Abstract:
An apparatus and method for induction hardening a workpiece can first include fastening a workpiece in a clamping assembly. The clamping assembly is provided with a plurality of hardness testing devices. Alternatively, one or more hardness testing devices are provided directly to the induction hardening head. The induction hardening head is moved over the workpiece to harden a portion thereof, such as an edge. Then, a series of hardness measurements are taken with the plurality of hardness testing devices to allow an operator or controller to adjust the input to the induction hardening head. This allows the workpiece to be provided with a predetermined hardness profile within a desired tolerance.

Description:
REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of priority to U.S. provisional application 60/392,345, filed on Jun. 28, 2002, which is hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a method and apparatus for induction hardening workpieces, and more particularly to a method and apparatus for maintaining a consistent hardness profile for an elongated workpiece. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a method and apparatus for induction hardening elongated objects such as cutting blades for use in the manufacture of cardboard and paper materials. The manufacture of paper and cardboard often requires predetermined lengths of such materials to be cut by automated cutting machinery. This machinery employs elongated tubular cylinders having a plurality of knives or blades fastened thereto. Each knife blade comprises an elongated rectangular steel member having a sharpened edge. It is desired to provide an edge that stays sharp for the longest amount of time possible since blade replacement or refurbishment adds to the cost of manufacturing end products. 
   The conventional method for providing an extended life sharp edge is to induction harden the edge of the blade. However, one must ensure a consistent hardness profile across the length of the workpiece to prevent uneven wear, which would compromise the blades cutting abilities. Conventionally, an operator must periodically remove the blade at predetermined intervals during an induction hardening procedure and manually measure the hardness value. The primary disadvantage of this method is that it takes additional time for the steps of removing and re-securing the workpiece each time a measurement is taken. These additional steps prolong the manufacturing time and add to the labor costs. Additionally, by increasing frequency of the measurements (resolution) to increase the hardness consistency over the length of the workpiece, adds even more to the costs. Therefore, there is a continuing need to reduce the time and cost required to produce a cutting blade having a hardened edge that has an approximately uniform hardness value. 
   SUMMARY OF THE INVENTION 
   An apparatus and method for induction hardening a workpiece that addresses the disadvantages of the prior art is disclosed. When using the apparatus, the method may first comprise the fastening a workpiece in a clamping assembly. The clamping assembly is provided with a plurality of hardness testing devices. Alternatively, one or more hardness testing devices are provided directly to the induction hardening head. The induction hardening head is moved over the workpiece to harden a portion thereof, such as an edge. Then, a series of hardness measurements are taken with the plurality of hardness testing devices to allow an operator or controller to adjust the input to the induction hardening head. This enables the workpiece to be provided with a predetermined hardness profile within a desired tolerance, without the necessity of removing and re-mounting the workpiece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a knife blade according to the prior art. 
       FIG. 2  is an end view of a knife blade according to the prior art. 
       FIG. 3  is a top view of an induction hardening apparatus for induction hardening a knife blade according to the prior art. 
       FIG. 4  is a side view of an induction hardening apparatus for induction hardening a knife blade according to the prior art. 
       FIG. 5  is a top view of an induction hardening apparatus for a knife blade according to an embodiment of the present invention. 
       FIG. 6  is a top view of an induction hardening apparatus for a knife blade according to an embodiment of the present invention. 
       FIG. 7  is a top view of an induction hardening apparatus for a knife blade according to an embodiment of the present invention. 
       FIG. 8  is a top view of an induction hardening apparatus for a knife blade according to an embodiment of the present invention. 
       FIG. 9  is a top view of an induction hardening apparatus for a knife blade according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  illustrate a side view and end view of a knife blade  20 , respectively, for cutting paper and cardboard products in automated production machinery. Each blade  20  comprises a first side  22 , a second side  24 , a first end  26 , a second end  28 , a bottom surface  30 , and a cutting edge  32 . A plurality of mounting holes  34  are provided to the blade  20  in communication with both of the first  22  and second  24  side surfaces. 
   The sharpened edge  32  is preferably hardened during the blade&#39;s manufacturing process to provide for a longer lasting sharp edge. Once the edge  32  is no longer sufficiently sharp to adequately cut the paper or cardboard products, it must be replaced and refurbished. Thus, it is desirable to achieve the longest lasting edge sharpness possible, thereby minimizing downtime and the associated costs of blade replacements and/or blade refurbishing. To that end, the cutting edge is hardened by the process of induction hardening. U.S. Pat. No. 3,738,636, hereby incorporated by reference, discloses a typical induction hardening apparatus for holding and induction hardening elongated workpieces. 
     FIGS. 3 and 4  illustrate a respective top view and side view of a conventional induction hardening apparatus  36  for knife blades  20  used in the paper and cardboard manufacturing industry. A clamping assembly  38  is disposed on a base  40  for clamping the blade  20  during a hardening procedure. The clamping assembly  38  includes a plurality of fasteners  39  that hold the position of the blade  20  in place during a hardening procedure. An induction hardening head  42  is slidably mounted to a portion of the clamping assembly  38  so that the cutting edge  32  of the blade  20 ) may be induction hardened. Power for the induction coil (not shown) in the hardening head  42  is supplied by an induction controller  44 . A control motor  46  rotates a shaft  48  having threads  50  thereon, which communicate with the induction head  42 . Such communication allows controller  44  to controllably move the induction head  42  along the length of the blade  20  during an induction hardening procedure. 
