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Tips for Choosing a CNC

Ed Sinkora
By Ed Sinkora Contributing Editor, SME Media

It’s not as scary as you might think

Like most of the digital architecture of manufacturing, computer numerical controllers (CNCs) have advanced rapidly in recent years, producing far more processing speed and implementing advanced algorithms, while at the same time offering simpler, more intuitive user interfaces. So how to choose between the different types of CNCs? Need to settle on one? And how would you introduce new versions, or entirely new CNCs?

Large touch screens are the CNC interface of choice for new-generation machinists, like this example from Heidenhain.

Let’s get one critical issue out of the way at the start: there are probably more options than one might think. As Gisbert Ledvon, director of business development, machine tool, for Heidenhain Corp., Schaumburg, Illinois, explained, many people assume they can only get the control they saw in the machine demo, or what the salesperson presents. But that’s generally not the case. He cites the example of DMG Mori, a large builder of sophisticated machines. “You can buy a DMG machine with the Heidenhain control,” he said, “[or] get it with a Siemens, or with a FANUC. The mechanics, the casting, the ball screws, the service support, and so forth are all the same.” Or as Paul Webster, CNC engineering manager for FANUC America Corp., Hoffman Estates, Illinois, put it: “The machine tool builder decides what control is going to go on [its machines]. But the end user influences that decision to a great extent by specifying what they want.”

Ease of Use Considerations

Ease of use is the foremost consideration in choosing a CNC for many shops, probably due to the challenge of finding enough skilled labor. “Most of the time,” said Webster, “they want what they already have in the factory. And going back to the ‘70s, ‘80s and early ‘90s, FANUC had the most reliable control and the most consistent control.” While there is some debate about how user friendly FANUC controls are (more on that shortly), they are certainly ubiquitous. “FANUC’s user interface has grown over 40 years of history,” observed Webster. “And a lot of factories still have FANUC 6M, 6T, and 10T controls that are 30-plus years old.” This also points to the fact that there is an appropriate FANUC control for virtually everything in a factory that needs a CNC, whether it’s a motion controller for ancillary equipment like a conveyor, or a punch press, a five-axis machining center, or an Index turning machine with eight independent spindles, each running a different process. “They are different types of control systems, but they all act and feel similar,” explained Webster. “So the guy that runs the machine tool could jump on the ancillary equipment and run it, troubleshoot it, and do maintenance without any issues.”

Todd Drane, regional sales manager for Fagor Automation –USA, Elk Grove Village, Illinois, also thinks it’s helpful to standardize on a control across different manufacturing areas. And Fagor implements the same user interface from application to application. “With Fagor Automation, if you learn our turning CNC, then you know our milling CNC too, because the menus and methods of creating and executing the programs are identical,” said Drane. “Of course on a turning machine you are calling up different canned cycles than on a mill, but the method in calling them is identical. The obvious benefit is that your shop floor personnel are more interchangeable and versatile.” Drane added that Fagor has also developed CNCs for a variety of applications that go beyond traditional milling and turning, to include “grinding, lasers, routers, waterjet, and general purpose motion control applications. We also have the ability to create custom editors, screens, pages and routines on all of our CNC platforms quickly and easily, hence, whatever the customer requires, we can accomplish.”

Controls 2.jpg
For more than 60 years, Cox Manufacturing has been serving a variety of industries including aerospace, defense, firearms, oil and gas, electronics, and medical with high-quality machining services. Company Owner and President Bill Cox, shown here at a machine control, standardized his machines on FANUC CNCs.

Both Webster and Drane point to the user interface, or HMI (human-machine interface) as a key consideration. But strictly speaking, the HMI is distinct from the CNC, and in some cases the machine tool builder overlays its own customized HMI. The builder is more likely to do that for specialized applications, like grinding, and sometimes they do so to create what they hope is a competitive advantage over a more “generic” interface. (Ledvon noted Heidenhain users are an exception in that “the whole interface, the keyboard, and the touchscreen itself, always shows Heidenhain functionality. We don’t really have anybody overlaying that, except for some of their own cycles.”) Exploring those variations and how they were created is beyond the scope of this article. We’ll concentrate instead on distinctions between what the major CNC providers offer.

Broadly speaking, the ubiquitous FANUC control we referenced earlier offered M&G code programming from a keyboard and wasn’t very flashy. You could say it was easy to use because “everyone” knew how to use it. When it came to five-axis machining, an engineer created a machining program with a CAD/CAM package and used a post-processor to generate the M&G code that ran on the machine. Users didn’t, and generally still don’t, program five-axis work on the control. Ledvon said the world is moving beyond the approach of defining a line or a radius in abstract language. We’re moving instead toward conversational programming with “shorter, clear instructions that say ‘I want to run a drilling cycle,’ or ‘I want to run a skiving cycle.’ You just answer a few questions and the control does the rest for you. That’s where we are now. It’s going to be more interactive and simpler.” And—no surprise—the on-machine programming will be via larger touchscreens with smartphone-like features (like pinch-to-shrink and touch-and-swipe) to tag and copy, and so forth.

