Patent ID: 12202185

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described.FIG.1shows a molding line from a molten resin to a molded product in the embodiment of the present invention. A molten resin extruder10, a roller array12to pull out a strip-shape softened resin sheet “S” from the molten resin extruder10and control the temperature of the strip-shape softened resin sheet “S”, a cutting unit14to cut the strip-shape softened resin sheet “S” to a softened unit resin sheet “U” (hereinafter, referred to as a unit resin sheet “U”) which is a material for one press molded part by press-molding (in the present embodiment, as described below, one press molded part comprises a portion which becomes a pair of left and right resin fender protectors of the vehicle body as a product and a rest portion which becomes a scrap), a heating machine16to heat the unit resin sheet “U” up to a temperature suitable for press-molding with two stages, a manipulator (a robot)18to handle the unit resin sheet “U” whose temperature is controlled to the temperature suitable for press-molding by the heating machine16, and a press-molding machine20to press-mold the unit resin sheet “U” ejected from the heating machine16by the manipulator18and make the press molded part, are disposed along a molding line. Further, a manipulator22to eject the press molded part “P” which is press-molded by the press-molding machine20and a post-process line24are disposed in a downstream side of the molding line.

Although the explanation order is different from a sequence of the molding line, the press-molding machine of the unit resin sheet “U” whose temperature is controlled by the heating machine16will be described. The press-molding machine20comprises a male mold20-1and a female mold20-2. In a mold-opening state, the manipulator18holds the unit resin sheet “U” which is heated up to the temperature suitable for press-molding by the heating machine16, by a suction cup, and sets the unit resin sheet “U” to a predetermined position between the male mold20-1and the female mold20-2in the mold-opened press molding machine20. When the unit resin sheet “U” is set to the press molding machine20, the female mold20-2downwardly moves to the male mold20-1by the hydraulic cylinder20-3, the unit resin sheet “U” is shaped to the press molded part depending on the mold cavity by mold-clamping, the cooling is performed in the mold for a while, the female mold20-2upwardly moves and separates from the male mold20-1by mold-opening, the press molded part “P” is ejected from the press molding machine20by the suction cup22-1of the manipulator22and is mounted on the conveyor24-1of the post-process line24. The illustration is omitted since the post process is deviated from the main object of the present invention. In the post process line24, the press molded part “P” is conveyed by the conveyor24-1and is cooled by a cooling machine, the cooled press molded part “P” is separated to a portion which becomes a product (a pair of left and right resin fender protectors of the vehicle body in the embodiment of the present invention) and a rest portion which becomes a scrap, and the post process (chipping) for recycling to the raw materials of the strip-shape softened resin sheet “S” is performed to the portion which surrounds the product and becomes a scrap.

In the continuous molding line for extruding the strip-shape softened resin sheet “S” of the present invention, cutting from the strip-shape softened resin sheet “S” to the unit resin sheet “U” by the cutting unit14, heating the unit resin sheet “U” by the heating machine16and press-molding the heated unit resin sheet “U” by the press molding machine20and obtaining the press molded part, the cycle time “ST” is a time which is required for molding one press molded part. As the common general technical knowledge of a person skilled in the art, the cycle time “ST” is determined by the time which is required for a series of processes for mold-opening in the press molding machine20, setting the unit resin sheet “U” from the manipulator18, press-molding of the press molded part by mold-clamping, mold-opening and ejecting the press molded part by the manipulator22. However, in the resin sheet continuous pressing method, the resin temperature decreases for cutting the strip-shape softened resin sheet “S” to the unit resin sheet “U” and the temperature of the unit resin sheet “U” needs to increase up to the temperature suitable for press-molding and keep the temperature uniformity. Conventionally, since the time for increasing the temperature is needed, the cycle time is restricted by the time which is required for the heating process of the unit resin sheet “U”. In the embodiment of the present invention, shortening the heating time is possible because of improving the heating machine16. Thereby, shortening of the cycle time “ST” can be achieved. Synchronizing with this setting cycle time “ST”, the strip-shape softened resin sheet “S” is extruded from the molten resin extruder10, the strip-shape softened resin sheet “S” is cut to the unit resin sheet “U” by the cutting unit14described below, and the temperature control of the unit resin sheet “U” is performed by the heating machine16. Accordingly, in this time, the substantial retention of the continuous molten unit resin sheet “S” is not occurred and the waiting time for substantial arrival of the unit resin sheet “U” at the press-molding machine20is not occurred.

