Method and device for controlling injection molding machine

Abstract

To provide an injection molding method capable of suppressing an increase in a temperature of a molten resin in a screw groove when an end of a molding operation is approaching.SOLUTION: An injection molding method includes the steps of: performing a molding operation by repeating a plurality of molding shots under a first group of molding conditions including a plurality of types of molding conditions (1); and performing a molding operation by repeating a plurality of molding shots under a second group of molding conditions including a plurality of types of molding conditions (2). In the injection molding method, a raw material inlet is closed, and a process moves from the step 1 to the step 2. In the step 2, molding operation is performed with the raw material inlet kept closed, and the second group of molding conditions is changed from the first group of molding conditions in terms of molding conditions related to temperature suppression of a molten resin.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for controlling an injection molding machine. [Background technology]

[0002] When starting up injection molding using an injection molding machine, it is necessary to gradually change the molding conditions such as injection speed and pressure to normal stable molding conditions. This is because the resin temperature is unstable at the start of molding, and if molding is performed under stable molding conditions from the beginning in this state, there is a possibility of defects such as flash formation on the molded product and damage to the mold. Regarding this problem, Patent Document 1 proposes a control device for an injection molding machine that can automatically change molding conditions from initial molding conditions to stable molding conditions at the start of molding.

[0003] The resin to be injection molded is fed from the rear side of the screw (screw base) and is transported toward the front of the screw as the screw rotates. The transport force of the resin inside the screw groove is greatly affected by the frictional force between the solid raw material at the screw base and the inner circumferential surface of the heating cylinder (barrel) that houses the screw. For this reason, when the raw material resin at the screw base is in a starvation state where there is little raw material resin, that is, when there is little raw material resin in the screw base and the contact area (friction area) between the raw material resin and the inner circumferential surface of the heating cylinder is small, the raw material resin transport capacity decreases and the raw material resin transport speed slows down. The raw material resin starvation state typically occurs after the end of injection molding is approaching and the supply of raw material resin is no longer being performed. When the conveying speed of the raw resin decreases, the time required for the raw resin to travel a unit distance in the screw groove increases, and the raw resin in the screw groove is subjected to shearing in the screw groove by the rotation of the screw for a longer period before being discharged from the tip of the screw. This causes the temperature of the raw material discharged from the screw (molten resin temperature) to rise. When the molten resin temperature increases, the resin viscosity decreases and becomes easier to flow, changing the flow state of the resin filled in the molding cavity of the mold, which may cause inconveniences such as overfilling under the molding conditions used in the previous molding operation. Overfilling can cause damage to the mold. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 189131 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0005] In contrast, Patent Document 1 sets molding conditions for stable molding during the process in which the screw groove fills with resin at the start of molding, the raw material conveying speed increases, and the molten resin temperature decreases, but it cannot address problems caused by the rise in resin temperature in the screw groove as the molding operation nears its end. In view of the above, an object of the present invention is to provide an injection molding method capable of suppressing an increase in the temperature of the molten resin in the screw groove as the end of the molding operation approaches. [Means for solving the problem]

[0006] The injection molding method of the present invention comprises the steps of: Step 1 of performing a molding operation by repeating a plurality of molding shots under a first molding condition group including a plurality of types of molding conditions; and step 2 of performing a molding operation by repeating a plurality of molding shots under a second molding condition group including a plurality of types of molding conditions. After the raw material inlet is closed, step 1 is followed by step 2. In step 2, the molding operation is carried out with the raw material inlet closed. The second group of molding conditions is different from the first group of molding conditions in that the molding conditions involved in suppressing the temperature of the molten resin are changed.

[0007] In step 2 of the injection molding method of the present invention, preferably, The second group of molding conditions is changed every predetermined number n (n≧1) of molding shots.

[0008] In step 2 of the injection molding method of the present invention, preferably, When the retraction speed of the screw in the metering step or the retraction amount of the screw in a predetermined time falls below a predetermined value, the second molding condition group is changed.

[0009] In step 2 of the injection molding method of the present invention, preferably, When the screw driving torque in the metering step falls below a predetermined value, the second molding condition group is changed.

[0010] In the injection molding method of the present invention, the molding conditions related to suppressing the temperature of the molten resin are as follows: At least one of the molding conditions in the injection process, or At least one of the molding conditions is set in the plasticization and metering process.

