Injection molding machine

Abstract

To provide an injection molding machine that can manufacture high-quality molded products with a high yield. [Solution] The injection molding machine comprises a cylinder having a nozzle for injecting molten resin into a mold, a screw configured to move back and forth within the cylinder, a heater positioned on the outer circumference of the nozzle, and a control device that controls the movement of the screw and the operation of the heater. The control device operates the heater at a predetermined current value during a predetermined period in the molding cycle, which is part of the injection process in which the molten resin is injected into the mold as the screw moves forward, thereby heating the nozzle.

Description

Technical Field

[0001] The present invention relates to an injection molding machine for producing a molded product by injecting molten resin into a mold.

Background Art

[0002] Patent Document 1 discloses an injection molding machine for producing a molded product by injecting molten resin into a mold. The injection molding machine includes a nozzle attached to the tip of a heating cylinder and a heater wound around the nozzle. In this injection molding machine, the heater is heated at a predetermined energization current value for a predetermined time during a predetermined process period in the molding cycle, specifically, during the mold closing process period. By making the amount of heat given from the heater to the nozzle constant in each molding cycle, a high-quality molded product can be produced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to improve the yield of molded products, it is desired to further improve the quality of molded products.

[0005] In view of the above circumstances, one object of the present invention is to provide an injection molding machine capable of producing high-quality molded bodies with good yield.

Means for Solving the Problems

[0006] As a result of earnestly studying the above problems, the present inventor has obtained the knowledge that in the injection process in the molding cycle, the injection pressure of the molten resin from the nozzle is likely to be disturbed, and that disturbance affects the quality of the molded product. Based on that knowledge, the present inventor has completed the injection molding machine of the present invention shown below.

[0007] An injection molding machine according to one embodiment of the present invention comprises a cylinder having a nozzle for injecting molten resin into a mold, a screw configured to move back and forth within the cylinder, a heater arranged on the outer circumference of the nozzle, and a control device that controls the movement of the screw and the operation of the heater. The control device operates the heater at a predetermined current value during a predetermined period in the molding cycle, which is part of the injection process in which the molten resin is injected into the mold as the screw moves forward, thereby heating the nozzle. [Effects of the Invention]

[0008] The injection molding machine of the present invention can produce high-quality molded products with a high yield. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram of the injection molding machine according to Embodiment 1. [Figure 2] Figure 2 is a partially enlarged cross-sectional view of the vicinity of the nozzle in the injection molding machine shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing an example of the input device shown in Figure 1. [Figure 4] Figure 4 is an explanatory diagram illustrating the processes that make up the molding cycle. [Figure 5] Figure 5 is an explanatory diagram illustrating the predetermined period during which the heater that heats the nozzle operates in the injection process. [Figure 6] Figure 6 is a graph showing the change in resin injection pressure from the nozzle when the heater operation is controlled by PID control (Proportional-Integral-Differential Controller) during the injection process. [Modes for carrying out the invention]

[0010] The injection molding machine according to the embodiment will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same parts. The shapes, sizes, and positional relationships shown in each drawing are for the purpose of clarifying the explanation and do not necessarily represent the actual shapes, sizes, and positional relationships. The present invention is not limited to the configurations shown in the embodiments, but is intended to include all modifications within the meaning and scope of the claims, as indicated by the claims.

[0011] <Embodiment 1> The injection molding machine 1 of Embodiment 1 shown in Figure 1 is a device that produces molded products using molten material injected into a mold 10. The injection molding machine 1 comprises a molding unit 2, a control device 3, and an input device 4. The molding unit 2 is the main component of the injection molding machine 1. The molten material in the injection molding machine 1 is molten resin. The input device 4 is a device for the operator to input instructions to the injection molding machine 1. The control device 3 is a device that controls the molding unit 2 based on the instructions input by the operator. One of the features of the injection molding machine 1 in this example is the control of the heater 73 provided in the molding unit 2 of the injection molding machine 1. The following describes each component of the injection molding machine 1, and then the control of the heater 73.

