CLIAMS:We claim:
1) A fixture to facilitate in performing pitch milling on the root of the T-root blades, said fixture comprising:
a) a mounting block comprising a base block and a rectangular block, said rectangular block integrally formed at the edge of said base block resembling the shape of ‘T’ and supported on its back side by means of at least one rib projecting from said base block, said base block provided with a plurality of holes along its width on either ends to facilitate in locking of said mounting block to platform of a CNC machine, said mounting block provided with a plurality of holes on longitudinal surface, lateral surface and top surface of said rectangular block;
b) a clamping block provided with a plurality of through holes along its longitudinal axis, one hole provided at the center of the clamping block complementary to the hole on said mounting block facilitates in attachment of said clamping block to said mounting block by means of a hexagonal bolt, other hole provided at the bottom of the clamping block facilitates in adjustment of space between said clamping block and said mounting block by means of a hexagonal bolt passing through said hole and mounting against said mounting block and another hole provided at the top of the clamping block facilitates in holding of said blade firmly by means of allen screw;
c) a lever attached to said mounting block to form a fulcrum by means of allen screw passing through complementary holes provided on lateral face of said lever and said mounting block, said lever provided with a hole on its top face;
d) a top block fitted to said mounting block by means of a dowel bolt and hexagonal nut, said top block provided with a flat surface on its bottom face;
e) a support block attached to said mounting block on its lateral surface by means of allen screw; and
f) a pin press fitted in to the hole provided on top face of said lever.

2) A fixture to facilitate in performing pitch milling on the root of the blades as claimed in claim 1, wherein the distance between said mounting block and said clamping block can be adjusted depending on the width of the blades.

3) A fixture to facilitate in performing pitch milling on the root of the blades as claimed in claim 1, wherein a plurality of allen screws passing through holes of said clamping block, said mounting block and said support block holds the blade firmly and arrests the movement of the blade from three sides.

4) A fixture to facilitate in performing pitch milling on the root of the blades as claimed in claim 1, wherein said root of the blade is pushed against the bottom face of said top block by means of pressing down said lever.

5) A fixture to facilitate in performing pitch milling on the root of the blades as claimed in claim 1, wherein said top block is provided with a slot on its bottom face along its width to accommodate projections of said T-root blade.

6) A fixture to facilitate in performing pitch milling on the root of the blades as claimed in claim 1, wherein said top block is rotated to an angle of 180 degrees to provide space to perform machining operation on the root of the blades.

7) A fixture to facilitate in performing pitch milling on the root of the blades as claimed in claim 1, wherein said pin is integrally formed with two cylinders of different diameters.

8) A method to facilitate in achieving a uniform pitch milled surface on the root of the blades using a fixture, said method comprising the steps of:
a) placing and loosely holding the T-root blade with tapered face upwards between said mounting block and clamping block by means of tightening and adjusting the hexagonal bolts;
b) pressing down the lever such that said pin of the lever pushes the T-root blade against the bottom face of said top block and now, said T-root blade is tightly held in that position by further tightening the hexagonal bolt;
c) arresting the movement of said T-root blade on all the three sides by means of allen screws passing through said mounting block, said clamping block and said support block and mounting against said T-root blade; and
d) loosening the hexagonal nut and rotating said top block to an angle of 180 degrees to provide space for the tool of CNC machine to perform pitch milling operation on the root of T-root blades.

Dated this 6th day of March, 2013 (for Triveni Turbine Ltd)


Deepak Kumar Sen
GM
,TagSPECI: FORM 2
THE PATENT ACT, 1970
(39 OF 1970)
AND
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(See Section 10; rule 13)

A FIXTURE TO FACILITATE IN PERFORMING
PITCH MILLING ON THE ROOT OF THE T-ROOT BLADES

TRIVENI TURBINE LTD
an indian company,
of 12A, Peenya Industrial Area,
Banglore-560058.

The following specification particularly describes the present invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
The present invention relates to the field of fixture for holding blades during machining operation. Particularly, the present invention relates to a fixture that can hold blades during pitch milling operation and thereby helps in achieving a uniform pitch milled surface on the root of the blades.

