DESC:FIELD OF INVENTION
[001] The present invention in general relates to a method of manufacturing axle shaft. Particularly, the present invention relates to a method of manufacturing axle shaft by forging and welding technology.
BACKGROUND OF INVENTION
[002] Axle shafts are in pair which serves to transmit driving torque to the opposing laterally spaced wheels through differential assembly. Driving torque from engine through gear box is transmitted to propeller shaft and this driving torque is eventually transmitted by axle shaft via differential gear to road engaging wheels. Axle shaft has rigid flanges which are secured to wheels for transmission of driving power. In service, these drive axle shaft which have long unsupported length, are subjected to considerable torsional stress and sudden shock that are especially severe at the flange end.

[003] Axle shaft with flange is provided with holes for bolted arrangement to the wheels. Presently, axle shafts are manufactured by hot forging method from a single piece of bar. In the current forging method, axle shaft is forged with integral flange by upset forge method.

[004] It is known that expensive machinery and complex series of operations are required to forge the axle shaft in a single piece. Accordingly, there is a need for an alternate method to fabricate axle shaft in order to overcome afore mentioned drawbacks without compromising the strength and quality of axle shaft.

OBJECTIVE OF THE INVENTION
[005] It is an object of the present invention to provide a method to manufacture an axle shaft by using combination of forging and welding technology which effectively utilize input material.

[006] It is still another object of the present invention to provide a method to manufacture an axle shaft by using combination of forging and welding technology which is capable of producing a lighter axle shaft.

[007] It is still another object of the present invention to provide a method to manufacture an axle shaft which allows use of dis-similar material grades for flange and shaft structure.

[008] It is yet another object of the present invention to provide an axle shaft having pre-determined configuration obtained by a method involving combination of forging and welding technology.

[009] These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description of the invention in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS:

[0010] Figure 1A illustrates existing method of manufacturing axle shaft by forging technique;

[0011] Figure 1B illustrates one piece axle shaft made by the existing forging method;

[0012] Figure 2A illustrates a method for manufacturing axle shaft in accordance with one embodiment of the present invention;

[0013] Figure 2B illustrates an axle shaft made by the method in accordance with one embodiment of the present invention;

[0014] Figure 3A illustrates an Electron Beam Welding method for manufacturing axle shaft in accordance with another embodiment of the present invention;

[0015] Figure 3B illustrates a method for manufacturing axle shaft in accordance with still another embodiment of the present invention; and

[0016] Figure 4 illustrates axle shaft in accordance with one embodiment of the present invention.

[0017] SUMMARY OF THE INVENTION
[0018] In accordance with the present invention there is provided a method of manufacturing an integral axle shaft; said method comprises forging a flange and a shaft with spline end separately and electron beam welding of said flange and said shaft with spline end to obtain an integral axle shaft. In one embodiment, a flange, a shaft and a spline end are separately forged and electron beam welded.

[0019] In one embodiment of the present invention said electron beam welding is carried out in a vacuum environment to ensure weld quality.

[0020] In one embodiment of the present invention said method comprises steps of deciding a split line by FEA (Finite Element Analysis) of axle shaft to identify the critical / high stress locations in axle shaft, aligning and maintaining alignment of said flange and said shaft while performing the welding operation, wherein said spit line is away from the maximum stress area.

[0021] In one embodiment of the present invention said electron beam welding comprises circumferential welding.

[0022] The present invention also provides an integrated axle shaft (100) comprising a flange (12) and a shaft (14) with spline end (20), said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange, whereas said shaft (14) comprises a pilot hole (18) or a pilot stub of pre-determined size and shape at the centre of one ends of said shaft and a spline end (20), wherein said flange and said shaft being forged separately and joined together by circumferential electron beam welding.

[0023] In another embodiment of the present invention said axle shaft comprises flange (12); a shaft (14); and a spline end (20), wherein said flange; said shaft; and said spline end being forged separately and joined together by circumferential electron beam welding. Typically, each of the flange, shaft and spline consists of either a pilot hole or a pilot stub for joining with each other.

DETAIL DESCRIPTION OF INVENTION

[0024] Driveline systems where rotary power is distributed from differential to pair of axle shafts are used in many automotive applications. Typically, the axle shaft includes a flange portion which is in contact with wheel and a shaft portion which connects said flange to differential. Conventionally, (Figure 1A) axle shaft is formed as a single piece part by using combination of forging and machining. However, fabrication of axle shafts in this way is known to have number of drawbacks.

