Method for carrying out a remelting/hardening treatment

Remelting/hardening treatment is carried out for a work by a remelting/hardening treatment apparatus including a torch for heating the work. First, the work is firmly placed in position in the remelting/hardening treatment apparatus and a temperature of the work is then measured by a temperature detector. When the measured temperature is lower than a lower limit temperature of a predetermined or particular temperature range, a level of output from the torch is lowered and a part of the work other than a part thereof to be treated is then preheated by the torch. Thereafter, the part of the work to be treated is subjected to remelting and hardening with the aid of the torch. Consequently, production of unacceptable works can be prevented reliably, since remelting/hardening treatment is not carried out at all while the measured temperature is lower than the predetermined or particular temperature range. Alternatively, a preheating operation is performed by the torch while an insufficiently preheated work is placed in position in the remelting/hardening apparatus. After completion of the preheating operation, the work is subjected to remelting and hardening in the same manner as mentioned above.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a method for carrying out a 
remelting/hardening treatment. More particularly, the present invention 
relates to a method for carrying out such remelting/hardening treatment 
for a preheated work with the aid of a torch, wherein when the work is 
preheated at a lower temperature, a preheating operation is additionally 
performed for the work by using the torch and the remelting/hardening 
treatment is then carried out on the properly preheated work. 
2. Description of the Prior Art 
It is known in metallurgical technology to chill a metallic structure of a 
surface of a work or article made of cast iron or cast steel by allowing 
the surface of the work to be subjected to remelting and hardening, 
thereby to improve wear resistance and shock resistance of the work. 
For example, a procedure for carrying out remelting/hardening treatment 
across the full width of a cam surface by rotating a preheated cam shaft 
while reciprocatively displacing a preheating torch in the axial direction 
of the cam shaft has been disclosed in an official gazette of Japanese 
Unexamined Patent Publication (Kokai) No. 60-258421. 
According to such prior procedure, when the cam shaft is not preheated 
within a predetermined or particular temperature range before the cam 
shaft is subjected to the remelting/hardening treatment, it has been 
reported that there arises a malfunction such as surface crack or the like 
due to cooling at an excessively high speed after completion of a melting 
operation. For this reason, it is necessary to carefully control a 
preheating temperature (usually ranging from 150.degree. to 400.degree. 
C.) of the cam shaft which is to be subjected to remelting and hardening. 
Generally, a preheating station is arranged on the upstream side in a 
remelting/hardening treatment line along which cam surfaces on the cam 
shaft are successively subjected to remelting and hardening, at a 
plurality of treatment stations arranged on the downstream side of the 
remelting/hardening treatment line. 
With respect to the foregoing remelting/hardening treatment line in which 
each cam shaft is successively subjected to remelting and hardening, there 
is a possibility that a temperature of the cam shaft is lowered during 
treatment in a plurality of treatment stations even through the cam shaft 
is correctly preheated to a predetermined temperature in the preheating 
station. In addition, there is a possibility that the temperature of the 
cam shaft is lowered due to unexpected line stoppage or similar 
malfunction. 
Once the temperature of the cam shaft is lowered, there arises a problem 
that the remelting/hardening treatment will be carried out on the cam 
shaft that no longer is at a sufficiently high preheating temperature, in 
the event that the temperature of the cam shaft is not measured at each of 
the treatment stations. As a result, an unacceptable cam shaft may be 
produced undesirably. 
On the other hand, in the event that the temperature of each cam is 
measured in the respective treatment station. If at any such station the 
preheating temperature is too low, the cam shaft may be returned to the 
preheating station. In such case, however, a conveying system extending 
across the remelting/hardening treatment line becomes complicated in 
structure. Also, many man-hours are consumed for returning insufficiently 
preheated cam shafts to the preheating station. Further, the 
remelting/hardening treatment is carried out at a low operational 
efficiency. Moreover, cam shafts can not smoothly be delivered to a 
subsequent step, i.e, an engine assembling step. 
SUMMARY OF THE INVENTION 
The present invention has been made in consideration of the aforementioned 
problems. 
