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. 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.