Patent Publication Number: US-2022234125-A1

Title: Reverse face angle gear cutter and coolant delivery assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/EP2020/025459 filed Oct. 16, 2020, which claims the benefit of U.S. Patent Application No. 62/916,490 filed Oct. 17, 2019 and U.S. Patent Application No. 63/001,884 filed Mar. 30, 2020. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates generally to a gear cutter that forms gear teeth on an inner diameter of a working piece and a related coolant delivery assembly. 
     BACKGROUND 
     Gear manufacturers utilize various machining processes and corresponding tools to produce gears. Exemplary processes can include hobbing, shaping, milling, shear cutting and grinding. The process selected by the gear manufacturer can depend on the type of gear being machined and the tolerances within which the gear is produced. Other considerations in selecting the method can include the size of the gear, the configuration of internal sections or flanges, the quantity of gears to be produced, and gear-to-pinion ratio and costs. 
     Gear teeth adjacent to other part features are currently limited to production methods such as shaping or rack rolling. For internal gear teeth, shaping or broaching are the traditional manufacturing methods, but each process is limited to the part type. In other words, broaching must have a completely un-obstructed part layout so the tool can pass completely through the part. Gear shaping allows teeth to be cut against an interfering surface, but is inherently slow in terms of machine cycle and flexibility. 
     Gear skiving is a recent development in gear manufacturing that reduces traditional gear shaping cycle times by up to 80%. While extremely fast, traditional skiving is limited to cutter clearances and part configurations. 
     SUMMARY 
     A coolant delivery assembly configured for use with a gear cutter tool that cuts gear teeth into a workpiece to form a gear includes a retaining cooling nut, a tool holder and a coupling member. The retaining cooling nut has a nut body that defines a plurality of coolant flow passages therein. The tool holder supports the gear cutter tool. The coupling member couples the retaining cooling nut to the mount. The retaining cooling nut is configured to receive coolant and deliver the coolant through the plurality of coolant flow passages and direct the coolant toward the gear cutter tool. 
     In other features, the nut body further comprises an engaging end that is configured to engage the gear cutter tool and an opposite end. Each flow passage of the plurality of flow passages defines a coolant inlet and a coolant outlet. Each coolant inlet is defined at the engaging end. The plurality of coolant flow passages each define a linear portion and an arcuate portion. The linear portions communicate coolant from the engaging end toward the opposite end. The arcuate portions route the coolant from the linear portions in a direction toward the cutting tool away from the opposite end. 
     According to additional features the coolant delivery assembly further includes a plenum disposed between the tool holder and the engaging end of the retaining cooling nut. The plenum is configured to provide circumferential coolant communication between the tool holder and the engaging end of the retaining cooling nut. The retaining cooling nut secures the gear cutter tool to the tool holder. The coolant delivery assembly can further include the gear cutter tool. The gear cutter tool has a plurality of cutting teeth. Each cutting tooth of the plurality of cutting teeth has a tooth face that defines a tooth face angle relative to the workpiece during cutting into the workpiece wherein the tooth face angle is non-parallel relative to the workpiece. The tooth face angle is sloped to the left relative to a rotational axis of the gear cutter tool. 
     A method of forming a gear using a gear cutter tool and a retaining cooling nut that retains the gear cutter relative to the tool holder is provided. The gear cutter tool is coupled relative to the tool holder with the retaining cooling nut. The gear cutter tool has a cutting face. The gear cutter tool is advanced into engagement with the gear while rotating the gear cutter tool around an axis of rotation. Coolant is delivered through at least one coolant passage defined in the retaining cooling nut. Coolant flows through the at least one coolant passage and out a coolant outlet in a direction toward the cutting face such that coolant is sprayed directly onto the cutting face. 