Therefore, an object of the present invention is to provide a method for 
carrying out a remelting/hardening treatment, wherein when a work is 
initially preheated at a lower temperature, it also is possible to perform 
an additional preheating operation by using a torch of the type preferably 
employable for the remelting operation. 
To accomplish the above object, there is provided according to one aspect 
of the present invention a method of carrying out a remelting/hardening 
treatment for a work wherein the work is firmly placed in position in a 
remelting/hardening treatment apparatus including a torch for heating the 
work. A part of the work to be treated is then subjected to remelting and 
hardening with the aid of the torch. Prior to remelting, the temperature 
of the work is measured. If such measured temperature remains within a 
predetermined or particular temperature range, the work to be treated to 
the be subjected to remelting and hardening treatment. However, when the 
measured temperature is lower than the lower limit temperature of such 
predetermined or particular temperature range, the torch is used to 
additionally preheat a non-treated part of the work other than the part 
thereof to be subjected to the remelting/hardening treatment. Thereafter, 
the part of the work to be treated then is subjected to remelting and 
hardening. 
With the method of the present invention, the additional preheating 
operation is performed on the non-treated part of the work while the torch 
is continuously displaced, and after completion of the additional 
preheating operation, the torch is continuously displaced from the 
non-treated part of the work to the part of the same to be treated. 
In addition, with the method of the present invention, at least either of a 
level of output from the torch or an additional preheating treatment time 
is adequately determined based on the measured temperature before the 
additional preheating operation is performed. 
An apparatus for carrying out the method of the invention comprises 
temperature measuring means for measuring a temperature of the work, work 
driving means for, when a temperature measured by the temperature 
measuring means remains within a predetermined or particular temperature 
range enabling, the part of the work to be treated to be subjected to 
remelting and hardening, but, when the measured temperature is lower than 
the lower limit temperature of the predetermined or particular temperature 
range ensuring that, a level of output from the torch is lowered and the 
part of the work to be treated is subjected to remelting and hardening 
only after a non-treated part of the work other than the part thereof to 
be treated is preheated by the torch; torch driving means, and controlling 
means for properly controlling the work driving means and the torch 
driving means. 
With the method of the present invention, a remelting/hardening treatment 
is carried with the aid of the remelting/hardening treatment apparatus 
including a torch. A temperature of the work is first measured by the 
temperature measuring mean. When the measured temperature remains within 
the predetermined or particular temperature range, the part of the work to 
be treated is then subjected to remelting and hardening. Thus, production 
of an unacceptable product, e.g. a cam shaft, can be prevented reliably, 
since the remelting/hardening treatment is not carried out at all as long 
as the measured temperature of the work is lower than the predetermined or 
particular temperature range. Consequently, the part of the work to be 
treated is subjected to remelting and hardening only under conditions 
ensuring high quality. 
When the measured temperature of the work is lower than the lower limit 
temperature of the predetermined or particular temperature range, a level 
of output from the torch is first lowered and the part of the work to be 
treated is then subjected to remelting and hardening only after the 
non-treated part of the work other than the part thereof to be treated is 
sufficiently preheated by the torch. Thus, since the remelting/hardening 
treatment and the additional preheating operation both are carried out by 
the same torch while the work is firmly held in position in the 
remelting/hardening apparatus, such malfunctions as reduced efficiency and 
a complicated structure of conveying system extending across the 
remelting/hardening treatment line can be avoided. 
Further, since the non-treated part of the work is preheated while the 
torch is continuously displaced, such preheating can be achieved uniformly 
at a high operational efficiency. Moreover, an occurrence of incorrect 
local melting of the work can be prevented without fail. Additionally, 
since the torch is continuously displaced from the non-treated part of the 
work to the part thereof to be treated after completion of the preheating 
operation, the remelting/hardening treatment can be carried out at an 
improved operational efficiency. 
In addition, since at least either of the level of output from the torch or 
the preheating treatment time is determined based on the measured 
temperature of the work before the preheating operation is performed, the 
preheating operation can be performed for the work while a preheating 
temperature remains within the predetermined or particular temperature 
range. 
