Apparatus and process for manufacturing a centrifugal pump with a rotor within a single piece housing

This application claims the benefit to U.S. Provisional Application 62/192,433 filed on Jul. 14, 2015 and entitled APPARATUS AND PROCESS FOR MANUFACTURING A CENTRIFUGAL PUMP WITH A ROTOR WITHIN A SINGLE PIECE HOUSING.

This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA) and the Army Contracting Command—Aberdeen Proving Grounds (ACC-APG) under Contract/Purchase Order number W911NF-15-P-0063. The United States Government has certain rights in the invention. Distribution Statement A: Approved for public release, distrubution unlimited.

The present invention relates generally to a centrifugal pump for a liquid rocket engine, and more specifically to a centrifugal pump manufactured with a single piece housing using a metal additive manufacturing process.

Prior art manufacturing methods used to produce liquid rocket engine components have historically led to high manufacturing costs. A current challenge in the rocket propulsion industry base is lack of modernization in manufacturing processes and inefficiencies in production. With the low qualities inherent in space propulsion hardware, and an ever increasing drive toward reduced cost, there is an increased interest in design for manufacturability. An optimal balance between commercial best practices and advanced manufacturing techniques could be implemented to meet the future requirements of the rocket propulsion industry. There is potential for significant advancement in cost reduction, design and manufacturing for turbopumps through the application of additive manufacturing (AM).

FIG. 1 shows a LOX pump 10 with an extremely efficient design. The LOX pump is formed from only eleven part numbers (not including fasteners) and is very compact. The pump is located in the center and is a back-to-back design similar to the SSME High Pressure Oxidizer Turbopump (HPOTP). This reduces/eliminates rotor axial thrust imbalance. There is an inducer in front of each impeller to improve cavitation performance and the impellers are shrouded to minimize secondary flow leakage without requiring extremely tight tolerance. The bearings 12 straddle the impellers 15 and are cooled by recirculating the inlet LOX with the natural pumping of the rotor. The bearings 12 are axially held on the rotor by identical spanner nuts 14 . To minimize assembly time and components, the impellers 15 are integral with the shaft. To minimize cost, the two bearings 12 are the same, and the spanner nuts 14 are the same. To conserve weight and minimize seals, the inlets and discharge connections are integral 37 degree flared fittings. Finally, since the size is so small and the discharge pressure is low, the rotor design speed is low so the stresses on the parts will be extremely low.

The LOX pump in FIG. 1 includes a cover plate 13 held on by several bolts 31 , a forward seal 16 , and aft seal 17 , a main housing 11 , a threaded nut 18 to secure the forward and aft seals 16 and 17 to the housing 11 , an aft housing 19 , and a spring 22 . Forward and aft labyrinth seals 28 are formed with the impeller 15 all as a single piece where the lab seals form a seal with stationary seal members 16 and 17 secured on the main housing 11 .

The LOX pump in FIG. 1 is assembled axially. First, the impeller 15 is assembled from right to left into the main housing 11 . Second, the aft housing 19 is assembled over the impeller 15 , also from right to left, and is mechanically attached to the main housing 11 using bolts 31 . Then, bearings 12 and other features such as spanner nuts 14 , spring 22 , and seal 21 are assembled from the ends of the turbopump. Finally, the cover plate 13 is attached and held on with several bolts 31 .

A turbopump such as a LOX turbopump for a liquid rocket engine is formed using a metal additive manufacturing process in which a single piece impeller is formed within a single piece housing in which the impeller is trapped within the single piece housing. The housing is formed with a fluid inlet and a fluid outlet. The impeller is formed with an axial bore in which a shaft is inserted after the impeller and housing have been formed. Forward and aft bearing support surfaces are machined on to the outer surfaces of the impeller and then two bearings are inserted into the housing and secured by a tie bolt fastened on one end of the shaft. A forward cover plate encloses a forward opening of the housing and a buffer seal encloses an aft opening of the housing.

