Injection molding method and injection molding machine

Abstract

To provide an injection molding method that can easily improve the springback phenomenon that occurs during the changeover from the injection process to the pressure holding process.SOLUTION: In the trial molding process, where the injection process is performed under speed control and the pressure holding process is performed under pressure control, the switching position VP from speed control to pressure control, the pressure holding completion position SE under pressure control, and the pressure holding time HT under pressure control are determined, the difference between the switching position VP and the pressure holding completion position SE is the pressure holding travel amount HL, and the holding speed VH of screw 15 to compensate for cooling and solidification shrinkage is calculated from the pressure holding travel amount HL and holding time HT, and set in the injection control unit 40, and for mass production molding following trial molding, the pressure holding process is speed-controlled based on the pressure holding speed VH.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an injection molding method in which the forward movement of a screw is controlled in the injection process to inject and fill molten resin stored in an injection cylinder into a mold cavity, and new molten resin is replenished from the injection cylinder to the mold cavity in the pressure holding process to compensate for the amount of shrinkage that occurs when the injected and filled molten resin cools and solidifies.

[0002] Injection molding using an in-line injection molding machine, which simultaneously plasticizes, stores, and injects resin material, begins by feeding the resin material into the injection cylinder. The resin material is plasticized by shear heating due to the rotational motion of a spiral-flighted screw and heat from a heater or other device attached to the injection cylinder, and is then stored as molten resin in the injection cylinder at the tip of the screw. As the metered resin is stored, the screw retreats, stopping its rotation at a predetermined retreat position to maintain its position. Resistance is applied to this screw retreat to adjust the melt-mixability of the stored metered resin (called backpressure control). This process is called the metering process. The screw advances to the injection process, where the metered resin is injected and filled into the mold cavity; the dwelling process compensates for the shrinkage of the molten metered resin upon cooling and solidifying; and the cooling process cools and solidifies the molten metered resin within the mold cavity. The mold is then opened and the resulting injection-molded product is removed from the mold cavity.

[0003] Furthermore, even in injection molding using a pre-plasticization injection molding machine, in which the plasticization, storage, and injection of the resin material are different, the metered resin is stored in the metering process, and the metered resin is injected and filled into the mold cavity in the injection process, followed by the pressure holding and cooling processes. In either case, speed control is used in the injection process, where the forward speed of the screw is controlled to inject and fill the resin, and pressure control is used in the pressure holding process, where the forward thrust of the screw is controlled to fill the resin at pressure holding.

[0004] During the injection process, the flow pressure of the resin flowing through the mold cavity can reach high pressures of over 100 MPa (equivalent to resin pressure). It has been reported that even higher pressures can occur depending on molding conditions, such as resin materials with high melt viscosity or mold cavity shapes with long filling distances and thin walls. Therefore, to ensure speed control during the injection process, an injection pressure higher than the flow pressure is set in the injection unit. In contrast, the flow pressure required for the dwell filling process during the dwell filling process can be relatively low, sufficient to compensate for cooling and solidification shrinkage. Applying excessive resin pressure during dwell filling can lead to molding defects, such as product deformation due to residual stress. Therefore, it is recommended that the injection pressure set in the injection unit during the dwell filling process be less than half that of the injection process.

[0005] This difference in injection pressure can cause the screw to retract significantly (a phenomenon known as springback) when switching from the injection process to the holding process (called holding pressure switching). This springback phenomenon can cause resin flow disturbances, such as the resin injected into the mold cavity flowing back toward the injection unit, or the resin flow in the mold cavity stopping or flowing backward. This resin flow disturbance can cause many molding defects, such as fluctuations in the injection filling amount (product weight), product appearance defects such as flow marks and transfer failures, internal product defects such as voids and foreign matter contamination, and product short circuits. For this reason, many proposals have been made to prevent the springback phenomenon from occurring when switching between holding pressures.

