FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Complete Specification
(See section 10 and rule 13)
A Process For Forging A Crankshaft
Bharat Forge Limited
An Indian company registered under the Indian Companies Act, 1956. Mundhwa, Pune - 411036, Maharashtra, India
The following specification particularly describes the invention and the manner in which it is to be performed.

Field of invention
The present invention relates to a method of manufacturing crankshaft which is used in an internal combustion engine or any similar kind of application. Particularly, the present invention relates to use of closed die hot forging process for manufacturing a crankshaft.
Introduction
Crankshaft is one of the most important and critical components of an Internal Combustion engine (IC engine). In an IC engine, the linear reciprocating motion produced by combustion of fuel in a piston cylinder assembly is converted into rotary motion by a crankshaft. The rotary motion is further transferred to wheels through a gear box and the transmission system of a vehicle.
The crankshaft has to face critical loads during its working which include bending loads as well as torsional loads. These loads are not continuous in time and are alternating in the direction of their application, which leads to bending and torsional fatigue loading on the crankshaft.
The crankshaft has to be designed such that it should be able to withstand these fatigue loads. Various factors have an effect on this, one of which is the manufacturing process used for producing a crankshaft. One of the most popular methods to produce a crankshaft is hot forging. The microstructure and grain flow obtained during the hot forging process gives optimum fatigue resistance to a

crankshaft. These properties are not achievable through other manufacturing processes, for example casting.
A typical crankshaft is shown in Figure 1. The crankshaft (1) shown in the figure is a 6-cylinder crankshaft. A crankshaft has a longitudinal central axis (2). On the one end of a crankshaft is a flange (3) and on the other is a tail (4). Journals (5) lie on the longitudinal central axis (2) of crankshaft (1). The journals (5) along with bearings are assembled with the engine block. Pins (6) lie on their own axes (7) which are parallel to the longitudinal central axis (2) of the crankshaft (1) but are offset from it by a distance which is called the throw (T) (shown in Figure 2) of the crankshaft (1). Journals (5), pins (6), tail (4) and flange (3) together are called barrels or cylinders.
The pins (6), tail (4) and flange (3) are connected with journals (5) by webs (8). Counterweights (9) are provided on the webs (8) for the balancing of the crankshaft (1). These counterweights (9) can be manufactured either integrally or separately with web (8) (bolted or welded to web).
The number of pins (6) and journals (5) in a crankshaft (1) depends on the number of cylinders present in the IC engine. The number of pins (6) is always equal to the number of cylinders in the IC engine while number of journals (5) is equal to number of pins (6) plus one. The pins (6) and journals (5) are numbered starting

from tail (4) side and moving towards flange (3). Thus, the journal (5) closest to tail (4) is numbered as J1 and so on. Thus, the journals (5) are numbered from J1 to J7 in a 6-cylinder engine crankshaft. Similarly, pins (6) are numbered from P1 to P6 in a 6-cylinder engine crankshaft. Number of pins (6) in a crank or crankshaft defines the shape and configuration of the crankshaft (1). For example, a 4-cylinder crankshaft will have axes (7) of all pins (6) in the same plane while in a 6-cylinder crankshaft the axes (7) of pins (6) lie in 3 planes (OA, OB, and OC) situated 120° apart from each other. Figure 2 shows schematically the position of pins (6) with respect to journals (5) of a 6-cylinder crankshaft (1). As can be seen the Journals (5) lie on the central longitudinal axis (2) while axes of pairs of pins each lie on different planes which are 120° apart i.e., P1 and P6 on plane OA, P2 and P5 on plane OB, and P3 and P4 on plane OC. The throw (T) is also shown in Figure 2.
The configuration of a crankshaft has significant effect on the hot forging process used to produce it. Due to the shape and configuration of a crankshaft, the shape and configuration of the forging dies changes. The forging dies for 4-cylinder crankshaft are plane while for 6-cylinder crankshaft the dies have locks, and thus, are not plane. Further, 4-cylinder crankshaft, generally, does not require reduce rolling (RR) operation, but, for 6-cylinder crankshaft, RR is required in most cases. Thus, basically when you move from 4 cylinder to 6 cylinder, the forging process design philosophy changes completely.

The hot forging process starts from a “rolled” round or rounded corner section (RCS) billet which is then subjected to various forging operations. Typically for a 6-cylinder engine crankshaft (1) the forging process consists of Reduce Rolling (RR) – Blocker Forging (BLK) - Finisher Forging (FIN). These are explained briefly.
1. Reduce Rolling – Billet has to first undergo a reduce rolling operation. The reduce rolling operation reduces the cross-sectional dimension (diameter or RCS) of the billet at the locations where the material requirement is less while keeping these dimensions unchanged where the material requirement is more. In a 6-cylinder crankshaft which is forged in position, normally in reduce rolling operation the cross-sectional dimension is reduced in the region of pin numbers P2 and P5. In some cases the dimension is reduced even in the tail region. In the conventional manufacturing process, the axis of the reduce rolled preform remains straight.
2. Blocker forging – The reduce rolled preform is further subjected to blocker forging operation to produce a blocker preform. The blocker dies have cavities in both top and bottom die which have rough external shape of the crankshaft. Maximum material deformation and hence, material flow is produced in the blocker forging.