BACKGROUND OF THE INVENTION:
Figure 1 illustrates an isometric view of T root blade.

Figure 2 illustrates a side view of T root blade.

Figure 3 illustrates an assembled side view of T root blades.

It is evident from figure 2 that one side of the root of T root blade has flat face F and other side of the root of T root blade has tapered face T. The tapered face T of one T root blade is adapted to mate perfectly with flat face F of other T root blade as shown in figure 3 by means of small tilt provided to the other T root blade during assembling of T root blades on to a disc of a rotor.

During machining of the T root blades, an excess material of +0.05mm than the desired thickness is kept on every root of the T root blade purposefully such that the disc of the rotor would not be left with a space that is more than the thickness of the closing blade leaving a gap therein.

Figure 4 illustrates an isometric view of T root blades assembled on to a disc of a rotor without closing blade.

Due to provision of excess material on the root of the T root blades, the space left out for the closing blade in the disc of the rotor after assembling of all the blades may not be sufficient to accommodate the closing blade. In this context, the closing blade can be accommodated in the space left out in the disc of rotor by means of two methods:
1) By removing the material on the root of the closing blade and bringing the thickness of the closing blade to accommodate in the space left out in the disc of the rotor.
2) The extra space in the disc of the rotor that is required to accommodate the closing blade is provided by removing a material of uniform thickness on the blades.
The uniform thickness of the material that is to be removed on the blades is calculated by the following formula:
Uniform thickness of material that is to be removed on the blades= Extra space in the disc of the rotor that is required to accommodate the closing blade/Number of the blades on which the excess material is to be removed.

The method of removing the material only on the closing blade results in the concentration of stress on the closing blade and probability of failure of the closing blade during the rotation of the rotor is very high.

Therefore, traditionally, turbine OEM’s follow the method of removing uniform thickness of material on multiple blades. To remove uniform thickness of material on the blades, an operation called pitch milling operation is performed.

Figure 5(a) and 5(b) illustrates a pictorial representation of T root blade fitted on conventional vice.

The conventional vice V is mounted and locked on the platform of CNC machine. A T root blade is placed between the jaws of the conventional vice V with tapered face T facing upwards. To remove uniform thickness of material from the root of T-root blade, the root of the blade should have plane surface. The plane surface on the root of T root blade is achieved by tapping the T-root blade and checking the flatness on the root by means of dial gauge. The dial gauge is made to touch at different points on the root of t root blade, if dial stands at zero position without any deflection then the surface of the root of T root blade is flat, if dial deflects from zero position then the surface of the root of T-root blade is not flat.

The disadvantages of conventional method of pitch milling are as follows:
a) It is very difficult to achieve accurate plane surface on the root of T-root blade.
b) It takes a lot of time to do setup.

Therefore, there is felt a need for development of a fixture to overcome the drawbacks of the prior art.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide a simple fixture to facilitate in performing pitch milling on the root of the blades.

Another object of the present invention is to provide a fixture wherein set up of the blades for pitch milling operation can be done in less time.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates an isometric view of T root blade;

Figure 2 illustrates a side view of T root blade of figure 1;

Figure 3 illustrates an assembled side view of T root blades of figure 2;

Figure 4 illustrates an isometric view of T root blades assembled on to a disc of a rotor without closing blade;

Figure 5(a) and 5(b) illustrates a pictorial representation of T root blade fitted on conventional vice;

Figure 6 illustrates a front view of fixture in accordance with the present invention;

Figure 7 illustrates a side view of fixture of figure 6;

Figure 8 illustrates a front view of mounting block of fixture of figure 6;

Figure 9 illustrates a side view of mounting block of figure 8;

Figure 10 illustrates a front view of clamping block of fixture of figure 6;

Figure 11 illustrates a side view of clamping block of figure 10;

Figure 12 illustrates a front view of lever of fixture of figure 6;

Figure 13 illustrates a side view of lever of figure 12;

Figure 14 illustrates a top view of lever of figure 12;

Figure 15 illustrates a top view of top block of fixture of figure 6;

