Advanced hot bonding system for repair of Aerospace Structures

摘要

Repair techniques play an important role in increasing the useful life of the aerospace structures. They increase the confidence level of the user and promote the application of composites. Among the various repair techniques, hot bonding is widely acclaimed for its ability to restore the strength close to the original values. It is used for the repair of metal or composites structures. Hot bonding performed using flexible heater blanket and vacuum bag is the most suitable method for in-situ repair. Hot bonding is performed through elevated temperature cured adhesive system, which increases the glass transition temperature and hence the service temperature of the final product. These adhesive systems are sensitive to temperature gradient. If the gradient exceeds ±5oC, the cross-linking process and the quality of repair is adversely affected. In the hot bonding process, only the repair area is heated and the rest of the part is left in atmospheric condition. Due to partial heating, the region below the centre of the heater gets hotter than the surrounding. This problem worsens if the job has skin and spar construction or has non-uniform cross-section as in the case of aircraft control surfaces or windmill blades. The hot bonding equipment currently being imported (none manufactured within India) does not ensure temperature uniformity.udThis paper discusses the design and development aspects of multi-zone, portable hot bonding equipment, which overcome the above problems. Multiple numbers of appropriately placed heater blankets, sensors and a data acquisition device coupled with a novel control algorithm and multi-threaded software has resulted in the portable and reliable hot bonder. The equipment was tested on typical aircraft parts, such as an aluminium rudder and a composites fin tip. The conventional single heater blanket method has resulted in a temperature gradient of over 12oC, while this product has limited the temperature gradient to within ±1.5oC.