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Energy Parts Machining

Geoff Giordano
By Geoff Giordano Contributing Editor, SME Media

Multi-tasking machines, ceramic inserts, additive manufacturing and automation help produce a large mix of energy industry parts

The ever-volatile oil and natural gas industry—roiled most recently by September’s drone attacks on Saudi Arabian oil facilities that temporarily reduced the kingdom’s output by nearly half (about 5 percent of global production)—faces particularly challenging requirements for machined components to meet evolving supply targets.

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Heavy duty gas turbine components continue to grow in size, with GE’s largest machines exceeding 15’ in diameter and 30’ in length.

While additive manufacturing and automation are increasingly figuring in to energy industry machining practices, unique requirements like highly specific thread designs, large parts and superalloys require special understanding of how to make components that can perform optimally in harsh environments.

“If one were to sum up CNC machine tool characteristics required for a sizable portion of oil-and gas-related parts with a single word, that word would be ‘large,’” said Ted Winkle, Houston Tech Center Coordinator for Okuma America Corp., Charlotte N.C. “Downhole well-completion tools parts frequently have a long length-to-diameter ratio, necessitating lathes and mill-turn centers with long beds and steady-rests. These long parts often require lathes equipped with long projection, damped boring bars for extended reach [for] internal machining.”

Meanwhile, machining parts for wellhead equipment like blowout preventers and fracking blocks and fluid ends require milling centers with large work envelopes, he added. “Heavy machining of the high-temperature superalloys frequently specified for oilfield parts favors machines with high-torque spindles and box ways. Oilfield pipe threading operations require large lathe spindle through-bores.”

Ultimately, however, part production for energy extraction is a high mix/low volume affair; components range from “palm-sized, weighing ounces to vehicle-sized, weighing tons. Despite the fact so many energy sector parts share common traits—for example, so many of them being round—there really is no ‘typical’ energy part because of the ever-changing, highly engineered, application-specific nature of parts used in downhole tool assemblies,” said Winkle.

Given this diversity of part sizes and geometries, many machine tools used for energy parts on the smaller end of the scale are the same as those used for producing parts in other industries.

Large workpiece envelopes and high precision machining with small features are the hallmark of contemporary energy part production, according to Blake Fulton, senior advanced manufacturing engineering manager for GE Power, Pittsburgh.

“One of the common paths to a higher efficiency HDGT (heavy duty gas turbine) is to increase the volume of air passing through the machine while minimizing surface area, resulting in larger components,” Fulton noted. “Components over 3' (0.9 m) long are no longer uncommon, and in the case of turbine wheels and casings, 6', 8' and even 10' (1.8 m, 2.4 m, and 3 m) dimensions are now commonplace.”

Yet while the overall size of components has grown over time, he added, “individual features and tolerances for improved sealing and leakage have continued to shrink. HDGT’s are relatively simple machines in principle; however, GE differentiates its products by paying close attention to the small features and controlling tight tolerances.”

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While additive manufacturing enables significant design changes, it also can require very intricate post-process machining of complex superalloy components for final assembly.

Typical oil and gas shops have machines “that can take large depth of cuts but lack capabilities for true high-feed machining due to the horsepower and torque curves,” noted Dennis Kidwell, machining specialist for Sandvik Coromant, Fair Lawn N. J.

Equipment vs. Material Issues

A key influence on machine choice is the predictably unpredictable ebb and flow of the fortunes of the energy industry.

“Manufacturers find that they do not have time to experiment with new machines and processes when the consumption of oil is up, and don’t have the money to do it when oil is down,” Kidwell explained. “For many years, the attitude toward newer machines [has been], ‘If it isn’t broke, don’t fix it!’ The parts are processed the same way as 20 years ago using the older horizontal boring machines and slant turn lathes.”

Among the key characteristics of machine tools used for machining energy parts, Kidwell noted, include:

  • Geared headstocks and horizontal boring mills with indexing B-axis,
  • Vertical machining centers with a fourth-axis rotary table,
  • Large horsepower slant bed lathes with static tools, and
  • FANUC/Mazatrol machines.

