The accuracy of 3D printing usually includes multiple aspects such as dimensional accuracy, resolution, surface accuracy, repeatability accuracy, detail accuracy, and geometric accuracy. The accuracy we usually refer to mainly refers to dimensional accuracy and resolution.
Dimensional accuracy: Dimensional accuracy refers to the deviation between the actual size of the part and the designed size, usually expressed by a ± value. For example, if the designed model size is 100mm, and the actual printed size is between 99.8mm and 100.2mm, then its dimensional accuracy is ±0.2mm.
Resolution: It refers to the minimum movement increment of the 3D printer in the three coordinate axes (X, Y, and Z). It is usually measured in micrometers (μm). Higher resolution means that the printer can move and print materials with greater precision in smaller increments.
Resolution can be divided into planar resolution (XY axis) and layer thickness. Planar resolution refers to the resolution in the X and Y axis directions, indicating the minimum point spacing that the printer can accurately measure in the horizontal direction. Layer thickness refers to the resolution in the Z axis direction, that is, the thickness of each layer, commonly ranging from 0.025mm to 0.3mm.
Currently, the accuracy of planar resolution can reach 2μm or even at the nanometer level, and the accuracy of the Z axis can reach around 5μm.
The accuracy of 3D printing depends on various factors, including printing technology, materials, equipment quality, and printing parameters. However, printing accuracy is still the most important influencing factor.
1. Machine accuracy
Machine accuracy is an extremely important parameter for 3D printers. This parameter can be used to determine which printer is more precise. Many manufacturers provide standard size accuracy to enable customers to manufacture their meticulously designed parts on machines with good performance.
2. Materials
Choosing the correct material for the object you need to print will significantly improve its printing accuracy. For example, compared to flexible SLA resin, standard SLA resin has higher size accuracy.
3. Object size
Generally, the printing accuracy of small objects is higher than that of large objects. Larger objects have a greater margin for manufacturing errors.
4. Warping and shrinkage
The process of 3D printing is very likely to cause materials to warp and shrink. Large areas of material, flat surfaces, and unsupported structures are prone to distortion, which should be avoided as much as possible in the final design.
5. Support structures
The presence of support structures is almost inevitable for achieving high accuracy. However, removing these support structures after printing will also affect the surface finish of the product, which is a trade-off.
6. Post-processing
The processing made in the final stage of printing may affect the accuracy of the end product. Sometimes, an appropriate cooling program is needed to keep the object in the desired shape. The choice of 3D printing process is mostly for achieving specific purposes. For example, prototypes are printed using FDM technology, and complex objects are made using selective laser sintering, etc. When choosing the process, consider the size accuracy. Even if a printing method has been selected, understanding the standard accuracy and common failure reasons will help optimize the design process.
The following is the description of the accuracy of common 3D printing processes.
1. FDM
Fused Deposition Modeling (FDM) is one of the most common 3D printing processes, often used for producing rapid prototypes or functional components. The layer thickness of FDM is generally between 0.05 and 0.3 millimeters, and the dimensional tolerance of industrial FDM printing is ±0.15%, with a minimum of ±0.2mm. FDM 3D printing creates objects by heating the nozzle to extrude thermoplastic. One layer is printed at a time, and these layers cool at different rates according to their size and structure. This can cause warping and minor changes in the final object, requiring materials with higher printing temperatures, such as ABS, which have a greater risk of warping.
2. SLA
Stereolithography (SLA) printing can produce smooth and visually precise components made of cured resin. The layer thickness of SLA printing can reach 0.025 to 0.1 millimeters, with a precision of ±0.05 millimeters or even higher. The dimensional tolerance of industrial SLA printing is ±0.15%, with a lower limit of ±0.01 mm. The resin used for SLA printing requires time to fully harden. When printing large, unsupported materials, they may deform under their own weight or the weight of the surrounding layers. At the final stage of the printing process, when the object is removed from the printing bed, the material may also warp.
3. SLS
Selective Laser Sintering (SLS) is a highly precise process, typically used for manufacturing complex geometries. The dimensional tolerance of SLS printing is ±0.3%, with a minimum of ±0.3 mm. SLS printing uses a laser to fuse the powder layers together. Although this process is more accurate than FDM, there is still a possibility that the layers will not cool at the same rate. This can lead to warping, especially in larger SLS components. The solution is usually to leave the object on the powder bed until it has completely cooled.
4. MJ
Material Jetting (MJ) is the most precise 3D printing process. The dimensional tolerance of material jetting is ±0.1%, with a lower limit of ±0.05mm. During the material jetting process, no heat is involved, so warping and shrinking problems are impossible. However, thin-walled and extremely detailed features may not be printed correctly. The objects made by MJ are not as durable as those made by FDM. When exposed to high temperatures or humid environments, they may warp.
5. Metal 3D Printing
Metal 3D printing is very similar to other 3D printing processes. The dimensional tolerance of metal printing is ±0.1mm. Although there are several different metal 3D printing technologies, the most common one is using a technology similar to selective laser sintering. The metal powder is heated and fused into layers, as these layers may cool at different temperatures, so warping is a consistent problem. Metal printing requires support structures, and usually, a thermal stress elimination treatment based on heat is used to prevent warping after production is completed.