Abstract:
The present invention relates to a honing method and apparatus which provides greater control over the edge shape, as well as reductions in the effort required to hone multiple edges on workpieces. The invention accomplishes these improvements by controlling the speed of the abrasive wheel, as well as the orientation and position of the workpiece prior to and/or while it is in contact with the abrasive brush. This provides for greater control over the hone shape, hone size, and hone distribution along all the cutting edges of the tool.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to a method and apparatus for honing precision edges on a workpiece, such as a cutting tool, using an abrasive brush. The invention particularly relates to a process and apparatus for controlling the position of a cutting tool edge relative to an abrasive honing brush in order to provide precise controlled edge honing. 
     BACKGROUND OF THE INVENTION 
     Cutting tools for cutting and shaping materials must be very hard to maintain their edges and withstand the high concentrated forces which are present at the cutting edge of the tool. These tools are frequently fabricated from carbide, ceramic, diamond coated carbide, CBN coated carbide or other tool materials which possess the necessary hardness. The disadvantage of using a hard material is that such materials tend to be brittle, and susceptible to crack formation. When cracks form, the material begins to chip, destroying the utility of the tool. 
     The predominant method of forming carbide edges on cutting tools uses a powder metallurgy process which involves placing powdered materials into a mold, and mechanically compacting them into specific tool geometric forms. The compacted tool form is then densified through a sintering process. The edges created by this process, however, are rough. Rough edges can adversely affect the performance of the tool, by increasing the tendency of the material to crack or chip. Furthermore, forces applied to the rough edge are not evenly distributed but, rather, are concentrated on high points of the edge. The low points of the edge tend to be sharp creating stress concentrations that increase the likelihood of crack formation. The rough edges on cutting tools can be smoothed by honing the edges before the tool is used in a machining process. Honing involves forming a rounded shape on the cutting edge of the tool. Early shapes were directed towards true radii, where the curvature of the smoothed edge was uniform across both surfaces adjacent to the edge. 
     More recently, edges having varying taper, i.e., non-uniform tapers about the periphery of the edge and generally called waterfall hones (see, FIG. 3 c ). Also, the correct sizing of the edge hone has been shown to affect tool life. As a result, the higher the precision with which the tool edges can be formed, the greater the resultant tool life. 
     Many different processes were originally used to smooth the edges of a cutting tool, including vibratory honing, mass media honing, slurry honing, honing inserts with media impregnated rubber wheels, dry blasting, wet blasting, and tumbling. These methods have several disadvantages, including intense labor requirements and poor predictability of edge hone characteristics between different tools exposed to the same honing process. 
     During the late 1970&#39;s, a process of honing using a brush having bristles impregnated with abrasive media was developed. In this process, bristles are forced into contact with the edge of the cutting tool. The forced contact results in the removal of material along the edge. Brush honing the cutting tool edges has typically required high brush rotational speeds, resulting in the abrasive bristles striking the cutting tool edge, rather than being dragged across the edge. 
     In a conventional honing process, the brush is rotated such that the speed of the tips of the brush range from 3,000 to 12,000 feet per minute. In order for these conventional processes to be commercially feasible, a high speed has been necessary in order to hone a sufficient quantity of cutting tools in a short period of time. 
     The apparatus used in conventional honing processes require the placement of the cutting tools to be honed on a rotating table. As the table rotates, the part is translated along an arcuate path past a rotating abrasive brush. The rotating table allows a continuous honing process to be used, with cutting tools being loaded at one position, honed at a second position, and removed from the table at a third position. The individual cutting tools were rotated as they are passed through the stationary, rotating brush. The circular formation of the table also presents a compact area within which the honing process can be accomplished. 
     One drawback to the use of a rotary table to feed the cutting tool to the honing brush is that the arcuate path produces an uneven hone on the work piece. More particularly, the arcuate path causes the contact between the tool edge and the honing brush to vary depending on the location of the tool on the path. As such, the resulting hone will vary across the edge of the part making precision honing very difficult. 
