Patent Publication Number: US-2022212383-A1

Title: Manufacturing method and injection molding system

Description:
CROSS-REFERENCE to RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application 62/849,693, which was filed on May 17, 2019. 
    
    
     FIELD 
     The present disclosure relates to an injection molding system. 
     BACKGROUND 
     Manufacturing of molded parts by an injection molding machine includes injecting a resin into a mold after clamping the mold, pressing the resin into the mold at a high pressure in order to compensate for a volume decrease due to solidification of the resin, keeping the molded part in the mold until the resin solidifies, and ejecting the molded part from the mold. 
     In the above-described molding approach, a method that uses two molds with one injection molding machine in order to enhance productivity has been proposed. For example, US 2018/0009146/Japanese patent publication No. 2018-001738/VN20160002505 are seen to discuss a system in which conveying devices  3 A and  3 B are arranged on both sides of an injection molding machine  2 . In this system, molded parts are manufactured while alternating a plurality of molds by the conveying devices  3 A and  3 B for the one injection molding machine  2 .  FIGS. 1-4  illustrate an injection molding system of US 2018/0009146/Japanese patent publication No. 2018-001738/VN20160002505. 
     In this system, cooling of the molds  100 A or  100 B is performed on the conveying machines  3 A or  3 B outside of the injection molding machine  2 . During cooling of one of the molds  100 A/ 100 B, each process of molded part ejection→clamping→injection/dwelling is performed by the injection molding machine  2  for the other mold  100 A/ 100 B. Since opening and molded part ejection are performed by the injection molding machine  2 , the conveying machines  3 A and  3 B do not need a function for opening and a function for molded part ejection. 
     This enables manufacture of the molded part P while alternating the plurality of the molds by the one injection molding machine  2 . This can reduce the overall cost of the system. 
     If the time required for all processes from the start of the mold replacement process, to the other mold ejecting process, injection process, and dwelling process, and up until completion of the mold replacement process once again fits into the time required for cooling one of the molds, then productivity compared to normal molding is improved by a maximum of two times. That is, in addition to suppressing cost increases, there is the merit that it is possible to realize high productivity. 
     A compression molding technique is known. In this technique, the mold is slightly opened in advance to an injection molding. After the resin is injected into the mold, the mold is closed and the resin is compressed. According to the technique, uniform pressure can be applied, which enables production of molded parts with less warpage than standard injection molding techniques. 
     What is needed is an ability to perform compression molding while alternating (changing) multiple molds. 
     SUMMARY 
     A method for manufacturing a molded part with an injection molding machine and a conveying apparatus while changing between multiple molds, the method comprising conveying a first mold to a molding operation position in the injection molding machine, securing the first mold at the molding operation position with a platen, fixing the platen to the first mold, opening the first mold, ejecting a molded part from the first mold, placing the first mold into a state where the first mold is slightly opened, injecting a molding material into the first mold, applying pressure to the first mold by closing the slight opening of the first mold, releasing the platen from the first mold, conveying the first mold from the molding operation position to the conveying apparatus, and cooling the first mold on the conveying apparatus. 
     This and other embodiments, features, and advantages of the present disclosure will become apparent upon reading the following detailed description of exemplary embodiments of the present disclosure, when taken in conjunction with the appended drawings, and provided claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an injection molding system. 
         FIG. 2  is a side view of the injection molding machine. 
         FIG. 3  is an end view of a fixed platen, and a figure viewing from the arrow direction of the I-I line in  FIG. 2 . 
         FIG. 4  is a partial perspective view illustrating the configuration of a periphery of the molding operation position. 
         FIG. 5  illustrates flowcharts of a standard molding process and a compression molding process. 
         FIG. 6  is a flowchart illustrating an example of processing of a molding operation while alternating molds. 
         FIGS. 7A and 7B  illustrate a length of a gap between a mold and a platen. 
     
    
    
     Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject disclosure will now be described in detail with reference to the figures, it is done so in connection with the illustrative exemplary embodiments. It is intended that changes and modifications can be made to the described exemplary embodiments without departing from the true scope and spirit of the subject disclosure as defined by the appended claims. 
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present disclosure has several embodiments and relies on patents, patent applications and other references for details known to those of the art. Therefore, when a patent, patent application, or other reference is cited or repeated herein, it should be understood that it is incorporated by reference in its entirety for all purposes as well as for the proposition that is recited. 
     With reference to the drawings, the arrow symbols X and Y in each Figure indicate horizontal directions that are orthogonal to each other, and the arrow symbol Z indicates a vertical (upright) direction with respect to the ground. 
