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SLA 3D-Drucker im Einsatz
Details of additive manufacturing technologies

SLA and DLP 3D printing in comparison: Which process is the better one for your application?

Stereolithography and digital light processing are two similar 3D printing processes, but the difference lies in significant details. The different characteristics of both printing processes have their own individual advantages. In this article, you will learn exactly where the differences between stereolithography (SLA) and digital light processing (DLP) lie, what you can expect in terms of print quality and which process you should choose for you rapplication.

Similar 3D technologies with important details

Stereolithography (SLA)

Applications:

  • Rapid prototyping, functional prototyping.
  • Model making
  • illustrative or exhibition models
  • Design objects

 

Advantages:

  • Smooth surfaces
  • High accuracy
  • Low tolerances
  • Very small, fine components can be produced
  • Highly transparent components possible

Digital Light Processing (DLP)

Applications:

  • Prototypes
  • Spare parts
  • Injection thermoforming molds
  • Additive series production in the range of 100 to 1000+ pieces.

 

Advantages:

  • Very good surface quality
  • High detail accuracy
  • Even hollowed out parts can be printed
  • Large variety of materials
  • High printing speed
  • Quickly available results
  • Favorable unit price

The additive manufacturing technologies in detail

The SLA 3D Printing

Stereolithography is not only the oldest, but still one of the most precise 3D printing processes. SLA 3D printing was invented by Charles Hull back in 1984. In the SLA process, liquid photopolymers in the form of a resin are cured by a laser beam. The laser is moved in the horizontal axis over a resin shell, solidifying the material layer by layer, point by point. Modern SLA 3D printers work with two different approaches:

 

  • The platform with the resin shell is moved down the Z axis with each new layer - the laser here works from top to bottom.
  • The platform is moved upwards with each new layer on the Z-axis - here the laser works from bottom to top. In this process, the component is printed overhanging on its head.

The SLA printing process enables extremely smooth surfaces and thinnest layers with a thickness between 0.05 and 0.01 mm. In addition to high precision, this printing process also enables the creation of models made of composite materials or the combination of hard and soft materials.

 

DLP 3D printing

DLP printing is also an "old" process that emerged from image projection technology in the 1980s. DLP 3D printing, also known as LSPc (Lubricant-Sublayer-Photo-curing) depending on the manufacturer, uses a projector as the exposure medium. As with the SLA process, DLP 3D printing illuminates liquid photopolymer in a resin shell. However, a digital micromirror device between the projector and the surface of the resin enables highly accurate exposure of the entire layer in each pass. The individually controllable microscopic mirrors, which are installed on a semiconductor chip in the form of a matrix on the device, control the light extremely precisely so that the resin is cured with absolute precision.

 

A direct comparison of the additive manufacturing processes

Even though the printing processes of SLA and DLP are similar, and both methods deliver 3D prints with the finest details and smoothest surfaces, there are significant differences in a direct comparison that are crucial when choosing the appropriate printing process for a specific requirement.

 

 

 

Impact of the technology differences on the parts to be printed

 

Resolution

In 3D printing, resolution is distinguished between two-dimensional surface dimensions (X- and Y-axis) and layer thickness in the Z-axis. Both SLA and DLP offer the finest resolutions in the Z-axis and thus the thinnest layers of all 3D printing processes. Achievable resolutions for both SLA and DLP are in the range of 25 to 300 microns.

 

Differences are found in the resolution of the X and Y axes. In DLP printing, the resolution depends on the resolution of the projector and its distance from the so-called optical window. The projector determines the pixel size with which each layer of the model to be printed is produced. The most common resolution here is 1080p (Full HD). DLP 3D printers mostly offer a fixed resolution for X and Y. This is between 35 and 100 pixels. This is in the range between 35 and 100 micrometers.

 

In SLA printing, the resolution of the X and Y axes is defined by the step size of the laser beam and its dot size. The resolution is in the range of 25 micrometers.

