Research On Tool-path Planning For NC Plunge Milling Of The Semi-open Integrated Impeller

The semi-open integrated impeller is widely used in turbomachinery such as centrifugal compressor and blower. Such parts have complex structure and strict demands for machining precision. What’s more, they are usually made of difficult-to-cut materials and are recognized as the difficult-to-machine parts. Currently, such parts are mainly made from an integrated blank by milling using a5-axis NC machine tool. And the rough machining process has an important effect on its machining efficiency and production costs. Based on an efficient plunge milling process which associates drilling with milling, this paper researches its application in the rough machining of the channel of the semi-open integrated impeller. The primary items in this work are as follows:Firstly, specific to the problems of the conventional plunge milling, and combine with the latest tool technology, a plunge milling process that associates drilling with milling is proposed. Cutting experiments verify the feasibility of this machining technology. And experimental results show that the process has high material removal rate and good machining stability, and can also effectively avoid "tool collision" phenomenon. The concept of cross-section of the channel which characterizes the channel’s blank allowance is proposed and the feasible region of the channel’s rough machining is constructed by analyzing the plunge milling rough machining process of the semi-open integrated impeller.Secondly, the tool-path planning method of the plunge milling process for the semi-open integrated impeller is studied in detail. Based on the equal arc length method and the tool’s machining requirements, the family of the conical sections which evenly splits the channel along the flow direction is constructed with the help of the cross-section of the channel. The boundary cutter locations are then determined using the endpoints of the intersecting lines between family of the conical sections and the blade offsetting faces. The boundary cutter locations which lead to collision interference are amended using the method based on the detection of the distance between the point and face. Within each conical section, similarly based on the equal arc length method and the tool’s machining requirements, the tool center points and tool axis vectors are interpolated. And finally, the cutter location points which are evenly distributed among the channel are obtained. In addition, with the help of the cross-section of the channel, the condition of avoiding "tool collision" phenomenon in varying axis plunge milling is analyzed and the layer machining method is studied for the impeller with deep channel.Thirdly, the dedicated CAM module for the plunge milling rough machining scheme of the semi-open integrated impeller is developed using secondary development technology. For the deficiency of the current CAM software in multi-coordinate spot machining programming, the above-mentioned algorithms are integrated into software system using UG/Open, a secondary development tool of the UG software. Among that, the boundary points are firstly generated automatically using the UG/Open GRIP tool, and the tool paths are then generated automatically using the UG/Open API tool with C language programming. Thereby, the computer aided programming of the plunge milling machining scheme is realized and the development cycle is shortened greatly.Finally, the feasibility of the machining scheme is verified through cutting experiment. A semi-open integrated impeller which is produced actually is taken as example. The suitable five-axis NC machine tool and blank model are selected. Then, based on the NC codes which are obtained through post processing, the machining simulation is conducted on the VERICUT software platform. And the cutting experiment is then performed when there is no error during simulation. The experimental results verify the feasibility and high efficiency of the plunge milling rough machining scheme.