Punch assembly

Abstract: A punch assembly (1) wherein a portion of a toolholder body (4) is fitted in axially-movable manner inside a cylindrical tubular body (2), and is fitted integrally at one end with a punch (5) engaging in sliding manner a through hole formed in a blankholder disk (3) fitted integrally to one end of the cylindrical tubular body (2); an elastic element (14) being interposed between the cylindrical tubular body (2) and the toolholder body (4) to keep the toolholder body in a rest position wherein the punch (5) is withdrawn inside the cylindrical tubular body (2); the toolholder body (4) being defined by two elements (8, 10) screwed to each other to permit adjustment of the total axial length of the toolholder body (4), so that, when the toolholder body (4) is in the rest position, the cutting end (5a) of the punch (5) is positioned a given distance (D) from the through hole in the blankholder disk (3).

Description: The present invention relates to a punch assembly according to the preamble of claim 1 (see for example DE-C-19505754). Known punch assemblies comprise a cylindrical tubular body or casing extending coaxially with a reference axis and fitted integrally at the bottom end with a blankholder disk which is placed on the work sheet; and a substantially cylindrical toolholder body extending coaxially with the reference axis, and an end portion of which slides axially inside the casing. Known punch assemblies also comprise a punch screwed to the end of the toolholder body inside the casing, so as to engage in sliding manner a through hole in the blankholder disk; and an elastic element located between the top end of the casing which is not provided with the blankholder disk and the end of the toolholder body outside the casing, to keep the punch in a withdrawn position in which the cutting end of the punch engages the through hole in the blankholder disk but does not project outwards of the casing. The end of the toolholder body outside the casing is designed to receive a ram, which, for a given time, exerts such pressure as to overcome the resistance of the elastic element and move the punch from the withdrawn position into a work position in which the cutting end of the punch projects outwards of the casing through the hole in the blankholder disk. As is known, the cutting end of the punch is subject to wear, so that, to ensure consistently high-quality work, punch assemblies of the above type must be ground periodically to remove the worn material and so restore the cutting end of the punch to its original shape. A major drawback of punch assemblies of the above type is that repeated grinding eventually results in the cutting end of the punch backing up gradually inside the casing, so that the travel of the ram must be checked periodically by the operator to ensure the cutting end of the punch projects as required from the blankholder disk in the work position. It is an object of the present invention to provide a punch assembly designed to overcome the aforementioned drawbacks. According to the present invention, there is provided a punch assembly with the features defined in claim 1. The dependent claims define preferred embodiments of the invention. An embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a section of a punch assembly in accordance with the teachings of the present invention; Figure 2 shows a section, with parts removed for clarity, of a detail in Figure 1; Figure 3 shows a section along line II-II in Figure 2; Figure 4 shows a section along line I-I in Figure 1. Number 1 in Figure 1 indicates as a whole a punch assembly for use on a known punching machine. Punch assembly 1 comprises a cylindrical tubular body 2 extending coaxially with a longitudinal axis A and fitted at the bottom end with a blankholder disk 3, which is placed on the work sheet; a toolholder body 4 extending coaxially with axis A and having an end portion movable axially inside cylindrical tubular body 2; and a punch 5 housed inside cylindrical tubular body 2 and fitted integrally to the bottom end of toolholder body 4 facing blankholder disk 3. Punch 5 comprises a cutting end 5a, which engages in sliding manner a through hole formed in blankholder disk 3. With reference to Figures 2 and 3, in the example shown, cylindrical tubular body 2 comprises a liner 6 extending coaxially with axis A along substantially the whole length of cylindrical tubular body 2, and defining, inside cylindrical tubular body 2, a prismatic, substantially octagonal axial cavity 7. More specifically, the section of axial cavity 7 is defined by an octagon having four flat sides alternating with four curved sides in turn defined by respective arcs of the circle in which the octagon is inscribed. With reference to Figure 1, toolholder body 4 comprises two elements, in particular a prismatic body and a sleeve, connected to each other to permit adjustment of the total axial length of toolholder body 4. The prismatic body, hereinafter marked at 8, has a section complementary to that of axial cavity 7 so as to engage