Next, one example of the particular structure of the press molded part “P” which is press-molded from the unit resin sheet “U” by the press-molding machine20in the molding line will be described.FIG.2Ais a perspective view of the press molded part “P” andFIG.3is a plan view of the press molded part “P”. The press molded part “P” is integrated with left and right fender protectors for front wheels of the vehicle by press-molding the unit resin sheet “U”. The reference numerals P1and P2denote the portions of the left and right fender protectors which are obtained from the press molded part “P” and these portions P1and P2have a high vertical wall “W”. It is understood that the embossment portions “E” which serves as pedestals of bolts for assembling to the vehicle body are disposed on the upper surface of the vertical wall.FIG.3is a plan view of the press molded part “P” and the outline shape of the portions P1and P2which become the fender protectors is well understood. The portion P3of the press molded part “P” which is ranged from the outside of the portions P1and P2which become the fender protectors to an outer circumference P′ of the press molded part “P” is removed and becomes a scrap. As described below, according to the present invention, the slits C1, C2, C3, C4and C5along the portions “W” which become the vertical walls of the product and the portions “E” which become the embossments of the product in a state of the strip-shape softened resin sheet before cutting to the unit resin sheet “U” are formed on the portion P3which becomes a scrap. By forming the slits C1, C2, C3, C4and C5on the strip-shape softened resin sheet, the inflow property of the resin material is improved at the portions “W” which become the vertical walls and the portions “E” which become the embossments (these portions become a thin thickness in the deep drawing and the like) in press-molding the unit resin sheet “U” by the press-molding machine20, the thickness of the product becomes a good uniformity and the product quality can be improved.FIG.2Bschematically shows a state that the portion P3which becomes a scrap is removed and the press molded part is separated to the left and right fender protectors as a product. InFIG.1, for convenience, the male mold20-1and the female mold20-2in the press-molding machine20are depicted by a diagrammatic sketch. The actual mold surfaces of the male mold20-1and the female mold20-2are corresponding to the shape of the press molded product ofFIGS.2A and2B.

Next, inFIG.1, the configurations of respective portions until press-molding is performed in the molding line, that is, until the temperature-controlled unit resin sheet “U” is manufactured will be described. The molten resin extruder10itself is a well-known machine and is briefly described. The molten resin extruder10comprises a hopper26for feeding resin pellets, a screw extruder28, a heater30, a gear pump32and a die (an extrusion nozzle)34. In this embodiment, the resin material is the mixed resin of polypropylene and polyethylene and the pellets of polypropylene and polyethylene which have the predetermined mixing rate are fed into the hopper26. The screw extruder28mixes the pellets and conveys the pellets to the axial direction and the pellets are molten and are mixed by heat of the heater30. The gear pump32conveys the molten and mixed resin to the die34at a constant velocity and the molten and mixed resin is extruded as the strip-shape softened resin sheet “S” from the die having an elongated rectangular cross section. The resin temperature when extruding is in a range of 190 degrees Celsius to 220 degrees Celsius in a case of the resin of the present embodiment that is composed of about 50 weight percent of polypropylene and about 50 weight percent of polyethylene.

The roller array12comprises a pair of sheet pull-out roller pair36, a temperature-controlled roller38and40. The molten resin from the die is temperature-controlled by passing through the sheet pull-out roller pair36and the temperature-controlled rollers38and40. The preferable temperature range that the cutting unit14cuts the strip-shape softened resin sheet “S” to the unit resin sheet “U” is about 115 degrees Celsius to about 135 degrees Celsius. When this temperature is too high, there exists a malfunction that the strip-shape softened resin sheet “S” becomes too soft and the cutting unit14cannot cut the strip-shape softened resin sheet “S”. In order to smoothly operate the formation of the slits by the silt forming machine50of the present invention, it is preferable that the temperature of the unit resin sheet “U” before cutting is set to a suitable temperature so that the unit resin sheet “U” before cutting does not become too soft. The roll41of a laminate film (such as the nonwoven film having a thickness in a range of about 0.5 [mm] to about 5.0 [mm]) is disposed at an upper position, the laminate film “F” from the roll41is combined with the strip-shape softened resin sheet “S” at the temperature-controlled roller38and the laminate film “F” is on the surface of the strip-shape softened resin sheet “S” at the outlet of the temperature-controlled roller38.

