Automation in Mass Finishing: Get with the Program
A 21st Century Approach to an Age-Old Process...
By Dan Cassino
AAC
Engineered Systems, Inc.
Cinnaminson, NJ
Recently, at a regional metalworking trade show, a man who had
just invested nearly one million dollars in state-of-the-art metal
cutting, stamping and forming machinery spoke proudly about the
efficiency, measurability and output from his soon-to-be-delivered
computer-controlled CNC milling centers and the cell manufacturing
line that he would create around them.
“Sounds great,” someone said. “Now, how will you
deburr and radius those parts?” He looked at the speaker as
if he were from another planet and simply said, “Well, we’ll
put ‘em in tumbling barrels, like we’ve always done.”
Here was a manager who had just invested six figures into plant
modernization, yet he planned to use a finishing technology that
dates back to the Roman Empire and would take hours to finish the
parts that he had made in minutes. It illustrates just how little
consideration many manufacturers give to their mass finishing departments—and,
how far this segment of the metalforming industry has to go in applying
widely available automation technologies. (In 30 minutes of discussion,
including a full demonstration of an automated centrifugal disc
system, he was unconvinced that there might be a better way!)
Until fairly recently, there has been a rational reason for this.
While PLCs, touch screens and networking technologies have been
available for more than 10 years; the cost of adding such controls
to many mass finishing systems was prohibitive. For example, there
are super-sized centrifugal barrel systems that allow a single operator
to process and monitor literally tons of parts per shift. But, there’s
a cost for this kind of firepower, namely, an investment in computer
hardware, sensors, load cells, controls and customer-specific software
development nearing six figures. Not a very practical idea for a
$12,000 vibratory bowl.
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With relatively simple
automation technologies and programming, complex integrated
systems like this centrifugal disc burnisher/magnetic conveyor/rotary
dryer system can run unattended, including integration with
upstream fabricating and forming machinery.
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The past few years, however, have brought sharply decreasing hardware
prices and new, non-proprietary software platforms that have made
some sophisticated technology available for reasonable prices. Still,
technology for technology’s sake is never a good investment.
So, start by looking at your needs.
What Do You Have to Control?
The basic elements of mass finishing do not generally change
much, whether the machinery is a tumbling barrel, vibratory tub, vibratory
bowl, centrifugal disc, centrifugal barrel or spindle finisher. Water,
chemicals, media and parts combine into an abrasive soup that finishes
large numbers of small- to medium-sized parts faster than a production
team can do by hand. That’s the easy part. The hard part is doing
this while maximizing material removal, minimizing time and materials
handling, and making results consistent from batch-to-batch, hour-to-hour,
day-to-day, week-in and week-out. That is where process development
and controls come into play.
Do you want to use one piece of equipment to finish several different
parts or part families, perhaps changing part numbers and processing
parameters in consecutive batches? Do you need to monitor water
flow during the process or change it mid-cycle? Do you wish you
could know what may be going wrong with a batch of parts while there
is still time to do something about it? Has management (or, more
likely, customers) insisted on ever-tightening quality, consistency
or reporting standards? Some relatively simple systems can help
you get there.
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User interface terminals,
such as the Allen-Bradley Panel View, can give operators “at-a
glance” information about (or even input on) process time,
machine status, operating speeds, water flow and more.
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A Mass Finishing Technology Menu
The modern metal finisher has many control technologies from
which to choose. Budget, customer demands and experience should be
the guide. Begin with the basics, and then explore the alphabet soup
of process technology.
Automatic timers, pumps and switches. Don’t
laugh (and, if the following describes your finishing department,
you won’t). There are still mass finishing departments crammed
with vibratory bowls and tubs that shake and shimmy endlessly,
waiting for their every-hour-or-so visit from “Earl.”
Earl has been working in the department since the plant was built
and is the only guy in the building who can declare a part “done”
or a finishing solution “right.” He does this by rubbing
the part or a handful of water between his experienced thumb and
forefinger. Problem is, one day Earl will retire. If you do not
at least have timers on your machines and automatic mixing pumps
delivering chemical solutions to the process, dust off your catalog
or find your metal representative’s number and make a phone
call.
