The turbine shell parts are processed by die casting technology

1. Design of turbine casing pouring system

The internal and external contours of turbine shell parts are relatively complex. When designing the casting system, factors such as the casting and exhaust of the outer mold and sand core should be considered, and factors such as sprue, runner, ingate, riser and air outlet bar should be set, as shown in the figure. The set parameters and methods are correct and reasonable, which can ensure the casting quality of turbine shell parts.

2. Parting design of turbine shell sand core and outer mold

Because there are complex cavities and pipes inside the turbine shell parts, the outer mold and sand core of the parts should be divided first. After obtaining a complete sand core, the sand core should be reasonably divided into upper, middle and lower parts according to the processing requirements and restrictions.

The parting surface of the outer mold of the turbine shell is set at the place with the largest outer diameter of the shell, and the upper plane of the inner runner can be used as the parting surface to ensure that the outer mold is easy to be milled after parting.

3. Positioning design of turbine shell sand core and outer mold

The outer mold and the sand core are assembled and used together in turn for the mold of the turbine shell, so the positioning design shall be made among the three sand cores. The lower sand core and the middle sand core adopt the positioning conical pin and conical hole design, and the middle sand core and the upper sand core adopt the positioning design of square conical pin and conical hole to limit the freedom of rotation and ensure the accurate positioning between the sand cores.

In order to ensure the accurate positioning of the lower sand core and the outer mold during assembly, the z-direction rotation freedom of the sand core in the outer mold must be limited. A “core head” can be made at the sand core, which can be embedded into the groove of the outer mold when the sand core is assembled with the outer mold, which limits the freedom of rotation of the sand core along the Z axis inside the outer mold, so as to better ensure the assembly accuracy of the sand core and the outer mold.

4. NC programming processing of turbine shell sand core and outer mold

With the help of the powerful NC programming and processing function of UG software, the required tools and processing methods (cavity milling and depth profile milling) are set according to the established processing technology of each sand core unit, and the cutting parameters are reasonably set to generate the machining tool path. The simulation processing function of the software is used to verify the correctness of the cutter path, and the required processing program is generated through the post-processing function. The above four steps complete the preparatory tasks of the turbine shell part classification and positioning design and NC programming processing.

5. Cutting of turbine shell sand core and outer mold

After the NC programming processing of the turbine shell is completed by using UG software, the generated program is transferred to the equipment of the digital die-free casting precision forming machine, the sand blank is installed on the workbench, and the cutter setting operation of the milling cutter is carried out. After the program is verified to be correct, it is divided into several steps such as rough milling plane, rough milling cavity contour and finish machining according to the developed processing technology. Pay attention to the back draft of the cutter during processing The reasonable setting of the spindle speed and feed can clean up the accumulated sand in time and ensure the machining accuracy.

6. Precision inspection of mould

After the processed mold is cleaned, it is pasted with light marks, scanned with a scanner and vxelements, a special software for scanning, to obtain the contour and size data of the part. Through geomajic control software to detect and analyze the data, it can quickly and accurately judge whether the accuracy of the mold meets the requirements, and improve the efficiency and accuracy of detection.

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