Increasing the efficiency of slotting deep fir trees in gas turbine discs made of heat-resistant alloys by applying a combined method of hydroabrasive treatment and broaching

Abstract

The efficiency of the application of a new technology for fir-tree slots treatment in turbine discs based on a combination of pre-slotting operations of the «house» by hydro-abrasive treatment (HAT) and final broaching of the herringbone on a CNC machine in comparison with milling, deep grinding and EDM-ing methods is viewed. Problems arising within manufacturing and operating of broaches often cause down-time of both types: main and tool production. At the same time, the set high growth rates of production of gas turbine engines are inevitably restrained, the costs of manufacturing sets of multi-section fir-tree broaches are significantly increasing. To solve the problem, various combined processing techniques are proposed for the application, i.e., the pre-slotting of the «house» of broaches is carried out by various productive cutting methods such as deep grinding, milling, EDM-ing and HAT, while finishing is carried out using finishing profile broaching tech-nique. The pre-liminary calculations of labor intensity and production costs carried out during comparative tests of various combined variants of pre-slotting have proved the advantages of HAT cutting. As a result of the experimental studies, conducted on slotting, using HAT technique with subsequent broaching under final form broach, it was found that channel profile of the preliminary slot with allowances, made for measured profile devi-ation, is in the tolerable limit before final shape of the final broaching, which bears evidence of the slot appropriateness made by HAT method and its readiness for final broaching. After herringbone final broaching an electronic control was conducted and it was found that all the main dimensions in the herringbones are within tolerance limits and are suitable according to technic specifications. It is proposed to carry out further experimental work on particular stock-produced tur-bine disks for making a decision on the introduction of a new technology into mass production.