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Simplifying and Moving Beyond Five-Axis Machining

Ed Sinkora
By Ed Sinkora Contributing Editor, SME Media

Machine builders add features and software that make five-axis machining more compelling

Machine tool builders are making complex five-axis setups easier, such as this one from DMG Mori.

Five-axis machining, once a novel and somewhat forbidding technology, has become routine in many shops. Meanwhile, some organizations are still hesitant to use it, largely due to programming concerns. No matter which camp you belong to, you should know that machine builders are adding features and software that make five-axis machining more compelling for an ever broader set of applications.

Let’s explore the key additions.

Virtually all five-axis programming occurs in the office using CAD/CAM software, which has become awesomely powerful. But it hasn’t solved every challenge, and every machine builder we spoke with has introduced new products that plug the gaps. For example, DMG Mori USA, Hoffman Estates, Illinois, has released 42 Technology Cycles, covering a broad range of technologies. These are canned routines for a variety of machining cycles provided by DMG that complement a user’s CAM software. According to General Manager of National Engineering Jeff Wallace, some CAM packages “do not have the native capability to do some of the more advanced routines right out of the box.”

Users have to write something custom, cheat the system, or create additional geometry to drive the cutter a certain way. Polygon turning is a good example. “Most systems can’t just spit that out. But you can invoke our Technology Cycle and enter simple pass variables. It’s a canned cycle they can call up,” he said. “And it’s an editable cycle too. Let’s say the programming department makes a mistake, and for whatever reason the operator needs to call this cycle up and make some adjustments. It’s already there.”

Gear skiving is another “big one,” said Wallace. “There is no CAM system I’m aware of that can generate the right code for any kind of gear skiving. It either has to be done longhand, or the way Sandvik approaches it, with a spreadsheet you fill in that then spits out G-code you load into the machine.” These techniques work, but are cumbersome. With DMG Mori’s Technology Cycles, the operator can enter variables at the control, or “if you set up your CAM system’s post processor correctly, you pass the variables to it and you have what looks like a canned routine coming out of your CAM system to do gear skiving.”

FreeTurn is another example of the DMG Mori Technology Cycles. It automatically moves the rotary A axis to keep a turning tool perpendicular to the part, no matter the shape you are trying to cut, explained Wallace. “That has multiple advantages. You get the surface footage you planned on, and you get better surface finishes.” And, for tough materials that would cause excessive tool wear, he added, “you can roll around the radius of a cutting tool and move that cutting notch to different locations once your tool starts to wear. It’s very difficult for any CAM system to program this and I do not know of any that can do it natively right now. There are several that can cheat it. You have to build additional geometry, and so forth.” With FreeTurn a user can pass the variables to the cycle without having to drive the moves from their CAM system.

The Methods MB 450U five-axis machining center comes with FANUC’s FAST Package III, which extends and perfects what is exported from CAM packages.

Wallace added that FreeTurn works with both a standard multi-axis lathe configuration (what you might call a conventional mill-turn) and a vertical five-axis machining center. You wouldn’t ordinarily think of the latter as a mill-turn, but put a three-jaw chuck on the rotary C-axis table and it becomes a lathe’s rotary axis, while the spindle holds a turning tool, explained Wallace.

Better Models, Better Toolpaths

For Methods Machine Tools, with corporate headquarters in Sudbury, Mass., the goal is to provide Methods brand five-axis machines so complete “there’s nothing left to buy,” said Product Manager Nick St. Cyr. A key component is the inclusion of FANUC’s FAST Package III. FAST is an acronym for FANUC Advanced Surface Technology, a set of features St. Cyr said FANUC spent years researching and testing with the goal of extending and perfecting what comes out of a CAM package.

“You still need a CAD/CAM package to create that toolpath,” explained St. Cyr. “But the upgraded FAST Package III allows people to use new options that FANUC has only recently released to enhance the machine tool’s output so it closely matches the model.” For example, the tiny facets that approximate a curved surface will be smoothed out. “There’s a particular feature called smooth tolerance control that takes everything from nano smoothing to tool center point control, and it enhances all of that.” He went so far as to say this package “truly tells the customer ‘you can have your cake and eat it too.’ It not only makes your program go faster, it can also improve the surface finish.” St. Cyr admitted he’s often met with skepticism on this point, but said, “You have to trust the system, and program specifically for the part.”