3. Finisher forging – The blocker preform is next subjected to finisher forging operation to produce final forged crankshaft. In this operation, finisher dies are used which have cavities in both top and bottom die which have shape exactly same as the external shape of the crankshaft with machining allowances. Finisher operation produces the final shape of the forged crankshaft.
Due to complex shape of a 6-cylinder crankshaft, the conventional forging process sequence i.e., Reduce Rolling (RR) –> Blocker Forging –> Finisher Forging has certain disadvantages which are listed below:
1. Forging Defects – In a conventional forging process, the material distribution produced in the RR operation is not optimum and hence, die fill-up is not good in both blocker and finisher operation. This leads to defects in the final crankshaft like underfillings, coldshuts, cracks etc.
2. Poor Yield of forging – Yield of forging process is defined as the ratio of weight of input material (or billet) to the weight of the final forged crankshaft. In the conventional forging process explained above, excess material has to be provided in the billet in order to achieve final shape of the crankshaft and avoid the aforementioned forging defects. This reduces the yield of the process to 70 to 75%. This means up to 25 to 30% of the material is wasted in the form of flash formation.

3. Lower die life – Higher input material means more material flow which leads to early wear of the dies. Further, due to underfilling issues, higher pressures have to be produced in the forging die cavities for fill-up and this leads to die cracking.
4. Higher cost of production – Due to higher defect rates, lower yield, and lower die life, the cost of production is also unnecessarily high.
Thus, there exists a room for advancement over the existing technology for forging a 6-cylinder crankshaft to achieve better material distribution and, consequently, lower defects, higher yields, better die life and lower cost of production.
Objects of invention
It is an object of the present invention to provide a closed die hot forging process
for a 6-cylinder crankshaft.
It is another object of the present invention to provide a closed die hot forging process which reduces the defects produced during the conventional 6-cylinder crankshaft forging process.
It is still another object of the present invention to provide a closed die hot forging process designed to improve the yield of manufacturing a 6-cylinder crankshaft.

Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
Brief description of accompanying drawings
Figure 1 shows a 6-cylinder crankshaft
Figure 2 schematic representation of the relative position of pins and journals in a
6-cylinder crankshaft.
Figure 3 shows the conventional forging process for a 6-cylinder crankshaft.
Figure 4 shows the invented forging process for a 6-cylinder crankshaft.
Figure 5a shows a schematic diagram of front view of a reduce rolled preform
Figure 5b shows the schematic view of side view of the reduce rolled preform
Figure 6a shows the schematic view of the top view of the double plane bender
preform
Figure 6b shows the schematic view of the side view of the double plane bender
preform
Figure 7 shows the schematic view of the double plane bender dies
Summary Of Invention:
The invention discloses a method of manufacturing crankshaft which is used in an internal combustion engine or any similar kind of application. Particularly, the present invention discloses a closed die hot forging process for manufacturing a

six-cylinder crankshaft. The closed die hot forging process of the invention is characterised by introduction of a step of double plane bending between the steps of reduce rolling and blocker forging used in conventional methods.
To overcome the disadvantages of the conventional forging process, an innovative forging process has been designed which includes a step of double plane bending (102) between the reduce rolling operation (101) and the blocker forging operation (103). For this purpose, a special double plane bender die (82) has been designed and implemented.
During the double plane bending operation (102), the Reduce Roll (RR) preform (41) is placed and located on the bottom bender die (72). Next, double plane bending operation (102) takes place when top (71) and bottom (72) bender dies come together due to the forging stroke of the press. The RR preform (41) is deformed such that the axis of first (52) and second (56) smaller diameter’s portion corresponding to P2 and P5 (6) of crankshaft (1) remain same while all the bigger diameter portions (50, 54, 58) along with all the tapered portions (51, 53, 55 and 57) are deformed or shifted such that a bias in the material is formed towards the positions of counterweights (9) of crankshaft (1) which requires more material to fill-up. Due to this bias, the axis (221, 222, 223) of all the bigger diameter portions (60, 64 and 68) and all the tapered portions (61, 63, 65 and 67)

of double plane bender preform (42) shift downwards and towards counterweight side (9) as shown in Figure 6(a) and 6(b).
It can be seen from Figure 6(a) that the double plane bender operation (102) bends the RR preform (41) such that the axis (221, 222, 223) of all the bigger diameter portions (60, 64 and 68) become offset from the central longitudinal axis (2). Thus, the axis (221) of first bigger diameter portion (60) is offset from the longitudinal axis of bender preform (22) by a value of Y1 in Y direction and Z1 in Z direction. Similarly, the axes (222 and 223, respectively) of the second bigger diameter portion (64) and the third bigger diameter portion (68) are offset by a value of Y2 and Y3 in Y direction and Z2 and Z3 in Z direction, respectively. Thus, in the invented bender operation (102) the bending of the RR preform (41) occurs in 2 directions or 2 planes.
The bender die apparatus (82) disclosed in the invention consist of a Bender Top die (71) and a Bender Bottom Die (72). Each die, i.e. Bender Top die (71) and Bender Bottom Die (72), consists of 2 Dowel holes namely rectangular dowel hole (73) and round dowel hole (74). These dowel holes are used for the alignment of the bender top and bottom dies (71, 72) with the cassette (not shown) which is further assembled with die holders (not shown) on press bed and press ram. Without these dowel holes (73, 74) configuration in the bender dies (82), a mismatch may exist between the impressions of the bender top (71) and bender

