February 2012 / Volume 64 / Issue 2|
By Kip Hanson
| Manufacturers are using unattended horizontal machining cells to improve productivity and quality.
There are 168 hours in a week, and, if a machine shop is not running its machine tools for every one of those hours—including lights-out machining—it is losing an opportunity to make money. But revenue is not the only issue. Unattended machining can also increase part quality and reduce lead time to customers. Setting up an unattended-machining operation is not easy, and it’s certainly not cheap, but many shops say it is essential to stay competitive.
One key question is how unattended machining can be effective when the market is demanding smaller lot sizes, tighter tolerances and more complex parts. This feature focuses on how to accomplish that when unattended machining with horizontal machining centers.
Courtesy of Ross Machine
But why HMCs? After all, palletized vertical machining centers have been around for decades and have been automated as well. However, horizontals by their nature offer a number of advantages over their vertical cousins—greater tool capacities, better chip evacuation and easier four-sided machining—making them the machine of choice for unattended machining for most shops.Key Requirements
So what’s required for unattended machining? For one, you need a smarter machine. Jim Endsley, machining center product specialist for Okuma America Corp., Charlotte, N.C., explained that, to reduce labor costs, the human element must be removed from the equation as much as possible. “It’s a matter of replicating human intelligence,” he said. “If Joe has to walk to the back of the machine and kick it every now and then in order to make good parts, then you need a machine control that can replicate what Joe does.”
Okuma focuses on offering that capability across all of its products. The Intelligent Numerical Control, or THINC, is an open platform, PC-based machine controller developed by Okuma in collaboration with its “Partners in THINC.”
Courtesy of Okuma
So how does this replace Joe when even the smartest control can’t replace a human being? THINC does have a number of human-like qualities, including collision avoidance and 3-D virtualization (eyes) and adaptive cutting technology based on spindle and axial load monitoring (ears). “The control will adjust the feed rate if it senses a heavy load,” Endsley said. “If it encounters additional stock or a part that wasn’t positioned properly, it will back off until it gets past the rough spot and then resume its normal feed rate.”
And what if Joe quits and nobody is suitable to replace him? “Shop owners are always telling me I would buy your machine if you could find someone to run it for me,” Endsley said. “Over the years, [many companies have ended] apprenticeship programs and cut back on vocational training. Because of this, it’s getting very hard to find good people. This is a large part of what drives shops to go unattended.”
Mark Rentschler, marketing manager for Makino Inc., Mason, Ohio, agreed. “The way for American manufacturers to compete against low-labor-cost countries is to remove a big portion of their labor from the calculation.” That’s because of the challenges of competing against someone in Shanghai standing in front of a machining center. “You have to compete on application of technology,” he said.
Like Okuma, Makino offers an innovative machine control, one designed to augment traditionally human functions. Its MAS A-5 cell controller monitors production orders, workpiece and pallet status, machine capacity and tool availability. Combine these functions and you have a machine cell that can dynamically schedule jobs based on priority, route jobs to the next available machine and call up replacement tools. “As long as raw material and tools are available, the machine will keep making parts—all by itself,” Rentschler said.Loading Up
OK, you have a smarter machine. But how do you replace Joe’s hands? Like most machine builders, Makino and Okuma have answers. Okuma offers AMPS, a 12-pallet “container” system that, according to Endsley, is simple to retrofit. “Just slide the container to the front of the machine, bolt it on, connect a few wires and you’re able to run lights out.”
Okuma reports that AMPS is ideal for a small job shop that wants to buy an HMC today and add automation next year. Endsley said: “[Lights out] is a big pie to take a bite out of for a small job shop. Now they can do this in stages, expanding as the money becomes available. It’s like an erector set.”
Makino’s take on material handling is the Makino Machining Complex, or MMC2, a linear material handling system combined with its MAS-A5 cell controller. Rentschler explained that the A5 manages a servo-controlled vehicle capable of servicing up to 15 machining centers, four load/unload stations and 200 pallet stackers. “These types of cellular systems provide for easier load and unload, transforming many shop floors into extremely competitive environments,” he said.
All of this sounds complex and expensive. Yet both builders claim that, because their pallet systems are modular, they’re within the reach of even small shops. “It’s important to understand there is a cellular system available for most any shop,” Rentschler said. “You can get started very quickly and the initial investment is relatively low. As your business grows, your cell can grow with you.”
