FORGED FRONT AXLE BEAM

Field of invention

The present invention relates to a heat treatment process. Particularly, the present invention relates to the heat treatment process for a front axle beam.

More particularly, the present invention relates to distortion free heat treatment of a front axle beam and an apparatus for the same.

Introduction

Components of automobiles are made from steel. These components are typically made using the process of hot forging followed by heat treatment. This is further followed by machining and other special processes.

Front Axle Beam (FAB) is one such part used in the automotive industry. The FAB is the element which connects the front two wheels of an automobile and carries one third weight of the automobile. The FAB is normally used in Light Commercial Vehicles (LCV) and Heavy Commercial Vehicles (HCV). Figure 1 shows a general figure of Front Axle Beam (1). The various parts of the FAB are also numbered in the figure. The two ends of the FAB are called King Pin Boss or KPB (2). The central part of the FAB (6) is called I Section. Next to KPB is an upwardly raised portion called cobra (3). Between the I-section and cobra are provided two parts called a deep pad (4) and a T-section (5). The names of the different regions are indicative of the shape of the cross section of the FAB at these regions.

The FAB is a safety-critical component and should have very stringent properties. Therefore, the FAB is normally produced using a hot forging process. The forged FAB is then heat-treated in order to achieve the best possible combination of strength and toughness.

The heat treatment process used for FAB generally has the sequential steps of austenizing - quenching - tempering. During the quenching process the microstructure of the FAB changes drastically due to which the FAB undergoes distortion/bending. This distortion/bend of the FAB is not desirable and leads to problems in further processing stage such as machining. To avoid these problems, a bend/distortion correction has to be applied to the FAB. The bend/distortion correction process is normally carried out in cold conditions. In this process the FAB is clamped in a fixture and then straightened by application of force in the bent region in a direction opposite to the bend thus, producing minor plastic deformation. This minor plastic deformation corrects the bend. The force for bend correction is normally imparted using a hydraulic system. Bend/distortion correction induces residual stresses in the FAB. These residual stresses have to be removed by giving a stress relieving heat treatment to the part.

It should be noted that roughly, in 90% of the parts, the distortion/bend is so high that it will be out of tolerance limits and hence, will require bend/distortion correction. In some of the FAB’s, this bend or distortion is of such high value that they have to be rejected or scrapped.

The distortion of FAB during the quenching heat treatment leads to requirement of additional steps of bend/distortion correction and stress relieving heat treatment (or in some cases rejection of some of the parts) for these 90 % of the parts.

Thus, there exists a room for advancement over the existing heat treatment technology in that a method and apparatus for heat treatment for FAB should be designed such that it will avoid the distortion of FAB and reduce manufacturing cycle time as well as reduce the number of parts to be rejected or scrapped.

Objects of invention

Some of the objects of the present disclosure which at least one embodiment herein satisfies are as follows: It is an object of the present invention to provide a method of heat treatment of FABs to get distortion free parts.

It is another object of the present invention to provide an apparatus for the heat treatment of FABs which avoids the distortion of the part during heat treatment.

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 typical FAB

Figure 2 illustrates the conventional method of stacking FABs during the heat treatment process.

Figure 3 illustrates the method of supporting and clamping the FAB for the heat treatment process according to the invention.

Figure 4 shows a flow diagram of the heat treatment process of invention

List of parts

1. Front Axle Beam (FAB) 4. Deep pad

2. King Pin Boss (KPB) 5. T-section

3. Cobra 6. I- secti on 7. Clamping direction 8A. Support location

7A. Clamping location 5 9. Direction of actuators

8. Support direction

Summary of invention

The present invention is directed towards a method of heat treatment and an apparatus for the same which can be used to avoid the distortion or bending of a Front Axle Beam (FAB) during the process. The apparatus envisaged in the invention is designed such that it supports and/or holds the FAB at its most critical locations during the heat treatment process. Due to this, the FAB remains distortion-free and hence, does not require any bend/distortion correction and stress relieving after the heat treatment process.

Description of the invention

The present invention relates to the manufacturing of a front axle beam typically used in automotive industry. More particularly, it relates to the heat treatment process of the FAB such that distortion free FAB are produced.

In conventional method of heat treatment, the FABs are stacked one over the other in a cradle (Refer Figure 2) and then put in a furnace for austenizing. The same cradle is then put in the quenching medium for the quenching process. Thus, during the heat treatment process, the FABs are free to change shape or distort. The distortion of the FAB takes place due to the microstructural changes (phase change) and uneven heat transfer rates taking place during the heat treatment process. The distortion of the FAB manifests itself in the form of distortion of KPB or distortion of the Deep Pad/T Section during the dimensional inspection process step. During the machining process, the deep pad is considered as the reference surface. Hence, any distortion or bend in the FAB may manifest itself in the form of height wise distortion of KPB (Refer Figure 1). This distortion leads to unclean/excessive machining allowance during machining at the KPB in height wise direction. The distortion at deep pad/T section manifests itself in the form of unclean/excessive machining allowance during machining at the Deep pad in sideways direction (Refer Figure 1).