[0025] One of drawbacks includes cost of single piece axle shaft as its manufacturing requires number of forging and machining operations. As mentioned above, a single steel billet is formed into predetermined final shape of axle shaft by using forging and machining operations. However, numbers of forging operations are required so that initial billet which is having small diameter (usually of shaft size) can be converted into the flange which is having large diameter. Moreover, specialized forging equipment like upset forging is required for this conventional way of fabricating axle shafts. Furthermore, several secondary operations, like straightening are required to carry out which increases the cost of the axle shaft. The finish machining of axle shaft includes several turning, drilling, hobbing and broaching operations. All of these mentioned factors are not economical for manufacturing single piece axle shafts.

[0026] Another drawback is the material of axle shafts. Conventionally, automotive axle shafts have been manufactured from a single piece of material having same chemical composition throughout. However, the axle shaft may require different material properties at different regions of the axle shaft. Such as, flange may need higher hardness material since it is subjected to higher amount of contact stresses, whereas the shaft may need combination of strength and toughness so that it can tackle higher torsional and bending loads. Due to single piece construction, flexibility of choosing different materials for flange and shaft is not there and designer has to compromise in selecting same material for both.

[0027] In accordance with the first aspect of the present invention, there is provided a method of manufacturing an axle shaft; said method comprises forging a flange and a shaft with spline end separately and electron beam welding of said flange and said shaft with spline end to obtain an integral axle shaft. Figure 2A illustrates method of the present invention.

[0028] In accordance with another aspect there is provided an axle shaft made by the method of the present invention, said axle shaft (100) comprises a flange (12); and a shaft (14) with spline end (20). Said flange (12) comprises a pilot stub (16) of pre-determined size and shape at the centre of said flange, whereas said shaft (14) comprises a pilot hole (18) of pre-determined size and shape at the centre of one end of said shaft and a spline end (20). The axle shaft in accordance with the present invention is illustrated in figure 2B. Said flange and said shaft being forged separately and joined together by circumferential electron beam welding.
[0029] In another embodiment said axle shaft (100) comprises a flange (12); a shaft (14); and a spline end (20). Said flange (12) comprises a pilot stub (16) of pre-determined size and shape at the centre of said flange, whereas said shaft (14) comprises a pilot hole (18) of pre-determined size and shape at the centre of one end of said shaft and a pilot stub of pre-determined size at the other end. The spline end (20) comprises a pilot hole to be engaged with the pilot stub of said shaft. Said flange; said shaft; and said spline end being forged separately and joined together by circumferential electron beam welding.

[0030] In still another embodiment said axle shaft (100) comprises a flange (12); a shaft (14) with a spline end (20). Said flange (12) comprises a pilot hole of pre-determined size and shape at the centre of said flange, whereas said shaft (14) comprises a pilot stub of pre-determined size and shape at the centre of one end of said shaft and a spline end (20). Said flange and said shaft with spline end being forged separately and joined together by circumferential electron beam welding.

[0031] In yet another embodiment said axle shaft (100) comprises a flange (12); a shaft (14); and a spline end (20). Said flange (12) comprises a pilot hole of pre-determined size and shape at the centre of said flange, whereas said shaft (14) comprises a pilot stub (18) of pre-determined size and shape at the centre of one end of said shaft and a pilot stub of pre-determined size at the other end. The spline end (20) comprises a pilot hole to be engaged with the pilot stub of said shaft. Said flange; said shaft; and said spline end being forged separately and joined together by circumferential electron beam welding.

[0032] In a further embodiment, the spline end (20) comprises a pilot stub to be engaged with the pilot hole of said shaft.

[0033] In one embodiment, the shaft may have pilot stub at both the ends of which one stub will engage with the pilot hole of said flange whereas another stub will engage with the pilot hole of the spline end.

[0034] In another embodiment, the shaft may have pilot hole at both the ends of which one hole will engage with the pilot stub of said flange whereas another hole will engage with the pilot stub of the spline end.

[0035] In still another embodiment, the shaft may have pilot hole at one end and pilot stub at the other end. Accordingly, the flange and the spline end will have respective pilot stub or hole.

[0036] According to the present invention it is found that separate forging on a press allows further optimization of flange portion for weight reduction which is very difficult in case of conventional single piece forging. In single piece design of axle shaft, flange portion is having outer circular shape which supports holes. Whereas, the flange portion in accordance with one embodiment of the present invention can be optimized to flower shape (flange’s circumferential edge is curvilinear edge comprising a series of alternating crests and troughs) covering hole portions as per requirement (Figure 4).