[0011] The control device in the injection molding machine of the present invention comprises: Step 1 of repeatedly performing a molding operation by a plurality of molding shots under a first molding condition group including a plurality of types of molding conditions; and step 2 of performing a molding operation by repeating a plurality of molding shots under a second group of molding conditions including a plurality of types of molding conditions. The control device of the present invention comprises: After obtaining information that the raw material inlet has been closed during molding operation in step 1, the molding operation is shifted from step 1 to step 2 while the raw material inlet remains closed; The second group of molding conditions is obtained by changing the molding conditions related to the suppression of the temperature of the molten resin from the first group of molding conditions. Effect of the Invention

[0012] According to the present invention, after closing the raw material inlet during molding operation in step 1, the process moves from step 1 to step 2, and the second group of molding conditions is changed from the first group of molding conditions to molding conditions involved in suppressing the temperature of the molten resin. Closing the raw material inlet means that the molding operation is nearing its end, and according to the present invention, the molding conditions involved in suppressing the temperature of the molten resin are changed at an appropriate timing. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a plan view showing an injection molding machine according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a configuration of a control device of an injection molding machine according to an embodiment. [Diagram 3] FIG. 2 is a diagram showing the breakdown of one shot constituting a molding operation of the injection molding machine according to the embodiment. [Figure 4] 1 is a diagram illustrating an example of a molding operation from start to stop in an injection molding machine according to an embodiment. FIG. [Diagram 5] 11A to 11C are diagrams illustrating another example of a process from the start to the stop of a molding operation in the injection molding machine according to the embodiment. [Figure 6] FIG. 4 is a diagram showing an example of a first molding condition group in the injection molding machine according to the embodiment. [Figure 7] FIG. 11 is a diagram showing an example of a second molding condition group in the injection molding machine according to the embodiment. [Figure 8] FIG. 11 is a diagram showing another example of the second molding condition group in the injection molding machine according to the embodiment. [Figure 9] FIG. 11 is a diagram showing another example of the second molding condition group in the injection molding machine according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. 1, an injection molding machine 1 according to an embodiment includes a mold section 10, a plasticizing section 20, and a control device 50 that controls the operations of these sections. The injection molding machine 1 can suppress an increase in the resin temperature in the screw groove when the end of a molding operation is approaching, and prevent overfilling of the mold section 10. Hereinafter, the configuration and basic operation of the injection molding machine 1 will be described, followed by a description of a control procedure by the control device 50. Note that in the injection molding machine 1, a front (F) and a rear (R) are defined as shown in FIG.

[0015] [Mold section 10: see Figure 1] The mold section 10 includes a fixed mold 11 whose position is fixed, and a movable mold 13 that can move toward and away from the fixed mold 11. In a mold clamping state in which the fixed mold 11 and the movable mold 13 are butted against each other, a mold cavity 15 is formed between the fixed mold 11 and the movable mold 13. Resin plasticized in the plasticizing section 20 is injected into and fills the mold cavity 15. Although not shown in the figure, the fixed mold 11 is attached to the fixed platen, and the movable mold 13 is attached to the movable platen. A plurality of tie bars are provided between the fixed platen and the movable platen to connect them, and the mold is closed or opened by applying pressure from, for example, a hydraulic cylinder between the fixed platen and the movable platen via the tie bars. Also, although not shown in the figure, the mold section 10 is provided with an ejector pin that ejects the injection molded product from the mold in the open state.

[0016] [Plasticization section 20: see Figure 1] The plasticizing section 20 includes a heating barrel 21, a discharge nozzle 23 provided at the front end of the heating barrel 21, a screw 25 rotatably provided inside the heating barrel 21, and a heater 27 wound around the front side of the heating barrel 21. Pellet-shaped raw resin is supplied to the inside of the heating barrel 21 through a raw material inlet 29 provided in the heating barrel 21. The heater 27 heats the resin inside the heating barrel 21 according to an instruction from the control device 50. The heating barrel 21 is fixed in position, and the screw 25 can move forward or backward inside the heating barrel 21. The screw 25 includes a screw shaft 25A, a spiral flight 25B formed around the screw shaft 25A, and a fixed end 25C provided at the rear end of the screw shaft 25A and fixed to a screw drive shaft 45A described later.

[0017] The plasticizing section 20 also includes a first drive device 30 that moves the screw 25 forward or backward, and a second drive device 40 that rotates the screw 25 forward or backward. The first drive device 30 moves the screw 25 forward or backward via the second drive device 40.

[0018] The first drive device 30 comprises a first base 31 fixed to the outer periphery of the heating barrel 21, a pair of ball screws 33 extending in the front-to-rear direction through the first base 31, and a pair of injection electric motors 35 for rotating the ball screws 33 forward or reverse. The ball screw 33 includes a ball screw shaft 33A and a ball screw nut 33B fitted onto the ball screw shaft 33A. The ball screw shaft 33A penetrates the first base 31 at the front side and is provided rotatably relative to the first base 31. The ball screw nut 33B is fixed to a housing 41 of the second driving device 40. The injection electric motor 35 is supported by the first base 31 and has a ball screw shaft 33A and an output shaft (not shown) coupled thereto. The injection electric motor 35 is formed, for example, by a servo motor, and is provided with an encoder 36 that detects the rotation state of the output shaft. The control device 50 controls the rotation of the injection electric motor 35 while acquiring the rotation detection result from the encoder 36.

