Shop Solutions: Job Shop Hits Bull's Eye With Multitasking
Grauch Enterprises (Philpsburg, PA) does just about everything when it comes to processing materials—milling, turning, drilling, plastic injection molding, painting, and finishing. Materials processed include a full line of plastics (ABS, nylon, polycarbonates, laminates) and metals (brass, aluminum, stainless, alloy steels, titanium, Inconel, beryllium, copper, copper-alloy castings, cast aluminum, and cast iron).
Typical machined parts include more than 650 different items for the US Department of Defense (DoD). "They're all called knobs for one reason or another," explains Fred Grauch, owner and second member of the founding family—after his older brother—to run the company.
Grauch also produces commercial products as well. "There's very little we won't try, especially since we've acquired our two newest multitasking machines, a Quest 6/45 CNC and a Quest Super-Precision 10/65 CNC turning center, from the Hardinge Group [Elmira, NY]."
The Quest Super-Precision 10/65 was purchased principally to machine a switch bolt for the "Ma Duce" M2 .50 (12.7-mm) caliber World War II-era automatic, tripod or vehicle-mounted, belt-fed, recoil-operated, air-cooled machine gun. "The switch bolt technically is a miscellaneous part, but someone thought it looked like a knob and put it on the DoD parts list under 5355 [knobs]," says Grauch.
Grauch approached Hardinge at the IMTS 2006 Show where the switch bolt was shown to Hardinge engineers. It would be a challenge, they said. Their response was that the switch bolt would use everything on the Quest 10/65 machine, including the C axis, the Y axis, X/Y combination, C/Y combination, the sub-spindle, the live tooling.
When all was said and done (and programmed) cycle time was eight minutes. So much for the challenge, and a good thing, at that, because the DoD ordered more than 9000 of the switch bolts. The part starts off as bar stock 2" (50.8 mm) in diam and when finished, the widest diameter is still 1.811" (46 mm). The two ODs are -0.001" (0.03 mm), and everything else is 0.005" (0. 13 mm). Hole size is -0.001" (0.03 mm), and they hold 0.0002" (0.005 mm) on these two holes by reaming them. But the main tolerances are the two diameters. They fit very snugly into the machine gun.
The Quest Super-Precision 10/65 was followed within six months by the "unplanned" acquisition of the Quest 6/45. While running parts for government approval on the 10/65, Grauch received an order for 5000 assemblies consisting of 20,000 individual parts.
"Most of our parts are an inch [25 mm] in diam or smaller," he says. "The Quest 10/65 goes up to 2.935" [74.5 mm] through the spindle and that really increased our capability compared with our gang-style tooling machine, which is limited to 1.065" [27 mm]. Even the Quest 6/45 goes up to 1.625" [41.3 mm]. So both machines have really increased our ability to do larger diameters," Grauch explains.
The rationale was that if the company could run the Quest Super-Precision 10/65 at night on the switch bolts, it could use another Quest to do the assembly job and all its other parts. Grauch explains: "Brian Ferguson, our Hardinge rep, recommended the Quest 6/45 because of the size, quantity, and complexity of the smaller parts. Also, because he understood our need to run shifts through the night, he suggested we automate the machine with a bar feed, touch probe, and tool probe. No more than a month later, we decided to automate our first Quest in the same manner."
Grauch now has matching systems and can interchange between the two. The Quest Super-Precision 10/65 runs the switch bolt job at nights as well as during the day. The Quest 6/45 runs days and some nights and handles all of its other parts.
"Now I look back and wonder how I ran this place without these machines," says Grauch. "As time goes by, I can see us slowly replacing all of our gang-style machines with Hardinges. I can see us replacing two or three with a single Hardinge."
For Grauch, a small run is 1500 pieces and a longer run may be 10,000 parts. Right now, to be cost effective, the company is doing all of its long runs on the new Hardinges. Eventually, they intend to put shorter run jobs on the machines because changeover is a matter of just changing the tools, if that.
"We have designated certain tools in certain areas, so the changeover is not that long at all," Grauch says. "Even if we had to change the entire turret and all the tools, the touch probe for the tooling allows us to just touch them off, and you're done."