bottom (72) dies. For this alignment, two round dowel pins are available on the top cassette and bottom cassette.
Both top (71) and bottom (72) bender dies are clamped to top and bottom cassettes by any clamping means. For the purpose of clamping, the clamping slots (75) are provided in both top (71) and bottom (72) bender dies.
The impression (79) in the bender top (71) and bottom (72) dies is designed such that when the RR preform (41) is kept on the Bender Bottom die (72), it is properly located on the bottom die (72) and does not dislocate during the double plane bender forging operation (102). This location is achieved when the RR preform (41) is kept on the Bender bottom die (72) such that the first (52) and second (56) smaller portions of the RR preform (41) touches at least few portions of impressions (79) of the bender bottom die (72) that are producing the first (62) and second (66) smaller diameter portions of bender preform (42). Further the first (50) and third (58) bigger diameter portions of the RR preform (41) rests on at least few portions of impressions (79) of the bender bottom die (72) that are producing the first (60) and third (68) bigger diameter portions of bender preform (42).
The impression or cavity (79) in the bender top (71) and bottom (72) dies are such that when the RR preform (41) is deformed by keeping it in the cavity of the bender bottom die (72), it deforms into the bender preform (42) shown in Figure

6(a) and Figure 6(b). While manufacturing the bender top (71) and bottom (72) dies, in order to produce the required cavity (79), three locks (76, 77 and 78) have to be provided in the top (71) and bottom (72) dies. Locks here means the protrusion and depressions in the cavity surfaces of dies which correspond to the offsets Y1, Y2, Y3, Z1, Z2 and Z3 of the bender preform (42) (shown in Figure 6(b)).
List of parts
1. 6-Cylinder Crankshaft 42. Bender Preform
2. Longitudinal central axis of 43. Blocker Preform crankshaft 25 44. Finisher
3. Flange 50. First Bigger diameter portion of
4. Tail RR preform corresponding to
5. Journals Tail, J1, J2 and P1
6. Pins 51. First Tapering portion of RR
7. Longitudinal axis of pins 30 preform corresponding to
8. Webs Flange, J1, J2 and P1
9. Counterweights 52. First Smaller diameter portion of

21. Longitudinal axis of RR preform RR preform corresponding to P2
22. Longitudinal axis of bender 53. Second Tapering portion of RR preform 35 preform corresponding to J3, J4,
41. RR preform J5, P3 and P4

54. Second Bigger diameter portion 62. First Smaller diameter portion of of RR preform corresponding to bender preform corresponding to J3, J4, J5, P3 and P4 P2
55. Third Tapering portion of RR 25 63. Second Tapering portion of preform corresponding to J3, J4, bender preform corresponding to J5, P3 and P4 J3, J4, J5, P3 and P4
56. Second Smaller diameter portion 64. Second Bigger diameter portion of RR preform corresponding to of bender preform corresponding P5 30 to J3, J4, J5, P3 and P4
57. Fourth Tapering portion of RR 65. Third Tapering portion of preform corresponding to J6, J7, bender preform corresponding to P6 and Tail J3, J4, J5, P3 and P4
58. Third Bigger diameter portion of 66. Second Smaller diameter portion RR preform corresponding to J6, 35 of bender preform corresponding J7, P6 and Flange to P5

60. First Bigger diameter portion of 67. Fourth Tapering portion of bender preform corresponding to bender preform corresponding to Tail, J1, J2 and P1 J6, J7, P6 and Tail
61. First Tapering portion of bender 40 68. Third Bigger diameter portion of preform corresponding to bender preform corresponding to Flange, J1, J2 and P1 J6, J7, P6 and Flange

62. Bender Bottom Die 223. Longitudinal axis of 68
63. Rectangular Dowel Hole OA, OB and OC: Planes on which
64. Round Dowel Hole 25 the axes of pins of crankshaft
65. Die Clamping slots lie.
66. Lock 1 T: Throw of the crankshaft
67. Lock 2 J1 to J7: Journals of a 6-cylinder
68. Lock 3 crankshaft starting from tail to
69. Bender die cavities or 30 flange
impression P1 to P6: Pins of a 6-cylinder
81. Reduce Rolling Dies crankshaft starting from tail to
82. 2 plane bender die flange
83. Blocker dies Y1: Offset between Axis 22 and
84. Finisher Dies 35 Axis 221 in Y direction

100. Billet Heating Operation Y2: Offset between Axis 22 and
101. Reduce Rolling Operation Axis 222 in Y direction
102. Double plane Bender Y3: Offset between Axis 22 and operation Axis 223 in Y direction
103. Blocker forging operation 40 Z1: Offset between Axis 22 and
104. Finisher forging operation Axis 221 in Z direction
105. Post Forging Operations Z2: Offset between Axis 22 and