     Another deficiency with the prior methods of honing edges on the cutting tools is that the high bristle speeds result in the generation of excessive heat at the bristle tips. This heat causes the nylon bristles to partially melt, leading to nylon being deposited on the workpiece. The deposited nylon must then be removed before the tool can be coated, adding an additional step to the honing process. Attempts have been made to cool the bristles by using fluid coolants to alleviate or reduce the build up of heat at the bristle tips. The coolant, however, creates a material disposal problem which is not desirable. 
     Also, conventional processes for honing tool edges do not typically permit variation of the rotational speed of the brush during the honing process. Instead, the speed of the table is normally controlled to vary the amount of material removed from the tool. 
     The present invention overcomes the disadvantages of the prior art by controlling the contact of the cutting tool edge with the bristles of the abrasive brush so that the cutting tool edge moves through the volume occupied by the bristles. Thus, the material removal action is distributed over a greater portion of the bristle, thereby reducing the build-up of heat in the bristles. The movement of the cutting tool edge into the volume of the bristles further results in a greater material removal rate due to the greater contact between the individual bristles and the cutting tool edge. 
     SUMMARY OF THE INVENTION 
     An apparatus is disclosed for honing at least one edge on a workpiece, such as a cutting tool. In one embodiment of the invention, the apparatus includes a base with a variable speed motor mounted on it. An abrasive brush is mounted to the motor and includes a plurality of bristles attached to a hub. The bristles each have a tip end and an interior end, with the interior end being fixed to the hub. The motor is adapted to cause the abrasive brush to rotate about an axis of rotation. The width of the abrasive brush is defined by first and second ends. The combination of the width of the brush and the length of the bristles defines a volume. The honing apparatus also includes a rotational controller means for controlling the rotational speed of the motor. 
     A mount for holding a workpiece is attached to the base. The mount includes a fixture for holding the workpiece, and a translational movement mechanism for controlling the position of an edge of the workpiece along a path substantially parallel to the axis of rotation of the abrasive brush. 
     In another embodiment, the motor is a fixed speed motor and the position of the workpiece edge relative to the abrasive brush is controlled by horizontal and vertical movement mechanisms. 
     A honing process is also disclosed for controlling the formation of a hone on the edge of a workpiece by controlling the movement and positioning of the workpiece through the volume of the rotating bristles. The movement and position of the workpiece is controlled so as to control the angle of impact between the bristles of the abrasive brush and an edge of the workpiece. The process results in the formation of precise tapered edges on the workpiece edge. 
     The foregoing and other features and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments thereof, as illustrated in the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, the drawings show a form of the invention which is presently preferred. However, it should be understood that this invention is not limited to the precise arrangements and instrumentalities shown in the drawings. 
     FIG. 1 is a perspective view of an embodiment of a brush honing apparatus according to the present invention. 
     FIG. 2 is an illustration of several generic cutting tools showing a representative tool edge. 
     FIGS. 3 a - 3   c  are partial sectional views of the generic cutting tool of FIG. 2 showing variations in the honing of the edges in more detail. 
     FIG. 4 is a section view of the motor and abrasive brush. 
     FIG. 5 is a perspective view of an abrasive brush. 
     FIG. 6 is a side elevation of a motor and a vertical movement mechanism. 
     FIG. 7 is a perspective view of an alternate embodiment of the apparatus incorporating horizontal and vertical movement mechanisms into the mount. 
     FIG. 8 is a perspective view of an alternate embodiment of the apparatus incorporating a distance positioning mechanism into the motor and an orientation mechanism into the mount. 
     FIG. 9 is a side view of an abrasive brush and a cutting tool identifying an alternate orientation of a cutting tool to an abrasive brush. 
     FIG. 10 is a side view of an abrasive brush identifying reference points on the first end of the abrasive brush. 
     FIG. 11 is a side view of a cutting tool and abrasive bristle, showing the relation between the bristle and the cutting tool with the cutting tool inside the brush volume along a path through reference point A in FIG.  10 . 
     FIG. 12 is a side perspective of a cutting tool and abrasive bristle, showing the relation between the bristle and the cutting tool with the cutting tool inside the brush volume along a path through reference point B in FIG.  10 . 