The cutting unit14comprises a pinch roller pair42and a cutting unit44. The cutting unit44is disposed at an outlet of the pinch roller pair42and includes a pair of a lower fixed cutter44-1and an upper moving cutter44-2. The fixed cutter44-1and the moving cutter44-2have a cutting portion whose length is longer than a total width of the strip-shape softened resin sheet “S”. In a normal state, the moving cutter44-2is in a retraction position which is upwardly separated from the fixed cutter44-1. Every time the strip-shape softened resin sheet “S” is passed with a constant length, the moving cutter44-2is instantaneously and downwardly moved to the fixed cutter44-1and is immediately and upwardly driven to return to the retraction position, the strip-shape softened resin sheet “S” is cut to the unit resin sheet “U” having a constant length, and the unit resin sheet “S” is conveyed to the heating machine16. With respect to the cutting machine16, if necessary, the readers are also referred to the description of Patent Document 1.

The slit forming machine50for forming the slits C1, C2, C3, C4and C5at the portion which become to a scrap in the molded product which is described inFIGS.2and3is disposed at the front of the pinch roller42in the cutting unit14(see also,FIGS.13A and13B). The structure of the slit forming machine50will be described below. As shown inFIG.4, the slit forming machine50comprises three cutters52in a width direction of the strip-shape softened resin sheet “S”. As described below, the three cutters52can independently move to the upward or downward direction and the width direction. In a case that the distinction is needed, the left cutter inFIG.4is represented by “A”, the center cutter inFIG.4is represented by “B” and the right cutter inFIG.4is represented by “C”. As shown inFIG.5, a cutting edge52-1of the three cutters52is disposed between a pair of rollers53which are the receiving portion of the strip-shape softened resin sheet “S” when forming the slits. As described below, when the three cutters52for forming the slits downwardly move, the sharp cutting edge52-1penetrates the strip-shape softened resin sheet “S”. As schematically shown inFIG.6, each the three cutters52is detachably installed to the lower end of the piston rod56extending from the piston55(inFIG.5) of the air cylinder54. Normally, each the three cutters52is covered by a safety cover58, and the cutting edge52-1protrudes from the safety cover when forming the slits.FIG.4shows a state that the cutter52of the center portion “B” penetrates the strip-shape softened resin sheet “S” and the cutters52of the left side “A” and the right side “C” are covered by the safety covers58. The air cylinder54urges the piston55to the upper portion ofFIG.4and each the three cutters52is housed in the safety cover58. That is, inFIG.5, the piston55upwardly moves by the air pressure introducing from the lower air pressure port54-1of the air cylinder54(an arrow “a” direction inFIG.5) and the air pressure exhausting from the upper air pressure port54-2of the air cylinder54(an arrow “b” direction inFIG.5) and a state that the cutting edge52-1is housed in the safety cover58is shown. In contrast withFIG.5, the piston55downwardly moves by the air pressure introducing from the upper air pressure port54-2of the air cylinder54(an opposite direction of the arrow “b” inFIG.5) and the air pressure exhausting from the lower air pressure port54-1of the air cylinder54(an opposite direction of the arrow “a” inFIG.5) , the cutting edge52-1protrudes from the safety cover58, and the slits can be formed on the strip-shape softened resin sheet “S”.FIG.8shows a cross-sectional shape of the cutter52at the intermediate height in the horizontal surface. In order that the cutting portion52-2which is continued to the lower cutting edge52-1is opposite to the moving direction of the strip-shape softened resin sheet “S” (an arrow “f”) and the cutter52easily penetrates the strip-shape softened resin sheet “S” for forming the slits, the cutting edge52-1has a sharp shape.

Next, the support structure of the air cylinder54will be described. As shown inFIG.5, a horizontal moving member60is fixedly disposed on the back surface of the body of the air cylinder54. The support member62is uprightly disposed on the back surface of each the three air cylinders54inFIG.4and forms a guide path62-1for guiding the horizontal movement of the horizontal moving member60. In other words, each the air cylinders54and each the cutters52can independently move in the horizontal direction. For simplification, the mechanisms60and62for the horizontal movement of the air cylinders54are depicted by a diagrammatic sketch. The guide mechanism including the commercially available linear bearings can be used in the mechanisms60and62and precise horizontal position control of the air cylinders54can be performed by light driving force.

