Abstract:
Large, non-unitarily forged shaft workpieces such as a crankshaft have successive shaft features inductively heated and forged without cool down between each sectional forging process. The temperature profile along the axial length of the next section of the shaft workpiece to be inductively heated and forged is measured prior to heating, and the induced heat energy along the axial length of the next section is dynamically adjusted responsive to the measured temperature profile to achieve a required pre-forge temperature distribution along the axial length of the next section prior to forging.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/223,022, filed Jul. 4, 2009, hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to electric induction heat treatment of irregularly shaped shafts, and in particular to a class of irregularly shaped shafts known in the art as large, or non-unitarily forged shafts, such as large crankshafts and camshafts suitable for use in large horsepower internal combustion engines utilized for motive power in marine or rail applications, or for electric generator prime movers. 
       BACKGROUND OF THE INVENTION 
       [0003]    Large crankshafts, such as those utilized in marine main propulsion engines can exceed 20 meters in overall axial length and weigh in excess of 300 tonnes. A large crankshaft comprises a series of crankpins (pins) and main journals (mains) interconnected by crank webs (webs) and counterweights. The diameter of the journals can be as long as 75 mm (3 inches) and can exceed 305 mm (12 inches). Large crankshafts are heated and hot formed, for example by a hot rolling or forging process, which is favored over rolling. Steel forgings, nodular iron castings and micro-alloy forgings are among the materials most frequently used for large crankshafts. Exceptionally high strength, sufficient elasticity, good wear resistance, geometrical accuracy, low vibration characteristics, and low cost are important factors in the production of large crankshafts. 
         [0004]    One known process for manufacturing large, or non-unitarily forged, crankshafts is diagrammatically illustrated, in part, in  FIG. 1(   a ) through  FIG. 1(   g ). The term “non-unitarily forged” is used since the massive size of large crankshafts, and other irregularly shaped large axial shaft components do not permit forging of the entire crankshaft at one time, as is done, for example, with smaller crankshafts used in the internal combustion engines of automobiles. The feedstock, workpiece or blank  10  used in the process is typically a drawn cylindrically shaped blank as shown in cross section in  FIG. 1(   a ) at ambient temperature. Blank  10  may be, for example, a steel composition having an overall longitudinal (axial) length, L, of 20 meters and weight of 200 tonnes. Initially as shown in  FIG. 1(   b ) a first pre-forge section  12   a  (shown crosshatched) of blank  10  is positioned within multiple turn induction coil  20  as diagrammatically illustrated in cross section. Alternating (AC) current is supplied to the induction coil from a suitable source (not shown in the drawings) to generate a magnetic field that couples with pre-forge section  12   a  to inductively heat pre-forge section  12   a  to a desired pre-forge temperature. Upon achieving the desired temperature in pre-forge section  12   a , blank  10  is transported to a forging press (not shown in the figures) to forge an appropriate crankshaft feature or component, such as a first main journal or crankpin journal (referred to as the “first journal  12 ”). Forging temperatures typically used for steel compositions can range between 1093° C. to 1316° C. (2000° F. to 2400° F.). Subsequent to forging first journal  12 , entire blank  10  is cooled down to near ambient temperature. Second pre-forge section  13   a  (shown crosshatched) of the blank is then positioned within the induction coil to heat pre-forge section  13   a  to forge temperature as shown in  FIG. 1(   c ). Similar to the process for first pre-forge section  12   a , second pre-forge section  13   a  is forged as second journal  13 , after which the entire blank is again cooled down before heating the next section of the blank for forging. The process steps of section heating; section forging; and blank cool down are sequentially repeated for each subsequent feature of the large crankshaft, for example, as illustrated in  FIG. 1(   d ) through  FIG. 1(   g ) for journals  14  though  17 . 