While the machines might have generally remained similar over time, the materials they are machining have gotten much more demanding, “and that has resulted in a productivity gap,” Kidwell said. “We have to compromise between the cutting speed, depth of cut and feed per tooth that we want to run versus what the CNC machines are capable of running. This balancing makes it harder for productivity and profit gains that are needed for investing for future process improvement.”

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Okuma’s VTR-160A, a double-column vertical lathe with milling capability, is particularly useful for oilfield parts, according to the company.

Kidwell recalled that within the past 10 years, there has been a push here and there “from some energy service companies to invest in newer multi-task machines,” including, for example, Mazak Integrex machines and DMG Gamma/Beta dual-spindle machines. “This was with good intentions, but the results have been mixed, with many customers using the old processes and tooling on the new machines, which just didn’t show great improvement in throughput. It was obvious to many tooling companies that the problems were more from the lack of investment in new tooling and programming techniques that would have taken advantage of the newer machine technology.”

Sandvik Coromant tools are hardened and machined to reduce tool runout and pocket distortion and deformation when machining current superalloys, ensuring consistent long-term performance, Kidwell continued. “We also decided to initiate our own oil and gas component solutions that utilize standard and custom tooling, coupled with our own full-time programmers to offer proven, turnkey solutions to our customers. This has allowed them to implement new tools and programs faster than ever by having us come on-site and do the part run-offs with little investment of time from them. Our customers have taken advantage of our offer that they just place a PO for the tools [where] they have seen giant ROI with no risk.”

At Okuma, the company’s “Turn-Cut” is a relatively new machining center and multi-task machine option that emulates lathe turning by orbiting a single point tool, Winkle explained, “effectively replacing traditional U-Head tooling for turning and profiling off-center external and internal cylindrical and spherical profiles.”

Multi-task machines are ideal for minimizing setup time and floor space for downhole tools, which are overwhelmingly cylindrical but often include milled features “to some degree,” he explained. “Lathes with milling turrets and Y axis can handle light milling on predominantly turned parts, eliminating the need for secondary milling center operations. Multi-axis turn-mill centers with H1 dual function heads like Okuma’s Multus series are perfect for these ‘lathe’ parts that require more extensive milling, off-axis milling, angular bores, and multiple operations that benefit from having a sub-spindle and the ability to machine both sides of a part in a single setup.”

Image 4 Sandvik oil and gas threading action image.jpg
Sandvik Coromant’s CoroThread 266, available with an assortment of grades and geometries, is used for rigid external and internal thread turning in oil and gas applications. Over and under coolant provides chip control and adds process security, while iLock technology increases stability and provides accurate positioning.

The widespread use of high-temperature superalloys in oil and gas-related parts “has led to rapid improvements in traditional carbide tooling grades, as well as more exotic cutting tool materials, such as ceramics and PCBN, for both turning and milling,” Winkle continued. “Improvements and new developments in sintered powder substrates and coating technologies have doubled the cutting speed capabilities of a decade ago, along with fewer cutting tool grades required that cover a broader range of cutting conditions.”

The use of ceramic inserts offers customers “highly productive methods for machining superalloy-based parts,” noted Martin Dillaman, manager of applications engineering for Greenleaf Corp., Saegertown, Pa. Greenleaf offers grades including WG-300, WG-600 and XSYTIN-1.

“Ceramic inserts provide stable heat evacuation and predictable wear at speeds up to ten times faster than carbide alternatives,” Dillaman said. “Utilizing the heat resistance and strength of ceramics, higher speeds plasticize material in the shear zone of the cut, and then easily remove material with a sharp cutting edge. In one example with our XSYTIN-1 grade, we successfully cut the full length per index of an Inconel 718 part, 35" long (889 mm), running at a speed of 450 sfm, feed of 0.030 IPR, at a DOC of 0.075" (1.9 mm).”
Greenleaf also offers its Ring-Max products for cutting API grooves into blocks. “These grooves can be cut into the base material with carbide inserts, and into the Inconel overlay with ceramic inserts,” Dillaman said. “Both options are done with the same style cutter with a single plunge.”

