DLP (Digital Light Processing) and LCD (Liquid Crystal Display) are both resin-based 3D printing technologies, also known as photopolymerization. Both of these 3D printing processes use digital means to control the light source and the layer-by-layer solidifying of the liquid photosensitive resin, thus creating 3D objects.
Although they share the same resin-based 3D printing process, DLP and LCD 3D printing technologies differ fundamentally in their basic principles. This also results in differences between DLP and LCD 3D printers in terms of imaging quality, equipment durability, and overall post-processing costs.
Comparison of the Principles of DLP and LCD
DLP 3D printing technology utilizes a reflection-based projection method to create objects. First, the digital model of the printed object is sliced into countless layers using slicing software, and then we need to construct each layer to obtain the final print.
We can liken the entire DLP printing process to watching a movie. Each frame of the movie corresponds to each layer of the object to be printed. Imagine placing a miniature movie projector on a piece of photosensitive resin. During the ‘movie playback,’ each frame is projected onto the layer of photosensitive resin. The areas illuminated by light will solidify into a solid, gradually building up the shape of the object, layer by layer. The entire process is akin to gradually ‘stacking’ the object, ultimately completing the manufacturing process.
In more technical terms, DLP utilizes digital light processing to convert image information into digital signals. With the use of a digital micromirror device (DMD), which consists of millions of tiny mirrors, precise control of the light source can be obtained. By adjusting the tilt or rotation angle of this device, the desired image can be projected onto the surface of the resin. The light in this projection solidifies the resin on each layer it touches, layer by layer, ultimately constructing the desired physical object. In short, DLP 3D printing builds 3D objects layer by layer through projection and light-curing resin.
LCD 3D printing technology is based on the transmissive technology of liquid crystal display (LCD) to create objects. Similarly, before printing objects, we also need to use slicing software to slice the digital model into many layers, and then manufacture the final object through layer-by-layer construction.
Similarly to DLP, we can compare the entire LCD 3D printing process to playing a movie, where each frame of the movie corresponds to each layer of the object to be printed. However, it is important to note that, unlike DLP technology, LCD 3D printing is more akin to playing a movie on a television screen.
Imagine, on a piece of photosensitive resin, using a television to play a movie. During the « movie playback » process, each frame illuminates the resin layer. The subsequent building process is similar to DLP, where the resin layer exposed to light solidifies into a solid. The entire process is layered, ultimately forming a complete 3D object.
Technically speaking, LCD 3D printing technology controls imaging through a liquid crystal display (LCD) panel. LCD employs a UV LED array as the light source and utilizes the liquid crystal screen to control the orientation of liquid crystal molecules through the electric field effect, thereby controlling the brightness of pixels. When constructing each layer of the printed object, the liquid crystal units selectively block ultraviolet light, allowing only specific light to pass through and form the image to be printed for each layer. Through control of the liquid crystal display, the areas where light passes through cause resin curing, layer by layer accumulation, ultimately forming a 3D object.
The main difference between DLP and LCD principles
Based on the explanations of the two technologies above, DLP and LCD mainly differ in the liquid crystal screen vs. DMD, the way images are constructed, and the control of light.
(1) Differences in Display Technologies
LCD: Based on transmissive technology, it controls the direction of liquid crystal molecules through the electric field effect to adjust the brightness of pixels, thereby forming the projection of the video, similar to certain electronic watch displays.
DLP: Based on reflective technology, it utilizes a DMD device to control the reflection of light through the tilting or rotating angle of micro-mirrors, creating the projection image.
(2) Differences in Image Construction Methods
LCD: The liquid crystal screen constructs each layer of the image by selectively blocking ultraviolet light.
DLP: Images are constructed by adjusting the angle of the DMD micro-mirrors.
(3) Differences in Light Source Control
LCD: Adjusts the light transmission rate through the electric field effect of the liquid crystal, controlling the degree of light penetration.
DLP: Controls the direction of light reflection by adjusting the angle of the micro-mirrors.
(4) Response Speed
DLP: The tilt or rotation speed of DMD micro-mirrors is very fast, allowing for quick image switching.
LCD: The adjustment speed of liquid crystal molecules is relatively slow, resulting in a lower response speed.
Are 4K or 8K LCD 3D printers superior to 2K DLP 3D printers? Some drawbacks of LCD 3D printers.
