Control method and control device for 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 control method for an injection molding machine.

Background Art

[0002] When starting injection molding by an injection molding machine, it is necessary to gradually change molding conditions such as injection speed and pressure to shift 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, defects such as flashing on the molded product and damage to the mold may occur. Regarding this defect, 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 introduced from the rear side (screw base) of the screw and conveyed forward along with the rotation of the screw. The conveying force of the resin inside the screw groove is greatly affected by the frictional force between the raw material in a solid state at the screw base and the inner peripheral surface of the heating cylinder (barrel) that houses the screw. Therefore, when the raw material resin at the screw base is in a starving state, that is, when the amount of raw material resin in the screw base is small and the contact area (frictional area) between the raw material resin and the inner peripheral surface of the heating cylinder is small, the conveying ability of the raw material resin decreases and the conveying speed of the raw material resin becomes slow. The starving state of the raw material resin typically occurs when the end of injection molding is approaching and the supply of the raw material resin has stopped. When the raw material resin transport speed decreases, the time required for the raw material resin to travel a unit distance within the screw groove increases. As a result, the time the raw material resin in the screw groove is subjected to shearing due to the rotation of the screw increases before it is discharged from the screw tip. This causes the temperature of the raw material (molten resin temperature) discharged from the screw to rise. When the molten resin temperature rises, the resin viscosity decreases and it becomes more fluid, changing the flow state of the resin filling the molding cavity of the mold. This can lead to problems such as overfilling under the molding conditions used in the previous molding operation. Overfilling can cause mold damage. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 189131 / 1983 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In contrast, Patent Document 1 sets molding conditions for stable molding during the process in which the screw groove is filled with resin at the start of molding, the raw material transport speed increases, and the molten resin temperature decreases. However, it cannot address problems caused by the rise in resin temperature in the screw groove as the end of the molding operation approaches. Therefore, the present invention aims to provide an injection molding method that can suppress the rise in molten resin temperature 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 is Step 1 involves repeating the molding operation by performing multiple molding shots using a first set of molding conditions that include multiple types of molding conditions, Step 2 comprises repeating the molding operation by performing multiple molding shots using a second set of molding conditions that includes multiple types of molding conditions, After the raw material input port is closed, the process moves from step 1 to step 2. Step 2 involves performing the molding operation with the raw material input port closed. The second group of molding conditions differs from the first group of molding conditions in that the molding conditions involved in suppressing the temperature of the molten resin have been modified.

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

[0008] In step 2 of the injection molding method of the present invention, preferably, If the screw retraction speed during the weighing process or the amount of screw retraction over a predetermined time falls below a predetermined value, the second group of molding conditions is changed.

[0009] In step 2 of the injection molding method of the present invention, preferably, If the screw drive torque in the weighing process falls below a predetermined value, the second group of molding conditions is changed.

[0010] In the injection molding method of the present invention, the molding conditions that are involved in suppressing the temperature of the molten resin are: At least one of the molding conditions in the injection process, or It is at least one of the molding conditions in the plasticization and weighing process.

[0011] The control device in the injection molding machine of the present invention is Step 1 involves repeatedly performing a molding operation by using a first set of molding conditions that include multiple types of molding conditions, Step 2 involves repeatedly performing a molding operation by using a second set of molding conditions that includes multiple types of molding conditions, followed by step 3. The control device of the present invention is After obtaining information that the raw material inlet was closed during the molding operation in Step 1, the molding operation is moved from Step 1 to Step 2 while the raw material inlet remains closed. The second molding condition group changes the molding conditions involved in the temperature suppression of the molten resin and the first molding condition group.

Advantages of the Invention

[0012] According to the present invention, after closing the raw material inlet in the molding operation in Step 1, the process proceeds from Step 1 to Step 2, and the second molding condition group changes the molding conditions involved in the temperature suppression of the molten resin and the first molding condition group. The closing of the raw material inlet means that the end of the molding operation is approaching. According to the present invention, the molding conditions involved in the temperature suppression of the molten resin are changed at an appropriate timing.

