Twisting machine for polygonal cross-section bars

Abstract: A twisting machine for polygonal cross-section bars having an independent jaw chuck (3) fitted on a mandrel (2) and a counteracting support (4) slidable on a prismatic guide (5), which is firmly connected to the machine and parallel to said mandrel (2) is disclosed. The jaw chuck (3) comprises mutually co-operating means of rotary connection between said mandrel (2) and said chuck (3), in the form of a groove for ball re-circulating and means of mutually engagement, such as an abutment projection (20) diametrally projecting from and integral with the mandrel (2) and a longitudinal pin (9) connected to the chuck (3), which are adapted to drive into rotation the chuck (3) by means of the mandrel (2), after a free rotation of the mandrel along an arc with an angle less than 360°.

Description: This invention relates to a twisting machine for polygonal cross-section bars. Twisting machines of this kind, called also torsion machines, have an independent jaw chuck firmly fitted on a mandrel and a counteracting support, which is slidely connected to a prismatic guide parallel to the mandrel. A bar to be twisted is centered on the chuck and the support. The machines of this kind are affected by a problem related to the type of poly-angular jaws, having in general surfaces at right angle, which are necessary to hold polygonal cross-section bar against the rotation. When a bar has to be centered on the chuck and the counteracting support, their jaws must match, or more properly the space defined by the jaws of the chuck is necessarily equal and angularly equally arranged to the space defined by the counteracting support. One must try to achieve this position of the chuck by rotating the geared motor driving the mandrel, which is difficult to be achieved after several attempts by controlling the machine power. In twisting machines known a nonius with a pointer indicating precisely the desired position is provided. However, the difficulty in achieving this position is alleviated only a little. A difficulty similar to that one meets in centering a bar to be twisted is founded in removing the same, when the machining operation is finished or during a step which requires that the points of clamping the bar on the chuck or on the mandrel are changed. Obviously, when the mandrel is stopped, the bar remains stressed. Therefore, until now, in the operation one tries through the control of the geared motor power, to release the bar from the elastic stresses present inside so that the bar doesn't counteract the jaws to be removed. In the prior art the problem of releasing the bar from the elastic stresses is met in US-A-4,019,356. It discloses an apparatus for the cold working of a bar stock, comprising stationary fixing means and rotary fixing means motor-driven via a step-down gear. After a twisting operation the removal of a worked bar from the apparatus is facilitated by a handwheel enabling the operator to manually counter-rotate the rotary fixing means by a selected small angle. This manual operation, that is tiring and time-wasting, should be eliminated in an apparatus for twisting hollow rods that is disclosed in US-A-5,771,726 (nearest prior art). This apparatus comprises a rotatable first chuck connected to a motor and a substantially non-rotatable second chuck. This second chuck is provided with a proximity switch, that is closed when the second chuck is rotated slightly during a twisting operation. The proximity switch is electrically connected to a proximity sensor. A logic controller, which is connected to the proximity sensor and to the motor, provides an automated control of apparatus and performs the twisting operation, including the relieve of the spring-back. The apparatus, in spite of its complex structure, can achieve an automatic compensation of spring-back of the material, only when the logic controller is exactly programmed with all the parameters depending on the properties of the bar being twisted and the features of the twist to be obtained. A main object of this invention is therefore to provide a twisting machine which allows machining time to be shortened notably. Another object of this invention is to make easier the steps of centering a bar and removing the same in a safe way for the worker. These objects are achieved by the present invention which provides, such as defined and characterised broadly in the first one of the accompanying claims and in its more meaningful particular embodiments in the subsequent claims, a twisting machine for polygonal cross-section bars having an independent jaw chuck fitted on a mandrel and a counteracting support slidable on a prismatic guide, which is firmly connected to the machine and parallel to said mandrel, characterised in that said independent jaw chuck comprises mutually co-operating means of rotary connection between said mandrel and said chuck for the free rotation of the chuck; means of mutual engagement provided on said mandrel and, respectively, on said chuck, which are adapted to drive into rotation said chuck by means of said mandrel, after a free rotation of said mandrel along an arc with an angle less 360°. The invention is described more in detail below, in connection with a preferred embodiment thereof with reference to the accompanying drawing, in which: Figure 1 is a fragmentary side view, partially cross-sectioned, of a twisting machine embodying this invention when a square cross-section bar is being worked. Figure 2 is a cross-section view taken along line A-A in Figure 1. In the figures there are shown a twisting machine 1, a hollow mandrel 2 of the twisting machine, an independent jaw chuck 3, a counteracting support 4, and a prismatic guide 5. As shown in figure 1, a bar 6 to be twisted is centered between the chuck 3 and the counteracting support 4. Only by way of example, the independent jaw chuck 3 comprises a pair of jaws 30, 31, which have right-angled gripping surfaces and are approachable along a vertical straight movement. The movement of the jaws 30, 31 is controlled by their threaded connection means, i.e. adjusting screws 32, 33. Further, by way of example, the counteracting support 4 is a vice chuck comprising a pair of jaws 40, 41, which have right-angled gripping surfaces and are approachable along a vertical straight movement. The one jaw 40 is controlled by a threaded connection means 42 in order to make possible that a reference position is fixed depending on a bar to be worked. The other jaw 41 is controlled by an eccentric rod 43 having a handle control 44 and an eccentric 45. The eccentric rod 43 can be operated in the direction of an arrow F in order to move away the jaw 41 from the bar 6 to be worked. The counteracting support 4 has an upright 46 and, at its bottom, means of running fit with the prismatic guide 5. Such a means of running fit are obtained for example by opposite U-shaped profiles 47, 48, which are connected by screws 49 to a base plate 50 and are free to slide on a lower rail 51 fixed to a tubular element 52 connected to a machine body, both the lower rail 51 and the tubular element 52 constituting the prismatic guide 5. According to the invention, the independent jaw chuck 3 comprises cooperating means of rotary connection to the hollow mandrel 2 and means of mutual engagement with the hollow mandrel 2. In an embodiment of the invention said means of rotary connection consist of circumferential grooves having a semicircular cross-section (not denoted by numeral), which are carried out on the external surface of the mandrel 2 and correspondingly on the internal cylindrical surface of the chuck 3 so that the grooves are facing in order to function together as a ball race for balls 7, as in a re-circulating ball device. The circumferential groove of the chuck 3 is communicating with a diametral hole 70 carried out into said groove, said diametral hole being threaded and open into outside for the introduction of the balls and the subsequent closure by means of a security dowel (not shown). Yet in an embodiment preferred at present, the above said means of mutual engagement are constituted by an abutment projection 20 diametrically projecting from and integral with the mandrel, and a longitudinal pin 9 connected to the chuck. The means of mutual engagement are adapted to rotate the chuck 3 by means of the mandrel 2, after a free rotation of the chuck along an arc with an angle less than 360°. In another embodiment (not shown) the chuck has a slot extended along a certain arc of circumference in which a pin connected to the mandrel is housed. However, a person skilled in the art can conceive other rotary connections between the mandrel and the chuck. Although not shown, a revolution counter of the mandrel 2 in the form of a stop microswitch device, by which a number of revolutions may be set in order to achieve a desired twisting effect, can be joined to the twisting machine according to the invention. The operation of the machine is as follows. In a first step a bar 6 to be twisted is centered readily between the chuck 3 and the counteracting support 4 as the chuck is "idle" or freely rotating on the mandrel 2. In a next step a twisting operation, which is enabled by the driving engagement between the mandrel 2 and the chuck 3 through the longitudinal pin 9 of the chuck 3 and the abutment projection 20 of the mandrel 2. In a third step the twisted bar is removed from the machine. For this purpose the machine turns the bar in the opposite direction to the twisting direction, until the elastic limit of the material of the bar is exceeded. By virtue of the chuck 3 freely rotating on the mandrel 2, the twisted bar is able to be removed from the machine.

