Abstract:
A method for machining a surface on a workpiece having a member extending perpendicularly to the surface includes determining a position of a tool, determining a position of the workpiece, positioning at least one of the workpiece and the tool to a predefined position, rotating the workpiece, and rotating the tool to a predefined rotational speed. The predefined rotational speed synchronizes the rotation of the tool with the rotation of the workpiece in order to avoid unwanted contact between the tool and the member. The method includes the steps of translating at least one of the tool and the workpiece in a direction parallel to an axis defined by the workpiece, removing material from a first portion of the workpiece, translating at least one of the tool and the workpiece in a direction perpendicular to the axis of the workpiece, and removing material from a second portion of the workpiece.

Description:
FIELD 
       [0001]    The invention relates generally to a method for machining a carrier assembly, and more particularly a method for machining a surface on a carrier spider of a carrier assembly using epicyclical machining. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    A typical carrier assembly used in planetary gear sets includes a spider carrier welded to a carrier flange or shell. A plurality of pinions and pinion washers are supported for rotation within the spider carrier. The carrier spider must have a machined surface in order to accurately locate the pinion washers. However, the typical spider assembly has a plurality of legs or members that extend out from the surface. These legs can interfere with the machining process as they can obstruct the movement of the machining tool. 
         [0004]    One conventional method of machining the surface of a cast or forged spider carrier is to employ a traditional milling operation to produce a machined surface. However, this process requires multiple milling machines arranged in parallel to produce sufficient quantities to meet typical production volumes. An alternate solution is to make the spider carriers using net forging. However, net forged spider carriers may have a surface flatness that consumes about 70% to 80% of the total tolerance allowed in the finished welded carrier assembly. This can impede can make it difficult to meet the dimensional criteria for finished carrier assemblies. 
         [0005]    Accordingly, there is room in the art for a method of machining a surface of a spider carrier that has improved dimensional control of the finished carrier assembly and which reduces the cycle time and lowers the capital investment compared to traditional milling. 
       SUMMARY 
       [0006]    The present invention provides a method for machining a surface on a workpiece using a tool. The workpiece includes at least one member extending perpendicularly to the surface. The method comprises the steps of determining a position of the tool, determining a position of the workpiece, positioning at least one of the workpiece and the tool to a predefined position, rotating the workpiece, and rotating the tool to a predefined rotational speed. The predefined rotational speed synchronizes the rotation of the tool with the rotation of the workpiece in order to avoid unwanted contact between the tool and the member extending from the surface of the workpiece. The method also includes the steps of translating at least one of the tool and the workpiece in a direction parallel to an axis defined by the workpiece, removing material from a first portion of the surface of the workpiece, translating at least one of the tool and the workpiece in a direction perpendicular to the axis of the workpiece, and removing material from a second portion of the surface of the workpiece. 
         [0007]    In one aspect of the present invention, the workpiece is a spider carrier of a carrier assembly used in a planetary gear set. 
         [0008]    In another aspect of the present invention, the translation of the workpiece and the tool in directions parallel to the axis of the workpiece and perpendicular to the axis of the workpiece occur simultaneously. 
         [0009]    In yet another aspect of the present invention, the rotational speed of at least one of the tool and the workpiece is changed and at least one of the workpiece and the tool are translated such that the tool removes material from a top of the member. 
         [0010]    Further objects, aspects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
     
    
     
       DRAWINGS 
         [0011]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0012]      FIG. 1  is a diagrammatic side view of a system for machining a surface according to the principles of the present invention; 
           [0013]      FIG. 2  is an enlarged, diagrammatic end view of the system for machining a surface according to the principles of the present invention; 
           [0014]      FIG. 3  is a flow chart of a method for machining a surface using the system illustrated in  FIGS. 1 and 2  according to the principles of the present invention; and 
           [0015]      FIG. 4  is an enlarged, isometric view showing movement paths of a tool relative to a workpiece according to the principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0017]    With combined reference to  FIGS. 1 and 2 , a system for machining a surface is generally indicated by reference number  10 . The system  10  is employed to machine or finish (i.e. remove material from) an exemplary workpiece  12 , as will be described in greater detail below. The workpiece  12  generally includes an annular body  14  having a face or surface  16  and at least one extending member  18 . The extending member  18  is located along an outer edge  20  of the annular body  14  and extends perpendicularly out from the surface  14 . In the example provided, the workpiece  12  includes five extending members  18 , however it should be appreciated that the workpiece  12  may have any number of extending members  18  without departing from the scope of the present invention. Moreover, in the example provided, the workpiece  12  is a spider carrier used in a carrier assembly of a planetary gear set. However, it should be appreciated that the system  10  may be employed with any workpiece  12  having a surface  16  that requires machining with at least one extending member  18 . 
