It’s no surprise that in late 2023, the experts involved in making parts for energy production wanted to talk about wind turbines and batteries. But good old oil and gas shouldn’t be disregarded yet, and chasing tight tolerances is always an exciting endeavor.
Windmills are becoming an increasingly attractive method of generating electricity, as it’s becoming necessary to build them in the United States. As Eduardo Barocio, Ph.D, director of the Composites Additive Manufacturing and Simulation (CAMS) Industrial Consortium at the Composites Manufacturing and Simulation Center (CMSC) at Purdue University, West Lafayette, Ind., explains, the constant drive to boost efficiency demands higher energy production per windmill. This has resulted in scaling up blade sizes to 80 m or longer, which makes them impossible to transport over land. Such giant blades must be built near either a terrestrial wind farm or a port from which they can be shipped to an offshore site. What’s more, the usual approach to making wind blades is complex and labor intensive.
The CMSC at Purdue and its industry partners, Thermwood Inc. (Dale, Ind.), TPI Composites Inc. (Scottsdale, Az.), Dassault Systèmes (Waltham, Mass.), Dimensional Innovations (Kansas City, Mo.), and Techmer PM (Knoxville, Tenn.) are tackling these challenges by automating the production of segmented modular molds that can be transported on a standard truck and assembled on site.
The centerpiece of the approach is Thermwood’s large-scale additive manufacturing (LSAM) machine that features a “robust and repeatable” process that goes beyond common horizontal-layer printing to include vertical-layer printing and even “angle-layer printing,” according to Barocio. This allows the machine to produce continuous parts across the entire length of its 40-ft (12.2-m) bed—but achieving the accuracies and material properties required for the blade molds necessitated solving tough technical problems.
“Large-scale additive manufacturing is a multifaceted process,” Barocio points out. “There are multiple complex phenomena that occur simultaneously, and it’s always a balancing act.”
For starters, he lists carbon fiber as a key enabler to take AM technology from desktop to the multi-meter scale. But, in this case, the objective of adding the material isn’t to augment part strength but to combat thermal stresses.
“The thermal stresses that cause a part to warp or lift up are due to two factors,” Barocio explains. “One is the temperature difference between layers. And the second is the coefficient of thermal expansion (CTE). The CTE can be zero or, in some cases, even negative in carbon fiber along the fiber direction.”
By adding short fibers to the printing polymer, the CTE of the printed composite material is reduced in the direction of dominant fiber orientation.
“If we decrease the temperature difference between layers, the problem we might encounter if we go too far is that the previous layer hasn’t developed enough stiffness to support the next layer,” Barocio continues. “So, there is a problem of thermal management. But the more we reduce the CTE, the less differential shrinkage between adjacent layers will occur.”
Unlike subtractive machining, the AM process has a profound effect on the material properties of the resulting part. Taking this into account, the Purdue team developed a virtual twin of the manufacturing process.
Dubbed ADDITIVE3D, the new system involves the most relevant physics that develop in the process, according to Barocio. This includes anisotropic phenomena such as transient heat transfer, shrinkage, thermoviscoelasticity, polymer crystallization and melting kinetics, and interlayer fusion bonding. “It also captures complex interactions of the printed part with the ambient environment and with the substrate on which it is printed,” Barocio says.
Purdue’s simulation models anticipate cases in which the part is likely to fail due to delamination or even lift off the substrate due to residual stresses. “So instead of iterating, experimentally, until you get the process conditions right—spending potentially thousands of dollars in engineering time, machine time and material—you can do that virtually,” he explains. “You can print a geometry right the first time.”
A wind blade’s mold segments need to connect so well that they provide “vacuum integrity,” Barocio says. That’s no easy feat, given their size (about 2.5 m wide by 8 m long), with 10 to 12 segments making up the combined mold to create a blade. “Something that may seem rather simple, like alignment, obviously becomes more challenging,” he notes. “And since we’ll have a modular tool, we will have joints in both directions along the length and across the width. So it’s essential that we create the proper design and implementation of those joints.”
In addition to complex shapes, wind blades have varying thicknesses. Thus, the thermoset resins used to create a blade have different curing requirements in different sections, which necessitates localized temperature control in the mold.
“Traditionally, the way these tools are made,” Barocio explains, “is by embedding complex circuits of heating wire during fabrication, which is a labor intensive process. In our case, we will be printing the heating elements in situ with the LSAM system. That allows us to print heating circuits with varying power densities and with multiple regions per layer. Thus, providing local temperature control not only along the length, but also across the width of the plate.”
The program (recently funded by the U.S. Department of Energy) will also develop and demonstrate innovations in new composite materials systems for economy and performance, plus post tensioning of the modular assembly for support frame weight reduction.