When the part of the work to be treated is subjected to remelting and 
hardening by actuating the torch, a temperature of the work is measured by 
the temperature measuring means. In addition, the controlling means 
controls operation for the work driving means and the torch driving means 
of the remelting/ hardening treatment apparatus in such a manner that when 
a temperature of the work measured by the temperature measuring means 
remains within the predetermined or particular temperature range, the part 
of the work to be treated is subjected to remelting and hardening, but 
when the measured temperature of the work is lower than the lower limit 
temperature of the predetermined or particular temperature range, the 
non-treated part of the work other than the part thereof to be treated is 
preheated by the torch, and thereafter, the part of the work to be treated 
is subjected to remelting and hardening. 
Other objects, features and advantages of the present invention will become 
apparent from the following description which has been made in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, the present invention will be described in detail hereinafter with 
reference to the accompanying drawings which illustrate preferred 
embodiments of the present invention. 
According to a first embodiment of the present invention, cams on direct 
valve driving type cam shafts to be installed in a four-cylinder engine 
mounted on an automotive vehicle are successively subjected to remelting 
and hardening along a remelting/hardening treatment line. Description will 
be made below with respect to a method and apparatus for carrying out 
remelting/hardening treatment while defining the direction of installation 
of the remelting/hardening line with reference to FIG. 1 to FIG. 3. 
Referring to FIG. 1 and FIG. 2, a cam shaft is designated by reference 
character CS. Each cam shaft CS is made of ductile cast iron. As shown in 
the drawings, the cam shaft CS includes a first cam portion C1 to a fourth 
cam portion C4 each of which includes a suction or intake cam 1 for 
driving a suction or intake valve in each cylinder and an exhaust cam 2 
for driving an exhaust valve in each cylinder of the four-cylinder engine. 
In addition, the cam shaft CS includes at least journal portions 3 and 4 
at the foremost and rearmost ends thereof. An engagement hole 4a is formed 
on the rear end surface of the journal portion 4. 
Each of the suction cam 1 and the exhaust cam 2 has a cam surface 5, and a 
width of the cam surface 5 as measured in the axial direction of the cam 
shaft CS is dimensioned to be the same with respect to all the cam 
surfaces 5 on the cam shaft CS. A valve driving surface 5b on a nose 
portion of each of the cams 1 and 2 exclusive of a cylindrical surface 5a 
(i.e., a region extending from a melting operation start position M1 to a 
melting operation end position M2 located opposite to the melting 
operation start position M1 as represented by two-dot chain lines in FIG. 
3; wherein it should be noted that the foregoing region corresponds to a 
region to be treated) is subjected to remelting and hardening across the 
full width of the cam surface 5. As is apparent from FIG. 3, edges 5c are 
formed around the cam surface 5 on the fore and rear sides of the each 
cam. 
Next, description will be made below with respect to a remelting/hardening 
treatment line L and a remelting/ hardening treatment apparatus M which 
are installed for practicing a remelting/hardening treatment method of the 
present invention. Referring to FIG. 1 and FIG. 2 again, a cam shaft 
receiving station ST1, a vehicle type discriminating station ST2, a first 
preheating station ST3, a second preheating station ST4, a first treatment 
station ST5, a first waiting station ST6, a second treatment station ST7, 
a third treatment station ST8, a second waiting station ST9, a fourth 
treatment station ST10 and a cam shaft discharging station ST11 are 
successively arranged across the remelting/hardening treatment line L in 
such order as seen from the left-hand end of FIG. 1. In addition, a pit P 
is recessed across the stations ST1 to ST11 in the direction of 
installation of the remelting/hardening line L. 
An opposed pair of work receiving members 10 are arranged with the pit P 
therebetween in each of the cam shaft receiving station ST1, the first and 
second waiting stations ST6 and ST9 and the cam shaft discharging station 
ST11. A vehicle type discriminating unit 13 composed of an opposed pair of 
cam shaft supporting mechanisms 11 and an opposed pair of vehicle type 
discriminating mechanisms 12 is arranged in the vehicle type 
discriminating station ST2. A preheating unit 15 including an opposed pair 
of preheaters 14 is arranged in each of the first and second preheating 
stations ST3 and ST4. In addition, a torch displacing/driving unit 30, an 
opposed pair of TIG torches 40 and an opposed pair of rotational cam shaft 
supporting units 50 are arranged in each of the first treatment station 
ST5, the second treatment station ST7, the third treatment station ST8 and 
the fourth treatment station ST10. It should be noted that a work 
receiving portion 10a is formed at each of the left-hand end and 
right-hand end of each work receiving member 10. 
