JPH04355111A - Injection compressing molding method - Google Patents

Abstract

PURPOSE:To enable correction of an early filling quantity of a material, by a method wherein establishment of cavity capacity on a mold side is made unnecessary, a flow of a material at a compression process time is prevented without making use of a needle shut-off nozzle and following to a change of a molding condition is performed further. CONSTITUTION:Initial filling quantities of a material into molds 4, 5 are established by storke control of a plunger 26 and a screw head 41 which is free from a back current and at the time of compression process, hydraulic pressure of a mold clamping cylinder 7 and hydraulic pressure of injecting hydraulic cylinder 27 are changed at the same timing and rate, through which material pressure within an injection barrel 24 and material pressure within the molds 4, 5 which place a nozzle among those are balanced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the operation of an injection molding machine when performing injection compression molding.

0002

[Background Art] In injection molding of optical parts, for example, when molding lenses, it is necessary not only to prevent shrinkage and voids due to shrinkage of the material within the mold, but also to prevent distortion due to residual stress from remaining. Furthermore, in the molding of optical discs, transferability on the submicron level is required. When such high-quality, high-precision products are required, injection compression molding is performed, in which injection filling is performed with the volume of the mold cavity slightly increased, and the material is compressed from the mold side in the subsequent pressure holding process. Molding is performed by applying force to equalize the internal pressure of the material and bringing the volume of the cavity to the normal volume. According to such injection compression molding, it is possible to equalize the pressure gradient of the material inside the cavity (usually higher on the gate side) that occurs during injection filling and prevent distortion of the molded product due to residual stress. Transferability can be improved by actively compressing the surface of the product within.

[0003] To specifically describe the typical injection compression molding process conventionally carried out, first, the mold is closed with a relatively weak mold clamping force (preliminary mold clamping), and the mold is placed inside the mold cavity. Inject and fill the material. At this time, the movable mold moves back slightly due to the internal pressure acting on the cavity, and the volume of the cavity increases slightly. Then, during the subsequent pressure holding process, the movable mold is moved forward to compensate for the shrinkage of the molten material in the mold due to cooling, so that the volume of the cavity finally reaches a predetermined product volume.

In order to perform injection compression molding, it is necessary to be able to increase or decrease the volume of the cavity by an amount commensurate with the shrinkage of the material during injection filling, and to be able to increase or decrease the mold clamping force during the compression process. As a method of realizing the former, in addition to the method of slightly retracting the movable mold using injection filling pressure as described above, the ejector pin and hydraulic cylinder ram provided in the mold are moved back and forth to move the parting surface of the mold. A method of changing the volume of the cavity while keeping it in contact with the
34775), and a method in which a mold is attached via a mounting plate that can be moved back and forth and the mounting plate is moved back and forth with a cylinder or the like to change the volume of the cavity.

[0005] In the conventional method, the amount of retraction of the movable mold, hydraulic cylinder ram, etc. is mechanically regulated and the excess material is measured to compensate for the shrinkage by retracting the movable mold, hydraulic cylinder ram, etc. to its retraction limit during injection and filling. It had become.

If the structure for increasing or decreasing the mold clamping force during holding pressure is a direct pressure type or a mechanical lock direct pressure type, it is best to control the hydraulic pressure of the mold clamping cylinder by a timer using a proportional electromagnetic pressure control valve or the like. It is the simplest.

[0007] In normal injection compression molding, the mold clamping pressure is controlled using a shut-off nozzle or the like to prevent the backflow of material to the injection device side. A method has also been proposed in which the compression process is performed by applying a holding pressure from the injection device to keep the specific volume of the material in the mold constant while detecting the temperature of the material in the mold (Utility Model Publication No. 2-276615). (see publication).

[0008]

[Problems to be Solved by the Invention] In any case, in conventional injection compression molding, by mechanically regulating the amount of retraction of a movable mold and the amount of retraction of a ram built into the mold, it is possible to The volume of the cavity is adjusted to match the amount of shrinkage of the material. In order to perform accurate molding, for example, when controlling the position of a movable mold, it is necessary to control the position of the mold when filling is completed with an accuracy of about 10 microns, and that position is determined by the shape and dimensions of the product. Since it is necessary to change it depending on the type of material and material, there is a problem that the mold clamping device becomes complicated and highly accurate adjustment work is required.