       FIGS. 1-4  illustrate injection molding system  1  of US 2018/0009146/Japanese patent publication No. 2018-001738/VN20160002505 and are being provided herein for information/description purposes only. 
     The injection molding system  1  includes an injection molding machine  2 , conveying machines  3 A and  3 B, and a control apparatus  4 . The injection molding system  1  manufactures a molded part while alternating a plurality of molds using the conveying machines  3 A and  3 B for the one injection molding machine  2 . Two molds,  100 A and  100 B are used. 
     The mold  100 A/ 100 B is a pair of a fixed mold  101  and a movable mold  102 , which is opened/closed in relation to the fixed mold  101 . The molded part is molded by injecting a molten resin into a cavity formed between the fixed mold  101  and the movable mold  102 . Clamping plates  101   a  and  102   a  are respectively fixed to the fixed mold  101  and the movable mold  102 . The clamping plates  101   a  and  102   a  are used to lock the mold  100 A/ 100 B to a molding operation position  11  (mold clamping position) of the injection molding machine. 
     For the mold  100 A/ 100 B, a self-closing unit  103  is provided for maintaining a closed state between the fixed mold  101  and the movable mold  102 . The self-closing unit  103  enables preventing the mold  100 A/ 100 B from opening after unloading the mold  100 A/ 100 B from the injection molding machine  2 . The self-closing unit  103  maintains the mold  100 A/ 100 B in a closed state using a magnetic force. The self-closing unit  103  located at a plurality of locations along opposing surfaces of the fixed mold  101  and the movable mold  102 . The self-closing unit  103  is a combination of an element on the side of the fixed mold  101  and an element on the side of the movable mold  102 . For the self-closing unit  103 , typically two or more pair are installed for one of the molds  100 A and  100 B. 
     A conveying machine  3 A loads and unloads the mold  100 A onto/from the molding operation position  11  of the injection molding machine  2 . A conveying machine  3 B loads and unloads the mold  100 B onto/from the molding operation position  11 . The conveying machine  3 A, the injection molding machine  2 , and the conveying machine  3 B are arranged to be lined up in this order in the X-axis direction. In other words, the conveying machine  3 A and the conveying machine  3 B are arranged laterally with respect to the injection molding machine  2  to sandwich the injection molding machine  2  in the X-axis direction. The conveying machines  3 A and  3 B are arranged to face each other, and the conveying machine  3 A is arranged on one side laterally of the injection molding machine  2 , and the conveying machine  3 B is arranged on the other side respectively adjacent. The molding operation position  11  is positioned between the conveying machine  3 A and the conveying machine  3 B. The conveying machines  3 A and  3 B respectively include a frame  30 , a conveyance unit  31 , a plurality of rollers  32 , and a plurality of rollers  33 . 
     The frame  30  is a skeleton of the conveying machine  3 A and  3 B, and supports the conveyance unit  31 , and the pluralities of rollers  32  and  33 . The conveyance unit  31  is an apparatus that moves the mold  100 A/ 100 B back and forth in the X-axis direction, and that removes and inserts the mold  100 A/ 100 B in relation to the molding operation position  11 . 
     The conveyance unit  31  is an electrically driven cylinder with a motor as a driving source, and includes a rod that moves forward/backward in relation to the cylinder. The cylinder is fixed to the frame  30 , and the fixed mold  101  is fixed to the edge portion of the rod. For the conveyance unit  31  both a fluid actuator and an electric actuator can be used, where the electric actuator can provide better precision of control of the position or the speed when conveying the mold  100 A/ 100 B. The fluid actuator can be an oil hydraulic cylinder, or an air cylinder, for example. The electric actuator can, in addition to an electrically driven cylinder, be a rack-and-pinion mechanism with a motor as the driving source, a ball screw mechanism with a motor as the driving source, or the like. 
     The conveyance unit  31  is arranged independently for each of the conveying machines  3 A and  3 B. However, a common support member that supports the molds  100 A and  100 B can be used, and a single common conveyance unit  31  can be arranged for this support member. A case where the conveyance unit  31  is arranged independently for each of the conveying machines  3 A and  3 B enables handling cases where a movement strokes differ between the mold  100 A and the mold  100 B when conveying. For example, a case in which molds cannot be conveyed simultaneously since the widths of the molds (the width in the X direction) differ or the thickness of the molds (the width in the Y direction) differ. 
