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There is No Hold on Innovation in Workholding

Ilene Wolff
By Ilene Wolff Contributing Editor, SME Media

Companies are getting creative in order to make machining easier, faster and more precise

Enerpac’s SafeLink buys extra insurance that hydraulic clamping is ready to work.

When it comes to creative workholding solutions, Kurt Industrial Products Division doesn’t hesitate to replace one or even two of its old vises with a new one to get a better product.

Other workholding manufacturers—BIG Kaiser Precision Tooling, Fastems and Enerpac—are thinking of ways to make machine operators work better, whether it’s with five-axis capability, robotics, modularity or wireless monitoring.

Crossing Over to Improve a Vise

New from Kurt (Minneapolis) is the DX6 CrossOver vise.

“We’re calling it a CrossOver because actually we started this as a mix of two different vises,” said Steve Kane, sales and marketing manager for Kurt’s workholding tools. “One was our standard D688, and we took some features of our 3600V, which is what we call our CNC vise.”

Kane said Kurt melded some features from both vises, and then designed some new elements to make the DX6 more versatile.

Tyler Mardaus, design engineer for the DX6, said: “Of the bigger improvements that we did, one is we did a different type of brush seal from the original D688.”

The older vise had a manually pressed seal, meant to keep debris and coolant from the screw and nut assembly, but it was tricky to replace, Mardaus said. The new design features a special wave washer that creates force to hold the brush seal in place, and makes the task of removing the old seal and installing a replacement much easier because it’s a fitted component, Mardaus said.

Another change is the stationary itself.

The 688 has a stationary that was bolted through the body into the stationary from the underside, while the DX6 uses bolt-downs from the top that make it easier for the operator to remove. That’s because he doesn’t have to take it off the machine to get to the mounting bolts. The new design was also shown to reduce deflection in the stationary jaw.

Also new is the DX6’s ability to be mounted on a grid plate, something that wasn’t possible with the 688, said Steve Tschida (pronounced “cheetah”), engineering manager.

The new tool will mount on a 40-mm (1.57″), 50-mm (1.96″) or 50.8-mm (2.0″) grid pattern, an aid to precisely locating the vise on the table, which helps reduce setup time.

Another improvement relates to worktool changeover.

Because the DX6 is narrower (7.391″ [18.77 mm] than the DX688’s 8.75″ [22.23 mm] width), it may be possible to fit more of them on the worktable and maximize tool use.

“When it comes to utilizing your spindle and your machine, if you make one part at a time you [may] have many tool changes,” said Tschida. “So if you put two parts on the table, you cut your tool change time in half, if you put three parts you cut [it by one-third]. So density is sometimes important to help boost productivity.”

Kurt melded some features from two existing vises, and then designed some new elements to make the DX6 CrossOver more versatile.

Kane said, “You can put more parts on the plate or you can hold a longer part.”

Kurt is promoting other design and engineering elements, including the DX6’s lighter weight (65 lb vs. the 688’s 69 [29.25 vs. 31 kg]), its larger opening (9″ [22.9 cm] vs. the 688’s 8.8″ [22.4 cm]), and pull-style operation.

“With the pull-style vise you put virtually no stress into the body when you clamp, just into the end that’s stationary,” said Tschida. “If you reduce the stress into the body it helps keep the vise flatter and locates your part better when you clamp a part in it.”

Kane pointed out one last detail about the DX6’s design.

“They designed a through-body chip evacuation,” he said. “So with the D688, chips will go back and hit a wall and have to go out the sides of the device. With the DX6 they can flow straight through [and] right out the back.” This more direct way allows coolant and chips to exit the vise body and prevent chip build up.

Workholding Stacks Up

BIG Kaiser (Hoffman Estates, IL) is focusing on modular workholding for five-axis and five-sided machining, and said it’s all about flexibility.

“The uniqueness of our system comes in the fact that you can put it together to accomplish whatever you need for your specific part requirements,” said John Zaya, product manager for workholding. “With our five-axis system, we have flexibility at the table face, meaning we can put our units either in random locations on the table or we can put them in fixed locations via grid plates. We even have the ability to mount a knob to a grid plate or the T-slot.”