         [0005]    Cool down of the entire blank after each section forging is driven by the necessity of having the same initial thermal conditions throughout the longitudinal length of the next section to be pre-forge heated so that the induction heating process heats the next section to a substantially uniform temperature throughout the longitudinal length of the next section. Without the cool down step, heat from the previous (last) forged section will axially flow by thermal conduction into the next section to create a non-uniform temperature distribution profile across the axial length of the next section, which will result in a non-uniform temperature distribution profile across the length of the next section after it is inductively heated within induction coil  20 . These cool down steps are both time consuming and energy inefficient since heat energy dissipation to ambient in the cool down steps represents a non-recoverable heat and energy loss. Consequently overall energy consumption is dramatically increased with substantial reduction in overall process efficiency. 
         [0006]      FIG. 2(   a ) through  FIG. 2(   d ) illustrate the effects of an insufficient cool down of the blank after each section pre-forge heat step described in the  FIG. 1(   a ) through  FIG. 1(   g ) process. Depending upon the mass of the blank; material composition of the blank; and required pre-forge final temperature, it could take from around 30 minutes to more than 60 minutes to inductively heat the first pre-forge section  12   a  of the blank as shown in  FIG. 2(   a ). Due to thermal conduction, there will be a substantial quantity of heat flowing from inductively heated high temperature pre-forge section  12   a  towards the end of the blank at a cooler (ambient) temperature. Upon completion of the first heating stage for pre-forge section  12   a  shown in  FIG. 2(   a ), the blank is transported to the forging apparatus for forging the crankshaft feature in heated pre-forge section  12   a . Typically the transport-to-forge apparatus step consumes several minutes. Additionally it also takes several minutes to forge the heated pre-forge section of the blank into the required crankshaft feature, and then several more minutes to transport the blank back to the induction coil for coil insertion and heating of the next pre-forge section  13   a  of the blank as shown in  FIG. 2(   b ). Consequently during the forging and transport steps there is an appreciable time period for thermal conduction of heat from the already heated hot sections towards the cooler (unheated) sections of the blank, and when the next pre-forge section is positioned within induction coil  20 , for example, pre-forge section  13   a , as shown in  FIG. 2(   b ), there will be a substantial residual heat concentration in pre-forge section  13   a  before induction heating thanks to axial heat conduction (illustrated by the “HEAT” arrows in the figures) from forged section  12  to pre-forge section  13   a . More importantly the heat concentration in pre-forge section  13   a  will produce an appreciably non-linear initial temperature distribution along the length, L 13 , of pre-forge section  13   a.    
         [0007]    Furthermore during the induction heating step of pre-forge section  13   a , previously heated and forged first journal  12  (shown in dense crosshatch in  FIG. 2(   b ) to indicate above ambient heated temperature) will serve as a source of heat with conduction heat flow towards next pre-forge section  13   a , which will affect, in a non-linear manner, both transient and final temperature distributions in the blank, including the temperature uniformity of inductively heated pre-forge section  13   a . Similarly upon completion of the heating and forging steps for second journal section  13 , and prior to the heating step for next pre-forge section  14   a  as show in  FIG. 2(   c ), there will be further, and more complex, heat flow gradients within the not-yet-forged sections of the blank due to thermal