METHOD FOR CONTOUR GRINDING WIDE BLADES AT HIGH SPEED

Abstract

The invention relates to a method for contour grinding wide blades at high speed, according to which a wheel (1) is used the grinding contour of which has a width dimension that is less than the width of the tip of the blades to be ground, said contour being defined by a straight area followed by an arched area at one end, with the straight area of which a straight grinding is carried out to deburr the tip of the blades, whereas with the arched area the contour grinding is carried out by the interpolation of axes.

Description

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an elevational view of a conventional solution for grinding a large rotor “r” with multiple blades to be able to observe the interferences “i”.

FIG. 2 shows a cross-sectional view of a grinding wheel 1, the grinding contour of which is formed by a straight area 1.1 and another arc-convex area 1.2.

FIGS. 3.1 and 3.2 show, according to respective schematic views, the degrees of freedom of the machine configurations in which the method object of the invention can be developed.

FIG. 4 shows an elevational view of an example of straight grinding, by means of the planar area 1.1 of a wheel 1, according to the method object of the invention, applicable in this case to a blade “b” with a width of less than 73 mm.

FIG. 5 shows an elevational view of an example of contour grinding the tip of blade “b” of FIG. 4 by means of the arc-convex area 1.2 of the wheel 1, according to the method object of the invention.

FIGS. 6 to 8 show schematic elevation views of the deburring of the tip of a blade “b” in a multiple “plunging” straight grinding cycle.

FIG. 9 shows a view similar to the previous ones but now during the contour grinding by means of the arc-convex area 1.2 of the wheel 1.

FIG. 10 schematically shows how in the method object of the invention with a narrow wheel 1, the grinding of all the stages of the rotor “r” can be covered without any interference.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is related to high-speed contour grinders of the blades of a rotor, proposing a solution which thanks to its constructive and functional features is really advantageous for its application in grinding wide blades.

Grinding machines “m”, are known, the grinding wheels “g” of which have a width that is greater than the width measurement of the tips of the blades “b” of a rotor “r” of those used in the aerospace sector, as shown in FIG. 1.

With this solution, the method for grinding consisted of carrying out a first straight grinding operation for deburring the tip of the blade “b”, which straight grinding is carried out with the straight area of the wheel “g” in a single action called “plunging” and later, carrying out a contour grinding with the arched area of one of the edges of the wheel “g”.

The aerospace sector demands rotors “r” with wider blades “b”; such that the usual measurement, in which the tip of the blades “b” did not reach a width of 73 mm, has now been become large rotors with multiple stages, in which the blade “b” of at least some of the stages has a width dimension equal to or greater than 73 mm, hereinafter referred to as wide blades.

In this case, which is shown in FIG. 1, when rotors with multiple stages are ground, interferences such as those indicated by reference “i” in said FIG. 1 occur if wheels “g” with measurements greater than the measurement of the wide blades “b” are used. 1.

British patent document GB 2 270 485 describes a method for grinding wide blades by means of using a narrower wheel the grinding contour of which has an arc-convex profile. With this wheel and working by the interpolation of axes “X” and “Z”, the tips of wide blades “b” could be ground even when said tip had a non-straight profile, for example, an angled or arched profile.

With this solution, since the profile of the wheel “g” is arc-convex, the deburring phase for deburring the tip of the blade “b” cannot be carried out by means of a straight grinding and must also be carried out by the interpolation of axes “X” and “Z”, in a contour grinding process which is very slow, which worsens when a rotor with multiple stages is to be ground.

The object of the present invention consists of a method for contour grinding wide blades “b” of a rotor “r” at high speed.

The invention proposes the use of a wheel 1 which is narrower than the width dimension of the tip of the blades “b” of the rotor “r”, i.e., less than 73 mm, and has a grinding contour defined by a profile divided into two areas 1.1 and 1.2, one of which 1.1 is straight and the other of which 1.2 is arc-convex, as can be seen in FIG. 2

The machine configurations proposed in FIGS. 3.1 and 3.2 allow developing the method object of the present invention, having movement in axes “X” and “Z”, axis “X” being orthogonal to axis “Z”.

The movement in axis “X” determines the penetrating movement of the wheelhead 3 with respect to the rotor “r” and the movement in axis “Z” defines its transverse movement in relation to the rotor “r”.

Axis “Z” determines the transverse movement of the grinding machine, a movement parallel to the rotation of the working part, i.e., the rotor “r”, this axis “Z” being parallel to the axis of rotation of the rotor “r”.

The head 3 can further rotate according to the path indicated by the arc “B” in FIGS. 3.1 and 3.2, so as to position the angle of attack of the wheel 1 with respect to the blade “b” to be ground.

FIG. 3.1 shows a machine 2 with three degrees of freedom; whereas FIG. 3.2 corresponds to a machine 2 with four degrees of freedom, since it incorporates the possibility of movement of the head 3 according to axis “W”. Axis “W” is parallel to axis “Z”, but the movements in “W” can have a value different from the movements in “Z”.

The interpolation of axes “X” and “Z” and the rotation in “B”, together with the use of the different areas 1.1 and 1.2 of the wheel 1, according to the needs, allows grinding any type of blade “b”, whether it has a straight, angular or arched (concave or convex) profile, and whether it has a width of less than 73 mm or it is a wide blade with a width equal to or greater than 73 mm.

