WO2017163189A1

WO2017163189A1 - A method of manufacturing a crown wheel, and a crown wheel

Info

Publication number: WO2017163189A1
Application number: PCT/IB2017/051645
Authority: WO
Inventors: Babasaheb Neelkanth Kalyani; Basavraj Prabhakar KALYANI; Madan Umakant TAKALE
Original assignee: Bharat Forge Limited
Priority date: 2016-03-22
Filing date: 2017-03-22
Publication date: 2017-09-28

Abstract

The invention discloses a method of producing a Crown Wheel involving production of a ring by ring rolling process and further production of near net shape tooth profile by sequential stepwise forging. Conventional methods have several disadvantages e.g. excessive machining time, expensive gear cutting equipment, short life of cutting tools, possible strain hardening and residual stresses in the cold-forged parts and subsequent distortion during heat treatment and a high level of rejection of parts, among others. The invention discloses a method of manufacturing near-net shape crown wheel comprising the steps of making an annular ring using hammer forging, punching, piercing and ring rolling followed by blocker and finisher forging for manufacturing of gear teeth on the ring. Blocker forging is followed by trimming and piercing operation for flash removal. Hot forging operation (hammer blocker forging and finisher forging) is followed by cold coining process for improving the precision of the as-forged teeth profile.

Description

A METHOD OF MANUFACTURING A CROWN WHEEL, AND A

CROWN WHEEL

FIELD OF INVENTION:

This invention relates to a method of producing Crown Wheel. In particular, the present invention relates to production of ring by ring rolling process and further production of near net shape tooth profile on the ring by sequential stepwise forging process.

BACKGROUND OF THE INVENTION:

Crown wheel is commonly used in the power transmission applications. In motor vehicle, drive axles typically employ gear set comprising a drive bevel pinion and crown wheel. These gears are of hypoid or spiral type. Manufacturing with high degree of accuracy and finishing is one of the major requirements for smooth operation of this assembly.

The crown wheel generally is ring shaped part as shown in Figure 1 (A) & (B). The gear has gear teeth near its periphery as denoted by 1 in Figure 1. The gear has large hole in the center as denoted by 2 in Figure 1.

Conventionally, crown wheel, in particular for vehicle drive axle, are manufactured by starting with a forged blank without teeth. The forged blank is ring shaped i.e. it will have big hole in center similar to 2 in Figure 1, but it will not have the teeth as denoted by 1 in Figure 1. The teeth are then cut in this blank using special gear cutting machines. The crown wheel is then hardened and finished by lapping with the mating pinion. Lapping is a super-finishing operation which gives better surface finish to gear teeth and is helpful for better mating with drive pinion.

Patent US3069756, a patent granted in 1962, discloses a method of manufacturing a crown wheel through forging process in which an annular blank is produced from forging in which the teeth are cut later through machining process. Disadvantages of this process are excessive machining time and requirement of expensive gear cutting equipment. Also, cutting tools have a short life and are expensive to replace. Moreover, trimming of forged blank and cutting of teeth wastes large amount of the material. Further to this, the gear teeth cutting process leads to cutting of the grain flow lines which leads to presence of discontinuous grain flow lines in the teeth. This reduces their strength and consequently the benefits of hot forging process.

