Abstract:
A composite brake drum for use in a drum brake assembly includes a one-piece mounting flange and shell and a liner cast integrally in a shell portion thereof. The method for forming the composite brake drum of this invention includes the steps of: (a) providing a generally circular metal blank having an initial pilot hole inner diameter; (b) spin forming the metal blank to produce a one-piece brake drum component defining a center longitudinal axis and including a cylindrical shell having a squealer band which defines a squealer band outer diameter, a mounting flange extending radially inwardly from one end of the shell toward the center longitudinal axis, and an annular lip extending radially inwardly from an opposite end of the shell toward the center longitudinal axis, and wherein the shell, the flange, and the lip cooperate to define a cylindrical mold cavity; (c) subsequent to step (b), centrifugally casting a liner in situ within the mold cavity of the brake drum component to thereby produce the composite vehicle brake drum; and (d) subsequent to step (c), machining the initial pilot hole inner diameter to a final pilot hole inner diameter by locating off of the squealer band outer diameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Ser. No. 08/769,196, filed Dec. 18, 1996, now U.S. Pat. No. 5,782,324 which claims the benefit of U.S. Provisional Application No. 60/009,425, filed Dec. 27, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to vehicle drum brake assemblies and in particular to an improved structure for a composite brake drum for use in such a vehicle drum brake assembly and method for producing the same. 
     Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system includes either a disc brake assembly or a drum brake assembly for each of the wheels. The brake assemblies are typically actuated by hydraulic or pneumatic pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like. The structure and operation of the brake assemblies, as well as the actuators therefor, are well known in the art. 
     FIG. 1 illustrates a prior art pneumatically actuated drum brake assembly, indicated generally at  10 , typically for use with a heavy duty truck and trailer. As shown therein, the drum brake assembly  10  includes a backing plate  12  which is secured to a fixed, non-rotatable component of the vehicle, such as the vehicle axle housing (not shown). A pair of opposed arcuate brake shoes  14  (only one brake shoe  14  is illustrated) are supported on the backing plate  12  for selective movement relative thereto. Each of the brake shoes  14  has a friction pad  16  secured thereto. 
     The brake drum assembly  10  further includes a hollow cylindrical “heavy duty” composite brake drum  18  shown in prior art FIG.  2 . The brake drum  18  is disposed adjacent the backing plate  12  such that the brake shoes  14  extend within an inner cylindrical braking surface  24 A thereof. To effect braking action, the brake shoes  14  are moved outwardly apart from one another such that the friction pads  16  frictionally engage the cylindrical braking surface  24 A of the brake drum  18 . Such frictional engagement causes slowing or stopping of the rotational movement of the brake drum  18  and, therefore, the wheel of the vehicle in a controlled manner. 
     One or more actuating mechanisms are provided in the drum brake assembly  10  for selectively moving the brake shoes  14  outwardly apart from one another into frictional engagement with the cylindrical braking surface  24 A of the brake drum  18 . Usually, a pneumatically actuated service brake mechanism is provided for selectively actuating the drum brake assembly  10  under normal operating conditions. Typically, the service brake mechanism includes an air chamber device  26 , a lever assembly  28 , and a S-cam actuating mechanism  30 . To actuate the service brake, pressurized air is supplied to the air chamber device  26  to actuate the lever assembly  28  which in turn rotates the S-cam actuating mechanism  30  to move brake shoes  14  apart from one another into frictional engagement with the cylindrical braking surface  24 A of the brake drum  18 . A mechanically actuated parking and emergency brake mechanism is also usual provided for selectively actuating the drum brake assembly  10  in a similar manner. 
     FIG. 3 illustrates a typical sequence of steps for producing the brake drum  18  shown in prior art FIGS. 1 and 2. First, referring to the left hand side of FIG. 3, the steps involved in the process of forming a shell portion  22  and a liner portion  24  of the brake drum  18  are illustrated. Initially, in step  40 , a flat sheet of suitable material, such as for example steel, is formed into a generally flat band having a desired profile, such as by a roll forming process. Next, in step  42 , the opposed ends of the band are disposed adjacent one another and welded together to form a hoop. In step  44 , the hoop is expanded to produce the shell portion  22  having a desired profile shown in FIG.  2 . Following this, the liner portion  24  is cast in the shell portion  22 , preferably by a centrifugally casting process in step  46 . After this, in step  48 , the shell portion  22  and the liner portion  24  are rough machined. 