221. Longitudinal axis of 60 Axis 222 in Z direction
222. Longitudinal axis of 64

Z3: Offset between Axis 22 and Axis 223 in Z direction
Description of the invention
The present invention is directed towards the manufacturing of a 6-cylinder engine crankshaft (1) using closed die hot forging process such that the drawbacks of the conventional forging process like forging defects, low yield, low die life and higher production cost can be overcome. As previously explained, the above problems occur due to the complex geometry of the 6-cylinder crankshaft (1) and the forging process consisting of RR operation (101) – Blocker operation (103) – Finisher operation (104) being used for its manufacturing (refer Figure 3). The conventional manufacturing process is not able to produce optimum/proper material distribution in the preforms RR (41) and Blocker (43) produced by performing RR operation (101) and Blocker operation (103) on the input billet. This is considered as flaw in the conventional manufacturing process for causing all the above drawbacks.
It is to be noted that the Finisher operation (104) produces the final as forged crankshaft. Thus, the shape of the output the finisher forging step (104) is exactly same as that of final crankshaft (1). Thus, all the reference numerals and orientation of the crankshaft given in Figure 1 and 2 can be used as it is for the finisher (44).
Further, the blocker preform is a rough shape of the crankshaft or finisher and has same components i.e., pins, journals, tail, flange, counterweights and webs as that

of finisher. Further the orientation and relative positions of all these components is also same as that of finisher.
Thus, the schematic of Figure 2 is equally applicable for crankshaft (1), Blocker preform (43) and finisher preform (44).
The problem of material distribution arises because of the reduce rolling operation (101). This reduce rolling operation (101) is capable of reducing material only along the longitudinal axis of the billet. A typical schematic of RR preform (41) is shown in Figures 5a and 5b. During the Reduce Rolling operation (101) the billet is deformed such that its shape changes from cylindrical to a stepped cylinder shape shown in Figure 5(a). Here, the volume of material in the first (52) and second (56) smaller diameter portions of RR preform (41) correspond to volume of material in the P2 and P5 pins (6), respectively, of the crankshaft (1) (Refer Figure 1). While the volume of material in the first bigger diameter portion (50) along with the first tapering portion (51) correspond to volume of material in tail (4), J1, J2 (5) and P1 (6); volume of material in the second bigger diameter portion (54) along with the second (53) and third (55) tapering portions correspond to volume of material in J3, J4, J5 (5), P3 and P4 (6), while volume of material in the third bigger diameter portion (58) along with fourth tapering portion (57) correspond to volume of material in J6, J7 (5), P6 (6) and Flange (3). The axis (21) of the various smaller and bigger diameter portions on the reduce rolled preform (i.e., 50, 52, 54, 56 and 58) remains same. The RR preform (41)

has first (50), second (54) and third (58) bigger diameter portions, first (52) and second (56) smaller diameter portions and first (51), second (53), third (55) and fourth (57) tapering portions which are coaxially positioned with respect to the longitudinal axis (21) of the RR preform (41). It can be seen from Figure 5 (a), the first bigger diameter portion (50) and the first smaller diameter portion (52) are connected by the first tapering portions (51); the first smaller diameter portion (52) and the second bigger diameter portion (54) are connected by the second tapering portions (53); the second bigger diameter portion (54) and the second smaller diameter portion (56) are connected by the third tapering portion (55) and the second smaller diameter portion (56) and the third bigger diameter portion (58) are connected by the fourth tapering portion (57). Both the first (50) and third (58) bigger diameter portions are connected at only one end to the aforesaid portions and their other end is kept free.
As can be seen in Figure 2, the position of the journals (5) i.e., J1 to J7 are along the longitudinal central axis (2) of the crankshaft (1) (and thus, in blocker preform (43) and finisher (44)). Thus, when the longitudinal axis (21) of the reduce rolled preform (41) is matched with the longitudinal axis (23) of the blocker preform (43) during the blocker forging operation (103), enough material is available for the fill-up of the journals (5).
Contrary to this, as seen in Figure 2, the pins (6) are offset from the longitudinal central axis (2) of crankshaft (1) by the throw T and this offset doesn’t lie only in

one plane but, the offset lies in 3 different planes i.e., OA, OB, and OC (this phenomenon is same in blocker preform (43) and finisher (44)). In the orientation of Figure 2, when the RR preform (41) is aligned with the axis (23) of the blocker preform (43), there is material available for fill-up of P2 and P5 (6) but, at other pins (6) the axis (21) of the RR preform (41) is not aligned with the axis of P1, P3, P4 and P6 (6). The counterweights (9) are present on both sides (longitudinally) of all the pins (6) except P2 and P5 and are present in the diagonally opposite direction (transversely) with respect to the longitudinal central axis (2) of the crankshaft (Refer Figure 1) (same will be applicable for blocker preform (43) and finisher (44)). Thus, the material of RR preform (41) is neither properly aligned with the pins (6) or the counterweights (9). Further, the material required for the pins (6) and counterweights (9) is different (due to their geometry). Thus, counterweights (9) require more material than pins (6). In other words, the distribution of the material should be such in the preform that more material is available towards counterweight (9) and lesser towards the pins (6). As the RR (41) has no such biasing or distribution of the material, almost equal material flows towards pin (6) and counterweights (9) in the blocker forging operation (103). Therefore an excess volume of material has to be provided in RR preform (41) in the region of (50), (54) and (58) so that it fills up the counterweight (9) cavities in blocker (83) and finisher (84) forging dies. But, due to this, excess material flows towards the pin (6) cavities in blocker (83) and finisher (84) forging dies which leads to early fill-up of the pin (6) cavities in blocker (83) and finisher (84) forging dies and excess material is thrown out of blocker (83) and finisher (84) forging dies as flash.