[0006] For example, Patent Document 1 proposes a control method in which the forward movement of the screw is stopped before the mold cavity is filled with resin during the injection process, and the mold cavity is filled with resin by utilizing the compressibility of the resin, and then the process transitions to a pressure holding process. Patent Document 2 also proposes an injection control method in which the filling process and pressure holding process are controlled by injection speed control, and the injection speed is slowed when the effective pressure value approaches an upper pressure limit so that the actual measured pressure value does not exceed the upper pressure limit. Patent Document 3 also proposes a control method in which a pressure holding control system is provided with negative feedback of the injection speed, which is also used as speed feedback for the injection speed system, a switching process is provided between the injection process and the pressure holding process, and the switching conditions from the injection process to the switching process and from the switching process to the pressure holding process are set by pressure, and the control gain is adjusted during the switching process. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-74114 [Patent Document 2] Japanese Patent Application Publication No. 2-43021 [Patent Document 3] Japanese Patent Application Publication No. 3-243320 Summary of the Invention [Problem to be solved by the invention]

[0008] As noted in Patent Document 1, the pressure-controlled dwelling process can lead to springback depending on the injection pressure setting during the dwelling process. Even if the resin is filled into the mold cavity using the resin's compressibility, the degree of springback can lead to resin backflow into the injection unit and fluctuations in resin pressure within the mold cavity. Furthermore, fluctuations in the resin or mold temperature during continuous molding, as well as fluctuations in the additives contained in the resin, can cause fluctuations in the resin's compressibility and the degree to which the resin fills the mold cavity. These springback and compressibility fluctuations cannot reliably resolve molding defects caused by disturbances in the resin flow.

[0009] Furthermore, as described in Patent Document 2, injection speed control is performed during both the filling process and the pressure-holding process until the effective pressure value reaches the upper pressure limit, and then injection pressure control is performed when the effective pressure value approaches the upper pressure limit. As a result, after the effective pressure value approaches the upper pressure limit, the injection speed is decelerated so that the effective pressure value does not exceed the upper pressure limit. This phenomenon is called injection pressure plateauing in injection speed control, and the injection speed control becomes uncontrolled. In this case, the injection speed is uncontrolled during both the filling process and the pressure-holding process, and a stable injection speed cannot be expected. As a result, this does not improve molding defects caused by disturbances in the resin flow.

[0010] Furthermore, as shown in Patent Document 3, it is believed that continuity of injection pressure can be ensured when switching between processes. This is believed to improve the springback phenomenon. It is also believed that switching between processes is performed based on the injection pressure that increases as the resin is filled. However, injection pressure can fluctuate significantly due to, for example, temperature changes in the metered resin or mold during continuous molding, or fluctuations in the additives contained in the resin. Therefore, fluctuations in the timing of switching between processes can cause fluctuations in the resin flow state, potentially resulting in molding defects similar to or different from those caused by disturbances in the resin flow.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an injection molding method that can easily alleviate the springback phenomenon that occurs when switching from the injection process to the pressure holding process. [Means for solving the problem]

[0012] The injection molding method of the present invention comprises: In an injection molding method, a forward movement of a screw is controlled in an injection step to inject and fill a molten resin stored in an injection cylinder into a mold cavity, and new molten resin is replenished from the injection cylinder toward the mold cavity in a pressure holding step to compensate for cooling, solidification, and shrinkage of the injected and filled molten resin, an injection control unit that controls the speed and pressure of the screw; In a test molding in which the injection process is performed under the speed control and the dwelling process is performed under the pressure control, a switching position from the speed control to the pressure control, a dwelling completion position of the pressure control, and a dwelling time of the pressure control are obtained, the difference between the switching position and the dwelling completion position is set as a dwelling movement amount, and a dwelling speed of the screw that compensates for the cooling solidification shrinkage is calculated from the dwelling movement amount and the holding time, and set in the injection control unit; The mass production molding following the trial molding is characterized in that the speed of the pressure holding step is controlled based on the pressure holding speed.

[0013] In the injection molding method of the present invention, It is preferable to provide a pressure measuring means for measuring the injection pressure during the injection process and the pressure holding process, and to set an injection pressure setting value in the injection control section that is higher than the maximum injection pressure measured by the pressure measuring means. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an injection molding method that can easily improve the springback phenomenon that occurs when switching from the injection process to the pressure holding process. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram of an injection molding machine according to an embodiment of the present invention. [Figure 2] 1 is a diagram showing a setting procedure of an injection molding method according to an embodiment of the present invention. [Figure 3] 4 is a diagram showing an injection filling process based on the setting procedure of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solutions of the inventions according to the claims. Furthermore, in the present embodiments, the scales and dimensions of each component may be exaggerated, and some components may be omitted.

