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Raising the Stakes with High-Speed Aerospace CNCs

Pat Waurzyniak
By Patrick Waurzyniak Contributing Editor, SME Media

New features for fast milling and turning operations enable the latest CNC machine controls to up the ante in aerospace productivity

High-precision machining is mandatory for mission-critical parts in this aircraft turbine engine.

In the aerospace world, as in all sectors of manufacturing, the race is on for faster, more automated and connected machining operations. Aerospace builders have steadily pushed for more automotive-like automation over the past several years in order to improve productivity and more effectively handle large order backlogs in commercial aviation. Key aerospace and defense (A&D) CNC controls functionality offered today by most major machine control developers include faster cutting operations techniques for part cycle-time reduction combined with much smoother, more-efficient precision cutting to improve part quality.

The push toward digitalization in the manufacturing industry, with manufacturers leveraging Big Data and the networked machine tools of Industry 4.0/Smart Manufacturing, also is having a major effect on what CNC machine control developers offer A&D CNC users. The digitalization trend extends to the inclusion of more sophisticated links between machine programming and part programming. In addition, some other key trends in the aerospace sector include much wider use of robots and newer methods of machining the composite materials used for many aerospace components.

Digitizing and Robotizing

One of the big challenges in aerospace manufacturing lies in using the data generated by digital devices as they go about their normal routines, said Digital Factory Application Engineer Gabe Manescu, Siemens Industry Inc. (Elk Grove Village, IL). “A typical CNC controller generates a large amount of data that may hold values unknown until such data are analyzed and used in other ways,” Manescu said. “Generating new interfaces at the controller that allow the harvesting of such data gives way to new technologies. For example, by connecting a Sinumerik CNC controller to a simulation system, such as our NX–MCD [Mechatronics Control Designer] platform, we get the virtualized machine model, which now includes the physical behaviors and the real controller [Sinumerik CNC or Simatic PLC], including its front end [HMI], if necessary. With this tool, machine functions can be developed, tested and optimized under conditions very close to the real world. This way, we offer the convenience of a maximum degree of security and safety [for humans, machines and workpieces].”

At Siemens, this solution is Virtual Commissioning, Manescu said. “We consider it our answer to the ‘Fast-Safe-Precise’ trichotomy,” he added. “Another example of the power of digitalization resides in the use of analytic tools to study the behavior of mechatronic systems by examination of the data being generated as the systems do their work. This tool gives users the benefits of increased uptime and asset availability, asset optimization and maintenance efficiency.”

Five-axis machine techniques help FANUC CNC machine controls cut precision parts from hard-to-cut materials including Inconel.

With robotization, aerospace potentially can employ much more automation than in the past. “Robots are fast becoming a true success story in the aerospace and defense world,” noted Daniel Martinez, aerospace market manager, Siemens Industry Inc. “Siemens is bringing robots to the next level by offering three types of robotic integration to the CNC.” Martinez said this includes Siemens Sinumerik Integrate Run My Robot/Easy Connect, which quickly connects with plug-and-play integration. Used mainly used for machine tending, this integration facilitates the communication and coordination between robot and machine controllers, he said.

The Sinumerik Integrate Run MyRobot/Handling function allows users with no specific robot know-how to program and operate the robots, he said, as everything is interfaced via Sinumerik Operate. Finally, Martinez said Sinumerik Integrate Run MyRobot/Machining offers users continuous path control with integration of Siemens PLM Software’s NX CAM programming and VNCK (Virtual NC Kernel). “For a while now, there has been a push to use robots for secondary operations such as deburring and surface finish,” Martinez said. “This solution allows the programming of a robot in the same manner as a five-axis machine for light cutting applications.”

Fast, Efficient Machining

There’s no doubt that the continued digitalization of manufacturing is at the forefront of trends in aerospace today. “Process data tracking with integration into manufacturing systems is probably the most obvious trend,” noted Rick Schultz, aerospace program manager, FANUC America Corp. (Rochester Hills, MI). “CNCs have to easily have key performance data available for various data analysis systems.

“Another trend that isn’t as obvious is the trend from machine programming to part programming. In aerospace there are a wide variety of machines and due to legacy methods and difficulties with process certification, the programming methods are often inefficient and inflexible,” Schultz added. “The variety of machines and resulting CNC application inconsistency creates variation in programming leading to manufacturing delays and significant support costs.”

CNC developers need to assist the industry to adopt modern part-centric programming methods, Schultz noted, while taking advantage of the processing power in modern CNCs to do things like real-time spline algorithms that result in shorter cycle times, better part quality, and a more consistent/easier to maintain manufacturing process. “This mindset change is a much more difficult effort,” he said, “but the long-term rewards for production facilities is significant.”

