Abstract:
A method for manufacturing a one piece axle tube housing with an integral spindle includes providing a tube blank, providing the blank with a region of increased thickness, inserting a mandrel having a reduced diameter profile, passing a reducing die over the tube to conform the tube to the shape of the mandrel; and extraction of the mandrel from the tube to cause outward deformation of the tube at specific locations. A further swaging step may be used to form the final spindle structure.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/711,270, filed Aug. 26, 2005, the entire contents of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to axle housings and more specifically to a one-piece axle housing incorporating an axle tube and spindle. The invention also provides a method of manufacturing such axle housings. 
   DESCRIPTION OF THE PRIOR ART 
   Axle assemblies are well known in the art. Typically, such housings include an axle tube (which encloses the axle shaft), a spindle located at the terminal ends of the axle tube (for engaging the wheel or bearing parts), and other components such as brake flanges or spiders, spring seats, shock absorber pads etc. Generally, all of the aforementioned parts are formed separately and subsequently welded together to form the axle housing. However, the various forming and welding steps are time and labour intensive. 
   As is known in the art, axle spindles generally require a larger wall thickness than the axle tube due to the increased strength demands of such sections. As such, it is common for the spindles to be forged separately and subsequently attached (by such means as friction welding) to the axle tube. Examples of such a two step method are taught in U.S. Pat. Nos. 3,837,205 and 6,279,695. However, as indicated above, the requirement for welding increases the cost of the final article. Moreover, due to the high temperatures generated and required by the known welding methods, the strength of the metal surrounding the welded regions are known to be reduced. 
   In U.S. Pat. No. 5,303,985, a method is taught of forming a one piece axle housing by means of casting. However, although such methods avoid the need for welding sections together, the use of a common wall thickness over the entire length of the housing greatly increases the weight of the article. Moreover, the forging process results in a metal having inferior strength characteristics thereby necessitating the need for a thicker walled, and therefore heavier, housing. 
   U.S. Pat. No. 4,435,972 teaches a multi-step method for forming an axle housing wherein a series of mandrels is used to form the required cross sectional profile. Thus, this method involves a large cycle time. Further, this method is limited to forming tubes made of malleable steel having high formability characteristics and could not be used to form heavy duty axles housings. 
   A further method is taught in US application published under number 2004/0060385. This method results in a one-piece axle housing tube incorporating a spindle. However, the method taught in this reference requires multiple dies and, therefore, longer cycle times. 
   Thus, there exists a need for an improved axle housing and method for making same that overcomes at least some of the deficiencies of the prior art. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention provides an axle housing wherein the axle tube and the spindle are formed as a unitary structure. 
   In another aspect, the invention provides a method of forming an axle housing wherein the axle tube and the spindle are formed as a unitary structure. 
   In another aspect, the invention provided a method of forming a one-piece axle housing with an integral spindle, the method comprising:
         a) providing a tubular blank having an inner surface with a uniform first inner diameter, an outer surface with a uniform first outer diameter, and a uniform first wall thickness;   b) increasing the wall thickness of a region of said blank, said region being located proximal to a first end of said blank and corresponding to the location of the spindle;   c) providing a mandrel within said tubular blank, said mandrel having a cross sectional profile including a first reduced diameter portion at a first end of said mandrel, said first end being provided within said blank at a location corresponding to said region of increased wall thickness;   d) applying a radially inward force on said blank to force the inner surface of said blank to conform to said mandrel cross sectional profile while providing a reduced uniform second outer diameter on said blank, wherein, during application of said radially inward force, said region of increased thickness is forced into said reduced diameter end portion of said mandrel;   e) separating said mandrel from said tubular blank.       