Patent US2713277, granted in 1955, discloses a method to manufacture a crown wheel with teeth formed during forging process itself. This method used cold forging process for near net shape forming of gear teeth. The drawback of this process is that the cold forging operation produces strain hardening and residual stresses in the part. These later lead to distortion during heat treatment and machining process and hence, lead to high level of rejection of parts. Moreover, for the crown wheels used in large size automobiles (trucks, tippers, dumpers etc.) the shape and the large size of the final part do not allow use of cold forging operation as the load required for cold forging such large crown wheels is so high that it makes the whole process uneconomical. Further to this, the flowability of steel at room temperature is very low. Due to this, complicated shapes like the gear teeth do not fill properly during cold forging. This again leads to much higher level of rejections during the production. This also leads to high wear and tear of the forging dies and reduces the die life making the process further uneconomical. Patent US4761867 discloses a method of hot forging the crown wheel with teeth formation during forging. This process consist of closed die forging for the formation of toroidal shaped preform for ring rolling, followed by ring rolling then finish forging. This patent claims that using this process, near net shaped crown wheels can be produced. But, for mass production, this process has many disadvantages. The complete process is very lengthy due to which it has a large cycle time and becomes uneconomical. The forging process used for the formation of preform for ring rolling entails three steps of upset, blocker and piercing. The dies and forging process required for the formation of toroidal shaped preform increases the cost of the forging. Further, after the ring rolling process the rolled ring is put in finisher die to forge the final crown wheel. But, the ring produced using the ring rolling process generally has wrinkles on its surface. These wrinkles lead to formation of cracks, coldshuts after the finisher operation. The process disclosed in Ί867 does not teach how to overcome such flaws. Due to this the final product obtained after the finisher shows MPI (Magnetic particle inspection) indications. These parts have to be then reworked/salvaged or scrapped. Further to this, the teeth produced using hot forging are not very precise and accurate. Moreover, the heat treatment process also leads to some distortion. Hence, during machining process unequal machining allowance is found on the teeth. This unequal machining leads to distortion of teeth during machining and subsequent heat treatment process. This distortion later causes improper contact pattern between the crown wheel and pinion during its operation and leads to premature fatigue failure of the parts. Due to all these disadvantages the aforementioned process cannot be economically productionised.

Due to all the disadvantages explained in previous paragraphs the conventional method of teeth cutting using machining is the most commonly used method of producing crown wheel even though it has many disadvantages and limitations as described above.

The present invention discloses the method of manufacturing of crown wheel, and in particular as-forged spiral bevel teeth using forging process. SUMMARY OF INVENTION

In accordance with the present invention, the drawback of prior art are overcome by the method of manufacturing of crown wheel with as-forged teeth. This invented method allows considerable material and energy saving as compared with the prior art method. Also, strength of the produced crown wheel is higher due to continuous grain flow lines in view of prior art method. This invention also overcomes the drawbacks of prior art which claim to produce teeth in forging itself.

The present invention consists of a method of manufacturing crown wheel comprising the steps of making an annular ring using hammer forging, punching, piercing and ring rolling method followed by blocker and followed by a finisher forging step for manufacturing of gear teeth on the ring. The blocker forging step is followed by trimming and piercing operation for removal of flash. The hot forging operation (hammer blocker forging and finisher forging) is followed by cold coining process in order to improve the precision of the as forged teeth profile.

Preferably the annular ring is manufactured using hammer forging, punching, piercing and ring rolling operations, which gives better utilization of material and better strength with continuous grain flow lines across the contours of crown wheel especially along the contours of gear teeth. The forging of gear teeth profile is carried out using any type of forging equipment capable of applying sufficient amount of force and energy.

OBJECTS OF INVENTION

Some of the objects of the present disclosure which at least one embodiment herein satisfies are as follows:

An object of the present invention is to provide a method for forging of crown wheel.

It is another object of the present invention to produce as-forged spiral or helical gear teeth profile on forged ring.

It is yet another object of the present invention to provide better mechanical properties and continuous grain flow lines along the contours of the teeth profile.

It is yet another object of the invention to provide a forging process which produces substantially defect free crown wheel with better fatigue life. It is yet another object of this invention to provide the crown wheel gear teeth profile such that machining allowance is uniform for all teeth. It is yet another object of the invention to reduce the machining (gear teeth cutting) time required during the manufacturing of the crown wheel.

It is yet another object of this invention to provide the crown wheel gear having appropriate contact pattern with the mating pinion gear.

It is yet another object of the invention to reduce the input material required during the manufacturing of the crown wheel. It is yet another object of the invention to provide forging dies and tooling for manufacturing of the crown wheel.

BRIEF DESCRIPTION OF FIGURES

Figure 1(A) shows the top view and Figure 1(B) shows the 3D view of the crown wheel (final product).

