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The 3D printing FDM technology
Jan 25, 2018

You have a tube of toothpaste, and the toothpaste is hot, and you squeeze it out and you freeze it.Will you connect this toothpaste with upside down, on a level above crowded level direction, with the writing brush calligraphy, waiting for you to finish the work on the surface of the later, the plane suddenly dropped a bit, then in the second plane toothpaste, you before you come out of toothpaste and toothpaste stick together, you kept repeating the above process, the first toothpaste extruding curing, after becoming out of toothpaste.This is FDM!


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In 3d printing, FDM mechanical structure simple, design is the most easy, the manufacturing cost, maintenance cost and material cost is the lowest, so also is in household level desktop 3 d printer technology used most widely, and industrial-grade FDM machine, mainly represented by Stratasys products.

FDM technology has the advantage of simple manufacturing, low cost, but the desktop level of FDM printers, due to the discharge structure is simple, it is difficult to precisely control the material form and forming effect, at the same time for FDM molding temperature effects is very large, and FDM to desktop class 3 d printers are generally lack of thermostatic equipment, so the level based on FDM desktop 3 d printer product accuracy to 0.3 mm to 0.3 mm, usually a small number of high-end models can support 0.1 mm thick, but affected by the temperature is very large, the result is still not enough stability.In addition, most of the FDM models produced products are layered deposits have an edge effect "" steps, more difficult to achieve what you see is what you get 3 d printing effect, so the high accuracy requirement of less using FDM rapid prototyping domain.


The process principle of FDM.

FDM fusion layer deposition technology has been patented by STRATASYS in the developed countries of the world.The basic principle of FDM INSIGHT is to automatically stratify 3D mathematical models (from CATIA or UG, PRO-E and other 3D design software) to automatically generate model path and necessary support paths for each layer.The supply of materials is divided into model materials and supporting materials.The corresponding hot melt head is also divided into model material sprinkler head and supporting material sprinkler head.Hot melt head will get ABS material heated to 220 ° C into molten state, due to the molding chamber to keep 70 ° C, the temperature of molten ABS material can have good liquidity and can guarantee accuracy.After a layer of molding is completed, the machine table drops a height (that is, the layer thickness) to form the next layer.This is until the artifact is completed 



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The process of processing each product of molten deposition modeling technology, from the initial modeling to the final processing, is as follows :

(1) establish a three-dimensional CAD model of the forming parts.For 3 d CAD model data is the true information of the virtual description, which will serve as a rapid prototyping system input information, so before processing to make good use computer software to establish von berg systeme three-dimensional CAD model.This 3d model can be accomplished through Solid Works,Pro/E, UG and other software, and these software has good universality.

(2) approximate treatment of 3d CAD model.In order to facilitate the subsequent data processing and reduction of computation, we first need to approximate the 3d CAD model.Here we use the STL format file to approximate treatment model, its principle is to use a lot of small triangle plane instead of the original surface, equivalent to the original face of all the quantitative processing, and then use the normal vector of the triangle and its three unique identifier for each triangle vertex coordinates, can choose the size of the small triangle by controlling and to meet the precision requirement of what we need.Because of the convenience and convenience of STL format files and convenient data storage, this kind of file format has been widely used in the process of rapid prototyping.And computer aided design software has the function of output and conversion of this format file, which also speeds up the application and popularization of this data format.

(3) slice processing of 3d CAD model data.Rapid prototyping actually completes each layer of processing, and then the workbench or printing head occurs corresponding position adjustment, and then the layer of accumulation.So to get each layer of the print head, you have to get the data for each layer.Therefore, the model of the approximate treatment is sliced and processed, the section information of each layer is extracted, the data files are generated, and the data files are imported into the rapid prototyping machine.When slicing, the thickness of the slice is smaller, the quality of the forming parts is higher, but the processing efficiency is lower, while the molding quality is low and the processing efficiency is improved.

(4) the actual processing molding rapid molding machine under the control of the data file, each layer data information gained by the print head, in accordance with the scanning step by step, one layer of accumulation, finally complete the whole processing of von berg systeme.

(5) the post-processing of the forming parts is taken from the printer, and it is also needed to support, polish and polish, so as to further improve the printing quality.


Research status of FDM

At present, the companies that study this technology abroad mainly include MakerBot, Stratasys, 3D Systems, Israel's Object company, etc.Among them, Stratasys is in the position of leader. In 1993, it launched the world's first commercial model, the fm-16_50 rapid prototyping machine, and then introduced the serial products of this model.

MakerBot company as the leading enterprise personal level 3 d printing equipment and technology is, according to the space in the computer scan on the plastic thin layer coating raw materials, layer upon layer adhesion accumulation, forming a three-dimensional model of high accuracy.Its star product Replicator 2 has been selected as the world's best desktop 3D printer in the past, and its advantages in control, algorithm and materials are huge compared with previous generations.It launched its fifth generation product in 2014.But its sales have been disappointing.So far, though, MakerBot still occupies an important position in the personal 3D printing device.

