A Successful Switch from Large Parts Bins to Small Totes
|New conveying systems installed on 200-ton presses at Polaris feature a pair of conveyors (from QC Industries, Batavia, OH), with drives built into the drive-pulley assembly, that work together to deliver parts into small, plastic totes. The top conveyor slides in and out, adjusting to reach several different sizes of tools. To watch a video of the system in operation go to www.youtube.com/watch?v=uIuwEaQQ9jI.|
This new directive meant that press operators could no longer run large numbers of parts into containers and move the containers using lift trucks. Nor could they continue to rely on the press control’s batch counter to count press strokes until it reached a preset value, allowing thousands of parts to drop into each container before the counter would stop the press and trigger the operator to change bins and restart the press.
More Bin Changes Tough on Productivity
Switching to the use of small, plastic totes with a specific, small part count per tote created several challenges to the plant. The small bins cannot be placed on the floor, as had the large bins. And, coming off of the presses, the new setup had to ensure that the parts would consistently land in the small totes and not bounce out after a long drop from the bolster. There also were ergonomic issues, as the new system had to avoid requiring operators to bend over to lift totes from the floor.
Also of concern was accuracy of the part count, since the previous end-of-line method monitored press strokes and assumed that each stroke created a part. When filling huge bins, if the count was short by one or two parts, assembly operations hardly noticed. However, with new, smaller quantities specified, part count has to be dead-on, or problems will result downstream.
Press uptime, in lieu of added bin changes, posed another significant problem in designing a new end-of-line system. Previously, presses would stop when a parts bin was filled. A press running at 60 strokes/min., for example, would operate for 66 min. to fill a bin with 4000 parts. It might take the operator 10 min. to first notice that the press had stopped, signal a lift-truck driver, then move the full bin and replace it with an empty bin, and finally restart the press. That equates to a press uptime of 87 percent.
Switching to batch sizes of just 200, at 60 strokes/min. the small parts tote fills in just 200 sec. Assuming that an operator needs 1 min. to remove and replace the filled tote and restart the press, uptime falls to 77 percent. Bad enough, but at a batch size of 25, press uptime drops even more. Even if we assume that the operator never leaves the bins during the run, and reducing the time to move and restart the press to 20 sec., the result is 25 uptime seconds out of 55, for an uptime of only 45 percent.
These examples are, if anything, terribly optimistic. The time required to restart the presses presume that the operator is constantly available to restart the press and never is distracted. If the operator must constantly attend the press, he cannot tend to other chores—part inspections, paperwork, coil staging, etc., all jobs Polaris operators perform when presses run larger batch sizes.
The Solution: An Automated Conveying System
Making the move to small-batch production with plastic totes, any reduction of press uptime was deemed unacceptable by the Polaris engineering staff. Automating tote changes became the goal, and Polaris process-improvement technician Randy Osborne turned to equipment supplier TCR Integrated Stamping Systems, Wisconsin Rapids, WI, to provide a solution. TCR developed a conveyor system to count actual parts as they enter the bins, and automatically exchange full bins for empty bins without stopping the press. Several empty bins are prestaged, giving operators time to tend to other duties without interrupting production.
The conveying system developed by TCR can be used with any of several prepared presses at Polaris, regardless of passline height. It can handle three different bin sizes, and stamped parts no longer fall from a great height, eliminating concerns about finished parts bouncing out of the totes. And, ergonomic concerns were addressed as well, as full bins discharge onto a gravity conveyor at a comfortable work height.
with Part Sensors
Each of the three new conveyor systems at Polaris provides an operator touchscreen control interface loaded with valuable production information. Messages highlighted in blue display only when the described fault condition occurs.
Two conveyors work together to reach into the die—an upper conveyor extends out to reach smaller tools, and can be retracted to adjust for longer dies. Sensors count actual parts as they enter the tote. Empty strokes counted during coil threading, or parts that fail to properly land on the exit conveyor, do not create an error in the parts counter.
Four empty bins are staged so the press can run untended, based on the number of parts per bin. The configuration allows Polaris, in the future, to add an automatic empty-bin loader and longer cue for the full bins, to allow more prolonged operation without operator tending.
Sensors monitor the locations of empty and full bins, and the control software ensures that faults—such as no empty bin available or no place to put the next full container—will trigger the conveyor system and the press to stop.
A quick-disconnect cord allows the conveyor system to be quickly connected to any of the prepared presses. Casters allow an operator to easily move the system press to press without the use of a lift truck. The controller’s touchscreen interface employs simple commands for system setup, with screen prompts to assist with operation and troubleshooting.
Three Systems Installed
TCR produced three of the automated bin-changing systems for Polaris, all of which were installed earlier this year on 200-ton coil-fed presses—two gap-frame presses and one straightside—including Polaris’ construction of new guarding. Positive results were immediately realized.
Conveyor-system controls proved easy to use and understand. On the very first production run, a Polaris press operator ran three complete coils with 100 parts/bin without stopping production for bin changes. This provided plenty of time between press-tending responsibilities for the operator to perform other duties while the press ran—staging new coils on the coil car, handling required paperwork for shipping, and inspect parts as required. In fact, the plant realized an unexpected benefit regarding visual inspections. A Polaris operator noted that its standard sampling rate required a visual inspection of one part/hr., but, he said, “Because I did not have to constantly move bins and restart, I found that I was inspecting one part in every bin. This helps me catch problems more quickly, and reduce scrap and rework.”
Adds manufacturing supervisor Ehric Gullickson, “These systems will increase our press uptime while freeing up our operators to perform other duties.”
Stampers face new challenges every day, and innovative companies find ways to improve their bottom line and keep manufacturing strong in the face of global competition. MF
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