The recent success of Rocket Lab, putting small satellites into orbit with its Electron rocket, is a significant milestone in the evolution of space flight. The Electron rocket is powered by a set...
A blog on what's new, notable, and next in turbomachinery
By Mark R. Anderson
Mar 9, 2017
The primary options for laying out an impeller (i.e. flank milled versus point milled, open versus covered impellers, integral versus welded shrouds) determine the basic manufacturing process (see Manufacturing Methods Used for Turbomachinery for more info). Beyond the basic layout, there are several other details of the design that can significantly affect manufacturability. They include:
SIDE RULINGS POORLY ALIGNED WITH LEADING EDGE ELEMENTS (LEFT)
AND WELL-ALIGNED (RIGHT)
Swept edge construction is often used on splitter leading edges. This has the benefit of removing the thin tip of the blade that poses difficulty during milling and generating a smoother overall tool path. In general, the aerodynamic effects are limited if inlet and exit blade angle distributions are maintained. However, three-dimensional shape parameters, such as passage area, can shift and potentially affect characteristics such as choke margin and vibration frequency.
RULED ELEMENTS ALIGNED WITH THE SPLITTER LEADING EDGE (LEFT) AND A SWEPT SPLITTER EDGE WITH IMPROVED TOOL ORIENTATION (RIGHT)
EFFECT OF RULED ELEMENT ALIGNMENT
OF A COMPRESSOR DESIGN ON PASSAGE AREA
EFFECT OF RULED ELEMENT ALIGNMENT
OF A COMPRESSOR DESIGN ON VIBRATION FREQUENCY
RIBLETS ON THE HUB SURFACE RESULTING FROM A ROUNDED END MILL
So – how long is it actually going to take to machine your part on a 5-axis machine?
Estimated machining times can be calculated using a combination of primary rotor geometry parameters. These estimates need to be calibrated with actual production information from the shop floor and can vary from one place to another. The equations used are generally straight forward, but require an extensive database of real cutting times. Obviously, these can vary based on the resources available and experience level of the workforce. For this reason, these methods are usually highly customized and are generally proprietary in nature. The figures below show actual examples of estimation utilities developed for this purpose.
EXAMPLES OF SPREADSHEET METHODS FOR ESTIMATING CUTTING TIME FOR FIVE-AXIS MACHINING
What about Additive Manufacturing?
Despite the strong interest, there are still a huge number of practical issues that need to be resolved before additive manufacturing can be widely used in many turbomachinery applications. These issues include: residual stress levels, dimensional accuracy, and resulting material properties. The overall quality and tolerance of the finished product is also a concern, since they are usually not smooth enough for primary flow path regions. To resolve this, an additional conventional (subtractive) manufacturing process is usually needed to achieve an adequate surface finish. In short, additive manufacturing, while promising, is not going to completely replace conventional methods anytime soon. Conventional manufacturing methods offer too many advantages, at least that is, for conventional parts.
The real advantage of additive manufacturing is its ability to generate parts that cannot be made with conventional methods. New software, new analytical methods, and new design paradigms are needed to fully unlock the potential for additive manufacturing. Concepts NREC is working on additive manufacturing for several clients and is incorporating the knowledge gained into our products and services.
RADIAL TURBINE (LEFT) AND AXIAL TURBINE BLADE (RIGHT) PRODUCED BY ADDITIVE MANUFACTURING, (COURTESY OF Fraunhofer ILT, Aachen, Germany, and DMG Mori co. ltd)