DEVICE FOR THREADING HOLES IN PRESSING OPERATIONS

Abstract: The device comprises an upper part (2) to be fixed to the slider of the press and a lower part (1) to be fixed to its basis. The lower part (1) is equipped with a rack rod (4) and the upper part (2) is equipped with a mandrel (9) having a threading tap (10) and a gear transmission system which translates, by way of the said rack rod (4), the alternate motion of the slider of the press into a rotary motion of the mandrel (9), the rack rod (4) being coupled to the lower part (1) via a joint (23) adapted to allow, in axial direction, small elastic shiftings of rod (4) around one of its balance posi­ tions.

Description: "DEVICE FOR THREADING HOLES IN PRESSING OPERATIONS" The present invention relates to a device to be used during the pressing operations for threading metallic pieces obtained by way of this process. In fact the working through the pressing of metallic pieces often requires to obtain the thread of the holes previously sheared therein. Such a thread is carried out by known mechanical units consisting of an upper part to be fixed to the slider of the press which is also fixed to the punch, and of a lower part to be fixed to the basis of the press itself. The aforesaid upper part comprises a mandrel with vertical axes whose lower end is fixed to a tap arranged for threading the pre-sheared holes. The same part also comprises a chain transmission system which, by way of a rack rod fixed to the lower part of the device, translates the alternate motion of the slider of the press into a rotary motion of the threading tap, so as to allow the slider to perform at each stroke a thread in the pre-sheared hole of the metallic piece under pressing. However, such mechanical devices present various drawbacks: slow working speed allowed, need for frequent adjustment and maintenance operation (due to the trend of the chain to get loose), frequent breaks of the threading tap (due, among other things, to the unavoidable slacks of the chain during the motion transmission). The threading device according to the present solution aims to overcome the above mentioned drawbacks. It is mainly characterized by the fact that the transmission system of the motion to the mandrel is a gear assembly and that the rack rod is coupled with the lower part by way of a joint adapted to allow, in axial direction, small elastic shifting of the rod around one of its balance positions. The features of our solution will be better detailed in the following description and with reference to the accompanying drawings of a non-limiting embodiment in which: - Figure 1 shows a side view of the threading device with a cutaway view of the upper part, - Figure 2 shows a horizontal section of the transfer case 10 of Figure 1, - Figure 3 shows a side view of the rack rod and of the relating elastic joint with a cutaway view of the lower part. Figure 1 illustrates the lower part 1 of the device (to be fixed to the basis of the press), the upper part 2 (to be fixed to the slider), the rack rod 4 fixed to the lower part by way of joint 23, the transmission system being adapted to comprise the transfer pinions 6 and 7 (which respectively carry gears 12, 13 and 14, 15), gear 8, mandrel 9 and the threading tap 10 fixed thereto. Figure 2 illustrates the transfer case 11 of Figure 1, sectioned according to a ground plane across the axes of pinion 6. This section displays the presence in the transmission system of another transfer pinion, pinion 5 carrying gears 16 and 17 and located between rod 4 and pinion 6. When the slider of the press moves, the rack rod 4, whose teeth engage with those og gear 16, slides in the transfer case 11. Thus, the movement is transmitted through the gears to the mandrel which will therefore turn clockweise during the downward motion of the slider and ACW during the upward motion. In Figure 1 support 18 fixed to the threading tap is a Square-Sectioned slide which can slide in a similarly shaped hollow of the mandrel. Spring 19 is destined to make a pressure directed towards the low side of slide 18 so that, when during the downward motion the tap gets in touch with the piece to be threaded, it does not rigidly follow the downward motion of the press slider any longer, but engages itself into the piece and feeds for each revolution of a depth equal to the lead of the thread to be made. Figure 3 is a side view (partially in section) of the rack rod and of its joint coupling to the lower part of the device. In this figure the upper portion represents the geared part. It extends downwards by way of the threaded pin 20 which engages in the upper side into hollow 21 of the rod and may be screwed therein according to a changeable length and then blocked with nut 28 so as to allow an adjustment of the whole length of the rack rod. In the lower side the pin inserts slidely into the cylindrical hollow 29 present in joint 23. Figure 3 also illustrates the presence in joint 23 of a metallic disk inserted into the lower end of pin 20, of a bush 25 and of two rings 26 and 27 of elastic material, the one inserted in the lower part of pin 20, the other on bush 25. Besides being the seat of the ring, bush 25 is also adapted to fix disk 24 onto the lower head of the pin by way of screw 30. The elastic rings 26 and 27 are so seized as to exert, in rest conditions, some pressure against the bottom and the top cover of the cylindrical hollow 21. Moreover, the said bottom and cover provide two holes where the head of screw 29 and respectively of pin 20 may slide, so as to allow shiftings of the rack rod according to its vertical axes. Such shiftings result (with respect to the balance position indicated in Figure 3) of elastic sort due to the presence of rings 26 and 27. The utility of the elastic joint is particularly remarkable at the end of the upper and lower stroke of the slider of the press, when the joint causes a cushion to the sudden change in the motion of the mandrel. it may be easily under- stood that this feature together with the lesser slacks introduced by the gear transmission system in comparison with the chain system, can provide the previously mentioned advantages consisting in the higher working speed and in the less frequent maintenance requested on the transmission system and on the threading tap.

Claims: CLAIMS CLAIM 1 A device for threading holes in pressing operations, comprising an upper part to be fixed to the slider of the press and a lower part to be fixed to its basis, wherein the lower part is equipped with a rack rod and the upper part is equipped with a mandrel having a threading tap, as well as a transmission system adapted to translate, by way of the said rack rod, the alternate motion of the slider of the press into a rotary motion of the mandrel, characterized by the fact that the transmission system of the motion to the mandrel is a gear device to the mandrel is a gear device and that the rack rod is coupled to the lower part via a joint adapted to allow, in axial direction, small elastic shiftings of the rod around one of its balance positions. CLAIM 2 A device as claimed in claim 1, characterized by the fact that the rack rod is equipped with a device adjusting its length being it formed by an upper part and a lower part, which are separable from one another, and are coupled via a screw coupling susceptible of various locking positions. CLAIM 3 A device as claimed in claim 2, characterized by the fact that: - the joint comprises a cylindrical hollow equipped with two holes in the centre of its basis; - the lower part of the rack rod ends towards the low with a segment inserted in a shifting manner into the said cylindrical hollow across the said holes; - the said hollow comprises two rings in elastic material inserted into the said segment of the rack rod and separated from a metallic disk fixed to the segment itself.

Inventors: CANOBBIO, ANTONIO
Applicants: MECLOSTAMPI DI A. CANOBBIO & C. S.A.S.
Application year: 1985
Main classification: B23G3
IPC codes: B23G3