     FIG. 13 is a side perspective of a cutting tool and abrasive bristle, showing the relation between the bristle and the cutting tool with the cutting tool inside the brush volume along a path through reference point A′ in FIG.  10 . 
     FIG. 14 is a perspective view of an abrasive brush identifying reference elements of the honing process. 
     FIGS. 15 a  and  15   b  are cross-sectional illustrations comparing a workpiece with a constant hone and a workpiece with a variable hone. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numerals illustrate corresponding or similar elements throughout the several views, FIG. 1 is an isometric illustration of one embodiment of a honing apparatus  10  according to the present invention. The apparatus  10  is designed to provide precise honing of an edge of a workpiece  22 . The invention can be used on a wide variety of workpieces which require honing, including components subject to wear, such as seal rings, piston plungers, slitter knives, valve seats, counter-balance weights and carbide or ceramic bushings. The invention has particular use in honing edges of cutting tools, such as drills, end mills, milling inserts, threading tools, burrs, router bits grooving tools, form tools and tools designed to cut materials, such as metal and wood. 
     The apparatus  10  includes an abrasive brush  20  driven by a motor  24 . The motor  24  is mounted to a base  32 . The workpiece  22  is mounted such that its position relative to the abrasive brush  20  can be controlled to vary the shape of the resulting hone. 
     Referring to FIGS. 2, and  3   a - 3   c,  the workpiece  22  is shown with its edge  50  in an un-honed condition (FIG. 3 a ), with a radius hone  52  (FIG. 3 b ) and a tapered hone, such as the waterfall hone  54  (FIG. 3 c ). In order to form the various hones, the apparatus  10  is configured to control the position of the workpiece edge relative to the abrasive brush. In the embodiment of the invention shown in FIG. 1, the relative location of the workpiece edge from the abrasive brush is achieved by changing the position of the motor  24  through the use of a horizontal movement mechanism  26  and a vertical movement mechanism  28  as will be discussed in more detail below. 
     As shown in FIG. 4, the abrasive brush consists generally of a hub  60  to which a plurality of bristles  66  are attached. The bristles  66  have a tip end and an interior or root end  74 , which is attached to the hub  60 . The hub  60  is designed to removably attach to the motor  24 . As shown in FIG. 5, the width of the abrasive brush  20  is defined by a first end  68  and a second end  70 , and the radius of the brush is defined by the distance from the bristle tips  76  to the axis of rotation  44  of the brush. As is apparent from the figures, the width of the brush, in combination with the length of the bristles  66 , defines a volume  72  which is illustrated and preferably in the form of a right cylinder. Although the present embodiment shows the abrasive brush  20  having bristles  66  fully surrounding the hub, the bristles  66  may be located in discrete rows along the hub, with spaces between the rows, as shown in FIG. 6, or other patterns which do not completely fill the volume  72 . The preferred diameter for the abrasive brush is approximately 14 inches. 
     As described above, during operation, the contact between the bristles of the brush and a workpiece causes the bristles to heat up. In order to reduce the temperature of the bristles  66 , one embodiment of the present invention incorporates an impeller  62  in the hub that has a series of vanes designed to draw air into the hub  60  through an air intake  64 . The impeller  66  forces the air out through the bristles  66  of the abrasive brush  20 , thereby reducing their temperature. 
     In order to control the rate of material removal, the present invention preferably incorporates a means for controlling the speed of the abrasive brush. Referring to FIG. 4, in one embodiment, the motor  24  that drives the abrasive brush  20  is a variable speed motor. This permits that rate of material removal to be varied depending on the workpiece and/or material being honed. Alternatively, a transmission (not shown) could be interposed between a fixed speed motor  24  and the abrasive brush, allowing variation of the rotational speed of the abrasive brush. A continuously variable transmission (CVT) would be a preferable transmission if a fixed speed motor were to be used. 
