Tapping unit

Details Tapping unit Tapping unit

1999-10-21

2001-11-27

Howell, Daniel W. (Department: 3722)

Cutting by use of rotating axially moving tool

Means to drive tool

Universal or flexible drive connection to rotate tool

C408S137000, C408S138000

Reexamination Certificate

active

06322298

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a tapping unit adapted to be mounted on a machine body, a die, a hand, a jig, etc., of a press, an industrial robot, a transfer apparatus, etc., (hereinafter these are referred to generically as working machines), the tapping unit serving to tap a workpiece during the processes of the working machines.
DESCRIPTION OF THE RELATED ART
In the event that the workpiece is subjected to tapping by means of a tapper during the process of the press in continuous operations, the tapping time allocated to the one cycle of the press tends to become short, making it difficult to put the tapping timings in synchronism.
Furthermore, owing to the vertical movement and the horizontal movement effected between the feed position and the machining position when the workpiece is delivered to the next process, it is difficult to three-dimensionally precisely position the tap relative to the workpiece and to complete the forward and reverse rotations at accurate feed pitches.
In addition, a mechanism for tapping has to be incorporated in a limited space within the press die.
To address such problems, a variety of techniques have hitherto been proposed, as in for example Japan Patent No. 2,562,298. This has a structure as shown in
FIG. 13
in which a screw
ut system coupled to a movable part A
2
of a press A
1
toward a ram is used to convert the vertical movements of the movable part A
2
into forward and reverse rotational movements and in which the tap is driven by way of a transmission mechanism of a tapper A
4
mounted on a die associated with a bed, to thereby tap a workpiece W resting on the press A
1
.
As can be seen from Japan Patent Laid-open Pub. Nos. Hei 7-112324, Hei 4-289021 and Hei 7-060545, tappers have also been proposed in which a motor is provided and is fitted to the die or the press head without utilizing the movements of the press movable part as the driving forces.
Furthermore, as seen in
FIG. 14
, a technique is known in the past.in which the direction of rotations of an output shaft B
3
is changed by use of a rotation transmission cable B
2
extending from a tapping machine or a drilling machine having a multi spindle head B
1
, to rotate a spindle B
7
screwed with a master metal B
6
fitted to a press B
5
.
The technique shown in the diagram enables the hexagonal shaft or the sleeve with splines for rotating a spindle B
7
to be eliminated since the flexibility of the rotation transmission cable B
2
can accommodate the screwing stroke L of the spindle B
7
carrying a tap T, and is widely used typically as means for simultaneous tapping of the workpiece W from multiple directions after the completion of the pressing process.
Providing that the tapper is mounted on the die with high accuracy attachment machining and adjustment, the technique disclosed in the Japan Patent No. 2,562,298 enables the tapping work to be performed in a substantially perfect synchronism. with the pressing actions unless any mechanical failures occur, thereby achieving a high-speed operation.
However, due to the structure in which the reciprocating motions are converted into forward and reverse motions by way of the screw
ut system using the movement of the movable part as its reference, the pitch feed mechanism fitted with the tap and the spindle are fixedly secured to the die, or otherwise secured thereto while permitting only a slight vertical displacement, making it difficult to displace it in the horizontal direction, in particular, in to-and-fro directions.
The attachment positions have to be adjusted at two or more sites, and every time the die height adjustment is performed, that is, the ram height is adjusted depending on the type of the die used, the attachment positions need to be adjusted.
Furthermore, due to the fixed horizontal distance d in the to-and-fro directions (see
FIG. 13
) between the ram associated attachment part and the bed-associated attachment part, it is difficult to replace a die with another die having a different specification for each step, resulting in less versatility.
On the other hand, in case of those disclosed in Japan Patent Laid-open Pub. Nos. Hei 7-112324, Hei 4-289021 and Hei 7-060545, limitation is imposed on the reduction in size since the major part of the apparatus including the drive source (motor) is secured to the die or the press head.
Also, in spite of achievement of size reduction, a precise tap pitch feed mechanism may be omitted as described in Japan Patent Laid-open Pub. No. Hei 7-11232, or inversely, the measures for the correct pitch feed may impede the size reduction, resulting in a tapper dedicated to that die or the associated machine.
With respect to that shown in
FIG. 14
, it will ready be conceivable and has been attempted in fact to fit the master screw of the spindle coupled to the tip of the rotation transmission cable to the interior of the die to thereby extremely simply integrate it with the press.
However, due to the use of the rotation transmission cable as the means for changing the rotational direction of the output shaft for the transmission, it is possible to arrange the master metal and the spindle in close vicinity of the workpiece from every directions, whereas in terms of the structure of the cable, the permissible bend radius r is as large as approximately 150 mm in case of the 6-mm inner shaft lying within the rotation transmission cable, and a straight part must be provided at the rotation cable end, which may result in a deficiency that the length extending axially from the spindle may be increased.
Furthermore, the spindle has its axial feed stroke, so that it cannot be accommodated in the height H
1
of the lower platen, and even though successfully it has been attached within the permissible bend radium of the rotation transmission cable, the increased length results in an increase in the weight to be at all times born by the master metal.
In addition, there may occur a bend angle at the connection between the spindle formed with a master screw and the rotation transmission cable, the bending load resulting in a shock load which in turn combines with the load arising from the weight of the rotation transmission cable. The resultant combined load acts on the portion between the master screw and the master metal, whereupon the contact surface pressure between the two increases resulting often in a poor lubrication such as short of lubricant films. Additionally, because the master screw and the master metal do not have protection means against dusts, they may become abraded at an earlier stage.
Thus, the multiple head fitted with a multiplicity of elongated and weighted rotation transmission cables comes to have an increased rotational resistance due to the moments of inertia and frictions of their respective output shafts, which results in an increased power loss, whereupon it will be difficult for the power performance of the tapping machine designed to be originally operated solely to achieve a synchronism with the continuous operation of the press.
Furthermore, typical tapping machines use a three-phase induction motor as its drive source together with optional electromagnetic brake. When the motor is activated twice, i.e., forward, halt, reverse, halt for each stroke of the spindle carrying the tap, with the iteration of the advance/retreat stroke of the spindle, the motor may be subjected to a large current every time the rotational direction is changed over, resulting in possible burning of the oil or in possible failure of the relay circuit. The repetition of the advance/retreat stroke may further result in early abrasion of the brake.
On the contrary, proposed as measures to obviate the above deficiencies is one mechanically effecting the switching of the spindle forward and reverse rotations by use of a combination of a crank and a drive screw, or a rack and a pinion gear, with the motor rotating at all times in one direction (e.g., Japan Patent No. 2,130,082).
It would nevertheless be impossible for such measures to overcome the lim

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