     The plurality rollers  32  configure a row of rollers arranged in the X-axis direction, where two rows are configured separated in the Y-axis direction. The plurality of rollers  32  rotate around the axis of revolution in the Z-axis direction, and guide movement in the X-axis direction of the mold  100 A/ 100 B contacting the side surfaces of the mold  100 A/ 100 B (the side surfaces of the clamping plates  101   a  and  102   a ) and supporting the mold  100 A/ 100 B from the side. The plurality rollers  33  configure a row of rollers arranged in the X-axis direction, where two rows are configured separated in the Y-axis direction. The plurality of rollers  33  rotate around the axis of revolution in the Y direction, and cause movement in the X direction of the mold  100 A/ 100 B to be smooth, supporting the bottom surfaces of the mold  100 A/ 100 B (the bottom surfaces of the clamping plates  101   a  and  102   a ) and supporting the mold  100 A/ 100 B from below. 
     The control apparatus  4  includes a controller  41  for controlling the injection molding machine  2 , a controller  42 A for controlling the conveying machine  3 A, and a controller  42 B for controlling the conveying machine  3 B. Each of the controllers  41 ,  42 A and  42 B includes, for example, a processor such as a CPU, a RAM, a ROM, a storage device such as a hard disk, and interfaces connected to sensors or actuators (not illustrated). The processor executes programs stored in the storage device. An example of a program (control) that the controller  41  executes is described below. The controller  41  is communicably connected with the controllers  42 A and  42 B, and provides instructions related to the conveyance of the mold  100 A/ 100 B to the controllers  42 A and  42 B. The controllers  42 A and  42 B, if loading and unloading of the mold  100 A/ 100 B terminates, transmit a signal for operation completion to the controller  41 . In addition, the controllers  42 A and  42 B transmit an emergency stop signal at a time of an abnormal occurrence to the controller  41 . 
     A controller is arranged for each of the injection molding machine  2 , the conveying machine  3 A, and the conveying machine  3 B, but one controller can control all three machines. The conveying machine  3 A and the conveying machine  3 B can be controlled by a single controller for more reliable and collaborative operation. 
       FIG. 2  illustrates a side view of the injection molding machine  2 .  FIG. 3  illustrates an end view of a fixed platen  61 , and a figure viewing from the arrow direction of the I-I line in  FIG. 2 .  FIG. 4  illustrates a partial perspective view for describing the configuration of a periphery of the molding operation position  11 . 
     With reference to  FIG. 1  and  FIG. 2 , the injection molding machine  2  includes an injecting apparatus  5 , a clamping apparatus  6 , and a take-out robot  7  for ejecting a molded part. The injecting apparatus  5  and the clamping apparatus  6  are arranged on a frame  10  in the Y-axis direction. 
     The injecting apparatus  5  includes an injection cylinder  51  that is arranged to extend in the Y-axis direction. The injection cylinder  51  includes a heating device (not illustrated) such as a band heater, and melts a resin introduced from a hopper  53 . A screw  51   a  is integrated into the injection cylinder  51 , and by rotation of the screw  51   a,  plasticizing and measuring the resin introduced into the injection cylinder  51  are performed, and by movement in the axial direction (Y-axis direction) of the screw  51   a,  it is possible to inject a molten resin from an injection nozzle  52 . 
     In  FIG. 2 , an example of a shut-off nozzle as the nozzle  52  is illustrated. For an opening/closing mechanism  56  of  FIG. 2 , a pin  56   a  for opening/closing the discharge port  52   a  is arranged. The pin  56   a  is connected with an actuator (a cylinder)  56   c  via a link  56   b,  and by the operation of the actuator  56   c  the discharge port  52   a  is opened and closed. 
     The injection cylinder  51  is supported by a driving unit  54 . In the driving unit  54 , a motor for plasticizing and measuring the resin by rotationally drive the screw  51   a,  and a motor for driving the screw  51   a  to move forward/backward in the axial direction are arranged. The driving unit  54  can move forward/backward in the Y-axis direction along a rail  12  on the frame  10 , and in the driving unit  54 , an actuator (for example, an electrically driven cylinder)  55  for causing the injecting apparatus  5  to move forward/backward in the Y-axis direction is arranged. 
     The clamping apparatus  6  performs a clamping and opening and closing of the molds  100 A/ 100 B. In the clamping apparatus  6 , the following are arranged in order in the Y-axis direction: the fixed platen  61 , a movable platen  62 , and a movable platen  63 . Through platens  61  to  63 , a plurality of tie-bars  64  pass. Each of the tie-bars  64  is an axis that extends in the Y-axis direction, one end of which is fixed to the fixed platen  61 . Each of the tie-bars  64  is inserted into a respective through hole formed in the movable platen  62 . The other end of each of the tie-bars  64  is fixed to the movable platen  63  through an adjusting mechanism  67 . The movable platens  62  and  63  can move in the Y-axis direction along a rail  13  on the frame  10 , and the fixed platen  61  is fixed to the frame  10 . 