[0037] In one embodiment the integral axle shaft (100) comprising a shaft (14) and a flange (12) at one end of said shaft (14) and said shaft’s (14) other end being a spline end (20); said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange (12), whereas said shaft (14) with spline end (20) comprises a pilot hole (18) or pilot stub of pre-determined size and shape at the centre of one ends of said shaft with spline end (20), wherein said flange (12) and said shaft (14) with spline end (20) being forged separately and joined together by circumferential electron beam welding, characterized, in that, said flange’s (12) circumferential edge being defined as a circular edge or curvilinear edge comprising a series of alternating crests and troughs defining the entire circumferential edge.

[0038] In another embodiment, the integral axle shaft (100) comprising a shaft (14) and a flange (12) at one end of said shaft (14) and said shaft’s (14) other end being a spline end (20) connect to shaft via stub hole connection; said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange (12), whereas said shaft (14) comprises a pilot hole (18) or pilot stub of pre-determined size and shape at the centre of at least one end of said shaft, said spline end comprises a pilot hole or pilot stub of pre-determined size and shape at the centre, wherein said flange (12) and said shaft (14) and said spline end (20) being forged separately and joined together by circumferential electron beam welding, characterized, in that, said flange’s (12) circumferential edge being defined as a circular edge or curvilinear edge comprising a series of alternating crests and troughs defining the entire circumferential edge.

[0039] Thus, the optimized design can result in >4 % weight saving of axle shaft. Further, the optimized flange in combination with hollow shaft reduces overall weight of axle shaft by at least 12 %.

[0040] The present invention eliminates forging of one piece axle shaft which reduces manufacturing complexity by splitting them into individual components. According to the present invention each individual component can be easily forged on a comparatively small capacity forging equipment.

[0041] In one embodiment, the flange can be produced by using cold / warm forging with high production rates, which in turn can saves the energy required for heating up to forging temperature. Moreover, flange parts can be precision forged with better material utilization.

[0042] After separate forging of each individual component, a single piece axle shaft is formed by electron beam welding of the flange and the shaft with spline end. In accordance with the present invention, electron beam welding is specifically attempted considering its advantages as compared to other competitive joining technologies such as laser and friction welding.

[0043] In one of the preferred embodiments of the present invention, electron beam welding is carried out in a vacuum environment which ensures the weld quality. It is found that the electron beam welding provides very deep welds as compared to the laser welding wherein the weld depth is limited. In accordance with the present invention it is found that micro-structural and mechanical properties of EBW joint are superior than friction or laser weld joints.

[0044] The inventors attempted to split the axle shaft into two pieces appropriately in order to forge separately followed by joining in such a fashion that the strength of resultant axle shaft is not affected. In order to decide split line, FEA (Finite Element Analysis) of axle shaft is carried out to identify the critical / high stress locations. Accordingly, spilt line is taken away from this maximum stress area. Further, to perform precise welding said flange and said shaft are properly aligned in such a manner that their alignment is maintained during the welding operation. In one embodiment the split line is present 20 mm to 150 mm away from maximum stress concentration area.

[0045] In one embodiment said electron beam welding comprises circumferential welding. Typically, said circumferential welding is carried out by rotating the axle shaft.

[0046] In accordance with an illustrative embodiment, said method of manufacturing the axle shaft involves the following steps:
- forging flange and shaft with spline end separately;
- optionally, demagnetizing said shaft with spline end and said flange;
- heating said shaft or demagnetized shaft with spline end and flange or demagnetized flange, wherein said step of heating comprises either heating said shaft with spline end and flange in a heating furnace at a temperature of about 300 to 4000 C followed by placing said heated shaft with spline end and flange over fixtures or placing said ‘shaft or demagnetized shaft with spline end’ and flange or demagnetized flange over fixtures followed by heating said shaft with spline end and flange at a temperature of about 300 to 4000 C in a welding chamber using electron beam;
- electron beam welding of said shaft with spline end and flange circumferentially to form the axle shaft; and
- control cooling said integral axle shaft to room temperature.

[0047] In accordance with another illustrative embodiment, said method of manufacturing the axle shaft involves the following steps:
- forging flange, shaft and spline end separately;
- optionally, demagnetizing said shaft, said spline end and said flange,
- heating said shaft or demagnetized shaft, said spline end or demagnetized spline end and flange or demagnetized flange, wherein said step of heating comprises either heating said shaft, said spline end and said flange in a heating furnace at a temperature of about 300 to 4000 C followed by placing said heated shaft, said spline end and said flange over fixtures or placing said shaft or demagnetized shaft, spline end or demagnetized spline end and flange or demagnetized flange over fixtures followed by heating said shaft with spline end and flange at a temperature of about 300 to 4000 C in a welding chamber using electron beam;
- electron beam welding of said shaft, said spline end and said flange circumferentially to form the integral axle shaft; and
- control cooling said integral axle shaft to room temperature.

