Popular Science: Comparison of Common 3D Printing Technologies DLP, SLA, LCD, FDM

3D printing technology, also known as additive manufacturing technology, refers to the technology of generating three-dimensional entities by continuously stacking physical layers and adding materials layer by layer. This is different from traditional material removal processing techniques.

Today, we will introduce and compare four of the more common technologies: SLA, DLP, LCD, and FDM. Let's start with an overall comparison table for a first look. (Article compilation and writing by RAYSHAPE)

I. SLA (Stereolithography) 3D Printers (Article compilation and writing by RAYSHAPE)

SLA technology is the first-generation mainstream photocuring technology. It has various translations and names, such as stereolithography, stereoscopic printing, optical modeling, etc. SLA is not only the earliest rapid prototyping technology to emerge and be commercialized in the world but also one of the most deeply researched and widely applied rapid prototyping technologies.

The basic principle of SLA technology mainly involves using an ultraviolet laser (355nm or 405nm) as the light source and a galvanometer system to control the laser spot scanning. The laser beam draws the first layer shape of the object on the surface of the liquid resin. Then, the build platform descends by a certain distance (typically between 0.025mm and 0.1mm), allowing the cured layer to be submerged in the liquid resin again. This process is repeated until the physical object is completely printed.

II. DLP (Digital Light Processing) 3D Printers (Article compilation and writing by RAYSHAPE)

Digital Light Processing (DLP) emerged more than ten years after SLA technology. It is also recognized in the industry as the second-generation photocuring technology and has a development history of over 20 years. DLP technology is a rapid prototyping method that creates 3D printed objects by curing liquid photopolymer resin layer by layer using a projector.

This technology first uses slicing software to slice the 3D model into thin layers. The projector then projects images of these layers (like playing slides) onto the resin. Each layer image induces photopolymerization in a thin region of the resin, forming a solid layer of the part. The build platform then moves by one layer thickness, and the projector projects the next image. This cycle continues until the printing is finished, resulting in not only high precision but also very fast printing speed.

III. LCD (Liquid Crystal Display) 3D Printers (Article compilation and writing by RAYSHAPE)

LCD photocuring technology actually emerged around 2013. It is characterized by relatively inexpensive, open-source core components, but these core components are consumables.

Let's first talk about its principle. Compared to DLP technology, the simplest way to understand it is that the light source in DLP technology is replaced by an LCD screen; everything else is basically similar. The imaging principle of the LCD panel involves light passing through RGB color filters (which filter out infrared and ultraviolet light that can damage the LCD panel). The separated RGB light then passes through three liquid crystal panels to synthesize the projected image.

This technology requires the use of high-power ultraviolet light for curing. Only a very small amount of UV light passes through the LCD screen to cure the resin. LCD screens themselves are sensitive to UV light and age quickly when exposed. Besides withstanding heat and the challenge of high-temperature dissipation, this core component must endure hours of intense radiation from high-power 405nm LED arrays. Therefore, its lifespan is quite short. With frequent use, the LCD screen, the core component, often gets damaged within one to two months. If used improperly, it might need replacement in just a few hours.

IV. FDM (Fused Deposition Modeling) 3D Printers (Article compilation and writing by RAYSHAPE)

Fused Deposition Modeling (FDM) is a 3D printing technology developed after LOM and SLA processes. The technology was invented by Scott Crump in 1988, who subsequently founded Stratasys. In 1992, Stratasys introduced the world's first FDM-based 3D printer, the "3D Modeler," marking the commercialization of FDM technology.

Principle: Filamentous thermoplastic material is heated until molten and then extruded through a nozzle with a fine orifice. The printhead can move along the X and Y axes, while the build platform moves along the Z axis (mechanical designs may vary between different machines). The extruded molten material bonds with the previous layer upon deposition. After one layer is deposited, the build platform descends by a predetermined layer thickness, and the steps are repeated until the part is fully formed.

Advantages and Disadvantages of FDM

• Advantages: The overall system is simple in construction and operation, with low maintenance costs and safe operation. It can use non-toxic materials, allowing the system to be installed and used in office environments. The process is clean, simple, easy to operate, and generates no waste. The unique water-soluble support technology makes support removal easy and straightforward. It enables the rapid construction of bottle-shaped or hollow parts, as well as pre-assembled structures. Raw materials are supplied in filament spools, making them easy to handle and quick to change. A wide variety of materials are available, such as various colors of engineering plastics like ABS, PC, PPSF, and medical-grade ABS.

• Disadvantages: Lower forming accuracy compared to SLA, typically around 0.178mm. Surface finish is not as smooth as SLA. Relatively slower build speed.

V. Differences Between SLA and DLP Technologies (Article compilation and writing by RAYSHAPE)

Both SLA and DLP use photopolymer resin as consumables, and their working principles are quite similar. Therefore, the industry often tends to view them as similar technologies when studying 3D printing processes. However, there are still differences in many aspects.

1. Mechanical Structure: DLP uses the digital light source from a projector, while SLA uses an ultraviolet laser light source.

2. Printing Speed: Due to its working principle—using a digital micromirror device to project the cross-sectional image of the part onto the surface of the liquid photopolymer resin, curing the irradiated resin layer by layer—DLP printing is very fast. In contrast, SLA uses a laser beam to draw the object point by point and line by line on the resin surface to form the solid model, making its efficiency significantly lower.

3. Printing Accuracy: Theoretically, both technologies can achieve micron-level accuracy. DLP can achieve a minimum feature size/spot size of around ±50 microns, while SLA can achieve around ±100 microns. Higher power SLA lasers can easily lead to larger spot errors. Achieving micron-level precision with SLA places very high demands on the core components (laser and galvanometer), making domestic galvanometers often insufficient and significantly increasing costs for micron-level accuracy. Comparatively, achieving micron-level accuracy is easier with DLP. In summary, DLP printing accuracy is generally considered higher than SLA.

4. Print Size: Limited by the resolution of the digital micromirror device, DLP can typically only print smaller-sized objects compared to SLA.

Overall, both technologies have their pros and cons. However, in practical use, DLP 3D printers often demonstrate clear advantages.