Brief Description of the Drawings

[0013] [Figure 1] It is a plan view showing an injection molding machine according to an embodiment. [Figure 2] It is a diagram showing the configuration of a control device of an injection molding machine according to an embodiment. [Figure 3] It is a diagram showing the breakdown of one shot constituting the molding operation of an injection molding machine according to an embodiment. [Figure 4] It is a diagram showing an example from the start to the stop of the molding operation in an injection molding machine according to an embodiment. [Figure 5] It is a diagram showing another example from the start to the stop of the molding operation in an injection molding machine according to an embodiment. [Figure 6] It is a diagram showing an example of the first molding condition group in an injection molding machine according to an embodiment. [Figure 7] It is a diagram showing an example of the second molding condition group in an injection molding machine according to an embodiment. [Figure 8] It is a diagram showing another example of the second molding condition group in an injection molding machine according to an embodiment. [Figure 9] It is a diagram showing another example of the second molding condition group in an injection molding machine according to an embodiment.

Modes for Carrying Out the Invention

[0014] Embodiments of the present invention will be described below with reference to the attached drawings. As shown in Figure 1, the injection molding machine 1 according to this embodiment includes a mold section 10, a plasticizing section 20, and a control device 50 that controls the operation of these sections. The injection molding machine 1 can suppress the rise in resin temperature in the screw groove as the end of the molding operation approaches, and prevent overfilling of the mold section 10. The following describes the configuration and basic operation of the injection molding machine 1, followed by a description of the control procedure by the control device 50. In the injection molding machine 1, the terms "front (F)" and "rear (R)" are defined as shown in Figure 1.

[0015] [Mold section 10: See Figure 1] The mold section 10 comprises a fixed mold 11 whose position is fixed, and a movable mold 13 which can move forward and backward relative to the fixed mold 11. In the clamped state where the fixed mold 11 and the movable mold 13 are abutted together, a mold cavity 15 is formed between the fixed mold 11 and the movable mold 13. The resin plasticized in the plasticizing section 20 is injected and filled into the mold cavity 15. Although not shown in the diagram, the fixed mold 11 is attached to the fixed mold platen, and the movable mold 13 is attached to the movable mold platen. Multiple tie bars are provided between the fixed mold platen and the movable mold platen to connect them, and mold clamping or mold opening is performed by applying pressure, for example, from a hydraulic cylinder, between the fixed mold platen and the movable mold platen via the tie bars. Also, although not shown in the diagram, the mold section 10 is provided with ejector pins that push the injection molded product out of the mold in the open state.

[0016] [Plasticizing part 20: See Figure 1] The plasticizing unit 20 includes a heating cylinder 21, a discharge nozzle 23 provided at the front end of the heating cylinder 21, a screw 25 rotatably mounted inside the heating cylinder 21, and a heater 27 wrapped around the front side of the heating cylinder 21. Pellet-shaped raw material resin is supplied into the heating cylinder 21 through a raw material inlet 29 provided in the heating cylinder 21. The heater 27 heats the resin inside the heating cylinder 21 according to the instructions of the control device 50. The heating cylinder 21 is fixed in position, and the screw 25 is able to move forward or backward inside the heating cylinder 21. The screw 25 includes a screw shaft 25A, a helical flight 25B formed around it, and a fixed end 25C provided at the rear end of the screw shaft 25A and fixed to a screw drive shaft 45A, which will be described later.

[0017] Furthermore, the plasticizing unit 20 includes a first drive unit 30 that moves the screw 25 forward or backward, and a second drive unit 40 that rotates the screw 25 in the forward or reverse direction. The first drive unit 30 moves the screw 25 forward or backward via the second drive unit 40.