         [0018]    The system  10  generally includes a workpiece spindle  22  and a tool spindle  24 . The workpiece spindle  22  defines a workpiece longitudinal axis  26  and is operable to be rotated about the workpiece longitudinal axis  26  by a prime mover (not shown), such as an engine. The workpiece  12  is secured to an end  28  of the workpiece spindle  22  such that the workpiece  12  is centered along (i.e. concentric with) the workpiece longitudinal axis  26 . 
         [0019]    The tool spindle  24  defines a tool longitudinal axis  30  and is operable to be rotated about the tool longitudinal axis  30  by a prime mover (not shown), such as an engine. The tool spindle  24  includes a tool body  32  secured to an end  34  of the tool spindle  24 . The tool body  32  is substantially shaped like a planar disc and includes at least one tool holder  36  extending perpendicularly out from the tool body  32  along an outer edge of the tool body  32 . In the particular example provided, the tool body  32  includes five tool holders  36  spaced evenly along the outer diameter of the tool body  32 . However, it should be appreciated that any number of tool holders  36  may be employed without departing from the scope of the present invention. The tool spindle  24  also includes at least one tool insert  38  secured or held by the tool holder  36 . Again, while five tool inserts  38  are shown in the example provided, there may be any number of tool inserts  38  without departing from the scope of the present invention. 
         [0020]    The workpiece spindle  22  and the tool spindle  24  are arranged with respect to one another such that the tool holders  36  and the tool inserts  38  face the surface  16  of the workpiece  12  that is secured to the workpiece spindle  22 . Additionally, the workpiece spindle  22  and the tool spindle  24  are offset from one another such that the workpiece longitudinal axis  26  is parallel with the tool longitudinal axis  30  but the workpiece longitudinal axis  26  is spaced apart from the tool longitudinal axis  30  a first distance, indicated by reference number  40 . In order to machine the surface  16  of the workpiece  12 , either the workpiece spindle  22 , the tool spindle  24 , or both, are moved such that the distance between the workpiece  12  and the tool inserts  38  is adjusted and the distance between the axes  26 ,  30  is adjusted, as will be described in greater detail below. 
         [0021]    Turning now to  FIG. 3 , and with continued reference to  FIGS. 1 and 2 , a method for machining the surface  16  of the workpiece  12  is generally indicated by reference number  100 . The method  100  may be controlled by a CNC controller or other electronic device. The method  100  begins at step  102  when the rotational and directional position of the workpiece  12  and workpiece spindle  22  relative to the tool inserts  38  and tool spindle  24  are determined. More specifically, the rotational orientation of the workpiece  12  and therefore the workpiece spindle  22  is determined relative to the tool inserts  38 . Next, at step  104 , either the workpiece spindle  22 , the workpiece  12 , and/or the tool spindle  24  are positioned (i.e. rotated) to a predetermined position relative to one another. This predetermined position corresponds to a known orientation between the tool inserts  38  and the workpiece  12  and provides a starting orientation. It should be appreciated that the step of positioning the workpiece spindle  22 , the workpiece  12 , and/or the spindle  24  may be performed automatically by a controller (not shown). 