Each Quest has two probes. The tool probe is mounted on the wall of the machine by the spindle. When tooling is loaded and the turret moved back out of the way, the probe comes down and the turret is manually extended to touch the C and X positions. That information is loaded directly into the GE Fanuc control. All of the tools can be touched off in about five minutes, and changeover can be done in 15–30 min.
The second probe, the part probe, is used specifically on the .50 caliber switch bolt. Grauch says. "We're planning on running this at night in addition to during the day, and we have subprograms where the part probe mounts on the turret and the turret will come every so many parts, say 20, and it will touch the turned areas where we're trying to hold to 0.001" [0.03 mm] in alloy steel. It will adjust the offsets in the machine to hold that tolerance, and as we get into production, we can check every ten parts or five parts—every part, if we want—and the probe will tell us if we need to make an adjustment. It's all in the programming.
"During the day, if personnel are tied up watching other machines, the program that does self-inspection can be loaded—and the Quest will inspect itself. But, the main reason we have the part probe is to run the Quest Super-Precision 10/65 at night, when there's no one here, lights out," Grauch says.
In the milling sequence, the bar feeds material out to a given length. A roughing tool is used to rough the front end because the bar feed leaves about 0.010–0.020" (0.25–0.50 mm) to clean up the front finish. Then the OD is roughed down and tapered to the back smaller diam.
Next is the slot. It is angled on each end, so they're actually doing a Z-axis/Y-axis move: As they're milling from front to rear, they also move out, going straight across and then going back in. The mill slot through the front is what actually guides the bolt action loading the ammunition.
Next, after switching tools, a parting tool comes in and grooves out the backside of the part, making it smaller than the front side.
Then they spot and drill the locating holes with the same drill. Holes are located opposite one another, depending on which side the ammunition feeds through the machine gun, allowing them to be mounted side-by-side.
A milling operation from the top (X axis) angles the two sides, and is followed by a radial operation down those sides to allow grease to move through. The part now has two angles on the front edge.
A finish turn cleans the front side and turns the tight outside diameter.
Then they actually go back with a 45° six-blade chamfer tool, and chamfer (deburr) all the edges. They spot and drill a through hole. Next they finish hogging out the backside and put in a radius.
The part is now ready to be finished on the subspindle. Before this can happen, the last part still in the sub-spindle is removed by a robot arm. The subspindle moves forward, and the arm grabs the part, and drops the finished part on a conveyor belt, which carries it to a parts bucket. The subspindle picks up the next piece. It's in the middle of the program for the next switch bolt that they actually take the finished part out of the machine.
Just a little over eight minutes, start to finish.
The subspindle again comes up and grabs the next piece, and parts it off. Then they spot the back of all three holes and ream the two locating holes 0.201" (5.11 mm), ±0.0002" (0.005 mm), finally facing off the second tight tolerance diameter.
Just how accurate? "We're shooting to hold 0.0005", ±0.00025" [0.013, ±0.006 mm), on the .50 caliber switch bolt," Grauch says.
"Enough material is put into the bar feed to run for about 48 hr. If something happens—the feeder runs out of material, or the probe says we're not holding tolerance—the machine will stop and make a call. This is all done in the background, in the programming," says Grauch. "We knew the capability to do this kind of complex job was there, and that they had the engineering depth to know if they could make the part or not. If not, they wouldn't have sold us a machine."
High Fives For Inspection
Turbomachinery components are a challenge to five-axis inspection with constantly changing surface geometries, pin-wheeling shapes, and tight, intricate features. Impellers, blades, and blisks are some of industry's most complex and exacting shapes.
Part precision and uniformity are critical in providing dynamic balance, directed airflow and long, reliable service at high rotational speeds. CMM inspection, however, which Turbocam (TAPS; Barrington, NH) relied on to assure that critical complex parts meet demanding accuracy specifications, was frustrated by slow, tedious, stop-and-go measurement inspection on a legacy 3+2 axis CMM.
