Untitled record

(74) Agent: Danièle Laroche.

54) Machining process and device: lathe and in particular copying.

72) Invention of:

(33) (32) © Conventional priority

Sale of booklets at IMPRIMERIE NATIONALE, 27, rue de la Convention - PARIS (15^e)

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The invention relates to a lathe machining process and in particular to copying as well as a device allowing the implementation of such a process.

Various machining devices are known at the present time in which. the continuous advance of the tool obtained by regular movement of a carriage and a laggard is superimposed on a rectilinear reciprocating movement of fixed direction. During the phase during which the reciprocating movement is added to the continuous movement of the carriage, the tool penetrates more quickly into the material and then during the phase during which the reciprocating movement is cut off from the continuous movement of the carriage, the advance of the tool becomes zero and even negative, the tool no longer removes material and the chip formed during the previous phase comes off.

The device providing the reciprocating movement of the tool therefore makes it possible to split the chips into small elements and behaves like a chip breaker.

In addition, thanks to this reciprocating movement, it is known that one can obtain an advance of the tool per unit of time, greater than that which is obtained according to conventional methods.

The improvement in performance is explained by better heat dissipation during the tool cycle.

However, such a reciprocating rectilinear movement requires a certain power because of the mass driven in vibration and has so far been able to be achieved in a perfectly reliable manner only by implementing a hydraulic control; indeed, the mechanical controls cannot withstand accelerations due to oscillations for an extended time without undergoing abnormal wear.

This results in serious difficulties when it is desired to implement such a system in a device for copying a part having a symmetry of revolution and in which the movement of the carriage driving the tool comprises a hydraulic control while the movement the carriage carrier is carried out by means of a mechanical control.

In this case the stringer is driven in a continuous movement parallel to the axis of rotation of the part.

The carriage is arranged so that its movement moves the tool closer or further away from the axis of rotation. The combination of the two movements makes it possible to follow the profile of the part but the reciprocating movement retains a fixed direction. It follows that any movement of the tool parallel to the direction of vibration leads to a satisfactory surface condition, but on the other hand any movement of the tool in a direction different from the direction of vibration leads to a series of serrations at the surface of the workpiece; the surface condition is then very rough.

We thought of remedying this state of affairs by carrying out an order

11102 hydraulic for the movement of the carriage and the movement of the carriage. However, this solution raises difficulties; it is necessary to inject for each movement, along each axis, the quantity of oil provided under penalty of deforming the part to be reproduced. However, such an operation proved experimentally very difficult to carry out because it required the presence of two absolutely identical electrodistributors of oil leading to identical connections. The various experiments carried out in this direction have only led to very disappointing results.

Under these conditions, the inventor thought of replacing the reciprocating movement of the tool mounted on the carriage with a movement leading the tool to describe a closed loop without any sudden stop movement.

The lathe machining process and in particular copying of the invention according to which the workpiece is driven in rotation about an axis while the tip of the tool is driven by a drive movement along two axes defining a work plan and a cyclic relative movement, is characterized in that the cyclic relative movement causes the tip of the tool to execute a closed loop located in the work plan.

The absence of sudden movements then makes it possible to use a less powerful tool control, mechanical for example.

According to an important characteristic of the invention, the lathe machining device, and in particular the two-axis living room copying device, which comprises a tool holder mounted on a carriage and movable in two dimensions by means of a slider and the carriage thus allowing movement of the tip of the tool in a work plan, is characterized in that the tool holder comprises means driving the tip of the tool in a cyclic movement along a trajectory of substantially elliptical shape located in the work plane.

In the device according to the invention, the carriage and the drag are therefore not driven in movement with the tip of the tool in a cyclic movement, which makes it possible to further reduce the power used.

Under these conditions, the copying operations can be carried out with trolleys and laggards fitted with a mechanical, hydraulic or electric control or of any other type.

The description which follows with reference to the appended drawings given by way of nonlimiting example will make it easier to understand how the invention can be implemented.

FIG. 1 represents a machining device illustrating the state of the art.

Figure Figure Figure

2a is a 2b is a 2c is a schematic vertical section of the tool holder of the invention.

top view of the tool holder of the invention.

second vertical section of the tool holder of the invention.

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In these various figures only the elements necessary for understanding the invention have been shown.

In Figure 1 the machining device shown, which illustrates the state of the art comprises a lathe 1 driving in rotation a part 2 around the axis xy.

This device also includes a movable stroller 3 parallel to xy and a movable carriage 4 perpendicular to x y. Tool 5 is mounted on this carriage.

When it is desired to make two-axis copying, the carriage and the carriage move the tip of the tool in motion in a plane which we will call the work plane. This plane is parallel to the xy axis and to simplify the description below, we consider the work plane as horizontal.

In known devices, means for fragmenting the chip with unidirectional vibration are used.

According to the state of the art, the direction of vibration vv 'is chosen parallel to the axis xy, in this case, during the development of the curved parts of the part, the tool will poke into the material and surface finish will be of very rough quality.

Figure 2a shows a schematic vertical section of the tool holder of the invention.

