What’s on your pallet?

Courtesy of System 3R USA

System 3R’s WorkMaster Linear flexible manufacturing system.

Implementing automated pallet systems in small and medium-size shops can reduce labor costs and increase productivity.

More small and medium-size job shops are turning to unattended machining to compete effectively. A key part of many lights-out strategies is an automated pallet system to load and unload pallets of fixtured parts into and out of machine tools. By keeping a machine running through a second or third shift without adding personnel, shops can increase productivity.

While many consider automated pallet systems only suitable for large manufacturers, lights-out machining is something shops with five to 100 employees can achieve, according to sources interviewed for this article.

Courtesy of Kitamura Machiney of USA

Kitamura’s HX400i FTGA 8APC system is an HMC with an eight-pallet system.

“A 400mm or 500mm horizontal machine center is a big investment for any job shop, and for a small shop that investment is magnified,” said Robert Humphreys, international sales manager for Fastems LLC, West Chester, Ohio, a third-party integrator of flexible manufacturing systems. “So a small shop has to be as efficient or more efficient than who he is supplying to stay in the game. A lot of industries, especially the medical and aerospace, say, ‘Here is a 5-year contract but we want costs down over that 5 years.’ How are you going to offer price reductions unless you automate in some way and become more efficient?”

The main obstacle to small and medium-size shops taking advantage of automated pallet systems is the initial up-front investment. “Between the HMC, pallet system, additional pallets, fixturing and tooling, it may be overwhelming to some shops,” said Cari Vanik, assistant sales manager for machine tool builder Kitamura Machinery of USA Inc., Wheeling, Ill. “But with proper planning and guidance, the return on investment is often seen sooner than expected because of more efficient practices and unmanned machining.”

Kyle Klaver, product specialist for machine tool builder Okuma America Corp., Charlotte, N.C., gave this ROI example: “Say the shop rate is $100 an hour and they have a complicated job that takes 10 hours to set up. A 500mm pallet costs around $4,000. If they run that job four or five times a year, they could save $4,000 to $5,000 worth of setup time.”

A Fit for All Sizes

Generally, a standard HMC has two pallets, which the operator sets up manually. The most common size in the U.S. is the 500mm (20 “) square, followed by 400mm and 630mm square machines. The majority of automated pallet systems are used in conjunction with HMCs with 3-, 4- or 5-axis motion.

Linear-type automated pallet systems have a pallet carrier “crane” running on a rail-guided vehicle (RGV). The machine tool and load station(s) are on one side with the pallet storage rack on the other. A stacker crane runs in between on a linear rail.

There are also systems where the load stations can be opposite the machine. The RGV crane can move left and right, and has a pallet handling device that moves forward and back. The system brings the pallets to the load station and the system control informs the operator what actions to take, such as load, unload and where to put finished parts.

These types of systems are expandable. For instance, Okuma’s Palletace-M automated system is for one or multiple Okuma machining centers. It offers expandable capacity to 300 pallets, 10 machines and four workstations.

In addition to linear systems, “pallet pool” systems are available. A typical pallet pool shape is circular, but other shapes are used. These systems can hold eight to 40 pallets or more and are dedicated to a single machine tool. Pallet pool systems often offer shops vertical storage alternatives, an option for shops that need to conserve floor space.

Most metalworking professionals consider automated pallet systems as being for high-production, repetitive work. However, they are also good for small shops because they can use them for short runs while changing the tooling for the job that just ran or is going to run.

“The real strength of small shops is they can and will do a little bit of everything, so if someone comes with a rush job and they do a great job, it can lead to other jobs,” Klaver said. “With automated pallets, because all of your setups are taken offline, you can fit that rush job and keep the machine running to make other parts. As the shop realizes the benefits, it starts to migrate more work into that cell to take advantage of the spindle utilization.”

He added that eight to 10 pallets would be enough capacity for a small to medium-size shop starting with pallet automation. “Most companies have a 1- to 2-hour cycle time on a HMC for a four-sided tombstone on a pallet, so if you load the system with 10 pallets, at even an average of 1 hour machining time per pallet, you would have 10 hours of unattended machining, which could be your unmanned third shift,” Klaver said. In general, a two-pallet system can run unattended for 3 hours, an eight-pallet system can run for 8 to 12 hours, and a 40-pallet system can run an entire weekend.

Courtesy of Okuma America

Okuma’s MB-5000H HMC with a base Palletace C1000 10-pallet system. It is expandable to three MB-5000H machines and two additional C1000 extensions for a 30-pallet system.

For small shops with short runs, the real benefit to having more pallets is being able to leave complex jobs with long setup times permanently set up to run on demand rather than having to reset them for each run.

“If you set the job up again, you have to make a new prove out and validate it,” Fastems’ Humphreys said. “Whereas if you have it set up and haven’t changed anything and have all the tools in the magazine, you can load the pallet and be confident that the first-off part will be a good part—the same as the last part from the previous batch. When introducing new work to the pallet system and while first-article inspection is happening, you can run another proven part while waiting. When you get the green light that the new first-off part is good to run, it is easy to release the part for production.”

That is the challenge with a stand-alone machine—proving out parts. While waiting for the first-article inspection, typically the machine is just sitting there, Humphreys added.

And that is where shops can use a less- skilled operator. “All the operator has to do is load and unload the parts in the pallet. They don’t need to be the high-level machinist who does prove out and system validation,” Klaver said.

Super Pallets

One smaller shop that is utilizing pallet automation for unattended machining is West Valley Precision Inc., San Jose, Calif. The 35-man shop produces Invar, stainless steel, aluminum and plastic parts for medical instruments.

WVPI has about 20 machine tools, including a Kitamura HX500i horizontal machining center with 150-tool capacity and eight pallets, which it has had for about 3 years, and a Kitamura SuperCell 400mm 5-axis HMC with 190-tool capacity and 40 pallets, which it has had for about 2 years.

“The automated system has a huge tool library on it, so all of the tools you need to machine a setup pallet are on that machine,” said Dane Madsen, WVPI president. “Being able to use the same tool on many different jobs is a function of your tool library. Every time that job comes up, you just pull that program and it will grab that pallet with the material on it just like it was the next part on the machine, even a couple of months later.”

As for unattended machining, the shop’s longest production time is on the HX500, running eight pallets and having the machine busy for 56 hours.

Builder vs. Integrator

WVPI chose to use Kitamura factory-installed pallet pools for its automated pallet systems, but a third-party automatic pallet system builder that integrates its systems with existing machine tools is another option.

A linear-type automatic pallet system is appropriate when a shop plans to expand the system in the future. “Kitamura and our distributors also partner with Fastems,” Vanik said. “So if a customer is looking down the road and knows it is going to need to add more machines, pallets, robotics and so on, our partnership with Fastems allows us the flexibility to offer a more expandable-type pallet system.”