FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See Section 10; rule 13)
TITLE OF THE INVENTION
A Cutting tool
APPLICANTS
TATA MOTORS LIMITED, an Indian company
Having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Mr. Choudhary Sanjay B, Mr. Narade Subhash A and Mr. Dali Vinayak G
All Indian Nationals
of TATA MOTORS LIMITED,
An Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
Preamble to the description The following specification particularly describes the invention and the manner in
which it is to be performed.

Field of invention
This invention is related to a cutting tool capable of Hypoid gear cutting and sequential Profile Tip chamfering.
Background of the invention
Crown wheel & Bevel pinion is used for transmission of power from Propeller shaft to live axle driven wheels in automobiles. Crown wheel teeth are cut on Hypoid gear generators based on Continuous Hobbing principle. Special cutter body as shown in figure 1 is required for this type of gear generation. The cutter (A) comprises five sets of blades (a to e), with three blades in each set (B, C & D). Each set has one rougher blade (D) and two finishing blades (B and C) one for inside profile and one for outside profile of the gear tooth. Heat treatment follows gear cutting to increase wear resistance and fatigue strength to withstand vehicle dynamic load conditions. The tip chamfer operation on hypoid gears is traditionally done after heat treatment by pneumatic hand grinder. This tip chamfering operation is prerequisite before lapping and testing for removing High points which if not removed might add undesirable noise and vibrations for rear axle. The chamfer created by hand pneumatic grinder is-subject to vary as per the force applied by operator while chamfering. So, it is very unlikely to have constant chamfer on all teeth of crown wheel on both flanges (inner & outer or drive & coast). In addition to that, Manual Labor hours, Tools Cost, Grinding Wheel Cost, Compressed air Cost, increased work in Progress (WIP) after heat treatment are other cost contributing factors to this operation.
Summary of the Invention:-
It is there for an object of the present invention to overcome the disadvantages mentioned in the background.
Another object of the present invention is to combine the chamfering operation of the crown wheel teeth simultaneously with the teeth cutting process.
Yet another object of the present invention is to lessen the time taken and reduce the cost involved for separate hard chamfering process following heat treatment of crown wheels by using a pneumatic grinder manually.

Yet another object of the invention is to bring in consistency in the chamfering of the teeth, by having a chamfering blade controlled mechanically rather than having a manually controlled pneumatic operated grinder.
The objects are achieved by replacing one of inner and outer finishing blades with new designed chamfering blade. This is attempted with the introduction of a triangular insert chamfering blade in the place of one of the Inner finisher and outer finisher blades of the existing tool model.
According to the present invention cutting tool comprising a cutter body with plurality of sets of blades wherein each set having at least one blade selected from a group of cutting, inner finishing, outer finishing, inner chamfering and outer chamfering blades.
Brief description of the Drawings
Figure 1 shows the cutter body with the regular tool arrangements.
Figure 2 shows the plan and left side view, along with the cross-sectional view of the plan
view of the finishing blade.
Figure 3 shows the hypoid gear tooth with out chamfering edges,
Figure 4 shows the chamfer cut with the tooth profile generation
Figure 5 shows the cutter body with new chamfer blade arrangements.
Figure 6 shows the plan and left side view, along with the cross-sectional view of the plan
view of the proposed chamfer blade.
Detailed description of the invention
Referring now to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the invention only, and not for the purpose of limiting the same.
The crow wheel or bevel pinion gear teeth are cut by a cutter having plurality of sets of blades. Each set of blades will have three blades with one cutting and two finishing purposes. The finishing blades used to finish the inner and outer profiles of the teeth. The number of sets of blades used in a cutter decided based on the Cutting Method (Spiroflex or HN2). Figure 1 shows a cutter body with blades for cutting and finishing the teeth of crown wheel or bevel pinion. The cutter body having five sets of blades for cutting and finishing action. The number of sets of blades will vary according to the application. According to figure 1 the cutter (A) comprises five sets of blades (a to e), with three