     A toggle mechanism  65  is arranged between the movable platen  62  and the movable platen  63 . The toggle mechanism  65  causes the movable platen  62  to move forward/backward in the Y-axis direction in relation to the movable platen  63  (in other words, in relation to the fixed platen  61 ). The toggle mechanism  65  includes links  65   a  to  65   c.  The link  65   a  is connected rotatably to the movable platen  62 . The link  65   b  is pivotably connected to the movable platen  63 . The link  65   a  and the link  65   b  are pivotably connected to each other. The link  65   c  and the link  65   b  are pivotably connected to each other. The link  65   c  is pivotably connected to an arm  66   c.    
     The arm  66   c  is fixed on a ball nut  66   b.  The ball nut  66   b  engages a ball screw shaft  66   a  that extends in the Y-axis direction, and moves forward/backward in the Y-axis direction by rotation of the ball screw shaft  66   a.  The ball screw shaft  66   a  is supported such that it is free to rotate by the movable platen  63 , and a motor  66  is supported by the movable platen  63 . The motor  66  rotationally drives the ball screw shaft  66   a  while the rotation amount of the motor  66  is detected. Driving the motor  66  while detecting the rotation amount of the motor  66  enables clamping, opening, and closing of the mold  100 A/ 100 B. 
     The injection molding machine  2  includes sensors  68  for measuring a clamping force, where each sensor  68  is, for example, a strain gauge provided on the tie-bar  64 , and calculates a clamping force by detecting a distortion of the tie-bar  64 . 
     The adjusting mechanism  67  includes nuts  67   b  supported to freely rotate on the movable platen  63 , motors  67   a  as driving sources, and transfer mechanisms for transferring the driving force of the motors  67   a  to the nuts  67   b.  Each of the tie-bars  64  passes through a hole formed in the movable platen  63 , and engages with the nut  67   b.  By causing the nuts  67   b  to rotate, the engagement positions in the Y-axis direction between the nuts  67   b  and the tie-bars  64  change. That is, the position at which the movable platen  63  is fixed in relation to the tie-bar  64  changes. With this, it is possible to cause a space between the movable platen  63  and the fixed platen  61  to change, and thereby it is possible to adjust a clamping force or the like. 
     The molding operation position  11  is a region between the fixed platen  61  and the movable platen  62 . 
     The mold  100 A/ 100 B introduced into the molding operation position  11  are sandwiched between the fixed platen  61  and the movable platen  62  and thereby clamped. Opening and closing in based on movement of the movable mold  102  by movement of the movable platen  62  is performed. 
       FIG. 3  illustrates an opening portion  61   a  in a central portion of the fixed platen  61  through which the nozzle  52  moves forward/backward. To the surface on the side of the movable platen  62  (called an inner surface) of the fixed platen  61  a plurality of rollers BR are supported such that they are free to rotate. The plurality of rollers BR rotate around the axis of revolution in the Y-axis direction, and cause movement in the X-axis direction of the mold  100 A/ 100 B to be smooth, supporting the bottom surfaces (the bottom surface of the clamping plate  101   a ) of the mold  100 A/ 100 B and supporting the mold  100 A/ 100 B from below. On both sides in the X-axis direction of the fixed platen  61 , a roller supporting body  620  is fixed, and the plurality of rollers BR are supported by the roller supporting body  620 . 
     On the inner surface of the fixed platen  61 , grooves  61   b  that extend in the X-axis direction are formed. 
     The grooves  61   b  are formed in two rows separated vertically. On each of the grooves  61   b  a roller unit  640  is arranged. For the roller unit  640 , a plurality of rollers SR are supported such that they are free to rotate. The plurality of rollers SR rotate around the axis of revolution in the Z-axis direction, and guide movement in the X-axis direction of the mold  100 A/ 100 B contacting the outer surfaces of the mold  100 A/ 100 B (the outer surface of the clamping plate  101   a ) and supporting the mold  100 A/ 100 B from the side. As illustrated in the cross sectional view of the line II-II, while the roller unit  640 , by a bias of a spring  641 , is positioned at a position at which the roller SR protrudes from the groove  61   b,  at a time of clamping it is retracted in the groove  61   b,  and positioned at a position at which the roller SR does not protrude from the groove  61   b.  The roller unit  640  can prevent the inner surfaces of the mold  100 A/ 100 B and the fixed platen  61  from contacting and damaging the inner surfaces at a time of alternating the mold  100 A/ 100 B, and the roller unit  640  does not impede the inner surface of the fixed platen  61  and the mold  100 A/ 100 B being closed at a time of clamping. 
