WO2013114050A1

WO2013114050A1 - Machining head for multi‑axis machining centre

Info

Publication number: WO2013114050A1
Application number: PCT/FR2013/050209
Authority: WO
Inventors: Jacques Thibaut; Christophe Thibaut
Original assignee: Thibaut
Priority date: 2012-02-01
Filing date: 2013-01-31
Publication date: 2013-08-08
Also published as: FR2986172A1; FR2986172B1

Abstract

The invention relates to a machining head (1) for a multi‑axis machining centre, the head comprising a cradle (3) that can be rotated about an axis (B) with respect to a workpiece, and a tool‑holding arbour (4) mounted on the cradle and designed to turn a tool about an axis of rotation (R) of the tool, the machining head being characterized in that the arbour is mounted with the ability to effect a translational movement with respect to the cradle along the axis of rotation of the tool. The invention also relates to a machining centre for working along at least one axis, and preferably along several axes, the machining centre comprising: • a machining head (1) as described hereinabove, mounted to be able to rotate (axis B) with respect to the support (8), • a means (2, 7) for rotating (axis C) the support (8) with respect to a supporting structure, • a bed on which to hold a workpiece in position, and • a means (2) for driving the motion • a means for driving said bed in motion with respect to the supporting structure. Application to the five‑axis polishing of hard materials such as granite, marble, concrete, notably in the field of headstones, decoration, building, etc.

Description

Machining head for multiaxial machining center

Technical field and state of the art

The invention relates to a machining head for multiaxial machining center, head of the type comprising a cradle capable of being rotated about an axis with respect to a support, and a tool pin mounted on the cradle and adapted to drive a tool in rotation along an axis of rotation of the tool.

The invention finds particular application for the polishing of materials such as granite, marble, concrete and composite materials using a CNC machining center suitable for working in five continuous or positioned axes . The markets targeted by this application are mainly the field of funerary, decoration, building, etc. The polishing of materials such as granite, marble, concrete and composite materials is carried out today using a set of tools working under heavy watering (water or other lubricant). The abrasive tools used, based on diamond or synthetic silicon carbide, have a polishing surface of decreasing granulometry for an increasingly fine polishing, and ideally work in pneumatic pressure to have a constant effort on the material to polish regardless of the degree of wear of the tool. This stress on the polishing material, applied perpendicular to the surface to be polished, must be adapted according to the hardness of the material to be polished and the granulometry of the polishing surface of the abrasive tool. A fine tuning of this effort is necessary to obtain the required finish (softened without trace, polishing and uniform polishing, etc.).

The five-axis machining centers currently available on the market are equipped, in a known manner, with holding trays for the part to be polished, trays movable in translation along at least two axes, and rotary tool holders along the axes B and C. usual, the assembly for orienting and positioning the tool relative to the workpiece in all directions. They make it possible to work either in five positioned axes or in five continuous axes. The known tool-holder spindles are perfectly suitable for material removal work such as stone carving. By cons they are not suitable for polishing that requires a constant effort and perfectly controlled tool on the surface to be polished. Also, five-axis machining centers with conventional machining heads can only drill with a programmed feedrate. Indeed, the tools used for drilling are made of industrial diamond; in use, they can be satin and become less sharp, depending on the chosen cutting parameters or when drilling in unsuitable materials.

To overcome these difficulties, some manufacturers have developed spring-loaded mandrels to apply a force on the surface to be polished. The main disadvantages of this solution are on the one hand the high price (a spring mandrel is necessary for each abrasive tool) and on the other hand the lack of regularity of the applied force. Indeed, the force exerted by the springs varies according to the compression of these. It decreases during tool wear and therefore the force applied to the surface to be polished decreases. This results in a lack of uniformity of the highly detrimental polishing. Another technical solution available on the market is to obtain a so-called "electrical" pressure obtained by controlling the torque delivered by the axis motors or by controlling the speed of the spindle motors of the machining center. This solution makes it possible to obtain acceptable results (in terms of polishing uniformity) but this requires the use of specific geared motors and spindle motors which can generate additional costs and increased risk of malfunction.