[0019] The second drive unit 40 comprises a housing 41 provided behind the heating barrel 21, an electric motor for plasticization 43 attached to the rear end of the housing 41, and a transmission mechanism 45 that transmits the rotational driving force of the electric motor for plasticization 43 to the screw 25. The housing 41 includes an accommodation chamber 41A for accommodating the transmission mechanism 45, and a holder 41B for holding the ball screw nut 33B. Two holders 41B are provided to hold the ball screw nuts 33B of the pair of ball screws 33, respectively.

[0020] The plasticizing electric motor 43 rotates the screw 25 in the normal direction or in the reverse direction via the transmission mechanism 45. The plasticizing electric motor 43 rotates its output shaft 43A in the normal direction or in the reverse direction based on an instruction from the control device 50.

[0021] The transmission mechanism 45 includes a coupling 45B that connects the output shaft 43A of the plasticizing electric motor 43 and the fixed end 25C of the screw 25. The coupling 45B includes a screw drive shaft 45A that fixes the fixed end 25C of the screw 25 by fitting. The transmission mechanism 45 also includes a bearing 45C that rotatably supports the coupling 45B inside the accommodation chamber 41A, and a bearing 45D. The transmission mechanism 45 also includes a load cell 45E between the fixed end 25C and the screw drive shaft 45A, and can detect the pressure that the screw 25 receives in the axial direction C. The location where the load cell 45E is disposed is not limited to between the fixed end 25C and the coupling 45B, and may be between the coupling 45B and the bearing 45D or between the coupling 45B and the accommodation chamber 41A. The control device 50 controls the back pressure of the screw 25 during plasticization and other factors while acquiring the detected pressure from the load cell 45E.

[0022] The housing 41 is supported so as to be able to move forward or backward. When the housing 41 moves forward, the electric motor 43 for plasticization and the transmission mechanism 45 also move forward, and when the housing 41 moves backward, the electric motor 43 for plasticization and the transmission mechanism 45 also move backward.

[0023] [Operation of the plasticizing unit 20: see Figure 1] If the injection electric motors 35, 35 of the first drive device 30 rotate in the normal direction, the ball screw shafts 33A, 33A also rotate in the normal direction. Then, with the rotation of the ball screw shafts 33A, 33A, the ball screw nut 33B, 33B fitted to the ball screw shaft 33A, 33A, advances, for example. Since the ball screw nut 33B, 33B is fixed to the holders 41B, 41B, when the ball screw nut 33B, 33B advances, the housing 41 advances accordingly to the advancement of the holders 41B, 41B. At this time, the plasticizing electric motor 43 and the transmission mechanism 45 also advance. When the injection electric motors 35, 35 of the first drive device 30 are rotated in the reverse direction, the above operations are reversed, and the housing 41, the plasticizing electric motor 43 and the transmission mechanism 45 move backward.

[0024] If the plasticizing electric motor 43 of the second drive device 40 rotates in the forward direction, for example, the screw 25 rotates in the forward direction via the transmission mechanism 45, and if the plasticizing electric motor 43 of the second drive device 40 rotates in the reverse direction, for example, the screw 25 rotates in the reverse direction.

[0025] The injection molding machine 1 performs a series of resin injection molding operations by combining forward or backward movement and forward or reverse rotation of the screw 25.

[0026] [Control device 50: see FIG. 2] Next, the control device 50 will be described. The control device 50 is configured by a computer, and monitors the operating state of the injection molding machine 1 and controls the operations of the injection electric motor 35 and the plasticizing electric motor 43. Controlling the operations of the injection electric motor 35 and the plasticizing electric motor 43 means controlling the operation of the plasticizing unit 20. 1, the control device 50 includes a control unit 51, a storage unit 53, an operation unit 55, and a display unit 57. The control device 50 may include elements other than the control unit 51 to the display unit 57.

[0027] [Control unit 51] The control unit 51 executes various functions based on the programs read out from the storage unit 53. The functions include a first function of controlling the operations of the injection electric motor 35 and the plasticization electric motor 43, and a second function of controlling the setting / changing of molding conditions. The first function controls the electric motor 35 for injection and the electric motor 43 for plasticization based on the detection results of the encoder 36 and the load cell 45E. The second function sets / changes the molding conditions by referring to information on the molding conditions stored in the memory unit 53. The detection results of the encoder 36 and the load cell 45E may also be used in the second function. For example, the forward or backward speed and the backward amount of the screw 25 can be obtained based on the detection result of the encoder 36. In addition, the back pressure of the screw 25 in the metering process, the injection pressure in the injection process, and the dwell pressure in the dwell process can be obtained based on the detection result of the load cell 45E. The control unit 51 is composed of, for example, a CPU (Central Processing Unit).

