FORM 2
THE PATENT ACT 1970 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION
(See Section 10/ and rule 13)
1. TITLE OF INVENTION
A CNC GEAR HOBBING MACHINE
2. APPLICANT (S)
a) Name : PREMIER LIMITED
b) Nationality : INDIAN Company
c) Address : 58, NARIMAN BtfAVAN,
NARIMAN POINT/ MUMBAI-400 021/ MAHARASHTRA, INDIA
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed : -

FIELD OF INVENTION
The present invention in general relates to hobbing of gears and more particularly to a gear hobbing machine for gear cutting operation.
BACKGROUND OF THE INVENTION
Hobbing is a machining process for making of gears, sprockets etc. by a cutting tool called hob. It is a comparatively inexpensive process but suffers from a problem that the speed variations between the rotating workpiece and the hob can not be synchronized to the micro-level details. Also, a lot of time is required to mechanically change various settings of the machine, which increases the chances of human error. Thus such process is slow and lacks detailed precision while making gears by such hobbing process.
In the hobbing process workpiece and hob rotate together like pair of gears with crossed axes. Gear hobbing is a continuous generating process in which tooth flanks on the constantly rotating workpiece are formed by the equally spaced cutting edges of the hob. The table rotation and hob rotation are synchronized for gear generation. To synchronize the hob axis with the workpiece axis, is a challenge faced in such technological field from time immemorial.
Hobbing machine is equipped with automatic work cycles for Radial, Axial and Tangential hobbing and also in such combinations as Radial - Axial, Radial -Tangential, for setting every movement, machine can be actuated either in rapid traverse by push buttons or manually. Such manual operation may result in misalignment of the hob and workpiece resulting in faulty gear generation.
Further axial, radial and tangential hobbing is possible on hobbing machine during Climb hobbing or Conventional hobbing.

The different types of hobbing methods present in the art are detailed as follows:

Method Manner of operation Application
Axial method Climb Hobbing Hobbing with axial feed cutting direction and relative feed direction of workpiece are same. Spur gears with hob by hobbing method and with side milling cutter by index method.
Axial method Conventional hobbing Hobbing with axial feed. Cutting direction and relative feed direction of workpiece are opposite Worms with hob by hobbing method.
Worms with side milling cutter by index method.
Radial method Hobbing with radial feed Worm wheels with hob or fly cutter by hobbing method. Hourglass worms with Fellows type cutter by reverse hobbing method.
Radial-Axial Method Plunge to cutting depth with radial feed, immediately followed by hobbing with axial feed by climb or conventional hobbing. See Axial method above.
The gear blanks axe required to be produced with consideration of grade of accuracy of the gear, to be hobbed. Gear blank is the semi-finished part used for the manufacture of a gear by Hobbing operation.
The blank needs to be gashed all around to produce the required number of teeth and profile of gear. The gashes or the slitting saw allow the hob to cut and pull the blank around and cuts the correct no. of teeth.
The gear blank needs to be located and clamped at the specified height of hobbing machine and the whole blank needs to be stiff enough to resist cutting and clamping forces during the cutting process. Gear teeth needs to be exactly concentric and parallel to the table spindle axis. Such precision are almost impossible to achieve in manually set gear hobbing machines. Thus there existed a long felt need in the art to

develop a gear hobbing machine which can provide more precision and accurate gear tooth profile and finish of the gears as per the design of gear and also reduce the setting time, substantially.
All through out the specification including the claims, the words "Hobbing", "Gear", "Machine Bed", "Motor", "Servomotor", "Control panel", "Work piece", "Table slide", and "Hob", "Hob head", "Hob head slide" are to be interpreted in the broadest sense of the respective terms and includes all similar items in the field known by other terms, as may be clear to persons skilled in the art. Restriction/Limitation if any, referred to in the specification, is solely by way of example and understanding the present invention.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide a gear hobbing machine which is adopted to machine a gear in varied directions automatically so as to reduce the production time of each gear.
It is a further object of the present invention to provide a gear hobbing machine adopted to generate a gear to a predefined design which does away with the use of a manual alignment and setting of hob along different axes for hobbing different gears.
It is yet another object of the present invention to provide a gear hobbing machine wherein the drawbacks of manually aligning the hob to different angles accurately and precisely according to the rotation of the work piece is overcome.
It is a further object of the present invention to provide a Gear Hobbing Machine which is adopted to generate a gear to a predefined design, which can automatically align the Hob in varied angles along different axes as required for machining varied gears.