Figure 2 shows the invented process sequence of manufacturing of crown wheel. Figure 3(A) shows the top view and Figure 3(B) shows the 3 D view of the upset billet.

Figure 4 shows the 3D view of the pierced and punched disc.

Figure 5 shows the 3D view of the ring rolled disc

Figure 6(A) shows the 3D view and Figure 6(B) shows the section view of the blocker preform shape. Figure 7(A) shows the top view and Figure 7(B) shows the 3D view of the finish forged part.

LIST OF PARTS

1. Crown wheel 6B. Flash produced on the

2. Central hole 15 periphery of the blocker preform

3. Upset preform 6C. Pierced blocker preform

3A. Punched upset preform 6D. Heated blocker preform

4. Pierced preform 7. a finish forged part

5. Ring-rolled preform 7A. As-forged teeth

6. Blocker preform 20 8. Treated finish forged part 6A. flash produced in the central 9. Cold-coined part

hole of the blocker preform

DETAILED DESCRIPTION OF INVENTION

The present invention is related to the method of manufacturing Crown wheel used in automobile and industrial application.

The key inventive feature of the present invention is as-forged gear teeth formation during manufacturing of the crown wheel with better strength. According to the invented process, the manufacturing process starts with a forged billet as raw material. This billet is converted into the final shape of the crown wheel by taking it through various intermediate processes. As shown in Figure 1, a crown wheel (1) has ring type structure with a big hole in the centre (2). When the crown wheel (1) is made with the conventional forging process of upset, and blocker and finisher steps, lot of material at the centre of the part has to be discarded during the piercing operation. Moreover, large amount of material flow caused during the blocker and finisher operation, which tries to push material from the centre towards the periphery, causes large wear and tear of the dies and tooling's in which the forging is being done.

To overcome these problems, this invention discloses the use of a ring rolling operation as one of the steps in the forging process flow. The output of the upset operation, an upset preform (3), is shown in Figure 3. After the upset operation, piercing of the upset preform (3) is done in order to remove some material in the centre. This pierced preform (4, see Figure 4) is then put in the ring rolling machine for next process which produces a rolled ring or ring-rolled preform (5). The ring rolling machine basically consists of three rollers of which two rollers maintain the height of the ring while the third roller increases the diameter of the part. The ring-rolled preform (5, see Figure 5) is then provided as input to the blocker operation. The use of ring rolling gives following benefit:

1. This significantly reduces the loss of material which was happening in the conventional method. This reduces the input material requirement.

2. This also gives better material distribution which leads to better material flow in blocker and finisher. This further reduces the input material requirement.

3. The better material distribution and flow, as explained above, also reduces the wear and tear of the blocker and finisher dies leading to increased die life.

The ring rolling operation is followed by a blocker operation to produce a blocker preform (6, see Figure 6) which is followed by the finisher operation to produce a finish forged part (7, see Figure 7). As described earlier, the ring rolled preform (5) has some inherent defects on its surface called wrinkles. If the ring rolled preform (5) is directly given as input to the finisher, these wrinkles lead to formation of cracks and cold shuts in the finished parts. To avoid this problem, as an aspect of the invention, a blocker operation has been introduced before the conventional finisher operation. The purpose of the blocker operation is to iron out the wrinkles thus avoiding any cracks or coldshuts in the final part. The advantages of introduction of blocker are as follows: 1. The blocker operation improves the material flow during the forging process and hence reduces the wear and tear of the finisher die. This helps in getting a consistent teeth profile in the final part.

2. The blocker operation irons out all the surface defects formed during the ring rolling process like wrinkles and thus completely avoids formation of the cracks and coldshuts (MPI indications) in finished part.

It should be noted that rough teeth shape is not formed in the blocker dies as any small mismatch in the blocker and finisher impression will lead to formation of multiple coldshuts and cracks on the teeth surface.