Robin Cave, software engineer for Mazak Corp., Florence, Ky., echoed the importance of improving the link between the CAD/CAM system and the machine control. It’s something Mazak focused on in creating its new SmoothAi control, which was designed specifically for simultaneous five-axis machining, and its own Project Manager software.

As Cave explained, Mazak worked with various CAD/CAM vendors to enable a much higher level of communication between the machine and the off-line programming station. “The CAM system can, at any time, get parameters out of the control: 3D models, stroke limits, rapid feed maximums, and feed rate maximums. It can get the current tool data out of the control and all the current work offsets,” he said.

Thus it goes well beyond the built-in machine models that come with most good CAD/CAM packages. As Cave put it, a setup might look perfect in the simulation when using a canned model, “but out on the floor, especially on a five-axis machine, you’ve got tool reach, you’ve got part location on the table. … It’s really easy to say the part is dead center on the table, but in reality it’s pretty hard to actually put it there. That’s okay if you create the part from raw stock, but if you’re working with a forging, it’s where the forging is fixtured. By inputting the offsets from the machine for that fixture or for the part, and importing all of the tool data directly from the machine, I know exactly what that machine’s tooling is capable of. And I can specify any needed changes.”

Equipped with a Fagor Automation control, this Soraluce floor-type HMC can switch between multi-axis machining heads from the cabinet at left, changing its kinematics on the fly.

Cave added that if the machine has a trunnion table, the part position is perhaps even more important. If the part isn’t on center, “tools reach farther to get to the part.” And even though the control supports offsetting that “allows you to put the part anywhere you want to in the envelope,” larger offsets can cause problems.

“If the offset is within a couple hundred thousandths of center, that’s OK,” Cave continued. The tools aren’t going to vary that much. But if the part is three or four inches away from center, those tools have to reach a lot farther across the table to do their job on certain aspects of the part. That could create a situation if the tools aren’t properly spec’d for the length they need.” Plus an operator may use a big collet system to hold an end mill that needs to stick out three inches, observed Cave, and that might interfere with the part. But if the engineer in the office sees the actual offset (as enabled by Project Manager), “he can run a simulation independent of the machine and find that kind of information out.”

Fagor Automation’s Artur Gugulski, CNC sales manager for the Elk Grove Village, Illinois-based company, said its control is unique in being able to define incline plane and combine it with a rotation tool center point (RTCP) algorithm simultaneously, and “very easily. This way, a machine has the ability to align and cut large, five-axis parts without having to relocate them.” What’s more, he said, Fagor also satisfied customer requests to be able to jog the tool during the execution of five-axis programming. “Our virtual axis has the ability to follow the real-time angular position of the head. Instead of using a single standard axis of movement like X, Y, and Z, the virtual axis is imaginary and it represents the direction in which the tool is itself oriented at all times. What makes our virtual axis unique is that it follows the programed toolpath. The operator can jog the tool in and out, increasing or decreasing the depth of passes. All this happens on the fly, [when] machining the part. You can combine the virtual axis with all the other functions, RTCP and incline plane. This feature is widely used in automotive prototyping applications, custom aerospace parts, and semi-finishing passes.”

More Ways to Ease Setup

It’s not a new idea, but some shops underestimate the value of zero-point fixturing when it comes to easing the setup burden. According to DMG Mori’s Wallace, that’s especially true when you add automation to try and “feed the beast” (your super-productive five-axis). “The big pallets from Erowa are an example. It’s very easy to fixture parts outside of the machine, or set up a new part, and then auto-load parts.” If you have a robot and smaller parts, he added, you can put diverse parts into 3R Erowa chucks and “within two minutes you’ve got one part out and the second part in, with no set up, because they’re repeatable to microns.”

Smart probing is also essential in automating the steps required to start machining. St. Cyr said all Methods MBU series five-axis machines come with both a Blum spindle probe for locating the part and a Blum laser for measuring tool length and detecting tool breakage. If the shop includes a probing routine in its part program, “they can put that part into any kind of fixture or any kind of workholding, and immediately the probe does all the hard work,” said St. Cyr. “So there is no more finding the center of the part, no more resetting a workpiece coordinate system. And even if it is a five-axis part and they need to find the kinematic center, all of that is already installed in the machine and ready to operate right out of the box.”

