Conveyors and Lean
Posted: January 26, 2007
 The trend toward lean manufacturing and work cells has, in some
instances, been hard on the conveyor industry. An emphasis on
flexibility and the ruthless elimination of waste doesn’t always
leave room for powered material transport.
For example, traditional fixed conveyors can represent a substantial
capital investment and require periodic maintenance—a source of waste
according to the lean manufacturing philosophy. They also take up
valuable production space and can be difficult or even impossible to
reconfigure in response to product or volume changes.
Then there is the danger of that most insidious of wastes,
overproduction. Saddled with an expensive conveyor-based system,
production managers may be tempted to run a line at a higher than
optimal rate to reduce unit costs and create the illusion of efficiency.
Nonetheless, conveyor manufacturers have not been sitting still. Over
the years, their products have continued to evolve, so that today’s
conveyors offer a host of technologies allowing them to play a roll
in a variety of production environments.
“One of the common rebuttals I get is that we already work with lean
cells, and we don’t want to use conveyors,” says Will Hunter, general
manager at Montech LLC (Huntersville, NC). However, Hunter emphasizes
that it’s important to make sure these kinds of investment decisions
are based on a close evaluation of a particular manufacturing process
and not just a hunch. “Just because you’re doing lean doesn’t mean
you have to go with [manual] build-and-pass,” he says.
Along these same lines, workstation manufacturer Lista International
Corp. (Holliston, MA) recently began offering its Arlink 8000 series
with an optional supplied conveyor system feature. Fully modular and
marketed specifically with lean manufacturing needs in mind, Lista
engineers have configured the workstations so they can be used with a
wide range of conveyor types. Clearly, in their opinion, powered
conveyors still have a role to play in the world of lean manufacturing.
Multiple Factors
 When thinking about material handling in a workcell or lean
production setting, there are a number of factors to keep in mind
before making a final decision. These include everything from
production cycle times to the presence or absence of feeder lines,
throughput, product mix, batch sizes, and product size and weight.
Then there are process-specific issues to take into consideration.
For example, does a build process include an automated pressing or
dispensing station where parts need to be fixtured?
“While manual production may be the optimal solution for some
assembly applications, others are better served with a mix of manual
and automated systems,” says Mark Dinges, product manager for
material flow automation technologies at Bosch Rexroth Corp.
(Buchanan, MI). “It’s critical that any manufacturer considering lean
production approach it from the standpoint of reducing waste. Finding
the most economic assembly solution depends on a variety of factors
such as part size, part weight, cycle time, Takt time, product mix,
changeover time and volume.”
With regard to size and weight, for example, Lista product manager
James Anderson says there comes a point when it simply doesn’t make
sense to have human operators doing the grunt work of moving product
down the line. According to Anderson, specific weight limits vary
widely, depending on cycle times and throughput. But generally,
manufacturers will find it falls somewhere between 15 and 40 pounds.
Hunter adds that even in those cases where weight doesn’t pose an
undue burden, it still pays to look at just how much time operators
are spending moving product down the line—an activity that adds zero
value to the process. Even a couple of seconds of transfer time can
add up, given high enough throughputs. This kind of waste is
especially costly when you consider the fact that time spent pushing
a pallet down a bunch of rollers is time that could be better spent
doing something else, like organizing parts and tools.
“When the conveyor is doing the moving, the operator can be getting
ready for the next assembly,” Hunter says.
Anderson notes that conveyors can be especially effective at carrying
product to or from a workcell—say, from a subassembly feeder line, or
to an inspection station—chores that might otherwise be performed by
human operators pushing around sets of carts. The idea, Anderson
says, is to eliminate the “walking wages” that result from people
having to spend an inordinate amount of time delivering things.
Along these same lines, manufacturers need to take a close look at
how operators are spending their time in mixed-mode manufacturing
production lines where assemblies are passing through one or more
automated workstations.
Because an automated station generally requires some kind of fixturing
—whether that station is dispensing an adhesive, driving threaded
fasteners, executing some kind of a test, or performing some kind of
pressing or welding operation—an operator in a passive material
transport setting will have to devote at least a portion of his time
to loading and unloading work-in-process from the station.
In contrast, when using a powered, pallet-based conveying system,
engineers can install a positioning and fixturing element, so that
the machine can do its job without human intervention. As Hunter puts
it, you no longer have a situation in which “a machine and a person
are doing what the machine could be doing by itself.”
Dinges notes that this arrangement provides an added safety benefit,
because you no longer have a human being working in such close
proximity to a potentially dangerous machine.
Modularity and Flexibility
 With regard to flexibility, conveyors have evolved so that they are
increasingly able to respond to changes in production volumes,
product lines and product mix. Of course, these are areas in which
manual workcells truly excel. Being relatively inexpensive and low-
tech, workcells are easily reconfigured. Engineers can even add or
subtract entire cells, if necessary. Nonetheless, today’s modular
conveyors are fully capable of being reconfigured to meet changing
market needs.