According to another aspect of this invention, the finisher dies are designed in such a way that, this will produce required teeth profile in the as-forged condition (see Figure 7). For this to happen, the impression in top die is designed in such a way that it has cavities shaped similar to the teeth profile of the crown wheel. The design of the teeth profile in the finisher dies is a very critical process. The shape of the cavities has to be designed in such a way that it has compensation for the forging temperature, shrinkage, scale loss, non-uniform temperature distribution, coining allowance, machining allowance, warpage allowance etc.

An iterative simulation approach for evaluation of numerous manufacturing concepts was used to optimize the part geometry of near net shape, forging die design and manufacturing process sequence using virtual manufacturing techniques. Forging part geometry i.e. near net shape and process was optimized using 3D metal flow simulation. Based on simulation results, an optimal die design and process sequence was developed for manufacturing crown wheel.

The formation of the teeth profile in finisher operation gives following benefits:

1. This significantly reduces the machining to be done for teeth formation.

This reduces the machining time as well as input material requirement.

2. As forged teeth profile ensures that the grain flow lines remain continuous along the contour of gear teeth profile and are not broken in the machining operation. This significantly enhances the strength of the teeth which leads to better performance of the crown wheel with higher service life.

After the iterative design and trial process, it is found that the machining allowance of 0.8 mm is required for proper machining.

Based on the finisher die cavity shape, the blocker die cavity shape has to be designed. The shape of the blocker die cavity is designed to give required material distribution and shape to the ring rolled preform.

The teeth profile formed in the conventional hot forging process is not very precise and accurate due to the inherent nature of the forging process. Due to this, sufficient machining allowance has to be given for proper machining of the crown wheel teeth. But, even after that it is found that the machined crown wheel teeth profile gets distorted during machining and post machining heat treatment. This minor distortion leads to inappropriate contact pattern between crown wheel and mating pinion leading to premature fatigue failure in service.

To overcome this technical difficulty of the conventional processes, in one aspect of the invention, a cold coining operation is introduced in the manufacturing process of the crown wheel. The cold coining operation has following benefits:

1. The minor cold plastic deformation done during the cold coining operation produces very precise and accurate teeth profile.

2. Due to this, during machining process uniform machining allowance is present along the complete profile of the teeth. This significantly reduces the distortion of teeth during machining.

3. The uniform machining allowance also reduces the uneven residual stress pattern generated during the machining process thus significantly reducing the distortion during post machining heat treatment process.

The crown wheel (1) showed in Figure 1 is the final finished product which goes into the assembly in the vehicle. The crown wheel shown in Figure 7 is the output of the finisher operation, or in other words it is as-forged crown wheel (7). A nominal machining allowance is left on the as-forged crown wheel. During the machining operation this allowance is removed giving it the required surface finish and geometric tolerances and the holes shown in Figure 1 are produced. Crown wheel manufacturing process

As shown in Figure 2, the invented crown wheel manufacturing process typically involves the following steps:

1. Billet Heating (first heat)

A billet of the required material chemistry is taken for this process. The section and length of the billet taken for this operation is predefined based on the material requirement for the part to be produced. This billet is heated in the oil or gas fired furnace in the temperature range of 1150-1280 °C for sufficient soaking time (first heat) to achieve uniform temperature in the heated billet.

2. Upsetting

This operation is carried out on the heated billet of step 1 using forging equipment for e.g. in a hammer. Two flat dies of predefined dimensions are used for the upset operation. The heated billet is placed on a bottom upsetting die and then upsetting operation is carried out. It is the operation to reduce the height and increasing the diameter so as to form a flat disc of dimensions required for next operation. The upsetting step results into an upset preform (3) as shown in Figure 3. Punching and Piercing

In this process firstly a blind hole or simply a hole (2) is made in the upset preform (3) of step 2 by punching on the disc to produce a punched upset preform (3 A), which is further subject to a piercing operation. This step leads to a pierced and punched disc termed as pierced preform (4) as shown in Figure 4. The pierced preform (4) has a ring type shape. The outer as well as the inner diameter of the pierced preform (4) is not as per the requirement of the crown wheel, therefore it is further processed in the ring rolling mill. Ring rolling

