IS IT TIME TO REBUILD OR RETROFIT YOUR HYDRAULIC PRESS?
By Tim Wilson
Hydraulic press operators must keep their costs down while meeting shorter lead times and the demand for higher precision parts. New press technology has already outdated some presses that were purchased as recently as ten to fifteen years ago. Is new machinery the only answer?
Today’s fabricators face shorter manufacturing lead times as well as more demanding requirements for producing parts to meet tighter tolerances and strict quality guidelines – all while keeping their costs down. For those using hydraulic presses, advancements in press technology may make some presses purchased as recently as ten to fifteen years ago outdated.
There are numerous reasons to consider a press rebuild or retrofit. Slower cycle times and inconsistent part runs can be by-products of older presses. At the heart of older press technology will likely be a control panel which has limited functionality compared to today’s programmable logic controllers (PLCs).
Older operator interfaces have monochromatic keypad displays and provide a slow update time for viewing critical data. These controllers do not offer a way to automate press runs, thus manual instructions need to be entered each time a job is set up. An all-manual set up increases cycle time length and the likelihood of errors due to the manual reprogramming required for each job.
Presses of a decade ago may include a manual proximity switch for the function of positioning on reversal, a critical process for producing accurate parts. This manual switch is only as accurate as the human hand is steady, meaning parts may eventually fall out of tolerance.
Older presses that required accurate position control were designed with small proportional directional valves that provide a slow penetration speed into the part in order to achieve reversal position. Achieving positional accuracy with old valves is difficult. Modern servo-quality proportional directional valves can achieve positional accuracy with very high flows because of the response time of the valve.
Aging pumps, motors and even hydraulic fluids are simply not efficient by today’s standards. Due to enhancements and new options, older power units may also not be economical as new equipment – and as shops grow and add larger presses, the amount of power needed for consumption increases.
Safety is another important area that may need updating. Upgrading to ANSI B11.2-1995 (R2010) and adding light curtains allows the press to be run by an auxiliary piece of equipment (like a feeder or foot switch) to reduce cycle time.
Significant improvements that are now available in press technology make modern hydraulic presses faster and more reliable than ever before. The technology has gone through constant change in the last decade as PLCs and other electronically-based controls have improved speed and flexibility.
To reduce cycle times and improve part quality, better valves and high performance PLCs provide faster speeds and excellent positional accuracies. Servo-quality proportional valves have fast response times, even in larger size valves that can handle the required flow and faster cycle times.
Proportional valves offer a better level of control over older servo valves without the sensitivity to contamination that can lead to maintenance issues. And the newest PLCs have scan times that are fast enough to achieve ±.001 in positional accuracy with a D08 size valve and provide monitoring of the linear transducer to achieve the reversal/positional accuracy of the press. The controllers offer high speed rapid advance ramp coupled with the ability to manage the increased speed.
With new valves and PLCs cycle times can be improved using simpler circuits that are easier to troubleshoot. Variable displacement piston pumps allow flow and pressure to be controlled directly at the pump, simplifying the hydraulic circuit as well as optimizing horsepower to improve the circuit’s efficiency. Increasing circuit efficiency reduces wear on the oil and hydraulic components, resulting in a much lower maintenance burden.
Through touch screen press controls all press set points, including those for top stop, slowdown and reversal, can be easily changed to eliminate the need for time-consuming manual adjustments. This “closed-loop” system always adjusts itself against stored parameters. A control’s artificial intelligence can even reject incorrect settings to prevent costly accidents.
Ram position is tracked by a linear transducer that rarely needs calibrating. The control can be integrated with a precision digital control system that enables actual position accuracies of ±.001 in and reversal at ± 1 percent specified tonnage.
Repeatability has drastically improved by using new PLCs and valves. Press operators can now store multiple programs or “recipes” which can be accessed as needed versus manually entering the parameters each time a new job is run. This new automatic process may eliminate the need for a set up operator to be involved in the job, requiring only the press operator to call up a program that already has values set and checked by performing qualifying run-offs.
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