Next, a chain-type driving mechanism for independently occurring the horizontal movement of each the air cylinders54will be described. InFIG.4, looped chains68are wound around sprocket wheel pair64and66which are located at both ends above the strip-shape softened resin sheet “S”. In order to independently move the three air cylinders54in the horizontal direction, the three looped chains are disposed. Corresponding to the respective three looped chains68, three sprocket wheel pairs64and66are also disposed. The sprocket wheels64are served as a driving side and the sprocket wheels66are served as a driven side. For simplification, one chain pitch68-1is depicted in an upper lane and a lower lane of the respective looped chains68. As well-known, one looped chain68is constituted by connecting one chain pitch68-1using a pin. For simplification, only one chain pitch68-1of the plural upper side chain pitches and one chain pitch68-1of the plural lower side chain pitches in one looped chain68are shown inFIG.5. This one chain pitch68-1is fixed to the corresponding air cylinder54and one air cylinder54which is fixed to the looped chain68can move in the horizontal direction. That is, inFIG.5, upper and lower bracket plates70and72are fixed to the outer surface of the air cylinder54which is opposite to the support member62(the front surface side) by welding or the like in a cantilever manner. One chain pitch68-1(if necessary, a few adjacent chain pitches) of one looped chain68is fixed to a portion between the bracket plates70and72by welding or the like. Thereby, a horizontal driving force can be applied to the air cylinder54by the looped chain68. As shown inFIG.9, the driving side sprocket wheel64is supported in a gear box74by an axis64-1, and the rotation of the rotational axis76-1of the servo motor76can be transmitted to the driving side sprocket wheel64via a pair of bevel gears78and80. The rotation of the rotational axis76-1of the servo motor76is transmitted to the looped chain68via the driving side sprocket wheel64, the air cylinder54in which the horizontal moving member60is guided to the support member62horizontally moves in a width direction of the strip-shape softened resin sheet “S” and the cutting edge52-1of the cutter52can accurately be controlled to the width direction position in the strip-shape softened resin sheet “S”. The three servo motors76for independently and horizontally driving the three looped chains68are disposed. Corresponding to the reference numerals “A”, “B” and “C” in the air cylinders54ofFIG.4, the servo motors76are represented by the reference numerals “A”, “B” and “C”. Thus, the three air cylinder54A,54B and54C can independently and horizontally move in the width direction of the strip-shape softened resin sheet “S” by the servo motors76A,76B and76C. The precise position control (the servo control) in the width direction of the strip-shape softened resin sheet “S” in the cutting edge of the cutter52can be performed and the cutting edge of the cutter52can form the slits on the strip-shape softened resin sheet “S”. That is, inFIG.5, by the air pressure introducing from the upper air pressure port54-2of the air cylinder54(the opposite direction of the arrow “b” inFIG.5) and the air pressure exhausting from the lower air pressure port54-1of the air cylinder54(the opposite direction of the arrow “a” inFIG.5), inFIG.6, the piston rod56is extended in the downward direction, the cutting edge of the cutter52downwardly moves to the strip-shape softened resin sheet “S” and the sharp cutting edge moves in the arrow “f” direction and penetrates the strip-shape softened resin sheet “S”. Since the cutter52which continues from the cutting edge52-1to the cutting portion52-2is directed to the moving direction “f” (see also,FIG.8), as shown inFIG.7, the cutter52moves on the strip-shape softened resin sheet “S” and forms the slit “Ca” parallel to the moving direction on the strip-shape softened resin sheet “S”. The lateral direction movement of the cutter52by the rotation of the rotational axis76-1of the servo motor76changes the slit direction in accordance with the movement of the strip-shape softened resin sheet “S”. When the cutter52moves in the left direction, the slant slit shown by the line “Cb” inFIG.7is formed. When forming the slant slit “Cb”, the cutting portion52-2of the cutter52is slightly slant from the facing position against the cutting direction (the moving direction). Since the strip-shape softened resin sheet “S” which is a cutting object becomes softened by warming, the strip-shape softened resin sheet “S” does not substantially become the cutting resistance of the cutter52and the smooth cutting can be performed.