To overcome this drawback of the conventional heat treatment process, an apparatus has been disclosed.

The apparatus for carrying out distortion free heat treatment of a front axle beam comprises:

a receptacle for placing the front axle beam to be quenched;

actuators for centering said beam axially and transversely inside said receptacle;

clamping mechanisms for vertical and horizontal clamping of said beam inside said receptacle; and actuators for constraining the distortion of KPB in vertical or transverse direction

The receptacle of the apparatus is designed in such a way that the FAB is supported and/or clamped and/or constrained at different predetermined locations so as to constrain the distortion of the FAB during the heat treatment process. The features of FAB which have significant impact on its assembly in the automobile are the Deep Pad/ T Section and the KPB. These are the locations where the connecting elements are assembled with FAB. Hence, normally these are the locations or features of a FAB which are machined. Thus, constraining and controlling the distortion at these locations is most important during the heat treatment process. In one embodiment, the support locations (8A) and the clamping locations (7 A) are shown in Figure 3. It can be seen that all the clamping or supporting locations defined on the FAB are on the deep pad, or the T-Section, or the KPB. This assures that the most critical features of the FAB, which are important for its proper assembly, remain undistorted. In another embodiment, the clamping mechanisms and actuators can be hydraulically, pneumatically or mechanically operated. In another embodiment, the FAB is supported or rested on its deep pads in the invented apparatus. This is denoted as 8A in Figure 3 (front view). As is seen in the Figure 3, the FAB is clamped at multiple locations and supported on a few locations. The location of clamping and support will depend on the type, size and shape of the FAB. The clamping location according to one embodiment is shown in Figure 3 and denoted by 7A. The clamping can be done using any of the mechanical means including hydraulically operated clamps. The FAB is a very long component and hence, it bends or distorts during the quenching process. As an example, the FAB can be held in the invented apparatus as shown in Figure 3. The KPB is constrained in order to avoid side wise or height wise distortion of KPB (direction 10). Similarly, the deep pads are clamped in sideways direction in order to avoid the sideways distortion (7 in Top View of Figure 3). The FAB is rested in the apparatus on its deep pads (8) and clamped from the T Section in order to avoid any depth-wise distortion (7 in Front View of Figure 3).

In another embodiment, hydraulic clamping mechanism is designed for the clamping of the FAB at locations denoted by 7 in Figure 3. The hydraulic clamping mechanism consists of hydraulic cylinders with clamping arms connected to the piston. These arms will have clamping blocks whose shape and size will match the shape of feature of FAB where this block will be used for clamping purpose. The number of hydraulic cylinder will be equal to the number of locations where the FAB is being clamped. The use of hydraulic clamping mechanism has some advantages. Use of hydraulic system increases the flexibility and reliability of the apparatus. Many different type of FAB can be processed using same apparatus.

The steps of heat treatment process using the apparatus of invention are given below (Refer Figure 4):

1. Heating of the part (FAB) to its austenizing temperature in a furnace.

2. Placing the hot part in a quenching apparatus having multiple actuators with adjustable stroke.

3. Axially centering the part using actuators. This is done by activation of axial actuators which come in contact with the KPB of the FAB and center the FAB in axial direction. These actuators act in the direction denoted by 9 in Figure 3.

4. Transverse centering of the part using actuators. This is done by activation of transverse actuators which come in contact with Deep Pad and center the FAB transversely. These actuators act in the direction denoted by 7 in Top View of Figure 3.

5. Clamping the FAB vertically at T section (in the direction denoted by 7 in Front View of Figure 3) using clamping mechanism which consists of hydraulic cylinders with clamping arms connected to the piston. The arms will have clamping blocks whose shape and size will match the shape of feature of FAB where this block will be used for clamping purpose. Clamping the FAB horizontally at Deep Pads (in the direction denoted by 7 in Top View of Figure 3) using clamping mechanism which consists of hydraulic cylinders with clamping arms connected to the piston. The arms will have clamping blocks whose shape and size will match the shape of feature of FAB where this block will be used for clamping purpose.

Retraction of axial centering actuators.

Moving forward the actuators at the king pin hub to their nominal positions in order to limit the king pin hub distortions (in both vertical and horizontal planes) within the desired range. The locations of these actuators are shown by 10 in Figure 3. Actuator arm (8 nos in total) move forward to pre-defmed positions (4 actuators for each king pin: 2 for vertical position control and 2 for horizontal position control). A gap is maintained between the king pin and the actuator arm tip. If the FAB tries to distort, it will touch one of the actuator arm, and which will not allow the FAB to distort any further. In this manner, the distortion of the FAB is either eliminated or limited.

Immersing the quenching apparatus along with FAB in a quenching tank. Adjusting the strokes of the actuators w.r.t. the contraction of the part due to cooling, thereby avoiding any distortion. A servo hydraulic equipment with feedback system is used for this purpose.

