3D printing can turn 3D modeling files in the computer into real objects. The printing process needs no intervention and the precision is far more than manual production. It sounds and uses pretty cool. Although they have been on fire for a long time, they are still mysterious in front of the public. Considering that many people don't really need it, but also have the urge to cut their hands, it is better to send science popularization.
This paper will carry out simple science popularization and literacy on 3D printing and 3D scanning from the aspects of "principle, classification, software and core components, printing process, accuracy, availability".
Principle and technical advantages
3D printing is a technology that creates 3D objects by stacking thin layers. Its key word is thin layer stacking. Through different principles, raw materials are formed and stacked layer by layer.
Although it sounds tall, the principle is probably just a nozzle that can move on the XY axis plane to precisely control the position of raw materials. After one layer is completed, the platform moves down (generally 0.1mm) and then another layer is completed until the entire finished product is printed.
Compared with traditional processing methods such as milling machine (cutting materials from outside to inside through milling cutter), melting casting (pouring into mold after melting), the biggest advantage of 3D printing is that it can produce finished products with complex internal space, and the utilization rate of materials is close to 100%.
Type of 3D printing
Classification of 3D printing principles and advantages and disadvantages
Print precision comparison
According to the different principles of raw material forming, the cost ranges from low to high, including deposition forming, photosensitive curing, powder bonding, and laser sintering. Their working principles are as follows:
Fused Deposition Modeling (FDM, full name of FDM), the nozzle heats, melts and extrudes the filamentous hot melt material, and the material solidifies after encountering the printing platform with lower temperature, forming the final product by stacking layer by layer.
SLA (Stereolithography Apparatus) irradiates the photosensitive resin material through ultraviolet light and other light sources to let it solidify layer by layer and form a complete finished product through layer by layer stacking. It is the earliest developed, most mature and widely used rapid prototyping technology.
Powder bonding (3DP, full name of Three Dimensional Printing and Gluing) sprays the adhesive on ceramic/metal/plastic powder and other materials through the nozzle, repeats the process of powder spreading, spraying and bonding, and obtains the finished product layer by layer.
SLS (Selecting Laser Sintering) is similar to the mixture of the above two technologies. It uses high-power lasers to irradiate metal powders and other raw materials to make them sintered/fused. Continue to repeat the process of powder spreading and sintering until the whole mold molding is completed. It is the 3D printing often mentioned in the industry.
Among the laser sintering and powder bonding technologies with the highest cost, there are very few desktop models, and even desktop products have not yet appeared. The price of models using UV curing technology generally rises from 20000 yuan, so the current civil 3D printers are basically using the lowest cost deposition molding technology, and many manufacturers can even control the price at about 2000 yuan. Therefore, they with the lowest threshold are the protagonists of this popular science article.
control software
In addition to the core mechanical parts, the printer also needs 3D modeling files that ultimately control the movement of the print head to work. Although the printers are basically equipped with display screens and control buttons, the 3D modeling files needed for printing still need the help of computers. Medium and high-end products can generally connect to computers and have special clients, while low-end products generally omit the connection function and can only print by reading the files in the SD card.
The 3D printer can only read the 3D modeling files that have been sliced (about equal to slicing the 3D digital model into N layers), and can directly convert them through the. stl. 3w format files output by 3Dmax, CAD, MAYA and other modeling software.
The material library and modeling website of many manufacturers' websites can find ready-made 3D modeling files, and users with software foundation can model by themselves. In addition to manual operation, the most popular gadgets for entry-level users are naturally mobile phone cases, pendants and other gadgets.
Description of core components
The key word of 3D printing is thin layer stacking. For 3D printers of deposition molding technology, the print head that can move in a two-dimensional plane is responsible for "thin layer", and the platform that can move up and down is responsible for "stacking". There are not many core components. Take the newly evaluated Sanwei da Vinci 1.0 AiO as an example:
The print head is a heating device that can move accurately on the XY track, which can heat and melt ABS/PLA materials. There is a gear pressed into the raw silk inside and a cooling fan behind it. The machine is driven by belt, the print head can move left and right on the X axis, while the print head and the entire X axis are mounted on the Y axis.
The printing platform is a glass plate with heating function, which can accurately control the moving up and down. The maximum heating temperature is 90 degrees (to prevent the ABS raw materials falling on the platform from sticking due to the low temperature). The power source is the motor at the bottom. Generally, there will be positioning points for calibrating the position and screws for adjusting the horizontal posture of the platform (forward tilt and backward extension, etc.) on the side of the platform.
raw material
In terms of raw materials, ABS resin and PLA (biodegradable plastic polylactic acid) materials are mainly made into wire rods (1.75mm) with fixed diameter and tied to the wire drum. The price is generally about 200 yuan/1kg. Some manufacturers will use box packaging and add chips at the bottom to provide the function of recording the type of raw materials and residual quantity, which will be more convenient to use, but the cost will naturally be higher.
Both materials can be dyed with different colors. Their use is different in melting point. ABS melting point is about 220 degrees. It is opaque and matt, and has higher strength. The platform needs to be heated to 90 degrees to form normally, but it is toxic. When used, it will have the smell of plastic burning. In addition, it has greater thermal shrinkage and lower precision of finished products
The melting point of PLA is about 200 degrees, so the energy consumption during processing is lower, the speed is faster, and its translucent texture is more bright. The platform can be formed normally when heated to 45 degrees. It is non-toxic, environmentally friendly, and almost odor free. ABS is slowly being eliminated as the main printing material.