[0048] Typically, said electron beam welding is carried out in two steps. The first tack welding is carried out to secure joint to be welded which is followed by full depth welding. Said electron beam welding method is illustrated in figure 3A.

[0049] It is observed that hardness in weld zone increases due to microstructural changes (martensite formation). This increased hardness is to be reduced to normal level before further processing of welded parts.

[0050] Accordingly, normalizing heat treatment (after EBW) is carried out to homogenize microstructure which reduces hardness and relieve residual stresses developed during EBW. After normalizing, axle shaft is subjected to pre-determined heat treatment preferably induction hardening followed by final machining.

[0051] In accordance with still another embodiment, there is provided a method for manufacturing the axle shaft; said method comprising the steps of separately forging three parts namely, a flange, a shaft and a spline end and joining said parts together by electron beam welding. Figure 3B illustrates said method.

[0052] Typically, the flange and spline end can be separately hot / cold / warm forged and then joined with hollow or solid shaft. Said method saves initial raw material required for central shaft and lightweight said axle shaft. In one embodiment the spline is solid. Each of the parts, namely, the flange, shaft and spline may have pilot stub or hole in order to get engaged or connected with each other.

[0053] The conventional method uses oversize billet than required as it undergoes multiple forging operations at both ends i.e. flange and spline. Separate forging of flange and spline end allows to use lower sized billets as compared conventional manufacturing method. These flange and spline can be subsequently machined to final dimension and thus save initial raw material required.

[0054] Additionally, existing single piece manufacturing of axle shaft requires straightening operation before the final machining since it involves hot forging operations at both ends. This straightening operation may be completely eliminated by using present multi-piece construction since flange portion and shaft portion can be forged separately.

[0055] In accordance with still another embodiment, there is provided a method for manufacturing the axle shaft; said method comprising the steps of separately forging a flange and a shaft with spline end and joining said parts together by electron beam welding, wherein the flange and shaft with spline end being made of different materials. Considering different strength requirement of flange and shaft with spline end which is not achieved by manufacturing them with similar metal, the present invention allows manufacturing the axle shaft using dis-similar material grades for flange and shaft structure.

[0056] The axle shaft made by the present disclosure exhibits similar or higher strength compared to the single piece axle shaft made by forging.

TECHNICAL ADVANCE & ECONOMIC SIGNIFICANCE:

[0057] The present invention provides the following advantages over the conventional methods of manufacturing the axle shafts:

[0058] It provides component with better strength to weight ratio.

[0059] It allows effective utilization of material.

[0060] It allows manufacturing the integral axle shaft using dis-similar material grades for flange and shaft structure.

[0061] Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0062] The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

[0063] Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

[0064] The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

[0065] While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:We Claim:
1. A method of manufacturing an integral axle shaft; said method comprises forging a flange and a shaft with spline end separately and electron beam welding of said flange and said shaft with spline end to obtain an integral axle shaft.

2. The method as claimed in claim 1, wherein said method comprises the following steps:
- forging flange and shaft with spline end separately;
- optionally, demagnetizing said shaft with spline end and said flange;
- heating said shaft or demagnetized shaft with spline end and flange or demagnetized flange, wherein said step of heating comprises either heating said shaft with spline and flange in a heating furnace at a temperature of about 300 to 4000 C followed by placing said heated shaft with spline end and flange over fixtures or placing said shaft or demagnetized shaft with spline end and flange or demagnetized flange over fixtures followed by heating said shaft with spline end and flange at a temperature of about 300 to 4000 C in a welding chamber using electron beam;
- electron beam welding of said shaft with spline end and flange circumferentially to form the integral axle shaft; and
- control cooling said integral axle shaft to room temperature.

3. The method as claimed in claim 1, wherein said method comprises separately forging a flange, a shaft and a spline end followed by joining with shaft using electron beam welding.