     The abrasive brush  20  is preferably rotated within a speed range which yields a linear speed of 180 to 1800 feet per minute at the tips of the bristles. The linear speed of the bristles tips can be calculated by multiplying the diameter of the abrasive brush times the rotational speed of the abrasive brush times π. As is obvious to one of skill in the art, the motor rotational speed does not need to be equal to the desired rotational speed of the abrasive brush, since gears or pulleys may be used between the motor and the abrasive brush to create non-unitary ratios of the rotational speed of the motor to the rotational speed of the abrasive brush. 
     The present invention also incorporates a controller  200  to allow an operator of the apparatus or a software program to control the rotational speed of the abrasive brush. The speed can be controlled depending on the desired hone, the location of the workpiece within the brush, and/or the type of material being honed. The controller  200  can be a conventional motor speed controller of a type dependent on whether the motor uses alternating current or direct current. If a CVT is used to vary the speed of the brush, the controller  200  could also be used to control the CVT. 
     The honing apparatus  10  also includes a mount  35  for positioning and moving the workpiece relative to the abrasive brush  20 . The mount includes a translational movement mechanism or translator  30  for moving the workpiece  22  along a linear path parallel to the axis of rotation  44  of the abrasive brush. It has been determined that linear translation of the workpiece through the abrasive brush produces a consistent and precise hone on the workpiece. The translational movement mechanism  30  is slidably attached to a guide  36  that preferably extends along a linear path parallel to the rotational axis of the abrasive brush  20 . The workpiece is held within a fixture  34  attached to the translational movement mechanism  30 . The translational movement mechanism preferably is driven along the guide  36  by a motor-driven screw drive. It is contemplated, however, that other drive systems can be substituted for the preferred screw-drive without detracting from the invention. 
     The present invention also preferably incorporates a controller (such as controller  200  discussed above) which includes a process control software program to accurately control movement of the workpiece on the translational movement mechanism with respect to the abrasive brush. For example, the controller  200  can be programmed to control the translational movement mechanism such that the workpiece moves in the forward direction through the abrasive brush, the reverse direction through the abrasive brush  20 , is stopped within the rotating abrasive brush, or oscillates in the forward and reverse directions within the abrasive brush. Those skilled in the art would readily be capable of making such a substitution. 
     In one embodiment of the invention, the fixture  34  that holds the workpiece  22  is attached to a rotating base  33 . The rotating base  33  is, in turn, attached to a positioning motor  37 , either directly or indirectly, through a transmission or direct drive. The positioning motor  37  positions or rotates the fixture  34  containing the workpiece while the translational movement mechanism  30  moves the workpiece  22  through the rotating abrasive brush  20 . A controller, such as controller  200 , controls the positioning motor  37  to vary the rotation of the fixture  34  in accordance with a predetermined program, such as a numerical control program, which accurately rotates, positions or stops the rotation of the positioning motor  37 . Alternately, the controller permits an operator to provide positioning commands to the motor  37 . 
     As shown in FIG. 1, a vertical movement mechanism  28  is employed which adjusts the vertical position of the motor  20  relative to the base. In one embodiment, the vertical movement mechanism  28  includes a screw driven actuator that is controlled either manually, as by a handle  46  (FIG.  1 ), or by a control motor  80  (FIG.  6 ). If a control motor  80  is utilized, the motor  24  is preferably engaged to one or more guide rails  84  through linear bearings  86 . A screw  82  turned by the control motor  80  passes through a threaded fitting on the motor  24 , such that rotation of the screw  82  causes the motor  24  to move up or down. It is contemplated that the movement of the motor  24  and abrasive brush  20  may be preprogrammed into a computer or other control device (such as the controller  200 ) to provide automated and repeatable workpiece honing. 
     The embodiment of the invention shown in FIG. 1 also preferably includes a horizontal movement mechanism  26  for moving the motor  24  and abrasive brush  26  relative to the base  32 . Similar to the vertical movement mechanism  28 , the horizontal movement mechanism  26  preferably uses a screw drive to control the position of the motor  24  relative to the workpiece. The screw drive may be controlled by a handle  46  or a control motor system as discussed above. 