Rentschler recently worked with a shop making mining components. By adding a linear pallet system, “They shifted the work of six horizontals to just two, and did so in a span of a month or two. If you have good support from your vendor, and an interface and control that are operator friendly, you’d be surprised how quick and easy your learning curve is.” Rentschler added that many shops are seeing an immediate return on investment, as well as reduced scrap and lead times, and spindle uptime as high as 98 percent.Cellular Strategy
MacKay Manufacturing Inc., Spokane, Wash., is one of these shops. It has a pair of machining cells—one for hard metals and one for aluminum. Each cell contains three Makino A-51 HMCs and is serviced by a robotic pallet stacker.
According to Gregg Meyer, CNC mill department supervisor for MacKay, the shop replaced 12 stand-alone machines with the two cells, allowing the company to greatly expand capability without increasing the number of operators.
“We run lightly attended, but not lights out. But we definitely have more machines than we do people,” said Meyer. “Each three-machine cell runs 24/7 and achieves up to 95 percent spindle uptime. Six years ago, we were seeing only 40 percent on our stand-alone machines.”
This level of uptime typically requires long production runs and MacKay does have some of that type of work. However, it is still a job shop and that means frequent changeover. “We have 40 pallets per cell,” Meyer said. “Each pallet has four faces, so that could mean four different customers, four different setups or four different jobs. With 160 tombstone faces to choose from, we have a lot of flexibility.
Courtesy of MacKay Manufacturing
“Let’s say you get a new order for 100 of the same widgets you made last month,” he continued. “Repeating that job is as simple as entering the job number and pushing start. If it was making good parts then, it will make good parts today.”
Most of MacKay’s setups are done offline. The shop uses a common fixture pattern across its jobs, so it can load a job onto any pallet. Tools are preset in the toolroom and the operator loads the tools and the fixture while the machine is running. When he’s ready, the operator runs a program to set the tool lengths, calls the job and pushes the cycle/start button. When the part is finished, the operator switches back to the previous job while the new one is being inspected. “He might have to tweak speeds and feeds, but the entire setup takes less than 10 minutes, and the first part comes out within ±0.005 " on the first go-around,” Meyer said.No Sick Days
Another builder advocating unattended machining on HMCs is Mitsui Seiki (U.S.A.) Inc., Franklin Lakes, N.J. Dennis Jones, engineered products manager, noted that unattended production is more consistent than attended production. “Machines don’t call in sick or take breaks,” he said.
There are several prerequisites to unattended machining, according to Jones. “Unless you have parts with 8-hour run times, you need a way to get blanks into the machine and finished parts out,” he said. “We’re seeing a lot of shops going to robots for this.” Jones pointed out that robots aren’t just stationary devices. “They can be mounted on an overhead rail, enabling them to service multiple machines, perhaps up to 20 with a single robot. It all depends on the cycle time. Since the investment is lower with a robot, it might be more cost-effective to go this way on long-cycle-time parts, provided the robot can keep up with load/unload demands.”
And robots can do more than load and unload parts—they can also carry tools. Jones explained that robots are frequently used in larger machining cells to carry spare tools from a common tool magazine. “If you are running the same part across multiple machines, you might end up buying and inventorying a lot of redundant tools,” he said. “But with a centralized tool system—one served by a robot—you can reduce tool inventory.”
Regardless of whether it’s a centralized robotic tool system or a traditional machine-integrated tool magazine, Jones said it’s critical to have enough tool stations. “You need to carry enough spare tools, based on tool life and run time, to go at least one shift. Our HMCs use a chain-style tool magazine and can carry upwards of 480 tools.”
In addition, broken tool detection is an integral part of any unattended horizontal-machining cell. Mitsui Seiki, like most builders, accomplishes this in a number of ways.
“Broken tool detection can be done by monitoring the amperage draw at the spindle and axes motors, but we generally use laser probing to check for broken or worn tools,” Jones said. Laser probing allows an operator to measure not only tool diameters and lengths, but also check part dimensions and compensate accordingly. And yet, despite the broad capabilities of laser probes, “Tool life expectations are typically learned as you go. Ultimately, you have to rely on the operator to set tool life parameters,” he said.
Does that mean you spent a lot of money to machine unattended but still need an operator to tell the machine what to do? Jones explained that the machine control’s tool management software does a great job of tracking tool usage; when the tool reaches its end of life, the software calls for a replacement tool. And if the required tool is unavailable, the machine can be put into an alarm status, the job can be sent to another machine or a different job might be called. “There’s a lot of flexibility in these systems, but you still need a human being to establish the rules,” he said.
