Abstract:
An induction heat treating process with a remote sensor for monitoring the duration of energization of an induction heating coil each time the induction heating coil is consecutively cycled. An identifying tag is preferably attached to, embedded within the induction heating coil or within the surrounding area of the induction coil and transmits a signal to a remote counting sensor that is preferably triggered by and responds to the change in voltage generated as the coil is energized. Alternative means of measuring a cycle may be implemented. The output data from the sensor provides useful information for determining the lifespan of an induction heating coil. Predicting the lifespan of a coil optimizes production by anticipating failure and replacement of a coil during a predetermined down time, limiting on-site inventory, and revolutionizing the billing cycle based on a per cycle cost while decreasing overall production costs and improving inductor coil quality.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 10/750,640 filed on Jan. 2, 2004. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates generally to a counting sensor for use in conjunction with an induction heat treating process. More particularly, the present invention relates to a system for counting the cycles of an individual inductor coil or the duration of energization of the induction heating coil or both and maintaining and transmitting this data to a remote unit location or self contained unit within the counting sensor.  
       BACKGROUND OF THE INVENTION  
       [0003]     The induction heat treating process is used in various applications for hardening, and annealing of metals. The process includes applying energy directly to metals and other conductive materials via an alternating electric current passing through an induction heating coil positioned in close proximity to a workpiece. The induction heating process is applicable to both continuous and component heating. Continuous heating relates to processes such as wire and strip manufacturing and includes induction heating coils used for forging products, billet heaters and tube annealing. Component heating is describes a process for heating one component, or workpiece at a time. Gears and axle shafts are generally hardened by component induction heating processes.  
         [0004]     A common use for component induction heating is case hardening of carbon steel, or alloy parts for use in the formation of automobiles, farm equipment, airplanes and other production apparatuses. Component induction heating rapidly heats the workpiece in a short period of time. The workpiece is then quenched and a hardened surface, or through hardened part is formed. The depth of the hardened surface is regulated by the frequency of current, temperature of the part surface, and quenching of the part.  
         [0005]     Additionally, induction heating coils may be used to continuously heat a workpiece, or billet, prior to stamping or other fabrication process. The billet is heated gradually to a desired temperature by passing through an extended induction heating coil or a series of induction heating coils of increasing temperature. The series of induction heating coils, or alternatively a single coil, will heat the billet by maintaining energization over the duration of the continuous heating process. More specifically, a helically wound induction heating coil or a series of coils may be used to continuously heat a billet prior to stamping. Each induction heating coil, or series of coils, is encased in refractory material to help retain the heat necessary to pre-heat a billet and act as a heat shield to protect the coil from excess heat. This continuous process may require an induction heating coil to be energized for extended time periods of 2000-4000 hours, or a lifespan of approximately one month.  
         [0006]     Much of the prior art is directed to systems for measuring and maintaining the temper and surface hardness to insure proper performance and quality control of the heated parts. The concept of monitoring an induction heating cycle is disclosed in U.S. Pat. Nos. 4,897,518 and 4,816,633 to Mucha et al. and for monitoring the current in an induction heating coil is disclosed in U.S. Pat. No. 5,434,389 to Griebel. These prior patents are incorporated by reference herein for general background information as they relate to the conventional induction heating treating processes. Similarly, U.S. Pat. Nos. 3,746,825 and 5,250,776 to Pfaffmann disclose a method for measuring input energy and temperature and heating rate of a workpiece, respectively. U.S. Pat. No. 6,455,825 to Bentley et al. discloses the use of miniature magnetic sensors strategically placed about the workpiece to monitor changes in the magnetic properties of the workpiece as it heats up during induction heating and cools down during quenching. These patents are also incorporated by reference for the further purpose of illustrating the state of the art of induction monitoring systems.  