[0017] (injection molding machine) First, an injection molding machine according to an embodiment of the present invention will be described with reference to Figure 1. Note that the injection molding machine described below is based on an inline injection molding machine that simultaneously plasticizes, stores, and injects a resin material, but is not limited to this and may also be a pre-plasticization injection molding machine in which the plasticization, storage, and injection of the resin material are performed separately. Also, although a horizontal injection molding machine is used as the base, a vertical injection molding machine may also be used, and any injection molding machine that plasticizes and stores a resin material and injects it into a mold cavity can be used as an injection molding machine according to an embodiment of the present invention.

[0018] The injection molding machine 100 shown in FIG. 1 includes an injection device 10, an injection mold 20, an injection drive unit 30, and an injection control unit 40.

[0019] The injection device 10 comprises a cylindrical injection cylinder 11 and a screw 15 disposed within the injection cylinder 11. A plurality of heaters 12 are disposed within the injection cylinder 11 and the nozzle 14 at the tip, and heating is controlled to a predetermined temperature pattern by a temperature adjustment device (not shown). The nozzle 14 is connected to and separated from the injection molding die 20 by a drive device (not shown). An injection control unit 40 operates an injection drive unit 30 to control the rotational movement and forward / backward movement of the screw 15. Here, with regard to the movement of the screw 15, the direction toward the injection molding die 20 is defined as forward F, movement toward the forward F as forward movement, the direction away from the injection molding die 20 as backward B, and movement toward the backward B as backward movement.

[0020] The screw 15 has a spiral flight 16 that extends from the rear B to the front F. The spiral direction and angle of the flight 16 are set relative to the rotation direction of the screw 15 so that the resin material supplied from the material hopper 13 at the rear B of the injection cylinder 11 can be rotated and transported to the front F. As shown in FIG. 1, the flight 16 is arranged in a single row at a fixed interval and a fixed angle, but this is not limited to this. For example, the interval and angle may be variable, or multiple flights may be arranged. Alternatively, the flights 16 may be arranged in a multiple row only in a portion of the screw 15.

[0021] The screw 15 has a conical shape with a diameter that gradually increases from the rear B to the front F. In other words, the volume of the gap between the screw 15 and the injection cylinder 10 is set to gradually decrease from the rear B to the front F. As a result, the resin material supplied from the material hopper 13 is transported forward by the rotation of the flight 16. The reduction in volume generates shear heat, and the combined effect of the heat from the heater 12 produces molten resin (called plasticization). The molten resin thus produced passes through a flow path in a backflow prevention ring 17 located at the tip of the screw 15 and the screw head 18, and is stored as metered resin at the tip of the injection cylinder 10 on the front F side. As the amount of metered resin increases, the screw 15 retreats to the rear B side, stops rotating at a predetermined retreat position, and maintains that position. The retreating movement of the screw 15 is restricted (called metering back pressure) to adjust the melting and mixing properties of the metered resin (called back pressure control). This process up to this point is called the metering process. In the injection process, the screw 15 is advanced to inject and fill the metered resin into the injection molding die 20. In this injection process, the flow path in the backflow prevention ring 17 is closed.

[0022] In the injection molding die 20, a fixed die 21 and a movable die 22 are supported by a die clamping device (not shown), and a die cavity 24 is formed by clamping the fixed die 21 and the movable die 22 together. The metered resin stored in the injection device 10 passes through the nozzle 14 and passes through a resin flow path 23 including a gate, where it is injected and filled into the die cavity 24. The injected and filled molten resin is cooled, and what is taken out of the die cavity 24 becomes an injection-molded product. In addition, the tip of the nozzle 14 is equipped with an opening and closing device 19 that is opened and closed depending on the injection molding operation, and is used to prevent leakage of the metered resin from the nozzle 14, etc. An opening and closing device may be provided in the resin flow path 23 of the injection molding die 20.

[0023] Here, for example, in the case of automotive interior parts, resin materials used in injection molding typically include thermoplastic resins such as polypropylene (PP) resin and polyethylene (PE) resin, with the addition of colorants such as black, red, and blue to adjust the color tone of the part. Various additives are also used, such as plasticizers that impart flexibility to thermoplastic resins, nucleating agents and clarifying agents that control the crystallinity of crystalline resins, flame retardants that inhibit combustion, antistatic agents that suppress static electricity buildup, lubricants that improve fluidity and mold release, weatherproofing agents and UV inhibitors that inhibit degradation due to ultraviolet light, and reinforcing agents such as glass fiber and carbon fiber. Other suitable thermoplastic resins include general-purpose resins such as polypropylene (PP) resin and polyethylene (PE) resin, engineering resins such as polyamide (PA) resin and polycarbonate (PC) resin, and super-engineering resins such as polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin. Thermoplastic resins and additives are collectively referred to as resin materials. Thermosetting resins such as phenolic (PF) resin and melamine (MF) resin may also be used instead of thermoplastic resins.