[0012] Molding Unit The molding unit 2 in this example includes a mold opening / closing unit 6 for opening and closing the mold 10, an injection unit 7 for injecting molten resin into the mold 10, and an ejector unit 8 for removing the molded product from the mold 10. The molding unit 2 may further include a spray unit for spraying air or a fluid such as a mold release agent onto the inner circumferential surface of the mold 10.

[0013] [Type opening / closing unit] The mold opening / closing unit 6 is configured to open and close the mold 10 and to clamp it. The mold 10 comprises a fixed mold 11 and a movable mold 12. The mold opening / closing unit 6 comprises a fixed die plate 61 that supports the fixed mold 11 and a movable die plate 62 that supports the movable mold 12. The mold opening / closing unit 6 further comprises a tie bar 63, a drive device 64 and a toggle link mechanism 65. The first end of the tie bar 63, which is located on the injection unit 7 side, is fixed to the fixed die plate 61. The second end of the tie bar 63, opposite to the first end, is fixed to the tailstock 66. The middle part of the tie bar 63 passes through the movable die plate 62. The movable die plate 62 moves along the tie bar 63 when the driving force of a drive device 64, such as a motor, is transmitted through the toggle link mechanism 65.

[0014] When the movable die plate 62 moves to the left in the plane of the paper, the fixed mold 11 and the movable mold 12 separate, and the mold 10 opens. When the movable die plate 62 moves to the right in the plane of the paper, the fixed mold 11 and the movable mold 12 come into contact, and the mold 10 closes. When the movable die plate 62 applies further pressure to the movable mold 12 of the closed mold 10 in the direction of the paper to the right, the fixed mold 11 and the movable mold 12 are clamped together.

[0015] [Injection Unit] The injection unit 7 is configured to inject molten resin into the clamped mold 10. The injection unit 7 comprises a cylinder 71, a screw 72, a plurality of heaters 73, and a hopper 74. The cylinder 71 has a nozzle 70 at its tip. The screw 72 is configured to move back and forth within the cylinder 71. In this example, the forward direction of the screw 72 is the direction in which the tip of the screw 72 approaches the mold 10. The backward direction of the screw 72 is the opposite direction to the forward direction.

[0016] Each of the plurality of heaters 73 is arranged on the outer periphery of the cylinder 71 and heats the cylinder 71. The plurality of heaters 73 can be controlled individually. Among the plurality of heaters 73, the heater 730 arranged on the outer periphery of the nozzle 70 shown in FIG. 2 has a great influence on the injection pressure of the molten resin 19 injected from the nozzle 70. By heating the nozzle 70 with the heater 730, the injection pressure can be reduced. A temperature sensor 79 is arranged between the nozzle 70 and the heater 730. The measurement result of the temperature sensor 79 is input to the control device 3 and used for controlling the heater 73. If the temperature of the cylinder 71 is too high, the molten resin 19 may deteriorate. By monitoring the temperature of the cylinder 71 with the temperature sensor 79, deterioration of the molten resin 19 can be prevented.

[0017] The cylinder 71 is a cylindrical member, and the nozzle 70 of the cylinder 71 is inserted into the through-hole 69 of the fixed die plate 61. The tip of the nozzle 70 is in contact with the fixed mold 11. The molten resin 19 injected into the mold 10 from the nozzle 70 is filled into the cavity 15, which is the internal space of the mold 10, to form a molded product. The hopper 74 is a funnel-shaped member for supplying resin chips, which are the raw material of the molten resin 19, into the cylinder 71.