In this step, the pierced preform (4) disc is transferred to ring rolling press. The ring rolling operation is carried out using three rolls. Two rolls maintain the height of the pierced preform (4) during the rolling operation while the third roll increases the internal diameter of the pierced preform (4). At the end of the process a ring-rolled disc (in the shape of a ring) with required dimensions is produced, also termed as a ring-rolled preform (5) as shown in Figure 5. Blocker Forging

The ring-rolled preform (5) is next forged in forging equipment (for e.g. hammer) in order to obtain the blocker preform (6) of required shape as shown in Figure 6. This forging operation produces some flash (6A, 6B, see Figure 6). Trimming and Piercing

Excess material coming out in the form of flash (6A, 6B) from the blocker preform (6) forming step is removed in the trimming press and another piercing operation is also carried out to obtain a trimmed and pierced blocker preform (6C). Blocker preform Heating (second heat)

The trimmed and pierced blocker preform (6C) is heated in oil or gas fired furnace up to 1150 - 1280°C for a soaking time (second heat) sufficiently long to achieve uniform temperature throughout said trimmed and pierced blocker preform (6C). The product resulting from this step is a heated blocker preform (6D). Finish Forging with near net shape crown wheel

The heated blocker preform (6D) is subjected to a finisher (or finish forging) operation on a forging equipment capable of producing required energy and handling force produced during the operation. A near-net shape gear teeth profile is forged by finisher forging operation. This operation produces a finish forged part also termed as a finish forged part (7) as shown in Figure 7. The finish forged part has near-net shaped as-forged teeth profile (7 A). 9. Post Forging treatments

After the finisher operation, post forging operations are conducted on the finish forged part (7) leading to a treated finish forged part (8). These operations include shot blasting, heat treatment, crack detection etc.

10. Cold Coining

The treated finish forged part (8) is subjected to cold coining operation on forging equipment. Preferably it is done on a hydraulic press. In the cold coining operation a final very small deformation, in the range of 0.2 to 0.6 mm, is given to the teeth profile (denoted by 6 in Figure 7) to correct any distortion present in them. The resultant product is a cold-coined part (9).

11. Machining

The cold-coined part (9) is subjected to a machining process to obtain the final crown wheel (as shown in Figure 1). The 0.8 mm machining allowance can be removed using any one out of the two different processes (a. or b.) explained below:

a. Finish machining operation is used for removing most of the machining allowance. This is followed by heat treatment process for the hardening of the teeth surface. This heat treatment is followed by lapping process which gives the required surface finish to the teeth surface.

b. Pre machining operation is done to remove some of the machining allowance. This is followed by the heat treatment process for the hardening of the teeth surface. This heat treatment is followed by finish grinding operation which gives the required dimensions and surface finish to the teeth surface.

The hole (2) made in the punching and piercing operation evolves into a larger size through the various steps of manufacture, and the final crown wheel is as shown in Figure 1.

ADVANTAGES OF INVENTION

1. This new product will ensure the integrity of the metal flow lines and improved strength.

2. This forging product can save material, cost and resources.

3. The invented process will reduce the rejection of parts due to cold shuts, cracks etc.

4. This process also produces parts having better fatigue performance under the service condition as it has better contact pattern with the mating pinion drive.

It is evident from the foregoing discussion that the invention has a number of embodiments. These are disclosed below.

1. A method of manufacturing a crown wheel (1), characterized in that the said method comprises the steps of: - billet heating;

- upsetting said billet to produce an upset preform (3);

- piercing and punching the upset preform (3) leading to pierced and punched disc termed as a pierced preform (4);

- ring-roiling said pierced preform (4) leading to a ring rolled disc termed as ring-roiled preform (5);

- blocker forging the said ring-rolled preform (5) to obtain a blocker preform (6);

- trimming the excess material from, and piercing, said blocker preform (6) to obtain a trim-pierced blocker preform (6C);

- heating said trimmed and pierced blocker preform (6C) to obtain a heated blocker preform (6D);

- finish forging said heated blocker preform (6D) to obtain a finish forged part (7) with flash (6A, 6B);

- providing post-forging treatment to said finish forged part (7) to obtain a treated finish forged part (8);

- cold coining said treated finish forged part (8) to obtain a cold coined part

(9);

- machining said cold coined pari.