Specialized part routines that are geared for aerospace help CNC operators cut parts more efficiently, with greater precision especially on the contoured components often encountered in aerospace machining operations.

New machine control routines like Advanced Dynamic Prediction on the Heidenhain Corp. TNC 640 CNC help users cut aerospace parts with high accuracy.

New trends for aerospace machinists include more automated processes, like automation of setups on five-axis milling and turning machines such as Okuma’s five-axis auto tuning function for its OSP controls, noted Brad Klippstein, CNC product specialist, Okuma America Corp. (Charlotte, NC). Most of Okuma’s aerospace customers are machining parts on Okuma five-axis MU series machines, he said, particularly on the company’s Multus lathes. “Right now we see quite a bit of traction there with volumetric errors, and our five-axis auto tuning enables users to easily make adjustments, using an algorithm to set parameters for a machine control.”

In addition, the Dynamic Tool Load feature offers a new control function for Okuma MU series milling machines, Klippstein said. “It’s targeted for aero because it’s for hard-to-cut materials like Inconel,” he said. “It helps with runout because as the tool rotates it’s going to automatically adjust the feedrate per insert blade. Let’s say you need to change a tool. It’s automatically going to change the rate for you—it equalizes the cutting force dynamically while the tool’s in motion.

“The new algorithm does this, giving you equal cutting force,” Klippstein said. “The goal is to increase tool life, and from the studies that we’ve done, it’s improved tool life by about five times for stainless, and about two times for titanium.”

Automating with Precision

Much of the automation added in aerospace CNCs revolves around precision machining. With the latest Heidenhain TNC 640 CNCs, aero machinists can automate monitoring functions and eliminate some human factors in production, noted Julian Renz, TNC product specialist, Heidenhain Corp. (Schaumburg, IL). “With aerospace, automation becomes more important,” Renz said. “Our Advanced Dynamic Prediction [ADP] is a feature for better smoothing. This is an algorithm that if there are too many data points, it can fix it and it optimizes feed rates.”

Automation can lessen or lower the need for operator intervention, particularly in monitoring functions, Renz said. Optimizing and smoothing techniques can remove chatter on the part.

“Basically it’s our path control concept. Instead of splines, we use a tolerance band to connect the data points. It lets the user decide the width of the tolerances and the corresponding acceleration and jerk values are determined in the back of the control. Thus, you let the CNC stay within those parameters with our Control Contour Cycle; it’s called Cycle 32.”

The new Advanced Dynamic Prediction also plays a role in the CNC’s look-ahead functionality, helping to determine how many lines ahead it can look during the cutting process, he added.

For Siemens Sinumerik CNC users, the company’s Top Surface contouring offers a better surface finish. “The functionality of MDynamics with Top Surface is a new option,” said Siemens’ Martinez. “We are getting independent of the CAM systems, thereby achieving the best surface quality.”

The Top Surface option offers three key features, he said, including surface quality enhancement that is improved with diagonal toolpaths for finishing. “[Quality is] significantly enhanced during bi-directional milling thorough direction independent identical smoothing of the milling paths,” Martinez said. This feature offers users preset values for contour tolerance and orientation tolerance, and increased independence from calculation tolerances used in CAD/CAM. New friction compensation also allows smoother finishes.

Velocity improvements also are gained, he added. “Due to the improved smoothing of the toolpath with Top Surface, the milling process tends to get smoother. … In certain cases, the reduction of machining times is possible when tolerances ≥10 mm are used.” Since it effectively uses larger tolerances; Top Surface keeps acceleration and jerk limits, he added, and in particular cases, the machine-specific dynamic parameters may be increased by the OEM in order to reach reduced machining times. Accuracy and precision are improved with Top Surface, making the new functionality “Smoothing” in Cycle 832 available, he said.

What CNC Operators Want

In aerospace, the most common request is data accessibility, noted Frank Nuqui, FANUC aerospace program manager. “In general, data accessibility is relatively simple. The FANUC CNC has easy-to-use, well-defined interfaces that can work with any manufacturing system or OEE-style data analysis system.

A titanium jet engine blade is precision-machined using the latest Okuma Corp. OSP open-architecture machine controls.

“Machinists are becoming a rare commodity in the industry and there’s often only a few true machinists in major facilities trying to support all production,” Nuqui added. “Due to the resulting incredible workload and the necessity to standardize on processes for certification reasons, most machinists ask for the functionality they’re already familiar with rather than new capabilities. It is common practice in aerospace facilities to take the latest FANUC 30i-B control on a new machine and use it the same way CNCs were used in the ’80s and early ’90s.”