[0018] As shown in FIG. 1, the injection unit 7 further includes a metering motor 75 and an injection motor 76. The metering motor 75 rotates the screw 72 in the metering process described later to convey the resin chips supplied from the hopper 74 toward the tip of the cylinder 71. The conveyed resin chips are melted by the heat of the heater 73. The injection motor 76 advances the screw 72 in the injection process described later to inject the molten resin 19 into the mold 10. The rotational force of the injection motor 76 is converted into the linear motion of the screw 72 by an appropriate mechanism. An encoder 77 as a position sensor for measuring the position of the screw 72 in the cylinder 71 is arranged on the injection motor 76. Further, a load cell 78 as a pressure sensor for measuring the injection pressure of the molten resin 19 injected from the nozzle 70 is arranged at the rear end portion of the screw 72 (not shown). The load cell 78 measures the pressure received by the screw 72 from the molten resin 19 in the cylinder 71. The pressure received by the screw 72 correlates with the injection pressure of the molten resin 19 injected from the nozzle 70. Therefore, based on the measured value of the load cell 78, the injection pressure can be obtained by calculation.

[0019] 〔Ejector Unit〕 The ejector unit 8 is configured to push out the molded product from the opened mold 10. The ejector unit 8 includes a plurality of pins (not shown) for pushing out the molded product and a drive device 84 such as a motor for advancing and retreating the pins.

[0020] ≪Input Device≫ The input device 4 is configured for an operator operating the injection molding machine 1 to give instructions to the injection molding machine 1. The instructions from the operator include a mode instruction specifying a specific operation mode selected from a plurality of operation modes, an operation instruction for the molding unit 2 in each operation mode, a setting instruction for molding conditions such as injection speed, and the like.

[0021] The operation modes include "OFF mode," "Exchange mode," "Manual mode," "Semi-automatic mode," and "Fully automatic mode." OFF mode is a mode for stopping the operation of the injection molding machine 1. In OFF mode, the power to the injection molding machine 1 can be turned off. In OFF mode, settings such as molding conditions can also be made. Exchange mode is a mode for changing the mold 10 or adjusting the operation of each unit 6, 7, and 8 in a series of molding cycles. In exchange mode, each unit 6, 7, and 8 operates at a low speed. Manual mode is a mode in which the operator manually instructs all operations related to molding, such as opening and closing the mold 10 and injecting the molten resin 19. Semi-automatic mode is a mode in which the operation of the molding unit 2 stops after each molding cycle is executed. Fully automatic mode is a fully automatic operation mode in which molded products are continuously manufactured by continuously executing a preset number of molding cycles.

[0022] An operation instruction is an instruction to start an operation on the components of the molding unit 2. For example, an operation instruction in manual mode might be an instruction to the mold opening / closing unit 6 to close the mold 10, or an instruction to the injection unit 7 to inject molten resin 19 into the mold 10. Also, an operation instruction in semi-automatic mode might be an instruction to the molding unit 2 to start a new molding cycle.

[0023] Figure 3 shows an example of the input device 4. In this example, the input device 4 comprises a housing 40, a plurality of mode selection switches 41, a plurality of operation start switches 42, and a display unit 45. The mode selection switches 41 are push-button type hardware switches that are pressed, for example, when an operator selects an operation mode. The operation start switches 42 are push-button type hardware switches that are pressed, for example, when an operator instructs the operation of the molding unit 2. The fact that the mode selection switches 41 and the operation start switches 42 are hardware switches makes it easier to prevent incorrect input by the operator. The display unit 45 displays the selected operation mode, the operation being performed, and the molding conditions. The display unit 45 may also include a touch panel type software switch. The software switch is used, for example, to set the molding conditions. The information displayed on the display unit 45 in Figure 3 will be described later.

[0024] ≪Control device≫ The control device 3 shown in Figure 1 comprehensively controls the operation of the injection molding machine 1. Instructions entered by the operator into the input device 4 are input to the control device 3 as electrical signals. The control device 3 controls the molding unit 2 based on a specific operation mode selected by the operator.