Due to this, following problems occur:
1. The overall yield of the process deteriorates and unnecessary extra volume of material has to be provided in RR preform (41).
2. More die stresses are produced in pin (6) cavities of forging dies which leads to cracking of the blocker (83) and finisher (84) dies.
3. Early fill-up and more material flow in pin (6) cavities lead to significant wear of the blocker (83) and finisher (84) dies in this area.
4. Higher cost of the crankshaft (1) forging due to excess material requirement and cost involved in die repair to be done for cracking and wear.
To overcome the above disadvantages of the conventional forging process, an innovative forging process has been designed which includes a step of double plane bending (102) between the reduce rolling operation (101) and the blocker forging operation (103). For this purpose, a special double plane bender die (82) has been designed and implemented. The reduce rolled preform or RR preform (41) is taken as input to the double plane bender dies (82). The double plane bender dies (82) consist of a top die (71) and a bottom die (72). The bottom bender die (72) is assembled to the bottom cassette (not shown) which in turn is assembled on the bottom die holder (not shown) which is installed on the bed of a closed die forging press (not shown). Similarly, the top bender die (71) is assembled on the top cassette (not shown) which is assembled on the top die holder (not shown) which further is attached to the RAM of the press (not shown). For the manufacturing of the crankshaft (1), any type of forging equipment like a mechanical press or a screw press or a wedge press or a hydraulic press or a hammer can be used. The reduce rolling operation (101) is carried out using

reduce rolling machine. The double plane bending operation (102), blocker forging operation (103), finisher forging operation (104) and post forging operations (105) can be performed either on the same forging equipment or different forging equipment. Preferably any type of forging press is selected for hot forging the crankshaft.
During the double plane bending operation (102), the RR preform (41) is placed and located on the bottom bender die (72). Next, double plane bending operation (102) takes place when top (71) and bottom (72) bender dies come together due to the forging stroke of the press. The RR preform (41) is deformed such that the axis of first (52) and second (56) smaller diameter portions corresponding to P2 and P5 (6) of crankshaft (1) remain same while all the bigger diameter portions (50, 54, 58) along with all the tapered portions (51, 53, 55 and 57) are deformed or shifted such that a bias in the material is formed towards the positions of counterweights (9) of crankshaft (1) which requires more material to fill-up. Due to this bias, the axis (221, 222, 223) of all the bigger diameter portions (60, 64 and 68) and all the tapered portions (61, 63, 65 and 67) of bender preform (42) shift downwards and towards counterweight side (9) as shown in Figure 6(a) and 6(b). This way the bending of the RR preform (41) is not restricted to one plane but takes place in two planes. Figure 6a shows the relative position of all tapered, bigger and smaller diameter portions of RR preform (41) after the bending operation (which is now a bender preform (42)). The bias of the material toward the position of counterweights (9) in crankshaft (1) is seen in these figures.

The bender preform (42) has first (60), second (64) and third (68) bigger diameter portions, first (62) and second (66) smaller diameter portions and first (61), second (63), third (65) and fourth (67) tapering portions which are eccentrically positioned with respect to the longitudinal axis (22) of the bender preform (42). It can be seen from Figure 6 (a), the first bigger diameter portion (60) and the first smaller diameter portion (62) are connected by the first tapering portions (61), the first smaller diameter portion (62) and the second bigger diameter portion (64) are connected by the second tapering portions (63), the second bigger diameter portion (64) and the second smaller diameter portion (66) are connected by the third tapering portions (65) and the second smaller diameter portion (66) and the third bigger diameter portion (68) are connected by the fourth tapering portions (67). Both the first (60) and third (68) bigger diameter portions are connected at only one end to aforesaid portions while their other end is kept free.
Figure 6 (a) and (b) shows the two views of the bender preform (42) along with the coordinate axes X, Y and Z. Figure 6(a) shows the top view of the bender preform (42) i.e., when the preform is seen along Z axis. Figure 6(b) shows the side view of the bender preform (42) i.e., when the preform is seen along the X axis.
From Figure 6(a) it can be seen that the bender operation (102) bends the RR preform (41) such that the axis (221, 222, 223) of all the bigger diameter portions (60, 64 and 68) become offset from the central longitudinal axis (22). Thus, the axis (221) of first bigger diameter portion (60) is offset from the longitudinal axis

of bender preform (22) by a value of Y1 in Y direction and Z1 in Z direction. Similarly, the axes (222 and 223, respectively) of the second bigger diameter portion (64) and the third bigger diameter portion (68) are offset by a value of Y2 and Y3 in Y direction and Z2 and Z3 in Z direction, respectively. Thus, in the invented bender operation (102) the bending of the RR preform (41) occurs in 2 directions or 2 planes.
In one embodiment of the invention, the offset in Z direction i.e., Z1, Z2 and Z3 are similar in value with a variation up to 25%. In another embodiment, the offset in direction Y i.e., Y1, Y2 and Y3 are similar in value with a variation up to 20%.
In one embodiment, the offset values in the bender preform (42) are derived in relation with the Throw (T) of the crankshaft. In one preferred embodiment, the offset values Y1, Y2 and Y3 are in the range of 20 to 45% of that of the value of throw (T) of the crankshaft, the offset values Z1 and Z3 are in the range of 32 to 47% of that of the value of throw (T) of the crankshaft and the offset value Z2 is in the range of 33 to 59% of that of the value of throw (T) of the crankshaft.
In the present invention, the inventors have tried to produce different configurations of bender preform (42) with the help of different configurations of impressions present in the bender dies (82). In one configuration i.e., single plane bend configuration, the inventor has compared the results of single plane bend preform with results of double plane bend preform and found following advantages of double plane bend configuration over the single plane bend configuration:

