Additive technology (AT) is a dynamic and promising direction of production. What are pros and cons, and what are the approaches to the design of parts. How can we get an economic effect? The ideas, based on existing experience, are outlined in this article. The foregoing is the opinion of the author, which may differ from the opinions of other people.
Examples of AT application
Analysis of possible applications of ATs should start with the statistics of reports of the annual conference at VIAM “Additive Technologies Present and Future” (Since VIAM is the main organization acting as a primary integrator in this area in Russia) in the “Experience in the development and application of additive technologies” area. This statistic indirectly estimates the amount of work done in one direction or another. The number of reports is given in table 1.
Based on the available examples, it can be concluded that the main directions of AT implementation in our country at the moment are medicine and engine-building (turboshaft, liquid rocket).
The medicine area also looks promising for additive technologies because of its flexibility (ability to produce non-serial products of complex geometry at low cost). The main focus are prosthetics and orthotics.
Engine-building is also an industry where additive technologies have lots of practical examples. Many local and foreign project can positively say about future perspectives.
Nozzle head of a micro liquid-propellant rocket.
(Pictures are provided by Additive Technology Centre in Voronezh, Russian Federation).
The use of AT in engine-building is justified by several factors:
- The possibility of reducing the mass of the final product, due to the reduction of the material consumption of blank parts. The reduction of material consumption is caused by increasing the functionality of the placement of the material or reducing the number of parts. The reduction of the number of parts is possible because of removal of excess functional links caused by technology limitations in the manufacture or assembly procedure.
- Reduced production costs. The elements of turbojet engines and liquid rockets have a complex geometry. The manufacture requires expensive equipment and a large amount of manual labor. It is expected that with the help of AT we can get some gain in the manufacture of a number of parts. At the same time, a very significant gain can be obtained at the development stage by reducing the production time of prototypes and reducing the downtime of engineering divisions.
- It’s important to have a possibility to obtain a super-sum effect. During the manufacturing of structures, which can be obtained only with AT, an increase of specific parameters of a product can be observed. These improvements can downgrade negative effects such as cost increase.
Nevertheless, it’s not as good as looks at first sight. There are two factors that significantly limit the implementation of AT (mostly related to printing with metal-powder compositions). The first factor is cost. The market value of 1 cm 3 of a part printed, let’s say from stainless steel, is about 500 RUB. (used for further assessment), heat-resistant materials are even more expensive. High cost can be explained by rapid equipment depreciation. The second factor is the significant complexity of the certification of products manufactured by AT. This is caused by the complexity of the technology and many factors affecting the properties of the final product. Thus, if we consider the relevance of introducing AT into everything that flies, the unmanned equipment (including spacecraft) looks most promising due to the lack of stringent safety requirements and, as a result, a simplified procedure for certification or delivery of the product to the end-user customer.
Approaches to the design of parts using AT methods
Currently, majority of designers are divided into two categories - skeptics of AT and enthusiasts (people who think that everything can be printed). The population of the second group tends to decrease over time.
In our opinion, AT should be treated as a tool that a designer / technologist needs to understand and use in cases where it is justified. At the same time, AT in no case can replace traditional technologies in mass production, but only complement them, giving additional opportunities in the design and construction of new products.
In order to effectively use AT, we need proven approaches and resource-consuming technologies. And by and large nobody will help you in mastering the technologies.
Due to the large variety of parts that can be produced, it is not possible to justify the usage of AT in each case. Therefore, a preliminary screening based on qualitative features is necessary:
- Unit cost, costs vs weight;
- Production volume;
- Access to standard technologies*;
- Production risks;
- The possibility of specific parameters increase of the final product;
- AT orientation**.
* Note: by «access» to traditional technologies here we mean that a potential part can be made by traditional methods, but it is impossible to manufacture this part other than AT for one reason or another.
** Note: as well as machining, casting and other technologies, AT have technological limitations that determine the possibility or rationality of manufacturing. Orientation is that the part has typical properties that are inherent in parts, the manufacture of which the AT looks rational.
The importance of a particular criteria strongly depends on a specific situation, and here it is necessary to fully rely on the designer’s experience.
D200 is our first engine with max thrust of 20 kgf. AT were applied during the development
The weight of the gas generator is about two kilograms (excluding the starter, control unit, bearings and other components). Thus, if we would hypothetically want to print it out entirely, then the cost of blanks would be (given that support amounts to 30% of the mass of the part, which is very optimistic) 2000 / 7.8 * 1.3 * 500 = 165 tons. R. In the future, it is necessary to make cleaning from the supports and accurate processing of the seating surfaces, this would increase the cost of (serial ones!!!) final parts by about 50%. If you add to the above costs the cost of components and other costs: logistics, overhead costs, etc., then the cost of manufacturing a serial TRD will be around 350 – 400 thousand RUB. (by the most optimistic estimate), which significantly exceeds the market value of this engine. Thus, it can be concluded that it is not economically feasible to use printing and reverse engineering of the classical proven construction with the current cost of printing. Many respected organizations are involved in this issue.
Nevertheless, if we carry out a detailed assessment, provided that the engine layout implies the optimization of some components for printing, we can distinguish several types of parts that look promising: cast parts of the turbine stator and parts of complex geometry that are not in the hot part (implied that they can be made from heat-resistant or composite polymers). The switch to AT has reduced the weight of these parts by 30% and significantly reduce time and cost of manufacture.
D200 engine starter body.
A good example is the starter case made of a composite polymer with high heat resistance and strength. A starter of a turbojet engine and a speed sensor are located within the case. It is assumed that the node is partially non-separable and non-maintainable due to that all the components are low cost, simple and highly reliable. These parts can be fully substituted in case of failure. Inside the part there are channels and recesses for wiring and installing sensors. The design of the part is oriented for AT – the part has a relatively small base, and each previous layer is the basis for the subsequent one. The item has no technological support. The part contains only functional surfaces and elements, the size and thickness of which is minimally sufficient for them to perform work as intended in the manufacture of the selected materials.
Close attentions should be made to the optimization of parts manufactured by AT. Especially made of metal-powder compositions. Removal of non-functional elements and proper organization helps to turn down the number of supports is minimal. It significantly reduces the cost of mass production by reducing the printer’s operating time and material costs. Even when printing with polymers, where the cost of materials is not great, it is worth remembering that high-quality printing of even small parts takes considerable time (for example, the print time of the starter case is 14.5 hours!).
Turbine nozzle is made of heat-resistant alloy “ПР-08ХН53БМТЮ”. Parts are made by the Center for Additive Technologies based in Voronezh, Russia. The part is installed in the structure as a crimped insert. Such an approach made it possible to reduce the weight of the part and avoid entering non-functional elements into the part, which positively affected the final cost.
Blank turbine nozzles D200 engine before and after removing the backings.
The work done is an adaptation of our turbojet engines for AT, where it was justified. This work required time and efforts; nevertheless, the experience gained turned out to be very useful in terms of integral assessment of approaches to the creation of equipment using AT. This approach is useful when the shape of a part (construction / layout) is the result of the function being performed, not of the applied technologies.
We hope to continue using AT in the further development of the project. We also hope that the cumulative effect (in terms of increasing specific parameters) of AT will help to achieve non-ordinary development solutions and provide a competitive advantage over similar ones in the existing market.