[0025] The control device 3 is comprised of a computer. The computer may be located within the enclosure 40 of the input device 4 (see Figure 3). The computer comprises a processor 30 and a storage medium 31. The processor 30 is one of various processors suitable for computer control. Examples of processors include a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), and ASIC (Application Specific Integrated Circuit). There may be one or more processors 30. Multiple processors 30 may be physically separated and cooperate with each other to perform processing. The storage medium 31 stores a program for the injection molding machine 1 to produce a molded body. The storage medium 31 is typically ROM (Read-Only Memory) and RAM (Random Access Memory). The execution of the program read from the storage medium 31 by the processor 30 causes each component of the injection molding machine 1 to operate.

[0026] The computer that comprehensively controls the operation of the injection molding machine 1 may be a separate computer connected to the injection molding machine 1 via a network such as a LAN (Local Area Network), WAN (Wide Area Network), or the Internet.

[0027] ≪Heater control in the injection molding process≫ In the injection molding machine 1 of this example, the control device 3 operates the heater 73 at a predetermined current value during a predetermined period, which is part of the injection process in the molding cycle, to heat the heater 73. The heater 73 controlled in this example is the heater 730 located on the outer circumference of the nozzle 70 shown in Figure 2. The heater 730 is never turned OFF during the predetermined period.

[0028] In explaining the injection process, the molding cycle for producing a molded product will be described based on Figure 4. Figure 4 shows the relationship between the steps that make up the molding cycle and the operations of the mold opening / closing unit 6 and the injection unit 7 in each step. In Figure 4, time progresses from right to left on the page. The molding cycle comprises a mold closing step, a mold clamping step, an injection step, a metering step, and a mold opening step. The molding cycle may also include a product removal step, which is not shown. The product removal step is the step of removing the molded product from the mold 10 by the ejector unit 8.

[0029] In the mold closing process, the mold opening / closing unit 6 performs a mold closing operation to close the mold 10. The mold closing operation involves bringing the fixed mold 11 and the movable mold 12 closer together and bringing them into contact. In the mold clamping process following the mold closing process, the mold opening / closing unit 6 performs a mold clamping operation to tighten the mold 10. The mold clamping operation involves increasing the pressure of the movable mold 12 toward the fixed mold 11. As a result, the fixed mold 11 and the movable mold 12 are clamped together with a predetermined pressure. Figure 4 shows the operation of the mold opening / closing unit, with "mold closing" followed by "mold clamping". After the mold closing process is completed, the mold 10 remains clamped with a predetermined pressure until the mold opening process, described later, begins.

[0030] In the injection process, molten resin 19 is injected from the injection unit 7 into the mold 10, and an injection operation is performed in which the mold 10 is filled with molten resin 19. During the injection operation, the screw 72 moves forward inside the cylinder 71. In addition, after the injection operation, a holding pressure operation is performed in the injection process. During the holding pressure operation, the screw 72 moves forward inside the cylinder 71 at a lower speed than during the injection operation. The distance traveled by the screw 72 during the holding pressure operation is very small.

[0031] In the weighing process, as the screw 72 retracts and rotates, a predetermined amount of resin chips is introduced from the hopper 74 into the cylinder 71. These resin chips are melted by heating with the heater 73. As a result, a predetermined amount of molten resin 19 is weighed into the cylinder 71.

[0032] In the mold opening process, the mold opening / closing unit 6 performs a depressurization operation that gradually reduces the clamping force between the fixed mold 11 and the movable mold 12. In the mold opening process, the mold opening / closing unit 6 further performs a mold opening operation that separates the movable mold 12 from the fixed mold 11. In other words, the mold opening process is a process that reduces the clamping force between the fixed mold 11 and the movable mold 12, and further separates the fixed mold 11 and the movable mold 12, so that the molded product can be removed from inside the mold 10.