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

[0019] The second drive unit 40 includes a housing 41 provided behind the heating cylinder 21, a plasticizing electric motor 43 attached to the rear end of the housing 41, and a transmission mechanism 45 that transmits the rotational driving force of the plasticizing electric motor 43 to the screw 25. The housing 41 comprises a housing chamber 41A in which the transmission mechanism 45 is housed, and a retainer 41B for holding the ball screw nuts 33B. Two retainers 41B are provided to hold the respective ball screw nuts 33B of the pair of ball screws 33.

[0020] The plasticizing electric motor 43 rotates the screw 25 in the forward or reverse direction via the transmission mechanism 45. The plasticizing electric motor 43 rotates its output shaft 43A in the forward or reverse direction based on instructions 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 to 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 and a bearing 45D that rotatably support the coupling 45B inside the housing chamber 41A. Furthermore, the transmission mechanism 45 is equipped with a load cell 45E between the fixed end 25C and the screw drive shaft 45A, which can detect the pressure exerted on the screw 25 in the axial direction C. Note that the location where the load cell 45E is placed is not limited to between the fixed end 25C and the coupling 45B; for example, it may be placed between the coupling 45B and the bearing 45D or between the coupling 45B and the housing chamber 41A. The control device 50 controls the back pressure of the screw 25 during plasticization and other parameters while acquiring the detected pressure from the load cell 45E.

[0022] The housing 41 is supported so that it can move forward or backward. When the housing 41 moves forward, the plasticizing electric motor 43 and the transmission mechanism 45 also move forward, and when the housing 41 moves backward, the plasticizing electric motor 43 and the transmission mechanism 45 also move backward.

[0023] [Operation of the plasticizing unit 20: See Figure 1] If the injection motors 35, 35 of the first drive unit 30 rotate in the forward direction, for example, the ball screw shafts 33A, 33A also rotate in the forward direction. As a result, the ball screw nuts 33B, 33B fitted to the ball screw shafts 33A and 33A move forward. Since the ball screw nuts 33B, 33B are fixed to the retainers 41B, 41B, when the ball screw nuts 33B, 33B move forward, the housing 41 moves forward in accordance with the movement of the retainers 41B, 41B. At this time, the plasticizing motor 43 and the transmission mechanism 45 also move forward. If the injection motors 35, 35 of the first drive unit 30 are reversed, for example, the housing 41, the plasticizing motor 43, and the transmission mechanism 45 will retract by performing the opposite operation.

[0024] If the plasticizing electric motor 43 of the second drive unit 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 unit 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 moldings by combining the forward or backward movement and forward or reverse rotation of the screw 25.

[0026] [Control device 50: See Figure 2] Next, the control device 50 will be described. The control device 50 is a computer that monitors the operating status of the injection molding machine 1 and controls the operation of the injection motor 35 and the plasticizing motor 43. Controlling the operation of the injection motor 35 and the plasticizing motor 43 means controlling the operation of the plasticizing unit 20. As shown in Figure 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 program read from the storage unit 53. These functions include a first function that controls the operation of the injection motor 35 and the plasticizing motor 43, and a second function that controls the setting / changing of molding conditions. The first function controls the injection motor 35 and the plasticizing motor 43 based on the detection results of the encoder 36 and the load cell 45E. The second function sets / changes molding conditions by referring to information on molding conditions stored in the memory unit 53. In the second function as well, the detection results of the encoder 36 and load cell 45E may be used. For example, the forward or backward speed and 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 holding pressure in the holding pressure 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 composed of an HDD (Hard Disk Drive), SSD (Solid State Drive), etc., and stores various programs and data necessary for the control unit 51 to execute the first and second functions. The storage unit 53 may be physically a single unit or may be physically divided into multiple storage elements. When it is physically a single unit, the storage area can be divided according to the type of data to be stored. When it is physically divided into multiple storage elements, the element to be stored can be identified according to the type of data to be stored.

