FIELD OF THE INVENTION
The invention relates to development of universal clamping fixture for clamping
of freestanding blades of low pressure steam turbine for tip milling during fir tree
root machining on CNC horizontal machining centre. More particularly the
invention relates to development of universal clamping fixture for clamping of
large size freestanding low pressure steam turbine blades profile at tip end of
210,250,500 MW rating for root and tip milling in single setting.
BACKGROUND OF THE INVENTION
Machining of fir tree freestanding low pressure steam turbine blades is carried
out in horizontal machining centre. The casting of precision forging is done in a
box for the purpose of clamping a blade in the fixture and for fir tree root
machining. Then the casting is melted and blade is taken out of box for further
operations.
The length cutting, tip copying and tip thinning is carried out on different
machines.
Due to manufacturing of blade in different settings, sometimes height variation
may take place and natural frequency of these blades gets varied. The problem
of height and frequency variation of turbine blade has been reported during
assembly operations.
OBJECTS OF THE INVENTION:
It is therefore the object of the invention to propose development of universal
clamping fixture for clamping of freestanding blades of low pressure steam

turbine for tip milling during fir tree root machining on CNC horizontal machining
centre which can accommodate the freestanding blades for root and tip milling in
single setting.
Another object of the invention is to propose development of universal clamping
fixture for clamping of freestanding blades of low pressure steam turbine for tip
milling during fir tree root machining on CNC horizontal machining centre to
ensure easy machining.
A further object of the invention is to propose development of universal clamping
fixture for clamping of freestanding blades of low pressure steam turbine for tip
milling during fir tree root machining on CNC horizontal machining centre which
maintains blades length for proper rotation drop of frequency during assembly.
Another object of the invention is to propose development of universal clamping
fixture for clamping of freestanding blades of low pressure steam turbine for tip
milling during fir tree root machining on CNC horizontal machining centre which
will reduce the cycle time of fir tree blade machining.
A still further object of the invention is to propose development of universal
clamping fixture for clamping of freestanding blades of low pressure steam
turbine for tip milling during fir tree root machining on CNC horizontal machining
centre which will provide a support to blade profile while machining thus
providing better machining accuracy.
SUMMARY OF THE INVENTION
Accordingly, there is provided a universal clamping fixture for clamping and
holding the blade profile during tip milling on horizontal machining centre
comprising mainly:

a) Fixture Base (1)
b) Fixture block (2)
c) Blade profile resting pad (3)
d) Dowel pin 2 No (4)
e) Screw (5)
f) Top Clamp (6)
g) Swivel type clamp (6A)
h) Bolt (7)
i) Nut (8)
j) Key (9)
k) Blade forging with casting (10)
During fir tree root machining the blade casting is held in a fixture. The blade is
cast near the root and the casting is done in such a manner that the centre axis
of blade lies horizontally. For tip milling, the external profile of blade (10) is
positioned on blade profile resting pad (3) at particular section. The Blade profile
resting pad (3) is mounted on the fixture block (2) with two Dowel pins (4) and
one screw (5). The fixture can move along the blade axis to match the profile at
required section of each type of blade. The Top clamp (6) is positioned with the
bolt (7) and Nut (8).
To match the profile at different section for different type of blades, the height of
the profile resting pad (3) is adjusted as per required section maintaining the
favorable machining conditions.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 (sheet no. 1) shows the Assembly sketch of universal profile clamping
fixture (11) for Tip milling during root machining of LP freestanding blades of
Steam turbine on CNC horizontal machining centre according to present
invention.

Fig. 2 (sheet no.2) shows the sketch of fixture base (1) of the universal profile
clamping fixture (11).
Fig. 3 (sheet no.3) shows the sketch of fixture block (2) of the universal profile
clamping fixture. (11).
Fig.4 (sheet no. 4) shows the sketch of blade profile resting pad (3) which has
two holes for two no dowel pins (4) and one threaded hole for tightening the
profile resting pad with fixture block (2).
Fig.5 (sheet no. 5) shows the sketch of top clamp (5).
Fig. 6 (sheet no. 6) shows the sketch of Swivel type clamp (6A). It is having the
swivel type clamp which can be adjusted as per any blade profile.
Fig.7 (sheet no. 7) shows the sketch of Key (9).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF
THE PRESENT INVENTION
Figure 1, shows the universal profile clamping fixture for Tip milling during root
machining of LP freestanding blades of Steam turbine on CNC horizontal
machining centre, which comprises Fixture base (1), Fixture block (2), Profile
resting pad (3), Dowel pin 2 No (4), Screw (5), Top Clamp (6), Bolt (7) and Nut
(8)
The Fixture block (2) is clamped on the Fixture base (1) with the key and
Screws. The Profile Resting pad (3) mounted on Fixture block (2) with the help
of Dowel pins (4) and Screw (5) on which the external profile of blade rest. The
Top clamp (6) is mounted on fixture block (2) with the help of Nut (8) and blot

(7). The Top clamp (6) is having a swivel type clamp (6A) which can be adjusted
as per blade profile during clamping. The Top clamp (6) is tightened by Lever
type mechanism. To achieve the favorable machining conditions, the fixture is
moved back and forward on machine table with the help of Guide key (9) in such
a manner, that centre axis of blade and fixture remain ideal.

WE CLAIM
1. Development of universal clamping fixture (11) for clamping of freestanding
blades (10) of low pressure steam turbine for tip milling during fir tree root
machining on CNC horizontal machining centre comprising:
- a fixture block (2); a blade profile resting pad (3) is mounted on the fixture
block (2) with plurality of dowel pins (4) and a screw (5); the fixture block
(2) is mounted over fixture base (1) with the help of key and screws;
- a top clamp (6) is mounted over the fixture block (2) with the help of nut
and bolt; the top clamp (6) comprises a Swivel type clamp (64)
characterized in that
- the swivel clamp (6A) can be adjusted to accommodate the blade profile
during clamping wherein the fixture can be moved back and forward on
machine table with the help of guided key (9) to match the blade profile.

2. The clamping fixture (11) as claimed in claim 1, wherein the profile resting
pad (3) and swivel clamp (6) are hardened.
3. The clamping fixture (11) as claimed in claim 1 wherein the axis of the blade
lies horizontally when casting box 'b' is held in root machining fixture
and profile on universal clamping fixture.
4. The clamping fixture (11) as claimed in claim 1 where the height of the profile
resting pad (3) can be adjusted in order to match the profile at different
sections for different type of blades.
5. An universal clamping fixture as substantially described and illustrated herein
with reference to the accompanying drawings.

ABSTRACT

Development of universal clamping fixture (11) for clamping of freestanding
blades of low pressure steam turbine for tip milling during fir tree root machining
on CNC horizontal machining centre comprising a fixture block (2), a blade profile
resting pad (3) is mounted on the fixture block (2) with plurality of dowel pins
(4) and a screw (5); the fixture block (2) is mounted over fixture base (1) with
the help of key and screws; a top clamp (6) is mounted over the fixture block (2)
with the help of nut and bolt; the top clamp (6) comprises a Swivel type clamp
(6A) characterized in that the swivel clamp (6A), can be adjusted to
accommodate the blade profile during clamping wherein the fixture can be
moved back and forward on machine table with the help of guided key (9) in
such a manner that the centre axis of blade and fixture remains ideal.