conduction. The initial temperature profile prior to induction heating of pre-forge section  14   a  of the blank is formed by complex thermal flow patterns in the blank resulting from the sequence of heating; transport-to-forge apparatus; forging; and transport-to-coil steps associated with forming first and second journals  12  and  13  as shown in  FIG. 2(   c ). Non-uniformity of the initial temperature distribution prior to induction heating of the next pre-forge section  15   a  will further increase due to the cumulative impact of the previously heated and forged first  12 , second  13  and third  14  journals of blank  10  as shown in  FIG. 2(   d ). 
         [0008]      FIG. 3(   a ) through  FIG. 3(   f ) further illustrate the effect of the initial temperature on the final thermal conditions of blank  10  without cool down after each induction heating and forging steps for a section of the blank with the process described in  FIG. 1(   a ) through  FIG. 1(   g ). As shown in  FIG. 3(   a ) at the beginning of the heating cycle, pre-forge section  12   a  is positioned inside of multiple turn induction coil  20 . AC current is supplied to the induction coil from a suitable source (not shown in the drawings) to generate a magnetic field that couples with pre-forge section  12   a  to inductively heat pre-forge section  12   a . Points, or nodes  1   12  through  3   12  (subscripts indicating sections in which the nodes are located), as illustrated in  FIG. 3(   a ), represent typical critical nodes at the surface of pre-forge section  12   a , which requires uniform heating by induction prior to forging. Node  4   13  is in section  13  of the blank located in proximity to the required uniformly heated pre-forge section  12   a . Initial axial temperature distribution (T INITIAL   12 ) prior to start of the induction heating step for first pre-forge section  12   a  is uniform, and typically corresponds to ambient temperature. The surface node locations versus temperature graph in  FIG. 3(   b ) shows an initial temperature distribution (T INITIAL   12 ) in the axial direction, and a required surface temperature distribution (T FINAL   REQ ) at the end of the induction heating step for pre-forge section  12   a . As described above, after the completion of induction heating of pre-forge section  12   a , the sequence of transport-to-forge apparatus; forging; and transport-to-coil for the next section heating steps are performed, after which pre-forge section  13   a  will be positioned within induction coil  20  as shown in  FIG. 3(   c ). During the time consumed by the above process steps, thermal conduction flow along the longitudinal axis results in a substantially non-uniform initial temperature distribution (T FINAL   13 ) prior to the start of the induction heating step for second pre-forge section  13   a  as shown in the surface node locations versus temperature graph in  FIG. 3(   d ). Temperature distribution (T INITIAL   13 ) will be substantially non-uniform and appreciably different from temperature distribution (T INITIAL   12 ). The initial temperature at node  1   13  (T 1 ) in the  FIG. 3(   d ) graph will be appreciably greater than the temperatures at nodes  2   13  (T 2 ),  3   13  (T 3 ) and  4   14  (T 4 ); generally, T 1 &gt;T 2 &gt;T 3 &gt;T 4 &gt;(T INITIAL   12 ). If the induction heating process for pre-forge section  13   a  is the same as that used for pre-forge section  12   a , the final temperatures (T FINAL   ACTUAL ) at the representative nodes will be noticeably higher then the required temperatures (T FINAL   REQ ) as graphically shown in the  FIG. 3(   d ). 
         [0009]    Process parameters playing a dominant role in the final temperature after the induction heating of each pre-forge section include: initial temperature of the pre-forge section; physical properties of the blank (primarily the specific heat value of the blank&#39;s composition); induced power in the pre-forge section; total induction heating time of the pre-forge section; and thermal surface losses from the blank due to heat convention and thermal radiation, which can be calculated from the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
                     T 
                     FINAL 
                   