   In another aspect, the present invention provides a method for manufacturing a tubular article having a desired cross sectional profile including regions of increased wall thickness, the method comprising:
         a) providing a tubular blank having an inner surface with a uniform first inner diameter, an outer surface with a uniform first outer diameter, and a uniform first wall thickness;   b) increasing the wall thickness of a region of the blank while maintaining the first outer diameter at the region;   c) providing a mandrel within the tubular blank, the mandrel having a cross sectional profile complementary to the desired cross sectional profile;   d) applying a radially inward force on the blank to force the inner surface of the blank to conform to the mandrel cross sectional profile and wherein the tubular blank is provided with a reduced, uniform second outer diameter;   e) separating the mandrel and the tubular blank whereby the blank outer surface is expanded to the desired cross sectional profile.       

   In another aspect, the present invention provides a method for manufacturing a tubular article having a desired cross sectional profile including regions of increased wall thickness, the method comprising:
         a) providing a tubular blank having an inner surface with a uniform first inner diameter, an outer surface with a uniform first outer diameter, and a uniform first wall thickness;   b) increasing the wall thickness of a region of said blank;   c) providing a mandrel within said tubular blank, said mandrel having a cross sectional profile complementary to said desired cross sectional profile;   d) applying a radially inward force on said blank to force the inner surface of said blank to conform to said mandrel cross sectional profile and wherein said tubular blank is provided with a reduced, uniform second outer diameter;   e) separating said mandrel from said tubular blank.       

   In another aspect, the present invention provides a method of forming a one-piece axle housing with an integral spindle, the method comprising:
         a) providing a tubular blank having an inner surface with a uniform first inner diameter, an outer surface with a uniform first outer diameter, and a uniform first wall thickness;   b) increasing the wall thickness of a region of the blank while maintaining the uniform first outer diameter at the region, the region being located proximal to a first end of the blank and corresponding to the location of the spindle;   c) providing a mandrel within the tubular blank, the mandrel having a cross sectional profile including a first reduced diameter portion at a first end of the mandrel, the first end being provided within the blank at a location corresponding to the region of increased wall thickness;   d) applying a radially inward force on the blank to force the inner surface of the blank to conform to the mandrel cross sectional profile while providing a reduced uniform second outer diameter on the blank, wherein, during application of the radially inward force, the region of increased thickness is forced into the reduced diameter end portion of the mandrel;   e) separating the mandrel and the tubular blank whereby the blank outer surface is expanded to the desired cross sectional profile.       

   In yet another aspect, the invention provide a one-piece tubular articles, such as an axle housing tube having a desired cross-sectional profile including sections of differing outer diameters and differing wall thicknesses. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein: 
       FIG. 1  is a cross sectional view of a tube blank to be used in the method of the invention. 
       FIG. 2  is a cross sectional view of the tube following the localized thickening step. 
       FIG. 3  is a cross sectional view of the mandrel used in the method. 
       FIG. 4  is a cross sectional view of the tube following-insertion of the mandrel. 
       FIG. 5  is a cross sectional view of a die of the invention. 
       FIG. 6  is a cross sectional view of the tube and mandrel complex, following passage of the die. 
       FIG. 7  is a cross sectional view of the tube after withdrawal of the mandrel. 
       FIG. 8  is a cross sectional view of the tube after swaging. 
   

   DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a tube blank from which the desired axle housing is formed. As shown, the tube blank  10  comprises a cylindrical tube having an initial outer diameter D 1  and an initial wall thickness T 1 , both of which are generally constant along the length of the tube&#39;s longitudinal axis  12 . This results in the tube  10  having a generally constant inner diameter D 2 . The outer diameter D 1  of the tube is less than the outer diameter of the desired final product, as will become clear in the following description. 
   As illustrated in  FIG. 2 , the first step of the method of the invention involves providing a thickened region, or localized area,  14  having an increased wall thickness T 2 . Such region  14  is provided on a first end  16  of the tube blank  10  and generally corresponds to the location of the spindle to be formed (which is described further below). The opposite, second end  18  of the tube blank  10  is not thickened in this manner. The thickening of the region  14  can be achieved using a variety of known methods as will be apparent to persons skilled in the art. In one aspect, the invention involves heating the region  14  and hot forging the blank  10  at the region  14  to obtain the required thickening. The heating of the tube blank  10  can be accomplished in a variety of known manners such as with an induction heating element, a flame, an oven or other such apparatus. In one aspect, an induction heating element is used since it provides an efficient means of obtaining the required discrete heating zone. The region  14  is heated until the reduction in yield strength (caused by the heating) renders the region  14  sufficiently malleable. The amount of heat required and the final temperature of the region  14  will be known to persons skilled in the art and will depend on various factors such as the composition of the tube, the thickness of the tube, the ambient temperature etc. 