Figure 16 illustrates a side view of top block of figure 15;

Figure 17 illustrates a front view of support block of fixture of figure 6;

Figure 18 illustrates a side view of support block of figure 17;

Figure 19 illustrates a front view of pin of fixture of figure 6; and

Figure 20 illustrates a top view of pin of figure 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Figure 6 illustrates a front view of fixture;

Figure 7 illustrates a side view of fixture;

In accordance with the present invention, there is provided a fixture 100 comprising a T-root blade 10, a mounting block 12, a clamping block 14, a top block 16, a lever 18, a fulcrum 20, a pin 22, a plurality of allen screws 24, two hexagonal bolts 26, a dowel bolt 28, a hexagonal nut 30 and a support block 32.

Figure 8 illustrates a front view of mounting block of fixture.

Figure 9 illustrates a side view of mounting block of fixture.

The mounting block 12 has the shape of inverted ‘T’ from front view with an integrally formed rectangular block R at one edge of the mounting block 12. The mounting block 12 includes a plurality of threaded holes H at base B of the mounting block 12 to facilitate in locking of said mounting block 12 to the platform of the CNC machine. The rectangular block R of the mounting block 12 is supported by means of welding three ribs RB arising from the base B of the mounting block 12.The base B of the mounting block 12 has length of 160mm, width of 50mm and thickness of 30mm and is generally indicated by reference numerals X1, Y1 and Z1 respectively. The rectangular block R of the mounting block 12 has length of 110mm, height of 140mm and thickness of 25mm and is generally indicated by reference numerals X2, Z2 and Y2 respectively. A threaded hole H1 of 10mm diameter is drilled on the rectangular block R of the mounting block 12 at a vertical distance of 66mm from the top of the rectangular block R and at a horizontal distance of 55mm from the side edge of the rectangular block R and is generally indicated by reference numerals D1, Z3 and X3 respectively. A through threaded hole H2 of 8mm diameter is drilled near to the top edge of the rectangular block R as shown in figure 8. A hole H3 of 6mm diameter and 10mm depth is provided on the top face of the rectangular block R of the mounting block 12 as shown in figure 9. A threaded hole H4 of 10mm diameter is drilled on the rectangular block R of the mounting block 12 at a vertical distance of 30mm from the top of the rectangular block R and at a horizontal distance of 24mm from the side edge of the rectangular block R and is generally indicated by reference numerals D2, Z4and X4

Figure 10 illustrates a front view of clamping block of fixture.

Figure 11 illustrates a side view of clamping block of fixture.

The clamping block 14 is of rectangular shape having tapered edges TE at both ends on top face. The thickness of the clamping block 14 is of 20mm gradually tapered to a thickness of 17mm at both ends as shown in figure 11 and is generally indicated by reference numerals Y3 and Y4 respectively. The clamping block 14 has length and height of 45mm and 135mm respectively and is generally indicated by reference numerals X5 and Z5 respectively. A through hole H5 complementary to threaded hole H1 of the mounting block 12 is drilled on the clamping block 14 at a horizontal distance of 22.5mm from the side edge of the clamping block 14 and at a vertical distance of 67.5mm from the bottom of the clamping block 14 and is generally indicated by reference numerals X6 and Z6 respectively. A through threaded hole H6 of 10mm diameter is provided on the clamping block 14 at a horizontal distance of 22.5mm from the side edge of the clamping block 14 and at a vertical distance of 20mm from the bottom of the clamping block 14 and is generally indicated by reference numerals X7 and Z7 respectively. A through threaded hole H7 of 8mm diameter is provided on the clamping block 14 at a horizontal distance of 30mm from the left side edge of the clamping block 14 and at a vertical distance of 20mm from the top of the clamping block 14 and is generally indicated by reference numerals X8 and Z8 respectively.

Figure 12 illustrates a front view of lever of fixture.

Figure 13 illustrates a side view of lever of fixture.

Figure 14 illustrates a top view of lever of fixture.

