SpinOffs

As discussed in my previous blog post, Flank Milling, How Hard Can it Be?, turbomachinery blades are commonly designed as ruled surfaces, with the goal of making manufacturing easier and faster with flank-milling.  While some non-ruled surfaces can be acceptably flank-milled, the programming and machining process for flank-milling is generally more dependable with ruled data. However, the ruled data should be well conditioned, and several pitfalls should be avoided during the design and construction process.

Valentine’s Day is February 14, and while some cynics refer to it as a “Hallmark holiday”, most people commemorate the day in some way. One of the biggest challenges is finding a card that perfectly captures the way you feel about someone, while also reflecting who you are.  Well, Concepts NREC has created some turbomachinery-themed Valentine’s Day cards for engineers. These fall into the Art end of our Art-to-Part Solution.

 When designing compressors, engineers often use ruled-surface blades with the goal of making a shape that’s easily manufactured on a 5-axis machine.  Theses blades can be quickly machined in one pass by aligning the side of a cutting tool to the rulings. This process is often referred to as “flank milling.”  The alternative is to make many passes with the tool tip, a process known as “point milling”. For the right application, flank milling is often favored for shorter cutting times and better surface quality, but there are some caveats.

Have you ever needed to know the exact geometry of a compressor that has been running for years in your process plant? Perhaps you need to analyze how it would perform if the process fluid had to be changed to meet new government regulations. Or maybe there has been damage to the impeller and a complete mechanical analysis is required before a new one can be put into service. Eventually, everything, even well-designed turbomachinery, needs to be replaced or upgraded.

The guiding principle behind Concepts NREC’s Computer-Aided Manufacturing (CAM) software, MAX-PAC, is to simplify the task of creating efficient milling toolpaths for turbomachinery. Since we are also users of MAX-PAC in our manufacturing facility, we see first-hand how new features and functionality impact day-to-day operations. This was true with the release of our powerful 3+2 Roughing Module. After a year of using it, our machinists were amazed at the results. In almost every instance, they saw a 50% reduction in roughing cycle times, compared to the way they were doing 5-axis roughing. Wow!

Wouldn’t it be ironic if the profession that is creating all the robots was eventually replaced by them? It could happen. Engineering is all about applying laws, measurements, facts, and analysis to solve a problem. Dealing with these finite things is exactly what robots do WAY better than people.

The contemporary gas turbine engine, developed in the 1940’s by Sir Frank Whittle (pictured), is still considered to be among the most efficient, external combustion engines. Today, there is a resurgent interest in power generation technology driven by humankind’s insatiable need for more power. A popular focus is to extend the Brayton Cycle, the thermodynamic basis for a gas turbine engine, to using CO₂ in a closed Brayton Cycle. This is commonly referred to as a Supercritical CO₂ (sCO₂) system. As the name implies, the CO₂ is at pressures above the critical point of CO₂ or 1,070 psia. The highest pressure in the cycle can often be designed to be 4 times this pressure and operate at temperatures as high as 700°C at the inlet to the turbine. 

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: 

There are two dominant manufacturing methods used to produce turbomachinery parts – Casting and 5-axis machining. This blog will explore some of the applications and restrictions of these two methods.