     On both sides in the X-axis direction of the fixed platen  61 , a roller supporting body  630  is fixed, and a plurality of rollers SR are supported by the roller supporting body  630 . 
     On the fixed platen  61 , a plurality of fixing mechanisms (clamps)  610  are arranged for fixing the fixed mold  101  to the fixed platen  61 . Each fixing mechanism  610  includes an engaging portion  610   a  that engages with the clamping plate  101   a,  and a built-in actuator (not illustrated) that moves the engaging portion  610   a  between an engagement position and an engagement release position. 
     Note that for the movable platen  62 , similarly to the fixed platen  61 , a plurality of rollers BR, the roller supporting bodies  620  and  630 , the roller unit  640 , and the fixing mechanism  610  for fixing the movable mold  102  are arranged. 
     As illustrated in  FIG. 4 , the periphery of the clamping apparatus  6  is surrounded by a cover (exterior covering plate)  60  for safety, but openings  60   a  through which the mold  100 A/ 100 B pass are formed on the sides of the molding operation position  11  for alternating the mold  100 A/ 100 B. Each opening  60   a  is typically continuously open, enabling free removal and insertion of the mold  100 A/ 100 B from and to the molding operation position  11 . 
     Returning to  FIG. 2 , the take-out robot  7  will now be described. The take-out robot  7  includes a rail  71  that extends in the X-axis direction, and a movable rail  72  that can move in the X-axis direction on the rail  71 . The movable rail  72  is arranged to extend in the Y-axis direction, and a slider  73  is arranged on the movable rail  72 . The slider  73  moves in the Y-axis direction guided by the movable rail  72 , and moves up and down an elevating shaft  73   a  in the Z-axis direction. On a lower end of the elevating shaft  73   a,  a vacuum head  74  is arranged, and on the vacuum head  74 , a chuck plate  75  specialized to a molded part is mounted. 
     The take-out robot  7 , after opening, moves the vacuum head  74  between the fixed mold  101  and the movable mold  102  as illustrated by broken lines in  FIG. 2  by the rail  71 , the movable rail  7 , and the slider  73 , sticks to the molded part, and conveys it outside the mold  100 A/ 100 B. 
       FIG. 5  illustrates examples of operation of the injection molding system  1 . Molding Process P 1  illustrates a standard molding process while Molding Process P 2  illustrates a compression molding process. 
     In the Molding Process P 1 , the fixed platen  61  and moveable platen  62  automatically close and contact with the mold  100 A/ 100 B in response to the mold  100 A/ 100 B being conveyed to molding operation position  11 . 
     In the step S 101 , the fixed platen  61  and moveable platen  62  move to a contact position where they contact with the mold  100 A/ 100 B. The fixed platen  61  and moveable platen  62  secure the mold  100 A/ 100 B. In step S 102 , the mold  100 A/ 100 B is locked (fixed) to both the fixed platen  61  and the movable platen  62  by driving the fixing mechanisms  610 . In step S 103 , the movable platen  62  is separated from the fixed platen  61  by driving the motor  66 . The fixed mold  101  is fixed to the fixed platen  61  by the fixing mechanisms  610 , and the movable mold  102  is fixed to the movable platen  62  by the fixing mechanisms  610 . The movable mold  102  separates from the fixed mold  101  and the mold  100 A/ 100 B is opened against a force, e.g., magnetic, of the self-closing unit  103 . 
     The molded part remaining on the side of the movable mold  102  of the mold  100 A/ 100 B is removed by driving the take-out robot  7  in step S 104 , and conveyed outside of the injection molding machine  2 . The vacuum head  74  is moved to a position where the chuck plate  75  faces the molded part P, and the molded part P is secured by suction. 
     In step S 105 , clamping of the mold  100 A/ 100 B by the fixed platen  61  and the movable platen  62  is performed by driving the motor  66  to drive the toggle mechanism  65 . In step S 106 , injection of molten resin is performed. 
     In step S 107 , dwelling of the molten resin is performed. More specifically, the injecting apparatus  5  is driven to fill molten resin into a cavity in the mold  100 A/ 100 B from the nozzle  52 , and to press the resin in the cylinder  51  into the mold  100 A/ 100 B at a high pressure to compensate for a volume decrease due to resin solidifying. 