InFIG.1, the heating machine16which controls the temperature suitable for press-molding the unit resin sheet “U” obtained by the cutting unit14comprises the first heating furnace84and the second heating furnace86which are continuously disposed in the conveying direction of the unit resin sheet “U” in the present embodiment. As shown inFIG.10, the first heating furnace84comprises a heating chamber84-1, a conveyor84-2which is disposed in the heating chamber84-1and conveys the unit resin sheet “U”, a series of the infrared heaters84-3which are opposite to the conveyor84-2and are disposed on the upper surface of the heating chamber84-1, and a series of the infrared heaters84-4which are disposed on the lower surface of the heating chamber84-1. The conveyor84-2is wound between the driving pulley84-2aand the driven pulley84-2band the rotational axis of the driving pulley84-2ais connected to the driving motor84-5which is schematically shown. The wavelengths of the radiation light of the infrared heaters (the ceramic heater or the like)84-3and84-4are in a far-infrared region, for example, in a range of 10 [μm] to 20 [μm]. As described below, the unit resin sheet “U” is continuously conveyed on this conveyor84-2. In this time, the conveying velocity of the unit resin sheet “U” by the conveyor84-2is set to, for example, 1.0 [m/s]. When the unit resin sheet “U” which is continuously heated by relatively low energy radiation in the far-infrared region is conveyed from the first heating furnace to the second heating furnace, the temperature of the unit resin sheet “U” is controlled in a range of 125 degrees Celsius to 135 degrees Celsius. Performing the previous process of forming the slits and cutting the strip-shape softened resin sheet “S” to the unit resin sheet “U”, when the unit resin sheet “U” enters the first furnace84, the temperature of the unit resin sheet “U” is in a range of 115 degrees Celsius to 125 degrees Celsius. By the heating process which is moderately occurred by the infrared ray having the relatively long wavelengths in the far-infrared region using the infrared heaters84-3and84-4in the first heating furnace84in which the unit resin sheet “U” is continuously conveyed, the temperature of the unit resin sheet “U” is controlled in a range of 125 degrees Celsius to 135 degrees Celsius. That is, the main object of the first heating furnace84is to heat the unit resin sheet “U”, and the additive object is to keep the uniform temperature of the unit resin sheet “U” over the entire surface before heating the unit resin sheet “U” in the second heating furnace86.

The unit resin sheet “U” which is heated by the first heating furnace84is conveyed to the second heating furnace86. The second heating furnace86comprises a heating chamber86-1, a conveyor86-2which is disposed in the heating chamber86-1and conveys the unit resin sheet “U”, a series of the infrared heaters86-3which are opposite to the conveyor86-2and are disposed on the upper surface of the heating chamber86-1, and a series of the infrared heaters86-4which are disposed on the lower surface of the heating chamber86-1. The wavelengths of the radiation light of the respective infrared heaters (the ceramic heater or the like)86-3and86-4are in a middle-infrared region, for example, in a range of 5 [μm] to 10 [μm] . The conveyor86-2is wound between the driving pulley86-2aand the driven pulley86-2band the rotational axis of the driving pulley86-2ais connected to the driving motor86-5which is schematically shown. The heating of the unit resin sheet “U” by the infrared heaters86-3and86-4in the second heating furnace86is performed in a state that the unit resin sheet “U” is fixed. The unit resin sheet “U” is rapidly heated by the infrared ray having the relatively short wavelengths in the middle-infrared region and the temperature of the unit resin sheet “U” after heating is controlled in a range of 130 degrees Celsius to 160 degrees Celsius. This controlled temperature is appropriately selected depending on the molded part which is molded by press-molding. The heating in the middle-infrared region in a state that the unit resin sheet “U” is stopped is performed in the extremely short time, for example 15 [sec], the desired temperature of the unit resin sheet “U” can be obtained and this heating can contribute to improve the product efficiency of the resin sheet continuous pressing method according to the present invention. In the configuration of the heating furnace in the conventional resin sheet continuous pressing method by the applicant, the heating method by the infrared ray in the far-infrared region is used for heating the unit resin sheet “U”. In this case, the heating time is needed for about 60 [sec] in the unit resin sheet “U” whose area is about 1500 [mm] x about 2000 [mm] and whose thickness is 1.6 [mm]. The time which is required for manufacturing one molded product by the resin sheet continuous pressing method (=the cycle time “ST”) is limited to the heating time in the heating furnace. In the new structure of the heating machine16according to the present invention, the cycle time “ST” can be set to 20 [sec] and the productivity is remarkably improved.