(1) Surface Light Field Effect on LCD Displays
In LCD technology, lenses are used to adjust the direction of light propagation to generate the required parallel light. LCD lenses are typically arranged in an array, with each sub-lens responsible for a small area. This arrangement and organization helps to ensure the overall uniformity of the liquid crystal display image.
However, there are some gaps between the sub-lenses of the LCD array lens, which can cause light scattering and interference during light propagation. When the light is projected onto the surface of the liquid crystal display, these gaps may form streaky light fields or other optical issues. Although increasing the aperture ratio of the sub-lenses can reduce the occurrence of optical problems to some extent, they cannot be completely avoided (the aperture ratio refers to the proportion of the transparent area in the grating structure, that is, the ratio of the area through which light can pass to the total area; the higher the aperture ratio, the more light can pass through). In contrast, DLP technology using digital micromirror devices (DMDs) does not involve aperture ratio issues and therefore does not produce optical problems.
At the same time, if the matching between the lens group and the light source is not good enough, it will result in a large amount of crosstalk light, affecting the clarity of the image. To address this issue, the backlight system of LCD 3D printers can install gratings to block some of the large-angle light. This device absorbs the blocked light, further reducing the efficiency of the optical system, but it still cannot completely filter out the large-angle light, and there is a certain reflectivity.
At the same time, if the lens set is not sufficiently matched to the light source, it will cause a large amount of crosstalk light. An LCD 3D printing backlighting system can be installed by the addition of a grille to block part of the large-angle light, however the device absorbs the blocking light, further reducing the efficiency of the optical system, but still cannot completely filter the large-angle light and has a certain reflectivity.
(2) Low Light Efficiency
LCD projection uses liquid crystal chips to transmit light, making it difficult to completely block out light, resulting in lower contrast and mediocre performance in displaying dark details, and unable to achieve true black. From the imaging test charts of LCD and DLP, it can be observed that LCD has lower contrast and relatively blurry edges in the graphics.
The light intensity of 3D printing is weak, with only 10% of the light able to penetrate through the liquid crystal screen, while 90% of the light is absorbed by the screen. Additionally, as mentioned above, local light leakage can cause excessive exposure of the photosensitive resin at the bottom, requiring regular cleaning of the tank.
(3) Spot shift and superposition effects
LCD backlight modules typically consist of multiple UV LED light sources and a corresponding number of collimated homogeneous array lens. In this module, the central or edge light emitted by adjacent LED light sources is mapped onto the surface of the liquid crystal display in a cross-combining manner. This mapping process may result in spot shifts and superimposed effects between different light spots, thus forming complex light and patterns on the display screen, ultimately affecting the printing results.
(4) The phenomenon of light leakage
The liquid crystal display (LCD) is one of the core components of LCD technology, containing liquid crystal molecules and color filter films, among other parts. Due to slight differences in the intensity of multiple ultraviolet light sources, this may lead to insufficient uniformity of light leakage between pixels on the LCD screen. Light leakage refers to the penetration of light colors from the light source into adjacent areas, resulting in inconsistent colors. During the 3D printing process, this lack of uniformity may result in inaccurate curing of printing layers, thereby affecting the final print quality.
(5) The LCD Screen Aging
The UV light source is used to cure the photosensitive resin, but it also accelerates the degradation of organic materials in the LCD screen. This degradation over time can lead to a decline in the performance of the LCD screen, thereby affecting the accuracy of 3D printing. With the degradation of organic materials, issues such as decreased brightness and weakened contrast may occur in the LCD screen, thereby affecting the consistency of printing results.
(6) Low Curing Efficiency
During operation of an LCD 3D printer, the LCD screen absorbs most of the energy. This is because the irradiance is controlled at a lower level to prevent rapid degradation of the LCD panel. However, this also brings a problem: in the subsequent curing process, areas with lower curing levels due to lower irradiance may result in lower mechanical performance in the final printed parts.
Advantages of DLP Over LCD in 3D Printing Image Quality
The Difference in Optical Components: DLP utilizes a Digital Micromirror Device (DMD) as its optical component, which contains millions of tiny movable mirrors. Each mirror represents a pixel, and by adjusting its orientation, the reflection of light can be controlled to form images. In contrast, LCD uses liquid crystal units to control light transmission and blockage, and the size and arrangement of these units may have an impact on resolution and image quality.