A method as disclosed in embodiment 1, characterized in that, in said step of billet heating, the heating of said billet is carried out in a furnace at a temperature range of 1150-1280°C for a first soaking time sufficiently long to achieve a uniform temperature in the heated billet.

A method as disclosed in embodiment 2, characterized in that in said step of upsetting, said heated billet is placed on a bottom upsetting die and the upsetting operation is carried out using a forging equipment, preferably a hammer, whereby said upset preform (3), which is a flat disc, of dimensions required for said piercing and punching operation, is produced.

A method as disclosed in embodiment 3, characterized in that in said piercing and punching step, a hole (2) is made in said upset preform (3) by punching on said upset preform (3), followed by carrying out a piercing operation on the punched upset preform (3 A), thereby forming said pierced preform (4). A method as disclosed in embodiment 4, characterized in that in said step of ring-rolling, said pierced preform (4) is ring rolled in a ring rolling press to obtain said ring-rolled preform (5) of a disc shape.

A method as disclosed in embodiment 5, characterized in that in said step of blocker forging, said ring-rolled preform (5) is forged in said forging equipment, preferably a hammer, to obtain said blocker preform (6), further characterized in that in said step of trimming and piercing, the excess material on said blocker preform (6) in the form of said flash (6A, 6B) is removed using said trimming and piercing operation in a trimming press to obtain said trim-pierced blocker preform (6C). 7. A method as disclosed in embodiment 6, characterized in that in said step of part-heating the trimmed and pierced blocker preform (6C), said trim-pierced blocker preform (6C) is heated in an oil- or gas-fired furnace up to 1150 - 1280°C for a second heat soaking time sufficiently long to achieve uniform temperature throughout resultant said heated blocker preform (6D).

8. A method as disclosed in embodiment 7, characterized in that said finish forging operation carried out on said heated blocker preform using a forging equipment capable of producing required energy and handling force produced during the operation, to produce said finish forged part (7) having a near-net shaped gear tooth profile formation.

9. A method as disclosed in embodiment 8, characterized in that in said step of providing post-forging treatment, the post-forging treatment comprises the steps of shot blasting, heat treatment, and crack detection, leading to said treated finish forged part (8).

10. A method as disclosed in embodiment 9, characterized in that said step of cold-coining, the cold coining operation is performed on said treated finish forged part (8) in a forging equipment, preferably a hydraulic press, to produce said cold-coined part (9) that has a distortion-free gear tooth profile.

1 1 . A method as disclosed in embodiment 10, characterized in that said cold- coined part (9) has a nominal machining allowance.

12. A method as disclosed in any of embodiments 1 to 11, characterized in that said step of machining, said cold-coined part (9) is subjected sequentially to a finish machining-allowance-removing operation, hardening of the teeth surfaces by heat treatment, and providing a surface finish to the teeth surfaces by a lapping process.

13. A method as disclosed in any of embodiments 1 to 12, characterized in that said step of machining, said cold-coined part (9) is subjected sequentially to a pre-machining machining-allowance-removal operation, hardening of the teeth surfaces by heat treatment, grinding of teeth surface.

14. A method as disclosed in any of embodiments 1 1 to 13, characterized in that said machining allowance is up to 0.8mm in magnitude.

15. A crown wheel (1) characterized in that said crown wheel (1) is produced using a manufacturing method of any of embodiments 1 to 1 1 wherein said crown wheel (1) has continuous grain flow lines along the contours of gear teeth profile.

