文献综述
1 BackgroundThrough mask electrochemical machining was first born in the 19th century by the printers and artists who wanted to process the surface of metal plates for writing or painting on them, due to the lack the technology and methods, it was carried out a series of studies. 1840, British scientists Thomas Spencer and John Wilson has provided the first thesis about electrochemical etching, which described a method of processing metal plates using electrolysis. Subsequently, William Grove demonstrated a method of etching silver-plated copper plates in a lecture at the London Electric Society in 1841. It was a modification of the daguerreotype process, one of the earliest imaging methods, which was created to be used for the reproduction of photographs. The following year, Gottfried Osann published his experiment results in Germany which described the process of etching experiments and showed the results he obtained. [1]This shows that the development of electrochemical processing has been uninterrupted since its inception, which confirms the safety and potential of this process. With the development of technology, good machining quality and precision are essential to manufacture and further explore new technologies or products. An example of this is the aero-engine. As technology and times advance, the reliability, lifespan, fuel efficiency and thrust of aero-engines have become more demanding, which makes the structure of aero-engines more complex and more difficult to machine. [2]2. Electrochemical machining Electrochemical machining is a method of processing metals by using Faradays Law and the phenomenon of electrolysis. In electrochemical machining, the workpiece acts as the anode and the tool as the cathode, both of which are immersed in an electrolytic solution and the workpiece is electrolysed into the desired shape under the influence of an external power source and the cathode. Based on this machining principle, electrochemical machining has the following characteristics.1. There is no direct contact between the tool and the workpiece during electrochemical machining, therefore no cutting forces are generated during the machining process, no residual stresses or burrs are generated on the surface of the machined part and therefore there is theoretically unlimited on the number of times the tool can be used2. The heat generated by the process is carried away by the electrolyte and the part is machined without temperature rise, making it suitable to manufacture heat-sensitive materials3. Due to the isotropic nature of the workpiece, electrochemical machining allows multiple parts to be machined at once and the surface of the workpiece to be optimised at the same time, which makes electrochemical machining relatively efficient4. Electrochemical machining is theoretically independent of the physical properties of the workpiece therefore it is often used to process difficult-to-machine materials [3]5. Anodic dissolution is a chemical reaction at the atomic level and therefore electrochemical processing by electrolysis is highly accurate Due to the nature of electrochemical machining, electrochemical machining has always been used in the machining of many parts. In addition, there were many blisks made in different materials, research shows us the blisk made in hard-to-cut materials and dense cascade passages hold 45% in the application of blisk and which was manufactured by ECM, where 10% of blisk with large size and multiple blades by Linear friction welding (LFW), 45% of blisk with easy-to-cut material and sparse cascade passages by high-speed cutting (HSC). [2] However, electrochemical machining also has many limitations, such as the difficulty in improving the accuracy and stability of electrochemical processing due to the number of influencing factors, which made the control of the machining process difficult. In addition, stray corrosion caused by stray currents during processing can affect the accuracy and surface quality of the workpiece [4], but in general electrochemical machining, the generation of stray currents is unavoidable. Scientists or academics have therefore focused on improving electrochemical processing, and this has led to the creation of a range of processing methods based on electrochemical machining. 3. Through mask electrochemical machiningThrough mask electrochemical machining (THECM) is a processing method derived from electrochemical processing, which has the characteristics of electrochemical processing and improves on it. TMECM is an electrochemical process that protected the surface of the workpiece that does not need to be machined by a protective film to further improve the accuracy of the process. In machining, the mask protects the unmachined parts of the workpiece from stray corrosion, which also makes it possible to machine the surface finished parts.This also extends the range of applications for electrochemical machining in advanced technologies such as micromachining, surface micro-structuring and large area array structures. Surface micro-structuring is a modern method of enhancing the physical properties of materials, allowing us to modify the