Page 19 - MetalForming April 2012

sal/positional accuracy of the press. The controller’s high-speed ramping functions provide the ability to manage the increased pressing speed.
Using today’s valves and PLCs, cycle times can be improved with simpler and easier-to-troubleshoot circuits. Variable-displacement piston pumps allow flow and pressure to be controlled directly at the pump, simplifying the hydraulic circuit and optimizing horse- power to improve the circuit’s efficien- cy. As efficiency increases, wear on the oil and hydraulic components is reduced, which in turn reduces the maintenance burden.
Using touchscreen press controls, all press-setup points—including those for top stop, slowdown and reversal— can easily be changed. This eliminates the need for time-consuming manual adjustments. This “closed-loop” sys- tem is always adjusting itself against stored parameters. A control’s artifi- cial intelligence can even reject incor- rect settings, preventing costly acci- dents. In addition, ram position is tracked by a linear transducer, which rarely needs calibrating. The control can be integrated with a precision dig- ital control system, which enables actu- al position accuracies of ±0.001 in., and reversal at ±one percent of speci- fied tonnage.
Repeatability has improved dra- matically thanks to the use of new PLCs and valves. Metalformers can store multiple programs or recipes in the controllers, which can be accessed as needed—a big advantage compared to manually entering program parame- ters each time a new job runs. This automatic process may eliminate the need for a setup operator, requiring only the press operator to call up the program already loaded with values that have been checked by performing qualifying runoffs. Depending on PLC memory capacity, hundreds of recipes can be stored, enabling the press oper- ator to change programs in just sec- onds and ensuring that parts are pro- duced precisely and repeatedly every time they are run. Also, modern PLCs are flexible enough to allow the use of
multiple programming languages to best suit the current requirement.
Barcodes in the Pressroom
Quality control is further improved with the use of barcode readers, a grow- ing trend during the last 5 yr. Metal- formers use barcode readers to scan the tool and the work order to automati- cally upload the new parameters for that component. Scans also can be used to validate the press and die against the work order, to ensure that the proper press is being used for the job. An employee’s badge also can be scanned to check for permission to operate the press.
New PLCs enable process automa- tion by controlling multiple presses within a line, or by integrating a press with auxiliary equipment. This automa- tion provides consistent control over all press operations. Typical applications include adding roll feeders for advanc- ing sheetmetal in a press, or integrating rotary-index tables into a pressline.
Motors and VFDs
Motors are much more efficient today than they were 10 yr. ago. They offer a reduced rotational mass and higher-quality copper for improved winding technology. Pumps are more efficient as well, as improved seals and
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MetalForming/April 2012 17
Out with the old...
Hydraulic presses pur- chased as recently as 10 to 15 years ago likely employ outdated technology that restricts cycle times and can cause inconsistent part runs. They also may include a manual proximity switch to signal positioning on reversal, only as accu- rate as your hand is steady.
and in with the new.
To reduce cycle times and improve part quality, a press rebuild includes installing servo-quality proportional valves and high-performance PLCs to offer faster response times and improved positional accuracies. Other rebuild services include replacing or rebuilding pumps and motors, rewiring electrical systems, rebuilding cylinders and replacing worn platen guides/slides.