axial cavity 7 in sliding manner, is fitted with punch 5 at one end, and comprises, at the opposite end, a threaded shank 9 projecting outwards of cylindrical tubular body 2. The sleeve, hereinafter marked at 10, extends coaxially with axis A and outwards of cylindrical tubular body 2, is at least partly screwed to threaded shank 9, and comprises a ring nut 11 at one end and a shoulder 12 at the other end. Shoulder 12 is shaped to engage axial cavity 7 in sliding manner, and ring nut 11 is screwed to the end of sleeve 10 opposite the end facing prismatic body 8. Sleeve 10 engages in sliding manner a bush 13 inserted inside a seat formed on the end of cylindrical tubular body 2 opposite the end fitted with blankholder disk 3; bush 13 is locked inside the seat, e.g. by means of a known lock ring 13a, and is so sized as to prevent withdrawal of shoulder 12 from axial cavity 7. Punch assembly 1 also comprises an elastic element 14 (in the example shown, a coil spring) extending coaxially with axis A and outside sleeve 10, so that a first end rests on ring nut 11, and a second end rests on the top end of cylindrical tubular body 2. In the example shown, the second end of elastic element 14 also rests on bush 13 of cylindrical tubular body 2. Elastic element 14 provides for keeping toolholder body 4 in a rest position, wherein shoulder 12 of sleeve 10 contacts bush 13, punch 5 is fully withdrawn inside cylindrical tubular body 2, and cutting end 5a engages the through hole in blankholder disk 3 without projecting outwards. Ring nut 11 is designed to receive a known ram, by which sufficient axial force is exerted on ring nut 11 to compress elastic element 14, move ring nut 11 towards bush 13 and toolholder body 4 towards the work sheet, and so move punch 5 into a work position wherein cutting end 5a engages the through hole in blankholder disk 3 and projects outwards of cylindrical tubular body 2. In the rest position, seeing as only sleeve 10 contacts bush 13 of cylindrical tubular body 2, the distance between prismatic body 8 and blankholder disk 3 may therefore be adjusted by screwing or unscrewing threaded shank 9 inside sleeve 10. Adjusting the position of prismatic body 8 inside axial cavity 7 provides for so adjusting the position of punch 5 that, in the rest position, cutting end 5a is located a given distance D from the end of the through hole in blankholder disk 3. This is particularly useful when, as a result of grinding, the axial length of punch 5 is reduced so that cutting end 5a withdraws inside the through hole in blankholder disk 3. With reference to Figure 1, punch 5 comprises a prismatic central portion 15 of a section complementary to that of axial cavity 7; a front portion 16 comprising cutting end 5a; and a substantially T-shaped rear portion 17, which engages a seat 18 formed in prismatic body 8, at the opposite end to threaded shank 9, to enable fast replacement of punch 5. More specifically, seat 18 is so formed as to enable rear portion 17 to be withdrawn from seat 18 by moving punch 5 perpendicularly to axis A with respect to toolholder body 4. With reference to Figures 1 and 4, the bottom end of cylindrical tubular body 2 comprises a seat 19 for housing blankholder disk 3, and which is substantially U-shaped and extends in a plane perpendicular to axis A to permit lateral insertion of blankholder disk 3. A substantially annular groove 20 is formed inside seat 19, at the extension of axial cavity 7, and is engaged by a lock ring 21 on the peripheral edge of blankholder disk 3. In the example shown, the top end of cylindrical tubular body 2 comprises an annular projection 22 coaxial with axis A, and on which an elastic element (not shown) of the punching machine abuts. Operation of punch assembly 1 is clearly understandable from the foregoing description with no further explanation required. The main advantage of punch assembly 1 is the possibility, when fitting punch 5 to toolholder body 4, of adjusting the position of punch 5 inside axial cavity 7, so that cutting end 5a of punch 5 is always the same distance from the end of the through hole in blankholder disk 3. As a result, the travel of the ram need no longer be checked each time cutting end 5a of punch 5 is ground, thus greatly reducing the routine maintenance time of the machine. Moreover, dividing toolholder body 4 into prismatic body 8 and sleeve 10 makes for a modular structure and for greatly simplifying assembly of punch assembly 1. Being engaged permanently between ring nut 11 of sleeve 10 and bush 13 of cylindrical tubular body 2, elastic element 14, in fact, may be extracted together with sleeve 10, with no need to fully dismantle punch assembly 1, as at present. A further advantage of punch assembly 1 is the particular shape of seat 19, which provides for faster maintenance of punch 5 by permitting fast removal of blankholder disk 3. Clearly, changes may be made to punch assembly 1 as described and illustrated herein without, however, departing from the scope of the present invention as defined by the appended claims.

