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Guide to Press Productivity
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Selecting a Hydraulic Press

  1. Tonnage. Is the tonnage required to do a job the same for a hydraulic press as it is for a mechanical press? The answer is yes. There is no real difference. The same formulae are used to determine tonnage. The tooling is usually interchangeable. There may be certain applications such as deep drawing where the full power stroke characteristic of a hydraulic press reduces the tonnage, but there are no known instances where using a hydraulic press requires more tonnage.

    Selecting press tonnage in the typical press room is often little more than guesswork. If, for example, a job is successful on a 100-ton mechanical press, it tends to stay there for the life of that job. The job may never have been tried at 75 tons or at 50 tons.

    With a hydraulic press, however, you can adjust tonnage quickly and easily, tuning the press to precisely the right tonnage for each specific job.

  2. The action of the machine. Even though the tonnage question might be settled, the question of the effect of the stroke on the work is often asked. Is it the same as with a mechanical press?

    The answer, again, is yes in most cases. There are some specific limitations. Drop hammers and some mechanical presses seem to do a better job on soft jewelry pieces and impact jobs. The coining action seems sharper if the impact is there.

    In deep drawing, however, the full power stroke of a hydraulic press produces significantly better results.

    Otherwise there are very few examples where the application of 100 tons of hydraulic force produces any significant difference in the character of the part given the same tooling.

    Shear in the dies will reduce blanking tonnage for hydraulic presses in the same way it does for mechanical presses.

  3. Type of press selection. Open-gap presses provide easy access from three sides. 4-column presses insure even pressure distribution. Straight-side presses offer the rigidity required for off-center loading in progressive die applications.

    The more critical the work and the more demanding the tolerances, the greater the reserve tonnage capacity should be.

  4. Accessories. Most hydraulic press builders offer a wide array of accessories. These commonly include:
    • Distance reversal limit switches
    • Pressure reversal hydraulic switches
    • Automatic (continuous) cycling
    • Dwell timers
    • Sliding bolsters and rotary index tables
    • Die cushions
    • Ejection cylinders or knockouts
    • Electronic light curtains and other devices
    • Touch screen controls
    • Servo system feedback for precise, consistent, repeatable stroke control
  5. Quality. The industry offers various levels of quality. There are light-duty presses that are capable of "spanking" the work momentarily and reversing, and there are heavy-duty machines designed for general purpose metalworking applications.

    Here are just a few construction points that will provide a basis for comparison of one machine with another:

    1. Frame. Look at frame construction-rigidity, bolster thickness, dimensional capacity, and other factors.
    2. Cylinder. What diameter is it? How is it constructed? Who makes it? How serviceable is it?
    3. Maximum system pressure. At what psi does the press develop full tonnage? The most common range for industrial presses is 1000 to 3000 psi.
    4. Horsepower. The duration, length, and speed of the pressing stroke determines the horsepower required. Compare horsepower ratings.
    5. Speed. See page 5 to determine the speed of a hydraulic press.

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