[0009] Furthermore, in the method of mechanically regulating the volume of the cavity during injection filling, if the molding conditions such as material temperature change during molding, the amount of shrinkage of the molded product changes, and the amount of shrinkage of the molded product changes. There is a problem in that it is extremely difficult to change the volume of the cavity by changing the volume of the cavity. If you try to control the amount of material replenishment or backflow during the compression process by controlling the holding pressure on the injection side in order to respond to changes in molding conditions, it may cause variations in product weight due to variations in the solidification timing of the material at the gate, or The problem arises that residual stress is generated.

[0010] In injection compression molding, the present invention eliminates the need to set the cavity volume on the mold or mold clamping device side, and also reduces the amount of material at the gate portion during the compression process without using a needle shutoff nozzle or the like. prevent flow,
Furthermore, it is an object of the present invention to provide a molding method that can also correct the initial filling amount of material into a cavity in accordance with changes in molding conditions.

[0011]

[Means for Solving the Problems] The method of the present invention uses a pre-plastic type injection device or an in-line screw type injection device in which a screw head 41 that does not cause backflow is provided at the tip of a screw 40, and the plunger 26 or the screw By controlling the stroke of the head 41, the initial filling amount of material into the cavities 35 of the molds 4 and 5 is set, and during the compression process, the hydraulic pressure of the mold clamping cylinder 7 and the hydraulic pressure of the injection hydraulic cylinder 27 are set at the same timing. A method is adopted in which the material pressure in the injection barrel 24 sandwiching the nozzle 25 and the material pressure in the molds 4 and 5 are balanced by changing the pressure at the same rate.

The cavities 35 of the molds 4 and 5 increase their volume during injection and filling by retracting the movable molds 5, ejector pins 57, etc., as in the prior art. The amount of increase in the volume of the cavity 35 at this time, that is, the movable mold 5
The amount of retraction of the movable mold 5 and the ejector pin 57 is determined by the amount of material to be injected and filled, which is different from the conventional method of mechanically regulating the amount of retraction of the movable mold 5 and the ejector pin during injection and filling. That is, in the method of this invention, FIGS.
As shown in FIG. 2, a margin of δ2 is left between the movable mold 5 and the ejector pin 57 that are retracted during injection and filling, and the member that mechanically restricts the limit of their retraction. The stroke of the injection plunger 26 and the screw head 41 can be performed by a conventionally known method of detecting the stroke using a linear scale 29 or the like and opening and closing a hydraulic circuit to the injection hydraulic cylinder 27.

Furthermore, in the above method, the final mold clamping position of the movable mold 5 is constantly monitored, and the position fluctuates (dispersion).
By controlling the stroke of the injection plunger 26 or the screw head 41 to cancel the fluctuation, even if the molding conditions fluctuate,
The initial filling amount into the cavity can be varied so that the final product always has a constant amount of compression.

[0014]

[Operation] In the method of the invention, a plunger-type injection device is used as the injection device without backflow, or a screw head 41 with no backflow at the tip of the screw is used as shown in the illustrated embodiment.
Using an in-line screw injection device equipped with
By controlling the stroke, an excess amount of material is initially filled to compensate for the contraction of the material in the mold, so there is no need to install a mechanical regulating device on the mold or mold clamping device. The initial filling amount can be controlled. In this case, the diameters of the injection plunger 26 and screw head 41 are usually smaller than the projected area of the cavity 35, so the accuracy of position detection of the plunger 26 and screw head 41 is the same as the accuracy of detecting the amount of movement of the mold. control with higher and therefore sufficient precision is possible.

[0015] During the compression process, the molds 4 and 5
When compressive force is applied to the material in the molds 4 and 5, the holding pressure on the injection device side is changed at the same time and at the same rate so that the material pressure inside the injection barrel 24 is balanced with the material pressure inside the injection barrel 24. This prevents the material from moving between the molds 4 and 5 and the injection barrel 24 during the compression process, so the amount of material initially filled into the cavity 35 does not increase or decrease due to backflow, and variations are prevented. It is possible to obtain uniform molded products.

Furthermore, changes in molding conditions can be responded to by detecting changes in the positions of the movable mold 5 and ejector pin 57 when the compression or pressure holding process is completed, and controlling the strokes of the injection plunger 26 and screw head 41 in feedback. The initial filling amount can be automatically corrected to the optimal value.

