Stamping welding shaping method of centrifugal pump impeller

Abstract: Concerning the stamping and jointing techniques of stainless steel impeller, a shaping method of centrifugal pump impeller is presented based on the structure characteristic of centrifugal pump, which introduces shrouds with taper and twist blade. Laser welding is used to joint the blades and the shrouds which tackles the distortion of hub according to the mechanical performance of the material. By avoiding the bunch flow phenomena in the impellers, the shroud and hub can ensure no-distortion, which improves the hydrodynamic performance effectively.

Key words: centrifugal pump; stamping; impeller; shaping technology

1. Stamping process of centrifugal pump impeller
In the pump stamping and welding process, in order to meet the requirements of the stamping process, the pump is decomposed into pump casing, water inlet, water inlet chamber, volute and impeller. These components are stamped and then combined for welding. During stamping, the impeller is further decomposed into front and rear cover plates and blades. (As shown in the figure) Finally, perform combined welding. For stamping processes, good process design is a condition for producing stamping parts with high quality, efficiency, low consumption, and safety. The stamping process is designed based on the structural characteristics of the stamping parts, production batches, mold making capabilities, and investment funds, as shown in Figure 2. The materials used for stamping parts, the structural craftsmanship of stamping parts, stamping process routes, equipment selection, and molds will all have an impact on the stamping process of the work piece. Therefore, when designing the stamping process of the work piece, various factors should be considered to ensure the accuracy of the work piece, reduce production costs, and improve production efficiency.
Pump impeller stamping process flowchart: impeller hydraulic design, stamping structure design, stamping mold design and manufacturing, part stamping forming, part finishing, component assembly and welding, component assembly, product inspection, and finished product warehousing.

2. Analysis of stamping process structure
2.1 Selection of materials for stamping of leaf parking fees
Considering the working environment of the impeller and the cost-effectiveness of various materials, SUS304, SUS316, and SUS316L stainless steel plates can be selected as the impeller forming materials. Our company mainly uses SUS304 stainless steel plate as the impeller forming material. Has a high cost-effectiveness.
2.2 Analysis of Impeller Stamping Process
Stamping process is the main process for impeller forming. The shape and accuracy of each part of the impeller are ensured by the mold. The mold is the guarantee of the entire stamping process plan, and the structural design of the mold should not only be reasonable, but also have good universality and interchangeability. For this reason, the entire mold consists of separate parts.
Due to the complex shape of the impeller, it is divided into four parts: the front cover plate, blades, rear cover plate, and wheel hub. The front cover plate, blades, and rear cover plate are all stamped and formed from stainless steel plates, and the wheel hub is turned. Finally, the various parts are combined and welded.

3. Stamping process flow of various parts of the impeller
3.1 Blade stamping process flow
The shape of the leaves is relatively complex. The forming process includes blanking, bending, and shaping. When the blade is bent, the material undergoes both elastic and plastic deformation. In addition to relying on molds to ensure this, it is also necessary to have an accurate blade unfolding shape.
3.2 Front cover plate stamping process flow
According to the shape and size requirements of the cover plate, the stamping process is developed as follows: blanking, punching, and flanging. First, the stainless steel plate is punched into a circular plate material, then flanging holes are punched on the circular plate material, and finally the edges of the holes are turned into vertical straight edges. Before determining the process, it is necessary to calculate whether the workpiece can be flanged and formed in one go. If not, the workpiece needs to be stretched or flanged multiple times before flanging.
3.3 Stamping process flow of rear cover plate
According to the shape of the cover plate, the stamping processes for each rear cover plate can be: blanking, stretching, punching, and flanging. Blanking and stretching can be combined into one process. Before flanging, it is also necessary to calculate whether the workpiece can be flanged and formed in one go.

Impeller's Vanes

4. Impeller welding process flow
The welding process is the final process for impeller molding. Before welding, it is necessary to first select a suitable welding method, which is related to the surface quality of the impeller after welding, the smoothness of the flow channel, and the strength of the welding point. The impeller material used by our company is SUS304 stainless steel plate, and the thickness of the blades, front and rear cover plates is between 1.5 and 3.0mm. The thickness of the stainless steel plate used is relatively small, and if resistance spot welding is used, it is easy to cause deformation, resulting in poor coupling between the impeller cover plate and the blade. Therefore, our company uses laser welding for impeller welding. Laser welding is used to weld the impeller. After welding, the impeller has no deformation, the weld seam is narrow and smooth, and the line sealing rate between the front and rear cover plates of the impeller and the blade is almost 100%. After using laser welding, some problems in impeller resistance spot welding were solved.

Laser Welding the Impeller

5. Conclusion
By studying the stamping process of impeller blades, front cover plates, and rear cover plates. The impeller made by stamping and laser welding technology has good coupling between the front and rear cover plates and the blades, avoiding the phenomenon of cross flow between the impeller flow channels. This technology can ensure that the front and rear cover plates do not deform basically, and the welding surface is flat, which can effectively improve the hydraulic performance of stainless steel impact welded impellers.

Impeller's Shaft