     Now, referring to the right hand side of FIG. 3, the steps involved in the process of forming a mounting flange portion  20  of the brake drum  18 , and the steps involved in the process of forming the brake drum  18  itself, are illustrated. In step  50 , a flat sheet of suitable material, such as for example steel, is formed into a mounting flange blank, such as by a stamping process. Following this, in step  52 , the mounting flange blank is formed into the mounting flange portion  20  having a desired profile by a stamping process. A. plurality of lug bolt mounting holes  20 C (only one lug bolt mounting hole  20 C being illustrated in FIG.  2 ), can be simultaneously formed in the flange portion  20 . As is known, lug bolts (not shown) extend through the lug bolt holes  20 C to secure the brake drum  18  to a vehicle wheel (not shown) for rotation therewith. In step  54 , an inner end  20 A of the mounting flange portion  20  is disposed adjacent an outer end  22 B of the shell portion  22  and welded together to join the shell portion  22  and the liner  24  portion to the mounting flange portion  20 . Next, a pilot hole  20 B is formed in the mounting flange portion  20  during step  56 . 
     In step  58 , the brake drum  18  is finish machined to predetermined tolerances. Following this, the brake drum  18  is typically subjected to a balancing operation in step  60 . In particular, one or more wheel balance weights (not shown) are usually attached to an outer surface of the shell portion  22  by welding to produce the finished brake drum  18 . Typically, the mounting flange  20  of the brake drum  18  defines a generally constant mounting flange thickness T 1 , and the shell portion  22  defines a generally constant shell thickness T 2  which is less than the mounting flange thickness T 1 . Alternatively, the brake drum can be a heavy duty “full cast” brake drum, indicated generally at  32  in prior art FIG.  4 . As shown therein, the brake drum  32  includes an integral raised squealer band  34  provided on an outer surface thereof. 
     The composite brake drum  18  illustrated in FIGS. 1 and 2 is considerably lighter than the full cast brake drum  32  illustrated in FIG.  4 . However, the full cast brake drum  32  can be produced using a simpler manufacturing process than the process used to produce the composite brake drum  18 . Also, each of the brake drums  18  and  32  typically incorporates a sufficient imbalance which renders them unsatisfactory for use on a vehicle without balancing. There are several known methods for correcting the imbalance of the brake drums  18  and  32 . Typically, the composite brake drum  18  is balanced by welding balance weights to the outer surface of the drum. While the full cast brake drum  32  can be balanced in a similar manner, it can also be balanced according to the methods disclosed in U.S. Pat. No. 4,986,149 to Carmel et al. and U.S. Pat. No. 5,483,855 to Julow et al. According to the method of the Carmel et al. patent, a crescent or wedge of material is preferably cut away from an outer surface of the squealer band by a lathe during an eccentric turning process to produce a final balanced brake drum. According to the method of the Julow et al. patent, a circumferentially extending substantially constant depth cut is made along a portion of the squealer band by a milling machine to produce a final balanced brake drum. Thus, it would be desirable to provide an improved structure for a composite brake drum and method for producing such a brake drum which is relatively simple and economical. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved structure for a composite brake drum for use in a drum brake assembly and a method for producing such a brake drum. The composite brake drum includes a one-piece mounting flange and shell having a liner cast integrally in the shell portion thereof. The method for forming the composite brake drum of this invention includes the steps of: (a) providing a generally circular metal blank having an initial pilot hole inner diameter; (b) spin forming the metal blank to produce a one-piece brake drum component defining a center longitudinal axis and including a cylindrical shell having a squealer band which defines a squealer band outer diameter, a mounting flange extending radially inwardly from one end of the shell toward the center longitudinal axis, and an annular lip extending radially inwardly from an opposite end of the shell toward the center longitudinal axis, and wherein the shell, the flange, and the lip cooperate to define a cylindrical mold cavity; (c) subsequent to step (b), centrifugally casting a liner in situ within the mold cavity of the brake drum component to thereby produce the composite vehicle brake drum; and (d) subsequent to step (c), machining the initial pilot hole inner diameter to a final pilot hole inner diameter by locating off of the squealer band outer diameter. 