   Once the region  14  is sufficiently heated, the blank  10  is subjected to a forming operation whereby the wall thickness at the region  14  is increased. In one aspect of the invention, the forming operation comprises a forging step wherein one end of the blank  10  is held in position and a compressive force (such as from a hammer mill etc.) is applied to the opposite end. It will be appreciated that any known forming operation can be used in the present invention for achieving the desired result. Due to the reduction in yield strength at the region  14 , it will be understood that the region  14  will undergo a deformation. As illustrated in  FIG. 2 , the forging step is conducted so as to increase the wall thickness of the region  14  to a thickness T 2 . In one aspect, this increase in wall thickness is obtained while maintaining the outer diameter D 1  constant. In another aspect, the outer diameter D 1  may be reduced during the thickening step depending upon the amount of wall thickening required by using an outer diameter (OD) die during application of the compressive force. It will be appreciated that various other forming operation for achieving this result will be known to persons skilled in the art. As will be understood, the inner diameter at the region  14  will, therefore, have a reduced inner diameter D 3 , which is less than the inner diameter D 2  of the remainder of the blank  10 . It will also be understood that, as shown in  FIG. 2 , the wall thickness of the region  14  will generally taper from the thickness T 2  to the thickness T 1  at each end of the region  14 . This type of transition will be known to persons skilled in the art as a common feature in forging operations. 
   The next step of the method of the invention involves the insertion of a cold forming mandrel into the tube blank  10 . The mandrel used for this step is illustrated in  FIG. 3 . As shown, the mandrel  100  is, one aspect, generally cylindrically shaped having a central axis  102  and a main body  104  of a generally constant outer diameter D 4 . It will be understood that the mandrel  100  is shaped and sized to permit insertion into a tube blank  10 . The outer diameter D 4  of the mandrel main body generally corresponds to the inner diameter D 2  of the tube  10 , however, as will be understood by persons skilled in the art, diameter D 4  may be slightly less than diameter D 2  in order to permit the mandrel to be inserted into the tube blank  10 . 
   In one aspect of the invention, the mandrel  100  includes a first end  108  and an opposite second end  110 . First end  108  of the mandrel has a complementary shape corresponding to the spindle end  16  of the tube  10 . The first end  108  of the mandrel  100  includes various sections indicated as  112 ,  114  and  116 , each having differing outer diameters D 5 , D 6 , and D 7 , respectively, wherein D 5 &gt;D 7 &gt;D 6 . Each of diameters D 5 , D 6  and D 7  are, in turn, less than the outer diameter D 4  of the mandrel main body  104 . It will be understood that, as shown in  FIG. 3 , the transitions between the diameters of each of sections  104 ,  112 ,  114 , and  116  may be gradual. 
   The second end  110  of the mandrel  100  is generally provided with a clamping portion  118  to which can be attached an arm or clamp (not shown) for moving the mandrel within the tube  10  (as discussed further below). In one embodiment, the second end  110  of the mandrel  100  is also provided with a reduced diameter section  120  having an outer diameter D 8  that is less than diameter D 4 . The purpose of sections  112 ,  114 ,  116 , and  120  will become apparent in the following description of the invention. It will also be understood by persons skilled in the art that the specific design and geometry of the mandrel  100  shown and described herein serves to form the axle housing from a tube blank as herein described. Therefore, it will be apparent to persons skilled in the art that where the method of the invention is to be used for forming any other tubular article, the mandrel used for the method will have a respective shape depending on the shape of the article being formed. 