         [0007]     Both conventional induction heat treating processes are detrimental to the perishable heat treating tool. The tool, or inductor coil, is designed and shaped specifically to the workpiece undergoing the heat treatment. An induction heating machine may include a specifically designed coil, or multiple identical coils mounted to the machine, or various coil designs mounted to a single machine in series, all used for heating or hardening various workpieces during production. Each coil may be formed of multiple copper parts and flux concentrators that are brazed or attached to form an inductor assembly. The joints have a limited life cycle and are prone to failure or leakage and must be repaired. Further, arcing often occurs where there are small air gaps between the tool and the workpiece causing stress cracks and damage to the coil. During continuous heat induction, the surrounding refractory material tends to breakdown due to the heat or other property failures. These examples only exacerbate the already short tooling life of a coil and lead to costly repairs. Each time tooling is changed, the induction heating machine and the heat treated parts must be validated to ensure that the new coil is performing per required specifications. Tooling and production shutdown are costly and time-consuming. Employing multiple coils with each machine, without knowing the cycle history of each individual coil increases the opportunity for production interruption.  
         [0008]     Currently, an end user/purchaser of induction heating equipment will contract an induction equipment supplier (OEM) to design an optimal coil configuration for the part requiring induction heating. Based on the quality of material used and quality of workmanship, the coil will need repairing after an unknown amount of cycles or duration of energization. More often than not, the end user will choose to send the coil to an after market company for the repair based mainly on the cost of the repair. A costly inventory of inductor coils is maintained at the production site for immediate replacement when a coil fails during production. Occasionally a replacement coil is removed from inventory without ordering new replacements, thus creating an immediate need for a new replacement coil.  
         [0009]     A blind count is recorded of how many times the induction heating machine is cycled for purposes of determining the amount of parts that have been heat treated. However, no record is kept of how many times each individual inductor coil is energized, or cycled, or the duration of energization of the coil during a heating process. Nor is a record kept of how many different inductor coils are used in a multiple coil machine. Therefore, no hard record is created to determine the cycle life of each inductor coil, i.e. how many cumulative cycles in the life of an average inductor coil or the duration of time the coil has been energized for heating a workpiece. Best estimates are that a perishable coil must be replaced approximately every 5,000 to 100,000 cycles based on each individual application or every 2,000 to 4,000 hours of prolonged energization. These tool costs are incorporated into the overall cost of each manufactured part.  
         [0010]     When an inductor coil fails, production stops. The coil must be changed and the machine and subsequently heat treated parts must be validated. This requires the transportation and quarantine of the parts to a separate storage area for analysis of quality control. If the parts do not meet the specified criteria, they are scrapped, resulting in an expensive waste of material and labor. The alternative option is to wait until the metallurgical results are verified before running production, this may take hours.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides an induction heat treating process with a sensor for counting the amount of cycles attributable to an individual inductor coil. Additionally, the sensor may be used to count the duration of energization of a coil, or both. The sensor is preferably a counting mechanism remotely located from the induction coil assembly and triggered by a signal, such as a designated radio frequency, emitted from an identifying tag attached to, embedded within or located within the area of the induction heating coil or bus bar assembly. The induction coil identifying tag triggers the remote sensor in response to the change in voltage generated as the coil is energized. The remote sensor may be any external data maintenance source, such as a control cabinet or personal computer for example, to register a consecutive count of cycles or duration of energization or both for the identified coil.  
         [0012]     Alternatively, the sensor may be attached to or embedded within the induction heating coil or bus bar and is triggered by and responds to the change in voltage generated as the coil is energized as described in the parent application entitled ENERGIZATION CYCLE COUNTER FOR INDUCTION HEATING TOOL and having Ser. No. 10/750,640, filed Jan. 2, 2004, now U.S. Pat. No. ______, and the Continuation-in-part application entitled ENERGIZATION CYCLE COUNTER FOR INDUCTION HEATING TOOL and having Ser. No. 10,953,800, filed Sep. 29, 2004, now U.S. Pat. No. ______.  