These changes are being driven in part by a younger generation of machinists entering the field, but Ledvon said older operators embrace these techniques as well, if possibly a bit more slowly. “In our experience, after three to six months they usually don’t want to go back to the other way,” he said.

Heidenhain has long taken the conversational approach, but FANUC hasn’t been sleeping. It introduced a friendlier touchscreen interface called iHMI in 2016 and have rolled out major improvements during the last few months. For example, Jody Michaels, FANUC America’s national sales manager, said the earlier interface made kinematic calibration so difficult it required a FANUC expert. Now it’s an icon on the HMI. “You just fill in the blank and press cycle start,” explained Michaels. “Obviously, you have to make sure that things like the probe and the stylus diameter are set up first, but it’s as simple as that.”

FANUC has also broken out some of the probing routines, so users can apply them without having to go through the old menus. It also added the ability to import tool data (feeds, speeds, coating information and other tool descriptions) from external sources, which is a common industry practice that FANUC had resisted.

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Fagor controls incorporate both G-code and conversational programming systems on the same CNC, plus on-board CAD/CAM systems, interactive editors, and help modes.

Michaels also said FANUC’s iHMI now enables the direct importation of actual part geometry into a conversational program. “We never had the possibility of doing that. Now you can import a DXF or IGES file, or a solid model, so you can program without having to draw the part on the control. That’s a big departure for us.” Ledvon said this capability is used a lot in Europe and is catching on in North America as well, especially for simpler parts and in mid-size job shops. “Taking advantage of a CAM importer to convert a DXF or IGES file into a machinable program, right on the control, is much more efficient than going back to the CAD/CAM guy and waiting in line, because he has to feed five, six, seven, eight, or ten machines.” Ledvon also sees this as a way to empower younger operators who embrace this approach, and theorizes that this will contribute to better retention across the industry.

Still, Webster cautioned against making radical changes to the user interface, using the analogy that switching the gas and brake pedals in a car would be disastrous. “We’re being pulled in two directions, because the people with factories full of FANUCs don’t want to change,” he said. “So we need to keep everything similar. But new operators coming out of school are used to smartphones and things like that, and they want to use a touchscreen and simplify it. The iHMI allows for some of that newer style but doesn’t pull us so far away from the existing interface that people panic.” He added that the vast majority of machines running the FANUC CNC use the FANUC HMI with only limited customizations “for the specifics of the machine tool, like maintenance screens and things like toolchangers or other parts that aren’t defined by the CNC itself.”

For its part, Fagor has incorporated both G-code and conversational programming systems on the same CNC, “plus on-board CAD/CAM systems, interactive editors and help modes combined with easy touch directly into the manuals right on the shop floor from the keyboard,” said Drane. “Once a programmer or operator learns and understands these CNCs, which is fast and often in less than a single day, we then stack additional new technology features on top of this same platform. Hence shop floor operators simply need to learn new technology features on a platform they are already familiar with. The comfort factor is evident and we see more new technologies being used by operators.”

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Edge computing keeps most calculations and processing on the edge device and not the CNC, while the machines continue to operate in real-time. This extends the capability of CNCs and lessens the importance of choosing a specific CNC.

Precision and Other Performance Considerations

Besides ease of use, other key considerations include machining precision, speed, and reliability. Heidenhain and Fagor are said to be the only control builders that can provide the entire motion control system. As Ledvon put it, “you get the drive from us, the scales, the encoders, the motors, and the control. Buying something from a third-party always leaves something out when you get into micro-accuracies and super surface finishes.” He credited Heidenhain’s leading position in the demanding moldmaking industry to this factor, and added that “99 percent of the time,” when a machine tool builder chooses the Heidenhain control they use them for the entire system. “Sometimes we don’t sell the motor,” said Ledvon, “but all Siemens motors have a Heidenhain encoder.”

Webster pointed out that all FANUC controls “do everything to the nanometer. Most scales aren’t accurate anywhere near a nanometer. The loss of resolution is not in the CNC. It’s definitely on the machine side, not on the control side. The scale manufacturers say their scales are much more accurate than the mechanical machine, which I agree with. And the machine guys say their machines are more accurate than the workholding. The workholding guys say [their devices are] more accurate than the tooling. It trickles down. But the CNC is not the limiting factor whatsoever. It’s not even close.” He added that FANUC builds its own motors and encoders, and the motor encoders have up to 32 million pulses per revolution. “When you’re talking about incrementing a single rotation of a ball screw into 32 million counts, that’s a lot of resolution to work with.” What’s the answer? Talk to users you trust and get a thorough demo!