Parallel Light Curing Process: DLP utilizes a DMD to control millions of tiny mirrors, with each mirror representing a pixel of the model. These mirrors can cure the entire layer simultaneously, enabling parallel processing. In contrast, LCD typically cures layer by layer or row by row, which may result in inconsistencies in details and curves within the image. The parallelism of DLP helps to improve printing speed and image consistency.
Uniform Illumination: The DLP system utilizes a light source to illuminate an array of tiny mirrors, ensuring uniform illumination. The state of each mirror (open or closed) is controlled by digital signals, allowing for more precise adjustment of the light intensity for each pixel. In contrast, the backlight of an LCD is typically evenly distributed across the entire screen, but may sometimes cause uneven light intensity in specific scenarios.
The contrast: DLP systems typically offer higher contrast, which refers to the difference in brightness between black and white. This can result in clearer, sharper images, which is crucial for handling details such as edges and microstructures of models. In some cases, LCD may experience lower contrast due to limitations in light transmission or the state of the liquid crystal.
Precision control: DLP systems can control the state of each pixel more precisely, including color and brightness. This enables DLP to excel in producing high-quality details in complex structures.
Why does the Raise3D DF2 have high-quality printing results?
1）Slicing Software ideaMaker Allows for Model Optimization
Raise3D’s slicing software ideaMaker, developed for the Raise3D DF2, incorporates powerful model optimization features based on enhanced algorithms. These include anti-aliasing, hollowing, punching, contour compensation, cup detection, automatic orientation, smart peeling stress analysis, and automatic generation of smart supports. These features help users optimize printing models, enhance printing details, and intelligently avoid certain aspects that may affect printing quality during the printing process, thereby achieving high-quality printing results.
Among these features, correct model positioning is one of the key factors in ensuring printing success. The “Automatic Orientation”, feature analyzes the model’s characteristics to provide users with optimal model placement suggestions, reducing the need for subsequent user adjustments and greatly enhancing printing success rates.
Moreover, any sharp changes to the gradient of model peeling stress will cause to a severe shrinkage and layer separation in the area. “Smart Peeling Stress Analysis” can assist users to identify the ‘dangerous’ regions to prevent failure before printing.
2）Optimized Resin Shrinkage Control
3D printing resin materials may experience shrinkage after curing, resulting in dimensional differences between the printed part and the original design model. The DF2 features optimized resin shrinkage control capabilities, which compensate for dimensional changes caused by resin shrinkage by making small adjustments to the boundaries of the part during the generation of the print path.
On the other hand, layer height compensation allows for fine-tuning in the vertical direction to control the impact of shrinkage on part dimensions. By optimizing resin shrinkage, it ensures a high level of consistency between digital models and actual printed parts.
3）High-standard Hardware Facilities
DF2 utilizes Texas Instruments’ first industrial-grade DMD chip specifically designed for 405nm 3D printing in its core light engine. Additionally, DF2 also adopts low-distortion glass, optimized for DLP technology lenses. The light density has reached 2.0mW/cm2. Furthermore, DF2 features a 402nm ±1nm curated LED light source with both active and passive cooling functions.
In terms of optical systems, the DF2 is equipped with high-transparency nFEP film. The protection glass is sourced from optical glass manufactured by Schott in Germany. Additionally, it utilizes front aluminum-coated reflective mirrors. The frame size error is ≤ ±0.1 mm, and the distortion rate is ≤ 0.1%.
Specially customized optical components can provide uniform light intensity and low distortion, thereby achieving more balanced printing speed, precision, and stability.
4）Automated System Calibration
To achieve better quality control of the optical system, the DF2 is equipped with an automated calibration system based on machine vision technology. The system uses metrology-grade instruments to perform all optical path calibrations for end-to-end frame size and distortion control, creating an enclosed optical chamber.
Conclusion
By comparing DLP and LCD 3D printing technologies, we can gain a more intuitive and in-depth understanding of their differences in working principles, imaging quality, and other aspects. DLP technology exhibits significant advantages in print quality and surface smoothness, making it more widely accepted by professionals and industrial-grade users. On the other hand, LCD boasts lower initial costs and is more suitable for applications with lower standards, but factors such as its fragile LCD screen and higher maintenance costs need to be taken into consideration.