    
    
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view, partially broken away, of a portion of a prior art heavy duty truck and trailer drum brake assembly. 
     FIG. 2 is a sectional view of a prior art brake drum illustrated in FIG.  1 . 
     FIG. 3 is a block diagram illustrating the sequence of steps for producing the prior art brake drum illustrated in FIG.  2 . 
     FIG. 4 is a sectional view similar to FIG. 2 of an alternate embodiment of a prior art brake drum. 
     FIG. 5 is a sectional view of an improved structure for a first embodiment of a brake drum in accordance with this invention. 
     FIG. 6 is a sectional view of an improved structure for a second embodiment of a brake drum in accordance with this invention. 
     FIG. 7 is a block diagram illustrating a first sequence of steps for producing the brake drum of the present invention. 
     FIG. 8 is a cross sectional view showing the initial forming of the one-piece mounting flange and shell for the brake drum illustrated in FIG. 6 
     FIG. 9 is a cross sectional view showing the final forming of the one-piece mounting flange and shell for the brake drum illustrated in FIG.  6 . 
     FIG. 10 is a block diagram illustrating a second sequence of steps for producing the brake drum of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, there is illustrated in FIG. 5 a first embodiment of a composite brake drum, indicated generally at  100 , in accordance with this invention. The brake drum  100  is associated with a rear wheel of a vehicle and includes a one-piece mounting flange and shell, indicated generally at  62 , and a liner  64 . As will be discussed below, the one-piece mounting flange and shell  62  is preferably formed from steel and the liner  64  is preferably formed from gray cast iron. The liner  64  includes an inner surface  64 A which is machined to define a predetermined braking surface. 
     The one-piece mounting flange and shell  62  defines a center longitudinal axis X and includes a generally closed end or mounting flange portion  66 , a transition section  68 , a generally axially extending cylindrical main body  70 , and an opened end  72  having an annular lip  72 A. The cylindrical body portion  70  defines an outer surface  70 A and, in the illustrated embodiment, includes a raised continuously extending annular squealer band  74 . The cylindrical body portion  70  has a corrugated section which defines corrugation peak outer surface  70 B, and a corrugation crest inner surface  70 C. The corrugation peak outer surface  70 B defines a body outer diameter D 2 , and the corrugation crest inner surface defines a body inner diameter D 3 . The squealer band  74  includes an outer surface  74 A which defines a squealer band outer diameter D. For discussion purposes, the mounting flange portion  66  of the one-piece mounting flange and shell  62  includes the mounting flange  66 , and the shell portion of the one-piece mounting flange and shell  62  includes a portion of the transition section  68  and the cylindrical main body  70 . 
     The mounting flange portion  66  of the brake drum  100  includes a generally centrally located pilot hole  66 A formed therein and a plurality of lug bolt holes  66 B (only one lug bolt hole  66 B being illustrated) spaced circumferentially around the pilot hole  66 A. The lug bolt mounting holes  66 B are adapted to receive wheel mounting studs (not shown) for securing a wheel (not shown) to the brake drum  100  for rotation therewith. 
     The mounting flange portion  66  defines a generally constant thickness T 3 , and the transition section  68  defines a generally constant thickness T 4 . The cylindrical body  70  defines a generally constant thickness T 5 , the squealer band  74  defines a generally constant thickness T 6 , and the opened end  72  defines a generally constant thickness T 7 . As will be discussed below, in the illustrated embodiment the thicknesses T 3  and T 6  are approximately equal to one another, and the thicknesses T 4 , T 5 , and T 7  are approximately equal to one another and less than the thicknesses T 3  and T 6 . 