   As indicated above, the next step in the method of the invention comprises the insertion of the mandrel  100  into the tube blank and this is illustrated in  FIG. 4 . In this step, the mandrel  100  is inserted into the tube blank  10  of  FIG. 2  by inserting the first end  108  of the mandrel into the second end  18  of the tube blank. As indicated above, the outer diameters D 4  to D 7  are sized so as to be slidably received within the inner diameter D 2  of the main body of the tube bank  10 . The mandrel  100  is then advanced until the first end  108  of the mandrel reached the first end  16  of the tube  10 . As shown in  FIG. 4 , the section  114  of the mandrel  100  corresponds in position to the region  14  of the tube blank  10 . It will also be noted that the outer diameter D 3  of the thickened region  14  generally corresponds to the outer diameter D 7  of section  116  of the mandrel  100 . Thus, during insertion of the mandrel  100  into the tube blank  10 , the blank is not materially deformed. 
   In a preferred embodiment, the first end  16  of the tube is crimped or “nosed”, so as to reduce the outer diameter thereof, prior to insertion of the mandrel  100 . Such “nosing” serves to limit the advancement of the mandrel  100  and prevent same from extending beyond the desired position. 
   Further, as known in the art, it is often preferred for the tube to be lubricated to facilitate passage of the mandrel. 
   In the above description, the mandrel is indicated as being advanced through the tube  10 . However, it will be understood that it is also possible for the mandrel  100  to remain stationary and for the tube to be advanced there-over. Similarly, it is possible for both the tube and the mandrel to be advanced together. 
   Once the mandrel  100  is advanced to the desired position within the tube  10 , a die  200 , such as a reducing die, is mounted over the first end  16  of the tube  10  and advanced in a direction shown by arrow  20  over the length of the tube  10 . It will be understood, and known in the art, that during insertion of the die  200  over the first end  16  of the tube  10 , and passage of the die over the length of the tube, the second end  18  of the tube will be anchored so as to prevent movement of same. 
   An embodiment of the die according to the present invention is shown in  FIG. 5 . As shown, the die  200  comprises a generally annular shaped body having two sections: a support ring  202  and a generally annular forming ring  204 . The support ring  202  may, as known in the art, include a recess  206  to receive the forming ring  204  and, preferably a shoulder  208  to maintain the forming ring in position. The forming ring includes an inner diameter D 9 , which corresponds with the outer diameter of the final desired article and which is generally less than the outer diameter D 1  of the tube blank  10 . It will be understood that various other configurations of the die  200  are known in the art and can equally be used in the present invention. 
   As indicated above, the die  200  is provided over the first end  16  of the tube having the mandrel  100  contained within. The die is then forcibly moved over the outer surface of the tube blank  10  in a direction towards the second end  18  of the blank. The terminal position of the die  200 , after traversing the length of the tube  10 , is shown in  FIG. 6 . As can be seen, the passage of the die  200  over the tube  10  forces the tube inner diameter to conform to the outer shape of the mandrel  100 . That is, after the die  200  is passed over the tube  10 , the inner wall of the tube  10  will include mirror images of the sections  112 ,  114 , and  116  of the mandrel. Furthermore, since, as indicated above, the inner diameter D 9  of the forming ring  204  of the die  200  is less than the outer diameter D 1  of the tube blank  10 , the tube outer diameter will be reduced during passage of the die. As can be seen in  FIG. 6 , once the die  200  is passed over the tube  10 , the tube is provided with a generally uniform outer diameter D 10 , which generally corresponds to diameter D 9 . However, since the outer diameter D 4  of the mandrel  100  is generally the same as the inner diameter D 2  of the tube, it will be appreciated that, during passage of the die  200 , the wall thickness of the tube blank  10 , over the section  104  of the mandrel, will be reduced. Such reduction in wall thickness will result in an accumulation of tube material ahead of the die  200  as it is passed towards end  18  of the tube. In the result, such accumulated material will concentrated within the space created by the reduced diameter (D 8 ) section  120  of the mandrel. Thus, the inner wall of the second end  18  of the tube  10  will generally assume the shape of the outer surface of section  120  of the mandrel  100 . 