     It is contemplated that the apparatus  10  may include a device for inverting workpieces  22  after they have been honed. A suitable inverting device  39  is shown in FIG.  1  and includes a parallel gripper  38  which is adapted to pick up workpieces from and place workpieces on the fixture  34 . A vertical actuator  42  is attached to the mount  36  and raises and lowers the gripper  38 . A rotary actuator  40  attaches the gripper  38  to the vertical actuator  42 . The rotary actuator  40  is designed to rotate the gripper  38  up to 180 degrees about a horizontal axis for inverting the workpiece  22 . 
     In operation, after the workpiece passes through the abrasive bristles  66 , the gripper  38  grabs the workpiece. The gripper  38  is then translated upward and rotated a suitable amount to position another edge in an appropriate position for honing. The gripper  38  is then lowered until the workpiece is again placed in the fixture. 
     An alternate embodiment of the invention is shown in FIG.  7 . In this embodiment, instead of the motor  24  and abrasive brush  26  being vertically and horizontally adjustable with respect to the workpiece, the workpiece is mounted such that it can be appropriately positioned relative to a fixed abrasive brush  120 . Preferably, one or more control motors are used to position the workpiece  122  horizontally and vertically relative to the abrasive brush  120 . Alternatively, manual handles can also be used, similar to the handles described in the previous embodiment. 
     More particularly, in this embodiment, a vertical movement mechanism  131 , preferably attached to the mount  135 , moves the fixture  134  vertically relative to the base  132 . A horizontal movement mechanism  128  is also preferably engaged with the mount  135  and is designed to move the fixture  134  horizontally toward and away from the abrasive brush (i.e., substantially parallel to the base  132 ). A translational movement mechanism  126  moves the workpiece  122 , fixture  134 , vertical movement mechanism  131 , and horizontal movement mechanism  128  along guides  136  which preferably define a linear path parallel to the axis of rotation  144  of the abrasive brush  120 . As with the previous embodiment, a rotating base and positioning motor can be incorporated to rotate the fixture and/or workpiece. As shown, an inverting device, including a parallel gripper  138 , a rotary actuator  140 , and a vertical actuator  142 , can be incorporated for inverting the workpiece after honing, as discussed above. 
     A further embodiment of the invention is shown in FIG.  8 . In this embodiment, a mechanism for controlling the distance between the workpiece edge  50  and the axis of rotation  144  of the abrasive brush  120  is incorporated into the apparatus  10 . Referring to FIG. 9, the position of the workpiece edge  150  relative to the abrasive brush  120  is shown. The orientation of the workpiece edge  50  is defined by the angle δ between a side surface  168  of the workpiece  122  and a radial line  170  extending from the axis of rotation  144  of the abrasive brush  120  through the workpiece edge  150 . Rotation of the workpiece  122  about the workpiece edge  150  causes the point of contact between the bristles  166  and a top surface  166  and the side surface  168  of the workpiece  122  to vary, thereby controlling the resulting shape of the hone. 
     Referring back to FIG. 8, an orientation actuator  160  is used to control the orientation of the workpiece (e.g., cutting tool) with respect to the abrasive brush  120 . The orientation actuator  160  includes a fixed portion  160 F and a rotary portion  160 R. The fixed portion  160 F is mounted to the base  132 . The rotary portion  160 R is rotatably engaged to the fixed portion  160 F. The guides  136  are attached to the rotary portion  160 R. The fixture  134 , which holds the work piece  122 , is slidably attached to the guides  130 . In order to rotate the workpiece, the orientation actuator  160  is controlled (e.g., via a controller, such as controller  200  in FIG. 1) so as to rotate the rotary portion  160 R. This, in turn, causes the guides  136  and the fixture  134  to rotate about an orientation axis of rotation  162 . Depending on the location of the guides  136 , fixture  134  and workpiece  122 , the orientation axis may lie along the workpiece edge  150 . Rotation of the workpiece  122  about this axis changes the angle δ between the side surface  168  and the radial line  170 . As such, the point on the workpiece edge  122  that contacts the abrasive brush  120  will vary. 
