FIELD OF INVENTION
The present invention relates to a 5-axis machining method for
pelton hydro turbine wheel in a single set up. More particularly the invention
relates to the special job holding fixture and methodology used for the 5-Axis
scoop milling of the Pelton Hydro Turbines from a single forged blank on the
suitable 5-Axis machine tool with rotary indexing table with both sides tilting head
configuration.
BACKGROUND OF THE INVENTION
Hydro Turbines are classified as Pelton wheel, Francis turbine, Kaplan
turbine and Hydro Pump Runners. In order to test the performance of designed
Hydro Turbines, tests are conducted on scaled down turbine models in Hydro Lab,
to demonstrate it to the customers. Pelton wheel is very critical because of its
complex & intricate shape of cups. The quality of the Pelton wheel decides the
overall performance of the Hydro Turbine Model. At present, it is being
manufactured using 3-Axis machines by machining each cup separately and
assembling them on a common hub. This process is cumbersome and involves
manual intervention. Due to this, the quality, strength & consistency of the Pelton
wheel is being adversely affected and the best performance is not being achieved.

However, this can be manufactured from a single blank using scoop milling
technology of 5-Axis CNC machining. This makes above component more complex
to manufacture from a single piece and in a single layout.
During the search of the patents (EP3208457A1 and
DE102016207879A1), it is observed that, discrete information about Impeller for
Pelton wheel and Pelton wheel are available. The patents have mentioned about
making of Pelton wheels in two different methods. None of them have described
anything about making a Pelton wheel from a single blank using scoop milling
technique on a suitable 5 axis CNC milling machine. There is no patent found in
the search that the Pelton Hydro Turbine wheel is 5-Axis scoop machined in a
single layout on the 5-Axis machine with rotary indexing table and both sides
tilting head, as proposed in the current invention.
Earlier two processes were being followed: First one, for smaller size
wheels, each cup is separately machined on a 3 axis CNC machine & assembled
on a common hub (time consuming, poor accuracies and material wastage) and
the second one, for larger size wheels, sand castings are made with the help of
patterns and the profiles are matched with manual grinding process using profile
templates (laborious and poor accuracies).
The single layout Scoop Milling Technology is developed for the Pelton

Hydro Turbine wheel. These Pelton Hydro Turbine wheelare machined on the
Chiron 5-Axis Machine with a rotary indexing table with both sides tilting head
configuration. The 5-Axis CNC part programs have been developed using the
Siemens NX CAM package for roughing, semi finishing and finishing of single forged
blanks. The special Modular and Bulb/Lollypop Cutters are used for the intricate
surface machining.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a 5-axis
machining method for pelton hydro turbine wheel in a single set up which is
capable of achieving better dimensional quality, cycle time reduction, process
repeatability avoiding multiple fixture lay out.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure-1: shows a view of the single layout 5-Axis scoop milling of the Pelton
Hydro Turbine wheel from the right side on the 5-Axis machine with
rotary indexing table with both sides tilting head configuration,
according to the invention.
Figure-2: shows a view of the single layout 5-Axis scoop milling of the Pelton

Hydro Turbine wheelfrom the left side on the 5-Axis machine with
rotary indexing table with both sides tilting head configuration,
according to the invention.
Figure-3: shows individual cup of Pelton wheel each separately machined in
Prior Arts.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The present invention relates to the special job holding fixture and
methodology used for the 5-Axis scoop milling of the integrally cupped Pelton
Hydro Turbine wheelfrom a single forged blank on the suitable 5-Axis machine
tool with rotary indexing table with both sides tilting head configuration.
In order to achieve better profile tolerances, cycle time reduction,
process repeatability and for achieving higher performance, it is thought of
machining on a 5-Axis CNC machine.
The fixture is designed in such a way that the total component can
be machined in single setup, where in the component can be held to the rotary
table and gives the proper tool approach for 5-Axis machining.

Scoop milling is a specialised process / programming capability of
extracting material from a passage where there is only two entries from inlet and
outlet sides. Since there is only restricted entries, there will be only plunging into
the material directly, which gives rise to harsh cutting forces. Necessary care and
suitable tools are to be selected in order to avoid collision and retract of the tool.
To avoid these conditions special programming and cutting methods are to be
used. Hence Scoop Milling process is a special cutting process.
In the embodiment of the present invention, the single layout
method consists of 5-Axis machine table 1 which moves in the X, Y and Z
directions linearly. On this table 1, the rotary indexing table 2 is mounted, which
rotates about X-axis, Clockwise positive A angle and counter clockwise negative A
angle. And this Rotary Table 2 rotates continuous + or - 360 degrees and it is a
roll over axis. On the Face plate 3 of the Rotary Table 2, the fixture plate 4 is
mounted with help of two locating pins 15 on this fixture plate 4, the Pelton
Hydro Turbine wheelblank 7 is mounted by locating with the help of two pins 14
which made in the extra holding plate 8 of the Pelton Hydro Turbine wheelblank
7. The both sides tilting head 9 of the 5-Axis machine can rotate about Y-axis
clockwise +110 degrees to counter clock wise -110 degrees. This titling head 9
consists of Tool Holder 11, which holds the multi master cutting tool shank 11.

This shank can accommodate different kinds of cutting tool heads 12 of different
forms based on the type of machining such as rough, semi-finish and finish
machining.
In the embodiment of the present invention, the Pelton Hydro
Turbine wheel 5, consisting of 22 nos. of integral Pelton Hydro Turbine wheel 6
cups, is to be 5-Axis scoop machined from a single forged blank 7. To
accommodate on the machine in a single layout extra holding plate 8 is included
in the forged blank 7. This forged blank 7 is held with the help of holding plate 8,
locating pins 14 and fixture plate 4 on to the face plate 3 of the rotary table 2.
Suitable 5-Axis CNC programs generated for machining of the right side 13 and
left side 16 Passages to cover the entire integrally cupped passages such as right
side area, left side area of Pelton Hydro Turbine wheel. These 5-Axis CNC
programs are developed with different configurations of the cutting tool heads 12
covering rough, semi-finish and finish machining with Flat end mill, Bull nose,
Tapered ball nose, Tapered bull nose, Lollypop, Bulb etc...forms. By running the
above CNC programs, machining from both right & left side passages and using
the above mentioned cutting tools, the total Pelton Hydro Turbine wheel 5 is
machined in a single layout on the 5-Axis machine with rotary indexing table 2 &
both sides tilting head 9.

WE CLAIM
1. A 5-Axis machining method for Pelton Hydro turbine wheel in a single set up,
the method comprising;
accommodating an extra holding plate (8) in a forged blank to hold the
said blank by means of locating pins (14) and a fixture plate (4);
arranging the fixture plate (4) to mount with two locating pins (15) on the
rotary indexing table (2) mounted on a table (1) capable of moving in X, Y and
Z direction and capable of rotating from 0o to 360o wherein
a 5-Axis CNC program is developed with different configuration of the
cutting tool heads (12) disposed on a both sides titlting head (9) of the 5-Axis
machine capable of rotating about Y-axis clockwise +110 degrees to counter
clock wise -110 degrees wherein the tilting head (9) having tool holder (11) to
hold different tool heads (12) for rough, semi-finish and finish machining,
moves according to developed program machining from both right (13) and
left side passages (16) with various cutting tools machining total Pelton Hydro
turbine wheel (5) in a single layout on the 5-Axis machine.

2. The 5-Axis machining method as claimed in claim 1 wherein, 22 numbers of
Integral Pelton hydro turbine wheel cups (6) are machined by 5-axis scoop
milling method from a single forged blank (7).