[0029] The program required for the control unit 51 to execute the first and second functions includes procedures related to injection molding. Among these, one relevant to this embodiment is the procedure for changing the molding conditions after the raw material inlet 29 is closed. For example, this includes the procedure for changing the second molding conditions every n (n≧1) of a predetermined number of molding shots after the molding operation has transitioned from step 1 to step 2 following the closure of the raw material inlet 29. Another example is the procedure for changing the second molding conditions if the screw retraction speed in the metering process or the amount of screw retraction in a predetermined time falls below a predetermined value.

[0030] [Operation unit 55, display unit 57] The operation unit 55 receives input operations from 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 in the operation unit 55 under the control of the control unit 51. Figures 6 to 9 show examples of the display of molding condition groups in the display unit 57.

[0031] The display screen of the display unit 57 is used for setting the injection molding machine 1. The operator sets the injection molding machine 1 by operating the control unit 55 while looking at the display screen shown on the display unit 57.

[0032] The operation unit 55 and the display unit 57 may be integrated, for example, by being configured as a touch panel. In Figure 2, an example is shown where the operation unit 55 and the display unit 57 are separate in order to clearly show their presence.

[0033] [Molding procedure using injection molding machine 1: See Figures 3 and 6] The injection molding machine 1 obtains one or more molded parts by performing a single-shot operation that includes the steps shown in Figure 3. As shown in Figure 3, a single shot consists of a mold closing step including mold clamping, an injection step, a plasticizing step, a mold opening step, and a removal step, which are performed in this order. The control device 50 controls the execution of this series of molding shots. Note that Figure 3 also shows an example of the ON / OFF states of the injection motor 35 and the plasticizing motor 43, but does not show the rotation direction of the motors (forward / reverse). Also, the steps listed above are examples, and other steps may be included. Furthermore, 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] Mold clamping process: The fixed mold 11 and the movable mold 13 are closed and clamped together under high pressure. In the mold clamping process, conditions such as clamping force are also set, but since these conditions are not related to the purpose of this embodiment, their explanation will be omitted. The same applies to the mold opening and removal processes.

[0035] Plasticization / Weighing 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 heating from the heater 27 and shear heat generated by the screw rotation torque applied by the plasticizing electric motor 43. The plasticized molten resin is then transported to the tip of the screw 25 for weighing, where a certain volume is accumulated. 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 rotations 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 injection speed VI, injection pressure PH, and switching position LI listed below. These molding conditions are involved in suppressing the temperature of the molten resin. Figure 6 shows an example of injection speed VI, injection pressure PH, and switching position LI, but the injection speed VI, injection pressure PH, and switching position LI are switched in stages. Injection speed VI: The speed at which molten resin is filled into the mold cavity, which is the forward speed of the screw 25. Injection pressure PH: The pressure used to fill the mold cavity 15 with molten resin, and the pressure used to advance the screw 25. Injection speed / pressure switching position LI; This is the position where the injection speed VI and injection pressure PH are switched during the injection process.

[0037] Holding pressure process: Pressure is continuously applied to the molten resin filled in the mold cavity 15 until it cools and solidifies. The molding conditions set in the holding pressure process are as follows: holding pressure PL, holding time TB, and holding gradient TP. Figure 6 shows an example of holding pressure PL, holding time TB, and holding gradient TP, but the holding pressure PL and holding time TB are switched in stages. Holding pressure PL: Pressure applied to the molten resin filling the mold cavity 15, which is the pressure due to the forward force of the screw 25. Holding pressure time TB: The time during which holding pressure PL is applied. Holding pressure gradient TP: The degree of change when the holding pressure PL is changed.

[0038] Mold opening process: The movable mold 13 is retracted from the fixed mold 11 to open the mold section 10. Removal process: The molded product, which has 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. In each of the mold closing process to the removal process that constitutes a shot, one or more types of molding conditions are set as described above. Each molding condition is input and set to the control device 50 as a parameter. In other words, a shot contains parameters as multiple types of molding conditions, and since it is a collection of individual molding conditions (parameters), the term "group" is used to distinguish it from "molding conditions". For example, the injection speed VI, injection pressure PH, switching position LI, holding pressure PL, holding pressure time TB, and holding pressure gradient TP shown in Figure 6 are each molding conditions, 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 the molding condition group.

