The roller ball table is made of magnetic
material, which demonstrates a key benefit of
magnetic lifting: the circuitry can be designed
to match the thickness of the load. In the ribs
application, the load is comprised of long, 3/16-
to ¼-in.-thick material. In this case, the magnetic circuit was designed to penetrate deep
enough to hold and lift the 3/16-in.-thick material
used to make the rib, but not so deep as to pull
against the roller ball table itself.
“You can design the [magnetic] circuit with
different shapes, sizes, grades, and arrangements of magnetic material to achieve the required magnetic circuit performance for an
application,” said Collins McGeorge, director of
sales at Industrial Magnetics. “For example, you
can configure a circuit that offers a very strong
surface hold, and yet is not a deep-reaching
circuit. This allows you to pick up only the top
sheet from a stack of metal, even if it has been
treated with a sticky, oily coating.
“This was the case in one of Mettler’s applica-
tions,” McGeorge continued, “and because the
magnetic circuitry [was designed] to reach only
so deep, the magnet could eliminate the need
for an air knife and other more manual separa-
The ability to integrate magnetic tooling into
a lift-assist is another benefit that’s put into
play at the plasma table, where a separate mag-
net lifts steel plates onto the table and then re-
moves cut pieces from the nest.
“The magnet is able to pick up an individual
blank sheet from the stack and load the plasma,”
said Brandon Koch, manufacturing engineer at
Mettler Toledo, who has been highly involved in
the Columbus plant’s recent improvement efforts. “Then, after cutting is complete, it’s able
to simultaneously pick up the separate nested
parts and release them individually in different
locations. Overall, we’ve been able to reduce the
number of hoists at the plasma by 35 percent.”
Koch added that the number of gripper tool
changes (compared to previous lifting methods)
at the plasma table fell by 25 percent. And the
number of hoists overall, for both the brake and
plasma system, has fallen by about 24 percent.
By early 2018 lifting efficiency was critical
because by that time the operation had transferred all of its previously sheared work to the
plasma cutting table. Managers decided to remove the shearing process altogether, which
freed up valuable floor space for the company’s
next improvement: robotic welding.
On to Welding
Mettler Toledo is no stranger to welding robots.
Robots mounted overhead perform the linear
welds that connect the ribs to the scale decking.
Each scale module has about seven ribs, which
adds up to a lot of welding. The product mix is too
large and variable for a hard fixture, of course,
so operators lay out the ribs onto the deck, tack
them, fixture them, then run the robot.
Until recently, welding the end plate assem-
blies remained a manual operation—and for
good reason. It remains one of the most com-
plicated joining applications in the plant. The
end plates have various small components
welded to them, but the plates themselves are
0.75 in. thick.
All that welding had previously led to exces-
sive heat buildup. Warpage was unavoidable,
which was a problem considering the end
plates needed to be straight for downstream
welding and assembly operations. So multiple
times during a shift, operators had to move the
end plate assemblies to a separate press for
The welding process itself couldn’t be elimi-
nated—and why automate the process if the
work had to be straightened in a secondary op-
eration anyway? Robots would simply push the
bottleneck in front of the straightening press.
Moreover, the operation didn’t have the
part mix traditionally thought to be suited
for robotic welding. Part geometry variation
among these end plates abounds. If the
company implemented robotics, the operators
would need to spend a lot of time with the
Of course, welding and robot programming
technology has evolved. First, engineers found
that pulse welding (GMAW-P) could reduce
problems with workpiece distortion. Combine
this with a large copper heat sink on the fixtur-
ing table, and engineers found that distortion
could be virtually eliminated. Working with
Wolf Robotics, Mettler installed a robot welding
cell that not only controls distortion of those
end plates, but also takes weld programming
and simulation offline.
Now operators receive a blank end plate and
place it in one of four adjustable jigs, which to-
gether account for all the base plate designs
for all the scale platforms the plant produces.
They then arrange the smaller components and
tack them in place, at which point they fixture
the assembly onto the table. The robot touches
off the wire tip to verify the part position, then
» Mettler Toledo is no stranger to robotic welding. For years the company has robotically welded stiffeners to scale
» Jigs are set adjacent to the end plate welding cell, where welders tack components in place before loading them
onto the fixture table.