Changing 3-D part geometries required many different probe orientations, plus frequent stylus and tip changes for difficult-to-reach features. Dave Romaine, quality assurance manager, explains: "We would have to stop the CMM and calibrate each re-orientation of the probe. That was compounded as we inspected multiple blades around a part."
Turbocam staff were quick to see the potential of the Renscan5 scanning system from Renishaw Inc. (Hoffman Estates, IL). A Renscan5 scanning-equipped Wenzel LH8.10.7 bridge-type CMM was installed at the company's Dover, NH, plant in January 2007.
The Renscan5 scanning system, which features continuous five-axis interpolated motion for automated, programmable five-axis measurement, is said to be able to achieve scanning speeds not possible before on a CMM. As a result, high-speed continuous probing routines have reduced programming, setup, and measurement times by 50%, and removed part measurement and inspection as bottlenecks.
Besides faster throughput, Renscan5 time-savings allow the taking of many more data points for greater measurement precision, as well as freeing up CMM time for qualification of turned blanks and in-process checks before final machining passes.
In early 2008, Turbocam added a second Renscan5-equipped CMM, and a larger Wenzel LH10.12.8, at its TAPS' facility in nearby Barrington. Romaine says that Renscan5 is an "essential resource" that is being developed to support higher-throughput production generated by around-the-clock, reduced-staff manufacturing. XSpect Solutions, now part of Wenzel, did the installation of Renscan5 on both CMMs.
Renscan5 uses two hardware innovations, the Revo probe head and laser-corrected tool tip, to speed part checking, generate more data points for analyzing part form, and increase available CMM run time.
The active probe head, called Revo, is a powered head, which provides infinite positioning capability between simultaneous coordinated motion in vertical and horizontal rotary axes. This allows the low-mass, two-axis head—a 3-D measuring device in its own right—to perform most of the motion during inspection routines. Infinite positioning allows continuous motion, optimizes part access, and delivers high-accuracy part measurements. The active head avoids dynamic errors caused in rapid accel/decel of the larger mass of a CMM structure. Low-mass, low-inertia design allows Renscan5 to measure at up to 500 mm/sec versus conventional CMM scanning that is typically limited to 5–15 mm/sec to avoid dynamic errors.
Revo repositions continuously on the fly, simultaneously with measurement, unlike indexing heads, which first must be locked into position, after which the CMM provides the measuring motion. On complex parts, says Romaine, "hundreds of calibrations have now been eliminated, saving us hours of calibration time."
Renscan5 allows the CMM's three-axis platform to be used primarily to "rapid" the Revo head into position for measurement. Where CMM motion is required for a measurement routine, it can usually be limited to a single linear axis and performed at constant velocity, minimizing dynamic effects on accuracy from accel/decel and inertia.
Laser-corrected probing is produced by a laser mounted within the head, which sends its beam down a hollow stylus to a reflector at the tip. The return beam is received by a position sensor, and any deflection is used to calculate true tip position. This allows Revo to perform a complete part inspection routine in a continuous operation without recalibration or stylus changes.
"Only one probe is typically used to measure an entire part with no tip change time," says Romaine. Tip Sense probes deliver 1µm accuracy at 250 mm from the axis of rotation. Sizes are available providing probe reach to 500 mm.
While the previous 3+2 axis CMM at Turbocam provided a two-axis head, vertical changes in probe angle could only be made in 2.5° increments, then calibrated and fixed at the position for measuring. "As we inspected more blades around a part, such as a blisk, it would obviously require more and more probe orientations and calibration. Programming, access, stylus change, and calibration were incredibly painful," notes Romaine.
Turbocam uses Renscan5 for both point-to-point probing to verify feature location and size and for contact scanning of part surfaces for shape and form data.
"On point to point, we are able to gather more data simply because the head can orient to any angle, and it's a simple setup to get more points," says Romaine.
Renscan5 high-speed scanning greatly increases data points. "Previously we might collect 50 or 100 points spaced over a blade," he says. "Now we can collect hundreds or thousands of points with a scan." In scanning mode, the probe moves continuously, adjusting to programmed changes in part geometry. Revo gives Turbocam up to 4000 points/sec in scanning mode.
