In die tapping allows threading to be done in a progressive tool without involving expensive secondary threading operations. In die tapping units are available in both mechanical and servomotor driven.

Mechanical driven tapping unit

hreading is done by a series of gears arranged in different ratios, which are driven by a vertical lead screw mounted on either the lower or upper tool die shoe. Threading can be done either from top down or bottom up.

Top down in die tapping is most commonly used in stamping operations of higher volume and higher speed (up to 250 spm). Top down tapping operation needs longer Tap travel length if the strip lift increases. Increased of tap travel length will also increase tapping rpm and increase tapping speed, resulting in tapping to be completed in shorter punching stroke length and shorter tap life.

Bottom up tapping unit, the material is pushed down onto the tapping head by the stripper, allowing the tap to thread the part in much the same way as if the part ran flat, rather than the tapping head compensating for strip lift. As strip lift increases, tapping from bottom up becomes more desirable.

Servo-Driven Tapping Unit

The advantage of using a servo driven tapping unit is that the servomotor controls the threading operation independently. It can tap more than 180 deg of the punching cycle at a specified rpm and allows rapid reverse in a shorter cycle time than a conventional mechanical driven unit.

Servo-driven in die tapping units particularly useful when facing large diameter taps.

Points to consider when designing a tapping tool

Material Lift. When tapping from the top down, it is best to keep material lift to a minimum. The lower the material lift, the lesser the tap travel length, and less tap travel translates into lower rpm and higher production rates. If the component requires higher material lift, tapping from bottom up is more desirable.
Stripper Travel. Most tapping dies require longer stripper travel then one without it. In most cases, the stripper must hold the material throughout the entire tapping process. Spring strippers are commonly used in tapping dies.

The die should also be designed with spring pushers on either side of the tapping unit to hold the material during tapping.

Piloting. Due to the longer stripper travel, tapping dies typically require longer pilots. It is a thump of rule to ensure the pilots are registered into the material prior to the tap entering the material.
In some cases, using long Pilots may not be possible, especially for smaller diameters. Thus, the pilots should be designed in the stripper plate or in the lower
die section.

Press Stroke. Most cases, tapping dies require longer punching stroke. In general, a 3 inches press stroke may be used. Higher press stroke length may be necessary when higher material lift is needed.
Gear Ratio. Gear ratio refers to the number of revolutions that the tap will make in 1 inch of length the press stroke traveled.
Example: A tapping unit with 5:1 gear ratio in a 4-in.-stroke press. So, 5 x 4 = 20.
The tap will make 20 revolutions Clockwise and 20 revolutions counterclockwise per press cycle.
If a M3 tap is to be threaded into a 2 mm thick material. The number of revolution required can be calculated as 2 / 0.5 = 4 (pitch =0.5mm) Once the number of required revolutions is determined, you can calculate press stroke and gear ratio.

As a general guide, a lower-stroke presses use higher-ratio tapping units

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