The conveyance of the unit resin sheet “U” from the cutting unit14to the press-molding machine20via the heating machine16, the transportation between the first heating furnace84and the second heating furnace86and the transportation operation to the press-molding machine20which is disposed at the downstream side will be described. The unit resin sheet “U” obtained from the cutting unit14is conveyed to the first heating furnace84. The unit resin sheet “U” is continuously heated in the first heating furnace84. Basically, the conveyor84-2continuously moves with a constant low velocity. In order to rapidly move the conveyor84-2for the carrying-in operation of the unit resin sheet “U”, the rotational velocity of the driving motor84-6used in the conveyor84-2can rapidly be increased. Basically, the rapid heating of the unit resin sheet “U” in the second heating furnace86is performed in a state that the conveyor86-2is stopped. In order to carry-in the unit resin sheet “U” from the first heating furnace84and transport the unit resin sheet “U” to the press-molding machine20which is disposed at the downstream side, the driving motor86-5can rapidly rotate. The rapid conveying velocity of the conveyor84-2in the first heating furnace84is the same as that of the conveyor86-2for the second heating, for example, 10 [m/s].

FIGS.11A,11B,11C,11D,11E,12A,12B,12C and12Dschematically show the cooperative operation of the process for transporting the unit resin sheet “U” from the cutting machine44to the press-molding machine20via the first heating furnace84and the second heating furnace86.FIG.11Ashows a state that the tip of the strip-shape softened resin sheet “S” is conveyed to the first heating furnace84. In this time, the conveying velocity of the conveyor84-2is the same as that of the strip-shape softened resin sheet “S” (the rotational velocity of the driving motor84-5is Low). The rapid heating of the unit resin sheet “U” is performed on the stopped conveyor86-2in the second heating furnace86.

FIG.11Bshows a state that the strip-shape softened resin sheet “S” is further conveyed in the first heating furnace84by the conveyor84-2and the unit resin sheet “U” is conveyed on the conveyor84-2with the low velocity. The rapid heating of the unit resin sheet “U” is continued on the stopped conveyor86-2in the second heating furnace86.

FIG.11Cshows the cutting of the strip-shape softened resin sheet “S” by the cutting machine44(at a timing tcofFIG.12A) and the cutting machine44cuts the strip-shape softened resin sheet “S” to the unit resin sheet “U”. At the timing t1ofFIG.12Bin which the time is slightly elapsed after cutting (this time is measured by the timer which is initiated at the cutting time tc), the conveyor84-2of the first heating furnace84switches from the low velocity driving (the rotational velocity of the driving motor84-5=Low) to the high velocity driving (the rotational velocity of the driving motor84-5=High) for a moment (the extremely short time, for example, 0.5 [sec]), as shown inFIG.11D, the unit resin sheet “U” on the conveyor84-2is rapidly conveyed to the middle position of the first heating furnace84. At this timing (the timing t2inFIG.12B(this timing is measured by the above timer)), the conveyor84-2is returned from the high velocity driving (the rotational velocity of the driving motor84-5=High) to the normal low velocity driving (the rotational velocity of the driving motor84-5=Low). In this way, the unit resin sheet “U” is gradually heated in the first heating furnace84under the low velocity movement and is rapidly heated in the second heating furnace86under the stopping state.

At the timing t3in which the required heating time in the second heating furnace86is measured by the timer (FIG.12C), the driving motor86-5of the conveyor86-2in the second heating furnace86switches from the stopping state to the high velocity driving (the rotational velocity=High). As shown by the arrow “m”, the stopped unit resin sheet“U” on the conveyor86-2begins to be transported to the conveyor18-2of the manipulator18for transporting to the press-molding machine. The conveyor18-2begins to rotate with the high conveying velocity which is the same as the conveying velocity of the conveyor86-2at the timing t4which is slightly delayed from the timing t3(FIG.12D).

At the timing in which the conveyor86-2of the second heating furnace86begins to convey the unit resin sheet “U” with the high velocity, as shown inFIG.11E, the upstream end of the unit resin sheet “U” which is placed on the conveyor84-2in the first heating furnace84inFIG.11Dis left from the conveyor84-2, the downstream end of the unit resin sheet “U” has already been placed on the conveyor86-2in the second heating furnace86and the unit resin sheet “U” is conveyed with the high velocity. At the timing t5, the driving motor86-5of the conveyor86-2switches from the high velocity driving (the rotational velocity=High) to the stopped state. As shown inFIG.11A, the unit resin sheet “U” which is transported to the conveyor86-2is stopped at the middle position of the second heating furnace86and the heating to the unit resin sheet “U” at the stopped state in the second heating furnace86is started.

