Options for storing, transferring materials
October 14, 2008
When fabricators decide to automate material handling in their laser cutting operations, they have several choices to make. The decision on whether to automate—and what kind of system makes the most sense—will depend on the shop's capabilities, its production capacity, and available floor space. The options cover the full spectrum, from basic systems that simply unload one pallet and bring in another to large racking systems that maintain a full inventory of raw material and cut parts and can transfer those parts to other machines in the shop.
If you decide to automate material handling in your laser cutting operations, you have several choices to make. The decision on whether to automate—and from there what kind of system makes the most sense—will depend on your shop's capabilities, its production capacity, and available floor space. The options cover the full spectrum, from basic systems that simply unload one pallet and bring in another to large racking systems that maintain a full inventory of raw material and cut parts and can transfer those parts to other machines in the shop.
For the most part, automating material handling will require you to choose from three types of systems. A pallet changer is the least expensive option, but adds only a basic level of automation. A stand-alone storage tower allows you to store material vertically, but usually requires structural alterations to the building. An integrated shelving system can comprise several towers and allow completely unattended operation, but it has the largest price tag and takes up far more floor space than the other two options.
A pallet-changing system provides the most basic type of automated material handling. In fact, it's very rare in the metal fabrication industry for a shop to invest in a stand-alone laser without adding at least this level of automation, according to Mike Monaghan, service manager, laser material handling, customer service and support, for Mitsubishi Laser/MC Machinery Systems, Wood Dale, Ill. With no material handling assistance, operators have to load raw material onto the laser manually, wait until the machine finishes cutting, unload the cut parts and scrap, and then load another sheet.
"If you have a pallet changer—which has two cutting tables that shuttle in and out of the laser—then you can load the first one, have it start cutting, and then prepare the second one," Monaghan said. "It gives you faster loading times."
"If you think in terms of delivering raw material to the machine, I can't imagine anybody today not at least automating the loading of the raw material onto a laser," said Bill Bossard, president of Salvagnini America, Hamilton, Ohio. "[The loading systems are] very simple devices, very straightforward, very reliable, and very adept at picking up raw material and transferring one sheet onto a laser. That's something you ought to do to keep that whole mechanism operating on a machine pace, as opposed to an operator pace."
An automated storage tower is the next step up from a pallet-changing system. Storage towers allow laser systems to process different types of raw material in an automatic sequence. They usually accommodate 14 or more shelves of material and can go as high as plant space allows, Bossard explained. Vertical construction allows shops to store materials without taking up a lot of floor space. But an investment in one of these machines will require a reinforced building foundation to support the tower.
"It's the static weight of, let's say, 15 packs of material, each weighing 6,000 pounds, so you have a 90,000-pound dead weight just in your storage tower," Bossard said. "The foundations have to be designed and built in such a way to support that static weight."
Some shops store more raw material than a stand-alone laser can handle. Many of these shops—some of which process material 24 hours a day in unattended operations on one or several laser cutting systems—then transfer the cut pieces to other departments to be bent or welded. Since a standard tower system won't provide enough storage space in these cases, the best option is a complex automatic system that comprises several shelving areas for raw and cut materials.
For example, an integrated shelving system might have 96 shelves and eight towers and have the ability to feed material to multiple lasers. In addition, it can transfer cut material to other machines, such as a shear or press brake, for subsequent operations. This type of system also is a good place to queue up work-in-process before the next operation, Bossard said.
"These systems are for people who have a real good handle on the material that they use and want to keep a full inventory control of what goes in and out of the building," Monaghan said. "What's handy about this is that all the material, when it comes in off the truck, goes right into these towers so that it's easily accessible. These warehouse systems are fast."
There are two reasons to automate laser cutting operations, according to Bossard.
"Number 1 is cost, and it all boils down to how many people you have running your machine and running material in and out," he said. "Number 2 is that the more time you spend doing things around a machine, the higher your costs. If you can speed up your operation so that you can pull raw material, cut it, and separate the parts—and you can do that on a constant loop—then you don't [have to use extra labor at the machine] because it's happening in an automated fashion."
In some fabrication shops, laser-cut parts are organized on individual carts according to thickness, so that each piece on a cart is identical. If various parts of different thicknesses are required for a kit that will be formed, welded, or bent, workers have to sort and separate parts themselves, slowing down the operation. Automated material handling systems address these types of issues, Monaghan said.
"If you have multiple carts and they're different thicknesses, then you can dedicate a cart to a kit and the kit can travel through the company and get bent up or welded or formed, instead of putting all the same thickness on one cart and all the same thickness on the other," he said. "You can dedicate one cart as a kit."
The mechanics of a storage system are straightforward and simple—the software is what will make or break its effectiveness, according to Bossard. The mechanical systems comprise static towers and a picker crane that runs back and forth, pulling shelves out as needed. The software keeps a constant inventory of all parts stored in the system, updating whenever a part is removed and tracking the part through the entire production run.
"Software is designed by the builder of the [storage system]," Bossard said. "The software not only has to serve the storage system, but it also has to be able to interface with the individual machines that are plugged into the storage system. There's a lot to it; it's not just keeping track of what's on shelf 4 and tower number 6."
How prevalent is the use of automated material handling systems among North American manufacturers compared to their counterparts in Europe? Bossard said he doesn't think the technology is catching on in North America at the pace it should be, but added that this is primarily a result of different circumstances under which European manufacturers operate. Floor space is much more limited in Europe because land is more limited—and expensive. Manufacturers have to conserve it as much as possible, so they expand vertically. The cost of labor also is higher in Europe than it is in North America.
There are other reasons North American manufacturers have been slower to adopt automated material handling systems. According to Bossard, the problem with material handling systems is that shops usually don't consider them a high priority, perhaps because of the cost. A stand-alone storage tower—a 60-in. by 120-in. by 6,000-lb.-capacity shelf, for example—probably would set a shop back about $150,000, while the large integrated system would cost about $1,500 per shelf, he said.
"In a fab shop, the hardest thing to justify is automating material handling and quality control equipment because they don't make any money," Bossard said. "You have to invest in them to maintain the level of performance of your shop, but they're not revenue generators. Typically, fabricators evaluate [reducing their cost of operation], but a major component in there is a revenue generator, so until people can begin to identify the improved revenue stream that's available from these material handling systems, I suspect that there's going to be a lack of enthusiasm."
After looking at the costs and benefits of each type of automated material handling system, also take into account strategies for growth and expansion.
"You have to have a plan," Bossard said. "Today's plan is fine and dandy, but you need to look down the road a little bit and decide what your longer-term plans are going to be, because once you put in one of these tower systems, you're not going to move it. So you need to make sure it's the right size, in the right position, and intended to do whatever it is you need it to do over the next several years."