[0017]

[Embodiment] Fig. 1 shows a first embodiment of the present invention, in which the injection device has a screw pre-plastic structure, and a structure is adopted in which the movable mold 5 is moved back to increase the initial volume of the cavity 35. are doing. In the figure, 1 is a fixed plate, 2 is a movable plate, and 3 is a support plate. The fixed plate 1 and the support plate 3 are connected by a tie bar (not shown), and the movable plate 2 is movable along the tie bar. 4 is a fixed mold mounted on the fixed platen 1, and 5 is a movable mold mounted on the movable platen 2. 6 is a small-diameter, large-stroke mold opening/closing cylinder that is attached to the support plate 3 and opens and closes the movable plate 2; 7 is a large-diameter, small-stroke mold clamping cylinder that is built into the support plate 3, and has a ring-shaped cylinder chamber 8; A piston 10 having a through hole 9 is fitted therein.

A mold clamping force transmission rod 13 that can pass through the through hole 9 is provided on the back side of the movable platen 2, and a male spline 14 provided at the tip of the rod 13 and a female spline provided at the tip of the mold clamping piston 10 are provided on the back side of the movable platen 2. 15, the mold clamping piston 10 and the mold clamping force transmission rod 13 are engaged and disengaged. That is, the female spline 15 can be rotated by a half-pitch of teeth by a drive device (not shown), and the male spline 14 can pass through the female spline 15 with the teeth of the male spline 14 and the teeth of the female spline 15 shifted by a half-pitch. Next, the mold is opened. Then, with the mold opening/closing cylinder 6 moving the movable platen 2 forward, the female spline 15 is rotated to match the phase with the teeth of the male spline 14, so that the teeth of the male spline 14 and the teeth of the female spline 15 are aligned. is locked, and the mold clamping force of the mold clamping piston 10 is transmitted to the movable platen 2.

The stroke of the movable platen 2 with respect to the support plate 3 is measured by a pinion 17 pivotally supported on the support plate side and a rack 18 on the movable platen 2 side that meshes with the pinion 17. That is, the movement of the movable platen 2 causes the pinion 17 to rotate, and the rotation is counted by a rotary encoder (not shown) to measure the amount of movement of the movable platen 2.

20 is a plasticizing barrel, 21 is a plasticizing screw, and the plasticizing barrel 20 is connected to a hopper (not shown),
A rotational drive mechanism that rotates the plasticizing screw 21 and a material flow path 2 that moves the plasticizing screw 21 forward and opens the material flow path 2 at its tip.
It is equipped with a hydraulic cylinder etc. for closing 2.

24 is an injection barrel, 25 is a nozzle at the tip of the injection barrel, 26 is an injection plunger, and 27 is an injection hydraulic cylinder. A piston 28 of the injection hydraulic cylinder is directly connected to the injection plunger 26. 26 strokes are measured by a linear scale 29.

The plasticizing screw 21 rotates when the products in the molds 4 and 5 enter the cooling process, causing the molten material to flow into the injection barrel 24, and when the injection plunger 26 retreats to a predetermined position. It stops rotating and moves forward, closing the material flow path 22 to prevent backflow of material during injection. The injection stroke of the injection plunger 26 is the material flow path 22
is measured relative to the final plunger position after the plunger is closed. Hydraulic pressure is supplied to the mold clamping side cylinder chamber 8 of the mold clamping cylinder and the injection side cylinder chamber 30 of the injection hydraulic cylinder through a proportional electromagnetic pressure control valve 31 and a proportional electromagnetic pressure flow control valve 32. mold clamping piston 1 with a pressure proportional to control signals PA and PB given from
0 and the injection piston 28. In addition, according to the present invention, since the initial filling amount is controlled by the stroke of the injection plunger 26, the mold clamping device may be a general direct pressure type mold clamping device.

In the apparatus configured as described above, injection compression molding is performed as follows. First, the mold opening/closing cylinder 6 advances the movable platen 2 to its forward limit. At this time, the parting surfaces of the movable mold 5 and the fixed mold 4 come into contact as shown in FIG. In this state, there is a play of δ1 between the tip of the mold clamping piston 10, which is moving toward the retreating side, and the tip of the mold clamping force transmission rod 13, as shown in the upper half of FIG. There is. In this state, the female spline 15 is rotated to move the mold clamping piston 10 forward as shown in the lower half of FIG. 2, thereby performing preliminary mold clamping. The mold clamping pressure at this time is set to a relatively low value. In this state, by controlling the stroke of the injection plunger 26 based on the detected value of the linear scale 29, an amount of molten material that takes into account the shrinkage within the mold is measured and injected into the cavity 35 of the mold. . At this time, due to the pressure of the material flowing into the cavity, the movable mold 5 moves to δ3.
only to retreat. At this time, there is a distance δ2 between the retracted position of the mold clamping piston 10 that retracts together with the movable mold 5 and its retracted limit.
(Fig. 1), and the movable mold 5 has not reached its mechanically regulated retraction limit. If the elongation of the tie bar is ignored, the sum of δ2 and δ3 is equal to δ1.