[0033] In the injection molding machine 1 of this example, the control device 3 controls the heater 730 to raise its temperature during a predetermined period of time within the injection process. The start and end times of this predetermined period can be set to any point in the injection process. The predetermined period is, for example, at least one of a period in the injection process during which the injection pressure changes sharply, and a period during which the injection pressure fluctuates without being stable. An example of a predetermined period 5 is shown in Figure 5. The hatched area in the injection process shown in Figure 5 indicates the predetermined period 5 during which the heater 730 operates. In this example, there are two predetermined periods 5: a first period 51 and a second period 52. The number of predetermined periods 5 may be one or three or more.

[0034] The first period 51 includes the initial phase of the injection process. The initial phase of the injection process is the first half of the time when the time from the start to the end of the injection process is divided into two equal parts. That is, the initial phase of the injection process includes the start time of the injection process. The second half of the time when the time from the start to the end of the injection process is divided into two equal parts is the later phase of the injection process. In this example, the heating start time S1 of the first period 51, that is, the timing when the power to the heater 730 is turned ON, coincides with the start time of the injection process. In this example, the heating end time E1 of the first period 51, that is, the timing when the power to the heater 730 is turned OFF, is within the range of the initial phase of the injection process. The heating end time E1 may also be within the range of the later phase of the injection process.

[0035] The second period 52 includes at least a portion of the later part of the injection process. In this example, the heating start time S2 of the second period 52, i.e., the timing of turning on the power to the heater 730, is around the start of the later part of the injection process. The heating start time S2 may also be within the range of the earlier part of the injection process. In this example, the heating end time E2 of the second period 52, i.e., the timing of turning off the power to the heater 730, is within the range of the later part of the injection process. The heating end time E2 may extend into the period during which processes following the injection process are carried out.

[0036] The reasons for selecting the first period 51 and the second period 52 will be explained based on Figure 6. Figure 6 is a graph showing the injection pressure of molten resin 19 from the nozzle 70 when the ON / OFF of the heater 730 is controlled by PID control during the injection process, unlike in this example. The horizontal axis is the position of the tip of the screw 72 with the origin as zero, and the unit is millimeters (mm). The origin is the position of the tip of the screw 72 just before the start of the injection process. Moving to the right on the horizontal axis means that the screw 72 is advancing toward the mold 10. The right end of the graph is the position of the screw 72 at the end of the injection process. The horizontal axis in Figure 5 can be considered to roughly coincide with the elapsed time from the start of the injection process. The value indicating the position of the screw 72 is a numerical value calculated by the computer constituting the control device 3 based on information from the encoder 77. The vertical axis is the injection pressure of the molten resin 19 injected from the nozzle 70 into the mold 10, and the unit is megapascals (MPa). The injection pressure is a value calculated by a computer based on information from load cell 78.

[0037] As shown in Figure 6, the injection pressure becomes very high in the early stages of the injection process when the screw 72 is close to the origin. This is thought to be because when the nozzle 70 contacts the mold 10, the nozzle 70 cools down, increasing the viscosity of the molten resin near the nozzle 70. When the injection pressure exceeds a predetermined level, PID control intervenes, the nozzle 70 is heated by the heater 730, and the injection pressure decreases. After the initial stages of the injection process, when the nozzle 70 is heated by PID control, the viscosity of the molten resin decreases, and the injection pressure stabilizes. However, in the later stages of the injection process, specifically from the middle to the end, the injection pressure fluctuates. This is thought to be caused by the alternating ON control of the heater 730 due to a decrease in the temperature of the nozzle 70 and the OFF control of the heater 730 due to a rise in the temperature of the nozzle 70, both by PID control. The fluctuations in injection pressure in the early and late stages of the injection process may cause inconsistencies in the quality of the molded product.

[0038] In the example shown in Figure 6, the injection pressure may fluctuate during the initial and later stages of the injection process. To minimize this fluctuation, the first period 51 and the second period 52 shown in Figure 5 are set. During periods other than the first period 51 and the second period 52, the heater 730 may remain OFF or may be turned ON / OFF by PID control. If the heater 730 is OFF during periods other than the first period 51 and the second period 52, the power consumption of the heater 730 can be reduced. Depending on the type of resin that makes up the molded product, the number and timing of the predetermined periods 5 for heating the heater 730 may differ from the example in Figure 5.