     According to additional features, coolant is delivered through a plurality of coolant passages defined in the retaining cooling nut. Each coolant passage of the plurality of coolant passages has a respective coolant passage that directs coolant onto the cutting face. Coolant is delivered through a plenum disposed between the tool holder and the engaging end of the retaining nut. The plenum is configured to provide circumferential coolant communication between the tool holder and the engaging end of the retaining cooling nut. 
     In other features, the gear is cut with the gear cutter tool during the delivering of coolant through the plenum. The gear cutter tool is rotated around the axis of rotation. Teeth formed on the gear cutter tool have a tooth face that defines a tooth face angle relative to the gear during cutting into the gear. The tooth face angle is non-parallel relative to the gear. The tooth face angle is sloped to the left relative to a rotational axis of the gear cutter tool. 
     A gear cutter tool for cutting internal gear teeth into a workpiece to form a gear is provided. The gear cutter tool has a plurality of cutting teeth. Each cutting tooth of the plurality of cutting teeth has a tooth face that defines a tooth face angle relative to the workpiece during cutting into the workpiece. The tooth face angle is non-parallel relative to the workpiece. The tooth face angle is sloped to the left relative to a rotational axis of the gear cutter tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1A  is a schematic, perspective view of an exemplary prior art gear cutter system including a gear cutter that is configured to cut an internal gear in a blank orientation; 
         FIG. 1B  is a schematic, perspective view of the system of  FIG. 1A , illustrating the cutter having produced a precision internal gear in a final orientation; 
         FIG. 2  is a schematic end view of the system of  FIG. 1A , illustrating a center distance between an axis of rotation of the cutter and an axis of rotation of the internal gear; 
         FIG. 3  is a schematic side view of the cutter and the internal gear of  FIG. 1A , illustrating a cross-axis angle between an axis of rotation for the cutter and an axis of rotation for the internal gear; 
         FIG. 4  is a side perspective view of an exemplary gear cutter according to another prior art example; 
         FIG. 5  is a side perspective view of an exemplary gear cutter according to one example of the present disclosure; 
         FIG. 6  is an enlarged view of the active profile section of the exemplary prior art gear cutter of  FIG. 4 ; 
         FIG. 7  is a detail view of a tooth of the prior art gear cutter of  FIG. 6 ; 
         FIG. 8  is a side schematic view of the prior art gear cutter of  FIG. 4 ; 
         FIG. 9  is a side schematic view of the gear cutter of  FIG. 5  according to one example of the present disclosure; 
         FIG. 10  is a schematic illustration of a proposed tooth surface superimposed over a traditional tooth leading surface; 
         FIG. 11  is a partial side view of teeth formed on a workpiece with the exemplary gear cutter of  FIG. 5 ; 
         FIG. 12  is a schematic illustration of a coolant delivery assembly constructed in accordance to one example of the present disclosure and shown delivering coolant toward an exemplary cutting tool; 
         FIG. 13  is a schematic illustration of a coolant delivery assembly constructed in accordance to Prior Art; 
         FIG. 14  is another schematic illustration of the coolant delivery assembly of the present disclosure; 
         FIG. 15  is a perspective view of a retaining cooling nut of the coolant delivery assembly of  FIG. 12 , the retaining cooling nut shown retaining an exemplary cutting tool shown in partial section view; 
         FIG. 16  is a top perspective view of an exemplary retaining cooling nut constructed in accordance to the present disclosure; 
         FIG. 17  is a bottom perspective view of the retaining cooling nut of  FIG. 16 ; 
         FIG. 18  is a side view of the retaining cooling nut of  FIG. 16 ; 
         FIG. 19  is a top perspective view of a retaining cooling nut constructed in accordance to the present disclosure and shown adjacent to an exemplary cutting tool; and 
         FIG. 20  is a side perspective view of the retaining cooling nut and cutting tool of  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary involute gear cutter system (hereinafter “system”) includes a computer numerically controlled (CNC) lathe and modified tooth proportion gear cutter (hereinafter “cutter”) configured to cut a gear in a blank orientation to remove shavings from the gear in multiple passes so as to produce a precision gear in its final orientation. The CNC lathe includes a chuck and an active sub-spindle, i.e. controlled rotating motion through CNC controls. The cutter can be mounted on the spindle, and the gear in the blank configuration may be attached to the chuck. More specifically, the cutter can have a plurality of cutting teeth, and each one of the cutting teeth can have a pair of cutting edges configured to cut the gear in the blank orientation to provide the gear in the final orientation. 