Stratasys is a leading manufacturer of 3D printers and a supplier of rapid prototyping and manufacturing application production systems.The company's patents include FDM (R) and PolyJet (R) (i.e., direct production of prototypes and finished products from 3D CAD files) and other 3D printing related technologies.The system includes economical and affordable desktop 3D printers for concept design, a series of prototype mechanism building systems, and large-scale production systems that are directly digitized.More than 130 species, 3 d printing material is most types of 3 d printing materials company in related industry, including more than 120 kinds of proprietary inkjet photosensitive polymeric material and 10 proprietary FDM based thermoplastic materials.Stratasys also manufactures Solidscape 3D printers and RedEye for on-demand digital manufacturing services.Israel the Object of the company as the world's ultra-thin layer thick photosensitive resin injection molding technology leader, creating ObietPolvJetMatrix technology, has realized the different model material injection technology at the same time, the material used is a mixture of ABS and thermoplastic plastics, the main products are 1200 es Dimension.It is reported that the two companies merged in 2012 and the new company continued to operate with the name Stratasys.

 

3d systems is the inventor of the SLA (Stereolithography) technology, and at the same time. The STL file format of the patent owner, and a selective laser sintering of SLS, more injection Modeling (Multi - jet Modeling) and membrane transfer imaging (film transfer imaging) technology.In the products based on FDM technology, 3D Systems has introduced a 3D printer Cube series for personal use, which is known for its simplicity and high reliability. The printed materials used are ABS and PLA.



Advantages and disadvantages of FDM technology and improvement methods.

Advantages of FDM [3] :

1. The manufacturing system can be used in the office environment without the danger of gas or chemicals.

2. Can quickly build bottles or hollow parts.

3, plastic wire, clean easy replacement: compared with other using powder and liquid materials process, silk material is more clean, easy to change, save, not near the equipment or in the form of powder or liquid pollution.

4. Without laser, maintenance is simple and cost is low: price is an important factor of whether the forming process is suitable for 3d printing.The 3d printer used for the concept design is not high on the prototype precision and physical chemistry characteristics, and the low price is the decisive factor for its promotion.

5. Various materials can be selected, such as staining ABS and medical ABS, PC, PPSF, etc.

6. Simple post-processing: it takes only a few minutes to a quarter of an hour to remove the supporting prototype.

Disadvantages of FDM [3-4] :

FDM type 3d printers, although after decades of development and has been widely used, but it still has many deficiencies, such as forming low accuracy, slow speed of print, low degree of intelligence, and the use of raw materials such as restrictions.

Defect 1: low molding precision and slow printing speed.This is the main limiting factors of FDM type 3d printers, however, because of the shape precision and is inversely proportional to print efficiency relations, namely high speed printing for low precision products, print at low speed for high precision products, blindly pursue high precision will make the print speed greatly reduce, this is not the industry.Therefore, to solve the problem of low accuracy and slow, both get enough attention, must be made at this point, we can make new technologies compatible and inherit the old technology, namely the increase of material manufacture cut cut material manufacturing technology, in particular, is the application of traditional machining to the 3d printing molding process, and low accuracy of printing process, ensure molding speed, and then used to remove material measures to ensure accuracy.

Defect 2: control system intelligence level is low.Although the FDM technology of 3d printer operation is relatively simple, but in the process of forming, still there will be a problem, which requires to operate machinery and technical personnel with rich experience, to observe the forming condition, because when abnormal molding process, the existing system can't identify, also does not automatically adjust, if not to human intervention, will cause cannot continue printing or a defect in the artifact, the restriction on operation will affect the popularity of 3d printing.Intelligent 3d printers are, therefore, very important, "intelligent recognition and feedback function" 3d printing system is the urgent need, can from the development of the software for 3d printers have self-learning function, finally realizes the 3d printer to "3d printing robot".

Defect 3: printing materials are more restrictive.At present there are many defects in the printing material, according to the above materials, you can see the material types and environmental protection problems are gradually solved, however, there are still many aspects to be further improved, such as FDM with printed material is easy to be affected with damp be affected with damp, forming process and forming after some shrinkage rate, etc.Be affected with damp be affected with damp, printed material will affect the melt extrusion flow, easy cause nozzle clogging, against the workpiece forming, therefore, used to store, FDM printed material to seal to take when using the appropriate drying process;Plastic material after melting solidification process, there are contractility, this problem is mainly caused by the print process workpiece warping or fall out and print after the completion of the workpiece deformation, affect the machining accuracy, the printing material, waste improvement measures mainly choose the material with low shrinkage rate, the constant temperature tank, etc.

 


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