It is yet another object of the present invention to provide a CNC Gear Hobbing Machine which is adapted to generate a gear to a predefined design, which possess an electrical control.
How the foregoing objects are achieved and the other aspects of the present invention will be clear from the following description, which is purely by way of understanding and not by way of any sort of limitation.
SUMMARY OF THE INVENTION
The present invention discloses a CNC Gear Hobbing Machine comprising, at least one machine bed, a Main Column fixedly mounted on said Machine Bed, a Tail stock Column mounted on said Machine Bed and being movable on a Table slide, a Hob head associated to a Hob head slide, atleast two start index table drive for mounting a workpiece for rotation about a defined axis, and an electrical panel for monitoring entire hobbing process.
In accordance to some preferred embodiment of the CNC Gear Hobbing Machine of the present invention:
- said table drive is integral part of Table slide with Rotary table and is mounted on said Machine Bed;
- said table drive is mounted on Tail stock Column
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature and scope of the present invention will be better understood from the accompanying drawings, which are by way of illustration of some preferred embodiments and not by way of any sort of limitation. In the accompanying drawings,

Fig la and lb illustrate perspective layout of the CNC gear hobbing machine of the present invention.
Fig 2 illustrates the linear X-axis layout of Table Slide radial movement of
the CNC gear hobbing machine of the present invention.
Fig 3 illustrates the linear Y-axis of CNC Gear Hobbing machine and
movement of Tangential slide.
Fig 4 illustrates the linear Z-axis layout of CNC gear hobbing machine for
Hob head slide vertical movement
Fig 5 schematically illustrates the X-axis movement according to the
present invention of X-axis Ball screw and motor.
Fig. 6 schematically illustrates the drive system of Z axis rotation according
to the present invention showing Z-axis Ball Screw and motor.
Fig. 7 illustrates the Indexing and Reversing arrangement for the gears
according to the present invention.
Fig.8 illustrates the differential arrangement for the gears according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
The following describes some preferred embodiments of the present invention, which are purely for the sake of understanding the present invention and not by way of any sort of limitation.

The present invention in general relates to production of gears and in particular to a gear hobbing machine and a methodology for hobbing of gears. The present invention aims to counteract the drawbacks of manual setting of various parameters of the machining process according to the varied gears and also the- controlling of speed of the hob in accordance with the speed of rotation of the workpiece. This is important for more precise and accurate generation of gears which overcomes the problems faced by varied speeds of the workpiece which resulted in improper machining. In the present invention the various setting parameters can be automatically adjusted to suit a variety of gears as and when the gears needed to be produced.
The present invention relates generally to CNC Gear Hobbing Machine and more specifically to a new and unique CNC Gear Hobbing Machine with two start index drive, which is adopted to regulate the speed of the Hob and workpiece to accurately machine varied gears precisely according to predetermined designs.
The CNC Gear Hobbing machine with Table drive comprising of two start Index Drive as disclosed in the present invention as illustrated in Figure la and lb primarily comprises of:
1 Bed
2 Control Panel
3 Machine Cladding
4 Universal Hob Head
5 Hob slide for Up-Down adjustment (Z axis) of Hob Head
6 Tail Stock column (Support Column)
7 Bed Bottom
8 Coolant tank
9 Magnetic chip conveyor for chip removal
10 Main column mounted on Bed