frictional properties, corrosion resistance, self-cleaning ability and other properties of the material. [5] Large-area array structures are currently used in aerospace, transportation, electronics and information technology, where it is widely used in the machining of these important mechanical component structures. However, due to the dense arrangement of the array structure and the large volume of the structure, high processing accuracy requirement, TMECM is one of the processing methods that meet the processing requirements.TMECM is a variation method on electrochemical processing, and there was also a lot of improvements have been proposed based on TMECM. As an example, there is an article in the Journal of Manufacturing Process on the use of electrically insulating masks and micro-drills to improve micro-hole processing. [5] However, the disadvantages of this method are obvious, which is the low processing efficiency, the fact that only one micro-drill can be used for the machining of one micro-hole and the high cost of the micro drills used as tools. Among the various existing methods of TMECM, the processing application of large-area template array technology is currently one of the most promising electrochemical processing methods. The array structure is a common structure with the main functions of improving frictional properties, improving thermal conductivity, improving liquid flow, etc. Automatic Through mask electrochemical machining is a highly efficient process that is often used in technologies such as cluster hole processing, micro-pit arrays and surface texture processing. It is a type of TMECM, which is characterised by its ability to handle large area arrays of structures. However, due to the area and accuracy required, the difficulty of control, accuracy and stability requirement, the influence in the machining process that must be considered increased dramatically.Automatic through mask electrochemical machining is based on the same principle as TMECM, with the process being divided into two main parts, electrochemical machining and photo-etching of the film. Photo-etching is used in the processing of masks. Photo-etching takes advantage of the fact that photoresists exposed to a specific spectrum of light will (positive photoresist) or will not (negative photoresist) be dissolved by the developer solution, and the arrays of holes in the film are processed by controlling the light exposure. These arrays of masks are then applied to the electrochemical process as a protective film. Unlike normal electrochemical processing, although investigations have indicated that the application of masks is effective in preventing lateral corrosion [6], it still cannot prevent undercutting, uneven current distribution, etc., which will affect processing accuracy. In addition, the supply of electrolytes is one of the most important factors affecting the quality of electrochemical processing. The electrolyte carries away the heat generated during the process and the precipitates that can hinder the process, and also acts as a medium for conducting ions, so a stable supply of electrolyte is key to ensuring the quality of processing throughout the electrochemical process. However, the large-area array structure manufactured by automatic through mask machining further increases the difficulty in stabilizing the electrolyte flow. On the other hand, automatic through mask machining has a great deal of scope for improvement and is highly adaptable, for example, there are many different approaches to improve the electrolyte flow and uniform electrolyte distribution. As an example, the Chinese Journal of Aeronautics and MDPI has recorded two different approaches to ensure the uniform flow and distribution of electrolytes. The first method is to improve the flow channel of the electrolyte by designing a serpentine flow channel through calculations and experiments, which is effective in allowing the electrolyte to flow at a uniform rate within the channel, thereby improving overall processing accuracy. [7] The method of the article published in the MDPI is to replace a cathode tool with high porosity and then inject the electrolyte into the tool, which distributes the electrolyte evenly over the machining area with the porosity of the tool. [8][9] Both methods are effective in improving the uneven distribution and flow rate of the electrolyte, thereby improving the overall machining accuracy. These two improvements are both aimed at enhancing the flow of the electrolyte. But in practice, there are many different parameters to be considered in automatic through mask electrochemical machining, where different control parameters and improvements are based on the different machining purposes. The main parameters to be considered in the machining process are the electric field strength, the flow of the electrolyte, the type of current (direct current/ pulsed current), the duty cycle of pulsed current and others. However, improvements are not only limited to these parameters, for example, the modification or replacement of the flow channel, application for a different type of mask or the addition of a nozzle is also a