Another possible solution would be the use of force sensor at the tool carried by the spindle. But this solution is very expensive and incompatible with the market price of polishing centers. Moreover, this solution is cumbersome at the spindle and generates an additional cantilever at the spindle.

The invention proposes a new machining head, particularly well suited for polishing and not having all or some of the disadvantages of the known solutions described above.

Description of the invention

Thus, the invention proposes a new machining head for multiaxial machining center, machining head comprising a cradle (3) capable of being rotated along an axis (B) relative to a support (8) , Support intended to be mounted movable relative to a workpiece in translation along axes (X, Y, Z) of a Cartesian coordinate system and rotated along an axis of rotation of the support (C) parallel to one of the axes (Z) of the Cartesian coordinate system, machining head also comprising a spindle (4) mounted on the cradle and adapted to drive a tool in rotation along an axis of rotation (R) of the tool.

The machining head according to the invention is characterized in that it also comprises a means for driving the spindle (4) in translation along a translation axis (W) parallel to the axis of rotation (R) of the tool until the tool is applied to the workpiece with a regulated axial pressure force. The axial pressure is preferably continuously regulated during the entire work on the workpiece. Thus, for polishing or surfacing in particular, it becomes possible to obtain a perfectly uniform surface including in the case where the axis of the tool is not vertical. In addition, the fact of applying the pressure at the spindle, that is to say closer to the tool, avoids moving large masses to apply the pressure. The machining of soft and fragile materials becomes possible regardless of the working angle of the tool.

The invention also makes it possible to make holes of good quality in all the angular positions, which does not allow a five-axis machining center with a conventional machining head; associated with the machine feed, that is to say the continuous displacement of the machining head as and when drilling, the application of a regulated pressure in this case to compensate for the lack of cutting d a satin tool; this protects both the tool from the risk of breakage, protect the integrity of all mechanical components of the machine and prevent damage to the workpiece.

Also, the race of the spindle along the axis of translation parallel to the axis of rotation of the tool increases the working capacity of the tool along its axis of rotation. The drive means of the spindle in translation comprises in one example a guide means (5a, 5b) in translation of the spindle (4) with respect to the cradle (3) along the axis of rotation (R) of the spindle tool, and at least one jack (6) arranged to drive in translation the pin (4) relative to the cradle (3) until the tool is applied to the workpiece with the regulated axial pressure force. These means make it possible to adjust the distance of the tool relative to the workpiece according to the axis of rotation of the tool, and to continuously adjust the pressure exerted by the tool on the workpiece.

In one embodiment, the guiding means comprises:

At least one linear guide rail, fixed on the spindle or on the cradle and

At least one guide shoe, fixed on the cradle or on the spindle, said rail and said shoe each comprising a longitudinal axis parallel to the axis of rotation of the tool, the shoe being adapted to slide along the rail.

The guiding shoe / guide rail association allows the translation movement of the spindle relative to the cradle.

Preferably, the jack is a pneumatic or hydraulic cylinder. In this case, the axial pressure is regulated from measurements of fluid flows between the chambers of the jack. These measurements, which can be easily performed with precision, allow fine and rapid adjustment of the axial pressure exerted on the workpiece.

The drive means of the spindle also comprises a control means arranged to control the actuator according to the regulated pressure force.

Alternatively, the control means is arranged to control the cylinder according to a pressure force regulated according to the advancement of the support of the spindle relative to the workpiece. The use of a continuously regulated pressure is particularly interesting for polishing operations that require a constant effort on the surface to be polished and perfectly controlled throughout the operations. This is also interesting for drilling operations, in particular to compensate for tool wear and to take into account the mechanical strength of the material to be pierced.

According to another variant, the control means is arranged to control the jack:

· With a locked cylinder position, for example on the rod side or on the cylinder bottom side, so as to secure the pin to the support, then

• with a pressure force regulated according to the progress of the support relative to the workpiece.