"Increased point data allows us to see a more complete picture of what we're manufacturing," says Romaine. "We can see deviations better as they increase and decrease along a blade or around a part. This lets us better trouble-shoot our manufacturing process." As an example, Turbocam has been able to detect tooling breakdowns based on Renscan5 surfacing data.
Parts inspected on the CMMs range from small impellers just 2" (50.8 mm) in diam to multi-vane components and impellers 36" (914 mm) in diam. Turbocam produces more than 400 different bladed part designs a year for compressor, turbine, and pump OEMs.
"Just as important as the inspection advantages," stresses Romaine, "are the programming benefits. This has been exciting. We've been able to apply our five-axis machine tool programming methods to drastically reduce programming time for five-axis inspection. This is only possible because of the infinite indexing of Revo and its programmability through the I++ DME protocol."
Renscan5's I++ interface gives the UCC2 controller cross-platform compatibility with measurement software packages and maintains user choice of CMM and software.
"On complex parts such as blisks [integral hub and blades machined from a monolithic blank], what used to take three days to program now takes three hours. The biggest time savings have come in programming and setup, even more than run time," Romaine says.
The ability to apply five-axis programming expertise makes it much easier and faster to provide programs for part inspection, increasing machine utilization for a wide range of parts. While Renscan5 integration is still evolving, Romaine estimates the CMM utilization has already increased between 30 and 50%.
ECDM Machine Roughs Blisks
A couple of years ago, GE Aviation (Evendale, OH) approached KRC Machine Tool Services (Independence, KY) to build two BlueArc machines. The machines are named after the environmental nature of the process as well as the color the electrode glows as it removes metal from the Inconel solid to create a blisk (bladed disk).
The fact that GE has come to your door and invited you to bid on a couple of roughing machines with a cost of about a million dollars apiece means something, especially because the machines use a process similar to ECM or EDM, but not really either, more like a combination of the two, an ECDM machine.
In this case, GE had already done its research, had worked with KRC many times before, and knew it was competent enough do the job (the upside). Because GE Aviation owns the IP (Intellectual Property), they also know that the winning bidder would have to play by their rules, which some companies consider just too great of a downside.
"KRC has worked on many projects together with GE over our 12+ years of doing business, and, in that time, we have developed a very good working relationship," says Scott Ashworth, KRC president. "What we didn't expect was a trip to China to see the GE research center where one of the prototype blisk machines would be running tests," says Ashworth.
"You couldn't actually see material removal because everything was taking place submerged," Ashworth says. "I later found out that submerging the process isn't for connectivity. In fact, the part can be machined dry. It's primarily to maintain consistent heat in the heat-affected zone. Plus, it helps with smoke by dampening it into the liquid. Further, as the process is noisy, the liquid helps dampen noise. But it was amazing to see the speed at which they were roughing the part out of Inconel. It was very fast, about 40 ipm [1 m/min]."
ECDM process basically uses a copper electrode, 7 mm in diam, and then a variable power supply that can control the voltage from 0 to 70 V and the current from 0 to 500 A. What made this process interesting, because EDM, ECM, or even ECDM aren't new or novel was the switching power supply, a fast-pulse power supply, and GE's software that communicates between the control and the power supply.
The ECDM process innovation is in monitoring the voltage, current, and feed rate, and continually manipulating them to maintain a constant arc, which is essential to precisely removing the metal.
"The agreement was that we were to build two roughing machines," Ashworth says. "Our expertise is in the machine and the control. GE already had a vendor for the power supply. GE's custom-developed proprietary software would run on a separate computer, which we were to purchase and mount."
After considering the specifications, travels, and building the machine, KRC contacted Mazak Corp. (Florence, KY), which agreed to supply two-thirds of the machine. KRC would finish the rest.
"What we got is a well-established and well-designed base, ballscrews, linear guide system, and tool changer, which was a bonus. We looked at it, got the drawings from Mazak, and realized we could modify and elevate the tool changer to be able to handle a 30" [762-mm] rod, which is being consumed during the machining of these blisks," Ashworth explains. GE wanted to be able to load the toolchanger (30 tools) and run it for hours, non-stop, which meant that KRC had to modify the way that the tool changer was mounted, but not the tool changer itself.