         [0013]     Alternative designs may measure current, magnetic field, frequency and/or temperature differentials on each individual coil. As described above, the remote sensor is a counting mechanism triggered by a signal emitted from an identifying tag, such as a transmitter, attached to, embedded within or located within the area of the induction heating coil or bus bar assembly. The identifying tag is particularly advantageous and applicable where the induction heating coil is located within an enclosed environment that may not be accessed without tripping an emergency stop or the like. The remote sensor may take the form of any type of external data maintenance source, such as a control cabinet or personal computer for example, to register a consecutive count of cycles or duration of energization or both for the identified coil. The data culled from the remote sensor or other data maintenance and retrieval sources provides useful information for determining the lifespan of an induction heating coil. Predicting the lifespan of a coil optimizes production by anticipating failure and replacement of a coil during a predetermined down time, limiting on-site inventory, and revolutionizing the repair billing cycle based on a per cycle cost while decreasing overall production costs.  
         [0014]     Initially, the sensor is used to measure the amount of cycles sustained by each individual coil until failure of the coil to establish a base line life span of a typical industrial application. In addition to, or alternatively, the sensor is used to measure the duration of a coil energization period. To do this, a sensor is preferably provided remotely from the induction coil assembly and is triggered by an induction coil identifying tag located within the surrounding area of the induction coil assembly capable of monitoring the change in voltage generated as the coil is energized. When the machine is activated, the induction coil identifying tag emits a signal to the remote sensor, which in turn responds to the voltage change across the bus bar and tallies a single cycle. Each activation, or cycle, of the induction heat treating coil registers a consecutive cycle. Similarly, when the sensor is measuring duration of energization for a continuous heating process, time is measured by the sensor from the beginning of a cycle through deactivation of the induction heating coil. The sensor tallies and stores the amount for reading. The remote sensor may also transmit to a second external device such as a bar code reader, hand held personal computer, cellular telephone, or any other device capable of receiving such transmitted information.  
         [0015]     Once an average baseline lifespan for each coil design is established, whether on a per cycle or duration basis, the monitoring system of the present invention can provide useful information to optimize the operation of each induction heating machine and overall production. The monitoring system includes providing an induction heating coil with an induction coil identifying tag attached to, embedded within each coil or within the surrounding area of the induction heating coil and access to a remote counting sensor. Preferably, a coil monitoring company provides an induction heating coil with an induction coil identifying tag and access to a remote counting sensor for lease, rather than purchase, by a company for use during production. As the sensor tallies cycles or duration for each coil, the coil monitoring company as proprietor of the monitoring system reads the output from the sensor and compares the total cycles or duration to the baseline lifespan of each coil design. When a predetermined threshold cycle count or duration period is met, the coil monitoring company as part of the overall monitoring system notifies the leasing company of an anticipated need to change a coil before failure. Once removed from the induction heating machine, the coil is preferably forwarded to the coil monitoring company for analysis and distribution to a coil manufacturing company for repair and reuse. Alternatively, the coil monitoring company may repair induction heating coils in-house. The leasing company is charged for each cycle or segment of time experienced by the induction heating coil and does not incur the cost of repair.  
         [0016]     Additionally, the system of the present invention provides an efficient method for monitoring on-site induction heating coil inventory. An induction heating machine using multiple designed coils for hardening various workpieces during production may require the removal of one coil design and replacement with a second coil design. When production using the first coil design resumes, the counting system provides a method for reading the output transmitted from each coil remote counting sensor. This application is also advantageous when induction heating coils are used in series for continuous heat treating of billets prior to stamping and when induction heating coils are located within an enclosed environment not readily accessible for reading a counter within the area of the coil itself. In a preferred embodiment, the remote counting sensor may be a hand held reading device such as a bar code reader or personal computer used to read and analyze the tallied count or duration period for each inventoried coil.  
         [0017]     Alternatively, or in conjunction with the remote counting sensor, an LED readout may be provided within the identifying tag counter mechanism and activated by the push of a button for viewing the number of cycles or duration period applicable to a particular coil. This educates the operator as to which coil best suits the needs of current production. The system also aids the operator in determining which coil should be used to replace the failed or failing coil in the examples set forth above. With this information the operator can predict and prepare for scheduled coil changeovers to eliminate production downtime.  
