Title of Invention

"A METHOD OF PRODUCING PRECISION IN VOLUTE PROFILE GROUND PINION WITH BALANCED CROWNING"

Abstract

The invention relates to a method of manufacture of balanced crowned involute -profile precision ground pinions comprising the steps of: i) soft turning the blank pinion in a lathe to provide various diameters (1,2,3,4,14,15) and dimensions (5,6,7) of the pinion; ii) hobbing the pinion for the teethproflle in a hobber; iii) drilling and tapping (8) the blank; iv) carburising , hardening and tempering of the blank. v) final turning of diameter (3) in a lathe after hardening, vi) grinding of the bore (3) of the pinion ; vii) grinding of teeth (A) in a fixture (12), said fixture having a teeth grinding bush (13) to which the bore (3) of the blank is fitted , and viii) grinding both flank of the teeth at a time using CNC dressing of involute form and maintaining temperature in the grinding zone at 25° + 1°C.

Full Text

The invention relates to a method of producing precision involute of balanced crowned profile ground pinions with balanced crowning particularly for use in locomotives. Involute profiles herein means the geometric curve 'involute' which is given to the pinion tooth/teeth during their manufacture. Precision means accuracy, involute profile precision means pinions made with accuracy to geometric shape of an involute. PRIOR ART There are disadvantages associated with the present system of manufacture of involute profile pinions with balanced crowning. The main disadvantage is that the component parts get rejected in grinding of tooth profile due to out of tolerance of involute profile, radial run-out and unbalanced crowning. Radial run-out herein described is a technical term in pinions which measures quantity of eccentricity, the greater the noise level, when pinion operates in mesh with a gear. Unbalanced crowning is opposite to balanced crowning. Unbalanced crowning leads to breakage of pinions in use. Crowning means giving edge-wise geometry to the teeth of pinions. BS436:1986 defines crowning as a crude form of modification used to compensate for manufacturing errors and deformations of the pinion/gear under load. However, in the present invention, crowning is considered not as a crude form of modification, but an intentional, specified and accurate parameter which leads to reduction in noise levels and pinion teeth breakage during use. Another disadvantage associated with the present system is that it cannot ensure consistency in dimension and can achieve only few of the precision dimensions in every member of a batch. Consistency herein means that profile of each tooth and each flank of a tooth is exactly similar. A pinion may have 43 teeth and, therefore, 86 flanks. Consistency means each of the 86 flanks will have exactly same profile. In the prior art either every pinion of a batch has to be checked for profile which is practically not possible and thereby accept some parts wherein all precision dimensions have not been achieved. It therefore, cannot ensure consistency of results over a period of time and between batches. The prior art uses a fixture for grinding teeth of pinions. The design of fixture does not ensure exact alignment of fixture axis and pinion axis. Fixture used in the process of manufacture did not consider, optimally, the exact place at which clamping of pinion is necessary for desired accuracy. The design of the fixture did not adequately consider whether the fixture itself should be mounted horizontally or vertically and that it is essential to butt the face of the pinion squarely on a bush assembled on the fixture. Yet another disadvantage associated with the present system is that it did not specify the role of grinding wheel used in form grinding with respect to profile form retention. The present system did not also specify frequency of dressing of grinding wheel to ensure consistency in profile form retention. Further disadvantage with the present system is that it has not specified any limits to control of temperature of coolant oil in grinding operation and the correction factor necessary due to rise in temperature of coolant oil. SUMMARY OF THE INVENTION Therefore the main object of the present invention is to propose a method of manufacture of balanced crowned involute-profile precision ground pinions for use in locomotives in which the noise level in gear/pinion is reduced substantially to 80 decibels. In any gear drive there is mechanical contact between a gear and a pinion leading to noise. Excessive noise is a pollution hazard and does irreparable damage to hearing senses of the human body. Hence noise level has to be controlled. Permissible level in gear drives is 85db. However, this invention assures noise control to much less level of 80 db (decibels). This invention reduces the noise level with the help of precision grinding of pinion. Another object of the present invention is to propose a method of manufacture which ensures dimensionally precision pinions in all parameters i.e. involute profile, pitch, vertical alignment, radial run-out, axial run-out, tip relief, crowning, balancing of crowning and surface finish. Yet another object of the present invention is to propose balance crowned involute-profile precision ground pinions which meet quality standard and does not require any rectification. This reduces the overall cost considerably. Further object of the present invention is to propose a method of manufacture of balanced crowned involute-profile precision ground pinion which is consistent in quality for any batch or quantity. Better quality standard ensures longer product life and trouble free running of