                   = 
                   
                     
                       T 
                       INITIAL 
                     
                     + 
                     
                       ( 
                       
                         
                           
                             P 
                             IND 
                           
                           × 
                           
                             T 
                             IND 
                           
                         
                         
                           m 
                           × 
                           c 
                         
                       
                       ) 
                     
                     - 
                     
                       Q 
                       SURF 
                     
                   
                 
               
               
                 
                   [ 
                   
                     equation 
                      
                     
                         
                     
                      
                     
                       ( 
                       1 
                       ) 
                     
                   
                   ] 
                 
               
             
           
         
       
     
         [0010]    where T IND  is the time (in seconds) of induced heating; P IND  is the power (in kW) induced in the pre-forge section; m is the mass (in kg) of the inductively heated pre-forge section; c is the specific heat (in J/(kg·° C.)) of the blank&#39;s material composition, and Q SURF  is the surface heat losses (in ° C.) including radiation and convection. Equation (1) illustrates that there is a direct correlation between final temperature T FINAL  and initial temperature T INITIAL , assuming all other factors remain the same. 
         [0011]    When pre-forge section  13   a  absorbs a sufficient amount of induced heat energy during the heating step shown in  FIG. 3(   c ), blank  10  is removed from induction coil  20  and is transported to the forging apparatus (not shown in the drawings) to forge second journal  13 , after which the blank is transported back to the induction coil for heating of next pre-forge section  14   a  as shown in  FIG. 3(   e ). However initial temperatures at nodes  1   14  through  3   14 , and  4   15  will now be appreciably higher as illustrated in the surface node locations versus temperature graph in  FIG. 3(   f ). With the process described in  FIG. 1(   a ) through  FIG. 1(   g ) this overheating will be further aggravated, and initial thermal conditions, (T INITIAL   14 ), prior to induction heating of the next pre-forge section will cause further increase in the final temperature (T FINAL   ACTUAL ) compared to the required final temperature (T FINAL   REQ ) as graphically shown in  FIG. 3(   f ). Overheating can result in irregularities such as grain boundary liquation, metal loss due to excessive oxidation and scale, decarburization, improper metal flow during forging, forging defects (for example, crack development), or excessive wear of forge dies. Any of these irregularities can result in degraded performance of the forged article of manufacture. 
         [0012]    Therefore with the conventional process described above, an uncertainty in the initial thermal profile along the longitudinal axis of the blank prior to heating the second, third, and successive pre-forge sections of the blank can lead to undesired thermal conditions in the pre-forge sections, including lack of temperature uniformity along the longitudinal axis in a pre-forge section. In the conventional process described above, this is avoided by the inefficient step of cool down after forging of each pre-forge section before induction heating of the next pre-forge step. 
         [0013]    One object of the present invention is to produce a non-unitarily forged article of manufacture, such as a large crankshaft from a blank, or other large shaft article with a plurality of irregularly shaped cylindrical components, by sequential induction heating of each pre-forge section without the necessity of cooling down the crankshaft after forging each heated pre-forge section, by utilizing the heat absorbed in the blank during previous cumulative heating steps and reducing the required energy consumption. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    In one aspect the present invention is a method of, and apparatus for, manufacturing a large, non-unitarily forged shaft workpiece having a plurality of irregularly shaped cylindrical components that are individually forged after induction heating separate sections of the shaft. Successive induction heating and forging of shaft components is accomplished without cool down between forging and heating steps by sensing the actual temperature distribution along the axial length of the next section of the shaft to be inductively heated and forged. The temperature profile of the next section is used to adjust the amount of induced heating power along the length of the next section so that a required (for example substantially uniform) temperature profile along the axial length is achieved prior to forging the next section. The sensed temperature profile data from a forged shaft workpiece may be used to adaptively adjust the amount of induced heating power along the length of the next shaft workpiece to be forged. 
         [0015]    In another aspect, the present invention comprises a large, non-unitarily forged shaft workpiece having a plurality of irregularly shaped cylindrical components that is manufactured by a process disclosed in this specification. 
