Binder Jetting (AKA: 3dp or powder bed and inkjet head 3d printing) metal 3D printed densified single alloy have little difference in their starting time at home and abroad. According to reports, Desktop Metal, HP, GE and etc. started to develop this technology in the past five years or so, and Exone was earlier. In China, EasyMFG has been focusing on binder jet 3D printing technology since 2013, and now has already commercialized and has been applied to some industries successfully. In this article, Dr. Cai Daosheng, founder of EasyMFG, will explain in detail the current challenges in the application of binder jet metal 3D printing technology.
Cai, Daosheng, CEO of EasyMFG
Overview of R&D of 3D printing technology for binder jetting metal 3d printer in China
Binder jet metal 3D printing technology has significant advantages of high speed, low cost, and high precision, and it is booming in foreign countries, especially in 2018, BJ was rated as one of the "Top Ten in the World" by the "MIT Report" Breakthrough technology".
More and more domestic teams have begun to pay attention to this technology, and some teams engaged in binder sand printing and powder metallurgy technology have also begun to try to develop this technology. Guangdong and Hubei provinces have included this technology as a key special project for support. But so far, only reports of EasyMFG’s basic application in this field have been seen in China, and tests have been conducted in many industries.
Although binder jetting and surface forming (LCD, DLP) 3D printing are very popular currently, people still have a lot of deficiencies in the understanding of this technology. Since the initial binder jetting was only used to print gypsum, the technique was considered to be poor in accuracy and strength. For binder jetting metal 3D printing, even some professionals mistakenly believe that this technology cannot be used for high-strength densified metal parts.
In fact, many materials with this technology have achieved high density, performance indicators that meet the vast majority of application scenarios; For scenes with special high-performance requirements, it can also be improved by heat treatment or hot isostatic pressing, and parts produced by vacuum sintering can basically achieve complete densification due to the vacuum state of internal voids by hot isostatic pressing.
Based on the in-depth analysis of the binder jetting technology and the previous ten years of 3D printing development experience, EasyMFG, with the technical support of Huazhong University of Science and Technology, has been focusing on the development and application of binder jetting since 2013. With the goal of realizing mass application, we started to develop binder jet metal printing technology in 2016 and successfully printed densified alloy steel parts in 2017.
It has realized the complete independent development of materials and processes from slicing software, printing data processing, inkjet printing control to binder and sintering process.
Judging from the current development status of domestic binder jet metal 3D printing technology, EasyMFG is currently the only team that has mastered the complete set of technologies from software to materials and sintering processes and has begun to try and apply it in multiple application scenarios. Within this year, batch applications will be realized in some areas.
Binder jet metal 3D printing technology is very complicated, and its complexity lies in not only too many basic sciences involved but also too many factors affecting the performance and accuracy of the final part. In addition to the software, control, and other technologies required to develop 3D printing technology, it is very important to master the binder, metal materials, sintering process, and the law of mutual influence. Due to the many influencing factors of the sintering process, it takes a lot of experiments to produce qualified parts continuously and stably, then we can conclude a set of definite process methods. Even if in the same material and print parameter background, we get different parts with different performances by using the same sintering furnace with different temperature curves. Not to mention any changes in any steps in the actual production process may cause differences in metal powder composition, particle size distribution, the difference of binder composition and proportion, temperature difference, the difference of heat transfer.
Binder jetting metal 3d printer: Easy3dp-M500
These differences, combined with the influence of gravity and friction during sintering, can easily cause the performance and size of the final part to vary greatly.
Through the development in recent years, the industry's understanding of binder jet metal 3D printing has improved. At present, people have believed that this technology can produce densified and high-performance parts. The main concerns about this technology are deformation and accuracy.
During the sintering process, the part will shrink, then be densified. And as long as the shrinkage is consistent, it can be compensated by software. To achieve consistent shrinkage, it is necessary to achieve consistent material, uniform sintering temperature field, and consistent influence of external force. The influence of external force is basically gravity and the friction generated by it. The influence of gravity and friction is also the most difficult to completely solve. In order to solve the shrinkage consistency problem, different teams adopted different methods according to their own understanding. Through these methods, most parts can be solved in terms of precision control.
Test part with the size of 3mm produced by Easy3dp-M500
At present, binder jet metal 3D printing is not good at manufacturing thin-walled parts, or branch tree-like parts, etc.printing technology that can be applied in industrial batches. Its fast speed, low cost, and digital flexible manufacturing characteristics will surely make it occupy a large proportion in the manufacturing industry. Of course, it also has its weaknesses. These weaknesses are basically caused by problems that the sintering process cannot or are difficult to overcome the influence of gravity and friction: for example, they are not good at processing large-area thin-walled parts without supporting
From the above analysis, it can be seen that in order to realize the real application of binder jet metal 3D printing, it is necessary to put forward the target requirements according to the actual application, select the metal material and the binder, print out the preliminary parts with the corresponding parameters, and then select the appropriate sintering Process to obtain parts, and may even require heat treatment process, and finally handed over to the application side for testing. During the entire production process, any change in any influencing factor may have a great impact on the final performance and accuracy of the part. This requires a large number of printing and sintering experiments in advance to determine a set of programs before the application can be finally realized. Coupled with the wide variety of materials and the changing application requirements, this determines that it will take a long time for the binder jet metal 3D printing to realize mass applications.
