DESC:FIELD OF INVENTION
[001] The present invention relates to manufacturing of steering knuckle used in automotive applications. In particular, the present invention relates to manufacturing of multi piece steering knuckle.

BACKGROUND OF INVENTION
[002] Steering knuckle is one of the main components used in the suspension system of automobiles. The steering knuckle is the connection between a tie rod, an axle beam and a wheel hub. It is connected to the axle beam by using a king pin. Another end of the steering knuckle is connected to the tie rod. Typically, the wheel hub is fixed over the steering knuckle using bearings. Steering knuckles are typically manufactured either by forging or casting technique. Since steering knuckle is subjected to different types of fatigue loading conditions, forging is popular and preferred method of manufacturing over casting.

[003] It is well known to provide a steering knuckle for heavy duty motor vehicles such as trucks, wherein the steering arm and the tie rod arm are fitted to a steering knuckle by means of a threaded portion and a fastening nut. The tie rod arm and steering arm are bolted onto the steering knuckle through a tapered joint in these designs.

[004] Integral steering knuckle designs are preferred since it eliminates tie rod arm-knuckle joint, and thus, results in savings in assembly time and weight. For instance, US Patent No. 3908480 discloses an integrated steering knuckle with tie rod arm, brake rails and separately formed lower knuckle and spindle. Another Patent US5624011 discloses a forged steering knuckle which has integrated steering and tie rod arms, a spindle, and support elements for a drum brake assembly. Further, a one-piece steering knuckle assembly wherein a flanged body, wheel spindle and tie rod are formed as a one-piece forging and wherein the flanged body is forged in the form of a brake spider to accommodate disc brakes is disclosed in US5219176.

[005] Since integral steering knuckle is having a spindle (Stem) at one side and a tie rod arm at another side, part complexity increases which makes it difficult to manufacture especially by forging. This complex design of integral steering knuckle may require number of forging operations to get the final shape. Further, extra care need to be taken during each forging operation to avoid forging defects like under-fill and cracks which also limits part cycle time for mass production. Still further, since steering knuckle is forged from a single billet, the percentage utilisation of the material is also low. All of these above mentioned factors contribute to increase the overall manufacturing cost.

[006] Another concern of integral design is the weight of steering knuckle. The steering knuckle carries the power thrust and hence it must be very strong, rigid and also as light as possible. Therefore, in view of this, material optimization and geometric optimization is the real need for the automobile industry without affecting strength and performance of steering knuckle. However, integral complex design of steering knuckle and forging as a manufacturing process puts restrictions to weight optimization.

[007] Accordingly, there remains a need in the art for an improved steering knuckle that can be more easily manufactured, economical and lighter in weight than conventionally forged integral steering knuckles.

OBJECTS OF THE INVENTION:
[008] It is an object of the present invention to provide a new process for manufacturing steering knuckle by which it can be more easily manufactured in a cost effective manner.

[009] It is another object of the present invention to provide a process for manufacturing steering knuckle with effective utilization of input material.

[0010] Still another object of the present invention is to provide a hybrid method for manufacturing steering knuckles which combines forging and welding.

[0011] 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 ACCOMPANYING DRAWINGS:
[0012] Figure1A illustrates existing design of an integral steering knuckle;
[0013] Figure 1B illustrates existing manufacturing process sequence;
[0014] Figure 2 illustrates separated parts of steering knuckle, namely tie rod arm, stem and base knuckle;
[0015] Figure 3 illustrates steering knuckle in accordance with one embodiment of the present invention;
[0016] Figure 4 illustrates a method of manufacturing a steering knuckle in accordance with one embodiment of the present invention; and
[0017] Figure 5 illustrates a method of manufacturing a steering knuckle in accordance with another embodiment of the present invention.
SUMMARY OF THE INVENTION
[0018] Accordingly, the present invention provides a method of manufacturing a steering knuckle; said method comprising forging a tie rod arm, a stem, and a base knuckle separately; and electron beam welding said tie rod arm and said stem to said base knuckle to form the steering knuckle.
[0019] Typically, the tie rod arm, stem and base knuckle are separately manufactured by hot forging.
[0020] In one embodiment, the method further comprises identifying the critical stress areas of a steering knuckle near stem and tie rod arm in order to split component away from the high stress zones; said identification is carried out by FEA(Finite element analysis) considering various loading and boundary conditions, thereby deciding a split line of arm and spindle on FEA results.
[0021] In accordance with another aspect of the present invention there is provided a steering knuckle (100) comprising a base knuckle (12); a tie rod arm (14); and a stem (16), wherein said tie rod arm (14) comprises a pilot stub or a pilot hole, said tie rod arm being electron beam welded to said base knuckle (12); said stem (16) comprises a pilot stub or a pilot hole, said stem being electron beam welded to said base knuckle (12), and said base knuckle (12) comprises a pilot stub or a pilot hole.