[0040] When producing the same molded product with injection molding machine 1, typically, as shown in the basic pattern of Figure 4, multiple shots (1 shot) are repeated from the start of the molding operation (START) to the stop of the molding operation (END). As the molding operation approaches its end, the supply of raw material resin into the heating cylinder 21 is stopped. Specifically, the raw material inlet 29 provided in the heating cylinder 21 is closed (CLOSE). This is for the following reasons. Note that before the inlet is closed (CLOSE), the raw material resin continues to be supplied into the heating cylinder 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 and no resin remains. 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 degrade due to heat during the process of heating the heating cylinder 21 when the molding operation is started up again. At this time, if the groove of the screw 25 is filled with resin and the amount of retained resin is large, the amount of resin that degrades due to heat will also be large, resulting in a large amount of heat-degraded resin that cannot be used for good molded products and must be discarded before the molding operation starts. Therefore, as the molding operation approaches its end (END), the raw material inlet 29 is closed to limit the amount of resin remaining in the groove of the screw 25. However, closing the raw material inlet 29 causes a state of resin deficiency at the base of the screw 25. This embodiment provides countermeasures against the state change of the plasticized molten resin between this deficiency state and a filled state.

[0041] [Measures against starvation: See Figures 4 and 5] I will explain measures to address the state of hunger. This countermeasure involves changing the molding conditions, but it is divided into two types, the first and second countermeasures, depending on the premise of the change. The first countermeasure changes the molding conditions according to the number of shots after the raw material inlet 29 is closed, and the second countermeasure changes the molding conditions according to the detection information regarding the retraction of the screw 25 after the raw material inlet 29 is closed. The first and second countermeasures will be explained below in that order. The molding conditions will be described later.

[0042] [First countermeasure: See Figure 4] The first countermeasure involves changing the set of molding conditions for every n (n≧1) molding shots. A more specific example is shown in Figure 4. Pattern 1, shown in Figure 4, illustrates an example where multiple injection molding shots were performed using the first set of molding conditions. However, after the raw material inlet was closed (CLOSE), the molding operation was switched to the second set of molding conditions at a predetermined timing, and injection molding was performed for three shots (3 cycles) until the molding operation was stopped (END). All molding conditions were the same for all three shots using the second set of molding conditions. In Pattern 2, multiple injection molding shots were performed using the first molding condition group. After the raw material inlet was closed (CLOSE), the process switched to the 2-1 molding condition group (Step 2-1) at a predetermined timing to perform two molding shots. Subsequently, it 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 using the 2-1 molding condition group were identical.

[0043] The above only shows an example where Step 2, based on the second molding condition group, is divided into two parts (n=2). However, in this embodiment, Step 2, based on the second molding condition group, can also be divided into three or more parts (n≧3). The molding conditions (set values) for each shot (each cycle) in each divided Step 2-n are the same. For example, the molding conditions for Step 2-n and Step 2-(n-1) may be partially the same or completely different.

[0044] [Second countermeasure: See Figure 5] The second countermeasure involves changing the molding conditions based on detection information regarding the retraction of the screw 25, more specifically, the retraction speed V25 of the screw 25 in the metering process or the retraction amount L25 of the screw 25 over a predetermined time. To change the molding conditions, a retraction speed threshold Vt or a retraction amount threshold Lt is set in advance and compared with the detected retraction speed V25 or retraction amount L25. Note that the retraction speed V25 compared with the retraction speed threshold Vt can be either an instantaneous speed or an average speed over a predetermined period. In Figure 5, Pattern 1 occurs 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 process switches from the first molding condition group to the second molding condition group.