Looking at all the companies engaged in binder jetting metal 3D in the world, almost no company has achieved mass application within five years. At present, everyone is in a similar state, and most of them are in the testing stage of a certain application scenario. It is expected that a breakthrough may be made at any time within one year.
It is different from the application characteristics of SLM, any breakthrough in any application scenario for BJ, even if it is limited to China, maybe an application scale of billions to tens of billions.
Since the emergence of binder jet metal 3D printing is aimed at batch applications, it must be developed in the direction of high-speed printing, continuously improve the printing accuracy, enrich the types of materials, and pay attention to environmental protection requirements.
It is based on the above ideas that EasyMFG has carried out the research and development and application promotion of binder injection technology. In the first three years from 2013 to 2015, the company started from scratch and developed printers based on the existing mature application materials (gypsum and sand molds). In 2016, the first consideration was to develop a new high-precision plastic 3D printer and then to gradually develop metal printing. However, based on the suggestions of partners, the focus was on metal printing. After two years of exploration, the first metal part was manufactured in early 2018.
After nearly six years of development of binder jetting technology, EasyMFG's understanding of binder jetting technology has also risen to a higher level, and based on its understanding, the inkjet printing system and software have been fundamentally upgraded to solve the problem of data processing and transmission issues. After 2018, printing and sintering experiments will be carried out almost every day. After tens of thousands of experiments, we have accumulated enough experience and understanding in iron-based powder printing and sintering. The density of printed 316L and 304L parts can reach 99%. The tensile strength can get to 600Mpa, and the elongation is >60%. Starting from 2021, the R&D focus has been on the development of high-speed, high-precision printing and environmentally friendly binder materials. At present, a complete set of printing, materials, and sintering technologies have been mastered. Several key technologies with distinctive characteristics are summarized as follows:
1、Large data volume and high-speed data processing software: Inkjet printing uses dot matrix data. When the 3D printing slice data is converted into high-resolution dot data, the data volume of one layer can even reach more than 1G, which takes up a lot of computer memory, especially large-format high-speed one-pass printing will directly cause the computer to crash. Therefore, it is necessary to output the print data in real-time based on the slice data online RIP to ensure the fineness of the printed ink droplets, while occupying a small amount of memory, and fine adjustment of the ink volume can be achieved.
2、Self-adaptive nozzle hole blocking inkjet printing method: According to the clogging of the nozzle, it can automatically print with small misalignment between different layers and tolerate printing defects caused by clogging of some nozzles.
3、Highly compatible spreading powder compaction technology: The powder spreading system is compatible with metal powders of different particle sizes and different morphologies.
In the process of powder spreading, the powder falls and is compacted by the roller, so as to achieve a uniform and compact powder spreading the whole working surface, reducing the impact of powder spread on the formed parts The impact. This is extremely important for large-table working cylinders. On the basis of ensuring the uniformity of spreading powder, it can increase the density of spreading powder by 5-10%.
4、High-speed printing system: When the nozzle hole width is only equal to the printing width of the working cylinder, printing can be completed without stopping the powder spreading, which greatly reduces the printing time, and the overall processing time is equal to the powder spreading time.
5、High-precision printing method: The printing accuracy of the sliced contour can reach 1200DPI. The ink droplet size and ejection speed are adjusted through the nozzle waveform and ink drop modification technology to achieve a stable inkjet while reducing the impact of ink droplets on the metal powder to achieve the best ejection effect.
6、Low carbon residue environmental protection binder: The new water-based environment-friendly binder has very low carbon residue and is suitable for the mass production of carbon-sensitive metal materials.
It is precisely based on the thinking of the driving force of the "industrial revolution" that the goal of EasyMFG is to develop a technology that has sufficient influence on the manufacturing industry. Binder jetting 3d printing is the most valuable industrial application of universal technology solutions. Once the raw material cost of this technology approaches two to three times that of the raw material cost of precision casting (a goal that will soon be achieved), many precision casting parts within tens of kilograms will be switched to binder injection 3D printing.
Therefore, we imagine a scenario: For metal parts, when people choose manufacturing methods, if the parts are relatively simple, use CNC technology; if the parts are relatively complex, use binder jet 3D printing; if the parts are large and heavy, choose the casting method; if the precision is relatively high, the binder jet 3D printing and casting are combined with CNC. For other 3D printing technologies, we should regard them as "special processing technologies", technologies with certain special features.