Claims: Twisting machine for polygonal cross-section bars having an independent jaw chuck (3) fitted on a mandrel (2) and a counteracting support (4) slidable on a prismatic guide (5), which is firmly connected to the machine and parallel to said mandrel (2), characterised in that said independent jaw chuck (3) comprises mutually co-operating means of rotary connection between said mandrel (2) and said chuck (3) for the free rotation of the chuck; means of mutual engagement provided on said mandrel (2) and, respectively, on said chuck (3), which are adapted to drive into rotation said chuck (3) by means of said mandrel (2), after a free rotation of said mandrel (2) along an arc with an angle less 360°. Twisting machine according to claim 1, characterised in that said means of rotary connection consist of circumferential grooves having a semicircular cross-section, which are carried out on the external surface of the mandrel (2) and correspondingly on the internal cylindrical surface of said chuck (3) so that said grooves are facing in order to function together as a ball race for balls (7); the circumferential groove of the chuck being in communication with a diametral hole (70) carried out into said groove, said diametral hole being threaded and provided for the introduction of the balls (7), said diametral hole being closed by means of a security dowel. Twisting machine according to claim 1, characterised in that said means of mutually engagement are constituted by an abutment projection (20) diametrally projecting from and integral with said mandrel (2), and by a longitudinal pin (9) connected to said chuck (3). Twisting machine according to claim 1, characterised in that said independent jaw chuck (3) comprises a pair of jaws (30, 31), which have right-angled gripping surfaces and are approachable along a vertical straight movement, said jaws (30, 31) being controlled by their threaded connection means (32, 33). Twisting machine according to claim 1, characterised in that said counteracting support (4) is a vice chuck comprising a pair of jaws (40, 41), which have right-angled gripping surfaces and are approachable along a vertical straight movement, at least one jaw (40) being controlled by a threaded connection means (42) and the other jaw (41) being controlled by an eccentric rod (43).

Inventors: CAPORUSSO ALESSANDRO, CAPORUSSO MARIO, CAPORUSSO, ALESSANDRO, CAPORUSSO, MARIO
Applicants: CML COSTR MECC LIRI SRL, C.M.L. COSTRUZIONI MECCANICHE LIRI S.R.L.
Application year: 1999
Main classification: B21D11
IPC codes: B21D11