A lift and carrier type conveying unit 20 is arranged across the pit P so 
as to successively convey each cam shaft CS from the station ST1 to the 
station ST11. 
The conveying unit 20 is composed of a driving mechanism (not shown) 
including a hydraulic cylinder and associated components, carriers 22 or 
the like, and operation of the conveying unit 20 is controlled by a 
conveyance controller 25 installed on a control board 16 located 
rearwardly of the cam shaft receiving station ST1. Each carrier 22 is 
cyclically driven by a predetermined distance by the driving mechanism 
arranged in each of the stations ST1 to ST11, not only in the vertical 
direction but also in the transverse direction of the remelting/hardening 
treatment line L. It should be added that a pair of cam shaft receiving 
portions 22a are formed on the upper surface of each carrier 22 with a 
predetermined distance therebetween. 
First, two cam shafts CS are received from a cam shaft production line (not 
shown) in the cam shaft receiving station ST1 from above by actuating an 
automatic loader (not shown). As shown by two-dot chain lines in FIG. 1, 
each cam shaft CS is placed on work receiving portions 10a located at 
opposite ends of the work receiving member 10 in the longitudinal 
direction of the remelting/hardening treatment line L. After completion of 
the loading operation, the two cam shafts CS received in the cam shaft 
receiving station ST1 are then successively conveyed from spacing by 
actuating each carrier 22. 
When the cam shafts CS are conveyed to the vehicle type discriminating 
station ST2, they are supported by the supporting mechanisms 11 and then 
rotationally driven about their axial axes so that they are placed at a 
reference phase position (e.g., a position where the nose portion of the 
suction cam 1 on a first cam portion C1 is oriented in the downward 
direction). Then, while the foregoing state is maintained, a specific 
vehicle type discriminating mark formed on the cam shaft CS is detected by 
the discriminating mechanism 12. Next, after the cam shaft CS is preheated 
for a predetermined period of time by a preheater 14, a working 
temperature of which is set to a predetermined temperature (e.g., 
200.degree. C.), in the first preheating station ST3, the cam shaft CS is 
heated up to an elevated temperature for a predetermined period of time by 
another preheater 14, a working temperature of which is set to a 
predetermined temperature (e.g., 400.degree. C.), in the second preheating 
station ST4. Subsequently, while the temperature of the cam shaft CS 
remains within a preset temperature range (e.g., 150.degree. to 
400.degree. C.) in the first treatment station ST5, the cam shaft CS is 
rotationally driven by a rotational supporting unit 50, and the suction 
cam 1 and the exhaust cam 2 on the first cam portion C1 are then subjected 
to remelting and hardening with the aid of a TIG torch 40 in the first 
treatment station ST5. Thereafter, suction cams 1 and exhaust cams 2 on a 
second cam portion C2, a third cam portion C3 and a fourth cam portion C4 
are subjected to remelting and hardening in the same manner as mentioned 
above at the second treatment station ST7, the third treatment station ST8 
and the fourth treatment station ST10. 
After completion of remelting and hardening treatments for the eight cams 1 
and 2 in the above-described manner, the cam shaft CS is conveyed from the 
cam shaft discharging station ST11 to an engine assembling line (not 
shown). It should be noted that the first and second waiting stations ST6 
and ST9 are arranged in the remelting/hardening treatment line L for the 
purpose of temporarily holding the cam shaft CS in a waiting state in the 
case of an occurrence of a malfunction such as line stop page or the like. 
Next, description will be made below with respect to the 
remelting/hardening treatment apparatus arranged in each of the treatment 
stations ST5, ST7, ST8 and ST10. In detail, as shown in FIG. 1 to FIG. 4, 
each remelting/ hardening treatment apparatus M includes a torch 
displacing/driving unit 30, an opposed pair of TIG torches 40 mounted on 
the torch displacing/driving unit 30, an opposed pair of rotational 
supporting units 50 and a torch power supply source unit 60. On the other 
hand, the control board 16 is provided with a control unit 80 for properly 
controlling four sets of remelting/hardening treatment apparatuses M. In 
FIG. 1, reference numeral 17 designates a hydraulic pressure supplying 
unit. 
