courtesy DMG Mori Click image to enlarge

Three-axis machining centres have long dominated the job shop world. But given that high-mix, low-volume work is the new normal for most machine shops, are they still the best choice?

By Kip Hanson

Walk into a typical machine shop and you’re likely to see a row of three-axis machining centres, each sporting a pair of six-inch Machinist’s vises and carousels filled with steep taper tooling. These popular machine tools are less expensive than their horizontal counterparts, simpler to set up, and it’s fairly easy to find people familiar with their programming and operations. Why change?

If your shop is machining large plates one day and small widgets the next, there's no need, as vertical machining centers provide the much-needed flexibility required to tackle such work. Also, if the majority of your jobs are simple parts requiring but one or two operations, the three-axis status quo is probably just fine, especially where higher production volumes are the norm and the shop can fill the entire machining center table with parts.   

Beyond medical

Many shops, however, face ever-dwindling order quantities and increased part complexity. Here, multiple fixtures, setups, and programs are required, driving up costs. And a large percentage of these parts are often smaller than a toaster—sometimes much smaller—leaving the traditional 20 x 40 machining centre table a mostly barren landscape. Still think three-axis verticals are the way to go?

Dave Lucius doesn’t, at least not in this scenario. The vice president of sales at Kitamura Machinery of USA Inc., Wheeling, Ill., points to the company’s MedCenter5AX five-axis vertical machining centre as an excellent solution for this last group of shops (as explained in the November 2020 issue of Shop Metalworking Technology). Since then, Kitamura has made it possible to add 12 or 24 pallets and up to 120 tools to the platform (even on existing machines), greatly increasing its ability to run unattended.

“We have a shop in New Jersey making bone plates for a large medical company and they’re seeing 90 per cent spindle utilization, seven days a week,” Lucius says. “We have a number of dental implant manufacturers who machine a tremendous amount of unique part numbers every day with practically no setup. And we have several government laboratories using our single pallet MedCenters for prototyping work. With or without automation, the machine offers a lot of capability in a very small footprint."

You might be thinking, ‘So what? We don’t make medical or dental parts, we do most of our prototyping on manual machines, and we certainly don’t have any five-axis work. I’ll stick with what’s kept the lights on and doors open for the past two decades.’

Meet the new paradigm

Maybe so, but consider this: when properly tooled, a compact, automation-ready machining centre like this makes it possible to produce the toaster-size and smaller parts mentioned earlier—whatever the industry—in a single operation, in very small quantities, and do so after everyone has gone home for the night. Better yet, you can fit two or more of them in the same space as most three-axis verticals.

“Three-axis verticals typically achieve 30 per cent utilization,” says Lucius. “We’re seeing 80 per cent or better with this approach, and ROI in as little as a year.”

Jeff Wallace, general manager for national engineering at DMG MORI USA Inc. in Hoffman Estates, Ill., agrees. "As everyone knows, it's hard to find workers at all these days, let alone ones who are talented, so the drumbeat we've been hearing is automate, automate, automate. Yes, medical and dental parts are candidates, but so are all manner of smallish components for the aerospace, automotive, and general industries. When equipped with a robot or pallet changing system, you can load up tens or hundreds of parts into one of our DMP 35 verticals, turn out the lights, and run it all night or even through the weekend.”

Introduced last June, the DMP 35 is a smaller version of DMG MORI's DMP 70. It's offered as a three-axis machine as standard, but has an optional five-axis configuration. And as Wallace indicates, the company also offers numerous automation solutions, the smallest of which—the tightly integrated WH 3 Cell—adds only 1.15 sq m (12.38 sq. ft.) of floor space to the DMP 35's already svelte 3.15 sq m (32.29 sq. ft.) footprint.

Gathering the puzzle pieces

Like Lucius, Wallace notes that there’s more to this equation than the machine and a robot. Because workholding plays such a large part in any automated machining scenario, the DMP series’ five-axis table is equipped with integral air activation, making it easy to load and unload pallets or individual parts. "In addition to the WH 3, we have customers using standalone drawer systems and robots, or a two-axis gantry that serves an entire row of machines stacked next to one another," he says.

One such workholding provider is EROWA Technology Inc. of Arlington Heights, Ill., where regional manager Fred Holzmacher notes that he’s equipping these and other CNC machine tools with the workholding just described as well as standalone pallet changing systems. “Our MTS zero-point workholding system is quite popular for production machining where positional tolerances are in the two to three tenths range (0.0051 to 0.0076 mm),” he says. “For anything closer than that, we have another system that gets you down to 80 millionths (0.002 mm) repeatability.”

Adoption of the digital twin is another crucial step in solving the automation puzzle. Wallace and Lucius each stressed the importance of toolpath simulation, especially in five-axis and 3+2 machining applications where quarters are typically tight. Not only does this eliminate crashes, but it significantly shortens setup times, often to zero.

Someone who knows all about it is Ivan Mikesic, product support manager for CAMplete at San Rafael, Calif.-based Autodesk Inc. He notes that the company has partnerships with many machine tool builders, Kitamura included, and works directly with their partners to develop accurate posting and simulation for their machines. Like the others, he emphasizes the need to simulate the machine environment.

“That’s true for any machining operation, but five-axis and 3+2 can require longer tool lengths so as to reach all of the workpiece as it swivels around the machine's rotary axes," he says. "Because of this, interference is a real possibility, as is an overtravel condition. This is even more likely on the compact machining centers we've been discussing. Not only that, but they're moving quite fast, so simulation is a must if you're going to avoid an expensive crash. By checking everything ahead of time, you also achieve a much higher level of confidence that when you send the program down to the machine, you know it's going to work correctly.”

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