     Referring now to FIG. 6, there is illustrated a second embodiment of a composite brake drum, indicated generally at  100 ′, in accordance with this invention. The brake drum  100 ′ is associated with a front wheel of a vehicle and includes a one-piece mounting flange and shell, indicated generally at  62 ′, and a liner  64 ′. As will be discussed below, the one-piece mounting flange and shell  62 ′ is preferably formed from steel and the liner  64 ′ is preferably formed from gray cast iron. The liner  64 ′ includes an inner surface  64 A′ which is machined to define a predetermined braking surface. 
     The one-piece mounting flange and shell  62 ′ defines a center longitudinal axis X′ and includes a generally closed end or mounting flange portion  66 ′, a transition section  68 ′, a generally axially extending cylindrical main body  70 ′, and an opened end  72 ′ having an annular lip  72 A′. The cylindrical body portion  70 ′ defines an outer surface  70 A′ and, in the illustrated embodiment, includes a raised continuously extending annular squealer band  74 ′. The cylindrical body portion  70 ′ has a corrugated section which defines corrugation peak outer surface  70 B′, and a corrugation crest inner surface  70 C′. The corrugation peak outer surface  70 B′ defines a body outer diameter D 2 ′, and the corrugation crest inner surface defines a body inner diameter D 3 ′. The squealer band  74 ′ includes an outer surface  74 A′ which defines a squealer band outer diameter D′. For discussion purposes, the mounting flange portion  66 ′ of the one-piece mounting flange and shell  62 ′ includes the mounting flange  66 ′, and the shell portion of the one-piece mounting flange and shell  62 ′ includes a portion of the transition section  68 ′ and the cylindrical main body  70 ′. 
     The mounting flange portion  66 ′ of the brake drum  100 ′ includes a generally centrally located pilot hole  66 A′ formed therein and a plurality of lug bolt holes  66 B′ (only one lug bolt hole  66 B′ being illustrated) spaced circumferentially around the pilot hole  66 A′. The lug bolt mounting holes  66 B′ are adapted to receive wheel mounting studs (not shown) for securing a wheel (not shown) to the brake drum  100 ′ for rotation therewith. 
     The mounting flange portion  66 ′ defines a generally constant thickness T 3 ′, and the transition section  68 ′ defines a generally constant thickness T 4 ′. The cylindrical body  70 ′ defines a generally constant thickness T 5 ′, the squealer band  74  defines a generally constant thickness T 6 , and the opened end  72 ′ defines a generally constant thickness T 7 ′. As will be discussed below, in the illustrated embodiment the thicknesses T 3 ′ and T 6 ′ are approximately equal to one another, and the thicknesses T 4 ′, T 5 ′, and T 7 ′ are approximately equal to one another and less than the thicknesses T 3 ′ and T 6 ′. 
     Turning now to FIG. 7, there is illustrated a block diagram of a first sequence of steps for producing the composite brake drum  100 ,  100 ′ of this invention. Initially, in step  80 , a flat sheet of suitable material, such as for example steel, is subjected to a stamping operation to produce a generally flat circular blank having a rough pilot hole formed therein. Following this, in optional step  82 , the blank is subjected to a stamping operation to produce a brake drum preform having a desired profile. In particular, during optional step  82 , the mounting flange portion  66 ,  66 ′ of the respective brake drum  100 ,  100 ′ can be formed to a desired profile. 
     Next, in step  84 , the blank (shown in phantom at  102 ′ in FIG. 8) or preform (not shown, if step  82  is performed), is supported in a suitable fixture, such as for example a well known mandrel-tailstock assembly, such as that indicated generally at  110  in FIG. 8, and is subjected to an initial forming process. During step  84 , preferably a spinning tool  104  is actuated and engages the material of the blank  102  as the spinning tool  104  is moved in the direction of the arrow S in order to spin form a partially formed one-piece mounting flange and shell  106 ′ having a desired profile. In particular, during step  84 , the spinning tool  104  makes multiple passes in order to form the desired profile of the partially formed one-piece mounting flange and shell  106 ′ of the associated brake drum (FIG. 8 illustrating a partially formed one-piece mounting flange and shell  106 ′ which can be used to produce the brake drum  100 ′ of this invention). Also, as illustrated and discussed below, during step  84  selected sections of the shell portion  106 ′ are preferably thinned to predetermined tolerances. 
