A Multitask Mindset
By Bill Kennedy, Contributing Editor
Multitasking means more than simply combining turning and milling on one machine tool. Specific strategic approaches provide maximum multitask utilization.
To maximize multitask machining effectiveness, strategic approaches are often needed that are different than those applied for single-purpose machines.
A key benefit of multitask machining is the reduction of the time required to set up parts on separate machines. Fewer setups also minimize fixturing inconsistencies and facilitate preservation of feature-to-feature and overall accuracy. But how to realize that benefit is the $64,000 question.
According to Travis Themas, transitioning to multitask machining requires a specific mindset and a team approach. Themas, the branch chief in manufacturing at the U.S. Department of Defense’s Rock Island Arsenal (RIA) Joint Manufacturing & Technology Center, noted that the transition can be a challenge. “It is hard to get your head wrapped around the idea that you are going to do lathe work, milling work and potentially grinding-style work on one piece of equipment at the same time,” he said. “It starts with process planners understanding the functionality and capability of multitask machines.”
Courtesy of DMG/Mori Seiki
A new multitasking technology developed for producing spur and helical gears employs a disc-shaped milling tool that follows an involute path with simultaneous motion of the X-B or Y-B axes (see sidebar below). Variations in the gear shapes are generated by the toolpath, not by the tool geometry, so a simple tool can produce a range of different gear configurations. The process was developed jointly by DMG/Mori Seiki and Sandvik Coromant.
To make products ranging from large artillery to small arms, RIA uses more than 300 CNC machine tools. Multitask machines help RIA deal with the new realities of military supply: shorter production runs.
“Historically, we’ve had long-running programs, such as the 155mm M198 howitzer and the 105mm M119 howitzer,” said Lon Lukavsky, RIA’s division chief of machining. However, production of the M198 has ended and the M119 will be completed in April. Other programs have also become more episodic.
Accordingly, the RIA commander and its marketing group have sought new sources of work. “It’s typically short-run work for which we have to be agile,” Lukavsky said.
“It’s not the army of old where we are going to have a 5-year program; instead, we may have a 5-month program,” he said.
When it moved into multitask machining, the shop jumped into the deep end. “We set up a cell with six Mazak Integrex machines,” Themas said. “The focus was to run all the components it took to manufacture a recoil system. We brought in the new machines and all the older machines were sent out. That forced us to understand how to get that equipment to work properly and get product out the door. That was our first big learning experience.”
After decades of using single-purpose machines, a major hurdle was convincing staff that multitasking was effective. “They could see videos of it working, but actually seeing it in-house was our biggest challenge,” Themas said. “Once we started getting that equipment in here, we had to first figure out how to program it. We worked diligently with Mazak for a quite a long time to get our programming systems up to snuff.” The shop uses Unigraphics CAD and programs mostly in EIA language.
The variety of multitask technologies gives rise to different definitions of the concept. According to Rich Parenteau, director of applications development for Methods Machine Tools Inc., Sudbury, Mass., full implementation of multitasking involves not simply performing turning and milling on one machine in serial fashion, but applying more than one tool cutting simultaneously in a twin-spindle, twin-turret machine.
As examples of effective twin-spindle platforms, Parenteau cited NTMX machines from Nakamura, which also have twin automatic toolchangers and a bolt-on lower turret in addition to a B-axis head that permits 5-axis machining. Parenteau said such machines are popular because production volumes are smaller than they used to be. “Manufacturers don’t get to make a million parts anymore; you have to be flexible and one machine has to do an awful lot for you. That’s where the B-axis ATC machine comes in. No matter what needs to be done, you can do it on that platform,” he said.
Courtesy of Methods Machine Tools
Methods Machine Tools offers NTMX machines from Nakamura-Tome that feature twin spindles, twin automatic toolchangers, a bolt-on lower turret and a B-axis head that permits 5-axis machining.
Use of twin-spindle machines requires strategic planning. Because the part is machined on one spindle and transferred to the other for further operations, the part’s configuration can affect the transfer. “With multitasking, you can make a very odd-shaped part,” Parenteau said. “But how do you grab that part and transfer it from spindle to spindle? It is important to have a good feature to clamp on to pass the part to the second spindle, and also that the feature is potentially a datum structure so you can control your location.”
Maximizing machine utilization requires balancing processing times between the spindles to assure one spindle does not sit idle waiting for the other. But even when one side of a part requires more machining than the other, there are ways to stay productive. Parenteau said: “Say you’ve got 3 minutes on one spindle and only 1 minute on the other. You can take advantage of that unbalanced time by performing deburring and other processes on the second spindle, and you get that for free. Now you are optimizing the operation and having the part come out of the machine complete.”
Courtesy of Derbyshire Machine
Derbyshire Machine bolted a Kurt vise to a homemade trunnion to create this fixture. It then was mounted between the chuck and tailstock of a MacTurn 50 multitask machine and used to position the part when milling a two-pronged bracket (inset) in one of the shop’s Okuma MacTurn 50 machines.