     In step S 108 , locking of the mold  100 A/ 100 B by the fixing mechanism  610  is released. This results in removal of the clamping force, and the movable platen  62  is slightly separated from the fixed platen  61 . In step S 109 , after a delay of a predetermined time from step S 108 , the motor  66  is driven to drive the toggle mechanism  65 . That is, the fixed platen  61  and the moveable platen  62  move to a retreat position where they do not contact with the mold  100 A/ 100 B. These movements result in a space forming between the fixed platen  61  and the moveable platen  62  for alternating (changing) the molds  100 A and  100 B. 
     After step S 109 , the mold  100 A/ 100 B is ejected from the molding operation position  11  to the conveying machine  3 A/ 3 B, where the mold  100 A/ 100 B is cooled to an appropriate temperature during a predetermined time period. A mold typically includes a channel running inside the mold. An external temperature controller is connected, via a hose, to an interface of the channel formed on a surface of the mold while the mold is prepared for injection molding. A fluid at a predetermined temperature flows from the temperature controller inside the mold to keep the mold at a predetermined temperature. During the injection molding processes, including the cooling process, fluid typically flows inside the mold. 
     After step S 108 , the mold is typically still heated up from the melted resin injected into the mold  100 A/ 100 B. In the cooling process, the fluid from the temperature controller causes the temperature to drop to a predetermined temperature, e.g., 60 degrees Celsius. The cooling process continues until a predetermined time period passes from the start of the cooling process. 
     In some injection molding processes, like heat and cool molding, the cooling process includes a dedicated temperature controller to cool down a mold to a certain temperature, which is different from a temperature at which the mold receives the melted resin from an injecting machine. 
     Turning to Molding Process P 2 , the fixed platen  61  and moveable platen  62  automatically close and they contact with the mold  100 A/ 100 B in response to the mold  100 A/ 100 B being conveyed to molding operation position  11 . 
     In step S 201 , the fixed platen  61  and moveable platen  62  move to a contact position where they contact the mold  100 A/ 100 B. The fixed platen  61  and moveable platen  62  secure the mold  100 A/ 100 B. In step S 202 , the mold  100 A/ 100 B is locked (fixed) to both the fixed platen  61  and the movable platen  62  by driving the fixing mechanisms  610 . In step S 203 , the movable platen  62  is separated from the fixed platen  61  by driving the motor  66 . 
     The fixed mold  101  is fixed to the fixed platen  61  and the movable mold  102  is fixed to the movable platen  62  by the fixing mechanisms  610 . The movable mold  102  separates from the fixed mold  101  and the mold  100 A/ 100 B is opened against a force, e.g., magnetic, of the self-closing unit  103 . The molded part remaining on the side of the movable mold  102  of the mold  100 A/ 100 B is removed by driving the take-out robot  7  in step S 204 , and conveyed outside the injection molding machine  2 . In step S 205 , fixed platen  61  and moveable platen  62  move in a direction to close the mold  100 A/ 100 B, but the mold  100 A/ 100 B is not completely closed and remains slightly open. 
     The length of a gap between different molds ranges from an order of several ten micrometers to several hundred micrometers. The length of the gap can change based on the molding material. Step S 205  can be performed via a two-sub-step process, where in the first sub-step, the movable mold  102  is moved relatively fast to a predetermined position near the closed position. In the second sub-step, the movable mold  102  is moved relatively slow from the certain position to a desired position to create the desired gap between the fixed mold  101  and the movable mold  102 . In the second sub-step, the movable mold  102  can be subjected to a feedback control using a sensor (not illustrated) dedicated to the precise measurement of the length of the gap. 
     The length of the gap should not be such that the melted material enters the gap while the melted material is being injected. In order words, the gap between the moveable mold  102  and the fixed mold  102  of the mold  100 A/ 100 B should be small enough that the melted material does not get into the gap. The length of the gap for a mold is typically determined via an experimental process, which takes into consideration various parameters including a type of material and pressure applied to the mold. 
     In step S 206 , the injecting apparatus  5  is driven to fill molten resin into a cavity in the mold  100 A from the nozzle  52 . In step S 207 , clamping of the mold  100 A by the fixed platen  61  and the movable platen  62  is performed by driving the motor  66  to drive the toggle mechanism  65 . In step S 208 , the cylinder  51  dwells in the mold  100 A at a high pressure in order to compensate for a volume decrease due to resin solidifying. In step S 209 , locking of the mold  100 A by the fixing mechanism  610  is released. This results in removal of the clamping force, and the movable platen  62  is slightly separated from the fixed platen  61 . In step S 210 , after a delay of a predetermined time from step S 209 , the motor  66  is driven to drive the toggle mechanism  65 . That is, the fixed platen  61  and the moveable platen  62  move to a retreat position where they do not contact with the mold  100 A/ 100 B. This movement of the fixed platen  61  and the moveable platen  62  results in formation of a space between them for alternating (changing) the molds  100 A and  100 B. 