Moving on to speed, the top CNCs all use state-of-the-art CPUs and more memory to process programs faster. That makes things like high-speed machining much better than years past. But besides more raw processing power, it pays to consider whether the control takes advantage of other clever methods to boost efficiency. That includes features like adaptive control, which automatically adjusts the feed rate based on the tool load, and automatic servo tuning.

The latter often relied on an expert from the CNC maker. But CNCs from FANUC, Fagor, and others are now better at “checking all the feedback on all the drives and motors and tuning them to the optimum setting automatically,” explained Michaels. That can make a significant improvement if you’ve put an unusual amount of weight on your machine table, or have otherwise changed your setup.

Image 5 Heidenhain - TNC640_DXF_de.jpg
An increasingly popular feature of today’s CNCs is the ability to convert a DXF or IGES file
into a machinable program, right on the control.

Ledvon highlighted Heidenhain’s push to add functionality to its conversational menus. “For example, jig grinding is now one of the features of the control. We can do pocketing with trochoidal milling. Things you would ordinarily do on a CAM system can now be done right on the control.” The goal is to do more things on a five-axis machine in a single setup. “You don’t have to go from a five-axis machine to a jig grinder to grind a certain portion of a specific part,” he said. “You can now do both on the five-axis machine because multi-functionality from different technologies can now be managed with one CNC.” Ledvon also observed that a good, stable machine tool equipped with Heidenhain scales is “almost like a CMM from an accuracy point of view, and you can at least do a pre-inspection on the machine before the part comes off.” This is one of many ways a machine tool serves as a “nerve center,” in Ledvon’s view, providing a wealth of useful information to the factory.

Tiansu Jing, product manager for Siemens Industry Inc., Elk Grove Village, Illinois, offered a different angle: edge computing. Edge computing keeps most calculations and processing on the edge device and not the CNC, while the machines continue to operate in real-time. “In the past, different CNCs focused on different applications and all related features, including hardware, were developed accordingly by control suppliers,” he explained. “Many shops chose a specific control because of this difference.” Edge computing breaks down this boundary and extends the capability of CNCs. “With edge computing, different applications can be used to offer more machine performance to increase cutting quality and productivity.” Jing added that by connecting the CNC to the edge device, local server and the cloud, “there are possibilities for different entities to offer their own expertise to the end-customer via apps in the cloud.”

On a related point, Jing said “remote service is becoming more reliable and cheaper. With the complete digital twin solution, which includes not only a virtual CNC but also virtual machine mechanics, machine tool builders and CNC suppliers can have a comprehensive solution to duplicate what machine shops are using and for troubleshooting customer problems. This methodology can significantly reduce the downtime caused by the issue and increase the productivity of end users. At the same time, this will dramatically reduce the service cost for machine builders.”

Things That Drive CNC Experts Crazy

It turns out that the major CNC providers often find their customers not fully using the amazing technology they’ve already paid for. According to Michaels, continuing to use the inverse time method in five-axis machining is a prime example. “We’re finally getting people to use tool center point control, tolerance control, and the machining conditions function where you can speed up roughing and slow down finishing independently within the program,” he said. “But it has taken years and there are still people asking their modern CAM software to generate a program with G93 inverse time code,” whereas the newer method yields both a faster cut and a better finish.

Ledvon said users often don’t take full advantage of the integrated machining cycles in the control, which can be much more efficient at making a part. He offered the example of a customer who forgot that his touchscreen had a right arrow key to reach another cycle. The customer wanted to add a drilling cycle to his program so he used his CAM software to create roughly 200 lines of code to do this, when he could have simply pushed the arrow and answered a few questions to create the drilling cycle.

“Many people assume the control does only what another machine did a year ago, or three years ago,” he observed, “and that’s not the case. That’s why we push training.”

Webster said the reluctance to embrace modern CAM programming is probably the biggest contributor to lost productivity. Sometimes it’s just a failure to use the latest post-processor. “There are helpful G-code features that people aren’t using, either because they don’t know they exist, or their CAD/CAM system doesn’t support it,” he explained. “We still see a lot of people posting programs out of their CAD/CAM system with straight G-1s. [They make] just very small line segment linear moves, even though there are many new programming techniques and functions. Many CAM systems and the post processors aren’t as up to date as the CNCs in the field, yet CAD/CAM is very inexpensive today and much easier to use.” Sometimes the best investment is fully using the investment you’ve already made.

So What To Get?

When choosing a CNC, take a serious look at your business model, advised Ledvon. “To do mostly production work with large lot sizes, with operators that are not that skilled, then certainly standardize on a control. But I don’t think that’s the way to make money anymore. To grow into new market segments, or to get a higher margin business with smaller lot sizes, you need flexibility in your setup.” This means multi-function machines and the best controls for the applications a company decides to pursue. “Because if you continue to buy the same control as the shop down the road, the only way you’re going to compete is on price. You need to find a way to differentiate yourself, and that’s one way to do it.”

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