After that, when the compression process begins, the timer clocks the proportional electromagnetic pressure control valve 31 and the proportional electromagnetic pressure flow control valve 32 to change the pressure at the same timing and at the same rate, and the injection plunger 26 causes the pressure inside the injection barrel 24 to change. While maintaining an equilibrium relationship between the holding force applied to the material and the compression pressure applied to the material in the cavity 35 by the mold clamping cylinder 7, the compression pressure is changed in stages, and the movable mold 5 is The compressor moves forward to the compression process completion position shown in the lower half of FIG. The position of the forward end at this time is detected by a rotary encoder connected to the pinion 17.

The above operation procedure is shown in a flowchart in FIG. In FIG. 8, the V-P switching position indicates the position where speed control is switched to pressure control during injection filling, and the injection side cylinder is The hydraulic pressure PB in the chamber 30 is PB1, PB2, PB3
At the same time, the hydraulic pressure applied to the mold clamping side cylinder chamber 8 is PA=PB1 ×α, PB2 ×α,
It is shown that it can be switched to PB3×α. Here, α is the value obtained by dividing the projected area of the cavity x the maximum injection pressure by the maximum mold clamping force, and the hydraulic pressure on the mold clamping side and the hydraulic pressure on the injection side are changed simultaneously while maintaining the proportional relationship α,
As a result, the pressure of the material in the mold cavity 35 is kept in balance with the pressure of the material in the injection barrel 24 while being compressed. α can also be corrected to a value that takes into consideration that the transmission efficiency of the hydraulic pressure PB on the injection side and the hydraulic pressure PA on the mold clamping side differs depending on the resin material and the shape of the cavity, gate, runner, etc.

The one shown in FIG. 1 uses a pre-plastic type injection device, but if a screw head 41 is provided at the tip of the injection screw 40, which can completely prevent backflow during injection, The method of this invention can also be applied to an in-line screw type. As shown in FIGS. 5 and 6, the screw head 41 at the tip of the screw 40 shown in the embodiment of FIG. A rotary screw head 41b with a vertical groove 42b is rotatably driven by a fixed angle with respect to the screw head 41a by an inserted rod 43, and the rotary screw head 41b is provided with its end surfaces in close contact with each other. By moving the fixed piston to align the vertical groove 42a with the rotating screw head vertical groove 42b, the plasticized material is delivered from the tip of the screw to the injection chamber, while when the screw 40 enters the injection operation, the rotating By rotating the screw head 41b and shifting the phase of the vertical grooves 42a and 42b, the screw head 41 prevents the molten material from flowing back into the screw 40 during injection.

Reference numeral 44 in FIG. 4 is a plasticizing motor for rotationally driving the screw 40, and a play is provided at the base end of the screw 40 to enable the rotary screw head 41b to rotate at a certain angle with respect to the screw 40. This makes the above operation possible.

In the above embodiment, the cavity volume of the mold at the time of initial filling is increased by retracting the movable mold 5, but as shown in FIG. At 51 it is possible to vary the volume of the cavity. In the embodiment shown in FIG. 3, with the stopper 53 advanced by the positioning cylinder 52, the compression plate 51 is advanced until the ejector plate 54 comes into contact with the stopper, and the cavity 35 is moved forward.
When the material inside is compressed, the mold is opened, and the product is removed from the mold, the stopper 53 is moved back by the positioning cylinder 52, and the ejector plate 50, that is, the compression plate 51 is further advanced to eject the product. The upper half of FIG. 3 shows the position of the compression plate 51 at the time of initial filling of material, and the compression plate 51 is retreated by δ3 from the position at the end of the compression process in the lower half. At this time, a play gap of δ2 remains between the compression plate 51 and its retreating end. That is, the compression plate 5
The volume of the cavity 35 is not determined by the mechanical retraction limit of 1, but the volume of the cavity 35 at the time of initial filling is limited by the stroke of the injection plunger 26 or the screw head 41. Note that 55 and 56 in FIG. 3 are rack and pinion devices for measuring the forward and backward positions of the compression plate 51, and have a structure in which a rotary encoder is connected coaxially with the pinion 17.

