FIELD OF INVENTION
The present invention relates to an attachment with self adjusting pad system
for radius milling operation of root and shroud of turbine blade in CNC horizontal machining
centre for a wide range of blade rhomboid angles and a method for the same.
BACKGROUND OF THE INVENTION
Root and shroud of a turbine blade are the two critical areas of a turbine
blade. For radius milling of root and shroud, alignment of the blades with the spindle's axis
is extremely important and has an effect on blade dimensions. For making different blades,
the adjustment of height of blade axis and alignment of the same is extremely important.
For the present fixture, root and shroud pads of complicated designs are manufactured for
different blades and rhomboid angles for the purpose of radius machining of the root and
shrouds of the blades.
Hence, there exist a need to invent an arrangement which can eliminate the
disadvantages of the prior art. During blade machining, for the aforesaid arrangement, for
individual blade, root and shroud pads are designed according to height and rhomboid
angle of the blade which consumes much material and machining time as well as man
hours. In BHEL HARIDWAR New Blade Shop, steam turbine blades are manufactured in 5
axis machines and the radius of root and shroud of the blades are achieved by Root and
Shroud milling in 4 axes horizontal single Spindle CNC Machines. The fixture arrangement
is schematically shown in Fig 1A and IB.
In present fixture, the blades are clamped with the help of the followings:
As shown in Fig 1A and IB, the items used in the fixture are,
• Changeable pad at root
• Changeable pad at shroud

• Root locator
• Shroud locator
• Root and shroud top thrust pieces
• Front thrust pieces
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an attachment with self
adjusting pad system for radius milling operation of root and shroud of turbine blade in
CNC 4 axis horizontal machining centre for a wide range of blade rhomboid angles and a
method for the same which is capable of operating on various rhomboid angles of blades.
Another object of the invention is to propose an attachment with self
adjusting pad system for milling operation of root and shroud of turbine blade in CNC 4
axis horizontal machining centre for a wide range of blade rhomboid angles and a method
for the same which is able to reduce consumption of materials, machining time and man-
hours.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig. 1A - Shows the fixture with changeable pad at root (R) according to the prior art.
Fig. 1B - Shows the fixture with changeable pad at shroud (S) according to the prior
arts.
Fig. 2 - Shows the isometric view of an attachment to the present fixture according
to the invention.
Fig. 3A - Shows a modified angle block according to the invention
Fig. 3B - Shows modified angle block according to the invention
Fig. 3C - Shows a modified angle block according to the invention

Fig. 4A and 4B - Shows a changeable base plate according to the invention
Fig. 5A and Fig. 5B - Shows an angle adjuster system holder according to the invention.
Fig. 6A and 6B - Shows an angle adjustment system.
Fig. 7A and 7B - Shows root, shroud, exit edge and rhomboid angle of a steam turbine
blade.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Fig. 2 Shows the isometric view of an attachment (A) which consists of the
following.
i) Modified angle block (1)
ii) Changeable base plate (2)
iii) angle adjuster system holder (3)
iv) angle adjustment system (4)
This attachment (A) is fixed to the fixture base. The attachment (A) consists
of an angle block (1) which is bolted to the fixture base. The changeable base plate (2)
rests on a rectangular plate of same length and Breadth as that of the angle block (1)
resting surface, and of 5mm thickness which is placed in between angle block (1) holding
surface and changeable base plate (2) to prevent wear and tear of the said base plate (2).
The rectangular plate is not shown in the drawing. The changeable base plate (2) is bolted
in the main assembly. The base plate height is precalculated according to blade drawing
and fixture axis location. Hence the changeable base plate is of variable heights according
to different blades. The changeable base plate is manufactured for height adjustment for
different blades. Angle adjustment system holder (3) is similarly be fastened by Grub
screws as shown in the assembly/attachment (A). The angle adjustment system (4) is
fitted on angle adjustment system holder (3) which is capable of rotating around the axis
of the angle adjustment system (4)

upto 10 degrees each direction (clockwise and anticlockwise). This feature covers blade
rhomboid angles ranging from 23 to 35 degrees.
The above arrangement is done for both root and shroud holding purpose of
the fixture. Now, the blade is rested upon the angle adjustment system (4). The exit edge
(5) as shown in fig. 7A of the blade is placed in such a way that it faces the locators (Root
and shroud locators 6 and 7 respectively). The initial axial rotation of angle adjustment
system (4) is now restricted to 10 degrees. Now as the front thrust piece (8) thrusts the
blade root (9) and shroud (10), the blade automatically is aligned according to the
rhomboid angle (11) and takes support from root and shroud locators (6 and 7). Now as
the top thrust pieces at root and shroud sides in the fixture (8) approach from the top,
causing the blade to be locked as desired for machining.
The arrangement/attachment is used for wide range of blade rhomboid angles
i.e. 23 degrees to 35 degrees. The changeable base plate (2) is used for height adjustment
for different blades.

WE CLAIM
1. An attachment (A) with self adjusting pad system for radius milling operation of root
and shroud of turbine blade in CNC horizontal machining centre for a wide range of
blade rhomboid angles comprising;
a plurality of angle blocks (1) bolted to the fixture base.
a changeable base plate (2) placed on the angle block (1) and bolted on the said
block;
a rectangular plate of same length and Breadth as that of a angle block (1) resting
surface placed in between angle block holding surface and changeable base plate
(2) for preventing wear and tear of the said base plate (2);
an angle adjustment system holder (3) fixed on the said base plate (2);
wherein an angle adjustment system (4) is disposed on the said angle adjustment
system holder (3) for enabling it to rotate around the axis of the angle adjustment
system (4) upto 10 degrees each direction of clockwise and anticlockwise for
covering blade rhomboid angles ranging from 23 to 35 degrees for holding both root
and shroud of the blade in the fixture.
2. The attachment as claimed in claim 1, wherein the height of the changeable base
plate is precalculated according to the blade drawing and fixture axis locations.
3. A method of radius milling root and shroud of the turbine blade with an attachment
(A) claimed in claim 1 comprising;
fixing the angle blocks (1) on to the fixture base;
placing and bolting a changeable base plate (2) on the angle block (1);
putting an angle adjustment system holder (3) on the said base plate;
placing an angle adjustment system (4) on the said angle adjustment system holder
(3) to enable it to rotate around the axis of the angle adjustment system (4) upto
10 degrees each direction of clockwise and anticlockwise to cover blade rhomboid

angles ranging from 23 to 35 degrees to hold both root and shroud of the blade in
the fixture;
wherein the blade is rested upon the angle adjustment system (4) with the exit edge
of the blade being placed facing the root and shroud locators when initial axial
rotation of angle adjustment system being restricted to 10 degrees and when a front
thrust piece (8) thrusts the blade root and shroud to make the blade automatically
aligned according to the rhomboid angle taking support from root and shroud
locators (6, 7) wherein the thrust pieces at root and shroud ends of fixture (8)
approaches from the top and clamps the root and shroud of the blade from top
causing the blade to be locked for the machining.

ABSTRACT

The invention relates to an attachment (A) used in a fixture for radius milling
operation of root and shroud of turbine blade. The attachment consists of a plurality of
angle blocks (1) bolted to the fixture base, a changeable base plate (2) is bolted on the
angle block, an angle adjustment system holder is fixed on the base plate (2) and an angle
adjustment system (4) is disposed on the said angle adjustment system holder (3) enabling
it to rotate around the axis of the angle adjustment system (4) upto 10 degrees each
direction of clockwise and anticlockwise covering blade rhomboid angles ranging from 23 to
35 degrees for holding both root and shroud of the blade in the fixture.