By Tim Heston
About a decade ago, if you had walked the floor of Mettler Toledo’s plant that pro- duces truck, rail, and high-capacity scales,
you would have seen a very different operation.
A plasma table cut some parts, but others came
from an aging shear, a machine that took up significant space and, thanks to its age, wasn’t very
reliable. Persistent reactive maintenance on a
primary cutting system is never a good thing.
Today that area of Mettler’s Columbus, Ohio,
plant has changed. The shear is gone, material
flows quickly to and from the plasma cutting
system and a nearby press brake, and an adjacent welding area has been utterly transformed.
The story exemplifies how one improvement
affects another, which in turn affects another—
a kind of “positive” domino effect that has positioned the operation for a much more productive future.
The Large-scale Scale
If you’ve purchased produce using a grocer’s automated checkout lanes, you’ve probably used
one of Mettler Toledo’s products. The company
makes the integrated scales that weigh the vegetables and fruits and anything else purchased
by the pound. It makes laboratory scales, inline
product inspection systems, and other products.
And all of them look nothing like the massive,
heavy fabrications at one Mettler Toledo plant in
The 120-employee plant does make scales,
only scaled up for industrial, rail, and truck use.
When a trucker pulls into a weigh station, he
will drive over a treaded plate or concrete that
was poured over a metal base. That’s the surface of a scale that can be dozens of feet wide
and long, depending on what the application
requires. The fabrications involved all lie underneath. Scales are fabricated in modules that
can be used alone or combined with others. In
this sense, the scales can be, well, scaled up to
meet the needs of the application.
Spanning the length of each module is a se-
ries of U-shaped, 3/16- to 1/4-in.-thick carbon steel
stiffeners, 10 to 20 in. wide and 15 to 23 ft. long.
Each module also has two 0.75-in.-thick end
plates that span the scale width, usually between
9 ft. 10 in. and 11 ft. 10 in. long. The end plates
hold various small parts, including the receiver
plates for the load cells that perform the actual
weighing and, if a scale uses more than one mod-
ule, the connection points to other modules.
This is classic, heavy-duty, large-workpiece
welding and fabrication, and until recently the
fabrication department had to deal with the
classic large-part-fabrication problems, especially when it came to material handling and
welding; three years ago, both created significant constraints.
Employees used a combination of vacuum
lifters and manual techniques to move sheets
and plates through cutting and bending. This
included a 100-ft. plasma table and a 600-ton
press brake used to form the U-shaped ribs.
Vacuum lifters work well in a variety of manufacturing environments, of course, particularly
those that involve nonmagnetic material. But
Mettler’s vacuum hoists needed to lift heavy
loads. It took more than 30 seconds for suction
pressure to build, and the suction pads had to
be replaced frequently.
So in late 2017 the company replaced the
vacuum-based system with magnetic lifters
from Industrial Magnetics. The magnets help
lift long steel rib parts to and from a roller ball
table in front of the press brake tooling. After
the first flange is formed, workers pull the
piece out, reset the backgauge, and form the
second flange. On the first part of a new batch,
brake operators use a test jig to ensure the
bend angles are correct.
The external bend angles are slightly less
than 90 degrees, giving the ribs an ever-so-subtle trapezoidal shape after they’re welded
to the scale’s deck plate. After inspection, the
magnetic hoist grasps the ribs by the bottom of
the channel and stacks them on wood blocks,
where they’re moved to welding.
Scaling up improvement
» A magnetic lifter removes a cut deck plate from the
plasma cutting table.
» A magnetic hoist places a blank that will be formed into a U-shaped stiffener on the press brake.