FIG. 4 shows the grinding of a tip of blade “b” with a width of less than 73 mm. The deburring is carried out by means of the planar area 1.1 of the grinding wheel 1. In this cycle, it is enough to move the wheel 1 closer by means of a movement in the axis “X” and rotate it by means of a rotation according to “B”, such that the tip of the blade “b” is deburred by means of a single “plunging”.

For the contour grinding of the tip of the blade “b” of FIG. 4, the grinding is carried out by means of the interpolation of axes “X”, “Z”, and the rotation of “B”, such that the movement carried out by the wheel 1 is adjusted to the profile of the tip of the blade “b”, i.e., carrying out a contour grinding, as shown in FIG. 3.

In other words, in this case, the planar area 1.1 of the wheel 1 is used for deburring the tip of a blade “b” in a single in-depth straight grinding cycle, in a single “plunging”, whereas the arc-convex area 1.2 is used in the contour grinding of the tips of the blades “b” by means of the interpolation of the axes of the grinding machine 2, generating the relative movement of the wheel 1 with respect to the tip of the blade “b”.

In the grinding of a blade “b” with a measurement equal to or greater than 73 mm, as is the case of FIGS. 6 to 8, the use of a wheel 1 which is narrower than the tips of the blades “b”, the interpolation of the axes which the machine 2 has, as well as the use of the two areas 1.1 and 1.2 which the wheel 1 has according to the features of each tip of blade “b”, allows carrying out a multi “plunging” grinding, which considerably reduces the working times.

Indeed, in the deburring phase, the wheel 1 is placed with the necessary angle according to the profile of the tip of the blade “b” by means of swiveling according to the movement “B”, and the debarring is carried out by means of multiple movements in axis “X” for moving the wheel 1 closer to the rotor “r”, in what is referred to as a multi “plunging”.

The deburring process is thus carried out much faster than if it were carried out with a narrow wheel with an arc-convex profile carrying out said deburring by the interpolation of the axes.

The final step of the grinding is carried out by means of the interpolation of axes “Z”, “X” and the movement in “B”, which the machine has, carrying out a contour grinding of the tips of the blades “b” by means of interpolation (straight, concave, convex) of the penetrating axis, bead 3, wheel 1, and the longitudinal axis, table 4.

If this method herein proposed is compared with the traditional method which used wide wheels, it is also found that this new method for contour grinding wide blades at high speed significantly reduces the total duration of the cycle necessary to machine large compressor rotors, compared with a contouring deburring and finishing process for the stages. If this new method is not applied, it is necessary to charge the wheel (a change from a wider to a narrower wheel) to complete the grinding of the narrowest stages of a compressor rotor, abruptly increasing the cycle and start-up times.

FIG. 10 shows a rotor “r” with multiple stages, it is specifically formed by fourteen stages, in which it can be seen how in some cases, the blades “b” of these stages have widths with a measurement that is equal or greater than 73 mm. This is the case of the first five stages of the left-hand part of this FIG. 4. The wheel 1 has a width of less than a 73 mm. As can be seen in FIG. 3, the interferences “i” occurring in the solution shown in FIG. 1 do not occur in the grinding of the narrow blades; such that it is not necessary to change the wheel 1 to complete the grinding of the narrowest stages of a compressor rotor, considerably reducing the working times because a wheel 1 that is narrower than the wide blades “b” can cover the grinding of all the stages of the rotor without any interference “i”.

FIG. 4 shows, in relation to the first stage, how the straight deburring grinding is carried out with the straight part 1.1 of the wheel 1 and by means of a multiple “plunging” grinding cycle.

Furthermore and according to the method object of the present invention, both if blades “b” the tip of which has width of less than 73 mm are ground, and if wide blades the tip of which is equal to or greater than 73 mm are ground, the measurement can be applied in the process because the contouring is obtained by means of the interpolation of axes that do not interfere with the axes necessary to operate the measuring device. This will lead to an increase of the precision and to a reduction of the cycle duration because the measurement and the grinding can take place simultaneously.

Claims

1. A method for contour grinding wide blades at high speed, for the type of blades the tip of which has a width dimension equal to or greater than seventy-five millimeters, characterized in that according to such method, a narrow wheel 1 is used, the grinding contour of which has a width dimension of less than seventy-five millimeters, said contour being defined by a straight area 1.1 followed at one end by an arched area 1.2; with this narrow wheel 1 and more specifically with its straight area 1.1, the “plunging” straight grinding process is carried out to deburr the tip of the blades in successive inlets in a multiple straight grinding cycle; whereas with the arched area 1.2 the contour grinding is carried out by the interpolation of axes.

2. A method for contour grinding wide blades at high speed according to claim 1, characterized in that the contour grinding with the arched area 1.2 is carried out by means of the straight, concave and/or convex interpolation of the penetrating axis, head 3, wheel 1, and the longitudinal axis, table 4.

3. A method for contour grinding wide blades at high speed according to claim 1, characterized in that to grind a rotor “r” with several stages in which some of its stages are formed by wide blades “b”, said grinding is carried out with the same wheel 1, without interferences upon grinding adjacent blade stages.

4. A method for contour grinding wide blades at high speed according to claim 2, characterized in that to grind a rotor “r” with several stages in which some of its stages are formed by wide blades “b”, said grinding is carried out with the same wheel 1, without interferences upon grinding adjacent blade stages.