Getting a grip on advanced workholding systems
Smart chucks and zero-point locating systems, quick-change vises and modular workholding are good examples of advanced workholding systems, but you might be thinking, “Who needs it? Give me a 6" machinist’s vise, a three-jaw power chuck, some toe straps and a few T-nuts and I’ll make whatever parts you send my way.” And while this attitude is a bit optimistic for very large or very small applications, few would argue that these traditional shop tools can hang on to the lion’s share of all workpieces. This helps explain why they have long been the go-to gripping methods for most CNC lathes and mills. Why change?
One reason might be that you’ve decided to plunk a robot down in front of your shiny new machining center but require hydraulic or pneumatic workholding to do so. Perhaps you want to run different jobs during the night on your CNC lathe and need a way to automate jaw or even chuck changes. Maybe you’re machining castings and can’t figure out why the darn things come loose whenever the operator turns his back. Or it could be that you keep losing work to the shop down the street and want to regain the upper hand.
Whatever the motive, ditching decades-old vises and chucks for a modern workholding solution is an excellent way to improve any shop’s bottom line. Significantly reduced setup times, more consistent gripping forces, better safety and ergonomics—these are just a few of the benefits available to anyone willing to invest a little time and a relatively small amount of money in workholding. And for shops that wish to add nights and weekends to their operating hours but can’t find enough qualified people to work the first shift, let alone shifts two, three, and four, automation is the only answer.
Bridging the Gap
The good news is adopting an advanced workholding strategy is easier (and probably less expensive) than you might think. Eric Nekich, responsible for operations, technology, and inside sales at Lang Technovation Co., Hartland, Wis., noted that tooling manufacturers have done a good job of standardizing interface connections, simplifying the path to automation.
“Consider a basic, self-centering vise,” he said. “The actual gripping technology hasn’t changed all that much over the years, but what has changed is the ability to work with a robotic gripper, for instance, or direct mount the vise to a popular pallet-changing system like Erowa or another modular workholding provider. In fact, we offer two vise lines that come out of the box with an automation interface that could also be used with our competitor’s products. So, even though a customer might not be ready for automation now, they can spend a couple grand on a pair of vises and a mounting plate, use it manually to start, and then build on it or automate as their budget allows.”
Once a shop has decided to automate, they then face another choice—use the robot to load and unload parts, or use it to exchange the fixtures. In the first example, Nekich noted that the machining center must be equipped with hydraulics or pneumatics to clamp and unclamp the vise; in the second, the robot itself can be used to mechanically activate a zero-point clamping system. This is the concept behind Lang’s RoboTrex Automation system. Depending on the part size, it can be equipped with up to 168 vises and offers pneumatic or mechanical activation. “For a shop with lots of high-mix, low-volume work and older machines that might not be equipped for automation, this is a great option,” he said.
A Place to Call Home
Zero-point is (or soon will be) a familiar term to anyone aiming to automate their workholding. Not only are these quick-change clamping systems an integral part of any initiative to reduce setup time, they also provide a consistent reference location for robotic part handling and simplifying programming. Additionally, they provide a fast, easy way to clamp practically anything to a machine table. They can also be used across the entire shop, allowing parts to be moved from mill to lathe to EDM or even 3D printer, often in a single clamping.
Here again, though, some decisions must be made early on as to their use. “When a customer’s looking to palletize something, they can either attach the zero-point retention knobs directly to the vise or fixture, or install them on the bottom of a pallet and then bolt everything to the top of that,” said John Zaya product manager for workholding at BIG Kaiser Precision Tooling Inc., Hoffman Estates, Illinois.
Either way, a series of mating zero-point receivers must then be attached to the machine table, preferably using a standard layout across all of the shop’s machining centers. Once this is in place, changeover becomes a matter of minutes rather than hours, and can be done manually or—if so equipped—in an automated fashion.
“One popular scenario would be a rack filled with fixtures preloaded with workpiece blanks,” explained Zaya. “This fixture and blank combination is then picked up and set down onto the UNILOCK system [BIG Kaiser’s version of zero-point] and can be controlled by the machine’s controller or some other control mechanism. That same robot might also be outfitted with multiple grippers, so assuming you have a hydraulic vise or fixture, you can then use it to change workpieces as well. A variety of options exist, but they all start with some type of zero-point system.”
Not So Fast
Colin Frost, COO of Carr Lane Manufacturing Co., St. Louis, Mo., warned that automated material handling isn’t as simple as bolting on a few zero-point chucks. “Robots, like CNC machines, are exact; they struggle to analyze and adjust to thousands of minutia related to the position of the workpiece, the machine, and the workholding. Therefore, workholding for use with robotic loading and unloading is quite complex,” he said. “It’s critical that it allows for small misalignments between these different systems and still ensures accurate locating and clamping of the workpiece.”
With unattended machining, there must also be some method of verifying that the workpiece blank is in position, he said. This has led Carr Lane to develop a new product—a part-sensing rest button—to ensure that workpieces have been loaded correctly before placing the machine in run mode. The company has also developed a new style of edge clamp that can be operated manually or converted to automatic clamping. It is in response to the increasing number of customers attempting to grip on as little material as possible, and therefore machine more of the workpiece in a single handling.
“Customers are also asking for ways to collect data about their machining operations, and this includes the workholding,” he said. “Our partner Roemheld, for instance, has developed a line of sensor-equipped vises that allow users to monitor clamping forces. This can be beneficial in an automated environment, where the machine can be stopped if clamping forces fall below a certain level, or in a manual situation—for instance, if the operator ignores the work instructions and simply clamps the vise as tightly as possible when management isn’t looking. This information could be used to activate an alert or deactivate the cycle start button.”