     Following this, the partially formed one-piece mounting flange and shell  106 ′ is supported in a suitable fixture, such as for example a mandrel-tailstock assembly, such as that indicated generally at  120  in FIG. 9, and is subjected to a final forming process in step  86 . During step  86 , preferably a first flow forming tool  112  and a second flow forming tool  114  are actuated and move in the direction of arrows T and U, respectively, to engage the material of the partially formed one-piece mounting flange and shell  106 ′ in order to flow form the material thereof against the mandrel and produce a finished one-piece mounting flange and shell having a desired shell portion profile (FIG. 9 showing the finished one-piece mounting flange and shell  62 ′ for used to produce the brake drum  100 ′ of this invention). 
     As shown in FIG. 9, the illustrated mandrel-tailstock assembly  120  used in the final forming process in step  86  includes an eccentric mandrel  122 . As shown therein, the mandrel  122  is operative enable the material of the shell portion  106 ′ of the partially formed one-piece mounting flange and shell  106 ′ to be flow formed against a portion/side of the mandrel, shown in FIG. 9 as flow forming the material against the portion/side of the mandrel  122  located in the upper half of the drawing. Due to the profile of the illustrated one-piece mounting flange and shell  62 ,  62 ′, namely due to the main body  70 ,  70 ′ provided with the corrugations and the annular lip  72 A,  72 A′, both of which extend radially inwardly toward the axis X, X′ thereof, the mandrel  122  is eccentric to enable the finished one-piece mounting flange and shell  62 ,  62 ′ to be removed from the mandrel-tailstock assembly  120  subsequent to step  86 . Alternatively, the mandrel-tailstock assembly  120  could be other than illustrated depending upon the structure of the finished one-piece mounting flange and shell  62 ,  62 ′. 
     Next, in step  88 , a gray iron liner  64 ,  64 ′ is cast in the shell portion of the respective one-piece mounting flange and shell  62 ,  62 ′. Preferably, the casting of the liner  64 ,  64 ′ is accomplished using a centrifugal casting process. However, other casting processes may be used as desired. After the casting of the liner  64 .  64 ′, the mounting flange portion  66 ,  66 ′ of the brake drum is coined in step  90 , and a respective pilot hole  66 A,  66 A′ is formed to a predetermined size along with the forming of the lug bolt mounting holes  66 B,  66 B′ during step  92 . Following this, the brake drum  100 ,  100 ′ is machined to predetermined tolerances during step  94 . Next, in optional step  96 , the brake drum is subjected to a balancing operation to produce the finished brake drum  100 ,  100 ′. 
     Referring now to FIG. 9, there is illustrated a block diagram of a second sequence of steps for producing the composite brake drum  100 ,  100 ′ of this invention. Initially, in step  180 , a flat sheet of suitable material, such as for example steel, is subjected to a laser cutting or stamping operation to produce a generally flat circular blank having a predetermined outer diameter and a predetermined inner diameter. Following this, in optional step  182 , the blank is subjected to a metal forming operation, such as for example a stamping operation, to produce a brake drum preform having a desired profile. In particular, during optional step  182 , the mounting flange portion  66 ,  66 ′ of the respective brake drum  100 ,  100 ′ can be formed to a desired profile. 
     Next, in step  184 , the blank (shown in phantom at  102 ′ in FIG. 8) or preform (not shown, if step  82  is performed), is supported in a suitable fixture, such as for example a well known mandrel-tailstock assembly, such as that indicated generally at  110  in FIG. 8, and is subjected to an initial forming process. During step  184 , preferably a spinning tool  104  is actuated and engages the material of the blank  102  as the spinning tool  104  is moved in the direction of the arrow S in order to spin form a partially formed one-piece mounting flange and shell  106 ′ having a desired profile. In particular, during step  184 , the spinning tool  104  makes multiple passes in order to form the desired profile of the partially formed one-piece mounting flange and shell  106 ′ of the associated brake drum (FIG. 8 illustrating a partially formed one-piece mounting flange and shell  106 ′ which can be used to produce the brake drum  100 ′ of this invention). Also, as illustrated and discussed below, during step  184  selected sections of the shell portion  106 ′ are preferably thinned to predetermined tolerances. 