         [0022]    Next, the workpiece spindle  22  and the tool spindle  24  are each rotated to predetermined rotational speeds at step  108 . The rotational speeds of each of the workpiece spindle  22  and the tool spindle  24  are synchronized by adjusting the rotational speeds so that they have a fixed rotational speed ratio relative to one another. The rotational speed ratio between the rotational speed of the workpiece spindle  22  and the rotational speed of the tool spindle  24  is calculated such that the tool inserts  38  pass between the extending members  18  on the workpiece  12  as the workpiece spindle  22  and the tool spindle  24  each rotate. Accordingly, the rotational speed ratio is determined from a number of factors including, but not limited to, the size of the workpiece  12 , the location of the extending members  18  on the workpiece  12 , and the location of the tool inserts  38 . 
         [0023]    Next, the workpiece spindle  22  and the tool spindle  24  are moved relative to one another until the tool inserts  38  contact the face  16  of the workpiece  12 . The distance the workpiece spindle  22  and the tool spindle  24  are moved towards each other is determined by the amount of material that is desired to be removed from the face  16  of the workpiece  12 . As each of the workpiece  12  and the tool insert  38  rotate, the tool insert  38  sweeps across the face  16  and removes material from the workpiece  12 . Turning to  FIG. 4 , an exemplary movement path of one of the tool inserts  38  is indicated by reference number  109 . The movement path  109  is an epicyclical path. It should be appreciated that the tool spindle  24 , as well as the workpiece spindle  24 , are not illustrated in  FIG. 4  in order to provide clarity. The tool insert  38  sweeps across the face  16  and passes between the extending members  18 . The tool insert  38  is prevent from contacting the extending members  18  by maintaining the synchronization between the rotational speed of the workpiece spindle  22  and the rotational speed of the tool spindle  24 . 
         [0024]    Returning to  FIG. 3 , the method  100  continues at step  110  where the tool spindle  24  is translated relative to the workpiece spindle  22 . However, it should be appreciated that the workpiece spindle  22  or both the workpiece spindle  22  and the tool spindle  24  may be translated without departing from the scope of the present invention. The tool spindle  24  is translated relative to the workpiece spindle  22  in a direction perpendicular to the axes  26  and  30 . Accordingly, the distance  40  between the axes  26 ,  30  is varied as the tool spindle  24  is translated. In the example provided, the tool spindle  24  is translated towards the workpiece  12  such that the distance  40  decreases during step  110 . As the tool spindle  24  is translated, the tool insert  38  contacts an area of the face  16  on the workpiece  12  that is different from the area of the face  16  contacted by the tool insert  38  prior to step  110 . With reference to  FIG. 4 , an exemplary movement path of the tool insert  38  after the tool spindle  22  has been translated is indicated by reference number  111 . The movement path  111  is an epicyclical path. The movement path  111  positions the tool insert  38  adjacent side walls  112  on each of the extending members  18  without contacting the side walls  112 . Alternatively, the tool inserts  38  can contact the side walls  112  in order to finish the side walls  112  in a manner similar to the finish of the face  16 . By translating the tool spindle  24  relative to the workpiece  12 , the tool inserts  38  finish a larger area of the face  16 . It should be appreciated that the method  100  may repeat steps  108  and  110  such that the tool spindle  24  is translated several times during the finish of the face  16  of the workpiece  12  and the tool spindle  24  may be positioned at various depths to provide various amounts of material removal from the workpiece  12 . Moreover, the tool spindle  24  and workpiece  22  may be translated as in step  110  and plunged as in step  108  simultaneously to create angled surfaces on the face  16 . 
         [0025]    In an alternate embodiment, the method  100  can be employed to create features on the workpiece  12  by further varying the movement of the workpiece spindle  22  and the tool spindle  24 . For example, by adjusting the distance the tool spindle  24  moves relative to the workpiece spindle  22 , by adjusting the amount of translation, and by adjusting the synchronization ratio between the rotation of the workpiece spindle  22  and the tool spindle  24 , the tool insert  38  can travel along a movement path  113  shown in  FIG. 4  that removes material from a top surface  114  of the extending members  18 . This removal of material from the top surface  114  creates shoulders  116  on the extending members  18 . These shoulders  116  may be used during assembly of the spider and planet carrier assembly to act as a stop as the finished workpiece  12  is pressed into the flange (not shown) of the planet carrier assembly prior to welding in order to eliminate spacer blocks. 
         [0026]    The description of the invention is merely exemplary in nature and 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.