FIELD OF INVENTION
The present invention relates to a mechanism to arrest vibrations during deep grooving machining of shafts of steam turbine blades. More particularly the invention relates to enhancing capability of existing tool holder for highly productive & vibration free cutting. It includes modification in the design and manufacturing a special mechanism to enable stronger mounting of grooving tools in grooving operation on rotor shaft to provide rigidity so that the higher cutting parameters can be used without any chattering, vibrations & line marks. This resulted in distinct advantages over conventional holding system, as existed on machine which do not have this provision.
BACKGROUND OF INVENTION
In machining of LP/HP/1P shafts of Steam Turbine blade T type groove machining is a very critical operation as these grooves are used for assembly of turbine blades on rotor. In HP rotor shaft, no. of stages of these blade grooves varies from 17 to 28 depending upon the design & rating of Steam Turbine. As there are many no. of stages, time taken in machining of these blade grooves is critical and takes major part of total cycle time of complete machining of such shafts on CNC lathe. Machining

operation for these T-type blade grooves takes substantial time for which suitable solutions are needed in order to result in total cycle time reduction.
The grooving tool holder used earlier have large overhang which makes the tool holder vibrate during machining. Because of vibrations the cutting parameters, used for machining, were very low to suit the machining. Quality of machined surfaces is also not satisfactory most of the times.
In view of above, it used to take very high machining time in carrying out the rough grooving operation. Time taken in machining of such grooves was high in previous method leading to less productivity.
Tool changing was required frequently which led to further delays.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a mechanism to arrest vibrations during deep grooving machining of shafts of steam turbine blades, which is capable of clamping grooving tool more rigidly to arrest vibrations.

Another object of the invention to propose a mechanism to arrest vibrations during deep grooving machining of shafts of steam turbine blades, which enables the tool to undergo higher cutting parameters without vibration.
A further object of the invention to propose a mechanism to arrest vibrations during deep grooving machining of shafts of steam turbine blades, which is able to improve productivity and quality.
A still another object of the invention to propose a mechanism to arrest vibrations during deep grooving machining of shafts of steam turbine blades, which is capable of reducing the process time for rough and finish machining of T grooves on a CNC lathe in shaft of steam turbine with lesser tool consumption and re-setting of tools.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.1 - Shows location of T-Grooves for blades in LP rotor.
Fig.2 - Shows standard shape of T-Groove.
Fig.3 - Shows existing tool and tool holder.
Fig. 3A- Shows existing tool
Fig.3B - Shows existing tool holder

Fig.4 - Shows developed grooving tool and tool holder according to invention.
Fig.4A - Shows the developed tool with added piece according to invention.
Fig. 4B - Shows the developed piece to be added to the existing tool.
Fig.5 - Shows a gap between tool and holder according to invention.
Fig.5A - Shows the slot cut on the face of the tool holder
Fig.5B - Shows taper wedges being fixed on the seat.
Fig.6 - Shows a seat prepared on tool holder according to invention.
Fig.7 - Shows the developed tool holder according to invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The object of the invention being vibration free machining and thus reduction of cycle time with improved quality on CNC lathe for rough and finish grooving of T grooves in shafts of Steam Turbine, new mechanism was developed & established with new CNC parametric program & existing tool holder.

The earlier grooving tool used for rough plunging of T grooves could run at lower cutting parameters. This process takes much time for roughing of Groove as the cutting parameter are very less such as cutting speed = 40-60 m/min and feed = 0.08 to 0.1 mm/rev. With even slight increase in cutting parameters, tool vibrates deteriorating machining performance & quality.
A new grooving tool was developed (Fig.3) and incorporated on the existing tool holder for highly productive machining. The new mechanism enabled to use very high cutting parameters such as cutting speed 75-90mm/min and feed of 0.15 to 0.22 mm/revolution during the rough machining of T groove. This reduced cycle time drastically with lesser tool consumption and requirement of re-setting of tools reduced substantially.
A new mechanism to add more rigidity and reduce vibrations, an extended piece (of length Y) was welded to protrude part of the tool.
A protrusion of length Y is added as shown in the fig. 4A above. Y is equal to 0.75X. The developed piece D was welded to the original tool (T). The piece length was kept at 0.75X. The length was chosen to be 0.75X as this was the optimum length which could control the vibrations. Extra length would add to the weight of the tool. The developed tool after welding is shown in the fig.4A. The added piece will reduce the vibrations in the vertical direction as more mass will make it sturdy.