16. A crown wheel (1) as disclosed in embodiment 15, characterized in that said crown wheel has a machining allowance of 0.8mm,

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

Claims

Claims:

1. A method of manufacturing a crown wheel, characterized in that the said method comprises the steps of:

- billet heating;

- upsetting said billet to produce an upset preform (3);

- ring-rolling said pierced preform (4) leading to a ring rolled disc termed as ring-roiled preform (5);

- cold coining said treated finish forged part (8) to obtain a cold coined part

(9);

- machining said cold coined part.

A method as claimed in claim 1, characterized in that, in said step of billet heating, the heating of said billet is carried out in a furnace at a temperature range of 1150-1280 °C for a first soaking time sufficiently long to achieve a uniform temperature in the heated billet.

A method as claimed in claims 1 or 2, characterized in that in said step of upsetting, said heated billet is placed on a bottom upsetting die and the upsetting operation is carried out using a forging equipment, preferably a hammer, whereby said upset preform (3), which is a flat disc, of dimensions required for said piercing and punching operation, is produced.

A method as claimed in any of claims 1 to 3, characterized in that in said piercing and punching step, a hole (2) is made in said upset preform (3) by punching on said upset preform (3), followed by carrying out a piercing operation on the punched upset preform (3 A), thereby forming said pierced preform (4).

A method as claimed in any of claims 1 to 4, characterized in that in said step of ring-roiling, said pierced preform (4) is ring rolled in a ring rolling press to obtain said ring-rolled preform (5) of a disc shape.

A method as claimed in any of claims J to 5, characterized in that in said step of blocker forging, said ring-rolled preform (5) is forged in said forging equipment, preferably a hammer, to obtain said blocker preform (6), further characterized in that in said step of trimming and piercing, the excess material on said blocker preform (6) in the form of said flash (6A, 6B) is removed using said trimming and piercing operation in a trimming press to obtain said trim-pierced blocker preform (6C).

7. A method as claimed in any of claims 1 to 6, characterized in that in said step of heating the trimmed and pierced blocker preform (6C), said trim-pierced blocker preform (6C) is heated in an oil- or gas-fired furnace up to 1150 -

1280°C for a second heat soaking time sufficiently long to achieve uniform temperature throughout resultant said heated blocker preform (6D).

8. A method as claimed in any of claims 1 to 7, characterized in that said finish forging operation carried out on said heated blocker preform using a forging equipment capable of producing required energy and handling force produced during the operation, to produce said finish forged part (7) having a near-net shaped gear tooth profile formation.

9. A method as claimed in any of claims 1 to 8, characterized in that in said step of providing post-forging treatment, the post-forging treatment comprises the steps of shot blasting, heat treatment, and crack detection, leading to said treated finish forged part (8).

10. A method as claimed in any of claims 1 to 9, characterized in that said step of cold-coining, the cold coining operation is performed on said treated finish forged part (8) in a forging equipment, preferably a hydraulic press, to produce said cold-coined part (9) that has a distortion-free gear tooth profile.

11. A method as claimed in claim 10, characterized in that said cold-coined part (9) has a nominal machining allowance. A method as claimed in any of the claims 1 to 11, characterized in that said step of machining, said cold-coined part (9) is subjected sequentially to a finish machining-allowance-removing operation, hardening of the teeth surfaces by heat treatment, and providing a surface finish to the teeth surfaces by a lapping process.

A method as claimed in any of the claims 1 to 12, characterized in that said step of machining, said cold-coined part (9) is subjected sequentially to a pre- machining machining-allowance-removal operation, hardening of the teeth surfaces by heat treatment, grinding of teeth surface.

A method as claimed in any of claims 11 to 13, characterized in that said machining allowance is up to 0.8 mm in magnitude.

A crown wheel (1) characterized in that said crown wheel (1) is produced using a manufacturing method of any of claims 1 to 14 wherein said crown wheel (1) has continuous grain flow lines along the contours of gear teeth profile.

A crown wheel (1) as claimed in claim 15, characterized in that said crown wheel (1) has a machining allowance of 0.8mm.