Device for locking in a centred position workpieces subjected to mechanical machining, particularly for the machining of brake discs for vehicles Technical field The present invention concerns a device for locking in a centred position workpieces subjected to mechanical machining having the characteristics mentioned in the preamble of main claim 1. Technological background

The invention is placed particularly in the specific technical field of mechanical machining, for example roughing, turning or other surface finishing machining, of brake discs for vehicles.

It is well known that in this field there are two major types of discs, that is to say, solid (unventilated) discs and ventilated discs, the latter having the particular feature of providing a plurality of radial passages formed in the thickness of the disc with the function of conveying air for ventilating and cooling of the surfaces of the brake disc.

For locking the semifinished brake discs on the worktables of the mechanical machining centres, clamp-type locking devices are typically provided, which are fitted on respective centring members (normally three or six in number), angularly spaced from one another at a regular pitch, and adjustably movable in respective radial directions with respect to the axis of rotation of the worktable. By means of such devices, the semifinished brake disc is centred and held locked in the centred position during the mechanical machining operations. In the case of brake discs of solid structure, locking with the clamp of the centring member takes place typically at the outer diameter of the disc, and for this purpose the clamp is provided with a locking surface suitable for engaging the surface of the disc by contact in order to effect the relative

locking thereof.

In the case of ventilated brake discs, however, it is known,, and proves more advantageous, to provide at the free end of the centring member a portion in the shape of a ferrule suitable for engaging at least part of the aperture defined by the corresponding radial ventilation passage of the disc, at the outer diameter of this latter. This type of locking is particularly advantageous, since it permits the machining of both the opposed surfaces of the disc, in order to remove the relevant removable stock, without there being any interference of the locking clamps at those surfaces. A recognisable limitation in the locking devices of known type lies in the need for disassembling and substituting the entire set of clamps whenever it is wished to change from one to the other type of disc to be subjected to mechanical machining, thereby involving an increase in the times required for the retooling of the worktable, with a consequent overall increase in the cycle times and in the corresponding overall production costs. Description of the invention

The problem underlying the present invention is that of providing a device for locking the brake discs subjected to mechanical machining that is structurally and functionally designed such as to make it possible to remedy the limitations mentioned with reference to the prior art cited.

This problem is solved by the invention by means of a device produced in accordance with the claims which follow.

Brief description of the drawings

Further characteristics and advantages of the invention will become clearer from the following detailed description of a preferred exemplary embodiment thereof, illustrated by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 is a partial view of a locking device associated with a brake disc of the ventilated type, produced according to the invention,

Figure 2 is a view of the device of Figure 1 associated with a brake disc of the unventilated type,

Figure 3 is a diagrammatic plan view from above of the device of the preceding figures in the operative state of Figure 2, Figure 4 is a partial perspective view on an enlarged scale of a detail of the device of the preceding figures, - Figure 5 is a plan view from above of an alternative embodiment of the device according to the invention, Figure 6 is a view corresponding to that of Figure 5 of a further alternative embodiment of the device according to the invention. Preferred way of implementing the invention

With reference to the drawings mentioned, the reference 1 indicates as a whole a device for locking in a centred position semifinished brake discs for vehicles, produced according to the present invention. The device 1 is provided on a worktable 2, for example equipped with a mandrel (not shown) rotating about a main axis X. The device is also to be understood as being incorporated in a machine tool, also not shown, in which one or more tools are operated, in association with the mandrel, to follow the operations of mechanical machining of semifinished brake discs, according to the work cycles envisaged. The device of the invention is advantageously applicable to the locking in a centred position of two main types of brake discs for vehicles: ventilated discs and unventilated discs. Figure 1 shows diagrammatically a semifinished ventilated brake disc,

indicated as a whole by 3, including an annular portion 4 having opposed surfaces 4a, 4b (capable of co-operating, in use, with the calipers of the brake) and also a central portion 5 having holes 6 for the attachment of the brake disc to the hub of the vehicle wheel. The disc 3 further comprises a plurality of radial passages 7, extending radially within the thickness of the disc, between the surfaces 4a, 4b. Said passages are angularly spaced at a pitch, and perform the function of channels for conveying air between pairs of corresponding fins for cooling the braking surfaces of the disc. Figure 2, however, shows diagrammatically a semifinished brake disc, of typical solid structure, of the unventilated type, in which, for the sake of simplicity of description, for similar details the same reference numbers are used as for the disc of Figure 1. In other words, the unventilated disc has a thickness between the braking surfaces 4a, 4b devoid of any radial passage. The device of the invention is designed in particular to be used for locking in a central position semifinished brake discs of both of the aforesaid types, as will appear clearly in the continuation of the description. The device is provided with three (or alternatively six) centring members 8, comprising respective base supports 9, illustrated diagrammatically in the drawings, and which are slidingly guided on the worktable. The centring members are mounted on the table 2 at a regular angular pitch from one another (at 120° to one another in the case of three centring members) and are arranged to act with one of their ends on the semifinished disc in predetermined radial directions of slide relative to the axis X, in order to obtain the centring and locking of the disc on the worktable. In the following, only one of the centring members 8 of the device 1 will be described in detail, the centring members being structurally identical to one another.