[0039] During the first period 51 and the second period 52, the heater 730 remains energized. The current value supplied to the heater 730 may be a predetermined value set in advance, or it may be a fluctuating value that changes according to the measurement result of the temperature sensor 79. In this example, the current value is a predetermined value set in advance. That is, in this example, the heater 730 is open-circuit controlled during the first period 51 and the second period 52.

[0040] The heating start times S1 and S2 for the predetermined period 5 are controlled by the control device 3, for example, triggered by any of the following information (A) to (C). The heating end times E1 and E2 for the predetermined period 5 are controlled by the control device 3, for example, triggered by the following information (A) or (B). (A) Position of screw 72 inside cylinder 71 (B) Time elapsed from any point in the molding cycle (C) Injection pressure from nozzle 70

[0041] The information in (A) above is the position of the screw 72, obtained, for example, from an encoder 77, which is a type of position sensor. Since the control device 3 controls the operation of each component of the molding unit 2, it also controls the timing of the start of the injection process. The control device 3 determines the heating start times S1, S2 and heating end times E1, E2 based on the position of the screw 72 in the injection process. The control device 3 turns on the heater 730 when the heating start times S1, S2 arrive and turns off the heater 730 when the heating end times E1, E2 arrive. For example, the control device 3 turns on the heater 730 when the position of the screw 72 is 1 mm from the origin and turns off the heater 730 when the position of the screw 72 is 5 mm from the origin. The position of the screw 72 at which the heater 730 is turned ON / OFF can be determined by the operator based on data obtained, for example, by performing pre-molding as shown in Figure 6.

[0042] The information in (B) above is the elapsed time from any point in the molding cycle. Any point in time is, for example, the start time of the injection process. For example, with respect to the heating start times S1 and S2, the control device 3 controls the heater 730 to be turned ON at the start time of the injection process or after a predetermined time has elapsed from the start time. With respect to the heating end times E1 and E2, for example, the control device 3 controls the heater 730 to be turned OFF after a predetermined time has elapsed from the start time of the injection process. Here, the heating end time E2 of the second period 52, which includes the latter half of the injection process, may be set by the elapsed time starting from the start time of the mold opening process.

[0043] The information in (C) above is the injection pressure, which is determined by information from, for example, a load cell 78, a type of pressure sensor. For example, the control device 3 starts heating the heater 730 when the injection pressure exceeds a threshold. The information in (C) above is not used as a trigger to terminate the heating of the heater 730. As shown in Figure 6, the injection pressure fluctuates up and down in small increments, especially in the later stages of the injection process, making it difficult to set an injection pressure threshold for determining when to terminate the heating of the heater 730.

[0044] The information from (A) to (C) above can be used in combination. For example, heating may be started using the information from (A) above as a trigger, and heating may be stopped using the information from (B) above as a trigger. Alternatively, heating may be started using the information from (C) above as a trigger, and heating may be stopped using the information from (B) above as a trigger.

[0045] An example of an operator setting the start and end times of heating via the input device 4 is explained with reference to Figure 3. In this example, the display unit 45 of the input device 4 shows the columns "Heater," "Start Mode," "Start," "Delay," "Output Stop," and "Stop." The names of each column are merely for convenience.

[0046] The "Heater" field is used to specify which of the multiple heaters 73 provided in the injection molding machine 1 should be operated. In the diagram, "Heater 1" refers to the heater 730 located on the outer circumference of the nozzle 70. The type of heater 73 to be controlled can be changed in the "Heater" field. For example, by changing "Heater 2" to "Heater 1" in the diagram, two predetermined periods 5 shown in Figure 5 can be set.