Claims: A punch assembly (1) comprising a cylindrical tubular body (2) extending coaxially with a given axis (A); a blankholder disk (3) at one end of the cylindrical tubular body (2); a toolholder body (4) having at least an end portion sliding axially inside said cylindrical tubular body (2); a punch (5), which is fitted integrally to the end of the toolholder body (4) facing said blankholder disk (3), and a cutting end (5a) of which engages in sliding manner a through hole formed in the blankholder disk (3); and an elastic element (14) for keeping said toolholder body (4) in a rest position wherein the punch (5) is withdrawn inside the cylindrical tubular body (2); wherein said toolholder body (4) is divided into a first (10) and a second (8) element connected to each other in such a manner as to permit adjustment of the total axial length of the toolholder body (4); the elastic element (14) being interposed between the cylindrical tubular body (2) and said first element (10); and the punch (5) being fitted integrally to said second element (8) to permit adjustment of the position of the punch (5) with respect to the blankholder disk (3), and so keep the cutting end (5a) at a given distance (D) from the through hole in the blankholder disk (3), by varying the total axial length of the toolholder body (4); the punch assembly being characterized in that said cylindrical tubular body (2) comprises a liner (6) extending substantially the whole axial length of the cylindrical tubular body (2), and so formed as to define an axial cavity (7) comprising a substantially polygonal cross section; and in that a shoulder (12) of said first element (10) is shaped to complementarily engage said axial cavity (7) in sliding manner. A punch assembly as claimed in Claim 1, characterized in that said polygonal section of said axial cavity (7) is an octagonal section defined by four straight portions alternating with four arcs. A punch assembly as claimed in Claim 1, characterized in that said second element (8) comprises a prismatic body (8), which complementarily engages said axial cavity (7) in sliding manner, is fitted with said punch (5) on the end facing the blankholder disk (3), and in turn comprises, at the opposite end, a threaded shank (9) screwed at least partly inside said first element (10). A punch assembly as claimed in Claim 3, characterized in that said first element (10) comprises a sleeve (10), which extends coaxially with said given axis (A), projects outwards of said cylindrical tubular body (2), in turn comprises an end portion at least partly screwed onto said threaded shank (9), and is fitted integrally with a ring nut (11) on the opposite end to the prismatic body (8); said elastic element (14) having a first end resting on said ring nut (11), and a second end resting on said cylindrical tubular body (2), so as to keep the ring nut (11) at a given distance from said blankholder disk (3) when said toolholder body (4) is in the rest position. A punch assembly as claimed in Claim 4, characterized in that the end of the sleeve (10) facing the prismatic body (8) comprises said shoulder (12) engaging in sliding manner said axial cavity (7); and said cylindrical tubular body (2) comprises, on the opposite end to the blankholder disk (3), a bush (13) engaged in sliding manner by said sleeve (10); said bush (13) being so formed as to prevent withdrawal of said shoulder (12) from said axial cavity (7); and said elastic element (14) keeping said shoulder (12) against said bush (13) when the toolholder body (4) is in the rest position. A punch assembly as claimed in any one of Claims 3, 4, or 5, characterized in that said punch (5) comprises a substantially prismatic central portion (15) engaging the axial cavity (7) in sliding manner; a front portion (16) comprising said cutting end (5a); and a shaped rear portion (17) engaging a first seat (18) formed on the end of the prismatic body (8) facing the blankholder disk (3). A punch assembly as claimed in any one of the foregoing Claims, characterized in that said blankholder disk (3) is housed inside a second seat (19) formed on the end of the cylindrical tubular body (2); said second seat (19) being substantially U-shaped to permit lateral insertion of the blankholder disk (3). A punch assembly as claimed in Claim 7, characterized in that the peripheral edge of said blankholder disk (3) comprises a lock ring (21) for engaging a groove (20) formed in said second seat (19).

Inventors: PERAZZOLO EUGENIO, PERAZZOLO, EUGENIO
Applicants: RAINER SRL, RAINER S.R.L.
Application year: 1997
Main classification: B21D45
IPC codes: B21D28, B21D45