The following article is from the two-machine power first
Siemens Energy is one of the largest technology companies founded in the early days of electrification and has grown with the progress of electrification, maintaining a leading position in technological development for more than a century, thanks to the regular evaluation and timely implementation of new technologies. This is an introduction to the additive manufacturing of gas turbine components from Siemens Energy.
Additive manufacturing from Siemens Energy
Siemens Energy's SGT6-9000HL gas turbine weighs 497 tons (1,095,000 pounds) and generates 593 megawatts. More than 63% efficiency can be achieved in the combined cycle. Every small improvement in efficiency is valuable – minimal downtime is just as important as long service life. However, there is a contradiction between these goals: the efficiency of a gas turbine increases with an increase in the combustion temperature, but an increase in temperature leads to a decrease in the performance of the gas turbine.
A few years ago, Siemens Energy introduced additive manufacturing (AM) technology in the production of turbine components to increase combustion temperatures and reduce maintenance time, and plans to apply AM technology to the production of around 200 parts by 2025.
In April 2019, more than 20 people from Siemens Energy worked full-time in additive manufacturing technology in Berlin. It is part of Siemens Energy's global strategy to implement additive manufacturing in the fields of gas, power and related services, with larger additive manufacturing centers in Finspoon, Sweden, Worcester, UK, and Orlando, Florida, USA. The team in Berlin focuses on material qualification for additive manufacturing and the integration of AM technology with conventional service and production processes.
Make AM the standard manufacturing route
At Siemens Energy, AM technology is introduced at three different stages of the product value chain: rapid technical validation, product production and component repair. In recent years, AM-based rapid prototyping technology has been established, enabling it to evaluate new blade cooling options in months rather than years.
The main driver of this technological revolution is the replacement of traditional casting by laser powder bed melting (L-PBF) forming, saving a lot of time. Laser powder bed melting, also known as selective laser sintering (SLM), is the gradual formation of parts in a powder bed. AM brings a completely new workflow, such as turning continuous development steps into parallel processes, with radical structural changes that can quickly achieve previously time-consuming and costly product development goals. In this way, AM reduces development cycle times by 75% while significantly saving costs for hot gas components such as turbine blades and burner components (Figure 1).
Figure 1 The SGT5-8000H gas turbine is equipped with additively manufactured burner nozzles and turbine blades
AM is used for maintenance and repair
As early as 2013, Siemens Energy introduced AM technology into the maintenance, repair and overhaul of its products. As with prototyping, a key driver for the introduction of AM technology in maintenance and repair is the significant reduction in handling time and costs. In addition, the replacement of traditional repair processes opens the door to design upgrades of critical components. The repair of AM applications to parts is a marker for the transformation of AM technology from laboratory to industrial applications.
A typical example is the repair of burner ends, where AM technology reduces lead times by 90% compared to conventional repair techniques. The ends of the burner are most susceptible to heat and heat radiation in the combustion chamber (fig. 2), where fatigue and oxidation often occur within 10 mm of the end. The traditional method of servicing is to cut off the damaged area 120 mm from the burner end (red line location in Figure 2) and weld new burner pipes (including fuel lines and meters).
Figure 2 Gas turbine burner repair
Based on the SLM plant, Siemens Energy has developed a matching AM process that makes the repair process faster and more economical while maintaining full component reliability. When servicing a burner with SLM, only 20 mm of damage is cut off from the top of the burner (purple wire in Figure 2) and the pre-treated burner to be repaired is placed in the SLM machine, where a camera precisely identifies the position of the burner end surface and generates the corresponding CAD repair model, which is then gradually additive to create new ends on the burner surface to be repaired.
The repair process development also includes other supporting technologies such as quality assurance and inspection methods, powder recovery and reuse, mechanical integrity calculations, etc. In addition, the SLM equipment needed to be properly adapted to accommodate the entire 720 mm burner and camera system. The modification of the SLM plant will have an impact on powder handling and airflow within the equipment.
The quality assurance system for this process was developed to ensure process reliability and complete traceability of test volumes, process settings and powder batches repaired by each burner under all conditions. To track this data, Siemens Energy adopted digital solutions and launched Manufacturing Execution Systems (MES) according to the latest standard of Siemens Energy Simatic IT "Unified Architecture (UA)".
Siemens Energy AM repairs the repaired burner without failure after more than 35,000 hours of operation. In addition, the burners after the refurbished operation have undergone rigorous non-destructive and destructive testing. Inspection tests showed that the oxide layer was up to 50 μm deep and that the hardness of the repair material between the guide hole and the burner tip changed very little. The SLM process is now considered a well-established technology and the process of choice for repairing burners.
Siemens Energy has also certified a number of other repair methods, such as laser metal deposition (LMD), which uses powder sprayed from nozzles instead of powder beds to manufacture structural parts. Siemens Energy has used LMD technology to repair blades as an alternative to traditional welding technology.
AM parts manufacturing
AM is extremely attractive in the production of spare parts: it can be used for the production of discontinued parts or even for the manufacture of parts based on reverse engineering. Compared to the casting process, AM has a much shorter lead time and is basically a tool-free process. For the manufacture of small batches of parts, the economic efficiency is particularly significant, but post-processing increases costs. The full potential of AM can only be fully exploited if structural design optimization is included.
Due to the complexity of its construction, the additive manufacturing of the constituent parts of the combustion system would be a very interesting thing, an example of which is the additive manufacturing of the combustion head of the SGT-1000F gas turbine (Figure 3). This part is part of an ignition burner that mixes fuel and air to create an ignition flame. Traditionally, it is an investment casting made of nickel-based superalloys.
Figure 3 Burner head manufactured using SLM technology
The entire AM process development includes the setting of SLM process parameters, material data evaluation, performance evaluation, prequalification, and process and product qualification (PPQ).