[0045] Pattern 2 in Figure 5 has two retraction speed thresholds Vt, vt1 and vt2. After the raw material inlet 29 is closed, the detected retraction speed V25 is compared with the retraction speed threshold Vt1, and when the retraction speed V25 falls below the retraction speed threshold Vt1, the molding condition is switched from the first molding condition group to the second-first molding condition group. The retraction speed V25 is continuously detected and compared with the retraction speed threshold Vt2, and when the retraction speed V25 falls below the retraction speed threshold Vt2, the molding condition is switched from the second-first molding condition group to the second-second molding condition group. It is not always necessary to switch the molding condition group when the retraction speed V25 falls below the retraction speed threshold Vt2. For example, to avoid detecting false signals due to noise, it is preferable to count the number of times a signal occurs in which the retraction speed V25 falls below the retraction speed threshold Vt2, and switch from the second-first molding condition group to the second-second molding condition group when this count falls below a predetermined number. Pattern 3 in Figure 5 has two recession thresholds, Lt1 and Lt2. After the raw material inlet 29 is closed, the recession amount L25 detected at a predetermined time is compared with the recession threshold Lt1, and when the recession amount L25 at the predetermined time falls below the recession threshold Lt1, the molding condition is switched from the first molding condition group to the second-first molding condition group. The recession amount L25 at the predetermined time is continuously detected and compared with the recession threshold Lt2, and when the recession amount L25 at the predetermined time falls below the recession threshold Lt2, the molding condition is switched from the second-first molding condition group to the second-second molding condition group.

[0046] The retraction speed V25 of the screw 25 during the metering process is proportional to the amount of resin discharged from the screw 25. Therefore, as the resin transport speed by the screw 25 decreases, the retraction speed of the screw 25 also decreases. By monitoring the decrease in the retraction speed of the screw 25, the degree of starvation in the screw groove can be detected. Thus, the temperature of the resin discharged from the screw 25 can be uniquely estimated and determined based on the retraction speed of the screw 25. By utilizing this, the filling status of the screw groove can be understood, and the molding conditions can be appropriately switched.

[0047] [Examples of switching molding conditions] At least one of the following molding conditions will be selected for switching. 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 reduced compared to before. This reduces the resistance to screw retraction. As a result, the molten resin pressure at the screw tip decreases, so even if the resin transport force within the screw 25 decreases, the decrease in transport speed can be minimized. This suppresses the increase in the time that the molten resin is subjected to shear force within the screw groove, thus suppressing the temperature rise of the molten resin. This reduces the risk of problems such as overfilling. The back pressure BP can be detected and feedback controlled by a load cell 45E installed between the fixed end 25C of the screw 25 and the screw drive shaft 45A.

[0048] (2) Rotational speed RS of screw 25 in the plasticizing / metering process The rotational speed RS of screw 25 is increased. By doing so, the resin transport speed within the groove of screw 25 is increased, and the time during which the resin is subjected to shear force within the groove of screw 25 can be shortened. This suppresses the temperature rise of the molten resin and reduces the risk of problems such as overfilling.

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

[0050] (4) Reduce the forward speed of screw 25 (ejection speed VI). The molten resin filling the cavity cools down upon contact with the low-temperature cavity wall. A lower injection speed VI increases the time during which heat is absorbed by the cavity wall during flow, resulting in a greater decrease in resin temperature. This increases the viscosity of the molten resin, which has already experienced a temperature rise and viscosity decrease during plasticization, during filling, thereby reducing the risk of problems such as overfilling.

[0051] (5) Injection speed switching position LI When the temperature of the injected molten resin rises, even if the temperature drops within the cavity, the temperature after the drop will be higher than the resin temperature during production operation. As a result, the resin viscosity at this time is also lower, and the degree of pressure drop during flow within the cavity during production operation is smaller. Therefore, even if the elapsed time from the start of injection is the same, the position of the flow end shifts further downstream than during production operation. In contrast, by changing the injection speed switching position, especially the holding pressure switching position, to the upstream side, the risk of problems such as overfilling can be reduced.