locomotives. Distinguishing features with respect to prior art is tabulated below for ready reference and comprehension. (Table Removed) According to the present invention there is provided a method of producing precision involute profile ground pinions with balanced crowning comprising the steps of 1. A method of producing precision involute profile ground pinions with balanced crowning comprising the steps of: (i) providing a blank pinion on a lathe, (ii) soft turning the blank pinion in the lathe to provide various dimensions in the form of diameter and profile at locations (1,2,3,4,5,6,7,14,15) of the blank pinion, (iii) forming teeth (ti-tn) on the pinion by a gear bobbing machine, (iv) drilling and tapping (8) the blank, (v) carburising, hardening and tempering of the blank. (vi) final turning of the bore (3) in the lathe after hardening, Characterized by comprising the additional steps of :- (vii) grinding the bore (3) to dimension 66.675/66.685 mm and grinding the face (7) to dimension 62.63/62.73 mm in one setting, (viii) providing a fixture (12) and a bush (13) corresponding to an optimal clamping location of the pinion allowing a maximum concentricity of ± 0.003 mm, and assembling the fixture (12) and the bush (13); (ix) holding the assembly (12,13) vertically in a teeth grinding machine, (x) mounting the pinion on the clamping zone of the fixture (12,13) such that a centre line (x)of the pinion coincides with a centre line (y) of the fixture (12,13) and the seating face is disposed perpendicular to the centre line (x) of the pinion, grinding both the flanks of each teeth (ti.tn) simultaneously using the technique of Computerised Numerical Control (CNC) dressing of involute form, by maintaining a temperature in the grinding zone at 25°C ±1°C, the dressing of the grinding wheel being undertaken after every 6 to 8 teeth to ensure consistency of involute profile on every tooth. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to the non-limiting exemplary embodiments of the invention represented in the accompanying drawings in which Figure 1 shows the sectional view of the blanks of the prior art. Figure 2 shows in a tabular form of the various processes along with the dimensions of the prior art. Figure 3 shows the teeth grinding fixture which is horizontally held as in the prior art. Figure 4 shows the blanks as per the invention. Figure 5 shows in a tabular form of the various processes alongwith dimensions of the blank of an invention. Figure 6 shows the vertically held teeth grinding fixture of the invention. Figure 7 shows the detail of teeth grinding bush. Figure 8 shows the graph of profile and crowning values of pinion obtained in prior art. Figure 9 shows the graph of profile and crowning values of pinion obtained in this invention. Detailed Description of prior art Figure 8 shows the pinion produced having an inaccurate involute profile and unbalanced crowning in prior art. Crowning values range from 0.040 mm to 0.060 mm, difference of 020 mm against permissible deviation of 0.010 mm. Also both right and left flanks have different values. The prior art method of manufacturing consisted of: (i) turning and facing operation in lathe machine to produce dimensions 190.5 mm, 142 mm, 60 mm, 108 mm, 38.1 mm, 15.25 mm and 63.1 mm (5,6,7,12,3,4) (ii) after the turning operation gear teeth cutting (hobbing) is done on a bobbing machine for getting a rough involute profile, (iii) the pinion is then heat treated (carburized), (iv) further turning is done for the diameters mentioned at step (i), (y) next driving and tapping is done followed by, (vi) hardening and tempering, (vii) the bore is ground to dimension 66.675/66.685 (3) followed by (ix) teeth grinding. Grinding is indicated by letter 'G' in figures for both prior art and present invention. The teeth grinding fixture is held horizontally and the pinion is held on a plotted bush which is mounted on the taper portion of the fixture. The pinion produced by the prior art could not ensure that the axis of pinion bore coincides with axis of fixture, because of sagging of the fixture itself held horizontally. Also the seating face of the pinion is not ground perpendicular to the bore in prior art. This results in getting unbalanced values of crowning as shown in the graph in Fig. 8. The prior art also does not have any control on the temperature in the grinding zone. As a result, distortions in profile of pinions take place due to heat generated in grinding leading to inconsistency in dimensions. Figure 4 shows the blank for the pinion as per the invention in which identical numerals have been used for identical parts. The process involved in the manufacture of balanced crowned involute-profile precision ground pinions are as follows: i) Turning operation on the rough blank is done to provide a machined blank on a lathe machine. The dimensions (5,6,7) and diameters (1,2,3,4,14,15) are developed in this operation. ii) Mobbing is done on a bobber for machining involute-profile of the pinions. iii) Drilling and tapping (8) is done and the threads are protected by using caps/putty, iv) The blanks are then carburised and v) Hardened and tempered and a vi) finish turning is done after hardening in which bore (3) turning is done using ceramic inserts, vii) Boring (3) on face (5) are ground which is a new method producing a better tolerance. Viii) Finally teeth grinding is done on a newly developed fixture (12) having a teeth grinding bush (13). The new fixture (12) provides better control on position of the job and grinding wheel is dressed after every 6 to 8 teeth using only CNC dressing of involute form. Grinding of both flank of the teeth (ti) is done at