         [0018]     When the failed coils are returned for repair, the coil monitoring company through the monitoring system, further provides a method for establishing industrial standards for induction heating coils. The coil monitoring company through the data culled from the monitoring system will maintain a database for recording the cycle lifespan or duration period of a certain coil design and the area of failure, for example. This information is accumulated and can aid in possibly improving the coil design by eliminating repetitive failure areas such as unnecessary or poorly brazed joints or use of inferior brazing material.  
         [0019]     The coil monitoring company through monitoring system also provides a means for renovating the costs associated with current production processes. Instead of purchasing induction heating coils and contracting for repair, the monitoring system provides a method for leasing induction heating coils and paying on a per cycle basis. Alternatively, payment may be based on a time basis when the induction heating coil is measured for duration of energization. A fixed per cycle or time bases cost will encourage coil manufacturers to manufacture coils of the highest quality and maintain continuous improvement of production induction heating coils. This eliminates repair costs and provides a known fixed production price per part. By monitoring the lifespan of an induction heating coil, the system eliminates unknown costs, increases production, limits inventory, decreases potential waste costs and establishes industrial standards for the manufacturing and design of heating coils.  
         [0020]     These and other objects of the present invention will become apparent upon reading the following detailed description in combination with the accompanying drawings, which depict systems and components that can be used alone or in combination with each other in accordance with the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  illustrates a first preferred embodiment of the apparatus and method for monitoring the amount of cycles or duration period experienced by an induction heating coil;  
         [0022]      FIG. 2  illustrates a second preferred embodiment of the apparatus and method for monitoring the amount of cycles or duration period experienced by an induction heating coil;  
         [0023]      FIG. 3  illustrates a preferred embodiment of the counter with circuitry for measuring voltage change across the bus bar to trigger the counter;  
         [0024]      FIG. 4  illustrates an induction heating coil counter block diagram of a preferred circuit for measuring the voltage change of  FIG. 3 ;  
         [0025]      FIG. 5  illustrates a third preferred embodiment of the apparatus and method for monitoring the amount of cycles or duration period experienced by an induction heating coil;  
         [0026]      FIG. 6  illustrates a fourth preferred embodiment of the apparatus and method for monitoring the amount of cycles or duration period experienced by an induction heating coil; and  
         [0027]      FIG. 7  illustrates a fifth preferred embodiment of the apparatus and method for monitoring the amount of cycles or duration period experienced by an induction heating coil. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     With reference to  FIGS. 1 and 2 , a monitoring system  10  of the present invention is there shown and includes an induction heating coil assembly  12  and subassembly  14 . The components of the induction heating coil assembly  12  include a Program Learning Center (PLC)  16  connecting a hard-wired Personal Computer (PC)  18  with a power supply  20 . In an industrial setting, the PLC  16  is connected to a control cabinet (not shown) for automation and control of the induction process. The personal computer  18  is illustrated as part of the assembly  12 , however, the personal computer  18  may be located off premises and connected to the monitoring system  10  via the Internet or other well-known communication devices.  
         [0029]     A transformer  22  is connected to the power supply  20  and connects the induction heating coil subassembly  14  to the monitoring system  10 . A cooling unit  24  for cooling the transformer  22  and coil subassembly  14  during the induction heating process is provided along with a quenching unit  26  for quenching a workpiece  28  after induction heating. The quenching unit  26  is preferably hard-wired to the PLC  16  for receiving information as to when to quench the workpiece  28 . The workpiece  28  is shown resting on a tooling nest  30  located on a turntable  32 .  
