JP2009083327A - Injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method for molding moldings having uniform and high quality by stabilizing control of pressure in processes from an injection process to a pressure holding process and preventing the occurrence of overshooting of pressure. <P>SOLUTION: In this injection molding method for switching the control in the processes from the injection process to the pressure holding process from speed control to pressure control, a target speed value for speed control is convergently changed to perform premolding for several times, the highest injection process speed V is obtained as the first injection speed V1 without causing overshooting of pressure, and the injection process speed V in the speed control is changed from the initial set injection speed V0 specified per product to the first injection speed V1 for injection molding. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an injection molding method, and more particularly to an injection molding method that stabilizes pressure control from an injection process to a pressure holding process.

There are an inline screw type or a plunger type as an injection device for filling the molten resin into the mold, but the present invention can be applied regardless of the injection device. Hereinafter, an inline screw type injection device will be described.
In an injection molding apparatus, in the filling process, generally, an injection process for filling a resin into a cavity of a mold, and a holding pressure for applying a predetermined pressure to the resin for a predetermined time after the resin fills the cavity. A process is provided. Regarding the switching timing between the injection process and the pressure-holding process, the setting screw position (position switching method) and the setting injection are performed by measuring the position of the injection screw used for injection and measuring the resin pressure at the time of resin filling. In general, a process of switching to a pressure holding process is performed by pressure (pressure switching method).

  In such a position switching method and pressure switching method, pressure overshoots at the time of holding pressure switching in which the pressure control in the injection process is switched to pressure control in the holding pressure process (the screw moves forward due to inertial force, After that, it is pushed back to the resin by the elastic force of the resin, so that there is a possibility that the uncontrolled state of the screw occurs at the time of holding pressure switching, and it becomes weak against disturbance), so the injection pressure between shots (each injection molding) The variation becomes large, and therefore the variation of the molded product becomes large.

  In the pressure switching system, the pressure change rate is controlled based on the difference between the resin pressure detected at the time of injection molding and the set pressure in order to suppress the pressure variation during the holding pressure transition due to the overshoot of the injection pressure. A control device for an injection molding machine is disclosed (for example, see Patent Document 1). Further, PID calculation is performed based on a deviation value between the set injection pressure setting value and the pressure feedback value from the molding machine, and the filling process to the pressure holding process is performed until the PID calculation output exceeds the injection speed setting value. If the injection speed setting value is exceeded when the switching is performed smoothly, the integration element of the first PID computing unit is stopped, and the switching from the filling process to the pressure holding process is continuously performed. A control device and a control method are known (for example, refer to Patent Document 2).

JP 2006-1134 A Japanese Patent Laid-Open No. 10-113970

  However, the control device described in Patent Document 1 does not suppress the occurrence of pressure overshoot itself, but suppresses variations in the peak pressure of the generated overshoot, and this overshoot itself occurs. The uncontrolled state is not completely avoided, and there is room for improvement in order to improve the quality of the molded product. Further, there is a possibility that the variation cannot be suppressed to be sufficiently small only by PID calculation control by the control device described in Patent Document 2, and there is room for further improvement.

  Here, for example, a plastic lens is lighter and harder to break than inorganic materials such as glass, and can be processed into various shapes, and is more advantageous in terms of cost than a glass lens. It is also rapidly spreading as an optical lens for information recording equipment. Along with this, it is required to increase the resolution, size, and thickness of the lens. In this case, for example, the dimensional and shape accuracy of the lens is required to be on the order of micron to sub-micron, so if a state that is vulnerable to disturbance such as pressure overshoot occurs, the manufacturing yield will be significantly reduced. There is a problem.

  The present invention has been made in view of the above circumstances, and its purpose is to prevent the occurrence of pressure overshoot in order to stabilize the pressure control from the injection process to the pressure holding process, to avoid an uncontrolled state, An object of the present invention is to provide an injection molding method capable of molding a high-quality molded product without variation.

