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Stamping/Presses

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By Bill Savela

Above: The spindle of the split-pulley press operates vertically. One hydraulic axis clamps a pulley blank from above. The knife tool splits the blank and the roller tool finishes forming the pulley.

New motion controller gives pulley manufacturing press a new lease on life

May 2016 - The scenario is common across industrial America: An aging machine begins to experience electrical glitches. Longer lead times for maintenance calls and a shrinking pool of experienced service providers becomes increasingly problematic. Controls begin to wear out, causing machine downtime and scrapping in-process materials. Knowing the machine still has a useful life ahead, and with the price tag for a replacement in the six-figure range, management seeks a fix that’s viable in the long run.

This is the story line that played out recently at Milwaukee, Wisconsin-based Capitol Stampings Inc. The fabricator’s vintage 1990s split-steel pulley manufacturing press was equipped with a failing CNC controller. At the time, programmable logic controllers (PLC) were limited in their ability to precisely control positioning, making CNC motion controllers the optimal choice.

Capitol Stampings’ machine employs three axes of control to produce pulleys ranging from 4-in. to 8-in. diameters for the lawn and garden equipment industry. 

One axis, mounted vertically, clamps the pulley blank. A second axis carries a knife moving in from one side to split the blank at its edge to begin forming the pulley shape. The third axis comes in from the opposite side with a roller tool to finish forming the pulley.

To solve the reliability and maintenance problems the press was having, Capitol Stampings brought in Dan Jensen, an engineer with systems integrator Control Automation LLC, Waukesha, Wisconsin. Jensen suggested replacing a few electrical subsystems and the obsolete CNC control with an RMC150 multi-axis motion controller from Delta Computer Systems Inc., Battle Ground, Washington.

FFJ 0516 stamping image1

Operators use the new HMI screen to adjust all parameters, such as the vertical position of the ram before and after pressing the part.

Save some, replace some

The existing control system controlled the knife and roller axes according to their position and speed. “Whoever designed the original machine knew what they were doing, and we were able to make use of many components of the old design,” says Jensen. “For example, the design had quadrature encoders on rack-and-pinion arrangements engineered to track the knife and roller axes as they move, and they had good rotary encoders installed. So we kept the encoders and wiring.” Control Automation also retained limit switches and proportional servocontrol valves during the controls upgrade.

The machine had an old DC direct motor with brushes that sparked. Jensen replaced this motor with a new 50 hp model, VFD control and a filtered power supply. Any components requiring 380 volts were replaced with 240-volt components and rewired.  

To work with the existing transducers, Jensen ordered the Delta RMC150, which is configured with two double-axis quadrature encoder interface cards and an analog card.

Adding a PLC

The Delta RMC is connected via EtherNet/IP to a new small PLC, which acts as a supervisor monitoring the hydraulic tank level and cooling pump control and lubrication to verify parameters. If all those functions work, the PLC gives the Delta instructions to run a “home” routine to start the process.

The PLC operates the main vertical ram according to overall operation sequencing controlled by the RMC. Since a simple on/off hydraulic valve is used, there’s no need for a proportional control for the vertical ram. A pressure transducer confirms that the ram is applying pressure above a set limit, indicating the pulley blank is clamped. The Delta motion controller monitors this pressure as a reference.

In addition to monitoring the hydraulic pressure in the vertical ram, Jensen added a linear transducer with analog output to monitor ram position. “Now we can measure both the pressure and location of the ram,” he says, “and we were able to eliminate the old switch contact blocks used to indicate vertical ram position.”

The old blocks had to be moved from their prior settings as the end product being produced was changed, lengthening the machine setup process time and injecting a source of possible operator error. With greater measuring precision and repeatability provided by the linear transducers, the new system can determine the number of pulley blanks that have been placed on the spindle, avoiding the production errors that occasionally occurred when zero or two blanks were placed by mistake.

FFJ 0516 stamping image2

The Delta RMC150 motion controller can control up to eight motion axes simultaneously.

Coding commands

Whereas the old controller was programmed using “G-codes,” a language designed for CNC machines, the new system uses Delta’s RMCTools software. RMCTools uses simplified  commands that make motion profiles easy to program and easy to maintain.

Motion programs are tuned graphically with Delta’s Plot Manager software and Tuning Wizard. “You run a couple of moves and output the graphs to Delta’s auto-tuning software,” explains Jensen. “Delta makes it so easy that I tend to recommend Delta RMCs all the time, versus PLCs for servo control [because] PLCs are very cumbersome to tune.”

Object oriented

The original pulley manufacturing press had a CRT-based human interface. It now features a 10-in. touchscreen HMI, which talks to the PLC and the RMC over EtherNet/IP. Machine status displayed on the screen is obtained directly from registers in the motion controller. “For example, if you touch on Batch Count, you can increase or decrease a data register’s contents in the RMC directly,” Jensen says.

The HMI supports object-oriented programming, which makes it easy to set up buttons and displays that access and modify register contents within the RMC150. Using this capability, Jensen was able to lay out the user interface similar to that of the machine’s existing screen layout to minimize training for Capitol Stamping’s operators and maintenance staff.

Like new

The machine retrofit project has met Capitol Stamping’s goals at approximately 25 percent less than the cost of a new machine. “With the old controller, we had to reboot the thing every couple days,” recalls Plant Manager Kevin Mullen. The press has produced good part quality, repeatedly, while being run continuously since it was brought online in late 2015. “Before,” says Mullen, “when we had to restart the system we might lose a part. Our scrap rate has also decreased.”

Jensen advises that anyone with a vintage machine “should consider that replacing the controls is a very easy thing to do. New controls are coming down in cost but drastically improving in functionality.” Replacing the intelligence is the easiest part of the task. “You end up with a new machine running again,” he concludes. FFJ

Bill Savela has more than 25 years of  industrial process and motion control experience in applications engineering, marketing and sales. A Registered Professional Engineer, Savela graduated from Michigan Technological University with BSEE and MSBA degrees. He has been at Delta Computer Systems Inc. since 2002 as director of marketing and sales.

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