The torch displacing/driving unit 30 includes a housing 31 and an arm 32 
projecting forward from the housing 31. The housing 31 is provided, as 
shown in FIG. 4, with a servomotor 34 for reciprocatively driving the arm 
32 in the forward/ rearward direction (X-coordinate direction) and another 
servomotor 35 for reciprocatively driving the arm 32 in the 
upward/downward direction (Z-coordinate direction). A supporting member 33 
extending in the leftward/rightward direction is mounted at the foremost 
end of the arm 32. As shown in FIG. 3, a TIG torch 40 and a temperature 
detector 45 for detecting a temperature of the cam shaft CS are arranged 
at each of the left-hand end and the right-hand end of the supporting 
member 33 so that valve driving surfaces 5b of the suction cams 1 and the 
exhaust cams 2 on the two cam shafts CS arranged on the right-hand and 
left-hand sides of the remelting/hardening treatment line L are 
successively subjected to remelting and hardening. It should be added that 
an infrared ray emitting type thermometer having a thermally deposited 
thermopile incorporated therein as a detecting element is preferably 
employable for the temperature detector 45. 
As shown in FIG. 2, the rotational supporting unit 50 is composed of a 
hydraulic cylinder 51 arranged rearwardly of the pit P, a support shaft 
member 53 operatively connected to a rod 51a of the hydraulic cylinder 51 
via a guide member 52, another hydraulic cylinder 54 arranged forwardly of 
the pit P while assuming a position opposite to the hydraulic cylinder 51, 
a servomotor 56 operatively connected to a rod 54a of the hydraulic 
cylinder 54 via a guide member 55 and a holder 57 mounted at the foremost 
end of an output shaft of the servomotor 56. 
The support shaft member 53, the servomotor 56 and the holder 57 are 
arranged in such a manner that they can be shifted as desired between 
advanced positions represented by solid lines in FIG. 2 and retracted 
positions represented by two-dot chain lines in FIG. 2. The holder 57 
includes three sets of holding portions 57a each adapted to selectively 
assume one of a holding position and a non-holding position as desired by 
actuating a hydraulic cylinder 58 (see FIG. 4). It should be noted that a 
pin 53a adapted to be engaged with engagement hole 4a of the cam shaft CS 
is disposed at the foremost end of the support shaft member 53. 
The advanced position of the holder 57 is shifted to the retracted position 
of the same and vice versa by driving the rod 54a of the hydraulic 
cylinder 54 with a full stroke in the forward direction or in the rearward 
direction. The advanced position of the holder 57 is set to be a reference 
point of the X-coordinate direction. 
When the cam shaft CS is conveyed to each of the treatment stations ST5, 
ST7, ST8 and ST10, the support shaft member 53 and the holder 57 in each 
of the treatment stations ST5, ST7, ST8 and ST10 are displaced to their 
retracted positions, and the working position of the holder 57 is shifted 
to its non-holding position. In addition, when the cam shaft CS is placed 
at a predetermined position in each of the treatment stations ST5, ST7, 
ST8 and ST10, right-hand and left-hand TIG torches 40 in each of the 
aforementioned stations are located not only at the central positions of 
the corresponding cams and 2 as seen in the direction of their width but 
also on their center lines extending through the axis line of the cam 
shaft CS in the upward/downward direction (Z-coordinate direction). 
Incidentally, the fact that the cam shaft CS is properly placed at a 
predetermined position in each of the treatment stations ST5, ST7, ST8 and 
ST10 represents the operative state that the foremost end surface of a 
journal portion 3 is held by the holder 57 while it is located at a 
reference position, and moreover, a journal portion 4 is supported by the 
support shaft member 53 via the engagement hole 4a. 
