WO2009144760A1

WO2009144760A1 - A device for securing in a centred position axially symmetric workpieces to be subjected to machining

Info

Publication number: WO2009144760A1
Application number: PCT/IT2009/000221
Authority: WO
Inventors: Roberto Sammartin
Original assignee: Maus S.P.A.
Priority date: 2008-05-27
Filing date: 2009-05-19
Publication date: 2009-12-03
Also published as: ITPD20080150A1

Abstract

A device for securing in a centred position axially symmetric workpieces, particularly rings (2) for bearings, to be subjected to machining comprises a device for centring the workpiece on a work table (3), including at least three centring elements (6) spaced at regular angular intervals, which can come into contact with the workpiece to move it to a centred position, each of the centring elements being movable in a predetermined radial direction, the radial directions intersecting on the geometrical axis (X) of centring of the workpiece. Means (7) for securing the workpiece are associated with the centring element (6), for securing the workpiece in the centred position which is reached, these securing means comprising, in each centring element, at least one securing clamp (8, 9) movable from and towards an operating position in which it keeps the workpiece bearing on a first bearing surface (10a, lla) of the centring element (6), the securing force being applied substantially in a direction parallel to the geometric axis (X) of the table (3).

Description

A DEVICE FOR SECURING IN A CENTRED POSITION AXIALLY SYMMETRIC WORKPIECES TO BE SUBJECTED TO MACHINING

Technical field

5 The present invention relates to a device for centring and securing axially symmetric workpieces to be subjected to machining, particularly rings for bearings, according to the preamble of Claim 1 which is the principal claim. The invention also relates to a machine tool comprising the aforesaid device. Technological background io The invention is particularly, but not exclusively, for use in the specific technical field of centring and securing axially symmetric workpieces to be subjected to machining, for example turning or other surface finishing processes, for the purpose of centring and securing workpieces with respect to the geometrical axis of rotation of the fittings or work tables typically provided in conventional is machining centres. Although the invention may be applied to any machining centre where it is necessary to centre workpieces having a substantially axially symmetric geometry, it has been devised with particular reference to the centring and securing of semi-finished rings for bearings, generally produced as semi-finished castings for subsequent machining by turning, the process being

20 typically one of roughing with subsequent surface finishing.

In this context it is necessary to centre and secure the ring on the self-centring table, this operation being commonly performed by means of a three-point centring device in which three centring elements, typically positioned at 120° to each other, are moved along guides which are radial with respect to the

25 geometrical axis of the device, in order to secure the workpiece in a centred position. Normally, the ring is secured, in successive steps, by means of its outer and inner cylindrical shell, respectively, to allow the whole of the corresponding surfaces to be machined. In both of the aforesaid positions, the securing forces exerted by the clamps of the centring elements act in a predominantly radial direction, giving rise to states of tension resulting in corresponding deformations of the workpiece. In rings of some sizes, these deformations, because of their extent, may be unacceptable in terms of the tolerances specified for the finishing of these workpieces. Additionally, the complete machining of the ring requires at least two different placements on the work table, with separate securing operations on the outside and inside of the ring, and the lifting of the ring to move it from one placement to the other. For this purpose, lifting means are typically provided in the self- centring table to lift the ring independently of the movement of the centring elements. Such a procedure therefore requires the provision of workpiece lifting members on the self-centring table, thus complicating the construction of the table.

Description of the invention

The problem underlying the present invention is that of providing a device for securing in a centred position axially symmetric workpieces to be subjected to machining, particularly rings for bearings, the device being structurally and functionally designed to overcome the limitations of the cited prior art. This problem is resolved by the invention by means of a device of the aforesaid type made in accordance with the following claims. Brief description of the drawings The features and advantages of the invention will become clear from the following detailed description of some preferred examples of embodiment thereof, illustrated, for the purposes of guidance and in a non-limiting way, with reference to the appended drawings, in which:

- Figure 1 is a schematic plan view of a device according to the invention; - Figures 2 and 3 are partial schematic front elevations of an example of a device for securing workpieces in a centred position, according to the present invention, in different operating conditions;

- Figure 4 is a further schematic view of the device of the preceding figures, illustrating a step in which the workpiece is moved between separate positions on the self-centring table.

Example of a preferred embodiment of the invention

With reference to the aforesaid drawings, the number 1 indicates the whole of an example of a device for centring and securing workpieces which may or may not be semi-finished, and which are intended for subsequent machining, made according to the present invention. This device is described in the following text with particular reference to semi-finished rings 2 for bearings, which are typically asymmetric solids, although it is to be understood that this application represents a preferred but non-limiting choice, and that the invention can be applied with equal efficacy in all cases in which it is necessary to centre and secure workpieces having an axially symmetric geometry (such as brake discs, wheels, flywheels, drums and the like). Figures 2 and 3 show, purely by way of example, an outer ring for bearings of the rolling type, although the invention is applicable to any type of ring for bearings. The numerals 2a and 2b indicate, respectively, the inner axially symmetric surface (the race) and the outer axially symmetric surface (the cylindrical shell) of the ring 2, with a circular profile, which are positioned axially between opposing annular faces 2c, 2d of the ring, as is clearly shown in Figures 2 and

3.