Wind turbines don’t spin fast enough to generate electricity without a transmission—and, as you might expect, that gearbox needs to be big. “The shaft itself, depending on the model, can be several feet in diameter, or several inches,” says Tom Dolan, vice president of Mitsui Seiki USA, Franklin Lakes, N.J. “The gearbox housings are quite big, up to several meters in length and perhaps a ton or more in overall weight.”
At the same time, a high degree of precision is required in order to ensure reliability and efficient power transmission. For example, a gearbox housing would generally include long bores and paired bores that must be an exact distance apart, with true centerline parallelism.
“We try to keep everything within five to 10 microns, both for the position of bores and the concentricity of bores, plus the alignment of bores,” Dolan says. “Machine tool geometry is critical to achieve those large bores and a long distance between bores. Essentially, one would have to rotate a gearbox 180° and approach it from both sides in order to make a tolerance that’s correct.”
As such, Mitsui Seiki would typically offer its HU100 or HU150 machining centers for this application. The setup would feature a rotary table, according to Dolan, and “anywhere from one and a half to two and a half meters of stroke to accommodate very large components that can weigh one to several tons.”
Dolan suggests that satisfying these tolerances takes a machine tool that’s “made perfectly well.” That includes hand scraping ways, which “allows you to achieve certain tolerances that machine tools themselves generally cannot. That is to create imperfect surfaces that become perfect when they’re assembled. Imagine putting a large component onto a machine tool table. The bed may distort a little due to the weight of the component and you would end up with sag in certain areas. So if we scrape, as an example, a crown of 3 or 4 microns across a long distance on two slide-way surfaces that are parallel to each other, we can actually accommodate any metal deformation due to workpiece load.” That’s just one example pointing to why, as Dolan points out, “there are just a few companies making machines for these applications.”
Marcel Schreiner, global segment director for Freudenberg Sealing Technologies’ energy sector (U.S. headquarters in Plymouth, Mich.), says the industry’s drive for greater efficiency places intense focus on developing engineering solutions that deliver long-term reliability under diverse and demanding conditions. The company provides sealing solutions for the main bearing, blade pitch, main gearbox, tower and nacelle of wind turbines.
Schreiner explains that both the form and the materials must be considered. “A turbine with a sharp, one meter rotor diameter, versus one that has two and a half meters, may need a different seal design. The edge for sealing grease is different from one sealing oil. You may also need a different kind of seal material if, for example, you want to place your turbine in low-temperature conditions, such as in Canada, where temperatures go down to minus 40° centigrade or colder, versus building it in Texas.”
Part of the challenge, Schreiner observes, is developing seals that operate across a wide range of temperatures, rotor diameters, shaft speeds and other variables, while also delivering solutions that work in the extreme cases. But, he adds, there is no single answer.
Much of Freudenberg’s engineering expertise goes into the proprietary elastomers that form the heart of many seals. Schreiner compares this to baking a cake, which requires both quality ingredients and a careful process to create the right material.
“Typically, an elastomer consists of the base rubber, which is something like MBR or EPDM or FKM,” he says. “We also add ingredients to support the vulcanization process, plus other additives that bring out special properties. Our mixtures are unique and customized to the evolving needs of the industry.”
Recently, for example, Freudenberg introduced a new EPDM material developed specifically for high-voltage cables that transport electrical energy from floating offshore wind turbines that are exposed to high stresses. Traditional high-voltage cables can only withstand water pressure up to a depth of about 50 meters. At depths of 100 meters or more, the resulting pressure requires that the cable be protected from damage by rubber blocks inside the modules. To this end, Freudenberg created a new EPDM material specifically for these extreme conditions to help a windpower customer achieve new depths.
Schreiner cautions against focusing on cost, which he says can lead to questionable purchasing decisions. With all the seals in a wind turbine only totaling about 0.1% of the total cost, he argues, it makes no sense to shave a few pennies by skimping on them. Especially since the seals can make the difference for maintaining shaft lubrication, leading to complete failure.
“Within one hour, you’ve lost more than the cost of the entire sealing package of a turbine,” Schreiner asserts, noting that it could take a month to get to the turbine, figuring out what went wrong and fixing it. “So the turbine stands still for one month because of a component that actually has no real budget impact.”
With the ongoing scale up of electric passenger vehicles, the competition for batteries is fierce. But there’s been much less interest and investment when it comes to electrifying heavy equipment, mining vehicles and marine craft. To serve these niches, Lithos Energy Inc. can quickly create new battery variations, without having to do “ground-up engineering every time,“ says CEO James Meredith.