The setups typical in multitasking can help improve cutting tool performance. According to Parenteau, the bar workpiece itself is a rigid fixture for the first operation in a multitask lathe. “Many cutting tools can be run at high speeds and feeds, and that requires a rigid setup,” he said. “That favors multitasking machines because you don’t have separate fixture components.”
Despite the clear benefits of multitask technology, some shops are still dead set against the concept, according to Chris Young, senior applications engineer at machine tool distributor Gosiger Mid-Atlantic, Exton, Pa. They say a shop’s lathe can be running while its mill is running.
“One customer said that, with a multitasking machine, a guy can’t run two machines, and for them the cell concept is working well,” he said. “But after they turn a part on their lathe, they have to fixture it on a mill and go in and probe to make sure everything is accurately located before they can start drilling holes.”
Some high-production shops contend that separate operations on single-purpose machines can produce parts faster than performing all the operations on one multitask machine. In reply, RIA’s Themas said: “It depends on how you define fast. If you define it as just throughput time, your throughput time immediately increases when you are on a multitasker because you are doing multiple machines’ work on one machine. But part quality goes through the roof because you don’t have to worry about three or four setups on a workpiece. There also is no work-in-process.”
Courtesy of Mazak
A progression from raw workpiece to a finished component at the Rock Island Arsenal.
RIA’s Lukavsky said, “There are so many more opportunities to make mistakes in between all those loads and reloads and fixturing. Your quality has a better chance of being sustained on multitasking machines, and all you have to do is focus on maintaining your machines.”
Maintenance is another issue that may be more important with multitask than single-purpose machines. “When we started using the multitasking machines, we started having part quality issues,” Themas said. “It was hard to diagnose, but the machine itself turned out to be the variable. We began using probing technology to line the machine up and check its accuracy and geometries. Once we did that, we could check that machine in a quarter of the time that it took us previously with indicators and levels.”
Gosiger’s Young said operating a multitask machine requires the user to think differently. “You have to analyze the machine’s capabilities and travel ranges, tooling and workholding. For example, if you only have so much Y-axis travel, you may have to rotate the C-axis, mill a feature, and then rotate it again.”
As an example of this approach, Young cited Tom Giannone, machine shop manager at Derbyshire Machine & Tool Co., Philadelphia. Most of the shop’s work involves government contracts, with a focus on making valves for the U.S. Navy. Derbyshire’s products meet the Navy’s Level 1 and submarine safety quality criteria.
Founded in 1905, the shop first put CNC equipment to use in 1967. Among Derbyshire’s machines today is an Okuma MacTurn 250 and, for larger parts, two Okuma MacTurn 50s from Gosiger. The MacTurn 50 machines have C and Y axes and a maximum turning diameter of 580mm and turning length of 1,500mm. With a 30kw, 2,800-rpm turning spindle and an 11kw, 40- to 3,000-rpm milling spindle, the machines have 50-tool automatic toolchangers.
“With multitasking, you have to think outside the box a little and you can accomplish a lot,” said Giannone. “You have to be ahead of the game.” Before the shop had multitask capability, he said, “We’d do a couple operations on a lathe, go to the milling department, do a couple operations in the milling department, come back to a lathe and back to a mill. We had six-operation jobs that we cut down to two on the multitasking machine.”
Although mixing turning and milling can be complex, it also frees up the operator’s imagination, according to Giannone. He described a rush milling job that appeared when all the shop’s milling machines were busy. He machined a bracket out of rectangular bar stock by mounting a Kurt vise on a homemade trunnion in the Okuma multitask machine’s chuck and tailstock.
“With the part in the vise, I could move my vise around with my trunnion, using the machine’s C-axis on the chuck as an indexer,” Giannone said. “I machined the part like it was in a regular milling machine.”
Software can further boost multitasking productivity. “Everybody loves the short cycle times they get on a multitasking machine but they fear the setup times, the potential of crashing the machine or the dry run time required for prove out,” Method’s Parenteau said. He recommends software simulation, noting that a simulation program developed for the Nakamura machines can provide a high level of confidence and increase efficiency as well (see “Get with the Program, page 34). “With an exact model of the machine on a laptop, you can manipulate the operations, drag and drop features, even optimize the process. You can simulate a program fully and post it out in the actual G code the machine is running, without spending 2 or 3 hours at the machine,” he said.
Courtesy of Derbyshire Machine
Machinist Karl Roth loads a copper-nickel ball valve body in one of Derbyshire Machine’s Okuma MacTurn 50s. The shop uses the multitask units to machine complex features.
For Derbyshire Machine, Young said he often provides macro programs that eliminate the need to program some operations individually. As a result, Giannone doesn’t have to figure out all the details, but instead calls up Young’s macro program and runs it. Said Giannone, “There are so many lines of information with multitasking machine programs, so we made some macros to shorten them. There is a simple macro for sending the machine home and shutting off different functions. Instead of having eight different commands, we put it into one.”
Initially, most shops used multitask machines exclusively as high-production machines, but stored part programs now allow them to handle small part runs more efficiently. “We were one of the first to utilize CNC machinery doing small run parts,” Giannone said.
