by Kip Hanson
When machined parts are the size of locomotives and pickup trucks, finding safe, efficient ways of handling them is critical to the success of any manufacturing company
It may seem obvious to anyone in the machining industry, but large boring mills and gantry style machining centres are quite expensive, as are the parts made on them. Cranes are needed to load and unload such machine tools, huge slabs of concrete required to support their extreme mass, and highly-skilled machinists available to operate them. The stakes are high, with billing rates in the hundreds of dollars per hour range and cycle times that may span days. For the owners and operators of these machines, it’s crucial to aim for the highest spindle utilization possible.
Zeroing in on downtime
One way to achieve at least some of this goal is with zero point fixturing systems. That’s according to Peter Zagorskis, inside sales coordinator at Mississauga-based machine tool distributor Megatel Inc., who says a number of his customers have either purchased an off-the-shelf quick change system or built their own.
“We offer a number of machine tools with rotary-style pallet changers, but these aren’t always feasible when you’re talking about ten ton workpieces,” he says. “By mounting the part to a quick change fixture of some kind, it can not only move from machine to machine with ease, but setup time becomes practically zero—you just position the part on the machine and go. Just as importantly, you don’t have to invest a quarter-million dollars in a massive pallet changer.”
Another way to increase large part machining efficiency is by supersizing the table. For instance, double-column machining centres and boring mills are often equipped with right angle heads, speeders, and tools too large to fit through the toolchanger. Carl Barthelson, regional sales manager at Doosan Machine Tools America, says if the table is large enough, these can be “parked” to one side in a wine rack-style fixture, then picked up automatically by the machine as needed. In addition, workers might actually be able to load and unload parts on one end while parts are being produced parts on the other.
“On machines with generous X axis travels, it’s pretty easy to establish A and B work zones to keep the operator safe while the machine is running,” he says. “I worked at a job shop in Schenectady, New York, making automotive stamping dies and turbine components for the power generation industry, and this practice saved us a lot of time—we could be roughing out a mould cavity on one end while setting up a finishing operation on the opposite side.”
Another way to increase machine uptime is with spindle probing. Assuming the machine tool is accurate enough (which virtually all newer ones are), it’s often more efficient to simply measure sofa sized parts in place rather than carting them off to a CMM for inspection.
Take it offline
Using a highly accurate machining centre can be a perfectly acceptable way to validate features and inspect parts, thus eliminating the need to re-fixture them offline. And quick change fixtures are a great way to reduce setup related downtime, regardless of machine size. But perhaps the best way to keep expensive spindles producing nearly non-stop is with an automatic pallet changer, noted Robb Hudson, CEO of Mitsui Seiki (U.S.A.) Inc.
“I think zero point systems are fine when on smaller components, but when you’re talking about the massive castings and forgings you see in the aerospace and energy sectors, I would prefer palletization,” he says. “In this scenario, you’ll have a dedicated load and unload station away from the machine, with ready access to a crane or hoist. The operator can work at ground level to get large, bulky components mounted in place, after which the automation system will shuttle the pallet directly to an available machine, or back to a storage position for future scheduling.”
“Palletization is as much about safety as it is machine efficiency,” adds David Suica, president of automation system provider Fastems LLC. “Without a pallet system, the operator’s going to be standing up there on the table trying to maneuver some huge workpiece into position. He’s several feet in the air, crane control in hand. There are chips and cutting fluid underfoot. Considering the size of the parts, it can be dangerous. And while all this is going in, the machine’s sitting idle.”
Suica says that shops thinking about a pallet system should also consider ways to more effectively manage their cutting tools and toolholders—when large machine tools are automated (or any machine tool, for that matter), throughput goes up substantially, making it increasingly likely there won’t be enough cutting tools available to complete whatever work is in the queue.
“Suddenly you’re able to produce multiple parts and operations unattended, but many standalone boring mills and machining centres have relatively small tool capacities,” says Suica. “That’s why we often suggest a centralized tool system. This not only provides hundreds or perhaps thousands of tool storage positions, but because they can be shared across multiple machine tools, it actually decreases overall tooling costs. Between this and an automated pallet changer, it’s pretty easy to double machine capacity.”
Mitsui Seiki works closely with Fastems and other automation providers. Like Suica, Hudson believes that the larger the machine investment, the more important it is to automate. “We have several installations where we’re taking large, heavy, and very expensive raw material components—typically titanium or similar superalloys—and loading them onto pallets for offline storage,” he says. “A cell controller equipped with scheduling software then plans production based on what tools and machines are available, maximizing the efficiency of each.”
According to Hudson, the OEE in these installations can hit 90-percent or greater, and the chance of scrapping out a workpiece costing several hundred thousand dollars drops significantly. Fewer machines are needed, investment is maximized, as is the flexibility to meet customer demands quickly.
Granted, there are some drawbacks. Pallet systems and centralized tool storage hubs consume considerable floor space. Implementation of such systems requires months or sometimes years of planning, Employees will need training, and old school machinists must be brought into the automation fold. But for those shops that have made the leap to a large-scale FMS, the ROI is quite fast.
“We’re seeing a number of large manufacturers moving in this direction,” Hudson says. “They’re looking to reduce the amount of direct labour, in part because it’s very challenging to find skilled operators. To that point, I think automated environments are much more enticing to the next generation of people entering the trades, who will take on roles like cell technician and automation engineer rather than machine operator. Automation is simply a good move for everyone involved.”
One final piece of advice comes from Doosan’s Barthelson, who suggests that prospective automation customers shouldn’t sell themselves short on machine capacity. “I worked with a shop recently that was making fracking blocks roughly one-metre square,” he says. “They were looking at a machine just large enough to fit the parts, and my question to the owner was, ‘What’s the likelihood of producing even larger fracking blocks next year, or the year after that?’”
The message is clear: machining needs change. And where a large boring mill can easily machine smaller parts, a smaller boring mill is limited to small ones. Says Barthelson, “If you’re looking at the big picture, you want to buy the most capable machine possible as an investment in the future, and automation is part of that.” SMT