Among all 3D printing technologies, stereolithography (or SLA) might be one of the oldest techniques ever developed. If we take a quick look at the history of 3D printing, SLA appears to be the first concept of 3D printing. During the ’80s, a French team of engineers, Olivier de Witte, Jean-Claude André, and Alain Le Méhauté, was interested in stereolithography technology. Still, unfortunately, they abandoned their project and didn’t pursue their patent application due to a lack of business perspective. 

At the same time, Charles Hull was also interested in the technology and submitted the first patent for stereolithography (SLA) in 1986. Hull patented stereolithography as a technique to create 3D objects by successively adding thin layers of an object using a medium curable by ultraviolet light. This process started from the bottom layer to the top layer.

Charles Hull is now well known in the 3D printing industry as he also the 3D Systems Corporation, which released its first product, the SLA-1 3D printer, in 1988. 

How does SLA 3D printing work?

1 – Prepare your 3D file

The first step to start your manufacturing process with additive manufacturing is to create a digital 3D model of the product you want to make physically. You can do this by using 3D modeling software to create your object. Discover our selection of free CAD software to develop your project.

Preparing your file for 3D printing with SLA is an essential step in your process. This 3D file has to be perfectly printable. At Sculpteo, we see a lot of 3D models with errors, resulting in non-printable files. Moreover, even if the part is 3D printable, your part has to be resistant enough so it doesn’t break or be deformed. Find out how to overcome these common 3D printing mistakes. Good news for you, as the SLA technology can create a complex object, you will have the opportunity to have a detailed and exact 3D model for your project.

2- Get the SLA 3D printer ready to print

SLA 3D printers are usually desktop 3D printers with a high resolution. The majority of print settings are defined by the manufacturer and cannot be altered. The layer height and portion orientation are the sole inputs.

If you don’t have your SLA 3D printer, you can use an online 3D printing service such as Sculpteo, and any technical preparation will be done for you by our operators! Sculpteo uses Formlabs 3D printers to 3D print your parts with excellent quality and reliability.

3- 3D printing process

Once all setup checks have been made, the printer is prepared to print; the laser will cure the photopolymer resin according to your 3D model until the print is complete. 

There are two different setups for stereolithography 3D printers: top-down and bottom-up printers. 

Top-down printers place the laser source above the tank, and the part is built facing upwards. The build platform begins at the top of the resin vat and moves downwards after every layer.

Bottom-up printers place the light source under the resin tank, and the part is built upside down. The tank has a transparent bottom with a silicone coating that allows the laser’s light to pass through but stops the cured resin from sticking. After every layer, the cured resin is detached from the bottom of the tank as the build platform moves upwards. This is called the peeling step. 

4- Post-processing

After the 3D printing process, the parts need to be rinsed in isopropyl alcohol to remove the uncured resin from their surface. Some materials must be post-cured once washed sections have dried; this procedure helps components achieve maximum strength and stability. After removing supports from the printed parts, you can then sand the remaining support marks for a clean finish.  

What are the characteristics of SLA technology ?

There are different ways to print SLA; as we just saw, the main difference is their orientation. It can be a bottom-up or a top-down process, depending on the 3D printer. Indeed, desktop 3D printers use the bottom-up technique, like Formlabs 3D printers, while the top-down ones are more industrial 3D printers. Desktop SLA printers are cheaper and easier to operate. In contrast, industrial 3D printers allow the building of large-size objects thanks to their exciting build volume, but they need a specialized technician to be used. Moreover, these 3D machines are high-speed.

Another essential characteristic of SLA 3D printing is a support structure to print your resin part. Once again, these supports are easier to develop for desktop 3D printers as they are similar to Fused Deposition Modeling (FDM) supports. 

These are needed to print correctly any overhangs and bridges, for example. You can choose the part’s orientation, choosing which exposure requires less support structure. For industrial SLA machines, a support structure is still needed. All these supports have to be removed manually from the 3D-printed part. 

Moreover, post-processing is also part of the manufacturing process with Stereolithography. At the end of the process, the amount is removed from the platform, and the excess resin must be removed from the part. Then, the resin part will undergo a curing process in a UV oven, which will help the final piece reach its absolute stability.  

SLA detail

What are the advantages of stereolithography?

Choosing stereolithography for your project can offer various advantages for prototyping or production. It is a fast manufacturing technique, allowing accurate parts with a great smooth surface. These photopolymer parts do not have the strength of Selective Laser Sintering (SLS) or FDM 3D printed parts but can typically achieve much higher levels of detail and great complex geometries.