     In the final orientation, the gear has an involute tooth profile including a plurality of cut teeth and a plurality of valleys therebetween. The cutting edges may be configured to cut the gear in the blank orientation, such that the gear in the final orientation includes an active profile section and an operating pitch diameter that are spaced apart from one another. Thus, the cutter can apply a generally constant force in a single or unilateral direction along the surface of the gear to increase the accuracy of machining the gear within, for example, a 0.0010 inch tolerance, without requiring special cutting tools or cutting systems. 
     Referring to  FIGS. 1A-3 , an exemplary prior art system  100  includes a computer numerically controlled (CNC) lathe  102  having in part a chuck  104  and a spindle  106 . The system  100  further includes a cutter  108  that is attached to the spindle  106 , which is in turn configured to rotate the cutter  108  about a cutting axis  110  so as to cut a gear  112  in a blank orientation ( FIG. 1A ) and produce the gear  114  in the final orientation ( FIG. 1B ). The cutter  108  in this form is an external gear configured to cut an internal gear  112  in a blank orientation to produce the internal gear  114  in the final orientation. The internal gear  114  in the final orientation has a plurality of cut teeth  116 . The teeth  116  have an involute tooth profile  118  including an active profile section  120 , which is a portion of each tooth surface configured to contact the opposing teeth of a meshed gear. 
     The gear  112  in the blank orientation is mounted to the chuck  104 , which is configured to rotate the gear  112  about a cut axis  122  ( FIG. 1A ), such that the cut axis  122  and the cutting axis  110  are spaced apart from one another by a center distance CDw. In addition, the cut axis  122  and the cutting axis  110  are disposed at a cross-axis angle a with respect to one another when the gear  114  is in the final orientation. As used herein, the term “cross-axis” is an angle that defines the difference between the two rotational axes of the gear workpiece and the cutting tool. 
     The system  100  can further include a flushing device  124  configured to deliver a fluid to the gear  112  to remove shavings, chips or dust from the gear  112  when the spindle  106  rotates the cutter  108  to cut the gear  112  in multiple passes. The fluid can also remove heat from the system  100 . In one example, the flushing device  124  is a fluid line  126  communicating with a reservoir  128  to supply water, nitrogen gas or another fluid to the external gear  112 . In the final orientation, the gear  114  has an involute tooth profile including a plurality of cut teeth  116  and a plurality of valleys therebetween. The involute tooth profile  118  includes the active profile section  120 , and the operating pitch diameter is spaced apart from the same when the gear  114  is in its final orientation. Additional description of a prior art skiving tool may be found in commonly owned U.S. Pat. No. 10,016,827 the contents of which are expressly incorporated herein by reference. 
     The present disclosure allows the skiving of gear teeth previously not possible with current methods due to its ability to cut against interfering part geometries and can eliminate certain cutter/workpiece interferences. For particular gear components such as Heavy Duty Transmission mainshaft gears, the internal clutch teeth design in combination with the integral thrust washer provides a compact product design. In order to manufacture the clutch teeth, gear shaping is the only current method of production possible. As machine technology advances, the gear shaping machine has now become the constraint machine within production cells and manufacturing output is limited by the shaping process. Gear skiving can remove this constraint machine within the cell layout and reduce gear machining cycle times by approximately 50% for mainshaft gears. The present disclosure facilitates improvements in part geometry and cutter tool life which can allow gear skiving in a production environment feasible. 
