Slitting Line Out; Transfer Press In
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You know what they say about best-laid plans, and at Tennessee Steel Center those plans took a sharp right-angle turn beginning in 2007. That’s when Exedy, in need of stamping capacity, asked the service center to forego plans to install a slitting line and instead install a blanking press. That 600-ton press, a Seyi model, was tasked with feeding Exedy’s stamping presses with blanks of 1- to 3.6-mm-thick steel (primarily HR400 and HR440), to support production of torque converters and other transmission components.
The Plot Thickens
The plot thickened in 2010, when Exedy found it needed more than just blanking capacity—now it needed additional stamping capacity. Specifically, it asked Tennessee Steel to support its production of torque-converter stampings, by buying a transfer press to take on a set of dies being shipped across the pond from Japan.
“We looked at buying a transfer press, and it was too costly for what Exedy wanted us to do,” recalls Ivan Price, Tennessee Steel’s general manager. “So we looked for an alternative solution.”
That solution came early in 2012 in the form of four 200-ton Komatsu gap-frame presses linked by a servo-transfer system, from Linear Transfer Automation, Barrie, Ontario, Canada. In fact, Linear Transfer, along with its distributor Production Resources Inc., completed the entire turnkey project for Tennessee Steel, including a blank destacker, die carts (two per press), quick-die-change apparatus (hydraulic clamps, lifters and bolster extensions), safety light curtains, magnetic conveyors, electric scrap shakers, and even a new press foundation.
|A press operator visually inspects each support as it exits the line, at a production rate of 13 parts/min. When the firm replaces magnetic transfer tooling with grippers and shovel-style tools, it expects to be able to kick throughput up by at least a few parts/min.|
Rounding out the plant’s equipment list: three overhead cranes (one 25-ton model and two 10-ton cranes), a few forklifts and a truck and trailer rig.
The transfer line runs two shifts/day producing three torque-converter part numbers for Exedy—turbine and impeller cores, and torque-converter supports. A fourth part number is slated to make its to the line early next year—turbine shells—which will require running the transfer line around the clock. Of the firm’s 18 employees, four are trained on the transfer line. Two work the line at a time. Blanks feeding the transfer line come from the plant’s blanking press, and account for 20 percent of that press’s output; the remainder of the blanks gets shipped up the hill to Exedy.
“The cores are the easiest to run on the line,” says Price. “They are small (183-mm-dia. blanks), from 1-mm material and are lightweight. These take only three press operations, and here’s where the custom engineering provided by Linear Transfer really helps. They engineered the line so we can place an outbound conveyor anywhere between the presses, to remove parts from the line. We have the conveyor mounted on casters so we can easily move it along the line, to any of three stations where we typically pull parts off, depending on the job.”
Dies are on a customer-specified preventive-maintenance schedule. “We send the transfer-line dies up to Exedy for inspection and maintenance after 60,000 hits,” says Price.
Seven Press Stations, Four Presses
Stamping the supports requires a more complex process involving seven press operations. Blanks—295-mm dia. and 2 mm thick, in lot sizes of around 9000—feed through all four presses in the transfer line for trimming, shaping, coining and flanging. Between presses one and two the transfer system spins the stampings 180 deg. and flips them over. Once the production run has completed, the plant executes a complete die change on the four-press line and the stampings run through three additional operations, feeding in the reverse direction along the line—left to right.
In all, between blanking, production stamping, and warehousing and shipping coils up to Exedy, Tennessee Steel processes an average of 5.7 million lb. of steel/month.
Following on the theme of “best-laid plans,” Price admits that production on its servo-transfer line, while smooth and relatively trouble-free, remains a work in progress. For starters, it had expected to receive new dies with the project. Instead, the dies it received were repurposed from presses running in Japan.
“To get the dies to run in our line, we had to turn them 90 deg. on their base plates (compared to how they were running previously), and reengineer how we bring scrap out,” says Price.
The scrap solution: Shakers pull scrap from under the dies toward the front of the line, where chutes direct the scrap down and under the press to a magnetic conveyor running along the back of the line.
A Transfer-Tooling Upgrade
Also a work in progress is maximizing line speed and throughput. Cores run through the line at 15/min., while supports run at 13/min. Of note: all three jobs run through the press line completely free of stamping lubricant—mill oil only.
To enable a speed increase of another few parts/min., the plant is investing in new transfer tooling—grippers and shovel-style end effectors—to replace the existing magnetic tooling. The speed limiter using magnetic transfer tooling: “The blanks are never perfectly flat coming off the blanking press,” says Price, “particularly blanks at the leading and trailing ends of each coil. Without near-perfect flatness, we can’t dial up the speed without risking losing the grip on the work—especially the heavier support blanks. Shovels and grippers will avoid this issue.“This tooling upgrade doesn’t come easily,” continues Price. “We have to reconfigure the dies to provide the tools access to the parts. But the expected increase in throughput will be well worth the investment. The goal all along has been to run the line at a 65-percent on time, and we’re closing in on 70 percent. We’ll easily surpass that when the new tooling is installed.” MF
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