The device 1 comprises a supporting frame (not shown) on which is provided a self-centring work table 3, which preferably has a central through hole to allow access by moving and machining members.

Three guides 4 extending radially with respect to the central geometrical axis of the device, indicated by X, are provided on the table 3, and are positioned at regular angular intervals (at 120° to each other). Alternative configurations with different numbers of guides and correspondingly different angular intervals are possible.

Each guide 4 is associated with a corresponding slide 5 of a corresponding centring element 6 in such a way that the latter is guided in the corresponding radial direction (indicated by R in Figures 2 and 3) in a translational movement from and towards the axis X.

The centring elements 6 are structurally identical to each other and only one of them is described in detail below.

Actuator means are provided for the movement of each slide 5, and are preferably designed to move the centring elements 6 in a synchronized way, using for example the actuator system described in international patent application WO2006/001038, in the name of the present applicant, to which reference should be made for the relevant details.

Each centring element 6 is also provided with means for securing the workpiece which is to be centred, indicated as a whole by 7, these means comprising a pair of securing clamps 8, 9 mounted pivotably on the slide 5 in such a way that they can be moved from and towards an operating position in which one or other of them is pressed alternatively on to a portion of the face 2c of the ring 2, while the other face 2d bears on the centring element 6, to secure the ring appropriately. More specifically, each clamp 8, 9 comprises a corresponding securing arm 8a, 9a, which is mounted rotatably about a corresponding axis 8b, 9b parallel to the axis X, and which can be moved from and towards the corresponding operating position. Actuator means are provided to exert the desired securing pressure to each clamp in order to retain the ring 2 in the radial position reached after the centring step.

The numerals 10, 11 indicate corresponding seats formed in the centring element 6, which are designed to receive corresponding portions of the ring 2 which bear on them axially and radially. Each seat 10, 11 comprises a corresponding first axial bearing surface 10a, 11a which is capable of interacting with the corresponding securing arm to secure the ring 2 with a pressure substantially exerted in the axial direction, parallel to the axis X. Each seat 10, 11 also comprises a corresponding second radial bearing surface 10b, lib, which is designed to act on the outer and inner lateral surfaces of the ring, respectively, by contacting and supporting them in the steps of centring the workpiece, the centring elements being moved in their corresponding radial directions in these steps.

Each surface 10b, lib also extends substantially at 90° to the corresponding surface 10a, 11a, as is clearly shown in Figure 2. In operation, the semi-finished ring 2 is made to bear in a simple way on the self-centring table 3, as a result of which the lower face 2d bears on the axial bearing surfaces 10a of the centring elements. In a subsequent step, the centring elements 6 are moved in the corresponding radial directions R towards the axis X, until the ring 2 reaches its centred position, in which the outer shell of the ring bears on the surfaces 10b of each centring element. When the ring 2 reaches is centred position with respect to the axis X, the movement of the centring elements 6 is halted and the securing means 7 are activated, each arm 8a being moved on to the corresponding portion of the face 2c of the ring. Thus the axial securing force is exerted on the ring, this force being dissipated into the support of the centring element without causing radial deformation of the ring. The securing force of each clamp can be conveniently provided by means of hydraulic or pneumatic cylinders, or by means of mechanical clamps, depending on the specific application.

Provision is also made to secure each slide 5 relative to its guide 4 by means of corresponding securing means (not shown), comprising for example hydraulic or pneumatic cylinders which are suitably designed and supplied.

When the semi-finished ring 2 has been secured in the centred position which it has reached, the step of machining required by the corresponding machining cycle is commenced, this step being mainly concerned with the turning of the inner surface 2a (the race) of the ring, which is left free by the securing means, and those surface portions of the faces 2c, 2d which are left free by the securing means 7 of the centring element.

