Small UAV made of carbon fiber composite by vacuum bag pressing
Composite materials used in small UAV, such as fuselage, wing and other structural components, are mostly carbon fiber prepreg with higher specific strength and modulus. In recent years, the quality control of small UAV is more and more strict, the proportion of carbon fiber in composite UAV is gradually increasing, and even the small UAV made of all carbon fiber composite material appears. In addition, the low resistance of carbon fiber also makes it used in stealth design of aircraft.
There are many manufacturers of carbon fiber, and there are many types and specifications of carbon fiber. Their performance is also very different, so they can be selected according to the needs. According to the introduction of Suzhou Noen composites Co., Ltd. which has rich experience in carbon fiber UAV, the high strength t3000x 1775 standard type is mainly used for small UAV carbon fiber composites.
Due to the complex structure design of composite materials and the bending shape of fuselage of small UAV, aviation products have high requirements for material porosity. Honeycomb sandwich structure used for small UAV wing, v-tail, fuselage and other skin structures is basically manufactured by vacuum bag pressing process under the condition of ensuring the single side outline size of the product.
Vacuum bag pressing method is a method of applying pressure on the molded but uncured product through pressure bag or vacuum bag, so that the product or semi-finished product can be cured under pressure. The temperature and pressure of the vacuum bag pressing method are determined by the material system. The temperature is to reduce the viscosity of the resin and initiate a curing chemical reaction. This pressure is used to bond the laminate and inhibit the generation of voids. The vacuum bag pressing device is composed of pressure system, circulating water cooling system, vacuum system, compressed air system, heating system and electrical control system.
On the premise of meeting the aerodynamic design requirements, in order to reduce the weight and make use of the designability of carbon fiber composite materials, the fuselage beams, ring frames and corner boxes are laminated locally. The composite structure of small UAV is complex, and the requirements of design and quality control are high. Therefore, the manufacturing process of main structural components is usually very complex.
The honeycomb sandwich structure of skin structure is more complex, but the vacuum bag pressing process is usually carried out in the form of overall co curing, that is, the outer skin, honeycomb and inner skin are put into the female mold in turn, and then the outer skin, honeycomb and inner skin are solidified by one-time vacuum. The forming technology of honeycomb sandwich structure is very suitable for the forming of small UAV. The manufacturing structure is good on the whole, and the weight of and is relatively light. The main feature is the direct use of stretch formed sheet honeycomb. Therefore, how to place and accurately locate the honeycomb on the complex surface according to the design requirements is the key of this method. There may also be some unfavorable factors in the overall co curing vacuum bag composite and its honeycomb sandwich structure, that is, the thin-walled inner skin will inevitably sag towards the honeycomb direction, resulting in uneven phenomenon, the adhesive film between the honeycomb and the outer skin is often uneven, and the peeling strength between the honeycomb and the skin is not very high. In practical engineering, these problems are solved by controlling external pressure and adopting temperature measures.
The carbon fiber composite structure with vacuum bag pressing method has the characteristics of simple forming, low cost and short manufacturing cycle, which is easy to form complex aircraft structure as a whole. In addition, its high specific strength and specific stiffness can also meet the needs of light aircraft structure, which has a good application prospect in the field of small UAV.