very common and effective method. In electrochemical machining, electrically insulated masks are the most common type of mask, but in specific processes, such as micro dimples, micro-grooves etc., a conductive mask is also applied to reduce the impact of undercutting on the workpiece. [8][10] This is because the conductive mask can disperse the electric field concentrated at the boundary of the machining area, slowing down the anodic electrolytic reaction in the area and thus giving a result with a better etching factor (EF) value. In addition, the choice of the mask must also take into account the manufacture (lithographic, chemical or others) method of the mask, the fit of the mask to the workpiece, how the mask is removed, etc. The primary use of masks is to avoid stray corrosion during machining by separating the surface of the workpiece from the electrolyte, but as the explored in this field, they have found that masks can be used not only to prevent stray corrosion but also to improve the quality and efficiency of machining. Similarly, the design of automatic through mask electrochemical machining has been considered from a holistic perspective, rather than being limited to a variety of standardised processes, and these designs have yielded good results.4. SummaryFrom the description, we know there was many parameters or condition factors that can affect the machining quality, such as current distribution, type of voltage (pulse/direct current), the flow of electrolyte, type of mask (metallic/insulated), and others. From these experiments or research, we can find out the relationship between these parameters and the machining quality; thus, it was helpful to us to make improvements in the machining process. To find out how TMECM works, it was essential to know about ECM; because TMECM is a type of ECM, they have a similar machining process. Hence the article about ECM is carried out in this report to help us understand the character of machining and what should we mention in the machining process. It is essential to learn from a basis that allows us to know faster and more profound. After that, the TMECM and TMEMM are carried out further information. The difference between TMECM and TMEMM is about the size of the workpiece; where TMEMM is about to manufacture a microsystem, TMECM is used to machine small or micro-products. Furthermore, different surface textures and functions have been developed by using TMECM; it was used to improve the products properties to obtain a more durable and robust product.In conclusion, TMECM is a modern and potential machining method that people take attention to in the research to improve this method, it is valuable to figure out a more effective method by analysing and improving the different machining methods from these different articles.Reference:[1] Journal of The Electrochemical Society, Volume 165, Number 16, Through-Mask Electrochemical Micromachining, T. Baldhoff, V. Nock and A. T. Marshall[2] Chinese Journal of Aeronautics, Volume 34, Issue 2, 2021, Pages 28-53, ISSN 1000-9361, Electrochemical machining of complex components of aero-engines: Developments, trends, and technological advances, Zhengyang XU, Yudi WANG[3] Chinese Journal of Aeronautics, Volume 30, Issue 3, 2017, Pages 1231-1241, ISSN 1000-9361, Analysis of the current density characteristics in through-mask electrochemical micromachining (TMEMM) for fabrication of micro-hole arrays on invar alloy film, Da-som JIN, Kwang-ho CHUN, Eun-sang LEE[4] Journal of Manufacturing Processes, Volume 59, 2020, Pages 366-377, Electrochemical micromachining of the micro-hole using a micro drill with a non-conductive mask on the machined surface, Hang Zou, Xiaoming Yue, Haixuan Luo, Baohui Liu, Shiyi Zhang,[5] Surface and Coatings Technology, Volume 401, 2020, 126277, ISSN 0257-8972, Through-mask electrochemical micromachining of micropillar arrays on aluminium, Yankui Sun, Siying Ling, Danyang Zhao, Jiyu Liu, Ziai Liu, Jinlong Song,[6] Electrochimica Acta, Volume 364, 2020, 137300, ISSN 0013-4686, Research on the synergistic effect of megasonic and particles in through mask electrochemical etching process,Ke Zhai, Liqun Du, Shuxuan Wang, Yikui Wen, Junshan Liu,[7] Chinese Journal of Aeronautics, Volume 32, Issue 4, 2019, Pages 1051-1058, ISSN 1000-9361, Improvement of machining consistency during through-mask electrochemical large-area machining, Guoqian WANG, Hansong Li, Chao ZHANG, Di ZHU,[8] Procedia CIRP, Volume 95, 2020, Pages 787-792, ISSN 2212-8271, Through metallic mask electrochemical micromachining of micro-groove with a porous cathode, Xiaolei Chen, Guochao Fan, Krishna Kumar Saxena, Jun Qian, Dominiek Reynaerts[9] Micromachines (Basel). 2020 Feb; 11(2): 188., Through-Mask Electrochemical Micromachining with Reciprocating Foamed Cathode, Chenhao Zhao, Pingmei Ming, Xinmin Zhang, Ge Qin, Jiwen Shen, Liang Yan, Xingshuai Zheng, and Jun Cao[10] Journal of Materials Processing Technology, Volume 257, 2018, Pages 101-111, ISSN 0924-0136, Jet electrochemical machining of micro dimples with conductive mask, X.L. Chen, B.Y. Dong, C.Y. Zhang, M. Wu, Z.N. Guo,
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