The above object of the present invention is achieved by the following injection molding method.
(1) An injection molding method in which the control from the injection process to the pressure holding process is switched from speed control to pressure control (hereinafter also referred to as V / P switching).
The set injection speed value in the speed control is convergedly changed in a direction in which the pressure overshoot is reduced with respect to the set pressure for performing the V / P switching, and the first pre-molding is performed a plurality of times, Finding the fastest first injection speed V1 without causing overshoot,
When the initial injection speed (V0) set for each molding is overshooting the pressure at the time of V / P switching, the initial injection is set before the speed control setting injection speed reaches the V / P switching. An injection molding method characterized by switching from a speed V0 to a first injection speed V1.

  According to the injection molding method having the above-described configuration, the fastest first injection speed V1 is obtained without generating pressure overshoot with respect to the set pressure of the injection pressure at the time of V / P switching, and the injection process speed is controlled during speed control. Is changed from the initial injection speed V0 set for each molded product to the first injection speed V1, so that the occurrence of such overshoot can be suppressed, and high-quality molded products with little variation can be filled in a short time.・ It can be molded with pressure keeping time.

  (2) With respect to the speed switching timing from the initial setting injection speed V0 to the first setting injection speed V1, the pressure is exceeded from the position of the injection screw at the time of V / P switching when molding is performed at the initial setting injection speed V0. Implement a plurality of second pre-molding operations that converge the screw position in the opposite direction to the injection so that the chute is reduced, and identify the screw position corresponding to the speed switching time when pressure overshoot does not occur The injection molding method according to (1) above, wherein

  According to the injection molding method configured as described above, the speed switching timing from the initial setting injection speed V0 to the first setting injection speed V1 is determined from the position of the injection screw at the time of V / P switching when molding is performed at the initial setting injection speed V0. The screw position corresponding to the speed switching timing at which such overshoot does not occur is specified by multiple second pre-molding that converges the injection screw position in the metering direction so as to reduce pressure overshoot. Therefore, the injection filling time is the shortest in the molding where pressure overshoot does not occur. Thereby, a high-quality molded product with little variation in shape and dimensional accuracy can be molded in a short molding cycle time.

  (3) When injection molding is performed a plurality of times by speed switching control from the initial setting injection speed V0 to the first injection speed V1, each injection molding of the time range integral value from the start of injection to the gate seal point in the injection pressure curve The injection molding method according to the above (1) or (2), characterized in that the inter-variation is within ± 1.5%.

  According to the injection molding method having the above-described configuration, the shot shot of the molded product is obtained by setting the variation between shots of the value obtained by integrating the injection pressure curve in the time range from the start of injection to the gate seal time within ± 1.5%. Variations in intervals can be suppressed, and high-quality molded products can be stably obtained.

  According to the present invention, by preventing the occurrence of pressure overshoot at the V / P switching position, the pressure control from the injection process to the pressure holding process is stabilized, and a high-quality molded product with no variation is formed. An injection molding method can be provided.

Hereinafter, an injection molding method according to the present invention will be described with reference to the drawings.
The injection molding method according to the present invention is an injection molding method that prevents the occurrence of an overshoot in which the injection pressure exceeds a set holding pressure, while minimizing the injection filling time in the molding in which no pressure overshoot occurs.

  FIG. 1 is a schematic configuration diagram showing an example of an injection molding machine capable of performing the injection molding method of the present invention, FIG. 2 is a graph showing the relationship between the injection time and the injection pressure of the injection molding method of the present invention, and FIG. FIG. 4 is a graph showing the relationship between the injection speed and the screw position, FIG. 4 is a graph showing the relationship between the injection time and the screw position, and FIG. 5 is an outline of the injection molding machine showing the screw position at each injection time shown in FIG. It is a block diagram.

  As shown in FIG. 1, as a basic in-line type injection molding machine 1, a heating cylinder 3 having a nozzle 2 at the tip is provided, and an injection screw 4 is disposed in the heating cylinder 3. A heater 5 is attached to the outer periphery of the heating cylinder 3, and a hopper 6 for supplying the resin pellet 7 to the injection screw 4 is attached to the opposite end of the nozzle 2. At the opposite end of the nozzle 2, the screw 4 is rotated at the rear end of the injection screw 4, and the screw 4 is advanced in the axial direction (left-right direction in FIG. 1) with the set values of the hydraulic oil pressure and flow rate (speed). A hydraulic motor / cylinder set 9 for performing an injection operation and a load cell 8 for detecting injection pressure are provided. Further, the tip of the nozzle 2 is connected to a stationary mold 11 and a gate 13 of a movable mold 12 that form a cavity 10 therein.

