September 2012 / Volume 64 / Issue 9|
By Alan Richter, Editor
Many job shops think that their low-volume, small-batch runs aren’t suitable for producing in robotic work cells. They assume such an investment can only be justified for high-volume, large-batch runs. For instance, Mark Labbe, engineering manager at Connecticut Spring & Stamping, Farmington, Conn., voiced a popular refrain about automated work cells. “We’re a job shop. Many of our products are fairly short run and don’t lend themselves to setting up a cell like that.” CSS does, however, automate some of its parts handling using a rotary table (see sidebar below).
Although it’s a common perception at job shops that their frequent setups and changeovers preclude use of robotic work cells, they often don’t realize how often the parts they run have size and shape similarities—even if they’re not a family of parts. “Of course, the argument is ‘I don’t run enough volume,’ ” said Andrew Glaser about why machine shops are hesitant to integrate robotics. “My response is, ‘I am not concerned about the volume of a few part numbers; rather, I want to see the entire product mix.’ ”
Courtesy of Methods Machine Tools
Glaser is vice president of sales for Motoman Robotics, Miamisburg, Ohio, and author of the book “Industrial Robotics: How To Implement The Right System For Your Plant” (2009, Industrial Press Inc.).
Glaser recommends that shops examine the volume of parts they machine that fall within a similar shape and size range. Most shops will find they usually have enough product to justify automation.
“There will be a balance between how much flexibility is required to automate the part mix and the capital investment,” he said. “Without automation, the shop still has to pay the operator to load and unload the machine. The payback can be very good deploying automation, so the motivation is there for the shop to do the analysis for finding a large-enough part mix that can be automated within the return-on-investment constraints.”
In many cases, those parts are run in the robotic work cell during the second or third shifts while the first shift tackles the trickier parts—“the cats and dogs and strangers”—that don’t make sense to automate, he added.
Heavy parts typically fall into a shop’s outlier part category and require a significant jump in robot size—and price—to handle. Nonetheless, automated handling of those parts might be justified, according to Nathan Maholland, sales manager for Interactive Design Inc., Lenexa, Kan., a robot and machine vision integrator. “Heavier parts can be a safety risk and cause a lot of worker compensation claims,” he said. “So they may go ahead and get those parts automated. Other times, companies choose to stick with the 80/20 rule and automate their more standard parts, [which account for about 80 percent of their work], and leave the outliers to be handled manually. It comes down to each company’s needs and the key factors in their cost justification for the system.”
When parts become too heavy for a human to lift, automation justification is easier, noted John Lucier, automation manager for machine tool and automation supplier Methods Machine Tools Inc., Sudbury, Mass. This is because it generally takes a time-consuming crane operation to load and unload those parts in and out of a machine. “The robot picks it up and places it in less than a minute,” he said.
By running a low-end robotic work cell that costs about $80,000 to $100,000 for the automation, a shop can achieve an ROI in about 2 years if the machine tool is utilized at least 6 hours a day, according to Glaser. That amount of run time effectively exploits the labor savings and productivity gains a robotic cell provides, he added. “The more a company currently relies on operators to ensure machine tools are kept utilized, the better the case for automation,” Glaser said. “Is the operator going to be there every single cycle, every single day of the year? I don’t think so. He’s going to take breaks, talk to his buddy or come in late one day or possibly not at all.”Flexible by Design
To meet a job shop’s need for fast setups, quick changeovers, operator safety and production flexibility when operating a robotic work cell, Methods offers the JobShop Cell. It combines a FANUC RoboDrill vertical machining center with a FANUC 6-axis LR Mate 200iC robot, and comes with inbound and outbound conveyors, guarding and a work-handling interface that accommodates various hydraulic or pneumatic workholders. According to the company, the cell handles virtually any part that fits in its 6" vise or chuck.
The JobShop Cell, not including the RoboDrill VMC, starts at $80,000, Lucier noted. Methods focuses on robot programming through generic programs users can easily customize and modify to meet their needs, he said. This programming ability is a primary enabler of quick changeovers.