Referring to FIG. 1 and FIG. 2 again, to assure that the cam shaft CS which 
has been conveyed with the aid of each carrier 22 is properly placed in 
the above-described manner, work receiving members 18 each including a 
work receiving portion 18a are arranged at opposite sides of the pit P on 
the fore side of the support shaft member 53 as well as on the rear side 
of the holder 57. The work receiving member 18 located on the holder 57 
side is equipped with a non-contact type detecting switch 19 for detecting 
the cam shaft CS. 
As shown in FIG. 4, the torch power supply source unit 60 includes electric 
current adjusting portions 62 and 63 for properly adjusting an intensity 
of arc electric current to be fed to each of the left-hand and right-hand 
TIG torches 40. 
Additionally, the control unit 80 is essentially composed of a host 
controller 81 and four sub-controllers 82 (only one shown in FIG. 4) 
arranged corresponding to the treatment stations ST5, ST7, ST8 and ST10. 
The host controller 81 normally monitors the operative state of the 
remelting/hardening treatment line L. In detail, the host controller 81 
comprehensively controls operations of the vehicle type discriminating 
unit 13, the preheating unit 15, the remelting/hardening treatment 
apparatus M and the conveying unit 20 arranged in each of the treatment 
stations ST5, ST7, ST8 and ST10 in order that the remelting/hardening 
treatment line L is operated while maintaining an optimum state 
corresponding to, e.g., a quantity of the cam shafts CS conveyed in the 
remelting/hardening treatment line L, a type of employed vehicle and the 
present treatment state in each of the aforementioned stations. In 
addition, various kinds of data are input into the host controller 81 from 
each of the vehicle type discriminating unit 13, the preheating unit 15 
and the remelting/hardening treatment apparatus M in each of the 
aforementioned stations. 
Each of the sub-controllers 82 controllably drives the remelting/hardening 
treatment apparatus M in response to a control signal transmitted from the 
host controller 81. As shown in FIG. 4, each sub-controller 82 includes a 
microcomputer 85 composed of CPU, RAM, ROM and other components as well as 
an input/output interface 86. A control program for remelting/hardening 
treatments to be described later is previously stored in the ROM of the 
microcomputer 85. Drivers 87 and 88 for the servomotors 34 and 35 for the 
torch displacing/driving unit 30, drivers 91, 92 and 94 for solenoid 
valves 71, 72 and 74 adapted to control an intensity of hydraulic pressure 
to be supplied to the hydraulic cylinders 51 and 54 for the left-hand and 
right-hand rotational supporting units 50 and a driver 93 for the 
left-hand and right-hand servomotors 56 are electrically connected to the 
input/output interface 86. In addition, detection signals are input into 
the microcomputer 85 from the detection switch 19 and the temperature 
detector 45 via the input/output interface 86. It should be noted that the 
foregoing program for remelting/hardening treatment includes a plurality 
of processing routines each differing depending on a type of employed 
vehicle, and moreover, the control program is a program employable for 
realizing a remelting/hardening treating method to be described below 
wherein this program is previously stored in the microcomputer 85. 
Next, the present invention will be described below with respect to an 
example concerned with a method of carrying out remelting/hardening 
treatment for the suction cam 1 on the first cam portion C1 of each of the 
cam shafts CS in the first treatment station ST5 wherein one set of the 
cam shafts CS is normally composed of two cam shafts. 
First, when a cam shaft CS is conveyed to the first treatment station ST5, 
conveyance of the cam shaft CS is detected by the detecting switch 19. 
Subsequently, the cylinders 51 and 54 are driven so as to allow the rods 
51a and 54a to be displaced in the forward direction, and at the same 
time, the cylinder 51 is driven such that the cam shaft CS is firmly 
placed at a predetermined position in the foregoing station while it is 
held by the holding portion 57a of the holder 57. 
Next, the servomotor 34 is controllably driven so as to allow the torch 40 
to be displaced to a center of the cam surface 5 of the cam 1 as seen in 
the direction of its width. In addition, as the servomotor 35 is 
controllably driven, a height of the torch 40 is properly determined such 
that the torch 40 is located at a predetermined position above the center 
axis of the cam shaft CS. This positional state is illustrated in FIG. 5. 