[0028] [Storage section 53] The storage unit 53 is configured with an HDD (Hard Disk Drive), an SSD (Solid State Drive), etc., and stores various programs and data necessary for the control unit 51 to execute the first function and the second function. The storage unit 53 may be physically integrated, or may be physically divided into multiple storage elements. If the storage unit 53 is physically integrated, the storage area can be divided according to the type of data to be stored. If the storage unit 53 is physically divided into multiple storage elements, the stored elements can be identified according to the type of data to be stored.

[0029] The programs necessary for the control unit 51 to execute the first and second functions include those related to the procedure of injection molding. Among them, the procedure related to this embodiment is the procedure of changing the group of molding conditions after the raw material inlet 29 is blocked. For example, this corresponds to the procedure of changing the second group of molding conditions every predetermined number n (n≧1) of molding shots after the molding operation shifts from step 1 to step 2 after the raw material inlet 29 is blocked. Also, this corresponds to the procedure of changing the second group of molding conditions when the retreat speed of the screw in the metering process or the retreat amount of the screw in a predetermined time falls below a predetermined value.

[0030] [Operation unit 55, display unit 57] The operation unit 55 accepts an input operation by the operator of the injection molding machine 1, and outputs a signal corresponding to the input operation to the control unit 51. The display unit 57 displays an image corresponding to the input operation on the operation unit 55 under the control of the control unit 51. FIGS. 6 to 9 show examples of displaying molding condition groups on the display unit 57.

[0031] The display screen of the display unit 57 is used for setting the injection molding machine 1. An operator operates the operation unit 55 while looking at the display screen displayed on the display unit 57 to set the injection molding machine 1.

[0032] The operation unit 55 and the display unit 57 may be integrated, for example, by configuring them as a touch panel. In order to clarify the presence of both, an example in which the operation unit 55 and the display unit 57 are independent is shown in FIG.

[0033] [Molding procedure by injection molding machine 1: see Figures 3 and 6] The injection molding machine 1 obtains one or more molded products by performing one shot of operation including the steps shown in FIG. 3. As shown in FIG. 3, one shot is composed of a mold closing step including mold clamping, an injection step, a plasticization step, a mold opening step, and a removal step, which are performed in this order. The control device 50 controls the execution of the molding shot consisting of this series of steps. Note that FIG. 3 also shows an example of ON / OFF of the injection electric motor 35 and the plasticization electric motor 43, but does not show the rotation direction (forward / reverse) of the motor. In addition, the steps listed above are examples, and other steps may be included. In addition, multiple types of molding conditions in the steps listed below are stored as parameters in the storage unit 53, and the control unit 51 controls the operation of the injection molding machine 1 using the necessary parameters.

[0034] Clamping process: The fixed mold 11 and the movable mold 13 are closed and clamped under high pressure. In the mold clamping step, conditions such as the mold clamping force are also set, but since these conditions are not related to the object of this embodiment, the description thereof will be omitted. The same applies to the mold opening step and the removal step.

[0035] Plasticization / metering process: As the resin pellets, which are the resin raw material, are transported to the tip of the screw 25, they are melted and plasticized inside the heating cylinder 21 by heat from the heater 27 and by shear heat generated by the screw rotation torque applied by the plasticization electric motor 43. The plasticized molten resin is then transported to the tip of the screw 25 and metered to accumulate a certain volume. The molding conditions set in the plasticization / metering process are as follows. These molding conditions are involved in controlling the temperature of the molten resin. Screw 25 rotation speed RS Screw 25 back pressure BP

[0036] Injection process: The plasticized molten resin is injected and filled into the mold cavity 15 formed by the movable mold 13 and the fixed mold 11. The molding conditions set in the injection process are the following injection speed VI, injection pressure PH, and switching position LI. These molding conditions are involved in controlling the temperature of the molten resin. An example of the injection speed VI, injection pressure PH, and switching position LI is shown in Figure 6, but the injection speed VI, injection pressure PH, and switching position LI are switched in stages. Injection speed VI: The speed at which the molten resin is filled into the mold cavity, which is the forward speed of the screw 25 Injection pressure PH: pressure for filling the molten resin into the mold cavity 15, and for advancing the screw 25 Injection speed / pressure switching position LI: The injection speed VI and injection pressure PH are switched during the injection process, and this position is where this switching takes place.