   A blade  20 , having been induction hardened along its cutting edge  32 , provides a longer edge life compared to a blade that was not induction hardened. However, mere induction hardening the edge will result in uneven wear due to hardness variations along the blade&#39;s length. Therefore, there is a need to adjust the input voltage to the induction hardening device  36  in order to maintain a consistent hardness measurement (often measured as a Rockwell C value) along the length of the cutting edge  32  of the blade  20 . 
   Referring to  FIG. 5 , an induction hardening apparatus  100  according to an embodiment of the present invention is shown in a top plan view. A workpiece  102  is rigidly held in place by a clamping assembly  104 . The clamping assembly  104  is disposed atop a base  106 , thereby elevating the hardening apparatus to an ergonomically desirable height for an operator. A plurality of manual hardness testing devices  108  are provided to the clamping assembly  104  at spaced intervals along the length of the blade  102 . The hardness testing devices  108  are rigidly fastened to a first portion  110  of the workpiece clamping assembly  104 , and disposed over the sharpened edge.  112  of the blade  102 . The measuring devices  108  may be fastened to the clamping assembly by threaded fasteners provided to a bracket fastened to the measurement devices  108 . 
   A wide variety of commercially available manual hardness testing devices may be utilized in the above-described configuration. Rockwell C hardness testing devices are widely available and known to those having skill in the art. Suitable hardness testers are available from companies such as Ames. Suitable Ames Hardness testers may be purchased from Qualitest™ USA LC, 3706 N. Ocean Blvd., #200, Ft. Lauderdale, Fla. 33308, USA. Alternative types of hardness testing instruments may be used without departing from the scope of the present invention, such as Brinell hardness testing devices. 
   A greater number or lesser number of hardness testing instruments  108  may be provided to the clamping assembly  104  according to the present invention. For instance, five, six or more hardness testing devices may be disposed on the clamping assembly to provide a greater resolution of the hardness profile for the blade edge  112 . 
   Referring to  FIG. 6 , another embodiment of the present invention provides the hardness testing device  108  directly to the induction hardening head  114 . By providing the hardness tester  108  to the induction hardening head  114 , a hardness reading may be taken at any number of infinite points along the length of the workpiece  102 . The operator then uses the hardness measurement to adjust the voltage supplied to the induction hardening coil up or down, depending on the hardness value relative to a target value. The goal is to maintain a consistent hardness measurement throughout the length of the workpiece  102 . 
   Referring to  FIG. 7 , a second hardness measurement device  116  is provided to the backside  118 , or following side, of the induction hardening head  114 . The additional hardness testing device  116  allows the operator to take a hardness measurement after the induction head  114  passes in order to ensure that the edge  112  is hardening to the target value and that the induction hardening apparatus  100  is in correct working order. 
   Referring to  FIG. 8 , a plurality of automated hardness testing devices  120  are disposed along the clamping assembly  104 . Each of the automated hardness testing devices  120  is in electrical communication with a programmable controller  122 . The programmable controller  122  obtains a hardness reading from each of the sensors  120  and adjusts the voltage to the induction coil in the head  114  accordingly, to achieve a uniform target hardness value for the workpiece  102 . 
   Referring to  FIG. 9 , first  124  and second  126  automated hardness measurement devices are rigidly fastened to a respective forward side  128  and following side  130  of the induction hardening head  114 . Such positioning allows up to an infinite number of successive hardness readings to be taken prior to the induction hardening head  114 , passing a given point and, following the induction hardening head  114 , passing that same point. The hardness measurements are relayed back to the controller  122 , which then adjusts the voltage input to the induction coil in the head  114  to achieve a predetermined desired hardness value of the workpiece  102 . Additionally, the information supplied by the following hardness sensor  126  allows the controller  122  to alert the operator when it encounters a condition in the workpiece not within a predetermined tolerance. 
   A wide variety of commercially available computer interfaceable hardness testers may be utilized in the automated measurement embodiments. Suitable hardness measuring devices are available from companies such as Newage Testing Instruments, Inc., 147 James Way, Southampton, Pa. 18966, USA. 
   In operation, an operator enters a predetermined desired hardness value into a programmable controller  122 , which is in electrical communication with the induction hardening head  114  and hardness measurement devices  108  or  120 . The induction hardening process is begun at a first end of the workpiece  102  and proceeds towards the remote end. The forward hardness sensor  124  takes readings at predetermined intervals and relays that information back to the controller  122 . The controller  122  is programmed with an algorithm that adjusts the voltage input to the induction coil in the induction head  114  either up or down depending on a hardness value higher or lower than a target value for the unhardened workpiece  102 . The hardness sensor  126  following the induction head  114  takes hardness readings at predetermined intervals to create a hardness profile for the length of the workpiece  102 . 
   The controller  122  can use the profile information to sense whether the predetermined hardness value for the finished piece has been achieved. The profile of the entire length of the workpiece can also be inspected by an operator or analyzed by an automated device to determine whether the finished product meets certain quality standards. 
   Although the present invention has been described with reference to the preferred embodiments, workers skilled in the art will recognize changes may be made in form and detail without departing from the spirit and scope of the invention.