  The resin pellets 7 fed from the hopper 6 are subjected to plasticizing operations including resin transfer, compression, kneading, melting, and metering operations by the rotating injection screw 4 and the heater 5. Then, the injection screw 4 is moved in the direction of the nozzle 2 while the moving speed is controlled by the hydraulic motor / cylinder set 9, and the molten resin discharged from the nozzle 2 at a constant speed is filled into the cavity 10, and the setting is maintained for a predetermined time. The molded product is molded by being cooled while being kept under pressure.

Next, based on FIG.2 and FIG.3, the injection molding method of this invention is demonstrated in detail.
In order to facilitate comparison with the injection molding method of the present invention, first, a conventional injection molding method will be described. As shown in FIG. 3, when the injection screw 4 is moved forward to inject molten resin into the cavity 10 at an initial setting injection speed V0 set for each molded product (speed curve 21), the pressure curve 31 in FIG. Thus, the injection pressure P in the cavity 10 gradually increases, and eventually reaches the set holding pressure Ps at time t0, and the hydraulic motor / cylinder set 9 shifts from the moving speed control to the pressure control at the set holding pressure Ps. The filling of the molten resin into 10 is completed. When the injection pressure reaches the set holding pressure Ps, the injection speed V is set to 0 and the control is switched from speed control to pressure control (hereinafter also referred to as V / P switching). At this time, an overshoot 31a of the injection pressure is generated due to the inertial force of the injection screw 4, and the injection pressure P is stabilized at the set holding pressure Ps while converging the vibration. Thereafter, the set holding pressure Ps is maintained and controlled for a predetermined time.

  The occurrence of the overshoot 31a is the same as that in the control blank, that is, in the non-control state when switching from the moving speed control of the injection screw 4 to the pressure control at the set holding pressure Ps. In the injection molding method according to the present invention, the injection speed V is changed from the initial setting injection speed V0 to the first injection speed V1, thereby preventing the occurrence of an overshoot 31a and avoiding an uncontrolled state. Specifically, this is achieved by the following method.

That is, in the injection molding method of the present invention, first, the first pre-molding is performed a plurality of times while the set injection speed of the injection speed V is convergently changed in a direction in which the occurrence of overshoot of the injection pressure is reduced. The fastest injection speed V that does not cause pressure overshoot is determined as the first injection speed V1. In the first pre-molding, processing by PID calculation can be executed except that the injection speed V is changed.
In the injection molding at the first injection speed V1, as shown by the speed curve 22 in FIG. 3, after rising from the injection speed 0 to the first injection speed V1, the first injection speed V1 is kept constant and melting into the cavity 10 is performed. After the resin filling is completed until time t2, the injection pressure becomes the set holding pressure Ps, the injection speed V is set to 0, and the pressure holding control is performed.

The change in the injection pressure P at this time rises with a gentler slope than the pressure curve 31 at the initial setting injection speed V0, as shown by the pressure curve 32 in FIG. 2, and naturally the setting pressure is maintained without causing overshoot of the injection pressure. It approaches the pressure Ps and stabilizes at the set holding pressure Ps. The injection molding at the first injection speed V1 has the advantage that the quality of the molded product is stabilized because no overshoot of the injection pressure occurs as described above, but the injection filling time becomes long.
Therefore, in the injection molding method of the present invention, in order to shorten the injection filling time, as shown by the pressure curve 33, the molten resin is injected at the initial setting injection speed V0 at the initial stage of injection molding, and the elapsed time tx in the middle of molding. By switching to the first injection speed V1, the injection filling time is prevented from becoming longer.