[0037] Dwelling process: Pressure is applied to the molten resin filled in the mold cavity 15 until it cools and solidifies. The molding conditions set in the dwelling process are the following dwelling pressure PL, dwelling time TB, and dwelling gradient TP. An example of the dwelling pressure PL, dwelling time TB, and dwelling gradient TP is shown in Figure 6, and the dwelling pressure PL and dwelling time TB are switched in stages. Holding pressure PL: Pressure applied to the molten resin filled in the mold cavity 15, which is the pressure caused by the forward force of the screw 25 Holding time TB: Time to apply holding pressure PL Packing pressure gradient TP: The degree of change when changing the packing pressure PL

[0038] Mold opening step: The movable mold 13 is moved back from the fixed mold 11 to open the mold section 10. Removal step: The molded product that has been cooled and solidified inside the mold cavity 15 is removed.

[0039] Here, for example, the "group" in the first molding condition group has the following meaning. As described above, in each of the steps from the mold closing process to the removal process that constitute a shot, a single or multiple types of molding conditions are set. Each molding condition is input and set as a parameter in the control device 50. In other words, since a shot includes parameters as multiple types of molding conditions and is a collection of individual molding conditions (parameters), the "group" is used to distinguish it from "molding conditions." For example, each of the injection speed VI, injection pressure PH, switching position LI, holding pressure PL, holding pressure time TB, and holding pressure gradient TP shown in FIG. 6 is a molding condition, and the collection of the molding conditions injection speed VI, injection pressure PH, switching position LI, holding pressure PL, holding pressure time TB, and holding pressure gradient TP is a molding condition group.

[0040] When the same molded product is produced using the injection molding machine 1, typically, a shot (1 shot) is repeated multiple times from the start of molding operation (START) to the end of molding operation (END), as shown in the basic pattern of Fig. 4. As the molding operation approaches the end, the introduction of raw material resin into the heating barrel 21 is stopped. Specifically, the raw material inlet 29 provided in the heating barrel 21 is closed. This is for the following reason. Note that before the inlet is closed, raw material resin continues to be introduced into the heating barrel 21 from the raw material inlet 29. When the molding operation is stopped (END), it is desirable that the groove between the flights 25B of the screw 25 is empty with no resin remaining. If the machine is stopped with resin remaining in the groove of the screw 25, the resin in the groove of the screw 25 may be thermally deteriorated in the process of heating the heating cylinder 21 when the molding operation is started next time. If the groove of the screw 25 is filled with resin and the amount of resin remaining is large, the amount of resin that is thermally deteriorated will also be large, and the amount of resin that cannot be used for a good molded product and must be discarded before the molding operation is started will be large. Therefore, when the molding operation is about to be stopped (END), the raw material inlet 29 is closed to limit the amount of resin remaining in the groove of the screw 25. However, this closing of the raw material inlet 29 causes a starved state where there is little resin at the base of the screw 25. This embodiment provides a measure against the change in state of the plasticized molten resin between the starved state and the full state.

[0041] [Measures against starvation: see Figures 4 and 5] Explain measures to deal with starvation. This measure changes the group of molding conditions, but is divided into two, the first measure and the second measure, depending on the premise of the change. The first measure changes the group of molding conditions according to the number of shots after the raw material inlet 29 is closed, and the second measure changes the group of molding conditions according to detection information regarding the retreat of the screw 25 after the raw material inlet 29 is closed. The first measure and the second measure will be explained below in that order. The group of molding conditions will be described later.

[0042] [Measure 1: See Figure 4] The first measure is to change the group of molding conditions every n (n≧1) of molding shots. A more specific example is shown in FIG. Pattern 1 shown in Figure 4 shows a case where multiple shots of injection molding are performed under the first molding condition group, but after the raw material inlet is closed (CLOSE), the molding operation is switched to the second molding condition group at a specified timing, and injection molding with three shots (three cycles) is performed until the molding operation is stopped (END). All molding conditions of the three shots under the second molding condition group are the same. In pattern 2, multiple shots of injection molding were performed under the first molding condition group, but after the raw material inlet was closed (CLOSE), the molding condition group was switched to the 2-1 molding condition group (step 2-1) at a predetermined timing to perform two shots of molding, and then the molding condition group was switched to the 2-2 molding condition group (step 2-2) to perform one shot and then the molding operation was stopped (END). All molding conditions (set values) for the two shots under the 2-1 molding condition group were the same.

[0043] In the above, only an example (n=2) in which step 2 is divided into two by the second molding condition group is shown, but in this embodiment, step 2 by the second molding condition group can also be divided into three or more (n≧3). The molding conditions (setting values) of each shot (each cycle) in each divided step 2-n are the same. For example, the molding conditions of step 2-n and step 2-(n-1) may be partially the same or completely different.