The unit resin sheet “U” which is transported to the conveyor18-2of the manipulator18arrives at the specified position of the conveyor18-2at the timing t6(inFIG.12D), is sucked and held on the suction cup18-1of the manipulator18(inFIG.1) (see also,FIG.11A) and is press-molded by the press-molding machine20. A sensor88for detecting the arrival to the specified position of the conveyor18-2of the manipulator18is disposed (see,FIG.11E). (The sensor88is necessary for transporting the unit resin sheet “U” to the desired position of the press-molding machine20by the manipulator18.) When the sensor88detects the arrival of the unit resin sheet “U” to the specified position of the conveyor18-2, the timer is cleared and then the operations fromFIG.11AtoFIG.11Eare repeated. In the operations fromFIG.12AtoFIG.12D, the timer is initiated by detecting the cutting of the strip-shape softened resin sheet “S”. (The sensor (not shown) which detects the completion of the cutting operation of the strip-shape softened resin sheet “S” is disposed for initiating the timer.) The timings t1to t5are measured by the timer and the timer is cleared when the sensor88detects that the unit resin sheet “U” has been placed at the specified position on the conveyor18-2. Since the initiating (the timing tc) and the stopping (the timing t6) of the timer are determined by the sensor, the conveying operation of the unit resin sheet “U” in the first heating furnace84and the second heating furnace86shown inFIGS.12A to12Dcan surely be realized without stepping-out.

InFIGS.12A,12B,12C and12D, the time between the cutting timing tcfrom the strip-shape softened resin sheet “S” to the unit resin sheet “U” and the next cutting timing tcis set to the cycle time “ST” of the press molded part molding line in the present embodiment. A series of the press-molding processes of the unit resin sheet in the press-molding machine are performed within the cycle time “ST”. The stopping time “AT” of the second heating furnace86in the cycle time “ST” becomes the rapid heating time in a stopping state of the unit resin sheet “U” in the second heating furnace86.

In the present embodiment, the heating machine16divides into the first heating furnace84and the second heating furnace86. The above configuration can achieve the following features. In order to form the slits and cut the unit resin sheet “U”, the resin temperature is lowered. In the first heating furnace84, by moderately and continuously heating the unit resin sheet “U” in the cycle time, the resin temperature can increase up to the desired temperature and the overall unit resin sheet “U” can uniformly be heated and be kept to the desired temperature. Then, in the second heating furnace86, when the unit resin sheet “U” is the stopped state, the unit resin sheet “U” is rapidly heated by using the middle-infrared ray within the short time and can arrive at the optimal resin temperature for the press-molding process. Accordingly, the second heating furnace86can perform the required heating within a short time with a margin to the cycle time and the heating time can be shortened to 15 [sec] (“AT” inFIG.12C). In a case of the conventional heating furnace, the cycle time of the unit resin sheet “U” whose area is 1500 [mm]×2000 [mm] and whose thickness is 1.6 [mm] is limited to about 60 [sec] because of the restriction of the heating time. In the present embodiment according to the present invention, the cycle time can be shortened to about 20 [sec]. That is, the heating method of the present embodiment according to the present invention can realize that the production speed is three times higher than that of the prior art.

Next, the molding operation of the press molded part “P” in the press-molding machine20will be described. The unit resin sheet “U” which is heated by the first heating furnace84and the second heating furnace86in the heating machine16and increases the temperature up to the optimal temperature for press-molding is mounted on the male mold20-1of the mold-opened press-molding machine20. The female mold20-2moves downward by the hydraulic pressure cylinder20-3, and then the unit resin sheet “U” is molded to the shape of the cavity consisted by the male mold20-1and the female mold20-2. In the present embodiment, the molded part “P” which is integrated with the left and right fender protectors for front wheels of the vehicle by press-molding the unit resin sheet “U” is obtained. After mold-opening, the molded part “P” is ejected by the manipulator22and is conveyed to the conveyor24-1of the process line24. A series of the processes for conveying the unit resin sheet “U” to the mold, mold-clamping, mold-opening and ejecting the press molded part are performed within the cycle time, related toFIGS.12A to12D.