     Following this, the partially formed one-piece mounting flange and shell  106 ′ is supported in a suitable fixture, such as for example a mandrel-tailstock assembly, such as that indicated generally at  120  in FIG. 9, and is subjected to a final forming process in step  186 . During step  186 , preferably a first flow forming tool  112  and a second flow forming tool  114  are actuated and move in the direction of arrows T and U, respectively, to engage the material of the partially formed one-piece mounting flange and shell  106 ′ in order to flow form the material thereof against the mandrel and produce a finished one-piece mounting flange and shell having a desired shell portion profile (FIG. 9 showing the finished one-piece mounting flange and shell  62 ′ for used to produce the brake drum  100 ′ of this invention). 
     As shown in FIG. 9, the illustrated mandrel-tailstock assembly  120  used in the final forming process in step  186  includes an eccentric mandrel  122 . As shown therein, the mandrel  122  is operative enable the material of the shell portion  106 ′ of the partially formed one-piece mounting flange and shell  106 ′ to be flow formed against a portion/side of the mandrel, shown in FIG. 9 as flow forming the material against the portion/side of the mandrel  122  located in the upper half of the drawing. Due to the profile of the illustrated one-piece mounting flange and shell  62 ,  62 ′, namely due to the main body  70 ,  70 ′ provided with the corrugations and the annular lip  72 A,  72 A′, both of which extend radially inwardly toward the axis X, X′ thereof, the mandrel  122  is eccentric to enable the finished one-piece mounting flange and shell  62 ,  62 ′ to be removed from the mandrel-tailstock assembly  120  subsequent to step  186 . Alternatively, the mandrel-tailstock assembly  120  could be other than illustrated depending upon the structure of the finished one-piece mounting flange and shell  62 ,  62 ′. 
     Next, in step  188 , a gray iron liner  64 ,  64 ′ is cast in the shell portion of the respective one-piece mounting flange and shell  62 ,  62 ′. Preferably, the casting of the liner  64 ,  64 ′ is accomplished using a centrifugal casting process. However, other casting processes may be used as desired. After the casting of the liner  64 .  64 ′, the mounting flange portion  66 ,  66 ′ of the brake drum is coined in step  190 . 
     In step  192 , the brake drun  100 ,  100 ′ is supported on a suitable fixture (not shown) and the respective liner surface  64 ,  64 ′ is machined to define the predetermined brake surface  64 A,  64 A′ and the respective pilot hole  66 A,  66 A′ is machined to define the predetermined inner diameter D 1 , D 1 ′. To accomplish this, the brake surface  64 A,  64 A is machined to the predetermined size by locating off of the respective squealer band outer diameter D, D′, and the pilot hole  66 A,  66 A′ is machined to the predetermined size by locating off of the respective squealer band outer diameter D, D 1 . Alternatively, the brake surface  64 A,  64 A′, the pilot hole  66 A,  66 A′, or both the brake surface  64 ,  64 A′ and pilot hole  66 A,  66 A′, can be machined by locating off of a surface other than the squealer band outer diameter D, D 1 . For example, the brake surface  64 A,  64 A′, the pilot hole  66 A,  66 A′, or both the brake surface  64 ,  64 A′ and pilot hole  66 A,  66 A′, can be machined by locating off of an outer surface of the shell  62 ,  62 ′ at some point other than at the squealer band outer diameter D, D 1 . Such other outer surface of the shell  62 ,  62 ′ could be at the respective body outer diameter D 2 , D 2 ′, and the respective body inner diameter D 3 , D 3 ′, or at some point therebetween. Preferably, during step  192 , the brake surface  64 A and the pilot hole  66 A of the brake drum  100  are machined by locating off of the squealer band outer diameter D, and the brake surface  64 A′ and the pilot hole  66 A′ of the brake drum  100 ′ are machined by locating off of the body outer diameter D 2 ′. 
     Following this, in step  194 , the lug bolt mounting holes  66 B,  66 B′ are formed to a predetermined size by locating off of the pilot hole inner diameter D 1 , D 1 ′. Next, in optional step  196 , the brake drum is subjected to a shot peening process, and in optional step  198 , the brake drum is subjected to a balancing operation to produce the finished brake drum  100 ,  100 ′. 