 

The speed of 3D printers

In terms of printing speed, the advantages clearly lie with DLP printing. While in SLA 3D printing the resin is cured dot by dot, DLP allows printing of a complete layer. This advantage can be exploited in particular for the production of longer components or economical series production. In direct comparison, DLP is the decisive difference faster, which makes the process ideally suited for additive series production.

 

The build volume and maximum size

In both SLA 3D printing and DLP 3D printing, the build volume is always limited by the size of the tank containing the liquid resin. Another limitation concerns the so-called pull-off force. The larger the parts to be printed, the higher the forces that act on the printed object when the cured layer is detached from the tank. In terms of maximum build volume, the SLA process is ahead of DLP technology. Thus, on Jellypipe, a build volume of up to 1500x750x550mm is available in SLA, whereas in DLP the maximum is 380x200x310mm. (As of 03.03.2022)

 

The surface quality of additively manufactured components.

Both SLA and DLP are quite rightly regarded as the printing processes with the highest surface quality. Differences in surface quality can be seen primarily in the smallest details. In DLP prints, for example, rounded corners often appear "stair-stepped". The reason for this is the printing technology, which is based on rectangular pixels - so-called voxels. Nevertheless, the quality of DLP-printed components is high and roughly comparable to that of conventional injection molding.

Materials for 3D printed parts

Probably one of the most important selection criteria when deciding for or against a 3D printing process are the possible materials which a printed part is made from.

Some of the materials that can be processed with SLA 3D printing:

  • Accura 25:The material offers high detail resolution while maintaining high flex and impact resistance, a smooth surface and very good paintability.
  • ClearVue:(Image) The material is suitable for applications where transparency is critical. ClearVue has polycarbonate-like properties, is biocompatible and dental compliant, and enables printing of highly clear, translucent models.
  • Next: The material offers properties similar to ABS. It is high strength, brings high hardness and offers surfaces similar to thermoplastics.
  • Taurus: The material is characterized by high stability and temperature resistance.
3D-Druck Material xABS Black DLP

Some of the materials that can be processed with DLP 3D printing:

  • KeyGuide:Biocompatible material, especially for dental technology. The material can be polished and sterilized in an autoclave.
  • xMED412: The material offers high impact strength similar to polypropylene. It is biocompatible, easy to polish with a transparent finish and can be sterilized in an autoclave.
  • xPEEK147: This material is characterized by a very high temperature resistance of up to 230° C. The plastic is very dimensionally stable and features good surface qualities.
  • xCE-Black: This plastic offers high flexural strength and high temperature resistance.

Post-processing of the 3D printed parts

In all 3D printing processes with synthetic resins, post-processing of the printed parts is unavoidable. Especially for very filigree, fine models, support structures are necessary, which have to be removed manually after curing. Depending on the printed component, the post-processing tasks can be quite extensive - and should definitely be carried out by experts! In both the SLA and DLP printing processes, the manufactured parts must be cleaned of adhering resin after printing with isopropyl alcohol or tripropylene glycol monomethyl ether and then thoroughly dried. Depending on the area of application of the printed parts, additional grinding work as well as priming and painting may also be required. We strongly recommend having the finishing work carried out by specialists in order to avoid damage to the valuable parts. Just get in touch with us - we will be happy to advise you.

 

 

Areas of application for additive manufacturing technologies

The high quality of printed components makes both SLA and DLP printing particularly interesting for the dental and jewelry industries. In our portfolio you will find special resins optimized for use in medical applications. However, SLA and DLP are also frequently used in prototype construction, in the aerospace sector or for the production of injection molds.

 

Conclusion

Stereolithography and Digital Light Processing are two of the oldest, but also most precise processes in the field of 3D printing. SLA printing is ideal for filigree, small prototypes or demonstration models, whereas DLP printing can fully exploit its speed advantages, especially in the additive manufacturing of series parts. We would be happy to advise you in detail in a personal meeting on the specific advantages of both processes and the right 3D printing for your application. Just give us a call or write to us. We are already looking forward to soon being able to inspire you with our capabilities!

Autor

Markus Grimm
Chief Virtual Printfactory

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