The Lever 18 is of rectangular cross-section having length, width and height of 120mm, 20mm and 15mm respectively and is generally indicated by reference numerals X9, Y5 and Z9 respectively. A through hole H8 of 10mm diameter is provided from one side of the lever 18 to other side of the lever 18 complementary to threaded hole H4 of mounting block 12 at a distance of 43mm from one end of the lever 18 as shown in figure 12 and is generally indicated by reference numerals D3 and X10 respectively. A cylindrical provision P1 of 5mm diameter and 5mm depth is provided on the top face of the lever 18 at a distance of 30mm from the through hole H8 as shown in figures 12 and 14 and is generally indicated by reference numerals D4, Z10 and X11 respectively.
Figure 15 illustrates a top view of top block of fixture.
Figure 16 illustrates a side view of top block of fixture.
The top block 16 is of 61mm length, 55mm width and 15mm thickness and is generally indicated by reference numerals X12, Y6 and Z11 respectively. The top block 16 has flat surface on bottom face. A slot S1 of 8mm width and 5mm depth is provided on the bottom face of the top block 16 along its width at a predefined distance from the side edge of the top block 16 to accommodate the projections of T-root blade and is generally indicated by reference numerals X13 and Z12 respectively. A through hole H9 of 10mm diameter is provided at a distance of 12.5mm from the vertical edge of the top block 16 and at a distance of 27.5mm from the horizontal edge of the top block 16 and is generally indicated by reference numerals X14 and Y7 respectively.

Figure 17 illustrates a front view of support block of fixture of figure 6.
Figure 18 illustrates a side view of support block of fixture.
The support block 32 has two holes H10 and H11 as shown in figure 18. The support block 32 is of 25mm length, 20mm width and 5mm thickness and is generally indicated by reference numerals X15, Y8 and Z13 respectively.
Figure 19 illustrates a front view of pin of fixture.

Figure 20 illustrates a top view of pin of fixture.

The pin 22 resembles the shape of two cylinders of different diameters integrally attached to each other. The pin 22 has a diameter of 9mm at its top end and a diameter of 7.6mm at its bottom end and is generally indicated by reference numerals D5 and D6 respectively. The total height of the pin 22 is of 13mm wherein the height of smaller diameter cylinder is of 5mm and is generally indicated by reference numerals Z14 and Z15 respectively.

The configuration and method of working of the fixture 100 is as follows:
An Allen screw 24 is inserted in to the complementary holes H8 of the lever 18 and H4 of the mounting block 12 to form a fulcrum 20. A pin 22 is inserted in to the cylindrical provision P1 of the 0lever 18 and held in position by means of interference fit. A hexagonal bolt 26 is inserted in to the hole H6 of the clamping block 14. The clamping
block 14 is connected to the mounting block 12 by means of allen screw 24 passing through complementary holes H5 of the clamping block 14 and H1 of the mounting block 12 such that the head of the hexagonal bolt 26 rests against the mounting block 12. The two hexagonal bolts 26 facilitate in adjusting the clamping block 14 depending on the size of the T-root blade 10. A top block 16 is fitted to the mounting block 12 by means of dowel bolt 28 passing through complementary holes H9 of top block 16 and H3 of mounting block 12 and locked with the help of hexagonal nut 30. A support block 32 is attached to the mounting block 12 on its side face by means of allen screw 24 passing through hole H10 of the support block 32.

Firstly, a T-root blade 10 is loosely held between the mounting block 12 and the clamping block 14 with tapered face upwards by means of tightening and adjusting the two hexagonal bolts 26. Secondly, the lever 18 is pushed down such that the pin 22 pushes the T-root blade against the bottom face of the top block 16. Thirdly, the T-root blade is held tightly in position at hub by rotating the hexagonal bolt 26. Fourthly, the allen screws 24 are made to pass through the holes H2 of the mounting block 12, H7 of the clamping block 14 and H11 of the support block 32 and mount against T-root blade 10 firmly below the hub from all the three sides. Finally, the top block 16 is rotated to an angle of 180 degrees by loosening the hexagonal nut 30 such that the tapered face of the T-root blade 10 is ready for machining.

Although the invention has been described herein above with reference to the embodiments of the invention, the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.