DETAILED DESCRIPTION OF THE INVENTION:

[0022] In one aspect of the present invention, there is provided a method of manufacturing steering knuckle; said method comprises forging a tie rod arm, a stem (spindle), and a base knuckle separately; and electron beam welding said tie rod arm and said stem to said base knuckle to form the steering knuckle.

[0023] In accordance with another aspect of the present invention there is provided a steering knuckle obtained by the method of the present invention. Said steering knuckle (100) comprises a base knuckle (12); a tie rod arm (14); and a stem (16), wherein said tie rod arm (14) being electron beam welded to said base knuckle (12); and said stem (16) being electron beam welded to said base knuckle (12). In one embodiment said stem (16) being electron beam welded to said base knuckle (12) at a joint (18). In another embodiment said tie rod arm (14) being electron beam welded to said base knuckle (12) at a joint (18’). Said steering knuckle is illustrated in figure 3 of the accompanying drawings.

[0024] Each of the base knuckle (12); the tie rod arm (14); and the stem (16) comprises either pilot stub or pilot hole in order to fix or connect or engage the tie rod arm and the stem to the base knuckle.

[0025] The chassis system of heavy duty vehicle typically includes a steering knuckle. The steering arm or tie rod arm can be bolted or integral to the steering knuckle. Figure 1A shows existing integral steering knuckle where tie rod arm is an integral part of steering knuckle. This type of integral design is preferred since it avoids tie rod-knuckle joint and reduces assembly time. However this integration of tie rod arm to the steering knuckle increases the overall part complexity and makes it difficult to manufacture especially by forging. Moreover, a higher capacity forging equipment may be required for forging due to increase in part weight and complexity. This type of integral steering knuckle is manufactured from single billet by using a hot forging method. Due to increase in part complexity, number of forging operations are required to convert a single billet into final integral steering knuckle shape. Additionally, extra care must be taken during each forging operation to avoid forging defects like under-fill and cracking. This puts restriction on cycle time for mass production. Part complexity also affects the material utilisation. The existing process used to manufacture the existing integral steering knuckle is shown in figure 1B. After forging the steering knuckle, a heat treatment is carried out followed by final machining.

[0026] The inventors particularly focussed on providing a steering knuckle which is formed by electron beam welding of separately forged tie rod arm and stem to the base knuckle. The key aspect of the invention is to identify the critical stress areas of a steering knuckle near stem and tie rod arm so that the component can be split away from these high stress zones. For this, FEA(Finite element analysis) considering various loading and boundary conditions are carried out. The split line of tie rod arm and stem is decided based on this FEA results. Figure 2 shows separated parts of integral steering knuckle like tie rod arm, stem and base knuckle. In one embodiment of the present invention the split line is present 10 mm to 30 mm away from maximum stress concentration area.

[0027] It is found that the part complexity is much reduced due to the splitting method of the present invention in which the tie rod arm, stem and base knuckle are separately manufactured by hot forging. In accordance with the present invention, each individual component now can be easily forged and can be mass produced with economical process.