Courtesy of Motoman Robotics
“Instead of rewriting a program, it’s saying ‘remember when you picked up the last part and it was here, well the new part is over here,’ and by teaching this new position the program is adjusted a little bit,” Lucier said.
That robot teaching capability enables users with limited robot programming ability, which is easier than machine tool programming, to make changes to a program so it’s suitable for different parts, according to Lucier.
Another way of enhancing flexibility is an adjustable lane guide on the JobShop Cell’s inbound and outbound conveyors. By loosening adjustment screws and sliding the guide in or out, a job shop can switch, for instance, from a 2-sq.-in. part to a 4-sq.-in. one.Conveyors Don’t Get Nicknamed
The robot is often considered the “sexy” part of an automated work cell, but that’s an overrated perception. “The robot is the least exciting part of the cell; it’s simply a multiple-axis programmable manipulator,” Motoman’s Glaser said. “The key to these jobs is how you transfer parts into and out of the cell, as well as how the robot gripper interacts with the workholder in the machine in terms of orienting and locating the part correctly for the machining process.”
That could be on a conveyor or pallet, in a bin or drawer unit or from a bowl feeder. Another option is having parts come from a rack, according to Dan Barkley, president of J.O. Winter & Associates Inc., Huntertown, Ind., which supplies material handling, process and ergonomic equipment and specializes in part conveyance, including systems for automotive OEMs. The rack can be mounted on a turntable, enabling a robot to access two sides of the rack, he noted, and then material handlers use a forklift to move the rack out of the way once it is empty.
Operators can still play a role in the robotic work cell, but their function is more as a loader/unloader, placing workpieces onto the initial conveyance system and placing machined parts in a rack or dunnage prior to performing secondary operations or packaging and shipping parts, Barkley noted.
Regardless of how parts are transferred into and out of an automated cell, users must stage raw material, waiting to be queued, so an operator ideally doesn’t have to tend the robotic work cell for long periods of time, Glaser said. He added that one of the first criteria to qualify with a customer is how much raw material they want to have in that queue before an operator loads workpieces and removes finished parts.
Typical desired periods for unmanned run time before an operator returns to reload raw parts and remove finished pieces can range from 45 minutes of queue to several hours or more, depending on part size and practical considerations.
For example, although it might seem ideal to have enough parts on a conveyance system for an 8-hour shift, Methods’ Lucier pointed out that a conveyor would need to be excessively long for handling parts with a 30-second cycle time. “Initially, you get a customer who is a bit of dreamer, and then they see the cost and realize that’s going to be an expensive conveyor,” he said.
Therefore, one for handling 4 hours of parts might be more realistic. However, even a conveyor suitable for that amount of time can be excessive, depending on the workpiece material. When cutting difficult-to-machine materials, such as Inconel, Lucier noted a user might be paying too much for a conveyor if the cutting tools wear and need replacement after 90 minutes or less, enabling part replenishment at that time as well.Letting the Blind See
A basic industrial robot is blind, but can be programmed to repeatedly go to a location or locations to pick or place a part. For instance, a program can direct a robot to gather parts on a rack that has three rows of parts across and five rows of parts down and deliver them to the machine tool, explained J.O. Winter’s Barkley. Having preprogrammed points avoids the need for a vision system on a robot to locate parts.
“I don’t see vision systems on robots that often. It’s just an added expense that doesn’t need to be there,” he said. “If I want to make sure the part is there, I could have a sensor on the end of the robot gripper that says a part is there.”
Courtesy of Methods Machine Tools
Barkley pointed out, though, that one vision system his company integrated enables a robot to correctly grab the same parts randomly placed on a conveyor.
