SLA background

1. Define of SLA

Stereolithography (SLA) is the first method in the history of 3D printing which was invented by Chuck Hull( co-founder of 3D Systems). In1992, 3D Systems produced the first SLA machine.

2. Types of SLA

There are three main types of SLA: laser-based stereolithography (laser SLA), digital light processing stereolithography (DLP-SLA), and masked SLA (MSLA). For all these SLA, a tank of liquid resin is selectively exposed to light in order to form very thin solid layers that stack up to create one solid object.

• Laser SLA involved a UV laser solidifying photopolymer resin, a liquid with viscosity. This is the most popular in the world and we would introduce SLA according to laser SLA

  • Designer design 3D CAD model and generate the STL file;Translate to 3D printer's machine code that contains the information for each layer;
  • The build platform could move up and down in the tank of liquid resin. For the first layer, the distance from build platform to the surface of liquid is about one layer height;
  • Then a UV Laser irradiate across the print area of liquid resin( draw each layer of the object by two deflection mirrors driven by a motor, known as galvanometers (one on the X axis and one on the Y axis)) , solidifying resin as it moves along;
  • When a layer is finished, the platform moves one layer height and the sweeper blade re-coats the surface;
  • The process then repeats until the part is complete;
  • Once all layers are printed, the object needs to be rinsed with a solvent and placed in an ultraviolet oven to finish the process to get high mechanical and thermal properties. reference from formlabs

• DLP, similar with Laser SLA, they use light to solid layers that stack up to create one solid object. The difference is the light source. DLP use digital projector screen to flash an image across the resin tank at once, Thus all points of a layer can be cured simultaneously. So it would faster than laser SLA. In the meantime ,DLP has some limitation compare with SLA;

  • The DLP model similar with wax, the mechanical and thermal properties is low, so it can't be a true prototype in industry. But it can be a part of Lost-Wax process for jeweler;
  • The digital light projector has limited in resolutions. The model has minimum pixel size and surface quality is not good as SLA.
  • If we want get bigger model in some surface quality, we have to need high-definition projector but it lead to high cost;

• MSLA's light source is LED array, the light would irradiate across LCD panel(LCD panel is digital display and composed of square pixel, and the size of pixel would determine the precision of MSLA parts) ,then go to resin tank.Thus all points of a layer can be cured simultaneously.

3. Customer and Industry SLA 3D printer

There are two kinds of SLA machines depend on usage: Customer 3D printers include DLP, MSLA, and some desktop laser SLA. Most machines are desktop and designer can direct print model after design. Maker, designer and DIY would use them to make prototype, gift.

But industry SLA 3D printer would be more professional. It used in prototype test ,product. The following tab is the compare.

4. Benefits and limitations

SLA is very popular in prototype market because of the following, in the meantime there are some limitation during application benefits:

• It can offer higher resolution printing than many another 3D printing technology. You can get parts with fine detail and surface finishes.
• Similar with another 3D printing technology, SLA can easily make complex geometry which is impossible for traditional manufacturing. It is cool method for visual prototype;
• There are many different speciality SLA materials available for us , such as standard, clear, flexible, high temperature resistant;
• Normally, SLA 3D printer can finish 3D model in two days after confirm the data with vendor.

limitation

• The mechanical performance is not enough for functional prototype and product;
• The materials are limited compared with injection molding and CNC;
• For many material, the SLA parts' mechanical properties and color appearance would change minor

after some months. It may influence the usage;

• Most of SLA parts need support during SLA 3D printing, so it need post process and it will influence the surface and size. It need leave some space during design and manual experience in post process to reduce the influence.

5. Material

1 Material

There are many different speciality SLA materials available for us , such as standard, clear, flexible, high temperature resistant;

The table below show the description of application

6.Application

6.1. Rapid Prototyping

if designers own customer SLA 3D printer, they can quickly print the physical object after design.

* Verify initial ideals with low-risk quickly;
* After assembling functional prototype, designer can test the reliable and operation. 
* In this step we can choice material from rubber to rid, color from transparent to milky which is close to real production

• Pre- production: Before mass production, SLA can used in two aspects:
  • Direct make small batch：the cost in every may lower than injection molding or CNC;
  • We can use SLA to manufacture silicon rubber mold and it can use 20-100 times.So it can be used in small batch injection mold. Silicon rubber mold has advantage in cost and time comparing with steel mold.

6.2. Production

SLA has big advantage in some details(for example:channel in object ,complex shape). If we use traditional method ,the mold would be very complex; even we need cut one object to some piece, then manufacture and assemble them together, the workload is very high;

• Tool for mass production: For some injection object, its shape is complex and has high requirement in cooling, so engineer would design conformal cooling channels in injection mold. It will save cost and improve the quality.

6.3. Rapid mold

Some engine performance resign would have high performance in strength and wearing resistance，in the meantime it can be manufacture fast(1 or 2days，but tranditation stainless stell mold need at least 1month).So it is cool to make low volume product between prototype and mass production.

6.4. Customer production

Earphone's application in music especial for musician. Insole used for somebody have problem in foot,for example Diabetes foot， correct foot shape，etc

6.5. PDMS chip

PDMS chip can used in medical，biology ，chemistry test It build small space for test system