         [0016]    The above and other aspects of the invention are set forth in this specification and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The appended drawings, as briefly summarized below, are provided for exemplary understanding of the invention, and do not limit the invention as further set forth in this specification and the appended claims: 
           [0018]      FIG. 1(   a ) through  FIG. 1(   g ) diagrammatically illustrate a sequence of induction heating and forging steps used in a process to manufacture non-unitarily forged crankshafts. 
           [0019]      FIG. 2(   a ) through  FIG. 2(   d ) diagrammatically illustrate regions of elevated temperatures along the axial length of a blank as successive pre-forge sections are inductively heated along the length of the blank and forged if the blank is not cooled down to ambient temperature after forging each section of the blank. 
           [0020]      FIG. 3(   a ) through  FIG. 3(   f ) diagrammatically and graphically illustrate typical non-uniform initial temperature profiles prior to induction heating of the second and third pre-forge sections of a blank, and their effect on the final temperature distribution, and overheating, of each subsequent pre-forge section if the non-unitarily forged article of manufacture is not cooled down to ambient temperature after completion of forging the section of the article from each subsequent pre-forge section. 
           [0021]      FIG. 4(   a ) through  FIG. 4(   c ) illustrate one method of sensing the surface temperatures along the longitudinal axis of a pre-forge section of a shaft workpiece as used in the present invention. 
           [0022]      FIG. 5(   a ) through  FIG. 5(   i ) illustrate various arrangements of induction heating apparatus used in the present invention to dynamically control induced power applied along the longitudinal axis of a pre-forge section of the workpiece. 
           [0023]      FIG. 6  illustrates in block diagram form one example of a control system used with an application of electric induction energy for manufacture of non-unitarily forged workpieces utilized in the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 4(   a ) through  FIG. 4(   c ) illustrate one example of pre-forge temperature sensing along the axial length of a section that can be used in the present invention. In this example, the workpiece or blank  10  is cylindrical in shape and the axial length is measured parallel to the central (centerline) longitudinal axis of the cylinder. First pre-forge section  12   a  can be inductively heated (as shown in  FIG. 4(   a )) and forged as described above in the conventional process, if the initial axial temperature distribution profile of the first pre-forge section is as required, for example, at a uniform ambient temperature. 
         [0025]    Prior to loading the second (and subsequent) pre-forge section  13   a  into induction heating coil assembly  22 , a longitudinal axis (axial length) temperature distribution profile can be generated by measuring the temperature of the pre-forge section of the blank with suitable temperature sensing device (TS)  30 , for example, as the blank is loaded into coil assembly  22 . Temperature sensing device  30  may be, for example, a single pyrometer (or multiple pyrometers) distributed along the X-axis preceding the blank-entry end  22   a  of the coil assembly. The one or more temperature sensors can sense the surface temperature of the blank as it is inserted into the blank-entry end of the coil assembly (from left to right orientation as shown in  FIG. 4(   b )). Temperature readings may be continuous, or discrete, as the axial length of the blank passes the one or more temperature sensors. 
         [0026]    One or more of the temperature sensors may alternatively be of a type that measures temperatures into the thickness of the blank, or utilizes any range of the electromagnetic spectrum for temperature sensing. Multiple sensors may be assembled on a common support rack. The blank and/or sensors may be rotated, or the sensors may surround the perimeter of the blank if circumferential non-uniform temperatures are of concern. Alternatively one or more temperature sensors may be interspaced within coil assembly  22  so that the temperature sensing can be accomplished as the section of the blank is inserted into the coil, or after the section has been inserted into the coil. 
         [0027]    In one example of the invention, as the remaining non-forged portion of blank  10  moves into the heating position inside of induction coil assembly  22 , the initial pre-heat surface temperature profile along the longitudinal axis of the next section of the blank to be pre-forge heated can be sensed and monitored using a single pyrometer. The pyrometer is positioned in front of the entry end  22   a  of the coil assembly, and while the non-forged blank is inserted into the coil assembly via suitable conveyance apparatus, the pyrometer scans, or senses, the blank&#39;s surface temperature along the length of the next section to be inductively heated and transmits the scanned temperature data to control system (C)  32 , which in turn, controls components of the induction heating system via suitable interfaces, such as configuration of the coil assembly and the output parameters of the one or more power supplies connected to the coil assembly, to achieve a require temperature distribution along the axial length of pre-forge section  13   a  of the blank. 
