Composite powder metal variable boundary gear and method

Abstract

A forged composite gear and a method of making a forged composite powder metal gear. The forged composite gear includes a plurality of teeth extending from a core, a first section having a first powder metal material, a second section having a second powder metal material and a variable boundary profile. The variable boundary profile is formed between the first section and the second section, whereby said variable boundary profile exhibits greater tooth wear resistance on the teeth and greater impact resistance in the core.

1 . A forged composite gear comprising: 
 a core substantially comprising a first powder metal material;    a plurality of teeth extending from said core and at least partially comprising a second powder metal material; and    a variable boundary profile formed between said first powder metal material and said second powder metal material, wherein said first powder metal material exhibits greater impact resistance and said second powder metal material exhibits greater wear resistance.    
     
     
         2 . The forged gear according to  claim 1  wherein said second powder metal material has a surface hardness of at least 58 HRC.  
     
     
         3 . The forged gear according to  claim 1  wherein said first powder metal material has a hardness of less than 43 HRC.  
     
     
         4 . The forged gear according to  claim 1  wherein said first powder metal material is a non-hardening material and said second powder metal material is a hardening material.  
     
     
         5 . The forged gear according to  claim 4  wherein said variable boundary profile is forged in said plurality of teeth.  
     
     
         6 . The forged gear according to  claim 1  wherein said first powder metal material has substantially lower carbon content than said second powder metal material.  
     
     
         7 . The forged gear of  claim 1  wherein said gear is a bevel gear, said bevel gear having a rotational axis, said plurality of teeth extending radially in the same general direction as the rotational axis of said bevel gear, but inclined with respect to the rotational axis of said bevel gear.  
     
     
         8 . The bevel gear of  claim 7  wherein said bevel gear is a differential side gear having an axially splined internal section in said core.  
     
     
         9 . The forged gear of  claim 1  wherein each tooth of said plurality of teeth comprise a first surface comprising a tip surface, a pitch line surface, a root fillet surface and a root land surface, wherein said variable boundary profile is substantially represented by a boundary ratio satisfied by at least one of a root land surface to a root fillet surface of approximately 2:1, a tip surface to said root fillet surface of approximately 6:1, or a pitch line surface to said root fillet surface of approximately 19:4.  
     
     
         10 . A bevel gear comprising: 
 a gear core defining a rotational axis;    a plurality of radial teeth extending from said gear core and extending in the same general direction as said rotational axis of said gear core, but inclined with respect to said rotational axis of said gear core;    a first powder metal material at least partially forming said plurality of radial teeth; and    a second powder metal material forming said gear core and partly forming a core of said plurality of radial teeth, said first and said second powder metal materials being sintered and forged to form a variable boundary profile between said first and second powder metal materials, the first and second powder metal materials having different hardness properties.    
     
     
         11 . The bevel gear according to  claim 10  wherein said bevel gear is a pinion gear having an axial internal section in said gear core.  
     
     
         12 . The bevel gear according to  claim 10  wherein said first powder metal material comprises a surface hardness of at least 58 HRC.  
     
     
         13 . The bevel gear according to  claim 10  wherein said second powder metal material comprises a hardness of not more than 43 HRC.  
     
     
         14 . The bevel gear according to  claim 10  wherein said first powder metal material is a hardening material and said second powder metal material is effectively a non-hardening material.  
     
     
         15 . The bevel gear according to  claim 10  wherein said second powder metal material has substantially lower carbon content than said first powder metal material.  
     
     
         16 . A method of forming a gear from at least two different powder metal materials comprising the sequential steps of: 
 preforming at least two different powder metal materials into a preform comprising the steps of: 
 filling a first portion of a compaction form with a first powder metal material, said compaction form shape corresponding to the shape of said preform;  
 filling a second portion of said compaction form with a second powder metal material; and  
 compacting said powders in said compaction form to form said preform;  
   sintering said preform;    forging said preform at a forge temperature and a forge pressure to obtain a substantially dense, net shape, forged part having a first section having said first powder metal material and a second section having said second powder metal material, and a boundary profile formed there between; and    cooling said forged part.    
     
     
         17 . The method of  claim 16  wherein preforming further comprises separating during filling by inserting a separator into said compaction form for filling one of said powder metal materials, and removing said separator from said compaction form prior to compacting.  
     
     
         18 . The method of  claim 16  wherein said boundary profile is a variable boundary profile.  
     
     
         19 . A bevel gear having a gear core, a rotational axis, a plurality of radial teeth core and a plurality of radial teeth, said radial teeth extending in the same general direction as the rotational axis of said bevel gear, but inclined with respect to the rotational axis of said bevel gear, produced in accordance with the process of  claim 16 , wherein said first section substantially forms an exterior surface of said plurality of radial teeth, and said second section forms said gear core and a core of said plurality of radial teeth.  
     
     
         20 . The bevel gear of  claim 19  wherein each tooth of said plurality of teeth comprises a first surface comprising a tip surface, a pitch line surface, a root fillet surface and a root land surface, wherein said boundary profile is a variable boundary profile and is substantially represented by a boundary ratio satisfied by at least one of a root land surface to a root fillet surface of approximately 2:1, a tip surface to said root fillet surface of approximately 6:1, or a pitch line surface to said root fillet surface of approximately 19:4.  
     
     
         21 . The method of  claim 16  wherein said first and second powder metal materials are different low alloy ferrous materials.