[0028] In one embodiment, the tie rod arm and stem part may be produced by using cold / warm forging which can save the energy required for heating up to forging temperature. Moreover, each of these individual parts can be precision forged with effective utilisation of material. This in turn can reduce initial raw material required to produce said steering knuckle. Additionally, each part can be precision forged on a low capacity forging equipments with minimum forging operations.

[0029] In another embodiment of this invention, the stem can be hollow or solid thus reducing the material requirement as well as lightweighting of the steering knuckle. The optimized base knuckle and hollow design of stem can result in 8 to 14 % weight saving of integral steering knuckle.

[0030] In accordance with the present invention said electron beam welding (EBW) is specifically chosen since it provides certain advantages as compared to other competitive joining technologies such as laser and friction welding. In one embodiment of the present invention, electron beam welding is carried out in a vacuum environment which ensures weld quality. The EBW method of the present invention provides very deep welds as compared to laser welding method wherein weld depth is limited. It is found that micro-structural and mechanical properties of EBW joint are superior than the friction or laser weld joint.

[0031] Joint designing is very critical aspect in case of electron beam welding. The arrangements for stem welding such as pin and bore type joint , pilot hole and pilot stub can be used. When the pin is used in between the base knuckle and the stem, it facilitates locating of the stem over the base knuckle. The size of pin is selected according to FEA results. Preferably, pilot hole and pilot stub arrangement is used to connect the stem and tie rod to the base knuckle.

[0032] In accordance with one embodiment of the present invention, the electron beam welding of the stem comprises circumferential welding. In one exemplary embodiment, the method comprises placing said stem over the base knuckle; and performing circumferential electron beam welding (EBW) while rotating said base knuckle and stem provided on fixture.

[0033] In accordance with one embodiment of the present invention, electron beam welding of the base knuckle and the tie rod arm comprises holding said base knuckle and said tie rod arm on a special fixture in a ready to join condition and performing the EBW from one side by using linear welding. Figure 3 shows stem and tie rod arm joint.

[0034] In one embodiment, the method comprises machining of stub or hole of the stem and/or the tie rod and/ or base knuckle which is carried out after forging of each individual component.

[0035] In accordance with another embodiment the method comprises forging the components, namely the base knuckle, the stem and the tie rod arm separately; optionally, demagnetizing one or more said components; placing said parts over specially designed fixtures in ready to weld condition; heating said components at a temperature of about 300 to 4000 C; performing electron beam welding to form the steering knuckle; and control cooling said steering knuckle. In one embodiment said electron beam welding is carried out in two steps. First tack welding is carried out to secure joint to be welded followed by full depth welding. The method is shown in figure 5.

[0036] It is observed that hardness in weld zone increases due to micro-structural changes (martensite formation in case of steel alloy). This increased hardness must be reduced to normal level before further processing of welded parts. Therefore, a stress relieving heat treatment (after EBW) is carried out to reduce hardness and relieve residual stresses developed during EBW. After stress reliving, integral steering knuckle is subjected to predetermined heat treatment followed by final machining. The manufacturing sequence of electron beam welded steering knuckle is shown in figure 4.

[0037] The invention is now illustrated with the help of following non-limiting example. The example provided is for illustration purpose only and should not be construed as limitation of claim scope.

EXAMPLE

[0038] A steering knuckle was prepared by the following procedure. A base knuckle, a stem and a tie rod arm were separately forged by hot forging. The forged components were then demagnetized and placed over specially designed fixtures in ready to weld condition. These components were then heated around 300-4000 C. Finally, the stem and tie rod arm were electron beam welded to the base knuckle to form the steering knuckle followed by control cooling. The weight of the steering knuckle was found to be around 27kg compared to weight of integrated knuckle (30kg) made without separate forging of components and electron beam welding technique. Thus, around 10 % weight of knuckle can be reduced by the present method without affecting the strength and the performance of the steering knuckle. The weight was reduced by using hollow stem and optimized design.