The cover plate and the buffer seal form support surfaces for outer races of the two bearings. The single piece impeller is formed with forward and aft labyrinth seal teeth all as a single piece, and the housing is formed with seal surfaces for the labyrinth teeth that form forward and aft labyrinth seals between the impeller and housing.

FIG. 1 shows a cross section view of a LOX pump of the prior art.

FIG. 2 shows a cross section view of a LOX pump of the present invention.

The present invention is LOX pump used in a liquid rocket engine in which the rotor is formed by a metal additive manufacturing process and formed within a single piece housing that is also formed by a metal additive manufacturing process.

FIG. 2 shows an embodiment of the present invention of a LOX pump of the present invention that is formed by a metal additive manufacturing process in which a one-piece rotor is formed within a one-piece housing. The impeller 25 and the shaft 26 are simultaneously manufactured within the housing 29 , the forward seal 16 and the aft seal 17 and the threaded nut 18 of the FIG. 1 embodiment is eliminated, the requirement to finish machining of the housing for the bearing OD (outer diameter) 27 of the FIG. 1 embodiment is eliminated, and the FIG. 2 embodiment provides for the elimination of all machining operations from the shaft. The FIG. 2 embodiment also eliminates the aft housing 19 and associated interface flange, eliminates the seal and finish machining, and eliminates the screws required in the FIG. 1 embodiment. The single piece impeller 25 is printed with an axial bore in which the shaft 26 passes through.

In the FIG. 2 design, a double suction impeller 25 is trapped within the housing 29 since the outer diameter of the impeller 25 is greater than a minimum opening on either end of the housing 29 . This is achieved by printing the components simultaneously within the Selective Laser Melting (SLM) machine. Then, powder and support structure (if required) removal is performed. The bearings 12 are installed on the ends of the shaft 26 . Conventional manufacturing is required for the bearings 12 due to high precision requirements needed. With the exception of the shaft tie-bolt 30 and the shaft seal, all other components are printed on an SLM machine.

A forward and an aft labyrinth seal 28 are formed on the impeller 25 all as a single piece and form seals with the surfaces of the single piece housing 29 . The single piece housing 29 is formed with the impeller 25 and forward and aft labyrinth seals 28 inside the housing 29 . Outer surfaces of the impeller 25 where the bearing inner races are placed are machined while the impeller 25 is inside the housing 29 . The bearings 12 are then installed in place on the impeller 25 , and then the shaft 26 is inserted within the impeller 25 and secured in place with the shaft tie bolt 30 . A flange 34 is formed on the aft side of the shaft 26 and along with the shaft tie bolt 30 compresses the bearing inner races to flanges formed on the outer surface of the impeller 25 . A forward cover plate 32 is installed with a number of bolts 31 . A buffer seal 33 is installed on the aft end of the housing 29 and the aft bearing 12 . A number of bolts 31 are used to secure the buffer seal 33 to the housing 29 .

Rotor balancing is another critical area. Typically, an assembly balance of the rotor is performed for turbopump rotors. That is, the full rotor is assembled and balanced on a balance machine. Since the rotor 25 is printed inside the housing 29 , this method cannot be used without special tooling. In the present invention, a method of trim balancing is used where the rotor 25 is spun up to various high speeds and accelerometers on the housing 29 along with a proximity probe looking at the rotor is used to determine the rotor imbalance. The imbalance is corrected by grinding locations on each end of the shaft 26 .

By printing the pump impeller 25 within a one-piece housing 29 , a dramatic reduction in part count, procurement activities, and assembly time is achieved over the prior art, which directly translates into a reduction in recurring cost and lead time. These reductions are estimated to reduce the cost of the LOX pump by approximately 40%. Similarly, if not more (due to the higher part count), reductions will likely result for a hydrogen pump. The turbomachinery for a typical rocket engine accounts for about one-third of the cost of the total engine. Thus, significant reductions in turbomachinery cost have large impacts on the overall cost of the engine.