[0024] (Settings procedure) Next, the setting procedure of the injection molding method according to the embodiment of the present invention will be explained using Figure 2. Figure 2 is an enlarged view of area A shown in Figure 1, and parts not relevant to the explanation of the setting procedure have been omitted. After the metering process is completed, with a predetermined amount of metered resin PL stored at the front F of the injection cylinder 11, test molding begins, in which the injection process is carried out under speed control and the pressure holding process is carried out under pressure control.

[0025] First, as shown in Figure 2(a), in test molding, the injection control unit 40 operates the injection drive unit 30 based on a preset injection speed pattern to control the speed of the forward movement of the screw 15 and start the injection process (speed-controlled injection process). At this time, the opening and closing device 19 is in an open state, and the metered resin PL flows into the mold cavity 24 through the resin flow path 23. In addition, the backflow prevention ring 17, whose flow path was open during the metering process, is pressed by the screw 15, and the flow path is now in a closed state.

[0026] Next, as shown in Figure 2(b), the speed-controlled injection process continues until the screw 15 reaches a preset switching position VP from speed control to pressure control. The switching position VP is set in the injection control unit 40 as an appropriate screw 15 position just before the mold cavity 24 is completely filled with the metered resin PL. This is to reliably prevent overfilling of the metered resin PL during the injection process, resulting in molding defects (resin burrs) caused by leakage of molten resin from the mating surface (referred to as the mold PL surface) of the mold cavity 24. The reason for setting the appropriate screw 15 position is that priority is given to preventing resin burrs, since this can be reliably corrected by the speed-controlled injection molding method of the injection filling process, which will be described later.

[0027] During trial molding, when the position of the screw 15 reaches the switching position VP, the process switches from the speed-controlled injection process to the pressure-controlled dwell process. As a result, as shown in Figure 2(c), the difference in injection pressure between the injection process and the dwell process causes the screw 15 to move back significantly, resulting in springback, and molding defects due to disturbances in the resin flow. The further the springback retraction position SB moves backward B, the greater the disturbances in the resin flow.

[0028] Next, as shown in FIG. 2(d), the injection control unit 40 operates the injection drive unit 30 based on a preset injection pressure setting value, pressure-controlling the forward movement of the screw 15 to perform a pressure-holding process (pressure-controlled pressure-holding process). New molten resin is then replenished from the injection unit 10 to the mold cavity 24 to compensate for the cooling and solidification shrinkage of the molten resin PL injected and filled into the mold cavity 24 (referred to as pressure-holding filling). This pressure-holding filling causes the screw 15 to move forward again, moving from the retracted position SB through the switching position VP to the pressure-holding end position SE. In other words, because this pressure control is set to the injection pressure necessary to compensate for the cooling and solidification shrinkage of the metered resin PL in the mold cavity 24, the forward speed and forward stop position of the screw 15 are automatically determined based on the degree of cooling and solidification shrinkage of the metered resin PL in the mold cavity 24. The forward stop position of the screw 15 at this time is set in the injection control unit 40 as the pressure-holding end position SE. The position of the screw 15 is measured using known means such as a position sensor or an encoder that detects the amount of rotation of an electric servo motor that moves the screw 15 forward and backward.

[0029] The forward speed of the screw 15 during the dwelling process, from the switching position VP to the dwelling end position SE, is defined as the dwelling speed VH. The movement time from the switching position VP to the dwelling end position SE is defined as the dwelling time HT, and the movement amount of the screw 15 from the switching position VP to the dwelling end position SE is defined as the dwelling movement amount HL, both of which are set in the injection control unit 40. The injection control unit 40 calculates the dwelling speed VH from the dwelling movement amount HL and the dwelling time HT (VH = HL / HT). In an injection molding machine equipped with a display or the like that displays the movement speed of the screw 15 as the injection speed, the value displayed on this display may be used as the dwelling speed VH. The movement of the screw 15 from the retracted position SB to the switching position VP is an operation to return the metered resin PL, which has flowed back due to the springback phenomenon, into the mold cavity 24, and is therefore different from dwell filling, which compensates for cooling and solidification shrinkage. Furthermore, the springback phenomenon causes the backflow prevention ring 17 to separate from the screw 15, opening the flow path of the backflow prevention ring 17 and causing the metered resin PL in the injection cylinder 11 to leak out toward the screw 15. The springback phenomenon can be eliminated by using an injection molding method that controls the speed of the injection filling process, which will be described later, and this leakage can be eliminated as a malfunction.