     In step S 210 , the length of a gap between the mold and the platen ranges from an order of several millimeters to several hundred centimeters. This gap is illustrated as L 1  in  FIG. 7A . As described above, in step S 205 , the length of the gap between the molds ranges from an order of several ten micrometers to several hundred micrometers. This gap is illustrated as L 2  in  FIG. 7B . 
     After step S 209 , the mold  100 A/ 100 B is ejected from the molding operation position  11  to the conveying machine  3 A/ 3 B, where the mold  100 A/ 100 B is cooled as described above. The time period of the cooling process can vary depending on a mold or a parameter set at launch of a specific injection molding process. 
       FIG. 6  is a flowchart illustrating an example of processing of a molding operation while alternating molds executed by the controller  41 . In the following example, a case in which a molding operation is performed while alternating the molds  100 A and  100 B is envisioned, i.e., molding using mold  100 A→molding using mold  100 B→molding using mold  100 A, etc. 
     An initial setting is performed in step S 10  of  FIG. 6 . Here, for each of the molds  100 A and  100 B, operation conditions of the injecting apparatus  5  and the clamping apparatus  6  are registered. 
     The operation conditions include, for example, the process of molding (molding method), the amount of resin that is injected at one time, the temperature, the injection speed, the clamping force, the initial value of the position of the movable platen  63  in relation to the tie-bars  64 , etc. The operation conditions can differ even when the mold  100 A and the mold  100 B are the same. The operation conditions are stored in a memory of control apparatus  4 . 
     In step S 15 , as initial processes, the injection processes are performed for both the molds  100 A and  100 B. In the present example, the injection process is performed with the mold  100 A and then with the mold  100 B. First, the conveying machine  3 A moves the mold  100 A into the molding operation position  11 . If it is set that the Molding Process P 1  is set for the mold  100 A, then the injection molding machine  2  performs the processes of steps S 101 , S 102  and S 105 - 109 . If it is set that the Molding Process P 2  is set for the mold  100 A, then the injection molding machine  2  performs the processes of steps S 201 , S 202  and S 205 -S 209 . 
     The conveying machine  3 A moves the mold  100 A out of the molding operation position  11  and the conveying machine  3 B moves the mold  100 B into the molding operation position  11 . If it is set to perform Molding Process P 1  for the mold  100 B, the injection molding machine  2  performs the processes of steps S 101 , S 102  and S 105 - 109 . If it is set to perform the Molding Process P 2  for the mold  100 B, the injection molding machine  2  performs the processes of steps S 201 , S 202  and S 205 -S 209  for the mold  100 B. 
     In step S 20 , the mold  100 B is unloaded and the mold  100 A is loaded. If the mold  100 B is not at the injection molding machine  2 , only loading of the mold  100 A is performed. In step S 30 , the controller  41  selects the molding process for the mold  100 A is selected based on the information stored in the memory. If the Molding Process P 1  is set for the mold  100 A, the process proceeds to step S 40 . If the Molding Process P 2  is set for the mold  100 A, the process proceeds to step S 50 . 
     After completing step S 40  or step S 50 , in step S 60 , unloading of the mold  100 A and loading of the mold  100 B is performed. In step S 70 , the controller  41  selects the molding process for the mold  100 B based on the information stored in the memory. If the Molding Process P 1  is set for the mold  100 B, the process proceeds to step S 80 . If the Molding Process P 2  is set for the mold  100 B, the process proceeds to step S 90 . In step S 100 , the controller  41  determines whether a predetermined number of injections (number of molded parts produced) have finished. If the predetermined number of injections have not been finished, the controller  41  returns to step S 20 , and production of the molded parts is repeated. 
     If the predetermined number of injections has been completed, the process proceeds to step S 110 , in which the molded parts are ejected from both the mold  100 A and the mold  100 B. For example, the conveying machine  3 A moves the mold  100 A) located at the molding operation position  11  in step S 60  out of the molding operation position  11 . The conveying machine  3 B then moves the mold  100 B into the molding operation position  11 . The mold  100 B has previously been cooled on the conveying machine  3 B, while the Molding Process P 1  or Molding Process P 2  was performed for the mold  100 A in either steps S 40  or S 50 . The injection molding machine  2  performs either the processes of steps S 101 -S 104  and S 108  or the processes of steps S 201 -S 204  and  5208  for the mold  100 B. If it is set that the Molding Process P 1  is performed for the mold  100 B, the processes of S 101 -S 104  and S 108  are performed. If it is set that the Molding Process P 2  is performed for the mold  100 B, the process of steps S 201 -S 204  and S 208  are performed. 