         [0030]     The induction heating coil subassembly includes an induction heating coil  34  surrounding the workpiece or billet  28  and a bus bar  36  electrically connecting the induction heating coil  34  to the transformer  22  and power supply  20 . A counting sensor  38  is shown removably attached to the bus bar  36  in  FIG. 1 .  FIG. 2  illustrates a second preferred embodiment of the monitoring system  10  of the present invention with a counting sensor  138  embedded within a bus bar  136 .  FIGS. 5 and 6  illustrate a third and fourth preferred embodiment of the monitoring system  10  of the present invention with a coil identifying tag  238  located in the area of the bus bar, either embedded ( FIG. 5 ) or removably attached ( FIG. 6 ).  FIG. 7  illustrates a coil identifying tag  338  located within the surrounding area of the induction coil subassembly  12  and capable of monitoring the change in voltage generated as the coil is energized or any other chosen measurement as set forth below. A sensor  240 , 340  is preferably provided remotely from the induction coil assembly and is triggered by a signal, such as a designated radio frequency, cellular number, bar code, or any other sensing means received by the induction coil identifying tag  238 , 338 , respectively. When the machine is activated, the induction coil identifying tag responds to the voltage change across the bus bar and signals a single cycle to the remote sensor. Locating a transmitter, such as an identifying tag, within a limited area of the induction heating coil is advantageous where the coil is confined to a closed and monitored environment. Such an environment prevents a person from entering a restricted area to view the counting mechanism of the first preferred embodiment. Entering such an area during operation may trigger a stop mechanism and halt the induction heating operation altogether. As such, the remote counting sensor allows for reading pertinent information relating to the induction heating coil where direct access to the coil may not be possible or convenient.  
         [0031]     The sensor  38 , 138  may take one of several different forms. The sensor may include a counting mechanism within the body of the sensor, such as the nut and bolt combination illustrated in  FIGS. 1 and 3 , for after market attachment to an existing induction heating coil assembly or subassembly. The sensor, with counting mechanism, may also be embedded within the induction heating coil assembly or subassembly as illustrated in  FIG. 2 . Alternatively, as illustrated in  FIGS. 5, 6  and  7 , an identifying tag  238 ,  338 , such as a resistor pattern or transmitter, signals to an external source, or remote sensor  240 ,  340  located within a control cabinet, personal computer, bar code identifier, PDA, or cellular telephone, for example, the identity of a particular coil and instructs the computer to begin a consecutive cycle count or duration period. As with all forms of sensors, the cycle count or duration period along with other pertinent data is input, stored and retrieved for analysis on or off premise.  
         [0032]     As is well known in the art, the induction heating process relies on electrical currents within a material to produce heat. The power supply  20  sends alternating current through the induction heating coil  34 , generating a magnetic field. A workpiece or billet  28  is placed in the coil  34  and enters the magnetic field. Alternating current through the coil  34  during the heating cycle causes current flow within the workpiece or billet  28 , generating precise amounts of localized heat without physical contact between the coil  34  and the workpiece or billet  28 .  
         [0033]      FIGS. 3 and 4  illustrate a preferred embodiment of the counting or duration period sensor  38  and circuitry  40  for measuring the change in voltage across the bus bar  36  and triggering the counting or duration period sensor  38  when the induction heating coil  34  is cycled. The counting or duration period sensor  38  includes a bolt  42  and nut  44  that serves the dual purpose of housing the circuitry  40  and securing the bus bar  36  within the induction heating coil subassembly  14 . The bolt  42  and nut  44  are preferably formed of a non-conductive or minimally conductive material such as plastic, ceramic, brass or stainless steel as is well known in the industry, thus preventing overheating during the heating cycle. The nut and bolt combination provide an after market counting or duration period sensor that can easily replace an existing nut and bolt in induction heating coil assemblies already in production.  