[0030] (Injection molding method) In the injection molding method for mass production molding following the trial molding, the dwelling process is speed-controlled based on the dwelling speed HV calculated by the injection control unit 40. In other words, for convenience, the trial molding uses a molding pattern that is widely adopted and familiar in the injection molding field, with a speed-controlled injection process and a pressure-controlled dwelling process. Using the settings calculated in the trial molding, the entire range from the injection process to the dwelling process is speed-controlled for the injection filling process. This allows for easy and reliable improvement of the springback phenomenon. This can be particularly useful as an efficient improvement method in injection molding. A detailed explanation is provided using Figure 3.

[0031] An example of an injection molding method for controlling the speed of the injection filling process is shown in Figure 3. The horizontal axis in Figure 3 indicates the position of the screw 15, and the forward movement of the screw 15 (movement from right to left on the horizontal axis) causes the metered resin PL to be injected and filled into the mold cavity 24. The vertical axis indicates the injection speed and injection pressure. The solid line in the figure indicates the injection speed setting pattern IVS for the injection filling process, the thick dashed line indicates the injection pressure setting value IPS, and the thin dashed line indicates the injection pressure measurement value IPK. The injection pressure measurement value IPK is measured by a pressure measurement means provided in the injection unit 10. As the pressure measurement means, for example, a pressure sensor is attached to the rear end B of the screw 15, and the resin pressure received by the screw 15 during the injection filling process is measured by the pressure sensor and used as the injection pressure measurement value IPK. As other pressure measuring means, for example, if the injection drive unit 30 is a hydraulic drive device such as a hydraulic cylinder, the injection pressure measurement value IPK may be calculated from the hydraulic pressure supplied to the hydraulic cylinder, or if the injection drive unit 30 is an electric drive device such as an electric servo motor, the injection pressure measurement value IPK may be calculated from the output torque of the electric servo motor. Alternatively, a pressure sensor may be incorporated into the front F side of the injection cylinder 11 or the nozzle 14 to directly measure the resin pressure and use it as the injection pressure measurement value IPK.

[0032] From the start of injection (measurement completion position) to the end of injection (holding completion position SE), the injection driver 30 is operated based on the injection speed setting pattern IVS set in the injection control unit 40 to move the screw 15 forward under speed control, thereby injecting and filling the metered resin PL into the mold cavity 24. In other words, the period from the start of injection to the holding completion position SE is the injection filling process, and the metered resin is injected and filled using only speed control without changing the control mode. The period from the start of injection to the switching position VP corresponds to the injection process of the prior art, and the period from the switching position VP to the holding completion position SE corresponds to the holding process of the prior art. The period from the switching position VP to the holding completion position SE is set at the holding speed VH calculated in the trial molding. It is preferable to reuse the multi-stage injection speed settings (V1 to V4) used in the trial molding from the start of injection to the switching position VP, for example, as shown in FIG. 3.

[0033] Furthermore, during the speed control of the injection speed setting pattern IVS during the injection filling process, a malfunction known as "injection pressure plateau" is avoided by setting the injection pressure set value IPS in the injection control unit 40 to a value higher than the injection pressure measurement value IPK. The injection pressure set value IPS is the maximum allowable injection pressure compensation value under injection speed control. Injection pressure plateau occurs when the injection pressure measurement value IPK approaches or exceeds the injection pressure set value IPS. If speed control is continued, the thrust required for the forward movement of the screw 15 is insufficient, causing the actual forward speed of the screw 15 to automatically decelerate, resulting in an uncontrollable state and a significant deviation from the injection speed setting pattern IVS. This results in the same injection molding malfunction described in the prior art, resulting in molding defects due to disturbances in the resin flow. In other words, reliable speed control is desirable during the injection filling process.

[0034] (effect) In this way, the period from the start of injection to the end of holding pressure is treated as one injection filling process, preventing disruptions in speed control due to factors such as injection pressure hitting a plateau, and the metered resin is injected and filled into the mold cavity using continuous speed control. This completely eliminates the springback phenomenon that occurs when switching from the conventional injection process to the holding pressure process, and eliminates molding defects caused by disruptions in resin flow such as fluctuations in injection filling amount (product weight), product appearance defects such as flow marks and transfer defects, internal product defects such as voids and foreign matter contamination, and product short circuits, enabling stable production of high-quality injection molding.