[0052] (6) Injection pressure PH By lowering the injection pressure PH in the injection process, the velocity of the molten resin filling flow, which is a pressure flow, can be reduced, and the same effect as in (5) above can be obtained.

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

[0054] [Examples of switching between molding conditions: See Figures 6, 7, 8, and 9] Let's assume that the injection molding machine 1 is currently operating under the conditions shown in Figure 6 (initial conditions) and that an injection-molded product is being manufactured. If we consider injection molding under these first molding conditions as Step 1, then the process switches to Step 2, where injection molding is performed under the second molding conditions shown in Figure 7. As a prerequisite for this switch, the raw material inlet 29 is closed. After the control unit 50 detects that the raw material inlet 29 has been closed, the switching of the molding conditions is performed at a predetermined timing. The means by which the control unit 50 detects that the raw material inlet 29 has been closed is either by the operator manually inputting the information to the control unit 50, or by installing a sensor (not shown) near the raw material inlet 29 and automatically detecting the closure using this sensor or the like.

[0055] As shown in Figure 6, the first molding condition group has six injection speed settings within a single shot: 10.0, 20.0, 30.0, 40.0, 50.0, and 60.0 (%). Similarly, the injection pressure setting PH is also set in six stages. The switching position setting LI is six stages within a single shot: 105.0, 50.0, 40.0, 30.0, 20.0, and 10.0 (mm). For the holding pressure process, the holding pressure setting PL and holding pressure setting TB are set in four stages.

[0056] Upon closing the raw material inlet 29, the operation of the injection molding machine 1 transitions to step 2, which is governed by the second set of molding conditions. An example of the second set of molding conditions is shown in Figure 7. In the example shown in Figure 7, the injection speed VI and injection pressure PH are switched as follows, while the switching position LI remains the same. Note that for both injection speed VI and injection pressure PH, the upper row represents the conditions in step 1, and the lower row represents the conditions in step 2. Injection velocity VI: 10.0, 20.0, 30.0, 40.0, 50.0 and 60.0 (%) Injection velocity 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] Figure 8 shows another example of the second molding condition group. In the example in Figure 8, the holding pressure PL in the holding pressure process is switched to a lower value. The other molding conditions remain the same. Holding pressure PL: 10.0, 20.0, 30.0, 0.0 (%) Holding pressure PL: 5.0, 10.0, 20.0, 0.0 (%)

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

[0059] Furthermore, the switching between Step 1 and Step 2 of the rotational speed RS and back pressure BP of the screw 25, which are molding conditions in the plasticization / metering process, is the same as the switching between Step 1 and Step 2 of the injection speed VI, injection pressure PH, and holding pressure PL in the injection process described above, so the illustration is omitted.

[0060] [Effects of the embodiment] While the molding operation is in progress in Step 1, the control device 50 in the injection molding machine 1 transitions from Step 1 to Step 2 based on the closure of the raw material inlet 29, and the second set of molding conditions is changed from the first set of molding conditions to the molding conditions involved in suppressing the temperature of the molten resin. The closure 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, after moving to step 2, the molding conditions within the second molding condition group can be changed for each shot. Therefore, the remaining molding operation can be performed under conditions that correspond to small temperature changes in the molten resin discharged from the screw 25.

[0062] According to this embodiment, after moving to step 2, the molding conditions within the second molding condition group can be changed for every multiple shots. Therefore, the molding conditions can be changed in stages, reducing the time and number of shots required to reach the target state. Furthermore, if the weight of the molded product per shot is small and the amount of resin consumed in the screw groove is small, resulting in a small change in the starvation state, changing the molding conditions within the second molding condition group for every shot may lead to an unstable molding state. In this case, by changing the molding conditions within the second molding condition group for every multiple shots, it is possible to switch between molding condition groups while maintaining a stable molding state.

