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Impellers High Machining Accuracy Requirements
Nov 06, 2017

Impellers concept: The Impellers is equipped with moving blades of the wheel, is a part of the impulse steam turbine rotor, but also can refer to the roulette wheel and installed on the rotating blades of the general term. Impellers common are casting or welding, material according to the working medium selection.

Main role: The Impellers is the mechanical energy of the original motive to the work of the static pressure energy and dynamic pressure energy.

According to the blade form is divided into three kinds: open Impellers, closed Impellers, half open type Impellers.

The closed Impellers is composed of front and rear cover plates and blades;

The half-open Impellers is composed of blade and rear cover plate;

Open Impellers only blades with part of the rear cover plate or no rear cover plate.

Vane Impellers in the Half-open, open Impellers casting convenient, can be transported containing a certain solid particles of the medium, but because of solid particles abrasive flow path, will cause the pump efficiency to reduce.

Closed Impellers running high efficiency, can be a long time smooth operation, the pump axial thrust is small, but the closed Impellers is not easy to transport containing large particles or containing long fiber sewage medium.

The integral Impellers blade surface is complex, the machining space is limited, the processing precision is high, and the dynamic performance requirements are good, which has become one of the difficulties in the field of mechanical manufacturing. At present, NC milling, precision casting in the overall Impellers processing has been more application. However, NC milling for difficult cutting materials, small channel blades processing, due to the rigidity of the tool is difficult to process, precision casting production process complex, technical difficulty, high scrap rate, only applicable to cast alloy. The instantaneous high temperature produced by EDM is melted by the surface of the workpiece relative to the electrode, and the material is gradually eroded to achieve the process. Therefore, EDM in the no cutting force, not subject to the hardness of the workpiece has other processing methods can not be compared advantage.

The electrodes used in the EDM integral Impellers can design the form and the whole form of the component body, and the electrode form directly affects the precision of the machined parts. The machining of the split electrode is easy to form lap steps on the blade surface, which makes the profile error of the blade surface, which affects the forming precision of the whole Impellers. SolidWorks combined with the structural characteristics of the whole Impellers to design a monolithic electrode; In order to avoid the appearance of interference problem in the process of electrode machining, The electrode motion is simulated and the interference is examined, and the fabrication process of the forming electrode is studied.

The whole Impellers is composed of the wheel hub and the blades along the circumferential uniform. Blade modeling is the key to the overall Impellers shape, usually the surface data of the blade is based on the unsteady three-dimensional viscous fluid model for complex numerical calculation, and after the test was modified, generally can not be expressed by the analytic expression, but through a given blade of several truncated surface value points to describe. The basic method of blade three-dimensional modeling is: Point → line → surface, from the discrete data points to generate section curve, by the section curve according to certain rules to generate surface.