Parts that benefit from machining with ceramic inserts include fracking blocks, back flow preventers, various couplings and chambers used for the drilling industry.

“The equipment we see is mixed–older lathe and mill equipment—focused on a few features of a part, to modern multi-tasking machines capable of generating the geometry for the entire part, using turning, grooving and milling applications,” Dillaman explained. “We offer solutions for the customer in both instances, and will also custom design tooling that can provide additional productivity.”

With customers demanding faster delivery of products, “every second the part is at the spindle is critical. The material removal rates that our inserts and tooling offer can reduce operations that took hours to just minutes.”

GE Power’s Fulton concurs that ceramic milling inserts “have changed the game with how we rough components. New wear-resistant coatings come to market every day, as do better grinding abrasive and bond technologies.”

Handling Special Features

Those unfamiliar with the energy sector are typically surprised to discover how critical threading is to energy production parts and how extensive the range of oilfield-specific thread designs employed are, Okuma’s Winkle noted.

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Photogrammetry, or structured light metrology, collects hundreds of thousands of data points to give a holistic view of part compliance in a matter of minutes or seconds.

“No other industry has parts featuring such a wide diversity of special thread forms with such critical performance requirements and tight tolerances,” he explained. “Threads on energy parts are expected to both connect and seal, and continue sealing while subjected to tremendous pressures, temperature extremes, and dynamic loads. Some of these threads are proprietary designs requiring licensing to produce—VAM threads being a prominent example. As such, there is an abundance of cutting tools, toolholders, and indexable inserts designed solely for machining energy-specific threads, from single-point turning and thread milling to multi-tooth thread chasing and hobbing.”

Several tooling manufacturers have developed industry-specific cutting tool systems for machining common features like API seal ring grooves and hydraulic port profiles found on many oil and gas parts, he added.

“The long length-to-diameter ratio of many energy parts necessitates the use of ‘anti-vibration’ boring bars sometimes exceeding 10:1 overhang ratio. At the same time, oil and gas parts frequently have deep internal undercut profiles and acute undercut angles. Thus, special boring bars and replaceable boring bar heads with extended cutting projections and non-standard cutting lead angles are frequently required.”

Special combination tools are also common, he said, combining external and internal turning, facing and threading operations on a single toolholder.

Additive, Automation, Digital and More

In spite of the energy industry’s often small lot size, in-process automation has a definite place, said Okuma’s Winkle. Then there are items used in fracking and perforating operations that are non-reusable and produced in larger lot sizes, which makes automation—such as robotics for loading and unloading the machine tools machining these parts—a viable option. Machine pallet and fixture handling automation systems can likewise improve productivity by minimizing downtime associated with the machine waiting between cycles for parts to be loaded into fixtures. Automated bar-feeding and pipe-handling systems are common in energy parts machining due to the cylindrical forms of a sizable percentage of parts.

Another new technology that has potential in energy parts is combining additive material capability into traditional CNC machining centers, “a feature found in Okuma’s new Laser EX series hybrid machines.”

As its name implies, “Laser EX machines include a laser head that sinters powdered metals to fuse built-up solid features onto the workpiece,” said Winkle. “This permits part geometries that are simply not possible through conventional subtractive CNC machining and the ability to build-up structures, then selectively remove material from the structures within the same machine setup.”

The technology also allows manufacturers to build-up structures of one material type to the base workpiece of a different material, “which could be useful for hard facing on high-wear surfaces of energy parts. A version of the Laser EX technology also provides in-machine zone case-hardening.”

Meanwhile, digital “smart” tools can provide constant real-time feedback of cutting conditions so adjustments can be made on the fly to counter undesirable conditions such as chatter, he said. “This is especially useful in oil and gas shops due to the widespread need for extreme projection tooling.”

Also, coolant delivery, filtering and management help manage heat input into the components, said GE Power’s Fulton. “Both wire and sinker EDM power supply technologies improve with every generation, yielding lower recast and heat input. We’ve also seen significant improvement in laser processing capability, and hole-drilling technology continues to improve in many forms.”

