Pallets in the job shop

The days of dedicated, high-volumeproduction- only pallet magazines and pools are gone.

Today’s machine pallet systems provide shops the flexibility to add or subtract pallets or different types of machines to production cells at any time, and to apply palletization to manufacturing a high mix of low-volume jobs.

And, today’s pallet systems allow jobshops to invest on demand.

The decision to incorporate a palletized system no longer has to be made at the time a machine is purchased, so shops can incorporate palletizing systems to existing machine tools years after they’ve been purchased.

Several machine tool builders said flexible pallet systems owe their existence to technological advancements that include centralized cell controllers, common pallet receivers, standardized changer heights and interfaces, and the development of subplates (or subpallets).

Thanks to advanced central cell controllers/management systems, shops can operate several machine tools and their pallet system from one location. They can manage completely different jobs that run through the production cell instead of having to do it at each machine tool. With that ability, one operator can oversee a cell of multiple machines and multiple pallets, a job that used to require several operators.

Central cellmanagement systems eliminate job changeover time because jobs are queued in the system prior to starting any machine operations, so machines are not kept waiting while new jobs are being fixtured on pallets.

“Together, palletized systems and cell management drastically increase a machine’s spindle utilization rate. Typically, a standalone 2-pallet horizontal machining center’s spindle utilization is around 60 percent. Add palletization, and that rate jumps to almost 90 percent or better without having to increase labor,” Tim Jones, product line manager for horizontal machining centers at Makino (www.makino.com), said.

Jones pointed out that, in addition to increasing spindle use, pallet systems and cell controllers can extend the amount of hours a machine runs per year and make it possible to integrate different types of machine tools into one common pallet-management system. For example, Makino can integrate a three or four-axis horizontal machining center with a five-axis vertical machining center and process parts across the system accordingly. The company can also mix old machines with newer ones.

Bill Vejnovic, vice president of engineering at Toyoda (www.toyodausa.com), said controls, especially those that are PC-based, and software have had the biggest impact on pallet systems.

“Shops can schedule low-volume jobs to run one after another and manage hundreds of part numbers without the aide of a telephonebook- sized document for the operator to know what part goes with what fixture and what pallet,” Vejnovic said.

He cited one jobshop customer to emphasize the point: The shop has a 90-pallet system that serves five machines, and the 6-month-old cell already is running 180 part numbers and it is doing so with only 30 of the system’s pallets.

“This is the kind production setups jobshops are doing now,” Vejnovic said.

In addition, with central cell controllers, Vejnovic said all the work that took several of a shop’s talented schedulers now is generated automatically and quickly. And cell controllers can be part of a shop’s network, so the controls can be accessed remotely.

Besides tracking pallets and scheduling jobs, central cell controllers can manage tooling and provide valuable process information.

Tool management functions within a cell controller can monitor and extract the tools that are needed for a particular job while that job’s pallet is loading into the machine tool. If the tool is not there or is broken, the controller can skip that job and run the next one scheduled.

“Most of the time, jobshops want their pallet system cell controllers to track and report on information centered around tooling. They want intelligence built into the controller for organizing tools to streamline job changeovers. However, these days, shops are extremely process oriented and want information/tracking that’s even more customized to their specific businesses,” commented Jones.

To add pallet systems to older, existing machines and to different types of machines, most builders have standardized their palletmounting methods and have incorporated modular design concepts that transfer across their various machine models. Pallet receivers and changer heights are kept the same, so no matter how old a pallet system’s rail-guided vehicle is, a shop can add new machines without having to purchase a new vehicle.

“We have many installations where shops have three different generations of machine tools all served by the same pallet system and rail-guided vehicle,” Vejnovic said.

In another growing trend, some jobshops no longer move whole pallets from machine to machine, but instead fixture work on subpallets or subplates that mount to machine pallets. The machine pallets remain in the machine.

Locator systems qualify subpallets to machine tools by ensuring that subpallets are accurately positioned on the stationary machine pallets. The locator systems also can be used on subpallets and allow shops to fixture work in the same qualified position every time.

Subpallets simplify work loading, especially for 5-axis machining because the machine’s tilting and rotating main pallet does not leave the machine. Additionally, subpallets take up less storage space compared to whole pallets, letting shops stack subpallets both linearly and vertically and get more pallets in less space.

Robots, instead of rail-guided vehicles, are another burgeoning trend in palletization. Robots can either pivot from one stationary position or move along a rail to load pallets into machine tools. Having a robot ride a rail lets shops add more machines to the cell.

In Makino’s robotic pallet system, robots load subpallets to simplify operations. Since the robots grip only subpallets, which are all the same size, shops can use one standard gripper for the robots to pick up subpallets loaded with varying part shapes and sizes accessed remotely.

Besides tracking pallets and scheduling jobs, central cell controllers can manage tooling and provide valuable process information.

Tool management functions within a cell controller can monitor and extract the tools that are needed for a particular job while that job’s pallet is loading into the machine tool. If the tool is not there or is broken, the controller can skip that job and run the next one scheduled.

