Device for supporting and actuating a facing head

SPECIFICATION Technical field

The present invention relates to a device for supporting and actuating a facing head of the type comprising the features set out in the preamble of the main claim.

Facing heads are devices used in machine tools in order to displace transversely a tool engaged in a working movement on a workpiece for carrying out the machining of otherwise inaccessible recesses in the inner or outer surfaces of the workpiece.

Facing heads are mounted on support devices which also enable their actuation, generally by causing a tool-carrier slide to slide with respect to a guide as a result of the displacement of a pinion relative to a rack transversely with respect to the latter (i.e. in a generally axial direction of the head).

Normally, the pinion is actuated by a tie rod passing axially through the support device. This positioning of the tie rod and its need for actuation by a tie rod passing through the support nevertheless gives rise to a whole range of drawbacks and entails substantial equipment costs for the machining centre. Prior art

A support device for facing heads configured to remedy these problems is disclosed in EP 0 490 935. The technical solution described in this document is based on the idea that a flow of pressurised lubricating and cooling fluid is normally available in machine tools and can also be used to

control, by means of appropriate cylinder-piston actuators, the displacement of the pinion needed to obtain the corresponding translation of the rack and the slide associated therewith.

In this way, the head may be used without further modifying the machine tool or machining centre since the members required for its actuation are self-contained in the relative support.

However, the solution disclosed in EP 0 490 935 also has some drawbacks. One of the main problems lies in the fact that the pressure and flow parameters of the fluid supplied to the device cannot be modulated, since it is this fluid which is responsible for lubricating and cooling the tools. The base supply is of the ON/OFF type and has to be transformed to ensure that the facing head is moved at the desired speed, which is almost constant and free from pulses. Moreover, the arrangement of the actuator system is such that the overall device is relatively bulky, especially in the axial direction. The adjustability of the system could also be improved, as could access to the adjustment members. Lastly, the device is subject to possible problems connected with the possibility that air may be trapped in the actuator supplied with the lubricating and cooling fluid making the whole system resilient and therefore unsuited rigidly to counter the cutting forces of the tools. The system may also be subject to possible emulsifications of the lubricating and cooling fluid. Description of the invention

The technical problem that the present invention seeks to resolve is that of providing a device for supporting and actuating a facing head structurally and functionally designed to make it possible to remedy all the

drawbacks discussed with reference to the cited prior art.

This problem is resolved by the invention by means of a device for supporting and actuating a facing head embodied in accordance with the accompanying claims. Brief description of the drawings

The characteristic features and advantages of the invention will become clear from the following detailed description of a preferred but nonexclusive embodiment shown by way of non-limiting example in the appended drawings, in which : Fig. 1 is a axonometric view of a device for supporting and actuating a facing head of the present invention;

Fig. 2 is a front view of the device of Fig. 1;

Figs. 3 to 9 are views in longitudinal section, along different section lines, of the device of Fig. 1. Preferred embodiments of the invention

In the drawings, a device for supporting and actuating a facing head

2 is shown overall by 1. The device 1 includes a body 3 provided with an attachment device 4 of a type known per se which can be automatically locked in and detached from an appropriate housing of a tool-carrier spindle (not shown) belonging, for instance, to a machining centre.

The body 3 comprises an axial channel 5 supplying a pressurised lubricating and cooling fluid prolonged as a supply duct 6 opening into a cylindrical chamber 7 of a first actuator 8 of the cylinder and piston type.

The piston 10 of the actuator 8 is engaged in a leak-tight manner in the chamber 7 in order to provide a leak-tight seal 11 between its jacket 12 and

the jacket 13 of the chamber 7.

A second actuator 15 with a cylinder 16 and a piston 17 is housed in the body 3 on the side of the attachment device 4 opposite to the first actuator 8. The second piston 17 is shaped as a cylindrical annular projection projecting externally from the jacket of the first piston 10 and engaged in a leak-tight manner in the cylinder 16 by means of a seal 18 embedded in the jacket of the latter. The piston 17 separates the cylinder 16 into two chambers 21, 22 preloaded with an incompressible hydraulic fluid and communicating with one another via a plurality of valve-regulated ducts, as will be explained below.