         [0028]    As shown in  FIG. 4(   c ) data from temperature sensing device  30  is transmitted to control system  32 , and is used by the control system to modify the magnetic (flux) field distribution established by AC current flow through components of coil assembly  22  to redistribute induced power density within pre-forge section  13   a  that is being inductively heated in  FIG. 4(   c ) responsive to the required temperature distribution. The redistribution of induced power density compensates for the non-uniform initial (actual) temperature profile (T INITIAL   13 ) as graphically illustrated in  FIG. 4(   c ), and provides the required (for example, uniform) final heating conditions (T FINAL   REQ ) in pre-forge section  13   a . If the induced power density distribution was not modified, the non-uniform initial temperature, (T INITIAL   13 ), would result in an appreciably different final temperature profile (T FINAL   CONVENTIONAL ) compared to the required temperature distribution (T FINAL   REQ ). The lack of a controlled heating profile can lead to undesirable properties in the forging of any section of the blank. 
         [0029]    Depending upon the particular application of the present invention, alternative arrangements of induction coil assembly  22  can be used to redistribute and selectively control induced power density along the axial length of pre-forge section  13   a  (and each successive blank pre-forge section) that is to be inductively heated as shown in  FIG. 5(   a ). 
         [0030]      FIG. 5(   b ) illustrates one example of a coil assembly used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. Multiple turn solenoidal induction coil  23  includes multiple selective end tap assemblies  23   a  and  23   b  at opposing ends of the coil that can be used to compensate for a non-uniform (or otherwise undesirable) initial surface temperature profile of pre-forge section  13   a  when inductively heating pre-forge section  13   a . Control system  32  can control the positions of end tap connectors  23   a ′ and  23   b ′ to connect the appropriate coil end tap to the output of power supply  40 . Based on temperature data transmitted from temperature measuring device  30 , control system  32  switches between appropriate coil end tap terminals  23   a  and/or  23   b  at the coil end(s) prior to, or during, induction heating of pre-forge section  13   a  to modify the induced heat distribution in pre-forge section  13   a  to produce the required pre-forge temperature distribution along the axial length of pre-forge section  13   a.    
         [0031]      FIG. 5(   c ) illustrates another example of a coil assembly used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. By selectively connecting (for example, by contactors not shown in the drawing) one or more capacitive elements, C, in capacitor banks  24   a  or  24   b  across one or more coil sections of induction coil  24  (representatively shown in dashed lines), localized induced heating of the pre-forge section inserted in the coil can be achieved by increasing the magnitude of induced currents in the required regions from selective formation of localized coil-resonant L-C circuits that allow for compensation of a non-uniform initial surface temperature profile sensed by temperature sensing device  30 . 
         [0032]      FIG. 5(   d ) illustrates another example of a coil assembly used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. In this example at least two coil sections  25   a  and  25   b  of induction coil  25  are supplied power from two independently controlled power sources  40   a  and  40   b  (for example, two independently controlled power inverters outputting AC power). Separate control of power from each power source can be used to compensate for a non-uniform (or otherwise undesirable) initial surface temperature profile of pre-forge section  13   a  while also incorporating either the variable end coil taps, or capacitive elements shown in  FIG. 5(   b ) or  FIG. 5(   c ), respectively. Output power control from each power supply may be output frequency and/or output power magnitude accomplished, for example, by a pulse width modulated control scheme. 
         [0033]      FIG. 5(   e ) illustrates another example of a coil assembly used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. One or more switching devices, for example, illustrative switching devices  50   a  and/or  50   b  can be used to electrically short out one or more coil turns of multiple turn solenoidal induction coil  26  to redistribute induced power density along the axial length of pre-forge section  13   a  to compensate for the initial undesired surface temperature profile measured by temperature sensing device  30 . 
         [0034]      FIG. 5(   f ) and  FIG. 5(   g ) illustrate another example of a coil assembly used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. Induction coil  26  comprises a multiple layer, multiple turn induction coil that is utilized to redistribute induced power density along the axial length of pre-forge section  13   a  to compensate for an initial undesired pre-heat surface temperature distribution profile and establish the required final pre-forge thermal conditions in pre-forge section  13   a .  FIG. 5(   g ) illustrates the partial multi-layer coil arrangement at opposing ends of induction coil  26 . For example, switching devices  52   a  and/or  52   b  can be used to selectively alter the circuit configuration of coil ends  26   a  and  26   b , respectively, of multi-layer induction coil  26  to redistribute induced power density in pre-forge section  13   a  and compensate for the initial undesired pre-heat surface temperature distribution to establish the required final pre-forge thermal conditions in pre-forge section  13   a.    
