Power Generation: Machining Big, Heavy, Expensive Components
‘Everything is big, heavy and expensive’ for shops serving the energy industry. By Christopher Tate Each segment of manufacturing has unique characteristics. Automotive machining is characterized by high volume and low margins. Aerospace is highly regulated with tight tolerances. Medical machining is also highly regulated with difficult to machine alloys.
‘Everything is big, heavy and expensive’ for shops serving the energy industry.
Each segment of manufacturing has unique characteristics. Automotive machining is characterized by high volume and low margins. Aerospace is highly regulated with tight tolerances. Medical machining is also highly regulated with difficult to machine alloys. Every segment has different challenges and rewards.
Machining components for the power generation industry is no different. There are no commodity parts in a turbine. Everything is big, heavy and expensive. Machine tools are enormous, cutting tools are big and the setups can take days to complete.
The power generation industry, as the name implies, consists of manufacturing companies that supply the machines and devices that generate and transmit our electricity across the grid. Companies in the industry manufacture things like wind turbines, transformers, steam turbines and gas turbines. A large gas turbine can generate 350 to 400 megawatts (sometimes more). One megawatt is enough energy to power about 1,000 homes. So, a large frame gas turbine can power 350,000 to 400,000 homes. Therefore, these machines and their components can be immense, weighing over 500,000 lbs. and occupying a space that is 18' × 18' × 50'.
Although the turbine is assembled from smaller components, those components are enormous. Small turbine parts can be 5' in diameter and weigh 2,000 lbs. The large parts can be 12' square and weigh 50,000 lbs. or more.
Machining large parts requires large machine tools. There are two well-known large turbine manufacturers in Georgia and South Carolina that have the largest lathes in North America. These machines can swing 200-ton rotors that are 18' in diameter and 50' long. Vertical turret lathes that swing 12' are common in these shops, and the horizontal boring mills can cover 10,000 square feet of floor space. (Ship building and similar industries also machine large parts, but not in the same quantities.) Everything in a turbine goes across a lathe or a mill.
Not only are the parts big and heavy, they are expensive. It is common to have castings and forgings in front of the spindle that are worth $100,000, which makes this a high-risk endeavor. Much like aerospace machining, there is little room for error. A few microns of misalignment in the setup or a typo in the program can create a seemingly minor defect that will send that $100,000 part to the scrap yard.
Because the stakes are high in this game, companies that machine these components have very sophisticated processes that reduce the risk. These processes include detailed planning for the machining operations, well developed simulation programs and detailed quality plans. Creating these detailed plans requires a team of people that do nothing but program and write instructions for the machinists.
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It takes special people to generate these plans. These experts need to be skilled with CAD/CAM, machining techniques and metrology to be successful. Most of the manufacturing engineers that are good with large parts were the best machinists. Finding these people is very often like finding a leprechaun on a unicorn.
Having a good process plan for these large parts is just part of the equation. Finding machinists willing to run these large parts is also difficult. Obviously, this kind of machining comes with a large amount of financial risk, so pushing the start button can be a stressful situation, and some people can’t deal with the risks. It is also more physically demanding than “normal” machining. Large parts require large machines and large tools. Machinists have to walk longer distances, climb stairs and wrestle large tools. Setting up a large lathe can take several shifts, and the physical effort needed to make adjustments and clamp parts into place can be exhausting work.
Cycle times on these large parts are measured in days not minutes. Watching a VTL make the same motion over and over can also be draining for some. It takes a special person to tolerate the hours of mental and physical activity setting up followed by days of inactivity watching the repetitive motions of the machine.
Components are large and often made from difficult-to-machine alloys. There are no buttery smooth aluminum or brass parts in a turbine. Everything is made from alloys that are difficult to machine. The easy to machine parts are made from special steel alloys that don’t like to chip easily. The more difficult parts are made from high nickel alloys like Inconel and Hastelloy that can frustrate the most experienced machinists and programmers.
Unlike smaller parts, it can be impossible to spin these large parts fast enough to get the proper surface speed for machining. These large lathes are designed to rotate large diameters at proper cutting speeds. However, turbine discs often have smaller turned or bored features that require speeds that the machine cannot achieve. This makes the already difficult-to-machine alloys more difficult.
You might think milling would be straight-forward because the large parts are stationary. Not so. Inevitably, you will need to bore a hole that seems like it is on the other side of the state. The resulting tool is a stack of high dollar extensions that looks like a broom stick protruding from the spindle. On the worst days, that same tool extension gets a face mill on the end instead of the boring head and you spend multiple shifts trying to slay the chatter monster.
Machining power generation components was the most challenging work I have ever done. But it was also the most interesting. If you get the opportunity to visit one of these large manufacturing facilities, take it. There are things there that many people will never get to see.
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