Abstract:
The present invention is a novel method for the repair of cast aluminum wheels that leak air due to porosity caused during the casting process. It involves deep roller burnishing the surface of the wheel under controlled operating parameters to effectively seal the porosity so that the wheel no longer leaks air.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       REFERENCE TO SEQUENCE LISTING, A TABLE, OR COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX  
       [0003]     Not Applicable  
       BACKROUND OF THE INVENTION  
       [0004]     Cast aluminum wheels manufactured for the automotive market and other markets frequently have porosity in the material. This porosity is created during the molding or casting process during manufacture of the wheel. As the aluminum freezes from its liquid or molten state in the mold, the aluminum material contracts. This contraction occurs not only at the surface but throughout the interior of the wheel as well. The contracting interior material can develop openings or holes called porosity while accommodating the geometry constraints and cooling rates governing the shape of the wheel in the mold. This porosity is detrimental to the performance of the wheel and can be large enough to allow air to pass through the wheel. A tire mounted to such a wheel would not be capable of sustaining air pressure as the air would leak out through the porosity of the wheel.  
         [0005]     Such wheels are termed or known as “leakers” in the wheel manufacturing industry. They are undesirable. Efforts are made at wheel manufacturing facilities to test for leakers and remove them from the production line. Such wheels are then recycled generally by melting them back into liquid form and recasting the material into another wheel. Unfortunately, most of the cost to produce the wheel has already been spent by the time the wheel is tested for leaking. So, a wheel which has been determined to be a leaker and subsequently scraped or melted back down results in a significant loss to the manufacturer. High scrap rates due to leakers can have a dramatic impact on the cost of manufacturing cast aluminum wheels. Manufacturers go to great lengths to design and build molds and control freezing rates to reduce porosity as much as possible. Even with these efforts, porosity cannot be completely eliminated. As a result, some leakers will always remain.  
         [0006]     The object of the current invention is to provide a method of repair for cast aluminum wheels that leak air due to porosity. This would allow leaking wheels to be reclaimed and not scrapped or melted back down.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The invention involves repairing cast aluminum wheels that leak air due to porosity. A roller burnishing tool is used to deep roll the surface of the wheel such that the porosity becomes sealed and the wheel no longer leaks air. The wheel can be used in service and does not have to be discarded. By roller burnishing the surface of the wheel under controlled operating parameters, the plastic deformation of the surface and subsurface layers cause the material to flow and the porosity formed during the casting process to close. This effectively seals the wheel&#39;s surface permanently for the life of the wheel. 
     
    
     BRIEF DESCRIBTION OF THE DRAWING  
       [0008]      FIG. 1  is drawing showing the cross section of a typical wheel with a burnishing tool shown against the outer surface.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]     The invention involves using a roller burnishing tool to deep roll the surface of a cast aluminum wheel such that the porosity becomes sealed and the wheel no longer leaks air. Deep rolling is a method of roller burnishing where the parameters of the burnishing process are tightly controlled. Particularly, the parameters of applied force, feed rate, roller material properties, and roller geometry are required to be specified and validated. Unfortunately, past commercially available burnishing tools were not capable of maintaining tight control of the operational parameters to the degree necessary. Deep rolling produces cold work and plastic deformation in the surface of the wheel due to the Hertzian contact stress induced by the action of the roller under an applied load. This plastic deformation effectively closes the porosity in the near surface layers in the wheel material. The residual compressive stresses and cold work induced by the deep rolling process also acts to keep the porosity sealed for the life of the wheel.  
         [0010]     Referring to  FIG. 1 , the wheel  1  is shown in cross-section along with the rotational centerline  8  of the wheel. The spherical burnishing member  3  is brought into contact with the surface of the wheel  2 . The spherical burnishing member  3  is retained in housing  4  which also forms the hydrostatic bearing which is further described in U.S. Pat. No. 4,947,668. The piston  10  forces the burnishing member  3  against the surface  2  by a controlled amount of force which is directly proportional to the applied pressure supplied to the burnishing tool. This controlled applied force plastically deforms the surface and subsurface material and closes porosity. The piston housing  6  is mechanically connected to a machine tool shank  9 . The machine tool shank  9  is manufactured such that it will mount into the appropriate machine tool which will be used to perform the burnishing operation. The machine tool could be a lathe, milling machine, or a machining center. The wheel  1  is rotated about centerline  8  during the burnishing process as the spherical burnishing member  3  is feed at a controlled rate in an axial direction along the surface  2  while under controlled load applied by the piston  10  and the supplied fluid pressure. It has also been found that the applied load supplied by piston  10  to the burnishing member  3  must be done gradually at the start of the burnishing area and relieved slowly at the end of the burnishing area in order to create a smooth transition in the residual stress state and amount of cold work induced. In this manner, the entire outside diameter  2  and the bead seat area  5  are deep roller burnished. The inside diameter wheel surface  7  can also be deep roller burnished in the same manner as the outside wheel surface  2 . In fact, it is possible to deep roller burnish the entire surface of the wheel  1  or any part of the surface which is desired.  
         [0011]     The operational deep roller burnishing parameters of applied force, axial feed rate, the size and geometry of the burnishing member  3 , and surface speed are determined experimentally to yield the best results for a particular wheel  1  and amount of porosity. Once determined, these operational parameters must be tightly controlled to ensure reproducibility and repeatability during manufacturing repair processing. The tool shown in  FIG. 1  which is described in further detail in U.S. Pat. No. 4,947,668 is capable of operating under such controlled parameters. Other types of burnishing members such as asymmetrical rollers could also be used to generate similar results.