Page 41 - MetalForming-May-2018-issue

a larger tapping window
when compared to mechanical units. With
mechanical units, the tap
indexes forward as the
press ram moves toward
the bottom of the stroke,
and reverses the tap as the
ram moves from bottom
dead center (BDC) stroke
back up to top dead cen-
ter (TDC). Servo units, on
the other hand, allow for
tapping forward at any
time in the stroke, even
as the press reverses back
to TDC. This allows for a
larger tapping window,
which translates into higher produc- tion speeds in strokes/min., since the tap can retract from the strip at a faster rate than the controlled rpm while tap- ping occurs. With a mechanical tap- ping unit, the tap does not retract and allow the strip to feed until a specified number of tapping turns have been completed; with a servo tapping unit, strip feed occurs after a set amount of time, regardless of the number of tap turns.
Finally, servo control allows the cap- ture of processing data, which can sup- port preventive-maintenance and product-quality programs. For exam- ple, the stamper can prescribe torque
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Servo tapping units allow for tapping forward at any time in the stroke, even as the press reverses back to top dead center. This allows for a larger window for tapping than with mechanical units, which translates into higher production speeds.
Pros and Cons
Mechanical Tapping Units
Pros
Simplified engineering
Easy troubleshooting
Lower initial costs
Recommended for most applications
Servo Tapping Units
Pros
Not press-stroke specific Larger tapping window Data feedback
Cons
Press-stroke specific Possible speed limitations No data feedback
Cons
Higher initial costs Sophisticated engineering Complex troubleshooting
parameters and direct the press to shut down should torque vary outside those parameters. If torque climbs above the recommended setting, the tap likely has dulled and needs replacing. Con- versely, too little torque could indicate a broken tap.
The decision to use mechanical or servo tapping units is specific to each application. In most applications, either option would be a good choice. Ultimately, a company needs to access its requirements, assess its engineer- ing/support capabilities and justify its investment when choosing the tapping method best-suited to its plant and project requirements. MF