blades in each set (B, C & D). Each set has one rougher or cutting blade (D) and two finishing blades (B and C) one for finishing inside profile of the teeth and another one for finishing outside profile of gear teeth. The cutting blade located at centre of the set and finishing blades are at the sides of the centre cutting blade. The chamfering of the teeth is done manually after the cutting.
Figure 2 shows the finishing blade in the set of blades for the hypoid gear generator. The cutting edge angle a primarily resulting in the profile generation of the teeth and angle p is the corresponding cutting edge clearance angle provided to the cutting edge for the prevention of the chip accumulation around the cutting edge and to provide clearance of the blade from the generated profile.
The angle a is the non-cutting edge angle and angle 8 is the non-cutting edge clearance angle to prevent the tool surface rubbing with the profile. Angle Φ is the top face clearance angle to enhance the rake angle thus increasing the strength of the cutting edge. Angle Φ is the rake angle and angle y is the tip clearance angle to prevent the rubbing of the blade with the fillet (radius given at the root of the Gear Profile), profile or a root of the tooth generated. The height of the blade controls the tooth height from the root. The height of the cutting tip measured from the insertion base position. These angles correspond to the signature of single point cutting tool generating a profile based on hypoid gear generation principle. Figure 3 shows a gear tooth prepared using a cutting tool as shown in figure 1. The tooth tip is not chamfered and the high points will create undesirable noise and vibration to the rear axle.
Figure 4 shows a gear tooth prepared using a cutting tool as per the present invention shown in figure 5. The tooth tip is chamfered and done simultaneously with the cutting and finishing operation. The chamfered tooth will avoid undesirable noise and vibration. Figure 5 shows the cutting tool modified as per the present invention. The inner finishing blade of one set and outer finishing blade of another set is replaced with inner and outer chamfering blades respectively. So that the new cutting tool will have plurality of sets of blades with each set of blades having cutting, finishing blades and at least one set blades with cutting, finishing and chamfering blade. One set will have chamfering blade for inner chamfering while the other set with chamfering blade for outer chamfering. For Tip chamfering, minimum one set of inner chamfer and outer chamfer blades are required, Cutting load shared by each finisher tool determines the life of the cutter. Therefore, the

number of chamfer blade replacements should be restricted to minimum as it directly affects the life of the cutter. Moreover, the position of chamfer blades is independent of the set and position of the finisher blades. It can be placed in same set or in different set as per convenience. In each set of blades, the cutting blade is located at centre and finishing or chamfering blades are located at the sides of the cutting blade. The set of blades can be a combination of cutting; finishing and chamfering blades without repeating type of blade used or at least one blade selected from such blades.
Figure 6 shows the new chamfering blade to perform the chamfering operation. The chamfering is done along with cutting and finishing operation. Chamfering is the final stage operation which is done once teeth cut into required depth. The chamfering blade will not be in contact with the specimen till the required depth of tooth is cut and once required depth of tooth is completed chamfering blade will start chamfering the edges of the tooth. The height of chamfering blade is maintained less against the depth of tooth of the gear to achieve this process.
The required chamfering angle is controlled by the cutting edge of the chamfering blade. The chamfering blade maintains a cutting angle a' same for the inner and outer chamfering blades. The chamfering thickness is maintained by the positioning of the insert in the flat base. The relief angle y' based on the chamfering angle is maintained same as cutting edge angle a', The cutting edge clearance angle P' of the inner and outer chamfer blade need to be greater than that the corresponding angle p of the inner and outer finisher blades respectively. The rake angle is kept as 0 degree as chip generation is not significant in chamfering process. For typical crown wheel with 'n! teeth and set of V blades, the chamfering is done on (n/x)th tooth and their multiples in sequence.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

We Claim:
1) A cutting tool comprising a cutter body with plurality of sets of blades wherein each set of blades having at least one blade selected from a group consisting of a cutting blade, an inner finishing blade, an outer finishing blade, an inner chamfering blade and an outer chamfering blade.
2) The cutting tool as claimed in claim 1 wherein said inner and outer chamfering blades having a height less than the depth of tooth of the gear to cut.
3) The cutting tool as claimed in anyone of the preceding claims wherein said inner and outer chamfering blades having same cutting edge angle.
4) The cutting tool a claimed in anyone of the preceding claims wherein said inner and outer chamfering blades having a relief angle same as said cutting, edge angle.
5) The cutting tool as claimed in anyone of the preceding claims wherein said inner and outer chamfering blades having cutting edge clearance angle greater than the corresponding angle of the inner and outer finisher blades respectively.
6) The cutting tool as claimed in anyone of the preceding claims wherein said inner and outer chamfering blades having a rake angle of 0 degree.
7) The cutting tool as claimed in claim 1 wherein said cutting blades located at center of said each set.
8) The cutting tool as claimed in claim 1 wherein said blades are selected in such a way that said set will not have repetition of same type of blade.
9) The cutting tool comprising a cutter body with plurality of sets of blades wherein each set of blades having a cutting blade, an inner finishing or inner chamfering blade and an outer finishing or outer chamfering blade.
10) The cutting tool as claimed in claim 9 wherein at least one set having a cutting blade, inner finishing blade and an outer chamfering blade and another set having a cutting blade, an inner chamfering blade and an outer finishing blade.
11) The cutting tool as claimed in claim 9 wherein at least a set having a cutting blade, an inner chamfering blade and an outer chamfering blade.

12) The cutting tool as claimed in claim 9 wherein said inner and outer chamfering blades having height, cutting edge angle, relief angle, cutting edge clearance angle and rake angle as claimed in claim 2 to claim 6 respectively.
13) The cutting tool comprising a cutter body with plurality of sets of blades wherein each set of blades having a cutting, an inner finishing and an outer finishing blade wherein one of said inner and outer finishing blades are replaced with an inner and a outer chamfering blades respectively.
14) The cutting tool as claimed in claim 13 wherein said inner and outer chamfering blades having height, cutting edge angle, relief angle, cutting edge clearance angle and rake angle as claimed in claim 2 to claim 6 respectively.