A Multitask Mindset: 5-Axis Machining

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.” For a deeper look at Maxing out multitasking: 5-Axis Machining, see this supporting resource.

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.

Simultaneous Productivity

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.”

Cell Cycles

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.”

Creative Approach

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.”