     In this embodiment of the invention, the vertical position of the abrasive brush  120  is controlled by a distance positioning mechanism  164  which increases or decreases the distance between the axis of rotation  144  of the abrasive brush  120  and the workpiece edge  150 . Alternatively, the fixture  134  can be vertically translated or rotated relative to the abrasive brush  120  in a manner similar to the various embodiments described above. As with the above embodiments, an inverting device can be incorporated into the apparatus to invert the workpiece. 
     The apparatus described in the various embodiments above is useful for honing precise edges on work pieces. The process for honing those edges will now be described in detail. One feature of the process according to the instant invention is the placement of the workpiece edge to be honed at a specific location within the volume of the bristles of the abrasive brush. This proper positioning, in combination with the operation of the abrasive brush at a preferred rotational speed, permits high precision workpiece edge honing. 
     FIG. 10 illustrates a cross-sectional schematic of an abrasive brush  20 . As discussed in detail above, the present invention permits the workpiece edge  22  to be precisely located within the volume of the bristles. Various paths through the bristle volume  72  are shown in FIG. 10, each of which produces a different hone on the workpiece. At position A, assuming that the workpiece is oriented such that its top surface is parallel to the x-axis in the figure, a contact angle Φ between individual bristles  66  and the top surface  190  of the workpiece is relatively shallow (see, FIG.  11 ). This shallow contact angle results in more material being removed from the top surface  190  then the side surface  192 , producing a waterfall hone (shown by the dashed lines) on the workpiece edge. 
     If the workpiece were located at position B, an approximately even amount of material would be removed on the top and side surfaces  190 ,  192  by the bristles. This results in a radiused hone. 
     Referring to FIG. 14, the process according to the present invention involves first placing the workpiece  122  into the fixture  134 . The fixture  134  is then positioned relative to the abrasive brush  120  such that the workpiece edge  150  to be honed is located along a desired path  216  through the volume  172  of the abrasive brush. The location of this path in the volume  172  will depend on the desired hone shape as discussed above. The path  216  of translation through the bristle volume  172  is substantially parallel to the axis of rotation  214  of the abrasive brush. After proper positioning of the workpiece edge  150 , the fixture  134  is translated through the volume  172 . 
     Once the workpiece edge has passed through the bristle volume  172 , an inverting device can be utilized to reposition the workpiece in the fixture  134  to permit a different edge  50  to be processed. For example, since cutting tools typically have cutting edges on opposed sides of the tool, the parallel gripper  38  is rotated 180 degrees before the workpiece is returned to the fixture  134 . With the new edge positioned relative to the abrasive brush  20 , the fixture is translated back through the bristles of the abrasive brush  20 . If a different hone shape is desired on the new edge, the fixture can be repositioned relative to the abrasive brush prior to translation. 
     It is contemplated that the position and orientation of the work piece within the volume of bristles and the speed of rotation of the abrasive brush can be altered during translation (i. e., while the work piece is within the volume). This allows for the formation of a complex honed edge on the work piece and allows controlled variation of the hone along the workpiece edge. For example, in forming a threading tool, the hone on the thread forming edge can be intentionally varied from the tip end of the tool to the base of the tool. At the tip end, it may be desirable to have a larger hone to permit the thread forming edge, when in use, to dig through the raw material. Conversely, at the base of the thread forming edge it may be desirable to have a sharper hone to permit more precise finishing of the threads in the material. The present invention allows such precise hone control over the finished workpiece. 
     Another example of the use of the present invention for providing controller hone variation is shown in FIGS. 15 a  and  15   b.  FIG. 15 a  is a cross-sectional illustration of a grooving tool with a constant hone (designated “D” on all three sides). FIG. 15 b  is a cross-sectional illustration of a grooving tool with a controlled variable hone. As shown, the hone on the top (designated “D1”) is greater than the hones on the sides (designated “D2” and “D3”). 
     The various positioning mechanisms discussed above allow complex workpiece edges to be precisely honed. The use of a controller in the present invention allows the honing process to be programmed and automated to ensure repeatability. 
     Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.