[0044] [Second measure: See Figure 5] The second measure is to change the molding condition group based on the detection information regarding the retreat of the screw 25, more specifically, the retreat speed V25 of the screw 25 in the metering process or the retreat amount L25 of the screw 25 in a predetermined time. To change the molding condition group, a retreat speed threshold Vt or a retreat amount threshold Lt is set in advance and compared with the detected retreat speed V25 or retreat amount L25. Note that the retreat speed V25 compared with the retreat speed threshold Vt at this time may be either an instantaneous speed or an average speed in a predetermined section. Pattern 1 in FIG. 5 is a pattern in which, after the raw material inlet 29 is closed, the detected retraction speed V25 is compared with the retraction speed threshold Vt, and when the retraction speed V25 falls below the retraction speed threshold Vt, the first molding condition group is switched to the second molding condition group.

[0045] In the pattern 2 in FIG. 5, two retreat speed thresholds Vt are provided, vt1 and vt2. After the raw material inlet 29 is closed, the detected retreat speed V25 is compared with the retreat speed threshold Vt1, and when the retreat speed V25 falls below the retreat speed threshold Vt1, the first molding condition group is switched to the 2-1 molding condition group. The retreat speed V25 is continuously detected and compared with the retreat speed threshold Vt2, and when the retreat speed V25 falls below the retreat speed threshold Vt2, the 2-1 molding condition group is switched to the 2-2 molding condition group. When the retreat speed V25 falls below the retreat speed threshold Vt2, it is not necessary to switch the molding condition group. For example, in order to avoid detection of an erroneous signal due to noise, it is preferable to count the number of times a signal in which the retreat speed V25 falls below the retreat speed threshold Vt2 is generated, and to switch from the 2-1 molding condition group to the 2-2 molding condition group when the counted number falls below a predetermined number. 5, two retraction amount thresholds, Lt1 and Lt2, are provided. After the raw material inlet 29 is closed, the retraction amount L25 detected at a predetermined time is compared with the retraction amount threshold Lt1, and when the retraction amount L25 at the predetermined time falls below the retraction amount threshold Lt1, the first molding condition group is switched to the 2-1 molding condition group. The retraction amount L25 at the predetermined time is continuously detected and compared with the retraction amount threshold Lt2, and when the retraction amount L25 at the predetermined time falls below the retraction amount threshold Lt2, the 2-1 molding condition group is switched to the 2-2 molding condition group.

[0046] The retreat speed V25 of the screw 25 in the metering process is proportional to the amount of resin discharged from the screw 25. Therefore, when the resin conveying speed by the screw 25 decreases, the retreat speed of the screw 25 also decreases. For this reason, the degree of starvation in the groove of the screw 25 can be detected by monitoring the decrease in the retreat speed of the screw 25. Therefore, the temperature of the resin discharged from the screw 25 can be estimated and uniquely grasped based on the retreat speed of the screw 25. By utilizing this, the filling status in the screw groove can be grasped and the molding conditions can be appropriately switched.

[0047] [Examples of switching molding conditions] At least one of the following molding conditions is selected as the switching molding condition. The following conditions are factors that can suppress the temperature rise of the molten resin. (1) Back pressure (BP) in the weighing process The back pressure BP in the plasticization process is made smaller than before. By doing so, the resistance to the screw retreat can be reduced. This reduces the molten resin pressure at the tip of the screw, so that even if the resin conveying force in the screw 25 decreases, the decrease in conveying speed can be reduced. This prevents the molten resin in the screw groove from being subjected to a shear force for an increased period of time, thereby preventing the temperature rise of the molten resin. This reduces the risk of problems such as overfilling. The back pressure BP can be detected by a load cell 45E provided between the fixed end 25C of the screw 25 and the screw drive shaft 45A and feedback controlled.

[0048] (2) Rotation speed RS of screw 25 in the plasticization / metering process The rotation speed RS of the screw 25 is increased from the previous speed. By doing so, the resin transport speed in the groove of the screw 25 is increased, and the time during which the resin is subjected to a shear force in the groove of the screw 25 can be shortened. This makes it possible to suppress the temperature rise of the molten resin and reduce the risk of problems such as overfilling.

[0049] (3) Temperature Tc of the heater barrel 21 Since the resin in the screw groove receives heat from the high-temperature heating barrel 21, by lowering the temperature of the heating barrel 21, the amount of heat received from the heating barrel 21 can be reduced, thereby suppressing the rise in the temperature of the molten resin and reducing the risk of problems such as overfilling.

[0050] (4) The forward speed of the screw 25 (injection speed VI) is reduced. The temperature of the molten resin filling the cavity drops as it comes into contact with the low-temperature cavity wall. As the injection speed VI decreases, the time during which heat is lost by the cavity wall during flow increases, and the degree of drop in the resin temperature increases. This increases the degree of viscosity increase during filling of the molten resin, whose temperature has risen and viscosity has decreased during plasticization, reducing the risk of problems such as overfilling.