If the timing of switching from the initial setting injection speed V0 to the first injection speed V1 is too late, an overshoot of the injection pressure will also occur.
Therefore, the speed change time tx for switching from the initial setting injection speed V0 to the first injection speed V1 without causing an overshoot of the injection pressure is the speed from the time at the time of V / P switching when molding is performed at the initial setting injection speed V0. The degree of transition to the control side is convergently changed in a direction that reduces the occurrence of injection pressure overshoot, and multiple second pre-molding operations are performed, injection pressure overshoot does not occur, and default injection It is specified by obtaining the speed change time tx at which the injection time at the speed V0 is the longest, in other words, the injection time at the first injection speed V1 is the shortest. The process by PID calculation can be applied to the second pre-molding, except that the injection speed V is switched halfway.

  In the injection molding method of the present invention in which the speed is changed from the initial injection speed V0 to the first injection speed V1 during the molding as described above, the melting is performed at the initial injection speed V0 in the initial stage of injection molding as shown by the speed curve 23 in FIG. When the resin is injected, the initial injection speed V0 is switched to the first injection speed V1 at the speed change time tx obtained as described above, and when the injection pressure of the molten resin into the cavity 10 reaches the set holding pressure Ps, Set injection speed V to 0 and switch from speed control to pressure control.

  As shown in the pressure curve 33 in FIG. 2, the change in the injection pressure at this time is as follows. As shown in the pressure curve 33 in FIG. 2, the pressure rises rapidly in the same manner as in the conventional injection molding method. And stable at the set holding pressure Ps without overshooting. Thus, by obtaining the first injection speed V1 and the speed change time tx before the actual injection molding and setting the actual injection molding, the variation in the quality of the molded product due to the pressure overshoot is eliminated, Moreover, it can be molded with a short injection filling time.

  4 and 5 show the relationship between the injection time and the injection pressure (FIG. 2) described above by replacing the position with the injection screw 4 of the injection molding machine 1. The molten resin is injected at the initial setting injection speed V0 from the state where the injection screw position shown in FIG. 5A is at the initial position (time t0) to the injection screw position x (time tx) shown in FIG. Here, at the injection screw position x, the injection speed V is switched from the initial injection speed V0 to the first injection speed V1, and the injection screw position a in which the filling of the molten resin into the cavity 10 shown in FIG. Until (time t1), the molten resin is injected at the first injection speed V1.

  The relationship between the injection time and the injection screw position at this time is shown as a screw position curve 43 in FIG. The screw position curve 43 is a curve corresponding to the pressure curve 33 shown in FIG. FIG. 4 also shows screw position curves 41 and 42 corresponding respectively to the pressure curves 31 and 32 shown in FIG. 2 for reference.

  According to the injection molding method of the present embodiment, the shot-to-shot variation of the value obtained by integrating the injection pressure curve in the time range from the start of injection to the gate seal time in multiple injection moldings is within ± 1.5%, preferably This integral value indicates the area that the injection pressure curve 33 encloses until reaching the gate sealing time, thereby extremely reducing the variation in the molded product from shot to shot. (Variation in weight is 0.25%, preferably 0.08%), and a high-quality molded product with little variation in shape and dimensional accuracy can be molded in a short injection and filling time. As a result, for optical lenses for optical information recording equipment, etc., it is possible to satisfy very high demands on dimensional accuracy for miniaturization, thinness, and high resolution, and to provide high-quality molded products. it can.

FIG. 6 is a flowchart showing the injection molding control method of the present invention.
Starting from step S10, in step S12, measurement of the injection pressure overshoot at the time of V / P switching for switching from speed control to pressure control based on the initially set injection speed V0 is performed based on the data of the load cell 8. Next, in step S14, no overshoot occurs from the degree of overshoot of the injection pressure measured in step S12 by using a LUT (lookup table) in which the relationship between the degree of overshoot of the injection pressure and the injection speed is set in advance. A plurality of candidates for the first injection speed V1 that are expected to be set are set.

  In step S16, the first pre-molding is performed using each first injection speed V1 candidate. At this time, a commonly used PID calculation can be used. In step S18, the fastest injection speed is determined as the first injection speed V1 without overshooting of the injection pressure in the first pre-molding performed in step S16. In step S22, an appropriate speed switching timing is set so that the overshoot of the injection pressure at the initial setting injection speed V0 does not affect the first injection speed V1 from the slope of the pressure curve of the initial setting injection speed V0 and the first injection speed V1. (Second pre-molding). In step S24, the molding control setting is ended by the most appropriate speed switching timing extracted in step S22.