The Mazak was equipped with linear ways on all axes and direct-coupled servo motors. These inherent design features allowed it to perform at levels of a 5-g machine, which was needed for the rapid accel/decel in feed rates while they were monitoring the current.
KRC designed its own spindle, the only purpose of which was to rotate the tool. The machine is non-contact. "The good thing about this process is that there are no forces on the machine other than the axis moving. The machine has a 3-hp [2.2-kW] spindle motor, although we could have specified a 1- hp [0.75-kW] motor as all we're using it for is rotating the tool," says Ashworth.
"The difficult thing about the spindle was that it had to be completely isolated, because that's where the positive of the power supply comes through, that and the tool. The part is the negative. The design had to encompass the isolation of the power away from the machine as well as a slip ring assembly. This allowed only the spindle and tool to be energized. That took a little doing. The other thing is that they wanted a full five-axis- contouring machine.
"With the vertical machine and the way they wanted to present the part, we had to tilt the spindle as the part was rotating," Ashworth continues. "We mounted a rotary table on the Z axis and the spindle on that, which is where we got our rotation. The table was a Troyke [Cincinnati], and it's the first torque table they built configured in this manner. The table is very big.24.26" (610.660 mm), Ashworth says, "and it had to handle a three-stage, 32" [813-mm] blisk. You're talking about 800+ lb [360 kg] hanging off the front of the table. We're not talking about a table that's mounted in a horizontal plane; we're talking about one that's mounted vertically. Pretty amazing."
"The coolant system was designed by an outside vendor with our input," Ashworth says. "It's an extremely high-tech coolant system in that there are dual-filter systems that can be back-flushed while in operation. In effect, you have redundant systems there. The chip, or the remains of what is machined off, is similar to a grinding sludge, but not as fine. It might be five times as coarse. When you put it in your hand it's like a thick welding/grinding slag, small slag and fine dust. That's the byproduct.
"The coolant system is very large, and the tank had to be made of stainless. Plus, they had some pretty tough requirements on how fast they wanted the tank filled and then drained. When they put the part in, and hit Go, the tank fills in seconds, not minutes, and the tank is about 4 x 4 x 4' (1.2 x 1.2 x 1.2 m).
"Also, we chilled the coolant to within 1° C. When we finished the machine, we came in and started the testing, and the coolant flushing is huge at the point of the arc, at the point of the cut, just like it is with any machining process. This particular rod is 7 mm in diameter and had a through hole that we pumped coolant through at 100 psi [690 kPa], which was another big challenge.
"Then we had to devise a support, because the rod is so long you can't just put it in a spindle and start spinning it around. It would obviously whip, and as these rods aren't exactly perfectly straight, we had to come up with bottom support that the rod feeds through. We ended up making a custom air bearing," Ashworth explains.
"The bushing on the bottom side is a coolant ring as well," says Ashworth, "and it has coolant nozzles all the way around. What this nozzle does is create kind of a halo blast right where the tool moves around the part."
GE is roughing material out five times faster and, because of a more consistent surface being produced, the ECDM process time to produce the final feature is reduced by half. "When you look at the surface finish on this," Ashworth says, "it looks like a semirough end mill finished it. You can see the step lines as you progress down through your depth of cut. You can see them in the side of the part, just like a roughing end mill made them. That's how good it is, and they can machine it out five times faster than with a conventional mill.
"One of the problems removing material in this manner is a term called recast. After five years of research, I think they had a pretty good handle on it. And as a result, they're roughing this product out 4–5x four to five times faster than they could have with traditional machining," says Ashworth.
In the end, GE granted KRC a license to make and sell the technology world wide. KRC was the first BlueArc licensee in the United States. "This technology is not just relative to blisk machines, but has applications wherever rapid roughing of tough materials is needed. We have the green light to market and sell the technology to all users," Ashworth concludes.
This article was first published in the November 2008 edition of Manufacturing Engineering magazine.