The Unilock Modular Workholding System has the ability to handle large or small parts, with appropriate fastening devices for sizes at either end of the spectrum.

“We try to accommodate what we see in terms of the gamut of small parts and big parts in all types of five-axis machines as well as in standard three-axis machines,” Zaya said.

He pointed out that operators new to five-axis machining sometimes fall back on old ways for the proper sizing of the machine to do their workpiece.

“Let’s say for example a customer has traditionally been working with a three-axis machine, they have had the ability to handle workpieces that can range in a variety of sizes,” he said. “So they can handle small parts, you know parts as big as your fist, and other parts as big as you with a three-axis machine because they can move to whatever position they need. There’s usually lots of clearance available in just those three axes of movement.”

However, Zaya said, when the operator switches to five-axis machining and five-sided machining with a large trunnion or gantry-style machine, and tries to machine small workpieces, the amount of clearance needed from the machine to the table and the machine spindle to the workpiece, becomes very constrictive.

Zaya said one of the common areas of interference is between the table of the machine and the spindle housing, because the table, as it rotates and pivots, often can interfere with the spindle housing if the workpiece is at center position on the table.

“Then the machine has to try and reach across that large table,” he said. “To remedy that gap from the edge of the table to the center of the workpiece, or to the center line of the table, the operator can do one of two things.”

He can bridge that gap with very long toolholders and cutting tools that allow him to work closer to the center of the envelope. But that creates a new problem. As cutting tools get longer, they get less efficient because they have to run at lower speeds and lower depths of cut.

The other option to provide clearance is to elevate the workpiece off the table, Zaya said.

“That becomes a more viable solution because in many cases the system like Unilock’s five-axis stacking system is much more rigid than the tooling could ever be,” he said. “So the workpiece is then held more rigidly at a higher elevation off the table, and that provides the clearance that’s needed for the spindle over the table and shortens the gap. Now the tools can be shortened and they regain their efficiency.”

The system creates new opportunities along with solving problems.

If the operator attaches a Unilock knob to the workpiece, he can easily move a part from one machine to another, doing rough cuts on a three-axis machine and finish work on the five-axis. Zaya pointed out there’s a further advantage in being able to take a part attached to the workholding tool to the qualification room where it can be mounted in the exact manner as it’s held on the cutting machines.

In addition to base units and extensions with some very long lengths, BIG Kaiser has a modular stabilizer system for lateral support of large workpieces.

No Pallet, No Problem with Quick-Change Clamping

When Fastems (West Chester, OH) needed to pick a workholding system for its six-axis robot-powered RoboFMS, it went with “zero-point” clamping from Schunk Group (Heuchelheim, Germany), because of its quick-change ability and high repeatability, said California-based Robert Humphreys, Fastems international sales manager.

“Our core business is factory automation and primarily integration of metalcutting or composite-type machining centers,” Humphreys said. “And as a result of that business we’re obviously touching on other technologies, such as workholding, zero-point clamping and all those types of things that go hand and hand with creating a solution, so it’s something we’re very familiar with and use a lot.”

Humphreys explained that the Schunk quick-change system produces very high levels of clamping force.

“One-point-five, two, sometimes three tons of clamping force in some cases,” he said. “So we’re creating clamping forces equivalent to the clamping forces securing a machine pallet within a typical HMC [horizontal machining center].”

The Schunk quick-change system solves a number of problems, Humphreys said.

“It gives us a method of clamping a fixture plate in a very easy and cost-effective way into, for example, a five-axis trunnion machine with limited access,” he said.

In a normal flexible manufacturing system, machine pallets are required, which add to cost. But the RoboFMS doesn’t require pallets, and uses fixture plates and zero-point clamping instead.

BIG Kaiser’s chucks are easily mounted in custom fixture designs.

“So if your process has to go from a four-axis to five-axis to a turning machine or VTL [vertical turning lathe], normally this is not possible as machine pallets/workholding are not compatible with each other within those machine groups. Using a ZP system, such as Schunk, we can overcome the differences and allow all processes to be automated, so that’s a huge benefit,” he said.