Each centring member comprises a respective head 10 mounted on the support 9 so as to be capable of being oriented about an axis Y, directed perpendicularly to the table 2 and also parallel to the axis X. The head 10 comprises a first and a second part, indicated respectively by 10a and 10b, and which are capable of engaging by contact, alternately with each other, the cylindrical outer surface of the annular portion 4 of the disc. More particularly, the parts 10a, 10b are arranged in alignment with each other, on opposite sides with respect to the axis Y, so that the head 10 is capable of being oriented with a rotation of 180° between two operative positions in which it has one or the other part in contact with the outer surface of the disc, as is clearly illustrated in Figures 1 and 2. The first part 10a of the head comprises a seat 11 for the supporting and locking of a corresponding portion of the outer surface of a brake disc of the unventilated type. The seat is defined by a pair of surfaces 12, 13 extending substantially at right-angles, and capable co-operating respectively with part of the cylindrical outer surface of the disc and with the braking surface 4b of same. The surface 12 conveniently has a cylindrical profile such as to co-operate with the cylindrical profile of the outer surface of the disc, while the support surface 13 has a plane profile. In the surface 12 a recess 14 is further defined which delimits, on opposite sides, respective surface portions 12a, 12b of the surface 12. The surface portions make it possible to obtain more effective contact with the outer surface of the disc, even in the presence of discs having outside diameters different from those of the profile of the surface 12. The second part 10b of the head 10 has a substantial ferrule-like configuration 15, tapering in the direction of the free end of the part 10b. The ferrule-like configuration allows the part 10b conveniently to engage at

least part of a respective radial passage 7 of a brake disc of the ventilated type. By means of engagement of the ferrules in the corresponding radial passages facing them, the centring and consequent locking of the ventilated disc on the worktable is obtained. For fixing the head 10 in the preselected oriented position with respect to the support 9, screw means are provided, for example including a respective screw 15 directed coaxially with the axis Y and also constituting a pin for rotation of the head. The screw 15 is locked, via a through hole 16 in the head, by screwing into the support 9. In operation, whenever it is wished to change from one type of brake to the other in order to carry out the centring and relative locking thereof, the heads of the centring members 8 are suitably oriented, subject to loosening of the fixing screws 15, in order to obtain the configuration preselected from among those shown in Figures 1 and 2. This operation is advantageously rapid, not requiring any retooling of the table or disassembly of the centring members.

The centring members 8 are conveniently mounted on carriages (not shown) moved along the respective radial slide guides by means of actuation with digitally controlled positioning (CNC). Such a configuration further makes it possible to machine, with parity of disc type (ventilated or not), brake discs of different dimensions.

Figure 5 illustrates an alternative embodiment of the device according to the invention, in which details analogous to those of the preceding examples are designated by the same reference numbers. In this variant the head 10 of each centring member is also provided with a further third and fourth part 20a, 20b, in substantial mutual alignment and arranged on opposite sides with respect to the axis Y, with a direction of alignment perpendicular to the

direction of alignment of the parts 10a, 10b. The directions of alignment intersect on the axis Y of the head such that the parts 10a, 10b, 20a, 20b are angularly spaced by an angle of 90°. In this variant, provision is made for the parts 20a, 20b to be produced in a structurally analogous manner to the part 10a, that is to say, suitable for co-operating with the outer surface of unventilated solid discs. Provision may also be made for each of these parts to be produced with a corresponding surface 12 having a cylindrical profile with a different radius of curvature, in such a way as to permit the bearing contact of brake discs having different diameters comprised in predetermined ranges of values. In practice, each of the parts 10a, 20a, 20b is produced for optimum contact with discs having outside diameters comprised in respective ranges of values, thereby advantageously widening the range of discs of the unventilated type that can be centred and locked with the same device produced according to the invention. It is obviously possible to provide for the parts 20a, 20b to be configured instead as a ferrule, analogously to the part 10b, as illustrated in Figure 6. This configuration proves particularly useful and advantageous in the presence of ventilated discs with openings of the radial ventilation passages even having a shape and dimensions very different from one another. The invention thus solves the problem proposed, obtaining the advantages mentioned with respect to the known solutions.

Among them can be counted in particular the advantage of being able to change the type of disc (ventilated and unventilated) to be subjected to machining with reduced times for centring and locking on the worktable, without requiring retooling of the centring members and of the locking clamps associated therewith.