         [0034]     The head  46  of the bolt  42  is provided with a contact point  48  along the interior of the head  46 . A second contact point  50  is located within the interior of the nut  44 . Both contact points  48 ,  50  are preferably formed of a conductive material such as copper and will contact the bus bar  36  on opposing sides  52 , 54 , respectively, when the bolt  42  is placed in hole  56  in bus bar  36  and tightly secured by the nut  44 . These contact points,  48 , 50  may be located anywhere along the interior of the head  46  and nut  44  as long as contact is maintained with the bus bar  36  when the bolt  42  is secured. The contact points  48 ,  50  read the difference of electrical potential, or change in voltage, across the bus bar  36  when the induction heating coil  34  is cycled, in turn, closing the circuit loop  40  within the bolt  42 , triggering the counting sensor  38  to record a consecutive cycle count on a visual display  58 . A typical circuit loop  40  is illustrated with a 9-volt cell that connects to a light to illuminate the light when a cycle is visually displayed.  
         [0035]      FIGS. 5 through 7  illustrate a second preferred embodiment locating a counting sensor remotely from the induction heating coil. Preferably, a remote sensor  240 ,  340  is provided with the counter and circuitry illustrated in  FIGS. 3 and 4  and measures the induction heating coil cycles and/or duration of energization when the corresponding identifying tag  238 ,  338  transmits a signal to the remote sensor  240 ,  340  in response to the change in voltage experienced across the bus bar as described above.  
         [0036]     Numerous alternative embodiments of the counting or duration period sensor, means for measuring a cycle or duration period, means for reading the cycle count or duration period, and means for monitoring, recording, displaying and disseminating the cycle count or duration period for each induction heating coil are envisioned and include a counting or duration period sensor embedded within the nut and bolt as illustrated in  FIG. 2 . Alternative means for measuring a cycle or duration period include but are not limited to, measuring the change in current, frequency or temperature about the induction heating coil assembly or using a Hall effect device as described in U.S. Patent No. 3,388,318 and incorporated by reference herein. In general, the cycle or duration period is measured by any means known in the art upon the generation of a magnetic field about an induction heating coil.  
         [0037]     The consecutive cycle count or duration period may be recorded for reading visually as illustrated in  FIG. 3  or using a bar code reader  38 ,  138  as shown in  FIGS. 1 and 2 , respectively. Other recording and transmission devices may be used including a sensor in conjunction with a computer  18 , as shown in  FIG. 1 , that may be wireless or hard wired to the monitoring system  10  or any hand held device, commonly referred to as PDA&#39;s, for receiving transmitted information via radio or telephone transmissions (land line or cellular.)  FIGS. 5 and 6  illustrate the use of a remote sensor used in conjunction with an induction coil identifying tag.  
         [0038]     Initially, the monitoring system  10  of the present invention provides a method for establishing a baseline lifespan of an induction heating coil, both per cycle and energization duration period. An induction heating coil is provided with an identifying tag and remote sensor, or counting or duration period mechanism as described above, for use with an induction heating coil assembly in a production setting. The identifying tag may be provided as an aftermarket nut and bolt arrangement, may be embedded within the induction heating coil or bus bar when either is manufactured or simply located within the induction heat coil assembly area. The remote counting or duration period mechanism is triggered by a signal emitted from the identifying tag each time a magnetic field is generated about the coil (illustrated by arrows showing the flowing electricity through the induction heating coil in  FIGS. 1 and 2 , and  5 - 7 ), i.e. when the induction heating coil is cycled. When measuring the duration of energization, the induction heating coil cycle extends from the triggered moment until shutdown of the coil. In this instance, the sensor measures the time period the coil is energized and considers this as a single cycle. The counting or duration period sensor measures the change in voltage across the bus bar and consecutively counts or triggers to count a cycle or measure a duration period each time the magnetic field is generated. The induction heating coil is maintained in production and each cycle is counted or duration period measured and recorded by the counting or duration period sensor until the coil fails. The final cycle count or duration period is recorded by the counting or duration period sensor or by other means such as a personal computer receiving the output from the counting or duration period sensor. This final cycle count or duration period measured is recorded and maintained by the monitoring system to aid in establishing an average baseline lifespan of similarly shaped induction heating coils and subassemblies.  
