Research On External Thread Milling Of Superalloy Float-wall

Float-wall is the key part of flame tube in combustor, made up of nickel-based superalloy M951. At the present, external threads of the float-walls are machined by using screw die, which causes low production and high rejection rate. To solve the existing problems, external thread milling is researched in this study, the force optimization, tool wear analysis, fixture design, column adjustment and thread measurement are carried out. The research results can support the high-efficiency and precision machining of external thread of float-wall.The main work is summarized as follows:(1) The radial depth of cut is used as the variable for the expression of section area between two passes. The definition and expression of uncut chip thickness(tc) in thread milling are proposed, and the variation of tc is summarized. The cutting force calculation formula of thread milling is deduced. It is introduced that the same section area at every cutting step is used for optimizing cutting force of each cutting step.(2) In consideration of the feature of forming processing, dimensions of the thread are out of the tolerance range is used as the tool failure criterion. Three-dimensional microscope, SEM and EDS are used to analyze the wear feature and wear mechanism of thread milling tools. The relation between cutting force and tool wear is revealed.(3) In view of the structure feature of float-wall, the special fixture for float-wall is designed and manufactured. Coordinate measuring machine is used for three-dimensional reconstruction of columns on float-wall, and the NC machining program is generated by UG post-process module. Single and synthetical parameters of the thread are measured by using thread ring gage and tool microscope. The measurement results prove that thread milling process can meet the design requirement.