4. The method as claimed in claims 1 to 3, wherein said method comprises the following steps:
- forging flange, shaft and spline end separately;
- optionally, demagnetizing said shaft, said spline end and said flange;
- heating said shaft or demagnetized shaft, said spline end or demagnetized spline end and flange or demagnetized flange, wherein said step of heating comprises either heating said shaft, said spline end and said flange in a heating furnace at a temperature of about 300 to 4000 C followed by placing said heated shaft, said spline end and said flange over fixtures or placing said shaft or demagnetized shaft, spline end or demagnetized spline end and flange or demagnetized flange over fixtures followed by heating said shaft with spline end and flange at a temperature of about 300 to 4000 C in a welding chamber using electron beam;
- electron beam welding of said shaft, said spline end and said flange circumferentially to form the integral axle shaft; and
- control cooling said integral axle shaft to room temperature.

5. The method as claimed in claims 1 to 4, wherein said electron beam welding comprises tack welding to secure joint to be welded followed by full depth welding.

6. The method as claimed in claims 1 to 5, wherein said method further comprises a step of normalizing heat treatment post electron beam welding to homogenize microstructure which reduces hardness and relieve residual stresses developed during electron beam welding.

7. The method as claimed in claims 1 to 6, wherein said method further comprises subjecting said axle shaft to pre-determined heat treatment preferably induction hardening post normalizing followed by final machining.
8. The method as claimed in claim 1 to 7, wherein said electron beam welding is carried out in a vacuum environment to ensure weld quality.

9. The method as claimed in claims 1 to 8, wherein said method comprises steps of deciding a split line by FEA (Finite Element Analysis) of axle shaft to identify the critical / high stress locations in axle shaft, aligning and maintaining alignment of said flange and said shaft with spline end while performing the welding operation, wherein said split line is away from the maximum stress area.

10. The method as claimed in claims 1 to 9, wherein the split line is present 20 mm to 150 mm away from maximum stress concentration area.

11. The method as claimed in claims 1 to 10, wherein said electron beam welding comprises circumferential welding.

12. The method as claimed in claims 1 to 11, wherein said electron beam welding comprises circumferential welding which is carried out by rotating the axle shaft.

13. The method as claimed in claims 1 to 12, wherein the material of the said flange, said shaft and said spline end is same or different, said shaft is hollow or solid.

14. An integral axle shaft (100) comprising a flange (12) and a shaft (14) with spline end (20); said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange (12), whereas said shaft (14) with spline end (20) comprises a pilot hole (18) or pilot stub of pre-determined size and shape at the centre of one ends of said shaft with spline end (20), wherein said flange (12) and said shaft (14) with spline end (20) being forged separately and joined together by circumferential electron beam welding.
15. An integral axle shaft (100) comprising a flange (12), a shaft (14) and a spline end (20), said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange, whereas said shaft (14) comprises a pilot hole (18) or pilot stub of pre-determined size and shape at the centre of at least one end of said shaft, said spline end (20) comprises a pilot stub or a pilot hole of pre-determined size and shape at the centre of said spline end (20), wherein said flange (12), said shaft (14) and said spline end (20) being forged separately and joined together by circumferential electron beam welding.

16. The integral axle shaft as claimed in claims 14 and 15, wherein the shaft is hollow or solid.

17. An integral axle shaft (100) comprising a shaft (14) and a flange (12) at one end of said shaft (14) and said shaft’s (14) other end being a spline end (20); said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange (12), whereas said shaft (14) with spline end (20) comprises a pilot hole (18) or pilot stub of pre-determined size and shape at the centre of one ends of said shaft with spline end (20), wherein said flange (12) and said shaft (14) with spline end (20) being forged separately and joined together by circumferential electron beam welding, characterized, in that, said flange’s (12) circumferential edge being defined as a circular edge or curvilinear edge comprising a series of alternating crests and troughs defining the entire circumferential edge.

18. An integral axle shaft (100) comprising a shaft (14) and a flange (12) at one end of said shaft (14) and said shaft’s (14) other end being a spline end (20)connect to shaft via stub hole connection; said flange (12) comprises a pilot stub (16) or a pilot hole of pre-determined size and shape at the centre of said flange (12), whereas said shaft (14) comprises a pilot hole (18) or pilot stub of pre-determined size and shape at the centre of at least one end of said shaft, said spline end comprises a pilot hole or pilot stub of pre-determined size and shape at the centre, wherein said flange (12) and said shaft (14) and said spline end (20) being forged separately and joined together by circumferential electron beam welding, characterized, in that, said flange’s (12) circumferential edge being defined as a circular edge or curvilinear edge comprising a series of alternating crests and troughs defining the entire circumferential edge.

Dated this 11th day of August 2017

Chirag Tanna
Of NOVOIP
Applicant’ Patent Agent