Automation in Mass Finishing: Get with the Program

Article From: Products Finishing, from AAC Engineered Systems, Inc.

Posted on: 10/1/2003

A 21st Century Approach to an Age-Old Process...

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centrifugal disc burnisher/magnetic conveyor/rotary dryer system

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.

User interface terminals

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.

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.

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.

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.

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