1. The double plane bend configuration improves the stability of the bender preform (42) on the blocker dies (83). When the bender preform (42) from double plane bend configuration is placed on a blocker (83) bottom die, as all bigger diameter portions (60, 64, 68) of the bender preform (42) are placed on both side of the central axis as well as in downward direction, the stability of the bender preform (42) is much better as compared with the bender preform produced by single plane bend configuration.
2. As the positions of the P1, P6, P3 and P4 pins (6) and their corresponding counterweights (9) are offset from positions of the P2 and P5 pins (6) in two different directions, the bender preform (42) produced by double plane bend configuration helps in better material flow and fill-up of the blocker (83) and finisher (84) die cavities.
In one of embodiment, the invented process uses a die apparatus for bending the RR preform (41) during the double plane bender operation (102). This die apparatus i.e., Double Plane or 2 plane Bender Die (82) is shown in Figure 7. The bender die apparatus (82) consist of a Bender Top die (71) and a Bender Bottom Die (72). Both Bender Top die (71) and Bender Bottom Die (72) consist of 2 Dowel holes namely rectangular dowel hole (73) and round dowel hole (74). These dowel holes are used for the alignment of the bender top and bottom dies (71, 72) with the cassette (not shown) which is further assembled with die holders (not shown) on press bed and press ram. Without these dowel holes (73, 74) configuration in the bender dies (82), a mismatch may exist between the impressions of the bender top (71) and bender bottom (72) dies. For this

alignment, two round dowel pins are available on the top cassette and bottom cassette.
Both top (71) and bottom (72) bender dies are clamped to top and bottom cassettes by any clamping means. For this purpose of clamping, the clamping slots (75) are provided in both top (71) and bottom (72) bender dies.
The impression (79) in the bender top (71) and bottom (72) dies is designed such that when the RR preform (41) is kept on the Bender Bottom die (72), it is properly located on the bottom die (72) and does not dislocate during the bender forging operation (102). This location is achieved when the RR preform (41) is kept on the Bender bottom die (72) such that the first (52) and second (56) smaller portions of the RR preform (41) touches at least few portions of impressions (79) of the bender bottom die (72) that are producing the first (62) and second (66) smaller diameter portions of bender preform (42). Further the first (50) and third (58) bigger diameter portions of the RR preform (41) rests on at least few portions of impressions (79) of the bender bottom die (72) that is producing the first (60) and third (68) bigger diameter portions of bender preform (42).
The impression or cavity (79) in the bender top (71) and bottom (72) dies are such that when the RR preform (41) is deformed by keeping it in the cavity of the bender bottom die (72), it deforms into the bender preform (42) shown in Figure 6(a) and Figure 6(b). While manufacturing the bender top (71) and bottom (72) dies, in order to produce the required cavity (79), three locks (76, 77 and 78) have to be provided in the top (71) and bottom (72) dies. Locks here means the

protrusion and depressions in the cavity surfaces of dies which correspond to the offsets Y1, Y2, Y3, Z1, Z2 and Z3 of the bender preform (42) (shown in Figure 6(b)). While manufacturing the bender top (71) and bottom (72) dies, first rectangular die blocks are taken which are then machined in following order:
1. Sizing of the die blocks: Here the die blocks are machined to make it perfectly rectangular with required envelop dimensions.
2. Produce Dowel holes: Next, the round (74) and rectangular (73) dowel holes are produced by machining.
3. Produce the locks: With reference to these dowel holes, the 3 locks (76, 77 and 78) on the top surface of both dies are next produced by machining.
4. Produce the cavities or impression: Only after machining the locks (76, 77 and 78), the cavities (79) are produced by machining in the die blocks.
5. Produce auxiliary features: In this step, the auxiliary features like clamping slots (75) etc. are produced by machining.
The invented process will be now explained in detail.
1. Supplying Input Raw Material: According to the invented process, the manufacturing process starts with a forged, extruded or rolled billet as a raw material. The billet can be cylindrical or rounded cross section (RCS) billet.
2. Billet Heating (100): The billet is heated to the required temperature in a furnace. The billet can be heated in an oil fired or gas fired or electric or induction furnace. The billet is heated in the temperature range of 1150 to 1250 °C.

3. Reduce Rolling Operation (101): The heated billet is then transferred to reduce rolling machine where reduce rolling operation (101) takes place. A set of reduce rolling dies (81) are used for performing this operation. During the reduce rolling operation (101), the heated cylindrical or RCS billet is deformed into a stepped Reduced Rolled (RR) preform (41) as shown in Figure 5. The output of this process is an RR preform (41).
4. Double plane bender operation (102): The RR preform (41) is then transferred to forging equipment having double plane bender dies (82). During this operation, the RR preform (41) is deformed to produce the required bias in the shape of preform towards the counterweights (9) of the crankshaft (1). The output of this stage is Bender preform (42).
5. Blocker forging operation (103): Next, the Bender preform (42) is transferred to the blocker dies (83) where blocker operation (103) takes place. The blocker forging operation (103) produces rough shape of the crankshaft with maximum material flow happening in this stage with some excess material thrown out as flash. The output of this stage is the blocker preform (43).
6. Finisher forging operation: Next, the blocker preform (43) is transferred to the finisher dies (84) where the finisher forging operation (104) takes place. In this operation, the final shape of the forged crankshaft is formed with small amount of material thrown in the form of flash.