Printing process and maintenance
Before printing, the platform should be coated with solid glue, which serves as a barrier to facilitate the removal of the final finished product. The first step of printing is to heat the print head and the platform. The time consumption varies with the machine power. Machines below 500W can generally heat the print head in 1-2 minutes, but the platform takes about 5-6 minutes to rise from normal temperature to 90 degrees.
Then, the printing platform can start printing when it reaches the highest point. The process is repeated for many times: linear printing materials are heated and melted in the print head, flow out in a fluid state, and harden and stick after contacting the printing platform. The moving track of the print head will be "recorded" by these materials. After one layer is completed, the platform moves down, and the machine prints the second layer until the entire object is printed.
Raw materials can be dyed, but the deposition molding printer can only print objects with solid color or horizontal color change by changing raw materials halfway. So it is generally to print parts of different colors of the finished product separately, and then assemble them like models.
During operation, only three motors of XYZ axis and the cooling fan of the print head make little noise. However, if ABS resin is used, additional ventilation measures are required.
The desktop printer can be used directly after unpacking, but if the use time is too long, the finished product and the platform are always too tight and need to use a shovel and force, you need to level the printing platform by yourself. Otherwise, the molding quality may be affected. In serious cases, the print head may collide with the platform and cause deformation. In addition, the long used print head is also quite dirty, and occasionally I have to use iron wire to "defecate" the material outlet.
Scanning function
Now some high-end models of entry-level computers begin to have the 3D scanning function, which can scan objects and generate 3D modeling files, through which you can copy the same product again.
3D scanning can be divided into contact and non-contact. The former uses traditional measuring points to contact objects to collect spatial information, with high accuracy and cost, and extremely slow speed; The latter mainly uses laser, low-frequency acoustic wave, etc. for indirect scanning, which is fast but of general accuracy, and generally requires multiple scans for data correction.
3D scanning process
Scan files
Currently, laser scanning devices are usually built into printers. The scanned object is placed on a rotatable platform, the scanner sends out a laser plane to hit the scanned object, and the receiver calculates the space point data for removing the object according to the reflected light.
Unfortunately, even the scanning function of the 10000 yuan printer is basically unavailable. There are many restrictions on the scanning function. The material characteristics that will make the light scatter abnormally will almost affect the scanning effect. The final effect will be affected if the object is too low in height, too dark in color, too many color types, too smooth in surface, too complex in pit, and too deep in interior.
It is certainly not a problem to use it to scan simple geometry, but if you want to use it to scan complex manipulations, even as high as models, it is almost hopeless
In addition, models with more 3D scanning functions are generally 3 to 4000 yuan more expensive than native models, which is too expensive, so it is not recommended to purchase derivative models with 3D scanning functions.
Printing speed&precision
At last, I came to the core of 3D printer. The 3D printing speed is much slower than normal people think, but it is also easy to understand: if the printing thickness of each layer is 0.1-0.4mm (the raw silk extruded is 0.1mm wide), the product printed 1cm high will have to print more than 25-100 layers
The printing time is proportional to the printing accuracy/layer thickness, and because the raw material threading speed is fixed, their printing time is easy to calculate. As a reference, when the precision (layer thickness) is 0.3mm, it takes 30 minutes to print a 4g hollow case. If the printing task is a palm sized one and weighs more than 100 grams, the printing time will exceed 12 hours.
Actual printed sample
In terms of printing accuracy, many people think that the finished product of 3D printer can be used as the final product, but this is only for the printer formed by UV curing. The products of the other three types of printers are more like blanks. If the requirements for shape and accuracy are high, the finished product itself is still polished again.
What's more sad is that the lowest cost deposition molding printer has obvious bonding traces between each layer, commonly known as "step effect", resulting in its surface being quite rough. After seeing the works of the entry-level deposition molding printer, perhaps many users will have a certain psychological gap.
Actual Availability&Limitations
Although the thin layer stacking principle of 3D printing can cope with many complex internal structures, it also brings corresponding restrictions:
Inadequate transverse strength: no matter which principle the printer is, they are stacked in thin layers in the longitudinal direction, so the transverse strength will be far lower than the longitudinal strength;
Additional support mechanism is required for small down and large up objects: Due to the influence of gravity, it is impossible for 3D printing to print suspended objects, so additional printing supports or frames are required under suspended objects;
To print products with multiple colors, only change the raw materials or print separately in the middle;
The printer of deposition molding can only print finished plastic products, and the hardness of finished products is limited. Only powder bonding and laser sintering can print ceramics, metals and other products with real industrial use;
Contradiction between precision and speed: the thinner the thin layers stacked, the longer the number of layers and time required, and the speed can only be improved by working multiple nozzles at the same time.
summary
3D printer is still an emerging product. Although the principle of deposition molding printer is relatively simple, the water between different brands and product lines is deep. Before purchase, you need to have a simple understanding of common parameters. As for the deposition molding printer, there is not much room to choose. The printing head design below 10000 yuan is basically single printing head design, and ABS and PLA raw materials are supported.
The print size, the more natural the size, the higher the price, while the print size of the 10000 yuan printer is generally below 20 * 20 * 20cm; In terms of accuracy, 3D printers below 10000 yuan can basically reach 0.1mm layer thickness, and the printing speed (wire speed) is between 0.2-0.5mm/s.
At the end of science popularization, it is suggested that everyone should have a "big heart" and not have too high expectations for 3D printers below 10000 yuan. Although their threshold for hand chopping has fallen below 2000 yuan, they still have a strong toy nature. Their main purpose is to help enterprises and geeks test samples and save high mold opening costs. Normal users need to be cautious about hand chopping.