  • Watertightness

3D printing with resin technologies can offer water tightness, as the printed objects are continuous. This is quite useful if you are facing air and fluid flow challenges.

  • Precision

Why can 3D printing resin technologies such as SLA create specific parts? Temperature is a significant factor here. Lower printing temperatures than thermoplastic-based methods that melt the raw material result in better precision. The printing process in stereolithography takes place at a temperature that is very near to that room temperature. Therefore we don’t have to deal with thermal expansion and contraction. 

Moreover, the heated resin tank and the enclosed build space work together to create almost similar conditions for every print!

If you are looking for a 3D printing method offering a high level of detail, then SLA is the perfect solution for your projects.

  • Isotropy

A characteristic of extrusion-based 3D printing techniques like fused deposition modeling (FDM) is anisotropy, which refers to variations from layer to layer throughout the printing process. For specific applications, this anisotropy restricts the use of FDM or necessitates additional component geometry revisions to make up for it. With stereolithography, it’s a bit different. Indeed, stereolithography printers produce pretty isotropic parts. 

By combining material chemistry with the print process, it is possible to closely manage a variety of parameters that contribute to component isotropy!

  • Smooth surface

Resin 3D printing is also perfect for manufacturing decorative parts or finished end-use products thanks to great detail and smooth surfaces. You can easily access injection mold-like surface finishes by using resin technologies. In contrast with some other additive manufacturing techniques (Powder-bed fusion technologies or filaments), you can’t see the layers on a resin part; the surface is perfectly smooth. 

What are the disadvantages of stereolithography?

Stereolithography has many advantages but is not the perfect manufacturing technique for everyone. Let’s see some examples of disadvantages.

SLA components are typically fragile and inadequate for some technical or advanced projects. Also, as the photopolymer is UV sensitive, these products are susceptible to deforming and changing colors when exposed to sunlight. This means SLA components’ mechanical qualities and aesthetic quality can deteriorate over time.

Support structures can also be inconvenient. These supports are always needed, and the SLA section has to be post-processed to eliminate the visible markings left behind.

Which applications are best suited to stereolithography 3D printing?

SLA (Stereolithography) Prototyping resin is ideally suited to producing rapid aesthetic prototypes. SLA is commonly used to generate highly detailed artwork and non-functional prototypes and can be used to make molds in investment casting applications.

The finished product has a smooth, matte surface finish. SLA resin allows you to achieve a finished product look for your prototype. This SLA 3D printing technology is best suited to small/medium pieces with elevated details.

Thanks to its accuracy, this technology can be used in various industries such as medical, dental, product design, entertainment, jewelry, and so on!  

What materials are used in stereolithography?

SLA materials are liquid resins that may be selected for the part’s intended application, such as abrasion resistance, smooth surface finish, or temperature resistance. Compared to desktop SLA printers, industrial systems provide a greater variety of materials, giving the designer more control over the mechanical characteristics of the produced object.

Sculpteo offers the prototyping resin using SLA. This 3D printing material is ideal for rapid prototyping and might enhance your entire process. With the help of this resin, intricate pieces and unfinished prototypes may be produced. Products created with SLA resins and this photopolymer may change shape and color when exposed to sunshine. 

What are other resin 3D printing alternatives?

Maybe SLA is not the perfect resin technology for you. Discover some alternatives also available at Sculpteo.

The liquid resin is contained within a vat, or tank, cured against a build platform, slowly rising out of the tank as the part is formed, layer by layer. These two 3D printing technologies are similar but have one main difference: their light source.

Like inkjet printing, polyjet printing dispenses layers of curable liquid photopolymer into a build tray rather than individual drops of ink onto paper.

VeroClear

Carbon created this resin 3D printing method. Continuous Liquid Interface Production, or CLIP, improves upon the drawbacks of existing 3D printing technology by prioritizing a customizable photochemical process above a conventional mechanical strategy. 

Rigid Polyurethane RPU

Are you looking for a manufacturing partner to use stereolithography?

Upload your 3D file, choose your material and get your instant quote!

For your resin parts, Sculpteo offers the best online 3D printing services. Parts ordered in Prototyping resin can benefit from an “express” mode. Orders passed before 15:30 (GMT + 1) will be ready for pick up or shipping by 11:00 am (GMT + 1) the following day in our factory. A perfect option if you’re in a rush and need to validate a project as quickly as possible.

Contact our 3D printing experts if you have questions about stereolithography and all the possible applications.  

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