     During the gear skiving, the evacuation of chips is critical for the skiving process to be successful. Without successful chip evacuation, excessive tool wear, and even tool failure can occur very rapidly. For example, in one prior art skiving method, chips can be generated at a rate of 700 chips per second. Any stray chips that get reintroduced into the cutting zone can cause cutting edge damage on the tool or if severe enough can cause a catastrophic tool failure. The present disclosure provides an assembly and chip evacuation method that provides improved chip evacuation during the skiving process. 
     With reference now to  FIGS. 4, 6, 7 and 8 , a gear cutter constructed in accordance to one prior art example is shown and generally identified at reference  208 . The gear cutter  208  includes a plurality of teeth  232 . Each tooth  232  defines a helix angle  240 . The helix angle  240  is defined as an angle formed between a centerline or cut axis  243  of the gear cutter  208  and a line  245  transverse to a tooth face  241 . The tooth face  241  has a tooth face angle  242  relative to the workpiece  212  ( FIGS. 6 and 8 ). The tooth face angle  242  is perpendicular to the helix angle  240 . The tooth face angle  242  slopes downward and to the right as viewed from the cut axis  243  of the gear cutter  208 . In some examples, the configuration of the gear cutter  208  can experience localized or accelerated tool wear indicated generally at reference  250 ,  FIG. 7 . As shown in  FIG. 8 , the tooth face angle  242  is parallel to a workpiece  212 . The workpiece  212  is cut at the location shown by the arrow by the teeth  232 . During cutting, both the gear cutter  208  and the workpiece  212  are rotating, but at different revolutions per minute (RPM). 
     With reference to  FIGS. 5 and 9-11 , a gear cutter constructed in accordance to one example of the present disclosure is shown and generally identified at reference  308 . The gear cutter  308  includes a plurality of teeth  332 . Each tooth  332  defines a tooth face  341  and a tooth face angle  342  relative to the workpiece  312  ( FIG. 9 ). The tooth face angle  342  is an angle defined between the tooth face  341  and a face of the workpiece  312 . The tooth face angle  342  is sloped downward and to the left relative to a rotational axis  394  of the cutting tool  308 . Explained further, the tooth face angle  342  is sloped in an opposite direction as compared to the tooth face angle  242 . In this regard, the tooth face angle  342  defines a cut angle  360  that is not parallel to the workpiece  312  during cutting. The grind of the gear cutter  308  is angled differently as compared to the gear cutter  208 . More cutting occurs by providing a cut angle  360  as compared to the parallel relationship of the face angle  242  and workpiece  212  shown in  FIG. 8 . 
     The workpiece  312  is cut at arrow called  376  (internal spline of workpiece  FIG. 11 ) by the teeth  332 . During cutting, both the gear cutter  308  and the workpiece  312  are rotating, but at different RPM. In one example, the workpiece  312  can be tilted while the cutting tool  308  is advanced linearly along the tool feed direction  376  toward the workpiece  312 . In the example shown twenty-two teeth  332  are provided on the gear cutter  308 . In this regard, with each full rotation of the gear cutter  308 , twenty-two slivers of workpiece material are sequentially cut away from the workpiece  312 . As shown in  FIG. 10 , a cutter cross-axis  390  is defined between a first rotational axis  392  of the workpiece  312  and a second rotational axis  394  of the cutting tool  308 . 
     Additional advantages of the instant gear cutter  308  and related system for cutting the internal gear teeth or splines of a gear are realized by the instant disclosure. For example, the cutting action can be at a more aggressive angle without requiring the workpiece to be tilted more. The amount of time necessary for the gear cutter to operate in a negative rake angle condition is reduced. As a result, tool life is improved and costs are reduced. The geometry of the gear cutter  308  balances the active lengths of both gear flanks. This creates a more useable tooth length for more compact product designs. The gear cutter  308  is able to generate gear teeth closer to blind shoulders. This shortens the overall width of gear teeth which yields an increase in power-density for a geartrain system, or more power transferred per volume of the system. 