Maintaining Accuracy, Performance

The large size and complexity of energy parts can prohibit the use of CMMs and other common metrology equipment, cautioned Okuma’s Winkle.

“Many part features must be checked mid-process, while the part is still chucked or fixtured in the machine tool so that positional tolerances are maintained prior to proceeding with subsequent operations. Thus, in-machine metrology systems like part probes, laser measurement, robotics-assisted gaging, as well as specialty gages from manufacturers like GageMaker are widely used in the energy industry for part feature measurement.”

Machining HDGT components “is a paradox,” asserted GE Power’s Fulton. “While our components can be quite large and require high material removal rates to rough in a reasonable cycle time, the high temperature and stress that our engines endure require low residual stresses in the finished components. Workholding and tooling rigidity, tool sharpness and thermal management are all keys to [achieving] this end.”

While CMMs, CAM software, CNCs and high-pressure through-spindle coolant systems have all improved greatly, so too have quality, repeatability and cost.

“Measurement technology has also improved significantly since shop-floor stable coordinate measurement machines and higher-speed scanning heads are now common and reliable,” Fulton continued. “We’ve also embraced photogrammetry (commonly referred to as blue light or white light scanning) with high-speed collection of hundreds of thousands of data points to give a holistic view of part compliance in a matter of minutes or seconds.”

Furthermore, improvements in radiography (X-ray and CT) power and signal processing “allow us to inspect tiny internal cooling and fuel passages. Film cooling holes are critical to performance for us, and newer scanning technologies in this space that allow direct measurements of hole position along with diffuser shape and size are exciting. These technologies, coupled with more functional performance tests utilizing infrared and acoustic technologies, provide us with a better picture of component conformance to design intent than ever before.” 

Programmable Presses Speed Development to Manufacturing

When a Midwest customer that produces drill heads began developing a new product that required precision compaction of powders into near-net shapes before sintering and assembly, they turned to the Promess Electro-Mechanical Assembly Press (EMAP).

Programmable electric press technology, which has been used in the automotive industry for close to 20 years, is only now beginning to be recognized in the energy sector and other areas, said Glenn Nausley, president of Promess Inc., Brighton Mich. “The compelling benefits of this technology assure its rapid and widespread adoption.”

Typically, he explained, a product development team will use “off-the-shelf components to cobble together a system to do a production and assembly proof of concept. Then, once all the bugs are worked out, it will be up to your manufacturing engineering team to figure out how to produce the product in volume using an entirely different system with its own set of bugs and challenges.”

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A Promess customer that produces drill heads used the 300 kN Electro-Mechanical Assembly Press in the lab and later in production.

To produce drill heads for mineral exploration, coring, mining and oilfield applications, the process involved compressing a carbon diamond powder mixture into a mold with forces up to 60,000 pounds (267 kN); that pressure had to be held for a specific amount of time prior to sintering. “The compacting force and dimensional requirements for the ‘green’ components are critical process parameters.”

In the past, Nausley explained, “they would have used a hydraulic or pneumatic press in the lab and another on the production system.” But this time they chose the Promess 300 kN EMAP, “a fully programmable, all-electric servo-driven press equipped with integral force and position sensors that allow the process to be monitored and controlled in real time.”

Once development was complete, Promess’ customer was able to use the same EMAP work station in production.

“The lab-developed process was exactly duplicated in production, because the lab machine really is a robust production machine,” said Nausley. “And because it’s fully programmable, they use the same EMAP work station to press the finished inserts into the drill heads with force and position feedback to ensure consistent quality.”

Fully electric programmable presses like the Promess EMAP save users time and money by letting them seamlessly transition processes from the development lab to the production floor, he added. “While designed for the production floor, their programmability and built-in force and position sensing make them ideal for process development labs.

“Using the exact same equipment in the process development lab as you do on the production floor offers many advantages,” Nausley continued, “not the least of which is eliminating the often expensive and time-consuming task of re-engineering the production solution once the production equipment is available. An all-electric solution is also cleaner, quieter and much more energy efficient than a hydraulic or pneumatic alternative.”

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