Field of invention:
The present invention relates to design and development of a fixture for root base and tennon milling in one setup in horizontal milling machine as well as vertical milling machine with facility to orient the spindle in horizontal position. More particularly the present invention relates to a fixture for root base and tennon milling of steam turbine blades in single setup.
BACKGROUND OF THE INVENTION:-
In the present practice, the root and tennon milling are done in conventional milling machines in different set up. The blades are milled with technical allowance at both sides of root and tenon sides of the blades for holding. Root base is a flat surface which can not be machined in the five axis machine because of the technological allowance. Similarly tennon and radius on the tennon (fig.11) can not be made due to the reason that it is not possible for tool approach and technical allowance. After axis machining, the technological allowances are cut by band saw blade (in fig. 2). In the existing practice, the blades after cutting at band saw, were taken and clamped horizontally at first with a vice root base milling using manual milling machine. After this the blades were taken to a manual vertical milling machine where blades were to be clamped vertically with a fixture arrangement and tennon milling used to be completed. This process was consuming much more cycle time with more rejection rate.

Objective of the invention:-
The objective of the invention is to develop a fixture that can ensure roots and tennon milling of steam turbine blade in one set up in CNC horizontal and CNC vertical milling machine.
Another object of the invention is to develop a fixture for root base and tennon milling of steam turbine blades in single set up that reduces cycle time of production as well as reducing rejection rate.
Summary of the invention:-
To complete the drawing requirement at root base and blade tip, the fixture has been developed which hold the component during machining.
The fixture is used to align the blades as per blade axis so that the blade axis remains horizontal to the machine table surface as well as the blade axis lie collinear with the spindle axis during root base and tennon machining.
The fixture is used to hold the component during machining in the horizontal as well as vertical machines.
The fixture comprises an assembly (1) which further comprises subassemblies a holding fixture (3), a base plate (2), a profile pad (4), root locator exit edge (5), a root locator inlet edge (6), a taper pad for root (7), a top clamp 2 (8), a top clamp 2 (9), a upper clamp (10), a Turbine Blade (11).

Brief description of the accompanying drawings:-
Complete assembly (1) Fig.1 (Part-1), Fig.1 (Part-2) and Fig.1
(Part-3)
Base plate (2) Fig. 2
Holding fixture (3) --Fig.3
Profile pad (4) Fig. 4
Root locator exit edge (5) Fig 5
Root locator inlet edge (6) Fig. 6
Taper pad for root (7) Fig. 7
Top clamp (8) Fig. 8
Top clamp 2 (9) Fig. 9
Upper clamp (10) Fig. 10)
Turbine Blade (11) Fig. 11
Milled blade with technological allowance after CNC 5 Axis Milling – Fig 12
Technological allowance removal in Band saw machine – Fig 13
Blade with technological allowance removed Fig. 14
Blade loaded in Fixture on machine table Fig. 15
Finish blade Fig 16

Detailed description of a preferred embodiment of the invention:-
The blade from CNC 5 Axis milling machines are cut at root and blade tip for technological allowance removal in band saw machine (Ref Fig 12, 13, 14) respectively.
The base plate (2) is fastened with proper bolts into the holding fixture (3). The taper pad (7) for root is fastened with proper bolts to the base plate (2) (the taper of the taper plane ‘A’ as shown in fig. 7, is designed according to the root taper angle as shown in fig. 11. The blade (11) is aligned so that the blade axis remains horizontal to the machine table surface as well as the axis lie collinear with the spindle axis during root base and tennon machining . The Root locator exit edge (5) and Root locator inlet edge (6) are fastened on the Taper pad for root (7) and are designed according to the root dimension such that when blade is fitted, these restrict side wide and axial movement towards direction of root.
In this process pressure side (Ref Fig. 11) faces down on the profile pad (4) and taper pad for root (7). The distance of the profile pad (4) from the root taper pad (7) along the blade axis is determined as per the distance of the section ‘DD’ of the blade from section ‘AA’ as shown in Fig. 11. The profile pad (4) height and contoured surface is determined from the co ordinates given for pressure side of blade profile at section to be supported (in this case section ‘DD’ Ref Fig 11).
As the blade (11) is rested on the pads, Top clamp (8) and top clamp (9) are used to lock the blade from the top with upper clamp (fig 10) to completely prevent axial movement of the blade (11) the locking is ensured by suitable measure of nuts and adjusting bolts as shown in fig. 15 at sheet.
The machining of the root base for facing to generate perpendicular root

base is done. The blade tip is milled to machine the blade tennon as per drawing requirement. Machined blade is shown in fig. 16.
The present process is adopted for other various types of similar types of blades by changing dimensions and locations for the followings as required by the blade drawings:
i. Profile pad
ii. Root locator exit edge
ii. Root locator inlet edge
iv. Taper pad for root.
v. Upper clamp (10)

We claim:-
1. A fixture for root base and tennon milling of steam turbine blades in single setup comprising:
a base plate (2) assembled on a holding fixture (3);
a profile pad (4) fixed on the rear side of the assembly for supporting the tennon side of steam turbine blade blank (11);
a taper pad for root (7) fixed on the front side of the assembly for supporting the head of steam turbine blade blank (11);
a root locator exit edge (5) and a root locator inlet edge (6) assembled over taper pad for root (7) ; wherein top champs (1, 2) with the help of upper clamp (10) rigidly holds and locks the steam turbine blade blanks (11) during machining operation.