     Turning now to  FIGS. 12, 14 and 15 , a coolant delivery assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference numeral  400 . The coolant delivery assembly  400  generally includes a retaining cooling nut  402 , a tool holder or mount  404 , a plenum  405 , and a coupling member  406  that couples the retaining cooling nut  402  to the mount  404 . In the example shown in  FIG. 12 , the retaining cooling nut  402  secures a cutting tool  408  generally to the mount  404  during cutting of a workpiece  412 . The coupling member  406  can be a threaded shaft that threadably mates with a threaded bore  410  defined through the retaining cooling nut  402 . The cutting tool  408  can be any cutting tool such as the gear cutters  108 ,  208 ,  308  disclosed herein, or other cutting tool. 
     With particular reference to  FIGS. 15-18 , additional features of the coolant delivery assembly  400  will now be described. The retaining cooling nut  402  has a nut body  418  that defines a plurality of coolant flow passages  420  defined therein. Each of the coolant flow passages  420  define a coolant inlet and a coolant outlet  422  and  424 , respectively. As will become appreciated herein, coolant  440  is directed from a coolant source  426 , through the tool holder  404 , through the plenum  405 , and into the coolant inlets  422 , through the coolant flow passages  420  and directed out of the retaining cooling nut  402  from the coolant outlets  424 . 
     The plenum  405  can provide circumferential coolant communication between the tool holder  404  and an engaging end  436  of the retaining cooling nut  402 . The plenum  405  can provide a chamber that facilitates full  360  degree coolant supply to the retaining cooling nut  402 . In some examples, the coolant  440  can be configured to flow through the mount  404  from the coolant source  426  to the retaining cooling nut  402 . Other configurations are contemplated for providing coolant to the cooling retaining nut  402 . 
     With particular reference to  FIG. 15 , each of the coolant flow passages  420  define a linear portion  432  and an arcuate portion  434 . The linear portions  432  generally communicates the coolant  440  from the engaging end  436  of the retaining cooling nut  402  toward an opposite end  438  of the retaining cooling nut  402 . The arcuate portions  434  generally route the coolant  440  from the linear portions  432  in a direction toward the cutting tool  408 . The coolant flow passages  420  are configured to direct streams of coolant  440  onto a face  444  of the cutting tool  408 .  FIGS. 19 and 20  show the retaining cooling nut  402  and cutting tool  408  together. 
     The delivery of coolant directly to the cutting edge or face  444  yields a profound improvement of chip evacuation over conventional arrangements. The coolant delivery assembly  400  virtually eliminated a significant issue of chip re-cutting during the machining process. Chip re-cutting occurs when a fragment of metal (cutting chip) does not exit the cutting zone and gets pulled into the cutting zone a second time. This creates extreme tool pressure and can fracture the edge of the tooth resulting in a catastrophic failure of the tool. The coolant delivery assembly  400  that utilizes the retaining cooling nut  402  to both deliver coolant and secure the cutting tool creates a more compact design. This facilitates machining into tight workpiece clearances which leads to a more compact component design. 
     With reference to  FIG. 13 , a coolant delivery assembly  500  constructed in accordance to one prior art example is shown. The coolant delivery assembly  500  generally includes a deflector  510  that is configured to deflect coolant sprayed generally upward back toward the cutting tool  408 . The coolant delivery assembly  500  can be inefficient at directing the coolant flow. Cycle time and tool life of the coolant deliver assembly  500  are not cost effective. In particular, the re-cutting of chips slows down the machining process to make sure all the chips were evacuated. Cycle time using the coolant delivery assembly  400  is reduced by around 35% and tool wear is stabilized at around 30% of a typical wear value compared to conventional systems such as shown in  FIG. 13 . 
     The foregoing description of the many examples has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular aspect are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.