At Derbyshire, part volumes are not large, often comprising single-digit runs, perhaps 40 parts at most. “We have learned to work around that,” he said. “We have to make money setting up a job for two pieces. For repeat work, we have documentation, pictures and tooling, and that helps out a great deal. We have close to 18,000 programs in our database. If I need a repeat job, the operators go up and pull their own programs. We have direct numerical control so they can upload or download them.”
Fit the Machine to the Job
Shops typically can find the right multitask machine for specific parts or jobs. At the RIA, for example, machining operations for a wheel suspension assembly for the M119 howitzer were reduced from 17 to three through the application of Mazak’s Integrex e-1060 V-II Super Multi-Tasking Systems. “You have to look at how much you are trying to get done in one operation,” said RIA’s Themas. “The machines, which are basically VTCs with live milling spindles, had all the capabilities we needed.”
Courtesy of Mazak
The Rock Island Arsenal Joint Manufacturing & Technology Center designed special fixtures (inset) to perform offset turning on an artillery wheel suspension component using one of the shop’s Mazak Integrex e-1060 V-II Super Multi-Tasking System machines.
In machining a 150-lb. component that required offset turning, the challenge was designing balanced fixtures. “We had to do some interesting designing to tie all the weight together so that the machine was balanced,” Themas said. “We initially tried to hold ±0.0005 ” on diameter, but it was varying. We tied some of that variation back to machine geometry and thermal change, then we finally diagnosed that the part was moving in the fixture. We did some modifications to our fixture to tighten it up a little bit and that problem went away.” The solution eliminated a grinding operation that had been required to achieve the ±0.0005 ” tolerance, he said.
As with any advanced technology, there is a learning curve associated with the adoption of multitask machining. Themas likened it to a crawl-walk-run scenario. “If you pull up YouTube and see all the awesome machining that is done with a multitasker, you shouldn’t think of just buying a machine that can do that,” he said. “There are a lot of things that come into play to getting the equipment to behave that way. It’s a long journey. It took us a little over 2 years to really get comfortable with our machines. Multitasking requires a lot of development time.” CTE
About the Author: Bill Kennedy, based in Latrobe, Pa., is a contributing editor for CTE. He has an extensive background as a technical writer. Contact him at (724) 537-6182 or at [email protected].
Multitasking helps multiply new machining applications
Thinking outside the box when it comes to multitasking extends to the machine tool builders themselves. According to Greg Hyatt, vice president and chief technical officer for DMG/Mori Seiki U.S.A. Inc., Hoffman Estates, Ill., the range of multitasking applications keeps expanding. “We keep thinking we have figured out how to do everything possible on a mill/turn, and then we come up with 10 more ideas.”
Among those ideas is a joint project with toolmaker Seco Tools, Troy, Mich., to broach features such as keyways, ID splines and fir tree root forms on discs for aerospace engines and steam turbines. “The broach for ID work is an axially oriented tool,” he said. “We orient the B-axis of the multitasking machine as if we were going to drill the ID.” The broach is inserted into the hole, then pulled out to create the desired form.
For OD broaching fir tree root forms, DMG/Mori Seiki engineers designed a tool applied in a B-axis multitask machine spindle oriented at about a 45° angle. A component of the broaching force drives the tool back into the spindle, enabling the tool to handle high forces without chatter and with high stability, according to Hyatt. Unlike conventional broaches that may be several meters in length, the broaches developed for multitasking are perhaps 300mm long. “As a result, we can use the CNC to program multiple passes, and by inclining the ramp angle of the stroke, we can adjust the chip load on the broaching tool from one tooth to the next,” Hyatt said.
“Invomilling” is another new multitasking application, developed jointly by DMG/Mori Seiki and Sandvik Coromant Co., Fair Lawn, N.J., for producing spur and helical gears (see photo on page 40). The process uses a disc-shaped milling tool that rolls radially from the OD of the gear towards its center while the gear rotates. The tool follows an involute path with simultaneous motion of the X-B or Y-B axes. Because the variations in the gear shapes are generated by the toolpath, not by the tool geometry, a simple tool can produce different gear configurations.
The process stemmed from the companies’ dissatisfaction with the productivity of previous hobbing operations on multitask machines. “We had put hobbing tools on our machines and could produce high-quality gears, but the cycle time was slow,” Hyatt said. With the involute milling tools, cycle times are within ±20 percent of typical HSS hobs.“There is no significant penalty and sometimes a slight advantage in cycle time,” Hyatt said. “But there is a huge advantage in flexibility and agility, and, of course, in consolidation of operations because we are now doing turning, boring, facing and gear cutting in one operation.”
Dr. Stefan Scherbarth of Sandvik Coromant originally envisioned the involute toolpath (on which patents are pending), and initial development of the process was done in the Stuttgart technical centers of Sandvik Coromant and DMG/Mori Seiki.
Derbyshire Machine & Tool Co.
DMG/Mori Seiki U.S.A. Inc.
Methods Machine Tools Inc.
Rock Island Arsenal
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