Abstract:
A method or apparatus for implanting atoms of a filler material into surface voids of a metallic component. The resulting component surface has fewer and smaller pores or surface voids making a component failure due to stress cracking less likely.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to strengthening steel and cast iron components by filling surface voids to reduce stress concentrations.  
         BACKGROUND OF THE INVENTION  
         [0002]    Metallic components that experience high mechanical loadings are subject to stress cracking. These cracks are typically initiated on the surface of the component where the stress distribution has a high localized surface stress point. These regions of high localized stresses are typically where the surface of the material has an abrupt change in shape and/or a concentration of surface voids or pores are present. For automotive applications, a typical component that experiences high mechanical loads is a crankshaft of an engine. Much time and expense are dedicated to reducing regions of high localized stress build-up from a surface of a crankshaft.  
           [0003]    After the bearing surfaces are machined on a crankshaft the transition portions at either axial end of the bearing surfaces have abrupt changes in surface and often a concentration of surface voids. A typical method for reducing the mechanical stresses in these transition portions is to fillet roll the region. Fillet rolling, or plastic deformation rolling, involves turning the crankshaft while a hardened roller is pressed into the transition portions. The hardened roller has a rounded surface that complements the concave surface of the transition portion and has a higher Brinell hardness than the transition portion material. After fillet rolling, the transition portions are compacted resulting in a rounded surface with fewer and smaller surface voids. Thus provided, the fillet rolled crankshaft has a surface stressed distribution with lower localized stresses at the transition portions. A minimum transition portion axial length must be provided on a crankshaft in order to accommodate the hardened roller and perform the fillet rolling.  
           [0004]    What is needed is a method for reducing the surface voids on a metallic component to reduce the peak localized stress regions that cause component failure due to stress cracking.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a method and an apparatus for reducing the number and size of surface voids on a metallic component surface. In one aspect of the present invention, atoms of a filler material such as TiC, TiN, TiCN, or Al 2 O 3  are vaporized and directed by a laser into the surface voids of a metallic surface. In another aspect, the present invention provides an apparatus that utilizes a laser and feeds the filler material in a powder or wire form to the laser for subsequent implantation into the surface voids of the metallic component.  
           [0006]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 illustrates a portion of a crankshaft in accordance with the present invention;  
         [0009]    [0009]FIG. 2 illustrates an enlarged portion of the crankshaft of FIG. 1, showing surface voids or pores;  
         [0010]    [0010]FIG. 3 illustrates the crankshaft portion of FIG. 2 after the surface treatment of the present invention; and  
         [0011]    [0011]FIG. 4 illustrates an apparatus in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0013]    With reference to FIG. 1, a crankshaft  10  is shown to include main bearing surfaces  12 , rod bearing surfaces  14 , counter weights  16  and transition portions  18 . Preferably, crankshaft  10  is steel or cast iron of one piece cast construction. The casting process results in a relatively rough surface on crankshaft  10 . Main bearing surfaces  12  and rod bearing surfaces  14  are machined to a pre-selected tolerance after casting of crankshaft  10 . Transition portions  18  are portions with a reduced diameter provided at either axial end of bearing surfaces  12 ,  14  to allow bearing surfaces  12 ,  14  to wear (and, therefore, experience a reduction in diameter) without resulting in interference between transition portions  18  and the bearings (not shown) that ride on bearing surfaces,  12 ,  14 . In operation, transition portions  18  are subject to relatively high amounts of stress compared to other portions of crankshaft  10 .  
         [0014]    With reference to FIGS. 2 and 3, a cut away view of a transition portion  18  is shown to include a general substrate surface  30 . Substrate surface  30  is defined by a continuous area of surface voids  32  and peaks  34  due to a roughness resulting from the casting process. Stress cracking under tensile loading along substrate surface  30  is initiated in surface voids  32 . After cracks (not shown) begin, the cracks can grow and eventually result in a complete component failure. FIG. 3 depicts alien atoms  40  within surface voids  32 . Preferably atoms  40  are atomically, but not chemically, bonded to substrate surface  30 .  
         [0015]    As further shown in FIG. 3, some peaks are designated as peaks  34 ′ and are defined by a localized portion of substrate surface  30 ′ that extends above the average surface height H′. As shown in FIG. 3, some of the peaks  34 + are sheared from transition portion  18  after being impacted by atoms  40 . As atoms  40  are directed into surface voids  32 ′, the amount of shearing of peaks  34 ′ will vary with the speed or kinetic energy of atoms  40  as they impact substrate surface  30 ′. Substrate surface  30 ′ has fewer and smaller surface voids  32 ′ than substrate surface  30  of FIG. 2. Thus provided, substrate surface  30 ′ will have a more levelized surface stress distribution with lower peak stresses than substrate surface  30 . When compared to components with no surface treatment, components with a surface treatment described herein are expected to experience a lower failure rate when subjected to mechanical loadings.  
         [0016]    As shown in FIG. 4, an apparatus  60  is shown to include a laser  62 , a material feeder  64  and a component manipulator  66 . Laser  62  is preferably a diode laser with a 5 kW resonator. Laser  62  directs a pulsed beam  80  toward transition portion  18 . Material feeder  64  is preferably a device that feeds a filler material  82  into the path of beam  80 . Referring to FIGS. 2-4, beam  80  vaporizes atoms  40  or groups of atoms  40  of filler material  82  and directs atoms  40  toward substrate surface  30  of transition portion  18 . Preferably, filler material  82  is titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), or aluminum oxide (Al 2 O 3 ). Beam  80  imparts sufficient energy into atoms  40  that atoms  40  are atomically bonded within the surface voids  32 . Preferably, beam  80  imparts sufficient energy into atoms  40  to shear peaks  34 ′ from substrate surface  30 ′. As shown in FIG. 3, a substrate surface  30 ′ is produced from this operation. Preferably, component manipulator  66  moves crankshaft  10  rotationally and translationally relative to laser  62  in order to position all of the substrate surface  30  of transition portion  18  within the path of beam  80 . In this manner, surface voids  32  are filled and atomically bonded in a manner that provides a more continuous substrate surface  30 ′ on crankshaft  10  in order to reduce the surface voids  32  that can initiate stress cracks during mechanical loading.  
         [0017]    It will be appreciated of one of skill in the art that lasers other than diode lasers can be used to direct atoms  40  into surface voids  32  and that the laser used to vaporize or separate atoms  40  may be a different laser than that used to direct atoms  40  into surface voids  32 . While the process described herein references filler material  82  as being deposited within surface voids  32  in the form of atoms, it would be recognized that filler material may also be directed into surface voids  32  as molecules of a compound or groups of atoms or ions. Additionally, it will be recognized that material feeder  64  can be adapted to feed filler material  82  as a wire, powder, or other form that can be easily separated. Component manipulator  66  can move either crankshaft  10  or laser  62  or both.  
         [0018]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.