A tie rod 24 is coaxially rigid with the piston 10 so that it can move axially in the body 3 rigidly with the pistons 10, 17 for the operational actuation of the facing head. The latter has a conventional structure and is mounted on an end member 25 which closes the body 3 and forms an abutment for a spring-loaded system including a pack of cup springs 26 interposed between a collar 27 of the member 25 and the piston 10. The springs 26 are adapted to recall the pistons 10, 17 into a first position shown in Fig. 3 in which the piston 10 abuts against the base of the chamber 7 which thus assumes its minimum volume. A bleed duct 28 which is normally open extends from the single chamber 7 of the first actuator 8 in order to bleed any air supplied to and/or trapped therein. The bleed duct 28 causes a continuous run-off of cooling and lubricating fluid from the chamber 7 which is caused, via a passage 29 prolonged into the body 3, to supply this fluid into the vicinity of a tool or tool-carrier, shown diagrammatically by 30, mounted on the facing head for

the localised cooling of the latter and to promote the removal of shavings.

A drain 33 adapted to bleed any leaks of the lubricating and cooling fluid beyond the seal 11 is provided between the piston 10 and the jacket of the cylinder 7 of the first actuator 8, in a position between the seal 11 and a further sealing ring 32. This prevents the lubricating and cooling fluid from penetrating into the chamber 21 of the damper and emulsifying the incompressible fluid contained therein.

The chambers 21, 22 communicate with one another via two respective valve-regulated ducts 34, 35, one for controlling and regulating the working speed and one for controlling and regulating the speed of return of the facing head. By means of these two separate regulations, it is possible independently to regulate the working and return movements of the head, which enables a substantial increase in productivity. For instance, this enables a rapid advance of the tool and a return at working speed or vice versa.

The ducts 34, 35 are both provided with a respective one-way valve 36 disposed in opposite directions so as to enable a flow from one chamber to the other in one direction and a further flow in the opposing direction, and a respective regulation valve 37 accessible from the exterior of the body 3. The regulation valves 37 are housed in appropriate seats 38 provided in a disk body 39 separate from the other members of the body 3 and sandwiched between them. The body 39 also houses a compensation pump 40 adapted to enable the complete filling of the chambers 21, 22 with an incompressible hydraulic fluid and the subsequent discharge of the residual air in the plant, by means of the application of a slight preloading

to the hydraulic fluid.

The device operates as follows.

The second actuator is preloaded with a hydraulic fluid; as there is a closed circuit between the two chambers 21, 22, the passage of fluid from one chamber to the other is correlated with the displacement of the piston 17 and is regulated by the corresponding valve 37 of the ducts 34, 35. This means that the speed of displacement of the pistons 10, 17 can be varied at will and in an independent manner in the presence and respectively the absence of a fluid pressure in the chamber 7 of the first actuator 8. The presence of the bleed duct 28 enables continuous bleeding of the chamber 7 and improved cooling of the tool and the facing head. The run -off to which this gives rise does not, however, have an impact on the operation of the actuators bearing in mind that the flow of pressurised lubricating and cooling fluid is much greater than the flow which runs off through the duct 28.

Any leaks of lubricating and cooling fluid between the jackets of the piston and the cylinder of the first actuator are disposed of via the drain 33. It will be appreciated that the relative arrangement of the two actuators, with the first close to the lubricating and cooling fluid supply duct, makes it possible substantially to reduce the axial bulk of the device 1 which may therefore be embodied in a very compact way. Moreover, the independent regulation of the valve-regulated ducts 34, 35 enhances the device's production possibilities. The presence of the bleed 28 enables the device to be more rigid during operation, thus eliminating damaging pulses and vibratory problems.