In this application, 3D volumetric compensation teaches the control to automatically eliminate almost all machine errors, which is critical for making aerospace composites on large, light structure routers.

DMG Mori uses the same sort of 2D optical check of the tool, but Wallace said this approach doesn’t yield information about the condition of the tool farther behind the tip or in the flute face. “The tip may not be chipped, but most of the cutting may be a half inch up into the tool and there is no way to verify that area now. We will be introducing technology next year that takes a 3D scan of any tool, whether it’s a turning tool or a milling tool, that we can evaluate in three dimensions. We can check each flute, the length of the flute or flutes, and the corner radii. … We’re trying to make it more efficient. We’re trying to take user intervention out of the whole system.”

A more esoteric, and downright mind-blowing capability from Fagor is the ability to define and store up to six different machine kinematics and then change them on the fly. Gugulski explained that this comes into play with relatively expensive machines in which the user can change the entire head, as opposed to just a cutting tool—or perhaps change from a rotary table to a trunnion table. “You might have a five-axis head on the top and then add a rotary table to start making parts that require seven-axis machining,” Gulgulski offered. “Our custom definition allows the OEM to implement this so all the user needs to do is input the appropriate G-code.”

Making such changes otherwise would take hours, and, as Gugulski pointed out, improving changeover time is often at least as important as machining time when it comes to productivity and competitiveness. “Let’s say you are working on a job, and suddenly another customer offers to pay triple for a completely different job if you can deliver it quickly. If you can’t change over quickly, you cannot take the job. You have to refuse it.”

CAM systems can’t output gear skiving cycles, but one of 42 Technology Cycles from DMG Mori can.

Eliminating Machine Errors

One of the most profound, yet least understood, improvements in five-axis machining today is the ability to use the machine control to compensate for errors in every axis, across all six degrees of freedom. As Gugulski sees it, “kinematic calibration is absolutely critical for five-axis machining because machine dynamics change over time due to various factors like temperature fluctuations, wear and tear, and crashes.” Fagor’s volumetric compensation process starts with a 3D laser measurement of the machine, using systems available from several third-party vendors. From there, the operator need only add a few data points to a “simple and intuitive” HMI and the software automatically “makes corrections and lists the translation, rotation, and geometric errors for the entire machine,” explained Gugulski. “This functionality significantly improves machine precision, achieving up to 80 percent better accuracy after the compensation is applied.”

In one example Fagor provided, a machine’s X-axis position deviated from the intended position across a range of 0.28 mm over 3+ m of travel before volumetric compensation. After volumetric compensation, the maximum average error dropped to 0.01 mm, for an average error improvement of 96.4 percent. To take another example, Z-axis straightness relative to the X axis went from a maximum error of 0.12 to 0.02 mm, an improvement of 80.7 percent. “We have users that make very expensive parts who consider this feature absolutely essential to their process,” said Gulgulski. “They are blown away by how easy it is to use the feature, and they run the cycle before starting every expensive job. It is also extraordinarily helpful for the OEM when commissioning the machine. Without this cycle, you have to measure everything on the five-axis head down to the hair. With kinematics calibration, you can ballpark this measurement, even with just a tape measure, and the cycle will calculate the absolute measurement saving an incredible amount of time.”

Gugulski added that the feature is especially useful on the large routers used to cut aerospace composites. These routers are relatively “medium-duty, light-structure machines” because the application doesn’t require a heavy-duty machine. “But typically you can’t build a light-structure machine that’s as perfect as a heavy metal-cutting machine.” Yet aerospace customers require high accuracy, so volumetric compensation is critical. As Gugulski put it, you’re laying the responsibility for maintaining accuracy “onto the control.” He added that defense contractors, and aerospace contractors in general, have to regularly certify the accuracy of their machines, above and beyond proving that the components they produce meet quality standards. “You can’t sell a machine without this capability. If you can’t fix the imperfections by volumetric compensation or another kind of compensation, the aerospace customer will pick another vendor.”

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