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Understanding SLA 3D Printing

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Stereolithography 3D printing, also known as SLA 3D printing, refers to the technology that turns photoreactive liquid (generally referred as resins) into solid parts by curing them with a light source in a process called photopolymerization. Presently, the most common SLA 3D printers are Laser-Based SLA Printers, DLP (Digital Light Processing) Projector Printers and LCD Printers. These printers, although utilizing the same light curing technology, are differ in its light source and light directing methods. They also produce different print outputs. 

All SLA printers use UV 3D printing photoreactive liquid, which are poured into a tank, so called VAT. The liquid solidify, layer by layer, upon exposure to UV light, against the build platform and are engineered to solidify under predetermined UV light power with specific solidification depth and width, which are generally known as print definition. Strong UV light power results in faster solidification time. However, stronger UV power has other side effects, such as light-fragmentation that could cause ragging, rashing and over-curing. A weaker UV light takes longer time to solidify the liquid, hence, longer print time. When the UV light power is too weak, the needed penetration depth is insufficient, resulting in weak bonding between layers, inability to adhere to the build plates or failed prints.


Laser-Based SLA Printers

With concentrated laser light power, the fine laser light provides effective depth penetration. The finer the laser spot, the finer the print definition. Laser is an effective way of delivering UV energy to the 3D printing liquid for solidification. Through galvo optic system, laser-based SLA printers are able to deliver a larger print area compares to DLP projector printers. However, as the print size increased, so is the print time for laser-based printers. What laser-based SLA printer lacks in speed, it makes up by large volume detailed prints. It allows for larger, detailed prints as well as many intricate prints that are spread across the build platform.


DLP Projector Printers

DLP projector printers achieve faster prints, as they project lights on an entire layer rather than connecting dots to form a layer as in laser-based SLA printers. However, DLP projector printers often lack the UV penetration power when compare to laser-based printers. To compensate this effect, the photoreative liquid are engineered to give quicker solidification reaction than those for laser-based printers, so proper penetration depth may be achieved. A quick reaction liquid could potentially do more harm to Vat’s PDMS or Teflon film and causes print to bleed (unwanted solidification). Second, DLP projector printers generally have smaller build area vs. laser-based SLA printers. For DLP projector printers, the larger the print area, the bigger the pixel size gets and weaker the light power, resulting in degrading of print definition. However, with well-controlled small print area, DLP projector printers can produce some truly intricate prints.


LCD Printers

Combining LED array with LCD screen, this hybrid printer is to capture the best of low cost, fine definition and large print area. LED and LCD are lower cost and matured components. While the UV LED power continues to cost improve, the UV light penetration through LCD screen is low, and slow to improve. Thus, the high power LED is not as effective due to low UV penetration rate of LCD screen.

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