[0039] Microstructure, hardness and fatigue testing were performed on the parts. Microstructure testing showed that the microstructure at EBW zone and base material is same i.e. tempered martensite. Hardness testing showed that the hardness at the EBW zone and base material is similar in the range of 320 ~ 340 HV. Component level fatigue tests showed that the fatigue strength of the steering knuckle is comparable with the fatigue strength of steering knuckle produced using conventional process. Moreover, the failure location was not in the EBW zone.

TECHNICAL ADVANCE AND ECONOMIC SIGNIFICANCE:
[0040] The present invention provides the following advantages over the conventional methods of integral steering knuckle manufacturing:
- Component with better strength to weight ratio; and
- Effective utilization of material.

[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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 a steering knuckle; said method comprising forging a tie rod arm, a stem, and a base knuckle separately; and electron beam welding said tie rod arm and said stem to said base knuckle to form the steering knuckle.

2. The method as claimed in claim 1, wherein the tie rod arm, stem and base knuckle are separately manufactured by hot or cold or warm forging.
3. The method as claimed in claim 1, further comprises identifying the critical stress areas of a steering knuckle near stem and tie rod arm in order to split component away from the high stress zones; said identification is carried out by FEA (Finite element analysis) considering various loading and boundary conditions, thereby deciding a split line of arm and spindle based on FEA results.
4. The method as claimed in claim 3, wherein said split line is present 10 mm to 30 mm away from maximum stress concentration area.

5. The method as claimed in claim 1, wherein the electron beam welding is carried out in a vacuum environment to ensure weld quality.

6. The method as claimed in claim 1, wherein each of the tie rod arm and said stem comprises a pilot stub or a pilot hole to be engaged with a pilot stub or a pilot hole of said base knuckle .

7. The method as claimed in claim 1, wherein the electron beam welding of the stem comprises circumferential welding.

8. The method as claimed in claim 1, wherein the electron beam welding of stem comprises placing said stem over the base knuckle; and performing circumferential electron beam welding (EBW) while rotating said base knuckle and said stem provided on fixture.

9. The method as claimed in claim 1, wherein the electron beam welding of the base knuckle and the tie rod arm comprises holding said base knuckle and said tie rod arm on a fixture in a ready to join condition and performing the electron beam welding from one side by using linear welding.

10. The method as claimed in claims 1 to 6, wherein said method comprises machining of said pilot hole or pilot stub of said stem and/ or base knuckle and/ or tie rod arm after the forging operation.

11. The method as claimed in claim 1, wherein said method comprises forging the base knuckle, the stem and the tie rod arm separately; optionally, demagnetizing said base knuckle, the stem and the tie rod arm; placing said base knuckle, said stem and the tie rod arm over fixtures in ready to weld condition; heating said base knuckle, said stem and the tie rod arm at a temperature of about 300 to 4000 C; performing electron beam welding to form the steering knuckle; and control cooling said steering knuckle.

12. The method as claimed in claim 1, wherein the electron beam welding comprises first tack welding to secure joint to be welded followed by full depth welding.

13. The method as claimed in claim 1, further comprises a stress relieving heat treatment post electron beam welding to reduce hardness and relieve residual stresses developed during electron beam welding.

14. The method as claimed in claim 1, further comprises subjecting said steering knuckle to predetermined heat treatment post stress relieving followed by final machining.

15. A steering knuckle (100) comprising a base knuckle (12) having pilot stub or pilot hole; a tie rod arm (14); and a stem (16), wherein said tie rod arm (14) comprises pilot stub or pilot hole, said tie rod arm being electron beam welded to said base knuckle (12); and said stem (16) comprises pilot stub or pilot hole, said stem being electron beam welded to said base knuckle (12).

16. The steering knuckle as claimed in claim 15, wherein said stem (16) being electron beam welded to said base knuckle (12) at a joint (18) and said tie rod arm (14) being electron beam welded to said base knuckle (12) at a joint (18’).

17. The steering knuckle as claimed in claim 15, wherein said stem (16) is hollow or solid.

Dated this 12 August 2017

Chirag Tanna
Of NOVOIP
Applicant’ Patent Agent