In other words, in a first step, the jack is locked in abutment so that the pin is immobilized relative to the support. The machining head according to the invention can thus be used conventionally by moving the support relative to the workpiece, for milling operations, cutting, etc. Then, in a second step, the cylinder works under pressure, with a regulated pressure force, to achieve for example a polishing of the cut surface in the previous step.

The invention also relates to a machining center for a work along several axes, machining center comprising:

· A holding plate in position of a workpiece, A support (8) for the machining head,

A means (2, 7) arranged to drive the support (8) in movements relative to the workpiece, translational movements along axes (X, Y, Z) of a Cartesian coordinate system combined with a rotational movement along an axis of rotation of the support (C) parallel to one of the axes (Z) of the Cartesian coordinate system,

· A machining head (1) as described above, rotatably mounted (axis B) relative to the support (8).

Brief description of the figures

The invention will be better understood, and other features and advantages of the invention will emerge in the light of the following description of embodiments of a machining head according to the invention. These examples are given in a non-limiting manner. The description is to be read in conjunction with the appended drawings in which:

FIG. 1 is a perspective view of a tool head according to the invention mounted on a support,

• Figure 2 is an exploded top perspective view of the tool head according to the invention.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION As previously mentioned, the invention relates to a machining head 1 and a machining center comprising a machining head according to the invention, for example a machining center of five-axis type, three X, Y, Z translation axes of a Cartesian coordinate system and two axes of rotation B and C.

The machining center comprises in particular a holding plate (not shown) in the position of a workpiece, and a support 8 of the machining head. The support 8 is fork type in the example shown. The machining center also comprises a means arranged to drive the support 8 in motion relative to the workpiece, translational movements along the X, Y, Z axes of a Cartesian coordinate system combined with a rotational movement according to the invention. rotation axis C of the support 8, axis C parallel to the Z axis of the Cartesian coordinate system. In a practical example, the support 8 is fixed on a runner of a machining center via the plate 7; the flowing is movable in relative translation with respect to the plate along the three axes; in one example, the plate is movable in translation along two orthogonal and horizontal axes X, Y, and the flange is movable in translation along a vertical axis Z; the support is also rotated by means of a drive means 2 along an axis C parallel to the axis Z.

The machining center also includes a machining head 1 as described below. The machining head 1 is rotatably mounted relative to the support (8), along an axis B, in the example shown a horizontal axis. In Figure 2, the machining head 1 is shown alone, in exploded top view. In FIG. 1, the machining head 1 is rotatably mounted on the support 8, rotatable relative to a horizontal axis B in the example shown.

The machining head 1 according to the invention comprises a cradle 3 and a spindle 4 tool holder. The cradle 3 is rotatably mounted on the support 8 along the axis B. The spindle 4 is mounted on the cradle 3; pin 4 is adapted for driving a tool (not shown in the figures) in rotation along an axis of rotation R of the tool; in one example, the tool is a polishing tool.

According to the invention, the machining head also comprises means for driving the spindle 4 in translation relative to the cradle 3, translation along a translation axis W of the spindle parallel to the axis of rotation R of the tool, until the tool is applied to the workpiece with a regulated axial pressure force. The means for driving the spindle in translation comprises a guide means 5a, 5b in translation of the spindle 4 with respect to the cradle 3 along the axis of rotation R of the tool, and at least one jack 6 (two spindles). cylinder in the example shown) to fluid such as hydraulic or pneumatic cylinders.

In the example represented in FIG. 2, the linear guiding means comprises:

· Two rails 5a linear guide, fixed on the pin 4 and

• four guide pads 5b, fixed on the cradle 3

The rails 5a and the pads 5b each comprise a longitudinal axis parallel to the axis of rotation R of the tool, and each pad is adapted to slide along an associated rail.

Note that the stroke of the cylinders can be relatively low, of the order of 20 to 40 mm for example; indeed, the displacement of the spindle along the axis W is simply used to pressurize the tool on the surface to be worked, the approach of the spindle facing the part being carried out by moving the support 8 according to the usual axes X, Y, Z, B and C.

