FIELD OF INVENTION
The present invention relates to development of locating fixtures
for Root and Shroud milling operation on HMC machines to accommodate all
sizes tang height of new design steam turbine blades which could not be
machined in the existing system earlier.
BACKGROUND OF THE INVENTION
BHEL have 6 nos. Horizontal Machining Center (HMC) for machining
technological allowances provided at both root & shroud end of steam turbine
blades. These technological allowances (extra material) are provided at both
ends of steam turbine blades for clamping of these blades on 5-axis machines
while machining. After machining of these blades on 5-axis machines, the
technological allowances (extra material) are to be milled off on HMC machines
to maintain the drawing dimensions of blades at both root & shroud end.
The fixtures available on these 6 nos. HMC machines are capable of
machining technological allowances of 41K, 36K, 19K, 31K etc. design blades
having tang height 9 mm and more. But the new design 29K blades of HP
moving and HP Guide module are very smaller in size and also having lesser tang
height (less than 8 mm) as compared to other design.
When these new design blades are clamped in the existing fixture
of HMC machines, the tang height portion of blades rests inside the fixture,
which cannot be milled as the fixture will get damaged while maintaining 8 mm
tang height of the blade.
A new locating fixture is required on HMC machines, so that the
tang height portion of these blades rests outside the fixture, which can be easily
milled off by cutter to maintain 8 mm or lesser tang height without damaging the
fixture.
OBJECTS OF THE INVENTION
Therefore, the object of the invention is to propose a development
of a locating fixture for Root and Shroud milling operation on HMC machines,
which can eliminate the disadvantages of Prior art.
Another object of the invention is to propose a development of a
locating fixture for Root and Shroud milling operation on HMC machines, which is
capable of accommodating all sizes tang height of steam turbine blades.
A further object of the invention is to propose a development of a
locating fixture for Root and Shroud milling operation on HMC machines, which is
able to remove the barrier of limitation of milling technological allowances of all
sizes of new design blades in the same fixture of Horizontal machining center
machines.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - Shows a schematic diagram of new locating fixture according to
invention.
Fig.2 - Shows the blank and blade of the turbine with Total Blank length, final
blade length, tang height and technological allowance.
Fig. 3 - Shows the position of the locator shifted to outer edge of the bracket
and portion to be milled is disposed outside of the fixture for required
machining according to the invention.
Fig. 4 - Schematic diagram of main fixture with locating fixture and locating pad
according to invention.
Fig. 5 - Shows the locating fixture with main fixture body where tang height can
not be maintained as the portion to be milled is fouling inside the
fixture according to prior art.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
To cut technological allowances (extra material) of blade at both root
and shroud end, the blade is put in the fixture by taking reference at the root
slot (4 of Fig. 2) of blade with the help of locating pad (3 of Fig. 1) provided in
the fixture. The locating fixture (14) is designed in such a way that the
technological allowances (9) of blade at both root (10) and shroud end (5) will
hang outside the fixture, so that these technological allowances (9) can be milled
off with the milling cutter without damaging the fixture and the tang height (6)
at the root end and the blade length (7) can be maintained as per drawing
requirement.
To maintain tang height (6) of blade (B) at root end (10), it is
necessary to keep this portion outside the fixture. But in new design blades, the
tang height was mostly less than 8 mm and that were fouling inside the fixture.
The existing locating fixture (E) was designed in such a way that only tang
height of 9 mm and more can be maintained in this fixture.
To maintain 8 mm or lesser tang height of blade in the existing
fixture (E), it required either to cut the fixture or to move the locating fixture
(11, 13) outside the fixture so that the blade tang height can be moved outside
and can be easily milled off without damaging the fixture.
The fixture cannot be cut and the existing locating fixture (11) was
fixed in the fixture. Only the solution left was to modify the locating fixture (11).
In order to find a solution to this problem, the portion of the clamp, where the
root slot of blade is taking reference, can be shifted outwards, so that the blade
tang height portion (12) can move outside the fixture. And this can be done only
by making new locating fixture (14).
The new locating fixture (14) was manufactured (Fig. 1) and fitted
in the main fixture (16) (Fig. 4). Now, the new design blades (19) having tang
height (6) less than 8 mm to 5 mm can be milled off in the present fixture.
As shown in Fig. 1, the locating pad (3) is shifted towards outward
direction, when the position (21) of the locator (3) is shifted to outer edge of the
bracket as shown in Fig. 3, so that the portion (20) to be milled is outside the
fixture and hence machinable. The extra material (technological allowances) (9)
provided on the blade root end is outside the fixture and that can be easily milled
off.
Fig. 4 shows a root locating fixture (14) and a shroud locating
fixture (15) with clamping piston (17) to clamp the blade (19). The clamping
position is shown in Fig. 3. Both fixtures are fixed to the main fixture body (16).
Technological allowances (9) refer to the extra material provided
on both end of blades (B) at the blank stage for the purpose of clamping of the
blank at both ends in the 5-axis machine for machining of blades. These extra
material (technological allowances 9) are milled off on other horizontal machining
centre machine to maintain the blade dimension.
The reference pad (3) of locating fixture (14) gives the reference to
the blade at the slot in such a way that the extra material (technological
allowances) at root end comes out of the fixture and that can be easily milled off
to maintain the Tang height (6) of the blade (B).
The locating fixture (14) gets assembled with the main fixture (16)
with the help of 4 bolts and is fixed rigidly. The locating fixture consists of a base
plate (1), vertical column (2) and locating pad (3).
WE CLAIM
1. Locating fixture (14) for root and shroud milling operation on HMC
machines to accommodate all sizes tang height of new design steam
turbine blade comprising
at least one root locating fixture (14);
Characterised in that,
the fixture (14) is fixed to the main fixture body (16) along with shroud
locating fixture (15) when the locating pad (3) is disposed in the locating
fixture (14) for providing reference to the blade (B) at the root slot (4) for
allowing the extra material (9) at root end disposed out of the fixture for
being milled easily for maintaining the tang height of the blade.
2. Locating fixture (14) as claimed in claim 1, wherein the said fixture is
assembled to the main fixture body (16) with a plurality of bolts.
3. Locating fixture (14) as claimed in claim 1, wherein locating pad (3)
accommodates turbine blades for milling and maintaining a tang height of
5 to 8 mm.
4. Locating fixture (14) as claimed in claim 1, wherein the locating fixture
(14) consists of a base plate (1), vertical column (2) and locating pad (3).

ABSTRACT

The locating fixtures (14, 15) for root and shroud milling operation
on HMC machines to accommodate all sizes tang height of new design steam
turbine blade consist of one root locating fixture (14) and one shroud locating
fixture (15). Both fixtures are fixed to the main fixture body (16) when the
locating pad (3) is disposed in the locating fixture (14) for providing reference to
the blade (B) at the root slot (4) for allowing the extramaterial (9) at root end
disposed out of the fixture for being milled easily for maintaining the tang height
of the blade.