Next, a control method in the case of the second pre-molding based on the screw position will be described.
FIG. 7 is a flowchart of control in place of step S22 in FIG.
First, in step S221, the screw position at the time of V / P switching at the set injection speed V0 is determined. Next, in step S223, the screw position at the time of V / P switching, the LUT (the screw position switching timing corresponding to the speed switching predicted from the inclination of the screw position curve by the initial injection speed V0 and the first injection speed V1, respectively. A look-up table is prepared, and a plurality of candidates for screw position switching timing are determined thereby. In step S225, the second pre-molding is performed based on the plurality of candidates. In step S227, based on the result of the second pre-molding, a screw position corresponding to a speed switching timing at which there is no injection pressure overshoot and the injection filling time can be shortened most is determined.

  Although the injection molding apparatus can perform the molding operation according to the above flowchart, it is also possible for the operator to manually perform the above method along this flowchart. Further, when obtaining the first injection speed or obtaining the switching timing from the initial injection speed V0 to the first injection speed V1, a LUT (look-up) that sets the relationship between the degree of injection pressure overshoot and the injection speed in advance. In addition to using a table, a convergence calculation method such as Newton's method can also be used as a method that can convergeably change in a direction in which the occurrence of such overshoot is reduced.

In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. For example, in the above embodiment, the injection pressure of the screw is detected by the load cell. However, in order to make the weight supply rate to the nozzle constant, a sensor for detecting the pressure of the molten resin near the nozzle or a mold is used. An in-mold pressure sensor can be provided, and pressure overshoot can be specified and controlled based on the detected value.
The injection molding apparatus performs an injection operation by hydraulic pressure. However, the present invention is not limited to this, and an electric motor can be used instead of the hydraulic motor / cylinder set. In this case, the pressure overshoot is specified and controlled by providing a sensor for detecting the pressure of the molten resin near the nozzle or an in-mold pressure sensor installed in the mold as described above, and using this measured value. Can do. Moreover, the rotation speed and load of an electric motor can also be utilized.

It is a schematic block diagram of an injection molding machine. It is a graph which shows the relationship between the injection time of the injection molding method of this invention, and injection pressure. It is a graph which shows the relationship between injection time and injection speed corresponding to FIG. It is a graph which shows the relationship between injection time and a screw position. It is a schematic block diagram of the injection molding machine which shows the screw position in each injection time shown in FIG. These are the flowchart figures which show the control method of the injection molding of this invention. It is a flowchart figure of the control replaced with FIG.6 S22.

Explanation of symbols

33 Injection pressure curve V Injection process speed V1 First injection speed V0 Initial setting injection speed x Time point t when the initial setting injection speed is changed to the first injection speed t Injection time

Claims (3)

An injection molding method for switching from pressure control to pressure control from injection process to pressure holding process (hereinafter also referred to as V / P switching),
The set injection speed value in the speed control is convergedly changed in a direction in which the pressure overshoot is reduced with respect to the set pressure for performing the V / P switching, and the first pre-molding is performed a plurality of times, Finding the fastest first injection speed V1 without causing overshoot,
In the initial injection speed (V0) set for each molding, when pressure overshoot occurs at the time of V / P switching, the initial injection is set before the speed control setting injection speed reaches the V / P switching. An injection molding method, wherein the speed V0 is switched to the first injection speed V1.   Regarding the speed switching timing from the initial setting injection speed V0 to the first injection speed V1, pressure overshoot is reduced from the position of the injection screw at the time of V / P switching when molding is performed at the initial setting injection speed V0. In addition, a plurality of second pre-molding operations are performed in which the screw position is convergently changed in the direction opposite to the injection, and the screw position corresponding to the speed switching timing at which no pressure overshoot occurs is specified. The injection molding method according to claim 1.   When injection molding is performed a plurality of times by speed switching control from the initial setting injection speed V0 to the first injection speed V1, the variation in the time range integral value from the start of injection to the gate seal time is shown in the injection pressure curve. 3. The injection molding method according to claim 1, wherein the injection molding method is within ± 1.5%.

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