Machine Bed (1): The Machine Bed (1) supports the Main Column (10) and the Table with two start index drive (19) (not shown in fig 1) on which workpieces are mounted.
Table Drive: The Table drive indexing is integrated in the Table. The table rotation and hob rotation are synchronized for gear generation through change gears. The workpiece can be clamped on or in the table by means of hydraulic clamping fixture. Accuracy of hobbing depends upon the accuracy of index worm drive. A high contact ratio of gears ensures a high load carrying capacity and conservation of accuracy.
Table slide (13) is moved radially in and out (X-axis) by AC servo motor (11 A) and Preloaded ball screw (14A) for accurate depth.
Hob head (4) with tangential slide: The reduction ratio in the gear train to the hob is considerable so that the Hob head drive is subjected to only a small load.
Hob slide (5) is moved up and down (Z-axis) by AC servomotor (11C). Tangential slide is moved in and out (Y-axis) by AC servo motor (11B) which is used for hob shifting only.
Panel enclosure: The Panel enclosure contains all the electric and electronic components for controlling and operating the machine. The operating panel with keyboard and monitor is mounted on the operator side of the panel enclosure. The machine receives all operator inputs via. the operating panel, and all functions are displayed on the monitor.
Figure la and lb illustrate a perspective layout of the CNC Gear Hobbing Machine and all its different components. The Spindle motor (15) is closely associated with the Hob head (4) providing drive to the hob acting as the cutting tool. The figure illustrates the position of the Control panel (2). The Hob head (4) remains in

operative association with the Hob slide (5) along which the hob moves is also shown in the figure. The figure also illustrates the Main Column (10) and the Tailstock Column (Supporting column) (6) in which the latter houses the support slide along which the work piece translated to associate with the hob. The Machine cladding (3) and the position of the Bed bottom (7) are also specified in the said figure 1.
The CNC Gear Hobbing Machine in the present invention comprises a Column (10) with Hob head (4) and Hob slide (5) located on Machine Bed (1) which is mounted on leveling wedges. Hob head (4) is mounted on Column (10) slides up and down. Hob head slide (5) is mounted on Hob head (4) has tangential travel.
The said machine consists of a work piece mounted on table. The work piece receives motion from table index drive. Hob is mounted on Hob head Slide (5) which gets the motion from Spindle motor (15).
For swiveling of Hob Head (4), Worm (17) and Worm wheel (18) mechanism is provided (shown in figure 4).
The Tailstock Column (Support column) (6) is located on said Table slide being moveable in radial direction along X Axis. The Table includes a means for mounting a workpiece for rotation about an axis of rotation of said workpiece. A Hob head slide (5) located on said Hob head (4) being moveable along Z axis in a direction perpendicular to both Y and X Axis.
A Hob spindle housing comprises a means for mounting Hob spindle. The later further comprises a means for mounting hob for rotation about an axis of rotation of said hob means for controlling the movement of Hob slide in a direction along an axis Y means for controlling the movement of said hob in tangential direction.

The hob as disclosed in the present invention is a cutting tool having serrations along the cutter tooth flank which form series of cutting edges that remove the metal. The Hob head can be swiveled at an angle between -30 to +70 degree with respect to Hob head slide axis mounted on Main column.
The machine also comprises a separate Coolant Tank (8) and Magnetic Chip Conveyor (9) for the removal of chips.
Fig 2 and Fig 3 as illustrated, provides the linear X axis and liner Y axis layout of the disclosed CNC gear nobbing machine wherein the position of the AC servomotor is defined for radial as well as tangential movements of the hob.
The Machine Bed (1) supports the Main Column (10) the Table and Tailstock Column (Support column) (6). Universal Hob head (4) is mounted on Main Column (10) for vertical movement by a Ball screw (14) and Servo motor (11). A hob is mounted on a Hob head slide (4) which has tangential travel and rotate by a Spindle motor(15). The Machine Bed (1) is in box shape. For the sake of easy and accurate referencing the servo motors along X, Y and Z axis has been referred as 11 A, 11B and 11C and respective ball screws as 14A, 14B, and 14C and pulleys 16A, 16B and 16 C in all the figures. Further like reference numerals have been used to represent like features for sake of simplicity in understanding.
Figure 2 and 3 further illustrates the positions of the Table slide (13), pulley (16A, 16B) and encoder along Y axis (12B).
A work piece mounted on the table rotates through two start index drive provided for table and has radial traverse. A workpiece and Hob rotate together are like a pair of gear with crossed axes. The hob receives motion from the motor and drives the workpiece which is mounted between Tailstock center and Table. Said machine as in the present invention comprises 3 axes:

i. Horizontal Axis (Radial movement of Table) - X Axis ii. Vertical Axis (Vertical movement of Hob Head)- Z Axis iii. Cross Axis (Tangential movement of Hob slide) - Y Axis
The workpiece is axis perpendicular to the Table axis. The Hob comprises with its axis cross to workpiece and Table axis.
The machine as disclosed in the present invention possesses three axes. The work piece is mounted on Table which is driven by two start index drive. Rotary hob operates at max. Speed of 625 rpm. The hob removes metal to cut out the shape of the gear. The relationship of axis of hob and the axis of work piece is crossed.
In this machine vertical axis of Hob head movement is designated as 'Z' axis. Radial movement of the Table slide on Bed is designated as 'X' axis. Tangential movement of Hob slide is designated as 'Y' axis.
The complete chain of reversing and indexing change gears are required to cut any no. of teeth (within the machine capacity.)
Fig 4 and Fig 5 similarly illustrates the Z-axis and X-axis view of the gear hobbing machine. Similar numbering has been provided to identical components in said figure, as in earlier figures, only for the sake of easier understanding. In the said figures the position of the Ball screw (14A and 14C) is shown for the said machine. Figure 4 and 5 further illustrates the positions of the worm wheel (16), worm shaft (17), Pulley (16A), the AC servo motor (11A), the Table slide (13), Column (10) and the Machine Bed (1).
Fig. 6 schematically illustrates the drive system of Z axis rotation according to the present invention. Similar numbering has been provided to identical components in said figure, as in earlier figures, only for the sake of easier understanding. The said figure illustrates the position of the Worm shaft (17) and the Worm wheel (18).

The differential provides an additional motion (increment or decrement ) to the workpiece revolution(relative to the hob revolutions). Size and direction of this additional motion will be given by additional servo motor through programming with respect to axial feed in case of helical gear cutting and with respect to tangential feed in case of work wheel cutting.
Fig. 7 illustrates the Indexing and Reversing arrangement of the gears. There is a fixed relation between number of hob revolutions and number of workpiece revolutions. This relation can be altered by means of index change gears. By mounting of the respective index change gears any number of teeth can be hobbed.s Fig 7 shows the mounting of index change gears (27) with a Change gear pin (28), Spur gear (25) and Reverse gear (26).
Fig. 8 illustrates the differential arrangement of the gears showing the positions of Worm shaft (20) and Worm Wheel (21). It also indicates the positions of differential housing (22), Spur Gears (23) and Bevel Gears (24).
The following are the few non limiting advantages of the present invention:
1. Two cut work cycle
2. Skip feed
3. Automatic change for no. of teeth and cutting depth
5 Dipping device
6. Taper Hobbing, Crown hobbing / Copy hobbing
8. Automatic feed control
9. Reduction of set time
The present invention has been described with reference to some drawings and preferred embodiments, purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the, slope of what has been described herein before and claimed in the appended claims.

WE CLAIM:
1. A CNC Gear Hobbing Machine comprising, at least one machine bed, a Main Column fixedly mounted on said Machine Bed, a Tail stock Column mounted on said Machine Bed and being movable on a Table slide, a Hob head associated to a Hob head slide, atleast two start index table drive for mounting a workpiece for rotation about a defined axis, and an electrical panel for monitoring entire hobbing process.
2. The CNC Gear Hobbing Machine as claimed in claim 1 wherein said table drive is integral with said table slide and is mounted on said Machine Bed.
3. The gear hobbing machine as claimed in claim 1 wherein said table drive is mounted on said Tail stock Column.
4. A gear hobbing machine substantially as herein described particularly with reference to the accompanying drawings.
5. A method for hobbing of gear substantially as herein described particularly with reference to the accompanying drawings.