“Most of the time, jobshops want their pallet system cell controllers to track and report on information centered around tooling. They want intelligence built into the controller for organizing tools to streamline job changeovers. However, these days, shops are extremely process oriented and want information/tracking that’s even more customized to their specific businesses,” commented Jones.

To add pallet systems to older, existing machines and to different types of machines, most builders have standardized their palletmounting methods and have incorporated modular design concepts that transfer across their various machine models. Pallet receivers and changer heights are kept the same, so no matter how old a pallet system’s rail-guided vehicle is, a shop can add new machines without having to purchase a new vehicle.

“We have many installations where shops have three different generations of machine tools all served by the same pallet system and rail-guided vehicle,” Vejnovic said.

In another growing trend, some jobshops no longer move whole pallets from machine to machine, but instead fixture work on subpallets or subplates that mount to machine pallets. The machine pallets remain in the machine.

Locator systems qualify subpallets to machine tools by ensuring that subpallets are accurately positioned on the stationary machine pallets. The locator systems also can be used on subpallets and allow shops to fixture work in the same qualified position every time.

Subpallets simplify work loading, especially for 5-axis machining because the machine’s tilting and rotating main pallet does not leave the machine. Additionally, subpallets take up less storage space compared to whole pallets, letting shops stack subpallets both linearly and vertically and get more pallets in less space.

Robots, instead of rail-guided vehicles, are another burgeoning trend in palletization. Robots can either pivot from one stationary position or move along a rail to load pallets into machine tools. Having a robot ride a rail lets shops add more machines to the cell.

In Makino’s robotic pallet system, robots load subpallets to simplify operations. Since the robots grip only subpallets, which are all the same size, shops can use one standard gripper for the robots to pick up subpallets loaded with varying part shapes and sizes.

A big trend in pallets
Big is in for pallets.

More jobshops have realized that they can benefit from hitching pallet shuttle systems to their big machine tools to machine low-volumes of large components, especially for the wind-generation, oil and gas, heavy construction equipment and air compressor industries.

Ken Campshure, director of sales at MAG Giddings & Lewis (www.giddings.com), said his company has seen an increase in sales of large machines with multiple-pallet shuttle systems that have pallets that range in size from 1,250 mm to 2,500 mm (49.21 in. to 98.42 in.), and some shops want them even bigger.

“We’ve had requests to build pallets as big as 3.5 m (137.79 in.) But we are hesitant to do so because we don’t believe these customers realize just how much space such a system would require,” Campshure said.

Like smaller-size pallet systems, Giddings & Lewis’s pallets can serve different types of machines, such as vertical turning lathes and boring mills, within one machining cell.

The company builds most of its pallets and shuttle units/vehicles to order with modular designs that transfer across its machine product line along with master, or standardized, pallets. Together, these design features allow shops to add either machines or pallets to their cells at any time.

Victor Enterprises Inc. in Paducah, Ky., is a Giddings & Lewis customer that has benefited from incorporating a pallet shuttle unit and multiple pallet system.

While the shop has experienced increased machine spindle utilization, Ken Harlan, vice president of manufacturing at Victor, said the real payback has been with job scheduling.

The shop specializes in machining large parts, mostly for the aircompressor industry and mostly from cast iron, in job lot sizes of one. These parts typically require between one and two shifts’ worth of machining work and, quite often, the shop has to interrupt one job that’s running to fulfill a rush order.

Before installing the pallet systems, if the company had to change jobs in midstream, it had to shut down the machine, remove the part, break down the setup, fixture the urgent job and load it into the machine.

“We lost a lot of time,” Victor Sredl, vice president of administration for the shop, said.

With the pallet system, the shop keeps its machine spindles working right up to the point when the new part loads, he said. In addition, the shop can go right back to where it left off on the first part after finishing the rush job.

Victor Enterprises is used to using pallet systems. It has an existing sixpallet system on a machining center.

However, parts that require precision boring operations had to be transferred to a manual boring machine that slowed the manufacturing process.

So when the shop purchased a Giddings & Lewis HBM MC1600 boring mill, it opted for a threepallet shuttle system to streamline and automate operations and for the flexibility to handle future work.

The new system is not a typical Giddings & Lewis system because each of its three pallets is a different size. Harlan said the reason for this is to provide the increased flexibility the shop was looking for.

“If we have a part that requires a lot of radial work using all the machine’s B axis, large pallets can sometimes get in the way. So we had one of the three pallets made 63 in. square, which lets us work all the way around round parts, and the other two rectangular-shaped pallets measure 63 in. by 79 in. and 63 in. by 98 in.,” Harlan explained.

In addition to the different pallet sizes, Victor Enterprises had Giddings & Lewis locate the system’s shuttle unit at the side of the machine because of space constraints on the shop floor. Three pallet “stumps” for pallets to sit on are arranged in a semi-circle around the shuttle unit. The stumps eliminate the need for operators to get on the shuttle unit when fixturing work to a pallet.

The different sizes of pallets are immaterial to the machine because the shuttle unit moves them in the same fashion, and pallet-mounting bases are the same. This means the shop could add more pallets to the system if necessary.

The system shuttles workpiece loads weighing as much as 30,000 lb, and Harlan said they have had parts weighing almost that much on the system.