a time. The dressing of the grinding wheel as specified ensures a consistency in profile form retention. The centre line of the pinion and fixture is shown as X and Y in the drawings. The pinions manufactured by the present method is shown in Graph in Fig.9, wherein precision involute profile is obtained with crowning values from 0.036mm to 0.42mm i.e. well-balanced within 0.006mm. Both flanks have similar values of crowning, thus reducing unbalance in crowning from 0.020mm in prior art to 0.006mm in this invention, which has 233% better accuracy. These graphs in figures 8 and 9 were drawn on actual pinions by using a probe of an Involute Testing machine. Thus it can be ascertained that this present invention could produce precision involute profile pinions with balanced crowning. Another new feature is that the temperature is controlled in the grinding zone. Generally temperature in the grinding zone is maintained at 25°C ±1°C. This is done by cooling the coolant oil. Temperature in the grinding zone is maintained by a controlled, high velocity and high pressure flow of chilled coolant that takes away the heat developed in grinding operation. This coolant is directed at the grinding zone by suitable positioning of nozzles through which the grinding coolant flows. Coolant is chilled in a heat exchanger and pumped to the grinding zone. Heat developed during grinding is absorbed by the refrigerated coolant which is then sent through a heat exchanger back to the grinding zone. The heat exchanger controls the temperature of the grinding zone sufficiently to obtain temperature of 25°C ±1°C. Another novelty of the invention is in the fixture. In the prior art, fixtures used did not consider, optimally, the exact place at which clamping of pinion is necessary to get desired accuracy. It also did not adequately consider whether fixture itself should be mounted horizontally or vertically. Fixturing also did not consider that it is essential to butt the face of the pinion squarely on a bush assembled on the fixture. The teeth grinding fixture (12) of our invention is held vertically on the grinding machine. Then concentricity is maintained with ± 0.003 mm. The teeth grinding bush (13) is hardened and ground with face of bush maintained square and inside dia within ± 0.003 mm. The numerical figure means that deviation obtained in perpendicularity is maximum 3 microns either on positive or negative side, which is very critical for the final success of this invention. Any deviation above this amount may lead to unbalancing of crowning as in the prior art. CNC dressing herein employed means Computerised Numerical Control. In the context of the present invention, it means that the movement of dressing equipment, which dresses the grinding wheel (i.e. it gives shape to the grinding wheel), in 3 directions viz., x(horizontal), y (horizontal and perpendicular to x) and z (vertical) is programmed by a computer to obtain a precise involute shape. The movement of each axis can be controlled in the order of 0.001 mm. In the prior art, turning operation is done after carburising and in case of new method of the invention it is done after hardening. This has reduced manufacturing cycle time. The invention described hereinabove in relation to the non-limiting embodiments and as defined by the accompanying claims. WE CLAIM 1. A method of producing precision involute profile ground pinions with balanced crowning comprising the steps of: (i) providing a blank pinion on a lathe, (ii) soft turning the blank pinion in the lathe to provide various dimensions in the form of diameter and profile at locations (1,2,3,4,5,6,7,14,15) of the blank pinion, (iii) forming teeth (trtn) on the pinion by a gear bobbing machine, (iv) drilling and tapping (8) the blank, (v) carburising, hardening and tempering of the blank, (vi) final turning of the bore (3) in the lathe after hardening, Characterized by comprising the additional steps of :- (vii) grinding the bore (3) to dimension 66.675/66.685 mm and grinding the face (7) to dimension 62.63/62.73 mm in one setting, (viii) providing a fixture (12) and a bush (13) corresponding to an optimal clamping location of the pinion allowing a maximum concentricity of ± 0.003 mm, and assembling the fixture (12) and the bush (13); (k) holding the assembly (12,13) vertically in a teeth grinding machine, (x) mounting the pinion on the clamping zone of the fixture (12,13) such that a centre line (x) of the pinion coincides with a centre line (y) of the fixture (12,13) and the seating face is disposed perpendicular to the centre line (x) of the pinion, (xi) grinding both the flanks of each teeth (t1-tn) simultaneously using the technique of Computerised Numerical Control (CNC) dressing of involute form, by maintaining a temperature in the grinding zone at 25°C ±1°C, the dressing of the grinding wheel being undertaken after every 6 to 8 teeth to ensure consistency of involute profile pn every tooth.. 2. The method of manufacture of balanced crowned involute-profile precision ground pinions as claimed in claim 1 wherein the inside bore (3) of the pinion is maintained to a tolerance of + 0.01 , - Omm. 3. A method of manufacture of precision involute profile ground pinions with balanced crowning as herein described and illustrated with the accompanying drawings.

Documents:

501-del-2002-abstract.pdf

501-del-2002-claims.pdf

501-del-2002-correspondence-others.pdf

501-del-2002-correspondence-po.pdf

501-del-2002-description (complete).pdf

501-del-2002-drawings.pdf

501-del-2002-form-1.pdf

501-del-2002-form-13.pdf

501-del-2002-form-19.pdf

501-del-2002-form-2.pdf

501-del-2002-form-3.pdf

501-del-2002-gpa.pdf