[0051] (5) Injection speed switching position LI When the temperature of the molten resin being injected rises, even if the temperature drops in the cavity, the temperature after the drop is still higher than the resin temperature during production operation. Therefore, the resin viscosity at this time is also low, and the degree of pressure drop during flow in the cavity during production operation is also small. Therefore, even if the elapsed time from the start of injection is the same, the position of the end of the flow moves downstream compared to production operation. In response to this, the risk of problems such as overfilling can be reduced by shifting the injection speed switching position, especially the holding pressure switching position, to the upstream side.

[0052] (6) Injection pressure PH By lowering the injection pressure PH in the injection process, the speed of the filling flow of the molten resin, which is a pressure flow, is reduced, thereby obtaining the same effect as that of (5) above.

[0053] (7) Holding pressure PL or holding time TB By lowering the dwell pressure PL, the resin pressure at the end of the cavity can be reduced. Also, by shortening the dwell time TB, the time during which the resin pressure is applied to the end of the cavity can be shortened, thereby reducing the risk of problems such as overfilling.

[0054] [Examples of molding condition group switching: See Figures 6, 7, 8, and 9] Assume now that the injection molding machine 1 is operated under the conditions (initial conditions) shown in Fig. 6, and an injection molded product is produced. If injection molding under this first group of molding conditions is step 1, then it switches to step 2, which is injection molding under the second group of molding conditions shown in Fig. 7. As a prerequisite for this switching, the raw material inlet 29 is closed. After the control unit 50 learns that the raw material inlet 29 has been closed, the group of molding conditions is switched at a predetermined timing. The means by which the control unit 50 learns that the raw material inlet 29 has been closed may be a manual input by an operator to the control unit 50, or a sensor (not shown) may be provided near the raw material inlet 29 and the sensor may automatically detect the closure.

[0055] As shown in Fig. 6, in the first group of molding conditions, the injection speed VI is set to 10.0, 20.0, 30.0, 40.0, 50.0 and 60.0 (%), i.e., six steps per shot, during the injection process. The injection pressure PH is also set to six steps. The switching position LI is set to 105.0, 50.0, 40.0, 30.0, 20.0 and 10.0 (mm), i.e., six steps per shot. During the dwell process, the dwell pressure PL and dwell time TB are set to four steps.

[0056] With the closing of the raw material inlet 29, the operation of the injection molding machine 1 transitions to step 2 under the second group of molding conditions. An example of the second group of molding conditions is shown in Figure 7. In the example shown in Figure 7, the injection speed VI and the injection pressure PH are switched as follows while the switching position LI remains the same. Note that for each of the injection speed VI and the injection pressure PH, the upper row is the condition for step 1, and the lower row is the condition for step 2. Injection speed VI: 10.0, 20.0, 30.0, 40.0, 50.0 and 60.0 (%) Injection speed VI: 5.0, 10.0, 20.0, 30.0, 40.0 and 50.0(%) Injection pressure PH: 10.0, 20.0, 30.0, 40.0, 50.0 and 60.0 (%) Injection pressure PH: 5.0, 10.0, 20.0, 30.0, 40.0 and 50.0(%)

[0057] Fig. 8 shows another example of the second molding condition group. In the example of Fig. 8, the dwell pressure PL in the dwell step is changed to a lower value. The other molding conditions remain the same as before. Holding pressure PL: 10.0, 20.0, 30.0, 0.0 (%) Holding pressure PL: 5.0, 10.0, 20.0, 0.0(%)

[0058] Fig. 9 shows yet another example of the second molding condition group. In the example of Fig. 9, the switching position LI in the injection process is shifted upstream of the pressure holding switching position.

[0059] In addition, the switching between steps 1 and 2 of the rotation speed RS of the screw 25 and the back pressure BP of the screw 25, which are the molding conditions in the plasticization / metering process, is similar to the switching between steps 1 and 2 of the injection speed VI, injection pressure PH, and holding pressure PL in the injection process described above, so it is not shown in the figure.

[0060] [Effects of the embodiment] During molding operation in step 1, the control device 50 in the injection molding machine 1 transitions from step 1 to step 2 based on the closing of the raw material inlet 29, and the second group of molding conditions is changed from the first group of molding conditions to molding conditions involved in suppressing the temperature of the molten resin. Closing of the raw material inlet 29 means that the end of the molding operation is approaching, and according to the injection molding machine 1, the molding conditions involved in suppressing the temperature of the molten resin are changed at an appropriate timing.

[0061] According to this embodiment, the molding conditions in the second molding condition group can be changed for each shot after moving to step 2. Therefore, the remaining molding operation can be performed under conditions corresponding to small temperature changes of the molten resin discharged from the screw 25.

