Wang Lianfeng, senior engineer of Shanghai Aerospace Technology Research Institute, once said: Today's 3D printing , like the Internet in the 1990s, has accumulated front-end technology and hardware to a certain extent. Once developed, the application scale and output value of the back-end will be difficult to break out. The enormous energy of imagination. Nowadays, more and more people are beginning to contact and use 3D printing technology . However, when using ordinary desktop 3D printers , the printing accuracy is not satisfactory and is criticized. So in the 3D printing process ( FDM technology), what factors will affect the molding accuracy (including dimensional error, geometric error and surface roughness, etc.)? I have listed seven aspects. 1, material shrinkage The material undergoes a solid-liquid-solid 2 phase transition during 3D printing. When the material is solidified, the stress deformation caused by the shrinkage of the material will affect the accuracy of the formed part. If the material in the forming process is determined, the error can be eliminated by setting the "shrinkage compensation factor" in the three directions of x, y, and z in the slicing software. 2, nozzle temperature and forming chamber temperature The nozzle temperature determines the bond properties, build-up properties, wire flow, and extruded wire width of the material. It should not be too low, so that the viscosity of the material is increased, the speed of extrusion is slow; nor can it be too high, the material is biased to liquid state, the viscosity coefficient is small, the fluidity is strong, and the extrusion is too fast to form a precisely controllable filament. Therefore, the setting of the nozzle temperature should be selected within a certain range according to the properties of the wire to ensure that the extruded wire is in a molten flow state. The temperature of the forming chamber affects the thermal stress of the formed part. If the temperature is too high, although it helps to reduce the thermal stress, the surface of the part is easy to wrinkle; and the temperature is too low, the quenching of the wire extruded from the nozzle will make the formed part The increase of thermal stress is easy to cause warpage of parts. In order to form smoothly, it is better to keep the temperature of the forming chamber at 55 °C when printing ABS. However, if the PLA is used, it is better to keep the ventilation and heat dissipation as much as possible. 3, layer thickness That is, the layer thickness/layer height when slicing, because each layer has a certain thickness, it will produce obvious step marks on the solid surface after forming (the higher the layer thickness is, the more obvious), which will directly affect the dimensional error and surface of the formed body. Roughness. For the FDM process, this is a principle error. It is impossible to completely eliminate the step. The step effect can only be reduced by setting a small layer thickness. 4, the amount of compensation This refers to the distance between the actual machining contour of the part and the ideal contour. For models with high precision requirements, the general modeling should try to give compensation, especially the inner hole. The setting of this value is related to the diameter of the extruded wire, machine performance, etc., and you need to explore it yourself. 5, extrusion speed and filling speed Within the reasonable matching range of filling speed, as the extrusion speed increases, the cross-sectional width of the extruded filament gradually increases. When the extrusion speed increases to a certain value, the extruded filament may adhere to the outer conical surface of the nozzle. To the outer surface of the model, affecting the appearance. When the filling speed is faster than the extrusion speed, the material is insufficiently filled, and the yarn breakage occurs, making it difficult to form. On the contrary, the filling speed is slower than the extrusion speed, and the fuse is deposited on the nozzle, so that the material of the forming surface is unevenly distributed, and the surface is flawed, which affects the quality of the molding. Therefore, the filling speed and the extrusion speed should be matched within a reasonable range, and should satisfy vj / vt = a1 - a2 (wherein: a1 is the critical value of the occurrence of broken filament; a2 is the phenomenon of adhesion Critical value; vj is the extrusion speed; vt is the filling speed). 6, forming time The forming time of each layer is related to the filling speed, the size of the layer, and the complexity of the shape. If the layer area is small, the shape is simple, and the filling speed is fast, the time for forming the layer is short. On the contrary, time is long. Too fast forming will affect the printing effect. When printing, the forming time of each layer is controlled to obtain a high-precision molded part. 7, open and close delay That is to say, the start-stop effect of wire accumulation is mainly manifested by the change of the wire cross-section. The inconsistency of the pile-crossing section is likely to cause unevenness of the wire stacking plane, and defects such as voids and wire drawing. The most common "brushing" phenomenon can seriously affect the outer surface of the print and is very cumbersome to handle. The flatness of the wire stacking surface in the filling layer, if it is solved, the wire speed can be matched in real time to track the scanning speed, and the scanning speed can be adjusted accordingly to make the wire accumulation stable and reliable, and increase the wire accumulation. quality.
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7 factors that affect the accuracy of 3D prints
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