Unattended machining is particularly useful for part families. Lot sizes can run from one piece to thousands, but repeat work is essential. “The ROI is relatively short, especially if you have the right parts, but remember that this is an investment, one that requires a commitment between the customer and the manufacturer,” Jones concluded.Cool Runnings
One shop with the right mix is MAC Machine, in Baltimore. George McNab, president, said he has been performing lights-out machining for more than 20 years. “We’re taking advantage of new equipment, including 5-axis machines, but most of the advancements were made years ago. The overall philosophy and qualification of our processes haven’t changed.”
McNab schedules each of his 11-pallet cells 160 hours per week, with nearly 100 hours being unmanned. “All of our machines have coolant chillers, so we can maintain 70° inside even when it’s 100° outside. You have to develop a process that is so predictable that it is virtually impossible to make a bad part.”
That’s saying a lot, considering the materials MAC runs include titanium, magnesium and high-temperature alloys, such as vacuum-melt Inconel. “That’s about as bad as it gets,” McNab said.
Courtesy of Methods Machine Tool
Asked about setup time for unattended machining, MacNab replied, “That’s a loaded question. It all depends on the complexity of the part, the geometry and the overall challenge of the project. It’s not cut and dried. On some parts, you don’t know how you’re going to make them until you get into it.” According to McNab, once a job is set up, it’s very rare the first part isn’t produced correctly. “After the initial run, setup time is virtually eliminated on repeat jobs,” he said.
David Lucius, vice president of sales for Methods Machine Tools Inc., Sudbury, Mass., can testify to MAC Machine’s success. In the late 1980s, MAC had 15 VMCs. “They replaced them with five Matsuura HMCs, each of which has its own 11-pallet pool,” Lucius said. “The shop experienced a dramatic increase in output and improved part quality.”
Why did MAC choose to go with stand-alone machines with pallet pools vs. an integrated linear-pallet system, or FMS (flexible machining system), that can share work between machines? According to Lucius, pallet pools can be more cost-effective. “Figure a ballpark of $600,000 for a horizontal with its own pallet pool. Typically, you can get more pallets per dollar this way than you can with linear pallet systems.” This is due to the infrastructure required for an FMS—complicated cell controllers capable of scheduling multiple machines, a “railroad track” for the guided vehicle and the cost of the vehicle itself, all of which might increase pallet cost per machine by as much as 50 percent.
Courtesy of MacKay Manufacturing
Ross Machine Co., Belcamp, Md., also uses HMCs from Methods for unattended machining. With a product mix and machinery blend similar to that of MAC Machine, Ross has been running lights out for 10 years. Thomas Ross Sr., president, said labor—his biggest single cost—would double without lights out. “You simply can’t compete on a world market unless you lower your labor costs. That’s why we went to lights-out manufacturing.”
Ross runs a single manned shift, with half of his machines running around the clock. “To get into unattended, you’re buying machines that require significantly more initial capital,” he said. “Where you might spend $180,000 for a standard vertical machining center, a fully tooled multipallet HMC ready to run lights out can cost $600,000.”
While the additional upfront cost is substantial, Ross said running unattended is easy to justify. “We began seeing payback almost immediately.”
According to Lucius, “Ross has become one of the most efficient labor-hour-per-spindle shops in the country. Typically, 15 employees keep 38 spindles running, with a substantial number of them running 24/7.”
Does this mean machinists should start looking for new careers? Hardly. Unattended machining not only reduces the tedium of feeding the machines for operators, it also raises the bar for skilled machinists, giving them new challenges in programming, organization and advanced technology. And because shops that run unattended are more efficient, it should increase compensation for machinists and shop owners alike. So turn out the lights, the party’s starting. CTEAbout the Author: Kip Hanson is a manufacturing consultant and freelance writer. Contact him by phone at (520) 548-7328 or e-mail at firstname.lastname@example.org.
Courtesy of DMG/Mori Seiki USA
Courtesy of DMG/Mori Seiki USA
DMG/Mori Seiki USA Inc.
MacKay Manufacturing Inc.
Methods Machine Tools Inc.
Mitsui Seiki (U.S.A.) Inc.
Okuma America Corp.
Ross Machine Co.
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