7. Post-forging operations: The finisher operation (104) is followed by post forging operations like trimming, padding, shot blasting, heat treatment, machining etc. This produces the final crankshaft (1).
The benefits of this invention are as follows:
1. Forging Defects – The invented forging process leads to better material distribution in the bender preform (42) which leads to better die fill-up in blocker (83) and finisher (84) dies. This eliminates forging defects like underfilling, coldshuts, cracks etc.
2. Yield of forging – Better material distribution in the bender preform (42) ensures that very less material is wasted. Thus, with invented design of bender preform (42), the same crankshaft (1) fills up with lesser input material. Yield improvement of 10 to 15% can be achieved using the invented design thus, reducing the material wastage.
3. Die life – Better material distribution, improved fill-up and good material flow due the invented design of bender preform leads to improvement in blocker (83) and finisher (84) die life. Wear and cracks in the dies are reduced drastically improving the productivity of the forging process.
4. Cost of production – Lower defect rates, higher yield and increased die life helps in reducing the cost of production.

The invention is now illustrated with the help of non-limiting examples. The examples are merely for illustration purpose and should not be construed to limit the scope of the invention.
Example 1:
A 6- cylinder 4 counterweight crankshaft having throw 78 mm is being forged using invented method of closed die hot forging in which a double plane bending operation is introduced between steps of reduced rolling and blocker forging.
During the said double plane bending operation, it bends the RR preform such that the axis of all the bigger diameter’s portions of bender preform become offset from its central longitudinal axis.
The offset values in the bender die design are derived in relation with the Throw (T) of the crankshaft. The values of these offsets are selected such that the bending of RR preform is going to happen in double plane. Respectively, the selected offset values in Y directions i.e. Y1, Y2 and Y3 are 30%, 38% and 30% of that of the value of throw (T) of the 6 cylinder crankshaft. The selected offset values in Z direction i.e. Z1, Z2 and Z3 are 39%, 51% and 39% of that of the value of throw (T) of the 6 cylinder crankshaft respectively.

The offsets in Z direction i.e., Z1, Z2 and Z3 are similar in value with a variation up to 23% while the offsets in Y direction i.e., Y1, Y2 and Y3 are similar in value with a variation up to 20%.
Thus, the axis of first bigger diameter portion of bender preform is offset from its longitudinal axis by a value of 23.3 mm i.e. Y1 in Y direction and 30.45 mm i.e. Z1 in Z direction. Similarly, the axes of the second bigger diameter portion and the third bigger diameter portion of bender preform are offset by a value of 29.3 mm i.e. Y2 and 23.3 mm i.e. Y3 in Y direction and 39.55 mm i.e. Z2 and 30.45 mm i.e. Z3 in Z direction. Thus, in the invented bender operation, the bending of the RR preform occurs in 2 directions or 2 planes.
Due to incorporation of double plane bending operation between steps of reduced rolling and blocker forging, better material distribution in the bender preform is achieved. This ensures that very less material is wasted. It is thus clear from this example that with invented design of bender preform, the same crankshaft fills up with 10% lesser input material.
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.

We claim:
1. A method of manufacturing of a 6-cylinder crankshaft (1) from a forged,
extruded or rolled billet having cylindrical or rounded cross section (RCS)
by using a closed die hot forging process comprising the steps of:
a. heating the billet;
b. reduce rolling;
c. blocker forging;
d. finisher forging;
e. post-forging operations,
characterized in that a step of double plane bending is introduced between the steps of reduce rolling (b) and blocker forging (c).
2. The method as claimed in claim 1, wherein in the step of billet heating, the billet is heated to a temperature of 1150 to 1250 °C in an oil fired or gas fired or electric or induction furnace.
3. The method as claimed in claim 1, wherein in the step of reduce rolling, the heated billet is transferred to a reduce rolling machine having a set of reduce rolling dies (81) to deform it using reduce rolling operation (101) into a stepped reduced rolled (RR) preform (41).
4. The method as claimed in claim 1, wherein in the step of double plane bending, the RR preform (41) is transferred to a forging equipment, preferably a forging press, having a set of double plane bender dies (82) to deform it using a double plane bending operation (102) to produce a

bender preform (42) that has a bias in the shape towards the positions of counterweights (9) of the crankshaft (1).
5. The method as claimed in claim 1, wherein in the step of blocker forging, the bender preform (42) is transferred to the same or different forging equipment, preferably the forging press, having a set of blocker dies (83) to deform it using a blocker forging operation (103) to produce a blocker preform (43) which has the rough shape of the crankshaft (1).
6. The method as claimed in claim 1, wherein in the step of finisher forging operation the blocker preform (43) is transferred to the same or different forging equipment, preferably the forging press, having a set of finisher dies (84) to deform it using a finisher forging operation (104) to produce the final shape of forged crankshaft.
7. The method as claimed in claim 3, wherein the RR preform (41) has first (50), second (54) and third (58) bigger diameter portions, first (52) and second (56) smaller diameter portions and first (51), second (53), third (55) and fourth (57) tapering portions which are coaxially positioned with respect to the longitudinal axis (21) of the RR preform (41), wherein the first bigger diameter portion (50) and the first smaller diameter portion (52) are connected by the first tapering portions (51), the first smaller diameter portion (52) and the second bigger diameter portion (54) are connected by the second tapering portions (53), the second bigger diameter portion (54) and the second smaller diameter portion (56) are