The Haywood, Calif.-based company’s approach relies on its own system architecture, which uses standard 2170 cells. “The battery management system and electronic communication would carry over for each pack design,” Meredith says. “And we take that a step further, using the same mechanical, thermal and electrical connections to the cell. The way we build the modules and the assembly methods all stay the same.”
The architecture is scalable, and Meredith says there is a high confidence of passing certification tests each time a new form factor is created.
To date, the company’s battery packs have ranged from 2 kWh to multi-MWh, and from 40 to 1,500 volts. Most of its systems are in the 800-900-volt range, Meredith says. However, Lithos’ highest unit sales are for the electric hydrofoil surfboard, the LIFT EFOIL.
For automakers and their Tier 1 suppliers trying to cut EV battery costs, Ann Arbor, Mich.-based Coherix Inc. sells a pioneering system that inspects, and even controls, the application of adhesives. The system uses four laser sensors attached to the robotic nozzle to capture a 3D image of the adhesive bead as it’s being laid out at up to 800 mm per second. Software running on a high-speed computer simultaneously analyzes the image in real time.
Coherix has supplied more than 3,500 of these systems to 53 automotive OEMs worldwide, 17 of which are using them in battery projects. While many of the applications are strictly for inspection, General Motors, Ford, Mercedes, BMW and Toyota all use Coherix’s adaptive process control option to automatically adjust the nozzle’s vertical position. This ensures that the right volume of adhesive is applied, explains Chairman and CEO Dwight Carlson, in addition to tracking the X/Y position.
Carlson claims Coherix doesn’t have any competitors in 3D computer imaging, while 2D systems struggle with assessing volume or seeing anything when adhesive coloration matches the surface.
“Other technology can’t think fast enough to run autonomously and that’s exactly the sweet spot for Coherix,” Carlson says, estimating that 80% of the value is in the software. As he puts it, being able to both see fast enough and think fast enough to run autonomously is the magic combination that will facilitate the factory of the future.
Mitsui Seiki also boasts solutions for battery trays and electric motor core dies, two of the newer energy applications that introduce new challenges. But let’s instead consider the problem of how to satisfy the world’s demand for the ample supply of natural gas.
Outside of North America, exporting requires converting it from a gas to a liquid, greatly reducing its volume and “making it significantly more stable and less volatile for transport by ship,” Dolan explains. Doing so requires routing the gas through a 20-30-foot series of impellers and inducers that compress and cool the gas to a very low temperature. (Hence the name cryogenic pumping system.)
The compressor wheels range from about 15" (381 mm) in diameter down to 4" (102 mm), Dolan adds, and they “require a very accurate airfoil-type form.” The gas volumes are staggering, he observes, so these compressors have to run at high speed over long periods of time. And the blades have to maintain their precise shape throughout.
“Airfoil profile tolerances are typically measured in the one to two thousandths of an inch range,” says Dolan. “But 15 to 30 or 40 blades have to be made exactly the same and the profiles are complex. So this takes full, true five-axis simultaneous machining at speed to generate the needed surface finishes, tolerances and part volumes.”
Mitsui Seiki tackles this with its Vertex line of machines, featuring full direct-drive capability and high-speed spindles running at 25,000 rpm. Dolan describes them as “very high accuracy machines capable of running at speed for extended periods of time.”
New IQ chucks and mandrels from Hainbuch America Corp., Germantown, Wis., combine embedded sensors and MT Connect capability to communicate a wealth of information to the machine control or external analysis software. All with contactless transfer of data. Depending on the configuration, this can include workpiece diameter, workpiece contact, clamping force, temperature and spindle speed.
To ensure a machine cleared chips and has gripped the next part properly, for example, the chuck itself would detect any foreign objects thicker than 30 µm and send that data to the control, explains Al Dopf, Hainbuch’s national sales manager. No additional gauging is needed.
One large automotive company uses a Hainbuch mandrel in an off-line fixture to measure part IDs. “It’s a ‘go/no-go’ test they can make right at the machine, without having to send the parts to the quality lab,” Dopf says.
The system also supports more complex analysis, he adds. “For example, let’s say you cut a diameter in OP10 and then transfer to the sub-spindle for OP20. The chuck can measure that diameter and if the part is ‘going south,’ you can make changes on the fly to prevent having scrapped parts.” Or you can track changes in clamping pressure to predict maintenance needs or the need to make adjustments.
Hainbuch also offers an interface that enables a quick workholding change, even with existing workholding or gear from other companies. Called centroteX and centroteX AC (the latter for auto-loading), the system features a flange attached to the machine’s spindle nose with a bayonet attached to the drawtube, and a mating flange is attached to each chuck to dial it in.
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