Next, the present temperature of the cam shaft CS is measured by the 
temperature detector 45. When it has been found from such measurement that 
the measured temperature T remains within a predetermined or particular 
temperature range (e.g., 150.degree. to 400.degree. C.), the servomotor 56 
is rotationally driven so that the cam shaft CS is rotated by a 
predetermined angle (about 55 degrees) in the direction indicated by the 
arrow in FIG. 5, whereby the torch 40 is located opposite to a melting 
operation start position M1. 
Next, while the servomotor 56 is rotated at a very slow speed in the same 
direction, the torch 40 is fed with a predetermined intensity of driving 
electricity for remelting a part of the cam surface 5, and at the same 
time, the servomotor 34 is controllably driven so as to allow the torch 40 
to be reciprocatively displaced at a slow speed in the axial direction by 
a distance corresponding to the full width of the cam surface 5. Thus, a 
remelting/hardening treatment is carried out for the cam surface 5. During 
this treatment, the servomotor 35 is controllably driven such that the 
height of the torch 40 as measured from the cam surface 5 is kept 
constant. As shown in FIG. 6, the surface region ranging from the melting 
operation start position Mi to the melting operation end position M2 is 
subjected to remelting and hardening for about 40 minutes. After 
completion of the foregoing treatment, driving of the torch 40 is 
interrupted. In addition, rotation of the servomotor 34 is interrupted 
when the torch 40 reaches the position corresponding to the center of the 
width of the cam surface 5. Subsequently, rotational operation of the 
servomotor 56 is shifted to rotation at a high speed, and when the cam 
shaft CS reaches the operative state as shown in FIG. 5, driving of the 
servomotor 56 is interrupted. 
On completion of the aforementioned remelting/hardening treatment, the 
surface layer of the cam surface 5 remaining within the range from the 
melting operation start position M1 to the melting operation end position 
M2 is chilled, resulting in a metallurgical structure having excellent 
wear resistance and shock resistance in a surface layer of the cam surface 
5. 
When the above measured temperature T is not within the predetermined or 
particular range, but rather is in a range of 100.degree. 
C..ltoreq.T.ltoreq.150.degree. C., then prior to the remelting/hardening 
treatment, a preheating operation is performed on the cam surface 5 within 
a range or portion there of from melting operation end position M2 (i.e., 
a preheating operation start position) to a preheating operation end 
position M3 as shown in FIG. 7. 
When such preheating operation is performed, first, the servomotor 56 is 
controllably driven so that the cam shaft CS is rotated until the 
preheating operation start position M2 is located opposite to the torch 
40. Subsequently, rotational operation of the servomotor 56 is shifted to 
rotation at a very slow speed and the torch 40 is then fed with driving 
electricity for performing a preheating operation, the intensity of which 
corresponds to about 20 to 50% of the electricity required for a remelting 
operation. In addition, the torch 40 is reciprocatively displaced in the 
axial direction by a distance corresponding to the full width of the cam 
surface 5 by driving the servomotor 34. In this case, since the measured 
temperature or particular is slightly lower than the lower limit of the 
predetermined temperature range (150.degree. C.) for carrying out the 
remelting/hardening treatment, the preheating treatment range from the 
preheating operation start position M2 to the preheating operation end 
position M3 is limited to a narrow range corresponding to an angle of 
about 40 degrees. Thus, the entire region of the cam 1 on the cam shaft CS 
inclusive of its peripheral part is heated by such preheating to the 
predetermined or particular temperature range of 150.degree. to 
400.degree. C. necessary for performing remelting operation. It should be 
noted that the reason that the electricity is determined to have such a 
low intensity as mentioned above is to prevent the cam surface 5 from 
being made molten by the preheating operation. After completion of the 
preheating operation within the range from the preheating operation start 
position M2 to the preheating operation end position M3, driving of the 
torch 40 is interrupted. Additionally, when the torch 40 is located at a 
position corresponding to the center of the width of the cam surface 5 
driving of the servomotor 34 is interrupted, and at the same time, 
rotational operation of the servomotor 56 is shifted to rotation at a high 
speed, whereby the cam shaft CS is rotationally driven until the melting 
operation start position M1 is located opposite to the torch 40. 
Then, the above discussed remelting/hardening treatment of the cam surface 
5 within the range from the melting operation start position M1 to the 
melting operation end position M2 is carried out in the same manner as 
mentioned above. 