[0035] Furthermore, by performing a trial molding using an injection molding pattern with a speed-controlled injection process and pressure-controlled hold-pressure control, which is widely used in the field of injection molding, and then leading to a continuous speed-controlled injection filling process from this trial molding, even if springback occurs at the injection molding site and the quality of the injection molding fluctuates, it is possible to easily and reliably improve the quality.

[0036] Furthermore, the injection filling process with continuous speed control allows for stable injection molding to continue without being affected by changes in resin fluidity caused by, for example, temperature changes in the metered resin or injection molding mold, or fluctuations in the resin material or additives. Also, stabilization of the resin flow length results in stability of the product shape and weight. In particular, in multi-cavity injection molding, stabilization of the resin flow length can be achieved even for multiple mold cavities, resulting in stabilization of the weight of each product. It has also been confirmed that the wasted time required for screw retraction and return due to the springback phenomenon can be reduced, shortening the molding cycle.

[0037] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-described embodiments. Various modifications and improvements can be made to the above-described embodiments. [Explanation of symbols]

[0038] 100 injection molding machine 10 Injection device 11 Injection cylinder 12 Heater 13 Material hopper 14 nozzles 15 screws 16 flights 17 Backflow prevention ring 18 screw head 19 Switchgear 20 Injection mold 21 Fixed mold 22 Movable mold 23 Resin flow path 30 Injection drive unit 40 Injection control unit F forward B Back Area A PL metering resin VP switching position SB Backward position SE Holding pressure completion position VH Holding pressure speed HT: Pressure holding time HL Holding pressure movement amount IVS injection speed setting pattern IPS injection pressure setting value IPK injection pressure measurement value

Claims

1. An injection molding method comprising an injection step of controlling the forward movement of a screw to inject molten resin stored in an injection cylinder into a mold cavity, and a pressure holding step of replenishing the mold cavity with new molten resin to compensate for the cooling, solidification, and shrinkage of the injected and filled molten resin, an injection control unit that controls the speed and pressure of the screw; The injection molding method includes trial molding and mass production molding after the trial molding, In the test molding, In the injection process, the speed of the screw is controlled according to a predetermined setting pattern, In the pressure holding step, the pressure of the screw is controlled, a switching position from the speed control to the pressure control, a pressure holding completion position of the pressure control, and a pressure holding time of the pressure control are obtained, the difference between the switching position and the pressure holding completion position is set as a pressure holding movement amount, and a pressure holding speed of the screw that compensates for the cooling solidification shrinkage is calculated from the pressure holding movement amount and the pressure holding time, and set in the injection control unit; In the mass production molding, In the injection process, the speed of the screw is controlled according to the set pattern, The injection molding method, wherein the pressure holding step includes controlling the speed of the screw based on a set pressure holding speed.

2. a pressure measuring means for measuring the injection pressure during the injection process and the pressure holding process; 2. The injection molding method according to claim 1, wherein an injection pressure setting value higher than the maximum injection pressure measured by said pressure measuring means is set in said injection control section as the maximum allowable injection pressure compensation value.

3. An injection molding machine comprising an injection control unit that controls the speed and pressure of the screw, and that performs an injection process in which molten resin stored in an injection cylinder is injected into a mold cavity by controlling the forward movement of the screw, and a pressure holding process in which new molten resin is replenished into the mold cavity to compensate for the cooling, solidification, and shrinkage of the molten resin that has been injected and filled, Test molding and mass production molding after the test molding are carried out. In the trial molding, the injection control unit In the injection step, the speed of the screw is controlled according to a predetermined setting pattern; In the pressure holding step, the pressure of the screw is controlled, and the injection control unit determines a switching position from the speed control to the pressure control, a pressure holding completion position of the pressure control, and a pressure holding time of the pressure control, determines a difference between the switching position and the pressure holding completion position as a pressure holding movement amount, and sets a pressure holding speed of the screw that compensates for the calculated cooling solidification shrinkage from the pressure holding movement amount and the pressure holding time, In the mass production molding, the injection control unit In the injection step, the speed of the screw is controlled according to the set pattern, 4. The injection molding machine according to claim 1, wherein, in the pressure holding step, the speed of the screw is controlled based on the calculated pressure holding speed.

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