connected by the third tapering portions (55) and the second smaller diameter portion (56) and the third bigger diameter portion (58) are connected by the fourth tapering portions (57) and wherein the first bigger diameter portion (50) is connected at one end and its other end is kept free and the third bigger diameter portions (58) is connected at one end and its other end is kept free. 8. The method as claimed in claim 4, wherein the bender preform (42) has first (60), second (64) and third (68) bigger diameter portions, first (62) and second (66) smaller diameter portions and first (61), second (63), third (65) and fourth (67) tapering portions which are eccentrically positioned with respect to the longitudinal axis (22) of the bender preform (42), wherein the first bigger diameter portion (60) and the first smaller diameter portion (62) are connected by the first tapering portions (61), the first smaller diameter portion (62) and the second bigger diameter portion (64) are connected by the second tapering portions (63), the second bigger diameter portion (64) and the second smaller diameter portion (66) are connected by the third tapering portions (65) and the second smaller diameter portion (66) and the third bigger diameter portion (68) are connected by the fourth tapering portions (67) and wherein the first bigger diameter portion (60) is connected at one end and its other end is kept free and the third bigger diameter portion (68) is connected at one end and its other end is kept free.

9. The method as claimed in claim 8, wherein the eccentricities of each of the bigger diameter portions (60, 64, 68) of the bender preform (42) vary from each other by up to 20% in Y direction (Y1, Y2, Y3) and by up to 25% in Z direction (Z1, Z2, Z3).
10. The method as claimed in claim 8, wherein the eccentricities of each of the bigger diameter portions (60, 64, 68) are in the range of 20 to 45% of that of the value of the throw (T) of the crankshaft (1) in Y direction, Y1, Y2 and Y3 and are in the range of 32 to 47%, 33 to 59% and 32 to 47% of that of the value of throw (T) of the crankshaft (1) in Z direction, Z1, Z2 and Z3 respectively.
11. The method as claimed in claim 4, wherein during the double plane bending operation (102), the RR preform (41) is placed and located on the bottom bender die (72) such that the first (52) and second (56) smaller diameter portions of the RR preform (41) touches at least few portions of impressions (79) of the bender bottom die (72) that is going to produce the first (62) and second (66) smaller diameter portions of bender preform (42) and the first (50) and third (58) bigger diameter portions of the RR preform (41) rests on at least few portions of impressions (79) of the bender bottom die (72) that is going to produce the first (60) and third (68) bigger diameter portions of bender preform (42), followed by the top (71) and bottom (72) bender dies coming together due to forging stroke of the forging press, and wherein the RR preform (41) is deformed such that the

axis of the first (52) and second (56) smaller diameters portions corresponding to P2 and P5 (6) remain same while all the bigger diameter portions (50, 54, 58) of the RR preform (41) are deformed or shifted such that a bias in the material is formed towards the positions of counterweights (9) of the crankshaft (1).
12. A bending die apparatus (82) for manufacturing of a 6-cylinder crankshaft
(1), comprising:
a. a top die (71);
b. a bottom die (72);
c. a top cassette;
d. a bottom cassette,
Characterised in that the bottom bender die (72) is assembled to the bottom cassette which in turn is assembled on a bottom die holder which is installed on the bed of the forging equipment, preferably press, and wherein the top bender die (72) is assembled on the top cassette which is assembled on a top die holder which further is attached to a RAM of the forging press.
13. The bending die apparatus (82) as claimed in claim 12, wherein the bender
top die (71) and bender bottom die (72) consist of two dowel holes, a
rectangular dowel hole (73) and a round dowel hole (74), for alignment of
the bender top and bottom dies (71, 72) with the respective top and bottom
cassettes and avoiding a mismatch between the impressions of the bender

top (71) and the bender bottom (72) dies, and wherein clamping slots (75) are provided in both the top (71) and bottom (72) bender dies for clamping them with the respective top and bottom cassette.
14. The bending die apparatus (82) as claimed in claim 12, wherein an impression (79) is provided in both the bender top (71) and bottom (72) dies for producing the bender preform (42), wherein the impression (79) in the bender bottom die (72) is such that when RR preform (41) is kept in bottom bender die (72), the first (52) and second (56) smaller diameter portions of the RR preform (41) are touching at least few portions of the impressions (79) of the bender bottom die (72) that produce the corresponding first (62) and second (66) smaller diameter portions diameters of the bender preform (42) and the first (50) and third (58) bigger diameter portions of the RR preform (41) rests on at least few portions of impressions (79) of the bender bottom die (72) that produce the corresponding first (60) and third (68) bigger diameter portions of the bender preform (42).
15. The bending die apparatus (82) as claimed in claim 14, wherein the impression (79) in the bender top (71) and bottom (72) dies consists of three locks (76, 77 and 78) which correspond to the offsets Y1, Y2, Y3, Z1, Z2 and Z3 of the bender preform (42).