For example, engineers requiring basic material transport can go with
easy-to-use portable conveyor sections, like those offered by Dynamic
Conveyor Corp. (Muskegon, MI) or SmartMove Conveyors (Fall River,
MA). The former manufactures what it calls its DynaCon conveyor,
which can be literally snapped together and then rolled into place
with the help of casters. The latter manufactures plug-and-play belt
conveyor sections that can be mounted on interchangeable legs or
simply placed on a tabletop.
Assemblers can also go with programmable, sectional powered
conveyors, like those in the Quickdraw Conveyor line, manufactured by
MagStar Technologies (Hopkins, MN). Similar systems include the TB,
KTB and GTB belt conveyor systems manufactured by Montech. All of
these conveyors—which can be used with or without workpiece pallets—
include a wide range of modules that can do everything from locate
and fixture pallets for a pressing operation to elevate, rotate and
divert pallets along multiple tracks, depending on production needs.
Then there are those conveyors built around a system of standardized
extruded aluminum framing. Each of these lines includes an array of
standardized belts, chains, drives and other accessories that allow
users to mix and match parts as they please. Slots running the length
of the extrusions make it possible to install or remove accessories
like parts shelves or RFID readers using simple hand tools.
One of the leaders in the category is FlexLink Systems Inc., which
manufactures the XT line of twin-rail, or twin track, conveyors, as
well as the “X” series of single-track, chain conveyors. Similarly,
Bosch Rexroth offers what it calls its TS1, TSplus and TS4plus twin-
rail lines, as well as its VarioFlow single-track series. Another
example is Automation & Modular Components Inc. (AMC, Davisburg, MI),
which offers the Modu-Flex 83 single-track, chain-based conveyor, as
well as a number of different twin-track models as part of its Modu-
Con line.
For those engineers assembling larger, heavier products, there are
also LOGO!MAT S, XL and WalkOn pallet conveyors manufactured by
Logomat Automation Systems Inc. (Hebron, KY). Although these friction-
roller based systems are capable of handling loads as heavy as 600
kilograms, they are still fully modular in design. Even the WalkOn,
which includes a fully enclosed, low-profile track, can be fully
reconfigured as needs change.
“In the old days, if you wanted to make changes, you had to start
drilling holes,” says Ray Johnson, president of Automated Conveying
Systems Inc. (Bloomington, MN), which distributes a number of
conveyor types and manufactures the Link series of conveyors. “Now,
with T-bolts and slot nuts, you can add equipment as you need it.”
Any Which Way
 Finally, powered conveyors offer a ready means by which engineers can get a handle on process information, regulate production cycles and
support lean, demand-based production flow principles. Many of
today’s conveyors can be fully integrated into a plant’s process
monitoring system. This allows the conveyors to ensure that
production doesn’t outstrip customer demand. They can also be
equipped with “smart” RFID pallets and read-write units that make it
possible for engineers to obtain real-time information on shop floor
logistics, enhance quality through the use of electronic work
instructions, and enable traceability.
A prime example of this kind of technology is FlexLink’s Dynamic
Assembly System (DAS) concept, which includes interfaces that allow
it to be used with both manual and fully automated workstations. With
this product, the software that controls production flow can be
easily integrated with a customer’s order systems, enabling
variations in product mix and a “pull” approach to production.
“DAS offers the highest level of true flexibility. You can run a
batch size of one or a batch size of 1,000,” FlexLink Director of
Marketing, Paul Jarossy says.
Another example is Montech’s Montrac system, which turns the basic
idea of a conveyor system on its head by employing a battery of semi-
autonomous, self-propelled pallets that make their way along a fixed
monorail. Fully modular and installed using surprisingly simple tools—
mostly Allen wrenches—the Montrac’s motor-driven, smart pallets can
be programmed so that they behave differently, depending on the type
of assembly they are carrying.
These kinds of technologies are especially powerful when
manufacturing a mix of products in a single facility. In a manual
workcell environment, engineers create this kind of flexibility by
building multiple cells or equipping a single cell to produce a
variety of assemblies. With a smart conveyor, on the other hand,
engineers can accomplish the same thing by using diverters to guide
different product types through various loops or spurs where they can
be subjected to specialized processing.
Say, for example, an assembler is producing two product variants in
which one version receives a particular component or feature, but the
other doesn’t. Engineers can position the workstation performing that
operation off on a siding where only those assemblies requiring this
special treatment will receive it. Those that don’t require the
component can simply continue down the main line, bypassing the spur
or siding.
Again, these capabilities can be applied to products of all weights
and sizes. For example, at the high end of the weight spectrum, all
three Logomat conveyor lines come with a complete battery of lifting,
turning, diverting and elevation options to direct pallets wherever
they need to go. Logomat Vice President of Marketing, Michael Scott,
notes that, in addition to facilitating multiple product lines, these
features can be used to optimize flow and pacing. “One of the main
keys to a lean manufacturing assembly cell is rhythm and balance,”
Scott says.
At the low end of the scale, MagStar’s Quickdraw line does much the
same thing for smaller products, such as printed circuit boards. |
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