Page 35 - MetalForming Magazine August 2022
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 Blank Feeding WHY AND WHEN?
Blank feeding certainly can complicate things and require increased capital investment, yet improved material utilization and the ability to cost-effectively produce complex parts can lead to a quick return on investment. And, feeding blanks allows stampers
to continuously run their presses, optimizing overall equipment effectiveness.
BY BRAD F. KUVIN, EDITORIAL DIRECTOR
Iwanted to better understand why and when some metal stamping facilities may opt to feed their presses with blanks (whether cut inline or offline) rather than coil, so I posed the question to Paul Stirrett, vice pres- ident of sales at Linear Transfer Automation.
“We hear this question all the time,” Stirrett says. “Blank feeding certainly can complicate things and require increased capital investment. Often, the bottom line in the decision to feed blanks rather than coil comes down to material utilization and scrap costs. And certainly, in automotive and even appliance, some large class-A parts typically are blank-fed simply due to their size.”
Many OEM and Tier One suppliers of stamped parts, depending on the application, also opt to invest in a high- speed blanking press, with good coil feed and straightening equipment, that allows them to run at 50 to 60 strokes/ min., supplying multiple blank-fed press lines. This approach can prove more cost-effective than investing in multiple coil-fed lines.
“In addition, some customers can enjoy the best of both worlds by buying a slightly longer-bed press and a coil- fed progressive die to develop the blank in the first station, and then cut the blank off and use transfer tooling to move it through the remaining die sta-
tions,” says Stirrett. “This prog-to-trans- fer process or ‘trog’ die design—as some in the industry have come to call it—can require a stamper to add as much as 30 in. to the size of the press bolster. However, if they feed coil into a transfer tool, the transfer rails can be shorter. With a 240-in. bed, for example, the bars might only be 180 in. as the bars and tooling don’t need to extend into the press window and reach into that first station. This does simplify tooling-rail design.”
Decision Depends on Speed, Flexibility
Placing destackers at the entry side of a press—or “front-of-line automa- tion” as automotive OEMs call it, says Stirrett—requires stampers to select one of two methods for moving the blanks into the press: a gantry setup with overhead magnetic or vacuum tooling, or robots. The decision usually comes down to blank geometry, avail- able real estate and material type, and the required amount of speed and flex- ibility, Stirrett says, adding that, “with robots taking blanks from the destacker to the press, the stacks don’t need to be as precise as with a gantry setup. We adapt vision technology to the robot to check blank position and signal the required adjustments to ensure that the blanks precisely enter the press, as needed. However, with robots we can
typically only run a transfer press at 15 to 20 strokes/min.”
Want to run faster? That’s where gantry setups shine. “These simple two-axis gantry motion systems can allow a transfer press to top out at 30 strokes/min. or more,” Stirrett says, noting that instead of a vision system to orient the blanks coming from the stack, “we either ensure that the blank stack is set up as required on the han- dling system, or use vision and other dedicated equipment to identify and adjust each blank to present it to the transfer tooling. These setups include a physical mechanism able to stop the blank as it feeds on a conveyor and crowd it into position using a series of independently adjustable pins.”
Gantry setups, often custom devel- oped for the application, are T-style (with blanks moving from stacks per- pendicular to the feed direction, then turning 90 deg. to feed into the press) or inline. They use an overhead pick- and-place mechanism to move blanks from one or two stacks onto a shuttle, an infeed conveyor, or idle nest system for delivery to the press. One feed head serving one blank stack can feed at stroke rates in the mid-20s, Stirrett says, and faster by adding a second feed head.
When do metal formers opt for vision-guided robotics to feed blanks vs gantry systems? “Robots often are
32 MetalForming/August 2022
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