     One advantage of this invention is that the brake drum  100 ,  100 ′ includes a one-piece mounting flange and shell  62 , 62 ′ compared to the prior art composite brake drum  18  having a separate mounting flange  20  and shell  22  which were welded together. Also, by forming the one-piece mounting flange and shell  62 ,  62 ′ of this invention by using a spin forming process, the thickness of one-piece mounting flange and shell  62 ,  62 ′ can be varied along the length thereof and held to tight tolerances. 
     For example, when using a steel blank or preform having a thickness of approximately 0.25 inches, the spin forming process can be used to produce a thickness T 3  of approximately 0.25 inches in the mounting flange portion  66 ,  66 ′ a thickness T 4  of approximately 0.19 inches in the transition section  68 ,  68 ′ a thickness T 5  of approximately 0.19 in the cylindrical main body  70 ,  70 ′ a thickness T 6  of approximately 0.25 inches in the squealer band  74 ,  74 ′ and a thickness T 7  of approximately 0.19 inches in the opened end  72 ,  72 ′. In the prior art brake drum  18 , because the mounting flange  20  and the shell  22  were formed by a stamping and rolling process, respectively, it was not possible to thin either one of the flange  20  or shell  22  during the forming thereof. Also, using the spin forming process of step  84 ,  184  allows the squealer band  74 ,  74 ′ of the respective brake drum  100 ,  100 ′ to be formed of a thickness which, if necessary, is sufficient to enable the brake drum  100 ,  100 ′ to be balanced by removing material from the squealer band  74 ,  74 ′ such as by the methods disclosed in the above Carmel et al. and Julow et al. patents. 
     Although the brake drum  100 ,  100 ′ of this invention has been described and illustrated as forming the one-piece mounting flange and shell  62 ,  62 ′ by using a series of spin forming operations followed by a final flow forming operation, the one-piece mounting flange and shell  6262 ′ can be formed using other metal forming processes. Also, although the brake drum  100 ,  100 ′ of this invention has been described and illustrated in connection with a respective steel one-piece mounting flange and shell  62 ,  62 ′ and a gray cast iron liner  64 ,  64 ′, these components can be constructed from other metals. For example, the one-piece mounting flange and shell  62 ,  62 ′ can be formed from aluminum or alloys thereof, and the liner  64 , 64 ′ can be formed from nodular iron, austempered gray iron, or an aluminum composite material. In particular, the liner  64 ,  64 ′ may be cast from an aluminum based metal matrix composite (MMC). One particular MMC that can be used is an aluminum based MMC containing silicon carbide particulate reinforcement. Such an aluminum MMC is commercially available under the name DURALCAN, a registered trademark of Alcan Aluminum Limited of San Diego, Calif. However, the base alloy of the MMC can comprise other alloys, such as for example, magnesium, or titanium. Also, the particulate reinforcement material can comprise other materials, such as for example, alumina, silicon nitride, graphite, or ceramics. 
     Also, the brake drum  100 ,  100 ′ of this invention can be other than illustrated and described herein. For example, the brake drum  100 ,  100 ′ can be an “integral hub” brake drum (not shown). In addition, although the brake drum  100 ,  100 ′ of this invention has been described and illustrated in connection with the particular drum brake assembly disclosed herein, the brake drum  100 ,  100 ′ can be used in connection with other kinds of vehicles and/or other drum brake assemblies. For example, this invention may be used in an automobile and a light or medium duty truck, and/or in a “duo-servo” type of drum brake assembly (not shown), in a “dual mode” drum brake assembly (not shown), wherein the service brake is of the leading/trailing type and the parking and emergency brake is of the duo-servo type, in a “drum-in-hat” disc brake assembly (not shown), wherein the service brake is a disc brake and the parking and emergency brake is a drum brake. 
     In accordance with the provisions of the patents statues, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiment. However, it must be understood that the invention may be practiced otherwise than as specifically explained and illustrated without departing from the scope or spirit of the attached claims.