07 Sep 2017

Additive technologies in micro turbojet engines

Additive technologies is a rapidly developing area of production. One of key advantages is the possibility of creating details of almost any geometric shape. A perspective example of their use, where the shape means a lot, could be micro turbojet engines. Geometry requirements for the air-gas channel of an engine as well as the presence of parts in the design with a sharp transition of the functional properties of elements impose constructive limitations on both individual details and the structure as a whole. The use of additive technologies allows you to avoid a number of limitations and opens up a wide range of opportunities for a developer to optimize existing designs and create new layouts.

The pledge of a good jet engine is the balance of a number of properties: specific weight, overall dimensions, fuel consumption and engine price.

So what is the potential benefit from the implementation of additive technologies?

The most obvious answer to this question is the reduction of the final product weight. The use of additive technologies makes it possible to eliminate a number of excess functional connections inside the engine. What does it mean? Imagine we have a node consisting of two parts manufactured with traditional methods. Part A and part B. Functional load of part A is to be heat-resistant and rotate the air flow, part B is to be light and perceive forces in a certain direction. Part A will have to be made of a heat-resistant alloy (such alloys, as a rule, have a high density), and part B is made of aluminum. The place of joint of the parts will have to be strengthened and add fixing elements, which leads to the increase in weight of the node. Also with the use of traditional manufacturing techniques (machining, casting), there will remain some unextractable materials or extraction of the materials will significantly increase the cost of manufacturing.

When processing the node for additive technologies, the statement of the problem will look like this: you need to create a part for turning the flow by organizing its structure in such a way that it perceives forces in a given direction. With this formulation, the fastening elements are removed from the structure and the designer organizes the geometry in such a way that the pattern of the stressed state in it is homogeneous and corresponds to the required margin of strength (from homogeneity of the stressed state of the part directly implies its mass optimization). Because of the fact that additive technologies allow to create rigid thin-walled structures, the density of the material becomes a secondary factor, and its specific strength comes to the fore. Since the specific strength of high-temperature alloys is close to aluminum, the merge of parts A and B in a solid structure made of a heat-resistant alloy makes sense.

The second important advantage of the implementation of additive technologies is the elimination of a number of design gaps that arise due to the complexity of the parts manufactured and need for their splitting up (in order to be able to produce them with traditional technologies). Also optimizing the geometry of the engine's air-gas channel helps to improve the flow conditions of the working fluid along it resulting decrease of fuel consumption because of reduced wastes on friction, rotation and deformation of the flow.

The third advantage in the design of small-size turbojet engines is the significant reduction of costs and production time. During the process of design it is important to modify the air-gas channel, which leads to the creation of various nodes prototypes with complex geometry. With additive technologies there is no need in any preparation before production starts resulting decrease of prototype costs and production time.

Despite of the advantages described above, the implementation of additive technologies is conjugated with a number of difficulties. The main deterrence, in our opinion, is the extremely high cost of equipment and consumables. The second is the complexity of designing and constructing of components for additive technologies with little adaptation of CAD systems to solve this problem at the moment. Nevertheless, active work is being carried out on these issues and the new technologies will likely become more accessible soon.

In conclusion it can be added that all innovative technical solutions and projects were based on breakthrough technologies of their time. In order to be first and best in the industry it is important to explore and implement new technological tools along with search of new design solutions.

Our company is engaged in the development of micro turbojet engines and the adaptation of their design elements to additive production. We hope that with the help of additive technologies it will be possible to design an engine with competitive characteristics over existing analogues.