FIELD OF INVENTION
The invention relates to the process improvement for manufacturing of 250 MW,
T4-25, Bar type Steam Turbine blades. More particularly the invention relates to
improved process for groove milling and step milling on root of bar type moving
blades using fixture with a new developed clamp.
BACKGROUND OF THE INVENTION
Previously there was a large amount of rework and rejection in the process of
groove milling and step milling on root of T4-25 bar type blades of 250 MW. It
was necessary to develop a new process to minimize the nonconformance in
groove milling operation and to improve the accuracy and quality of groove. With
this invention, the rework and rejection considerably reduced.
As per the existing arrangement the blades were machined using milling fixture
where due to inadequate pressing and holding during horizontal milling, locating
of the job was inaccurate as it was with reference to shroud in place of desired
reference plane at the root of the blade.
Added to this, the magnetic chuck arrangement also had its problems due to
following reasons.
1. Inadequate magnetic holding power due to demagnetization of the chuck over
a continuous use.
2. The job gets inaccurately machined due to shifting away during root milling
operation.
Due to this inherent problem (i.e. due to inadequate holding of blades) in earlier
process step, there was variation in the step milling operation.

OBJECTS OF THE INVENTION
It is therefore the objects of the invention to develop an improved process for
groove milling and step milling on root of steam turbine blades which will
minimize the non conformance in groove milling operation.
Another object of the invention is to develop an improved process for groove
milling and step milling on root of steam turbine blades which will reduce the
rework/ rectification work to a considerable extent
A further object of the invention is to develop an improved process for groove
milling and step milling on root of steam turbine blades which will improve the
productivity.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1- Step Milling of Root on Magnetic check in the prior art.
Figure 2 - Groove milling on shroud copy milling operation fixture in the prior
art.
Figure 3 - Groove milling on perpendicular milling fixture according to the
invention.
Figure 4 - Step milling of Root on perpendicular milling fixture.
Figure 5 - Newly developed clamp.
Figure 6 - The arrangement of clamping of blade in the newly developed clamp.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
A new clamp has been developed to take care and to overcome the inherent
problems of step milling and groove milling operations of steam turbine blades.
Figure (3) shows the detailed description of the fixture.
Clamp (1) to press/ hold the blade (4) has been developed. This clamp (1)
properly press/ hold the blade (4) from both the ends Root and shroud of blade.
Support for location (2) is provided to facilitate proper reference from root end
of blade during groove milling (fig. 3) as well as step milling (fig. 4) processes.
Self explanatory process sketches have been shown in figure 3 for groove
milling of Bar Type blade and in Fig. 4 for step milling, the newly developed
clamp (1) in figure 5.
The improved process of groove milling (fig. 3) and step milling (fig. 4) also
indicate the arrangement of arbor (3) and cutter (4).
Figure (5) shows the developed clamp (1) and figure (6) shows the arrangement
of clamping/ holding with the blade.

WE CLAIM:
1. An improved process for Root Groove Milling and Root step milling of steam
turbine blades (5) comprising:
- placing the steam turbine blade (5) on the fixture;
- adjusting the blades (5) such that the root side of the blade takes location
from the support location (2);
- placing the clamp (1) over the blade (5) from the top side of the blade
and tightening the clamp (1) ensuring proper gripping of the blade (5);

- bringing the cutter from the root side with arbor in the vertical position for
performing the groove milling operation;
- removing the grooving tool, loading the milling cutter and bringing the
cutter to the root side for performing step milling operation and bringing the
cutter to the root side again to perform step milling operation;
2. The process as claimed in claim 1 where the steam turbine blade (5) is held
by a newly developed clamp (1).

ABSTRACT

The invention relates to an improved process for groove milling and step milling
on root of 250 mw, T4-25 bar type steam turbine blade by clamping with a newly
developed clamp.
The arrangement comprises holding and clamping the blade by the device,
locating the blade from the root side by support location and performing the
operation groove milling and step milling of root.