As shown in the figure 4B a separate piece was made as per the existing profile of the tool and then welded on to the tool. Once the trials were over a new integrated tool was developed.
A gap is being formed because of unevenness on the surface of the tool and tool holder. Even grinding both the surface after numerous times a small gap always exists. Even if the tool is pushed back till the extreme the gap still persists.
To fill up gap as shown in Fig.5, a set of taper wedges was fixed between tool holder bottom face & tool. This required making of seat on tool holder. Suitable tapered set was prepared and fitted between seat on holder and tool. (Fig.6)
In the step 1 a seat of length of 0.75X is made on the original tool. This length is made equal to the extra length added in the tool.
In the step 2taper wedge is fixed on the seat.
The wedges ‘a’ and ‘b’ are tapered. If the wedge is moved away from the surface it pushes wedge b which in turn eliminates the gap between holder and the cassette.
When we tighten taper wedge with its forward movement, it tightens tool's bottom face against tool holder, thus integrating tool holder with tool with high rigidity.

This new mechanism totally eliminates the vibrations thereby allowing us to use higher cutting parameters for machining rotor slots. This development shall be suitable for all grooving tools of similar design and even for turning tools with large overhangs. With this development no vibrations were observed and the grooving could be done at higher cutting parameters without any interruption. The cutting parameters used were cutting speed 90m/min, feed 0.22 mm/rev, compared to the earlier cutting speed of 40m/min and feed of 0.08 mm/rev.
Advantages and benefits
The following are the advantages and benefits accrued after improving the tool and tool holder design.
1) Productivity: Total machining time of rotor shafts on CNC Lathe reduced substantially.
2) Financial Benefit: As cycle time is reduced critical CNC machine availability is increased to take up more nos. of rotors.
3) Power Saving: Overall Productivity & Utilization of machine is increased hence power consumption was reduced.
4) Quality: With use of new mechanism, improved process and tools, quality of machining is also improved.

5) Health and working condition: As clamping and unclamping was reduced so machine operators were less fatigue.
6) Financial Saving: Time saved in machining of 1 Groove =1.8 hrs
Time saved in machining of all grooves of the shaft =20*1.8=36.0 hrs/shaft
Machining Cost = Rs. 6500 per hour. Total saving = 6500X36 = Rs. 2,34,000. Average No. Of shaft machined per year = 6 Total saving per year = 2,34,000x6 = Rs. 14,04,000 = 14.04 lacs.
7) Elimination of frequent insert changes due to vibrations
This process eliminates the frequent requirement of changing inserts due to breakage from vibrations. This in turn reduces the machining cost. Also this eliminates errors and rectification which may creep in due to frequent tool change and tool setting.
8) Tool Safety
As tool and its holder having improved geometry was used, this was much convenient and safer. Previously, due to vibrations it is unsafe to carry out machining as there were always chances of tool breakage.

WE CLAIM
1. A Mechanism to arrest vibrations during deep grooving machining of shafts of
steam turbine blades, the said mechanism comprising the step of;
arranging a separate piece (D) in accordance with existing profile of a grooving tool (T);
welding the piece (D) of optimum length ‘Y’ to the original tool (T) to arrest vibration, during machining;
forming a seats of length ‘Y’ on the original tool where the said length made equal to the extra length added in the tool; wherein
tapered wedges ‘a’ and ‘b’ are fixed in the slot(s) between tool holder bottom face and tool such that tightening the taper wedge with its forward movement, the bottom face of the tool is tightened against tool holder (H) integrating the tool holder (H) with tool (T) with high rigidity to arrest vibration of the tool (T) during machining.
2. The mechanism to arrest vibration as claimed in claim 1, wherein length ‘Y’ is
made equal to 0.75X where X is the length of the original tool (T).