[0047] The "Start Mode" field specifies the trigger for starting heating. In the diagram, "Injection Start" means that the timing of the start of heating in the injection process is used as the reference. The "Start" field specifies the timing for operating the heater 730 from the reference specified in the "Start Mode" field. The unit for the "Start" field is seconds (s). In the diagram, it is set to "0.00s," in which case heating of the heater 730 starts simultaneously with the start of the injection process. The unit for the "Start" field is automatically changed according to the reference specified in the "Start Mode" field. For example, if "Injection Position," which is based on the position of the screw 72 at the start of the injection process, is specified in the "Start Mode" field, the unit for the "Start" field will be changed to millimeters (mm).

[0048] The "Delay" column is used to specify a delay in the timing of the start of heating. By using the "Delay" column, the start of heating by the heater 730 can be delayed by the time specified in the "Delay" column after the conditions specified in the "Start" column have been met. Delaying the timing of the start of heating is effective for fine-tuning a predetermined period 5 to improve the quality of the molded product.

[0049] The "Output Stop" field is where you specify the trigger for ending the heating process. In the diagram, "Injection Position" means that the trigger for ending the heating process is set based on the position of the screw 72 at the start of the injection process. The trigger for ending the heating process is switchable. The "Stop" field is where you specify the timing for stopping the operation of the heater 730 from the reference point specified in the "Output Stop" field. In the diagram, it is set to "100mm," in which case the heater 730 will stop when the screw 72 has advanced 100mm from the start of the injection process. The unit in the "Stop" field is automatically changed according to the reference point specified in the "Output Stop" field. For example, if "Injection Start" is specified in the "Output Stop" field, the unit in the "Stop" field will be changed to seconds.

[0050] By implementing the control of the heater 730 as described above, the fluctuations in injection pressure during the initial and later stages of the injection process, as shown in Figure 6, can be reduced. As a result, the injection pressure can be leveled throughout the entire injection process, enabling the production of high-quality molded products with a high yield. [Explanation of Symbols]

[0051] 1…Injection molding machine 10…Mold, 11…Fixed mold, 12…Movable mold, 15…Cavity, 19…Molten resin 2…Molding unit 3…Control device 30...Processor, 31...Storage medium 4…Input device 40... Enclosure, 41... Mode selection switch, 42... Start switch 45…Display section 5…Specified period 51...first period, 52...second period S1, S2... Heating start time, E1, E2... Heating end time 6... Type Opening / Closing Unit 61...Fixed die plate, 62...Movable die plate, 63...Tie bar 64...Drive unit, 65...Toggle link mechanism, 66...Tailstock, 69...Passageway 7…Injection Unit 70...Nozzle, 71...Cylinder, 72...Screw, 73, 730...Heater 74... Hoppa 75... Measuring motor, 76... Injection motor, 77... Encoder, 78... Load cell 79…Temperature sensor 8… Ejector unit 84... Drive system

Claims

1. A cylinder having a nozzle for injecting molten resin into a mold, A screw configured to move back and forth within the cylinder, A heater arranged on the outer circumference of the nozzle, The system includes a control device that controls the movement of the screw and the operation of the heater, The control device operates the heater at a predetermined current value during a predetermined period of the molding cycle, which is part of the injection process in which the molten resin is injected into the mold as the screw moves forward, thereby heating the nozzle. Injection molding machine.

2. The injection molding machine according to claim 1, wherein the predetermined period includes at least a portion of the later stage of the injection process.

3. The system includes an input device for the operator to input the timing for the start and end of heating of the heater during the predetermined period. The injection molding machine according to claim 1 or 2, wherein the control device controls the start and end of heating during a predetermined period based on the input of the operator to the input device.

4. The injection molding machine according to claim 3, wherein the control device performs the heating start or heating end based on information of the position of the screw in the cylinder, information of the elapsed time from an arbitrary timing in the molding cycle, or information of the injection pressure from the nozzle as a trigger.

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