For a job shop, a vision system—including a 2-D or 3-D camera, lighting and software—can be especially beneficial because it communicates part orientation and location information to the robot, according to Interactive Design’s Maholland. “The big benefit of robots is their flexibility as opposed to having dedicated, hard automation,” he said, noting automatically changing a robot’s end-of-arm tooling enhances that flexibility. “Another major benefit of robots is they can be retrained for different parts or redeployed in completely different applications, which is especially important in a job shop, where things can change a lot.”
Eliminating dedicated feeding not only enhances flexibility but also can improve the work environment. “Bowl feeders are noisy,” Maholland added.
Balancing robotic work cell flexibility and cost is similar to riding a seesaw, according to Glaser. “Part of the game that goes on every time you look at one of these jobs is determining how much flexibility is needed vs. the capital investment and return on investment constraints,” he said. For example, machining gear blanks that only vary in height and diameter requires less flexibility and investment than automating production of parts where part geometry is considerably different.
A vision system enables a higher percentage of differently shaped parts to be automated while reducing costs related to expensive fixturing hardware. Without vision, a job shop would be hard pressed to justify a robotic work cell, according to Glaser. “Vision has been a key driver to penetrate job shops because it allows, at a fairly low cost, an immense amount of flexibility and sways that seesaw more in favor of the robot system,” he said.Don’t Go There
The old robotic adage is anything can be automated if you’re willing to spend enough time and money to do it, but that might just be a fairy tale. Noting that every engineer has an impossible project in his lower, left-hand desk drawer that he pulls out every year or two and tries to find somebody who’s willing to take it on, J.O. Winter’s Barkley emphasized that some projects are simply cost-prohibitive because the part throughput is unrealistically high or the size and scope of the part is too large. “The problem usually involves a customer’s misconception of what can be done,” he said.
Courtesy of Methods Machine Tools
Courtesy of Motoman Robotics
In addition to part size and shape, cycle time can be a limiting factor when automating parts handling. A machine processing a part with a long cycle time is already being highly utilized and the productivity gains are more limited vs. more frequent cycles, Glaser explained. “Something that has a 3-hour cut time provides 3 hours of unmanned machining. That’s a beautiful thing.”
On the other hand, in some cases it can make sense to have a robot tend a machine with a long cycle time. For instance, Methods’ Lucier pointed out that an operator attending a machine cutting parts with 1-hour cycle times might man one or more additional machines. However, if he returns every 70 minutes to load a new part, an expensive part’s worth of productivity is lost during a shift. And for an unmanned shift, a shop would produce an entire shift’s worth of parts even though the robot only loaded one part per hour.
“I find people have a hard time justifying that robot sitting there for an hour,” Lucier said. “They want to have it do something.” He added that a robot tending a machine producing parts with short cycle times looks like a better fit, but productivity can grow even with long cycle times.
Conversely, an articulating-arm robot can be too slow if the cycle time is too quick, Lucier noted. This is because the robot is very flexible and can be programmed to move in numerous ways, but can be slower compared to a loading device customized to perform only one move.
Even if the payback period, percentage of suitable parts and cycle-time scenario make installation of a robotic work cell a no-brainer, machining issues must be addressed prior to integration. One issue is potential chip problems, such as bird nests in chucks that inhibit robotic loading, according to Glaser.
Another is workholding. “If you can’t accurately locate the part or you don’t have a good workholding process, it makes no sense to put a robot on the machine,” Glaser said. “Your issues will only be compounded. Have a good manual process first and then automate redundant material handling tasks. But look at the sequence of machining operations as well, including any operations before and after machining, when considering how to apply automation.”
After a job shop establishes a proven manual process, it is then up to the robotic work cell designer to choreograph the automation. “There is a good amount of watching the operator to really understand what that operator is doing,” said Interactive Design’s Maholland. “There are a lot of subtle moves operators make that don’t always get transferred to automation if you’re not careful.” CTE
About the Author: Alan Richter is editor of CTE. He joined the publication in 2000. Contact him at (847) 714-0175 or email@example.com.
Parts shuttling boosts productivity
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