Two impressive discoveries were made during the process development. First, comparing the additively manufactured part prototype with the cast standard part, it was found that the material static mechanical properties and fatigue properties of SLM parts were substantially improved. Further dimensional testing revealed a maximum deviation of 0.2 mm for the additively manufactured part, which is much higher than the forming accuracy of the casting.
During the process prequalification phase, manufacturing trials are required to obtain the best print path scheme for the part, including the required support structure. These are closely related to the final print time as well as major cost factors.
During subsequent process and product qualification, the setup of the entire manufacturing process was investigated, including all required post-processing steps such as heat treatment, separation of printed parts from the substrate, and non-destructive testing.
Siemens Energy now has several AM-manufactured commercial combustion chamber components covering gas turbines of all power classes, with increased performance and cost savings, such as a reduction in lead time of around 15% for the SGT-700/800 gas turbine burners through a new AM optimized design.
Summary and requirements
AM allows for completely new design structures, which are decisive for further improving turbine efficiency and component durability. As a result, there are few alternative to AM technology to develop and produce new turbine components that withstand higher temperatures and thus achieve greater efficiency.
In addition, AM has been introduced into after-sales service and maintenance of Siemens Energy products, and the repair process is becoming more and more mature. The concept of "spare on demand" based on AM technology, where AM manufactured parts run without failure after thousands of hours of operation, has also been promoted.
AM technology is already involved in prototyping, production and maintenance in turbine manufacturing and beyond. While Siemens Energy's ultimate goal is to make AM technology as simple as printing on paper today, there were some issues during the development of the AM process:
- Standard AM equipment and its processes need to be standardized. Many AM equipment manufacturers focus only on the market for their products and pay little attention to commercial manufacturing and maintenance requirements or standards, and are unable or unwilling to develop and publish standardized SLM documentation. In the field of traditional welding processes, welding process specifications are a very critical document that must be standardized. Therefore, in the field of AM, standardization should be paid enough attention.
- Quality control. A large number of test specimens need to be prepared for different AM process quality assessments. Quality management using big data generated by various sensors and software based on digital twin technology will save time and materials, thereby greatly increasing productivity.
- Software. Several different software packages, from engineering to production, need to be integrated into one platform. For rapid prototyping, sophisticated simulation software analyzes heat flow and the resulting tension and warpage. By comparing simulation and actual manufacturing results, engineers can achieve fast and timely validation and optimization of processes.
- For production processes, it is important to connect different systems according to the workflow. While the original part can be designed in a regular CAD program, it requires a support structure designed for AM manufacturing in a second tool. The actual AM device may also require a CAM file from the third program. Siemens Energy has developed a specific toolkit within its NX system that connects CAD, CAE and CAM modules.
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On June 20, the signing ceremony of strategic cooperation between the Chinese Mechanical Engineering Society and the National Additive Manufacturing Product Quality Inspection and Testing Center was held in Beijing. The two parties will carry out all-round cooperation in various fields such as additive manufacturing (3D printing) group standard revision, technology research and development, application and promotion of scientific and technological achievements. The Chinese Mechanical Engineering Society decided to set up the secretariat of the Additive Manufacturing Technology (3D Printing) Group Standards Working Group Working Group at the National Additive Manufacturing Quality Inspection Center.
Lu Daming, Vice President of China Mechanical Engineering Society, Bao Jun, President of Wuxi Institute of Inspection, Testing and Certification, and Director of the National Quality Inspection Center for Additive Manufacturing Products, attended the ceremony and delivered speeches respectively.
Vice Chairman Lu Daming welcomed Director Bao Jun and his entourage to attend the signing ceremony, and introduced in detail the development history of the China Mechanical Engineering Society as a national 5A society for more than 80 years and the main work carried out in recent years, and placed high hopes on the in-depth cooperation between the two sides.
Director Bao Jun highlighted the achievements of the National Additive Manufacturing Quality Inspection Center in capacity building, qualification, standardization and service industry development in recent years, and put forward the idea of group standard revision in the field of additive manufacturing.
The teams of the two sides also conducted in-depth discussions and reached consensus on group standard research, industry technology research and development, scientific and technological information collection, enterprise demand docking, high-tech promotion, technological achievement transformation and other related matters.
The leaders of both sides said that they will take this strategic cooperation signing as an opportunity to give full play to their respective platform and resource advantages, jointly promote the technological progress and application of scientific and technological achievements in the additive manufacturing industry, and jointly promote the high-quality development of the additive manufacturing industry in mainland China.
Zuo Xiaowei, Deputy Secretary-General of the Chinese Mechanical Engineering Society, Tian Xiaoyong, Convener of the Group Standards Working Group of the Additive Manufacturing Technology (3D Printing) Branch and Professor of Xi'an Jiaotong University, Yuan Junrui, Deputy Director of the Academic Division of the Society, and Chen Lihong, Project Supervisor; Zhang Dongbing, vice president of Wuxi Institute of Inspection, Testing and Certification, deputy director of the National Additive Manufacturing Quality Inspection Center, and heads of relevant departments, Lv Xinfeng and Gao Yintao, attended the signing ceremony and participated in the exchange.
About the Chinese Society of Mechanical Engineering
Founded in 1936, the Chinese Mechanical Engineering Society is one of the earliest and largest engineering societies in mainland China. At present, there are 36 professional branches and 180,000 members, including more than 3,000 senior members, more than 500 corresponding members and more than 4,000 unit members.
The society is a national, academic and non-profit social organization voluntarily formed and registered according to law by mechanical science and technology workers with mechanical engineers as the main body and units and groups engaged in scientific research, design, manufacturing, teaching and management in mechanical engineering and related fields, and is a part of the China Association for Science and Technology.