[0063] The retraction speed of screw 25 during the metering process is proportional to the amount of resin discharged from screw 25. Therefore, as the transport speed of molten resin in the screw groove decreases, the retraction speed of screw 25 also decreases. By monitoring the retraction speed of screw 25, the degree of starvation in the screw groove can be detected. Thus, the temperature of the resin discharged from screw 25 can be uniquely determined by the screw's retraction speed. By utilizing this, the filling status can be understood and the molding conditions can be appropriately changed.

[0064] In addition to the above, it is possible to select or replace the configurations listed in the above embodiments, or to change them to other configurations as appropriate, as long as it does not deviate from the spirit of the present invention. In the injection molding method of the present invention, the molding operations in Step 1 and Step 2 can be used not only at the end of the production molding operation that produces the injection molded product described above, but also in combination with the preparatory molding operation before starting the production molding operation. In other words, a preparatory molding operation is performed at the start-up of the production molding operation, 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. Furthermore, instead of detecting the starvation state in the weighing process based on the screw retraction speed, the output torque (plasticizing torque) of the plasticizing electric motor 43 may be monitored by the current value supplied to the plasticizing electric motor 43 from a power source (not shown), and detection may be made when the plasticizing torque falls below a predetermined value. Specifically, as the amount of raw material resin in the screw groove decreases, the screw driving torque required for shear heating of the raw material resin also decreases. Also, when the screw base enters a starvation state and the amount of raw material resin decreases, the friction between the raw material resin at the screw base and the inner surface of the heating cylinder also decreases, so the screw driving torque decreases. As a result, the starvation state of the screw base can be detected by the driving torque of the plasticizing electric motor 43. [Explanation of symbols]

[0065] 1 injection molding machine 10. Mold section 11 Fixed mold 13. Movable mold 20 Plasticizing part 21 Heating cylinder 23 Discharge nozzle 25 Screw 25A Screw shaft Flight 25B 25C fixed end 27 Heater 29 Hoppa 30 First drive unit 31. Base No. 1 33 Ball screw 33A Ball screw shaft 33B Ball screw nut 35 Injection motor 36 encoders 40 Second drive unit 41 Housing 41A Confinement Room 41B Holder 43 Electric motor for plasticization 43A Output shaft 45 Transmission mechanism 45A Screw drive shaft 45B coupling 45C, 45D bearings 45E Load Cell 50 Control device 51 Control Unit 53 Storage section 55 Operation section 57 Display section

Claims

1. Step 1 involves repeating the molding operation by performing multiple molding shots using a first set of molding conditions that include multiple types of molding conditions, Step 2 includes repeating a plurality of molding shots using a second group of molding conditions that includes a plurality of types of molding conditions, and then ending the molding operation. After the raw material input port is closed, the process proceeds from step 1 to step 2. Step 2 involves performing the molding operation with the raw material inlet closed. The second group of molding conditions is set in a manner that, compared to the first group of molding conditions, the molding conditions involved in suppressing the temperature of the molten resin suppress the temperature rise of the molten resin.

2. In step 2, The second set of molding conditions is changed every n (n ≥ 1) of the predetermined number of molding shots. The injection molding method according to claim 1.

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

5. The molding conditions that are involved in suppressing the temperature of the molten resin are: At least one of the molding conditions in the injection process, At least one of the molding conditions in the plasticization and weighing process, The injection molding method according to claim 1.

6. Step 1 involves repeatedly performing a molding operation by using a first set of molding conditions that includes multiple types of molding conditions, A control device for an injection molding machine that sequentially performs the following steps: step 2, which involves repeating a plurality of molding shots using a second group of molding conditions including a plurality of types of molding conditions, and then ending the molding operation; The control device is After obtaining information that the raw material inlet has been closed in step 1, the molding operation is moved from step 1 to step 2 while the raw material inlet remains closed. The control device sets the second set of molding conditions to suppress the temperature rise of the molten resin, in relation to the first set of molding conditions.

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