On completion of the aforesaid step of machining, the ring 2 is disengaged from the securing means 7, is lifted in the direction X away from the centring elements 6 to enable the latter to move towards the axis X, into a condition in which, when the ring is lowered again (towards the centring elements), it comes to bear on the axial bearing surfaces 11a. The subsequent radial movement of the centring elements 6 away from the axis X, such that the machined surface 2a is contacted by the radial surface lib, causes the centring position of Figure 3 to be attained. When the ring is placed in this way, the clamps 9 are activated and their securing arms 9a are rotated to contact the face 2d of the ring in order to exert the corresponding securing force. When this secured condition is reached, in which it should be noted that, in this case also, the axial retaining force is dissipated through the support of the centring element and not in the radial direction, the specified machining is carried out, for example by turning the outer surface 2b of the ring and those portions of faces 2c, 2d which are not in contact with the securing means. According to a further feature of the invention, lifting means integrated into the tool holders of the machining centre associated with the self-centring table are provided, as an alternative to lifting means of the conventional type such as those using hydraulic or pneumatic actuators, for raising the ring 2 in the step of moving it from the first to the second position with respect to the self- centring table 3, as described more fully below.

More specifically, the machine tool is provided with at least one pair of tool holders 12, 13, which are only shown schematically, and which can move in a controlled way along one or more axes in order to follow the trajectories and paths specified in the machining cycles.

Each holder 12, 13 is additionally provided with a corresponding arm 12a, 13a projecting suitably from the holder and capable of acting on the ring 2 in such a way that the ring 2 can be moved from and towards the table 3 by being supported on the arms 12a, 13a, interacting with the centring device 1 when moving from one to the other of the positions described above in order to complete the ring machining cycle.

The arms 12a, 13a can be designed as clamping devices removably attached to the corresponding tool holders 12, 13. As another alternative, magnetic portions may be provided on these arms to secure the ring by magnetic attraction. This configuration can be produced by providing magnets of suitable size, designed to be applied to the arms 12a, 13a. Thus the invention resolves the initial problem and yields numerous advantages over the known solutions.

Above all it should be noted that, by using the device according to the invention, it is possible to secure workpieces in a centred position while reducing the radial deformations (due to the securing) because the necessary centring forces are reduced and are dissipated directly into the supports of the centring elements.

Another advantage lies in the fact that the semi-finished articles can be fully machined with a limited number of positioning operations, in which the centring is flexible and also allows a long travel of the centring elements, which is particularly suitable for the centred securing of workpieces (such as rings for bearings) having widely varying dimensions (for example, those having dimensions varying from a few tens of millimetres to several thousand millimetres).

Additionally, the provision of lifting means integrated into the machine tool and interacting with the centring device makes it possible to simplify the structure of the self-centring table while automatically controlling the steps of moving the workpiece directly by means of the controlled movement of the tool holders.

Claims

1. A device for securing in a centred position axially symmetric pieces, particularly rings (2) for bearings, to be subjected to machining, comprising: - a device for centring the workpiece on a work table (3), including at least three centring elements (6) spaced at regular angular intervals, which can come into contact with the workpiece to move it to a centred position, each of said centring elements being movable in a predetermined radial direction, said radial directions intersecting on the geometrical axis (X) of centring of the workpiece, means (7) for securing the workpiece, which are associated with said centring elements (6) and which are capable of securing the workpiece in the centred position which is reached; characterized in that said securing means comprise, in each centring element (6), at least one securing clamp (8, 9) which can be moved from and towards an operating position in which it keeps the workpiece bearing on a first bearing surface (10a, lla) of the centring element (6), the securing force being applied in a direction substantially parallel to the geometric axis (X) of the table (3).

2. A device according to Claim 1, comprising at least a pair of said clamps (8, 9) for each centring element (6), each of the clamps of said pair interacting with a corresponding bearing surface (10a, lla) provided in the corresponding centring element (6), said clamps (8, 9) alternatively acting in a corresponding first and second position for securing the workpiece to allow the machining of the inner and outer surfaces of the ring respectively.

3. A device according to Claim 1 or 2, in which each of said axial bearing surfaces (10a, lla) for the workpiece is formed on the corresponding centring element (6) in a corresponding seat (10, 11) provided for contacting and supporting the ring, each seat having a corresponding surface portion for radially contacting the workpiece in the step of centring and being capable of interacting with the inner or outer surface of the ring in the corresponding position.

4. A device according to any one of the preceding claims, in which each clamp (8, 9) comprises a corresponding securing arm (8a, 9a) which is rotatable about an axis (8b, 9b) parallel to the geometric axis of the table (3), from and towards said operating position.

5. A machine tool for machining workpieces, particularly rings of bearings, comprising a work table (3) and a device for securing in a centred position workpieces to be subjected to machining, the machine tool being constructed according to any one or more of the preceding claims.

6. A machine tool according to Claim 5, comprising at least a pair of tool holders (12, 13) which can move in a controlled way along one or more corresponding axes, each tool holder comprising an arm (12a, 13a) capable of acting on the workpiece, in such a way that said workpiece can be moved from and towards said table (3) by supporting the workpiece on said arms (12a, 13a) in such a way that it interacts with the centring device in its movement from one to the other of said positions for the complete machining of the surfaces of the workpiece.