[0062] According to this embodiment, after moving to step 2, the molding conditions in the second molding condition group can be changed for each of the multiple shots. Therefore, since the molding conditions can be changed stepwise and largely, the time and the number of shots required to reach the target state can be reduced. In addition, when the weight of the molded product in one shot is small and the consumption of the resin in the screw groove is small, so that the change in the starvation state is small, changing the molding conditions in the second molding condition group for each shot may cause the molding state to become unstable. In this case, by changing the molding conditions in the second molding condition group for each of the multiple shots, the molding condition group can be switched while maintaining a stable molding state.

[0063] Since the retreat speed of the screw 25 in the metering process is proportional to the amount of resin discharged from the screw 25, when the transport speed of the molten resin in the screw groove decreases, the retreat speed of the screw 25 also decreases. Therefore, by monitoring the retreat speed of the screw 25, the degree of starvation in the screw groove can be detected. Therefore, the temperature of the resin discharged from the screw 25 can be uniquely grasped by the retreat speed of the screw. By utilizing this, the filling status can be grasped and the molding conditions can be appropriately changed.

[0064] In addition to the above, the configurations given in the above embodiments can be selected or appropriately changed to other configurations without departing from the spirit of the present invention. In the injection molding method of the present invention, the molding operations in steps 1 and 2 can be used not only at the end of the production molding operation for producing the above-mentioned injection-molded product, but also in combination with a preparatory molding operation before the start of the production molding operation. In other words, at the start-up of the start of the production molding operation, a preparatory molding operation is performed in which molding conditions such as injection speed and pressure are gradually changed, and the present invention can also be applied at the end of the production molding operation. Also, the starvation state in the metering process may be detected not based on the retreat speed of the screw, but by monitoring the output torque (plasticization torque) of the plasticization electric motor 43 based on the current value supplied to the plasticization electric motor 43 from a power source (not shown), and detecting when the plasticization torque falls below a predetermined value. Specifically, as the amount of raw resin in the screw groove decreases, the screw drive torque required for shear heat generation of the raw resin also decreases. When the screw base becomes starved and the amount of raw resin decreases, the friction between the raw resin at the screw base and the inner circumferential surface of the heater barrel also decreases, so the screw drive torque decreases. As a result, the starvation state of the screw base can be detected by the drive torque of the plasticization electric motor 43. [Explanation of symbols]

[0065] 1 injection molding machine 10. Mold Department 11 Fixed mold 13 Movable mold 20 Plasticization Section 21 Heating tube 23 Discharge nozzle 25 Screw 25A screw shaft 25B Flight 25C fixed end 27 Heater 29 Hopper 30 First Drive Unit 31 The First Foundation 33 Ball screw 33A Ball screw shaft 33B Ball screw nut 35 Injection electric motor 36 Encoder 40 Second Drive Unit 41 Housing Containment Cell 41A 41B Holder 43 Plasticizing electric motor 43A Output shaft 45 Transmission Mechanism 45A screw drive shaft 45B Coupling 45C, 45D bearings 45E Load Cell 50 Control device 51 Control section 53 Storage section 55 Operation section 57 Display section

Claims

1. Step 1: performing a molding operation by repeating a plurality of molding shots under a first molding condition group including a plurality of types of molding conditions; and step 2 of repeating a plurality of the molding shots under a second molding condition group including a plurality of types of the molding conditions, and then terminating the molding operation. After the raw material inlet is closed, the process proceeds from step 1 to step 2, In the step 2, the molding operation is carried out while the raw material inlet is kept closed, The injection molding method, wherein the second group of molding conditions is a group of molding conditions that are different from the first group of molding conditions and that are involved in suppressing the temperature of the molten resin.

2. In step 2, changing the second group of molding conditions every predetermined number n (n≧1) of molding shots; The injection molding method according to claim 1.

3. In step 2, 2. The injection molding method according to claim 1, wherein the second group of molding conditions is changed when a retraction speed of the screw in the metering step or a retraction amount of the screw in a predetermined time falls below a predetermined value.

4. In step 2, The injection molding method according to claim 1 , wherein the second group of molding conditions is changed when a screw driving torque in the metering step falls below a predetermined value.

5. The molding conditions related to the suppression of the temperature of the molten resin are as follows: At least one of the above molding conditions in the injection step, or At least one of the molding conditions in the plasticization and metering step; The injection molding method according to claim 1.

6. Step 1 of repeatedly performing a molding operation by a plurality of molding shots under a first molding condition group including a plurality of types of molding conditions; a step 2 of repeating the molding shots under a second molding condition group including a plurality of types of the molding conditions and then terminating the molding operation, The control device includes: After acquiring information that the raw material inlet has been closed in step 1, the molding operation is shifted from step 1 to step 2 while the raw material inlet is kept closed; The second group of molding conditions changes the molding conditions related to the first group of molding conditions and the suppression of the temperature of the molten resin.

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