FANUC is trying to help educate and ease the machinists and programmers transition into adopting the latest functionality and help facilities gain significant benefits from new technologies that simplify postprocessors, Nuqui said. He added that speeding the time from art concept to part manufacture while reducing cycle time and improving part quality are also part of the goal. “This is one of the greatest challenges in aersospace production—breaking the cycle of ‘doing what we’ve always done,’ and stepping into the modern and much more efficient processes that modern CNCs can help enable.

Cutting Aero Composites

Another major trend in aerospace CNCs is the proliferation of the use of composites in airframe components, which are very difficult to cut without damaging the workpiece through delamination of the composites.

“More and more our customers are in need of advanced machining technologies to handle complex carbon fiber-reinforced polymer [CFRP] materials,” said Art Gugulski, Midwest regional manager, Fagor Automation Corp. (Elk Grove Village, IL; Mondragón, Spain). “Those materials are delivering high strength-to-weight ratio, durability, and extreme corrosion resistance to lightweighted structural components. The machines needed to handle those materials can be not as massive as for metalcutting, but on the other hand must be equipped with high-speed spindles, large machining envelopes and high measuring accuracy in three- and five-axis applications.”

Fagor CNC systems handle those challenges with advanced compensation tables for lead screw, axes cross-compensation and machine volume compensations—volumetric 3D table compensations, Gugulski said. “All those tables are applied continuously to axes positions to achieve high levels of machine accuracy,” he said. “Combining CNC compensation tables with high-performance temperature-independent linear rotary absolute encoders, Fagor created a win-win situation for OEMs and their very demanding aerospace machine users. This trend will continue since the carbon fiber materials are the main choice for aerospace applications.”

Some features offered to Fagor’s aerospace CNC users include the company’s Finetune auto-tuning software, Gugulski said. “This is a very fast process that automatically tunes the machine. It is possible to verify machine design without advanced knowledge of tuning or control system theory,” he stated. “The OEM is equipped with optimal adjustment for each machine they produce free of human errors. All this reduces the cost of the commissioning process for machine builders and savings for end users.”

Kinematics calibration enables users to to calibrate kinematics for the first time, said Gugulski, “and every so often, re-calibrate it to correct the possible deviations originated in the day-to-day machine work. This feature allows machine user to assure everyday machine accuracy required by the certification process.”

Other Fagor CNC features for A&D machinists include a new hand wheel with wireless technology, the High Speed Surface Accuracy with HSD Dynamic Override, nanometric interpolation advanced algorithms for smoothing tool’s speed, and advanced look-ahead algorithms to optimize part time, Gugulski said. “The machine operator can override in real time the parameters of the High Speed Surface Accuracy algorithms with HSD Dynamic Override,” he said. Fagor’s CNCs also have optimized HSC modes for each machining condition.

Moving into the IIoT World

No discussion of CNC development would be complete without including what developers and users are seeing in new technologies of Smart Manufacturing and Industry 4.0, as connected machines of the Industrial Internet of Things (IIoT) make fast, real-time sharing of shop-floor data a reality.

The drive toward more connected machines in the manufacturing world is starting to build momentum, as evidenced by small shop owners who previously didn’t see the need now being intrigued by the possibilities. While the demand for connected manufacturing simply hasn’t been there for the small shop, many shop managers and owners now want more.

Fagor’s Machine Dynamic Override algorithm helps operators ensure high-precision cutting with real-time adjustments as needed at the machine control.

“We have tools such as automatic transmission of data from the presetter to the machine control, and checking for run times,” said Heidenhain’s Renz. “Production data monitoring hasn’t been used as much in smaller shops, but it’s coming.”

“Everyone wants data and everyone is aware of all the buzzwords and acronyms. The problem is very few currently have a clear vision of what they plan to do with the data,” said FANUC’s Schultz. “As a result, the majority of the connected manufacturing efforts I’ve seen to date are segmented and small in scale. At any one aerospace company, there are multiple, distinctly different efforts to do connected manufacturing.

“From the FANUC CNC’s perspective, all data is available and easily accessible,” he added. “Accessing the data is the easy part—figuring out what to do with the data is what most aerospace facilities I visit struggle with.”

Siemens has developed multiple digital solutions to address the digital twin need from the machine/process perspective by completely digitizing the machine, noted Siemens’ Manescu, “thus allowing the OEM to bring to market machines with up to 30% reduction in the development time, plus the part perspective which subsequently can be run back into the virtualized environment. In such ways, non-productive machines aren’t present anymore on the shop floor, concepts and new avenues can be assessed and proven before the machine build. Likewise, expensive mistakes can be avoided before happening, so the proving tests are virtually risk-free.”

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