     The conveying machine  3 B moves the mold  100 B out of the molding operation  11 , and then the conveying machine  3 A moves the mold  100 A into the molding operation position  11 . Because the mold  100 B skips some of the processes, the period of time in which the mold  100 A has been cooling on the conveying machine  3 A is shorter than the normal period of time. Therefore, the cooling of the mold  100 A may not have been completed at the time the mold  100 A is moved into the molding operation position  11 . If the cooling is not completed, the injection molding machine  2  waits for the cooling process to be completed. 
     After the cooling process is completed, the injection molding machine  2  performs the processes of steps S 101 -S 104  and S 108  if it is set that the Molding Process P 1  is performed for the mold  100 A. The injection molding machine  2  performs the processes of steps S 201 -S 204  and S 208  if it is set that the Molding Process P 2  is performed for the mold  100 A. T The mold  100 A is then moved from the molding operation position  11  and the process ends. 
     In the above-described embodiment, both the conveying machine  3 A and the conveying machine  3 B include an actuator. According to another exemplary embodiment, an actuator is only provided with either the conveying machine  3 A or the conveying machine  3 B, In a case where only the conveying machine  3 A includes an actuator, the mold  100 A and the mold  100 B are connected via a metal connection part, which enables the single actuator to move both the mold  100 A and  100 B. 
     According to the above-described injection molding system, compression molding can be performed while alternating (changing) molds. This enables productivity improvement. 
     According to the above-described injection molding system, the molding process can be changed for each mold when performing the injection molding while alternating (changing) the multiple molds. 
     In the above-described embodiments, clamping, injection/dwelling, opening, and ejection are performed in the state where the mold is at the molding operation position  11  This is not seen to be limiting. In another exemplary embodiment, not all the processes need be performed at the molding operation position  11 . Some of the processes can be performed at a position different from the molding operation position  11 . 
     In the above-described embodiments, the cooling process is performed in the state where the mold is on the conveying machines. This is not seen to be limiting. In another exemplary embodiment, the cooling process need not be performed on the conveying machines. The cooling process can be performed at a position where the mold does not contact with the fixed platen and the movable platen. For example, the cooling process can be performed when a part of the mold is in the injection molding machine and part of the mold is outside the injection molding machine. 
     In another exemplary embodiment, in a configuration that a part of either of the conveying machines is located in the injection molding machine  2 , the cooling process can be performed in a state where a part of the mold is in the injection molding machine  2  and a part of the mold is on either of the conveying machines. 
     Definitions 
     In referring to the description, specific details are set forth in order to provide a thorough understanding of the examples disclosed. In other instances, well-known methods, procedures, components and circuits have not been described in detail as not to unnecessarily lengthen the present disclosure. 
     It should be understood that if an element or part is referred herein as being “on”, “against”, “connected to”, or “coupled to” another element or part, then it can be directly on, against, connected or coupled to the other element or part, or intervening elements or parts may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or part, then there are no intervening elements or parts present. When used, term “and/or”, includes any and all combinations of one or more of the associated listed items, if so provided. 
     Spatially relative terms, such as “under” “beneath”, “below”, “lower”, “above”, “upper”, “proximal”, “distal”, and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the various figures. It should be understood, however, that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, a relative spatial term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are to be interpreted accordingly. Similarly, the relative spatial terms “proximal” and “distal” may also be interchangeable, where applicable. 
     The term “about,” as used herein means, for example, within 10%, within 5%, or less. In some embodiments, the term “about” may mean within measurement error. 
     The terms first, second, third, etc. may be used herein to describe various elements, components, regions, parts and/or sections. It should be understood that these elements, components, regions, parts and/or sections should not be limited by these terms. These terms have been used only to distinguish one element, component, region, part, or section from another region, part, or section. Thus, a first element, component, region, part, or section discussed below could be termed a second element, component, region, part, or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “includes”, “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Specifically, these terms, when used in the present specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof not explicitly stated. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. For example, if the range 10-15 is disclosed, then 11, 12, 13, and 14 are also disclosed. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure. 
     It will be appreciated that the methods and compositions of the instant disclosure can be incorporated in the form of a variety of embodiments, only a few of which are disclosed herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the disclosure to be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Combinations of any exemplary embodiments disclosed above are also included as embodiments of the present disclosure. While the above-described exemplary embodiments discuss illustrative embodiments, these embodiments are not seen to be limiting.