         [0035]      FIG. 5(   h ) and  FIG. 5(   i ) illustrate another example of a coil assembly used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. Induction coil  27  comprises at least two coil sections  27   a  and  27   b  connected in parallel as shown in the figures. Referring to  FIG. 5(   i ) induction coil  27  has a double helix design representing two alternating helixes  27   a  and  27   b  connected in parallel. In this particular example of the invention, alternating turns of coil  27  comprise interlaced “even” coil section  27   a  (designated by the non-shaded squares in  FIG. 5(   i )) and “odd” coil section  27   b  (designated by the shaded squares in  FIG. 5(   i ). By energizing and de-energizing one of the odd or even sections (for example, odd section  27   b ), control device  32  redistributes induced heat sources (induced power density) along the axial length of the pre-forge section that compensates for an initially undesired (typically non-uniform) axial length surface temperature distribution and achieves the required final thermal conditions for the pre-forge section inserted in the induction coil. The example shown in  FIG. 5(   i ) also optionally includes the end multi-layer coil arrangement as described above relative to  FIG. 5(   f ) and  FIG. 5(   g ). 
         [0036]    In a particular application, various combinations of the coil assemblies described above may be used in the present invention to redistribute and selectively control induced power density along the axial length of a pre-forge section to be heated. 
         [0037]      FIG. 7  further illustrates one example of a control system for use with the present invention. Processor  80  can be any suitable computer processing unit such as a programmable logic controller. One or more temperature sensing devices  32  input temperature data along the axial length of the blank at least for the next pre-forge section to be inductively heated in the induction coil assembly for forging. Optionally the temperature along the entire axial length of the remaining blank may be inputted each time the blank is inserted in the induction coil assembly so that a dynamic change in heating profile along the entire length of the remaining blank is recorded. An additional input to the processor may be one or more position sensors  34  (such as a laser beam sensor), which coordinates the inputted temperature data with a specific location along the axial length of the blank. Processor  80  executes one or more heating computer programs that analyze the inputted temperature data to generate an actual blank temperature distribution profile. The program compares the actual blank temperature distribution profile with a required pre-forge blank temperature distribution profile that may be stored on digital storage device  86  or inputted via a suitable input device  88  by a human operator. The software generates an induction heating system control program for execution dependent upon the difference between the actual blank and required pre-forge blank temperature distribution profiles, and the particular installed induction heating system. Responsive to the induction heating system control regime, processor  80  outputs control signals via suitable input/output (I/O) devices  81  to electrical switching devices  83  associated with the particular installed coil assembly, for example, as alternatively described in  FIG. 5(   a ) through  FIG. 5(   i ), and to control circuitry associated with the one or more power sources associated with a particular installed induction heating system. For example IGBT gating control in the output inverter(s) of the one or more power sources may be used to control the magnitude and duration of output power of each of the one or more power sources. Application of induced power to the blank may begin while the blank is still being inserted into the coil assembly, or after the blank has been completely inserted into the coil assembly. For sequential heating of the sections of different blanks with the same physical and metallurgical compositions, the control system may recall from stored memory the heating system control regime used for the heating of the prior blank to expedite determination of the heating system control regime for the next similar blank. 
         [0038]    The relative term “large” as used is used herein refers to shaft workpieces that can not be entirely forged in one forging process. Generally these shaft workpieces include crankshafts with journals having a diameter greater than 75 mm (3 inches) and lengths in excess of 1 meter. 
         [0039]    While the article of manufacture described in the above examples of the invention is a non-unitarily forged crankshaft, the invention is more generally applicable to other non-unitarily forged articles of manufacture where a particular pre-forge axial temperature profile is desired for a section of the article. 
         [0040]    While a uniform surface temperature profile is designated as the required end temperature profile along the axial length of the pre-forge section inserted in the induction coil assembly, in other examples of the invention other non-uniform end temperature profiles can be achieved by the processes of the present invention. 
         [0041]    The present invention has been described in terms of preferred examples and embodiments. Equivalents, alternatives and modifications, aside from those expressly stated, are possible and within the scope of the invention.