Programmable Logic Controllers (PLC). The days
of relay logic are over for good. If your finishing equipment
is not running on Programmable Logic Controllers (PLCs), it will
be difficult to achieve the next level of process control. PLCs
are sort of a “central dispatcher” for automated machinery,
tying together materials handling components, timers, proximity
switches and more. Depending on the PLC’s processing power
and input/output (I/O) capacities, it can also store entire processing
programs or multiple programs, so operators need only load a batch
of parts, press start and walk away while the machine does all
the work. The system can even be programmed to accept automatic
parts loading, monitored by time, part count or weight, from “upstream”
production machinery like automated stamping, fine blanking and
powdered metal presses or automated conveying systems. At its
best, an intelligently-programmed PLC can even handle mid-process
changes. For instance, if a part could benefit from an aggressive,
15-minute, high-speed, low-water-flow cut-down cycle, followed
by a 20-minute polishing cycle that requires a change in machine
speed, chemistry and water flow. The PLC allows such changes,
as it ties together flow meters, chemical pumps, process timers
and motors, with a reliability and repeatability that makes customers
and QC departments smile.
Operator Interface Terminals/Graphical User Interfaces
(OIT/GUI). This can be something of an approach/avoidance
issue for many manufacturers. Argument number one is this: “My
operators aren’t programmers. I want them to push ‘Start,’
be nearby if something goes wrong and come back when it’s
done.” Argument number two goes “My operators need to
be able to make changes on the fly. Give them the tools to do
that.”
The Operator Interface Terminal (OIT) can be the answer
for both. Simply put, the OIT is a “window” (normally
a touch screen) on the PLC. It allows an operator or department
manager to see where a system stands in its process with information
like time in, time to go, water flow, chemical dispersion, machine
speed, air pressure and alarm status. The OIT can also allow operator
input (or not), allowing mid-course corrections as necessary.
Guided by the philosophy that a picture is worth a thousand words,
Graphical User Interfaces (GUI) kick OITs up a notch, displaying
information in intuitive, graphic displays. Want to change spinner
speed on your centrifugal disc system? Just touch the picture
of the spinner on the screen, select “Speed” from the
drop-down menu and select the up/down arrows to change that parameter.
Local Area Networks (LAN). Tying PLCs together
and letting machines “talk” to one another or to a central
monitoring station is the next step toward true, full automation.
Doing this requires creation of a LAN. Much like the ones that
allow office workers to share files and send e-mails, a LAN allows
a department full of machinery (or a complete manufacturing cell)
to carry on a sort of “binary conversation.” Is Stamping
Press No.1 ready to discharge a batch of parts, but Deburr Unit
No.1 still 10 minutes from completing its process? No problem.
Simply redirect Conveyer No. 1 toward Deburr Unit No. 3, which
discharged its load five minutes ago and stands idle. Is the recirculating
water treatment system malfunctioning? Not to worry. All systems
can be placed on standby until the alarm is cleared and before
water spotting becomes your next headache. The combination of
timers, PLCs, OIT and some smart programming makes it all possible.
Central Process Monitoring (CPM). Central Process
Monitoring might be described as the Holy Grail of process technology.
Once again, it’s not a question of “if,” but of
“why not?” CPM has been applied to CNC machines, stamping
presses, injection molders and warehousing pick/place systems
for more than a decade. With the demands placed these days on
everybody in the plant from loading dock workers to machinery
operators and upper management, there is simply no reason that
a plant manager or production engineer should have to leave the
desk to get simple answers like “How many parts did Manufacturing
Cell No. 7 produce so far today?” and “Is every deburring
unit in the finishing department working today?” Adding Ethernet
connections to a rudimentary LAN can get those answers with the
click of a mouse, even from offsite locations.
The Payoff
As stated earlier, technology for technology’s sake is
a bad reason to go PLC shopping. So, what’s the payoff for investing
in automation technology?
The answer begins with higher productivity. Downtime kills it.
Process changes slow it down. Manufacturing bottlenecks hamper it.
And, adding headcount is rarely the most efficient answer. By adding
automation and monitoring systems, these obstacles are better managed,
keeping productivity high and profit margins safe. But, there is
more to it than just numbers. Today’s quality standards are
simply brutal. With 0.01% out-of-spec part rates leading to refused
shipments and expensive rework (or worse yet, scrapped parts), absolute
uniform consistency is no longer a dream; it is a demand. Automation
and tight process monitoring is simply the only way to meet it.
The Final Word
Manufacturing has never been an easy way to make a living.
And, metal finishing departments are the final operation in many plants.
Still, customer demands continue trickling down to every operation,
every department and every process. As the technology becomes cheaper
and better, it makes more sense to bring mass finishing up to speed
with the rest of the plant. Over the years, the manufacturing plant
has matured from a place “where the stuff is made” into
an important part of any company’s management information systems
loop. Finally, mass finishing is ready to join the party. |