A similar solution comes from Hainbuch America Corp., Germantown, Wis., with its TOPlus IQ collet chuck, which the company introduced at EMO this past September. “TOPlus IQ is an intelligent chuck that constantly measures the actual clamping force on the workpiece with sophisticated, integrated sensor technology,” explained Marketing Director Michael Larson. “The measured data is relayed via the contactless transmission of data and energy directly to the machine controller, where it is analyzed. The controller executes a target value comparison, and, if required, messages are displayed, or a correction is initiated.”
As the need for unattended machining grows, so will the popularity of such systems. Another comes from Röhm Products of America, Suwanee, Ga., where CEO Matthew Mayer agreed that manufacturers are looking at automation as a means to solve problems, among them a shortage of workers, quality concerns, or less-than-ideal productivity. One example of this is a turnkey solution that his team provided for a customer struggling to grip parts on a gantry-loaded CNC lathe.
“This particular customer uses various casting and forging suppliers and was worried about inconsistency and size variation,” he said. “Our solution was to mount one of our F-90 digital sensor heads on the hydraulic cylinder to determine stroke position down to 10 µm; this, in turn, allows us to measure the jaw position and therefore the size of the raw workpiece prior to machining. We then sent that information to a PLC, and if the size falls out of a predetermined range, it stops the machining cycle and alerts the operator.”
Röhm engineers also equipped the lathe’s main and subspindle chucks with air sensing for workpiece seat confirmation. On the main spindle, they used push-button style workstops for part sensing because of the rough casting surface, but utilized open airflow sensing and a mandrel on the sub to grip the machined surface. “In either case, the sensors send confirmation to the machine control and can stop the cycle if they detect a misload,” Mayer said. “This is critical for any unattended operation, where even a single chip can lead to a scrapped workpiece, or worse.”
Baring Your E-motion
Larry Robbins, president of SMW Autoblok Corp., Wheeling, Illinois agreed that more and more customers are asking for automation-friendly products. Like others interviewed for this article, his company has responded with a range of “smarter workholding” options, including its APS zero point and CSSmatic chuck changing systems.
Yet it’s an entirely new technology that has Robbins the most excited about the future of workholding, automated or otherwise. It’s called e-motion, and as he explained, it provides servo motor-controlled actuation for workholding. This not only eliminates the need for hydraulic or pneumatic actuation systems and their attendant plumbing but opens the door to previously unavailable functionality. “We’ve patented the wireless transmission of power over a 3-mm gap up to 1.8 kW,” he said. “That allows us to power a rotating chuck, a fixture clamp, a vise or series of vises mounted to a tombstone, all from the same base unit. All that’s needed is a pair of puck-shaped inductive couplers, an AC-MM controller, and a power source.”
Wireless transmission of electrical energy is an undeniably cool technology, but what’s even more cool are the doors it opens. Robbins noted that the system supports data transfer as well, allowing users (or automated systems) to remotely monitor and control clamping pressures or transmit job and machine information, all while the lathe or machining center is busy making parts. Furthermore, no hydraulics means no oil, less hazardous waste, and machine tools that are simpler and less expensive. “It’s a game-changer, for sure,” he said.
All of these Industry 4.0-capable vises and chucks are good news for manufacturers, but what about the shops that have to build their own jigs, fixtures, and other types of workholding? “We get calls all the time from equipment builders, tool and die shops, and others looking to automate their clamping,” said Reese Johnson, customer support supervisor and applications specialist for Vektek LLC, Emporia, Kan. “It might be the workholding for a linear transfer machine, a robotic machining cell…there’s all kinds of equipment out there where parts need to be held down in a certain manner, and the only option is a custom workholding solution. And more often than not, the people building it ask about automation.”
One possible solution is Vektek’s newest Advanced Workholding Pump, which Johnson said is designed to be integrated into a CNC or PLC for automated clamping and unclamping of fixtures via a controller. There’s also the new Guardian Pallet Pressure Monitoring system. “On a horizontal machining center, for example, the pallets inside the machine are often decoupled from the hydraulic power source,” he explained. “This system mounts to the tombstone or fixture, and has a pressure switch that communicates wirelessly with an external controller—if it senses a problem, it can be used to signal the CNC, telling it to stop the machine.”
VAST Solutions: Teamwork in Action
Johnson said the manufacturing industry is changing rapidly, and it’s important to ask for advice when venturing into automation territory, something he says the Vektek support staff is well-equipped to offer. So, too, is Cleveland-based Jergens Inc. In fact, this is the reason for the company’s Value-Added Solutions Team (VAST), “an experienced team of product and application specialists that we pulled together to help customers develop custom workholding solutions and use our products in the most effective manner possible,” said Ted Hoyt, western technical sales manager.
One of the drivers behind this, he noted, is the need for more rigid workholding in the face of aggressive machining strategies. Rather than the traditional “grab all you can and hog like crazy” approach to metal removal, shops are more often gripping parts along their bottom edge and taking full-length axial cuts at high feed rates and light radial engagements. According to Hoyt, this requires fixturing that is much more rigid than traditional workholding methods.
“We just did a demo with Okuma at Hartwig’s facility in St. Louis,” he said. “They were using a high-efficiency milling strategy in titanium, and the applications people said they removed more material in less time than they ever have in the past. That probably wouldn’t have been possible without our ZPS zero-point system. It provides ultimate rigidity, is extremely accurate, and can be automated. We’re working on several projects right now where we’ll send an electronic signal to activate a ZPS receiver, or use a robot to move a pallet into and out of a machine tool. There’s still a lot of development to be done in this area, but automation is definitely the future of the workholding market.”