   In the above description, the die  200  is described as being advanced over the tube  10 . However, it will be understood that it is also equally possible for the die to remain stationary and for the tube to be inserted there-through. Similarly, it is possible for both the tube and the die to be advanced together. 
   Once the die  200  is passed over the length of the tube  10 , the die is removed. Subsequently, with the tube  10  retained in position, the mandrel is withdrawn from the tube  10 . Alternatively, it will be understood that the tube can be stripped from the mandrel. As will be understood by persons skilled in the art, the withdrawal of the mandrel  100  is accomplished by means of a clamp (not shown) grasping, for example, the end  118  of the mandrel and applying a pulling force thereon. Such clamp can also be used to maintain the mandrel in position while the tube is withdrawn. It will also be understood that as the mandrel  100  (or tube  10 ) is withdrawn from the position shown in  FIG. 6 , the outer diameter of the tube  10  will deformed as the larger sections of the mandrel pass through narrower inner diameter sections of the tube  10 . For example, as the mandrel section  104  is pulled through the second end  18  of the tube, the thickened section at such end will be forced radially outwards. Similarly, as the mandrel section  116  is drawn through the thickened tube section which had corresponded to mandrel section  114 , the outer diameter of the tube in such section will also be forced radially outwards. However, this will be dependent upon product design requirements. For example, in one aspect of the invention, the mandrel can be withdrawn without radial expansion of the tube. In such case, the mandrel at section  116  can be altered to suit different product designs. For example, if the diameter D 7  of section  116  of the mandrel is the same or less than the diameter D 6  at section  114 , then it will be understood that a radial expansion of the tube will not occur when the mandrel is withdrawn. 
   The cross section of the tube  10 , following complete withdrawal of the mandrel, is shown in  FIG. 7 . The thickened region  14  is also clearly observed. As described above, the main body of the tube  10  is provided with a reduced wall thickness T 3 , which is thinner than the initial thickness T 1 . Further, as also described above, the tube  10  is also provided with an increased wall thickness T 4  at the second end  18 . 
   Following separation of the mandrel  100  and the tube  10 , the resulting tube (i.e. as shown in  FIG. 7 ) can then be swaged or otherwise treated or formed at the first end  16  to arrive at the final shape shown in  FIG. 8 . The final profile provided on the tube  10  results in the first end  16  having the shape and structural features of a spindle  22 . As also shown in  FIG. 8 , in a preferred embodiment, the second end  18  of the tube  10  can also be swaged so as to provide the second end  18  with the same outer diameter D 10  as the body of the tube. 
   As will be appreciated by persons skilled in the art, the second end  18  of the tube is attached to the differential of an automobile. As such, the increased thickness provided at the second end  18  serves to provide the tube with increased strength at the point of such attachment. Similarly, the tube can be provided with other regions of strength (i.e. increased wall thickness) as needed. 
   As will be appreciated, the method of the present invention provides an axle housing tube that incorporates, as a unitary body, the required spindle. The method avoids the need for multiple welding steps as well as the possible deleterious effects resulting from the welding process such as structural weakening. Further, the method of the present invention permits the formation of a unitary tube having specifically localized regions of increased thickness for providing stiffness in areas subject to high stresses. In addition, by providing a method involving mainly the cold forming of the tubular blank, it will be understood that production costs will be lower with the invention (due to reduced energy demands by avoiding hot forging). Further, by using only a single mandrel and reducing die, the cycle time for producing tubular articles with the present invention is also greatly reduced. In the result, it will be appreciated that the present invention provides an efficient and cost effective method for producing tubular articles having various cross sectional profiles. 
   Although the present invention has been illustrated by means of referring to the manufacture of an axle housing, it will be appreciated that the present method can be used for manufacturing various types of tubular articles. Further, although the terms diameter, radius etc. have been used with reference to cylindrical articles, it will be understood that the invention is not limited to cylindrical or straight articles alone. In addition, even where the method is used to provide a generally cylindrical article, such article can, of course, be further formed into various shapes. 
   Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.