When the above measured temperature T is lower than 100.degree. C., first, 
i.e. prior to the remelting treatment, a preheating operation is performed 
on the cam surface 5 within a range or portion thereof from melting 
operation stop position M2 (i.e., a preheating operation start position) 
to a preheating operation end position M4 as shown in FIG. 8. 
This preheating operation is performed in the same manner as the 
aforementioned preheating operation. To this end, the intensity of driving 
electricity to be fed to the torch 40 is determined in the same manner as 
mentioned above. However, since the measured temperature T is 
substantially lower than the lower limit of the predetermined or 
particular temperature range (150.degree. C.) required for carrying out 
the remelting/hardening treatment, the range of this preheating treatment 
from the preheating operation start position M2 to the preheating 
operation end position M4 is determined to be greater, i.e. to an angle of 
about 65 degrees. Thus, the entire region of the cam 1 on the cam shaft CS 
inclusive of its peripheral part is heated by such preheating to the range 
predetermined or particular of 150.degree. to 400.degree. C. necessary for 
performing remelting. 
Subsequently, after completion of such preheating operation, 
remelting/hardening treatment for the cam surface 5 within the range from 
the melting operation start position M1 to the melting operation end 
position M2 is carried out in the same manner as mentioned above. 
In a case where the measured temperature T is lower than 150.degree. C., 
intensity of electricity required for preheating by the torch 40 may be 
adjusted depending on such measured temperature T, provided that the 
preheating range is kept constant. Alternatively, both the preheating 
range and intensity of the electricity required for the preheating 
operation may adequately be adjusted depending on the measured temperature 
T. 
FIG. 9 is a plan view which schematically illustrates the structure of a 
remelting/hardening treatment line L in accordance with a second 
embodiment of the present invention. This remelting/hardening treatment 
line L is substantially the same as that of FIG. 1 with respect to 
structure and function of each of respective stations thereof. According 
to the second embodiment of the present invention, a cam shaft receiving 
station ST21, a first preheating station ST22, a vehicle type 
discriminating station ST23, a second preheating station ST24, a first 
waiting station ST25, a first treatment station ST26, a second treatment 
station ST27, a second waiting station ST28, a third treatment station 
ST29, a fourth treatment station ST30 and a cam shaft discharging station 
ST31 are arranged one after another in such order from the left-hand side 
as seen in FIG. 9. A pit P is recessed in a floor F across the respective 
stations ST21 to ST31 while extending in the leftward/rightward direction 
as seen in FIG. 9. An opposed pair of work receiving members 10 are 
arranged peripheral to the pit P in each of the cam shaft receiving 
station ST21, the first and second waiting stations ST25 and ST28 and the 
cam shaft discharging station ST31 in the same manner as the 
remelting/hardening treatment line L in accordance with the first 
embodiment of the present invention. A vehicle type discriminating unit 13 
composed of an opposed pair of supporting mechanisms 11 and an opposed 
pair of vehicle type discriminating mechanisms 12 is arranged in the 
vehicle type discriminating station ST23. In addition, a preheating unit 
15 including an opposed pair of preheaters 14 is arranged in each of the 
first and second preheating stations ST22 and ST24. Additionally, a torch 
displacing/driving unit 30, an opposed pair of TIG torches 40 and an 
opposed pair of rotational supporting units 50 are arranged in each of the 
first treatment station ST26, the second treatment station ST27, the third 
treatment station ST29 and the fourth treatment station ST30. Also in the 
second embodiment, a remelting/hardening treatment apparatus M is 
constructed in the same manner as that in accordance with the first 
embodiment of the present invention, and moreover, exhibits the same 
functional effects as those obtained in accordance with the first 
embodiment of the present invention. 
It should of course be understood that the present invention can be applied 
to remelting/hardening treatment for various types of products other than 
the cam shafts CS, that the remelting/hardening treatment apparatus M 
which has been described above in conjunction with the first and second 
embodiments of the present invention is merely illustrative, and that the 
present invention can be applied to a remelting/hardening treatment 
methods employable by using other various types of remelting/hardening 
apparatuses without departure from the scope of the invention as defined 
by the appended claims.