The conventional lathe, laggard, carriage, etc. members of a machine tool, as shown in FIG. 1, have not been included in FIG. 2a or in FIGS. 2b and 2c.

The tool holder is intended to be mounted on the carriage of a machine tool in place of the tool. It can be mechanically fixed, for example by a pressure screw, inside the housing provided for the tool.

The tool holder comprises a slide 10 (which appears more fully in FIG. 2c) formed of two elements 11 and 12. The lower element 11 cut in Z-shape, the part opposite to the slide part is easily adaptable to the place the tool on the carriage (see figure 2c).

The tool holder also comprises a tool support 13 of rectangular shape at the end of which the tool 14 is fixed the tool support 13 is movable in two dimensions inside the slide 10, so that the tip 15 of tool 14 can move in the work plane that we choose in our example, horizontal.

In the tool holder 13, a cylindrical cavity 16 with a vertical axis m m ′ has been provided inside of which an eccentric 17 is disposed rotating around the vertical axis mm ′. A needle bearing 18 is disposed in the cavity 16 around the eccentric 17. The eccentric is held in position by two ball bearings 19 and 20 of axis mm 'located in the lower element 11 and in the element upper 12 of slide 10.

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A pneumatic motor 21 with a horizontal axis p p 'is housed on the upper element 12 of the slide 10 and drives the eccentric 17 in rotation by means of a bevel torque 22.

The motor 21 and the bevel torque 22 being well known to specialists have been indicated schematically in the various figures.

The tool support 13 has at its rear part a vertical axis 23 passing through a recess 24 of parallelepiped shape formed in the middle part over the entire width of the tool support 13. The recess 24 is intended to receive the arm 25 d 'A link 26 whose center 27 is integral with the slide (see Figure 2b).

In FIG. 2b representing the tool holder of the invention, the presence of the fixing screws 28 of the upper element 12 to the lower element 11 of the slide 10 is noted, as well as the pipe 29 of compressed air supplying the motor 21. There is shown the curve E described by the tip of the tool.

FIG. 2c is a vertical section of the tool holder on which the elements 11 and 12 of the slide 10 are shown in detail joined together by a screw 28.

The presence of a screw 30 used for fixing the motor 21 to the upper element 12 is noted.

When the motor 21 drives the eccentric 17 in rotation about the axis mm ', the tool support 13 slides back and forth in the slide 10.

The axis 23 drives the arm 25 of the link 26 from front to back. As it has a fixed center 27, any point on the axis 23 describes a portion of an arc of a circle.

The tip 15 of the tool then describes an elliptical curve E in the work plane (see FIG. 2b). this curve has a large axis b and a small axis a. During a copying operation along two axes, the tip of the tool is driven by a drive movement in the work surface thanks to the carriage and the drag.

The tip of the tool is driven in a cyclic movement along an elliptical trajectory so that the tool is released several times from the part and the chip formed is thus broken several times. The release time can reach three quarters of the time required to travel the curve E, which results in accelerated cooling of the tool and the machining speed can thus be improved.

In the case of a copying operation, the tool always retains the same orientation with respect to the axis and the ellipse described E is tangent to the part in variable portions of this ellipse. If the ratio - is very large, the quality of the surface state will be very variable, on the contrary, the more the ratio will tend towards 1, i.e. the more the ellipse will tend towards the circle, the more the quality of The surface condition will be constant.

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On the other hand, the quality of the surface finish increases when ”a” decreases (the ratio remaining constant).

The direction of rotation of the tool also has an influence on the quality of the finish. The tip of the tool is animated by an elliptical movement around the vertical axis Θ passing through the center of the ellipse E (see Figures 2a and 2b), this axis moving itself with a certain speed following a sense and in a given direction. During the rotation of the tool, it is clear that these speeds are added during approximately a half-turn of rotation of the tool and are cut off during the other.

The direction, the direction and the speed of movement of the axis Θ being imposed by working conditions which the machine must execute, it will suffice to obtain the best possible surface condition to animate the tool so that the speed of its tip is as low as possible at the time of contact with the part.

Many variants of the device described are possible in particular, the motor can be housed in the body of the tool support or in the lower part of the slide.

The drive can also be performed at the rear of the tool support, the link being then placed at the front of the tool support, the transmission between the motor and the eccentric being ensured by known conventional means ( gables, belts, etc ...). The motor can be pneumatic, hydraulic or electric.

Good results have been obtained using an electric motor.

Although the tool holder which has just been described seems the most advantageous for the implementation of the invention, it will be understood that various modifications can be made to it without departing from the scope of the invention, some of these elements being able to be replaced by other elements capable of ensuring there same technical function or an equivalent technical function.

One could also replace the rod and / or the eccentric with a tenon integral with the tool support moving in a groove traced in the slide and having a shape of line segment, circle or portion of circle.

It would also be possible to use only two rods or only two eccentrics. In the latter case, the tip of the tool could exactly describe a circle.

The properties of the tool holder of the invention also allow it to cut off by modifying the orientation of the slide by 90 °, the tip of the tool then describing a substantially elliptical curve situated in a plane perpendicular to the axis. of the tour.

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