The cylinders 6 conventionally comprise a piston sliding in a cylinder filled with fluid; for example, one end of the cylinder is fixed on the cradle and one end of the piston is fixed on the spindle; a control device (not shown) continuously measures the fluid pressure inside the cylinder and regulates the piston stroke as a function of a desired axial pressure of the tool on the workpiece. The assembly thus makes it possible to drive the pin 4 in translation relative to the cradle 3 until the tool is applied to the workpiece with the regulated pressure force. This linear guiding system inserted between the pin 4 and the cradle 3 allows the spindle to have an additional degree of freedom (a sixth axis of some kind) always oriented parallel to the axis of rotation of the tool, c that is, always perpendicular to the surface to be worked.

The control device makes it possible to drive pin 4 forward or backward with respect to cradle 3 (thus to bring the tool closer to or away from the surface of the workpiece); the control device also makes it possible, on the one hand, to apply a predefined pressure to the surface to be machined according to, for example, the size of the tool and, on the other hand, to maintain said predetermined pressure constant on the surface to be machined. whatever the orientation of the spindle in the space, the progress of the machining, the wear of the tool, the control device also makes it possible to immobilize the spindle 4 with respect to the cradle 3; for this, the control device regulates the axial pressure so as to hold the cylinder in abutment, either rod side or cylinder bottom side.

The tests carried out have shown that the invention makes it possible to obtain, especially for polishing operations, a required level of finish, even on particularly hard materials such as granite or softer materials such as marble, concrete, etc., and whatever the inclination of the axis of rotation R of the tool.

Claims

1. machining head (1) for multiaxial machining center, machining head comprising a cradle (3) capable of being rotated along an axis (B) relative to a support (8), support for to be mounted movable relative to a workpiece in translation along axes (X, Y, Z) of a Cartesian coordinate system and in rotation along an axis of rotation of the support (C) parallel to one of the axes (Z ) of the Cartesian marker, machining head also comprising a pin (4) tool holder mounted on the cradle and adapted to drive a tool in rotation along an axis of rotation (R) of the tool, machining head characterized in it also comprises a means for driving the spindle (4) in translation along an axis of translation parallel to the axis of rotation (R) of the tool until the tool is applied to the workpiece with a regulated axial pressure force.

2. Machining head according to claim 1, wherein the means for driving the spindle in translation comprises a guide means (5a, 5b) in translation of the spindle (4) relative to the cradle (3) according to the invention. axis of rotation (R) of the tool, and at least one jack (6) arranged to drive the pin (4) in translation relative to the cradle (3) until the tool is applied to the workpiece with the regulated pressure force.

Machining head according to claim 2, wherein the guiding means (5a, 5b) comprises:

"At least one linear guide rail (5a), fixed on the spindle or on the cradle and

At least one guiding pad (5b), fixed on the cradle or on the spindle, said rail and said pad each comprising a longitudinal axis parallel to the axis of rotation (R) of the tool, the pad being adapted to slide along the rail.

4. Machining head according to one of claims 2 or 3, wherein the cylinder is a pneumatic or hydraulic cylinder.

5. Machining head according to one of claims 2 to 4 wherein the spindle drive means also comprises a control means arranged to control the cylinder according to the controlled pressure force.

6. Machining head according to claim 5 wherein the control means is arranged to control the cylinder according to a pressure force regulated according to the advancement of the support relative to the workpiece.

7. machining head according to one of claims 4 to 5 wherein the control means is arranged to control the jack:

• with a position of the cylinder locked so as to secure the pin to the support, then

8. Head according to one of the preceding claims, wherein the pin carries a polishing tool.

Machining center for multi-axis work, machining center comprising:

• a holding plate in position of a workpiece,

A support (8) for the machining head, A means (2, 7) arranged to drive the support (8) in movements relative to the workpiece, translational movements along axes (X, Y, Z) of a Cartesian coordinate system combined with a rotational movement along an axis of rotation of the support (C) parallel to one of the axes (Z) of the Cartesian coordinate system,

• A machining head (1) according to one of the preceding claims, rotatably mounted (axis B) relative to the support (8).