As shown in FIGS. 1, 3, and 4, the following control is possible by detecting the position of the movable platen 2 and the position of the compression plate 51 using a rotary encoder or the like. That is, as shown in FIG. 7, the amount of opening of the mold from the position of the movable platen 2 when the compression process is completed, that is, the gap between the parting surfaces of the movable mold 5 and the fixed mold 4 is within an allowable range. If it is within the allowable range, one cycle is completed in which the product is cooled (at the same time, plasticizing and measuring operations are performed), the mold is opened, and the product is ejected. If the opening amount of the mold is out of the allowable range, and if it is greater than the set value, the initial filling amount will be reduced.
That is, the control value is corrected in the direction of decreasing the stroke of the injection plunger 26 and the screw head 41, and when the opening amount of the mold is less than the set value, the control value is changed in the direction of increasing the initial filling amount. The initial filling amount can be automatically and accurately set by detecting minute fluctuations in the mold stop position in a certain cycle and setting the strokes of the injection plunger 26 and screw head 41 in the next cycle. Furthermore, even when molding conditions such as material temperature change, it is possible to control the setting value of the initial filling amount to follow the change. Note that the mold opening amount can be detected at a certain time before the completion of compression, and in this case, it can be detected even when the filling amount is short-circuited. Even when such control is adopted,
Since it is not possible to frequently change the initial filling amount during a molding operation, it is recommended to increase the tolerance range or change the injection stroke only when the set value is exceeded several times in a row. Hunting can be prevented by a method such as correction. Note that the fluidity of the resin has not decreased immediately after filling is completed, so if there is a fluctuation in the stroke control of the filling amount by the plunger 26, the pressure on either the injection side or the mold clamping side is increased. Correction can also be made while detecting the stroke position of the plunger.

[0030]

[Effect of the invention] According to the method of this invention explained above,
By simply controlling the stroke on the injection side, it is possible to accurately measure and initially fill the excess material equivalent to the amount of material compressed in the mold, eliminating the need to regulate the opening amount of the mold, etc.
The structure of the mold and mold clamping device can be simplified, and there is no need for troublesome adjustment of the opening amount of the mold. In addition, since the mold clamping force and the holding pressure on the injection side are controlled while maintaining a balance during the compression process, it is possible to prevent material from flowing near the gate seal part of the cavity, thereby preventing product variations due to material flow during the compression process. can be prevented. Furthermore, a method of automatically setting the optimization of the initial filling amount can be adopted, and thereby the position of the optimal filling completion point of the movable mold can be automatically determined.

[Brief explanation of drawings]

[Fig. 1] A schematic cross-sectional view showing a first embodiment of the present invention.

[
Figure 2: A diagram showing the operation of the mold clamping device in injection compression molding along with Figure 1.

[Figure 3] A schematic cross-sectional view showing another structure that changes the volume of the cavity.

[Fig. 4] A schematic cross-sectional view showing a second embodiment of the present invention.

[
Figure 5: Side view of the screw tip in Figure 4

[Figure 6] Front view of the screw tip in Figure 4

[Figure 7] Flowchart showing control when automatically setting initial filling

[Fig. 8] Flowchart showing an example of injection compression operation

[Explanation of symbols]

4 Fixed mold 5 Movable mold 7 Mold clamping cylinder 26 Injection plunger 27 Hydraulic cylinder for injection 35 Cavity 40 Injection screw

Claims (2)

[Claims] Claim 1: A mold (4),
(5) In addition to setting the initial filling amount of material into the cavity (35), the mold clamping cylinder (
7) Compression is performed by balancing the material pressure in the injection barrel (24) with the material pressure in the molds (4) and (5) by synchronous control of the hydraulic pressure of the injection hydraulic cylinder (27) and the hydraulic pressure of the injection hydraulic cylinder (27). An injection compression molding method characterized by performing a step. 2. The method according to claim 1, wherein the movable mold (5)
The final clamping position of the mold is detected, and when the detected value fluctuates from the set value, the stroke of the injection plunger (26) or the injection screw (40) in subsequent cycles is controlled to compensate for the fluctuation. The injection compression molding method according to claim 1.