Bringing the assembly out of the tank after a specified time and removing the FAB from the apparatus. It is evident from the foregoing discussion that there are a number of embodiments of the invention. These are:

1. An apparatus for heat treatment process for forged front axle beam, said beam having

- two ends called king pin bosses (2),

- a central part in the form of an I-section (6),

- an upwardly raised portion called cobra (3) near each end of said beam, and a deep pad (4) and a T-section (5) placed between the I- section and each of the cobra,

characterised in that said apparatus comprises:

- a receptacle in which said beam is placed for quenching;

- actuators for centering said beam axially and transversely inside said receptacle;

- clamping mechanisms for vertical and horizontal clamping of said beam inside said receptacle; and

- actuators for constraining the distortion of king pin boss in vertical or transverse direction.

2. The apparatus as disclosed in embodiment 1, wherein said actuators for axial centering are actuated to come in contact with the king pin boss (2) of said beam (1) thereby enabling the axial centering of said beam (1).

3. The apparatus as disclosed in embodiment 1, wherein said actuators for transverse centering are activated to bring them in contact with said deep pads (4) thereby enabling the transverse centering of said beam (1). The apparatus as disclosed in embodiment 1, wherein said clamping mechanisms are operated hydraulically or pneumatically or mechanically. The apparatus as disclosed in embodiment 4, wherein said clamping mechanisms are hydraulic cylinders provided with clamping arms connected to pistons of said hydraulic cylinders and wherein said clamping arms have clamping blocks whose shape and size match the shape of feature of said beam (1) at a location where said clamping block is used for clamping purpose.

A heat treatment process for forged front axle beam (1), said beam having

- two ends called king pin bosses (2),

- a central part in the form of an I-section (6),

- an upwardly raised portion called cobra (3) near each end of said beam, and a deep pad (4) and a T-section (5) placed between the I- section and each of the cobra,

said heat treatment process characterised in that it uses a step of quenching of the heated beam by placing it in a receptacle as disclosed in embodiment 1 for further quenching, thereby avoiding distortion/bending of said beam during quenching, and whereby said treatment is devoid of a step of bend/distortion correction and stress relieving after the heat treatment process is complete.

The process as disclosed in embodiment 6 characterised in that said heat treatment process comprises the steps of:

a. heating said beam to its austenizing temperature in a furnace; b. placing the heated said beam in a heat treatment apparatus as claimed in claim 1 having multiple actuators with adjustable stroke wherein said heated beam (1) rests on its deep pads (4) on the support provided within said apparatus;

c. axially centering said heated beam (1) using axial-centering actuators; d. transversely centering said axially centered beam (1) using transverse- centering actuators leading to a centered beam (1);

e. clamping said centered beam (1) vertically at said T-sections (5) at multiple locations (7 A);

f. clamping said vertically clamped beam (1) horizontally at said deep pads (4) at multiple locations (7 A);

g. retracting the axial-centering actuators to their original positions;

h. moving forward the actuators at the king pin boss (2) of said centered beam (1) to their nominal positions in order to limit the distortion at said king pin boss (2) to within a desired range;

i. immersing the said heat treatment apparatus along with said centered and clamped beam (1) in a quenching tank;

j. adjusting the strokes of the actuators w.r.t. the contraction of the said axially centered beam (1) due to cooling, thereby avoiding any distortion;

k. bringing out said quenching apparatus out of said quenching tank after a specified time and removing the said quenched beam (1) from said quenching apparatus. 8. The process as disclosed in any of embodiments 6 and 7 wherein said axial centering of step c is carried out by activation of axial actuators in the direction 9 which come in contact with the king pin boss (2) of said beam thereby enabling the axial centering of said beam (1).

9. The process as disclosed in any of embodiments 6 to 8, wherein said transverse centering of step d is carried out by activation of transverse actuators along direction 7 which come in contact with said deep pads (4) thereby enabling the transverse centering of said beam (1).

10. The process as disclosed in any of embodiments 6 to 9, wherein said vertical clamping of step e is carried out along direction 7 using a clamping mechanism provided for vertical clamping.

11. The process as disclosed in any of embodiments 6 to 10, wherein said horizontal clamping of step f is carried out along direction 7 using clamping mechanism provided for horizontal clamping.

12. The process as disclosed in any of embodiments 10 and 11, wherein said clamping mechanisms are operated hydraulically or pneumatically or mechanically.

13. The process as disclosed in any of embodiments 10 and 11, wherein said hydraulic clamping mechanisms are hydraulic cylinders provided with clamping arms connected to pistons of said hydraulic cylinders and wherein said clamping arms have clamping blocks whose shape and size match the shape of feature of said beam (1) at a location where said clamping block is used for clamping purpose. While the above description contains much specificity, this should not be construed as limitation in the scope of the invention, but rather as exemplification of the preferred embodiments thereof. Many other variations are possible. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.