Humphreys makes a bottom-line case for investing in Schunk quick-change clamping systems.

“If you buy a machine tool that costs you a million bucks, if you can get your machine tool to run 85–90% spindle use, you’re getting the maximum out of the machine,” he said.

For a traditional machine shop, one that’s constantly changing over jobs, you’d be lucky [if you have a pallet changing machine] if you’re in the 40% region, 50% if you’re really lucky, Humphreys said.

“And if you’ve got no pallet changer, you might be getting 20%, 25%, so by automating you are effectively getting more hours out of your machine tool, and hours equal money,” he said. “And you can integrate not just one machine tool, but you can have three or four integrated and maybe have only one or two operators running the whole cell.”

Among the opportunities created by the Schunk quick-change system is the ability to automate a machine tool that traditionally is difficult to automate (eg, a five-axis vertical spindle that doesn’t have an automatic pallet changer), Humphreys said.

The second opportunity is the ability to integrate different types of machines.

“A good example would be I’ve got five-axis work, and I’ve also got some three-axis work and I could also do with a vertical machining center,” he said. “You could rough out your components on a four-axis machine or even a three-axis and put it in a five-axis for finishing in the same system. So you can then spread the load and actually control your investments.”

Wireless Insurance that Hydraulics Are Under Pressure

If a shop has a hydraulic workholding fixture on a disconnected system, and wants to be sure the hydraulic pressure is intact, Enerpac’s SafeLink Wireless Monitoring System may be of interest.

In a disconnected system, the fixture is pressurized and then isolated and “disconnected” from the hydraulic power unit. This allows the fixture to move freely into a machining center, without any cords or hydraulic lines. However, this leaves the fixture vulnerable to loss of hydraulic pressure.

“If you’ve got traditional hydraulic clamping, it requires hydraulic pressure to maintain the clamp,” said Douglas Lacina, Enerpac’s (Menomonee Falls, WI) production automation commercial leader. “So if you start losing hydraulic pressure, you will start losing your clamping force.”

Hydraulic pressure can fall for a variety of reasons, including leakage across a piston seal or rod seal on a cylinder, or leakage at any of the connecting boundaries.

“In some cases, operators have even been known to forget or improperly pressurize a fixture,” said Lacina. “But in any case, bad things can happen when a fixture is not pressurized.”

If hydraulic pressure is low or falls while the fixture is on the machine, the parts may chatter.

“So as you’re machining the part, if the part is not properly clamped, the forces of machining may cause the part to vibrate and move around,” Lacina said. “Obviously when that happens you can’t hold your tolerances. And, in the very worst case, you lose all your hydraulic pressure, or enough hydraulic pressure, and the part comes out.”

That may mean an expensive machine repair bill for the owner, and could be a safety hazard for the machine’s operator.

Enerpac’s wireless device consists of a send unit (powered by a lithium D battery that lasts for 2–3 years) that can monitor set points on up to three pressure switches. A receive unit is attached to the machine’s controller (powered by 24V DC), and can monitor multiple send units.

“When the pressure switch set-point on a fixture is reached, the receive unit provides a signal that can be used by the machine’s controller to shut down the machine, helping to prevent an out-of-spec condition on the part,” Lacina said.

“In most cases, standard hydraulic solutions hold pressure. However, when I’ve talked about loss of hydraulic pressure to guys in the industry, who are actually operating machines, I’ve seen people knock on wood to try to ward off the possibility that it happens to them. The point is that everybody has seen it in their career,” said Lacina. “And they know that when it does happen, often a spindle gets damaged, and that could be $25,000–$50,000 worth of damage.”

The other negative, Lacina points out, is unplanned machine downtime.

“Inevitably, unplanned machine downtime occurs just when you have an order that you’re rushing to get out the door,” Lacina said, “and now you can’t do it because you’ve got to repair your machine.”

SafeLink offers assurance that your system is in good working order, Lacina said. It helps to prevent bad parts and protects against unplanned downtime and expensive machine repairs.

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