The molding operation of the present invention in the press-molding machine20will be described in detail. When press-molding, it is necessary that the unit resin sheet “U” smoothly extends in accordance with the mold shape. As shown inFIG.2A, in the present embodiment, the molded product “P” has the plural high vertical walls “W” and the plural embossment portions “E”. When the smooth extension of the resin is prevented at these portions, the concern for generating the local thin portions is existed. In the present invention, the slits C1, C2, C3, C4and C5are formed at the portion P3of the continuous resin sheet “S” in which the material therein is out of the range of the product (the fender protectors P1and P2in a case of the present embodiment) when press-molding the unit resin sheet “U” after cutting the continuous resin sheet “S” and becomes a scrap so that the resin is smoothly extended in the mold when press-molding. That is,FIG.13Ashows a state that the slits C1, C2, C3, C4and C5are formed on the strip-shape softened resin sheet “S” by the slit forming machine50. The portions of the fender protectors P1and P2which become the product in the molded part which is molded by the press-molding machine20are shown by imaginary lines inFIG.13A. The slits C1, C2, C3, C4and C5are formed at the portion in which the material therein is out of the range of the fender protectors P1and P2in the molded part which is molded by the press-molding machine20and becomes a scrap, and the positions of the slits C1, C2, C3, C4and C5are formed along the portions of the vertical walls and the embossment portions in which there exists a problem that the inflow property of the material of the fender protectors P1and P2which is the product in the molded part which is molded by the press-molding machine20is insufficient. As described in the explanation ofFIG.4, the slit forming machine50has three cutters52which can independently control in the upward, the downward and the width directions and are named as “A”, “B” and “C”. In the present embodiment, it is understood that the slit C5is formed by the cutter52which is positioned at “A” inFIG.4, the slits C1, C2and C3are processed by the cutter52which is positioned at “B” inFIG.4and the slit C4is formed by the cutter52is formed by the cutter52which is positioned at “C” inFIG.4. After the slits C1, C2, C3, C4and C5are formed by the slit forming machine50, the strip-shape softened resin sheet “S” is cut along a front end edge e1and a rear end edge e2in the width direction by the cutting machine44. As shown inFIG.13B, the unit resin sheet “U” that the slits C1, C2, C3, C4and C5are formed prior to press-molding the molded part “P” by the press-molding machine20is formed.

The function of the slits C1, C2, C3, C4and C5Will be described when the molded part “P” is press-molded by the press-molding machine20. The resin is largely extended at the portions of the vertical walls “W” in the press molded part ofFIG.2A. Since the slits C3and C4are formed along the portions in which the material therein is proximate to the vertical walls “W” and becomes a scrap, the force that the slits C3and C4are opened in press-molding is applied to the part to be molded (FIG.2Aschematically shows a state that the slits C1, C2, C3, C4and C5are opened in press-molding). The inflow property of the resin at the portions in which the vertical walls “W” are molded in press-molding is improved and the needed thickness at the portions of the vertical walls “W” after press-molding can surely be obtained.FIGS.14A and14Bare a cross-sectional view schematically showing the portion of the vertical wall “W”. In a case that the slits C3and C4are not formed, the smooth inflow of the resin at the portions of the vertical walls “W” is prevented and the thickness δAis thinner than the desired value. In the present invention, since the smooth extension of the resin can be obtained by forming the slits C3and C4, the thickness δBafter press-molding which is equal to the desired value can surely be obtained. In the molded parts of the embossment portions “E” inFIG.2A, since the expanding force is applied to the part to be molded at the slits C1, C2and C3which are disposed in the middle portion, the inflow property of the resin to the mold cavity is improved and the desired thickness in the embossment portions “E” can be obtained.

EXPLANATION OF REFERENCE NUMERALS

10molten resin extruder

14cutting unit

16heating machine

20press molding machine

20-1male mold

20-2female mold

24post-process line

26hopper for feeding resin pellets

34die

44cutting machine

44-1fixed cutter

44-2moving cutter

50slit forming machine

52cutter

54air cylinder

54-1lower air pressure port

54-2upper air pressure port

55piston

60horizontal moving member of air cylinder

62support member of air cylinder

64,66sprocket wheel

68looped chain

68-1chain pitch

70,72bracket

76servo motor (A, B and C)

84first heating furnace

84-1heating chamber of first heating furnace

84-2conveyor of first heating furnace

84-3,84-4infrared heater of first heating furnace

84-5driving motor of conveyor of first heating furnace

86second heating furnace

86-1heating chamber of second heating furnace

86-2conveyor of second heating furnace

86-3,86-4infrared heater of second heating furnace

86-5driving motor of conveyor of second heating furnace

C1, C2, C3, C4, C5slits

P press molded part

P1, P2portions which become fender protectors of press molded part

P3portion which becomes a scrap of press molded part

W vertical wall of press molded part

E embossment portion of press molded part

S strip-shape softened resin sheet

ST cycle time

U unit resin sheet