         [0039]     Once an average baseline lifespan is established, the monitoring system of the present invention provides a method for monitoring the amount of cycles or duration period attributable to an induction heating coil in production. This method includes providing an induction heating coil assembly with an induction heating coil having a counting or duration period sensor or identifying tag with remote sensor. The counting or duration period sensor is triggered or the identifying tag triggers an external receiver, such as a remote sensor, with each cycle or duration period of the coil when a magnetic field is generated during the induction process. The counting or duration period sensor, the identifying tag, or the remote sensor may be read manually or the sensor may receive the counting data or measure of the duration period and transmit the output to a monitoring system having a computer or any type of PDA for receiving the output data. The consecutive count for each induction heating coil is maintained and monitored by the system. The monitoring system may provide a direct means for reading the count or duration period, such as a visual system, or may send out a notification via any means such as e-mail, cellular telephone, cellular PDA, cellular or hard-wired computer system, for example, to notify the production assembly of the consecutive cycles or duration period sustained by each coil. This cycle count or duration period may be compared to the established baseline lifespan of a coil and such information may be used to recommend replacing a coil prior to failure if the cycle count or duration period is within a pre-determined range of the average.  
         [0040]     Preferably, the monitoring system of the present invention is maintained and controlled by a coil monitoring company. The company provides the induction heating coils with sensors and identifying tags for lease, rather than purchase, by a company for use during production. As the sensor tallies cycles or duration period for each coil, the monitoring system reads the output from the sensor and compares the total cycles or measured duration period to the baseline lifespan of each coil design. When a predetermined threshold cycle count or duration period is met, the monitoring system notifies the leasing company of an anticipated need to change a coil before failure. Once removed from the induction heating machine, the coil is preferably forwarded to the coil monitoring company for analysis and distribution to a coil manufacturer for repair and reuse. Alternatively, the coil monitoring company may repair induction heating coils in-house. The leasing company is charged for each cycle experienced by the induction heating coil or a measurement of time interval, such as per minute, for the measured duration period and does not incur the cost of repair.  
         [0041]     Additionally, the coil monitoring company provides the monitoring system of the present invention for aiding the leasing company in monitoring on-site induction heating coil inventory. An induction heating machine using multiple designed coils for component hardening various workpieces or a series of coils for continuous heating of billets prior to stamping may require the removal of one coil design during production and replacement with a second coil design. When production using the first coil design resumes, the counting or duration period system provides a method for reading the output from each coil sensor or the identifying tag. In a preferred embodiment, a hand held reading device such as a bar code reader or personal computer is used to read and analyze the tallied count or duration period for each inventoried coil. Alternatively, an LED readout may be provided within the counter mechanism or the identifying tag and activated by the push of a button for viewing the number of cycles or duration period applicable to a particular coil. This educates the operator as to which coil best suits the needs of current production. The system also aids the operator in determining which coil should be used to replace the failed or failing coil in the example set forth above. With this information the operator can predict and prepare for scheduled coil changeovers to eliminate production downtime.  
         [0042]     When the failed coils are returned for repair, the monitoring system further provides a method for establishing industrial standards for induction heating coils. The monitoring system includes maintaining a database for recording the cycle lifespan or duration period of a certain coil design and the area of failure, for example. This information is accumulated and can aid in possibly improving the coil design by eliminating repetitive failure areas such as unnecessary or poorly brazed joints or use of inferior brazing material.  
         [0043]     The monitoring system also provides a means for renovating the costs associated with current production processes. Instead of purchasing induction heating coils and contracting for repair, the monitoring system provides a method for leasing induction heating coils and paying on a per cycle or time interval basis. A fixed per cycle or time interval cost will encourage coil manufacturers to manufacture coils of the highest quality and maintain continuous improvement of production induction heating coils. This eliminates repair costs and provides a known fixed production price per part. By monitoring the lifespan of an induction heating coil, the system eliminates unknown costs, increases production, limits inventory, decreases potential waste costs and establishes industrial standards for the manufacturing and design of heating coils.  
         [0044]     Although the invention has been described with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the following claims.