JP3123041B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin injection molding method, and more particularly to control of a process including a mold closing process and an injection process.

[0002]

2. Description of the Related Art In injection molding of a thermoplastic resin, respective steps of mold closing, injection, holding pressure, measuring, cooling, and mold opening are performed. In the mold closing step, the fixed mold and the movable mold are closed with each other, and a predetermined mold clamping force is applied to the fixed mold and the movable mold. In an injection step subsequent to the mold closing step, a molten resin is filled in a cavity formed between the fixed mold and the movable mold whose molds are closed. In this injection step, the molten resin is filled into the cavity at a high pressure. As a result, a high pressure is applied also to the fixed mold and the movable mold, so that the fixed mold and the movable mold are securely closed against the pressure. In order to maintain the state, a predetermined mold clamping force must be applied to the fixed mold and the movable mold as described above. In the mold closing step, the fixed mold and the movable mold are usually closed at a high speed at first, and then closed at a low speed to reach a predetermined mold clamping force. Initially, closing at high speed is for shortening the molding cycle.
This is to cope with an abnormality such as pinching of a foreign object and to finally generate a sufficient mold clamping force. In the mold opening step for taking out the product, which is the resin cured in the cavity, conversely, the fixed mold and the movable mold are opened at a low speed, and then opened at a high speed. Conventionally, after completion of mold clamping, that is, after a predetermined mold clamping force is applied to the fixed mold and the movable mold, the injection process is further performed after a delay time of 0.1 to 0.2 seconds for safety. Had started.

[0003]

However, in the above-mentioned conventional method, since the injection step is started after the mold clamping is completed, there is a problem that the molding cycle becomes long and the productivity is poor.

On the other hand, for example, Japanese Patent Laid-Open No.
No. 30 discloses that, in order to shorten the molding cycle, the injection process is started when a certain amount of mold clamping force is generated just before the mold clamping is completed. However, even in the molding method described in the above publication, the metering step (charging step) is started after the pressure holding step at a predetermined time is completed after the filling of the resin into the cavity is completed. There was a limit to shortening the cycle.

[0005] The present invention is intended to solve such a problem, and an object of the present invention is to shorten a molding cycle without hindering molding.

[0006]

According to the injection molding method of the present invention, in order to achieve the above object, a plurality of mold parts to be opened and closed are provided.
A cavity is formed between the materials and this cavity
Has a resin passage leading to the inside and keeping the resin in a plastic state inside
That a mold, the plurality of the mold closing device for providing a predetermined clamping force to the mold member is closed with opening and closing the mold members, a closed plastic state from the nozzle in a cavity formed between the mold members the resin provided with a an injection device for delivering and pressed by the pressing member, using a molding machine having a valve for opening and closing the nozzle, and an amount accumulating metering step of resin plastic state to the injection apparatus, a plurality of molds Closing the members and further applying a mold clamping force to these mold members; andinjecting the plasticized resin from the injection device after the measuring step into the cavity formed between the closed mold members. A pressure holding step of applying pressure to the resin in the mold member from the injection device after the injection step, and the mold clamping force applied to the mold member reaches the predetermined mold clamping force during the mold closing step. Multiple gold before Member starts injection step when in contact abuts against the other, pressing the mold member during the injection process
The obtained mold clamping force reaches the predetermined mold clamping force, and in the pressure holding step , the pressing member is pressurized at a constant pressure for a fixed time.
The pressure applied to the resin in the mold by the pressure member
Then, the valve is closed and the measuring step is started.

[0007]

In the injection molding method of the present invention, a predetermined amount of resin in a plastic state is stored in the injection device in the measuring step, and during the mold closing step, before the mold clamping force applied to the mold member reaches the predetermined mold clamping force. When the plurality of mold members abut against each other and come into contact with each other , the injection process is started, and the resin accumulated in the measuring process is pressed.
The resin is pressed by the pressure member and injected from the nozzle of the injection device, but in the initial stage of the injection process in which the cavity is not filled with resin, the pressure applied from the resin to the mold member is originally low, so the mold clamping force is predetermined. There is no problem even if the mold clamping force has not been reached, and the mold member does not open due to the resin pressure. Further , as the cavity is filled with resin in the injection process, the pressure applied from the resin to the mold member also increases, but at this stage, the mold closing device applies a mold clamping force to the mold member. The force has reached a predetermined mold clamping force, and the mold member is prevented from opening due to strong resin pressure. Further, in the pressure holding process after the injection step, the injection device smell
The pressing pressurizes the certain time pressing member at a fixed pressure Te
After applying enough pressure to the resin in the mold by the member
Then, the nozzle is closed by the valve , and the measuring step is started during the subsequent pressure-holding step. Resin into cavity in mold
Since the resin in the passage is kept in a plastic state, after the valve is closed, the pressure is maintained by the pressure of the resin in the mold.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. First, the configuration of the molding machine used will be described. This injection molding machine is of an in-line screw type. In FIG. 3, 1 is a fixed side platen, 2
Is a tie bar, 3 is a movable side platen, and 4 is a base. The movable platen 3 is driven by the mold closing device 5 to move the tie bar 2.
And moves toward and away from the fixed-side platen 1. The mold closing device 5 includes a toggle mechanism 7 driven by a servo motor 6 and the base 4.
And a hydraulic drive mechanism 8 acting on the tie bar 2. To the servomotor 6, control means 9 including a computer or the like is connected via a driving means 10 for the control thereof. Further, the hydraulic drive mechanism 8 is also connected to the control means 9 via the drive means 11 for the control.

Next, the configuration of the injection device 20 will be described. twenty one
Is a heating cylinder having a resin reservoir therein. The heating cylinder 21 is located on the opposite side of the movable side platen 3 with respect to the fixed side platen 1 and has a nozzle 22 at the left end. The nozzle 22 is provided with a rotary valve 23 for opening and closing the nozzle. As shown in detail in FIG. 3, the rotary valve 23 has a cylindrical shape, and is rotatably slidably fitted to a valve seat 25 formed in a resin passage 24 in the nozzle 22. Has a through hole 26 penetrating therethrough. Then, it is hydraulically driven, and the resin passage 24 and the through hole 26 are continuously opened as shown by a chain line, and are rotated by 90 ° and closed as shown by a solid line. The heating cylinder 21 is provided with a band heater 27 on the outer peripheral surface and a hopper 28 on the upper right side. A screw 29 as a pressing member is slidably fitted in the heating cylinder 21 in the left-right direction in the figure. The screw 29 is connected to an output shaft of a motor 31 via a gear train 30 so as to be movable in the axial direction, and is driven to rotate by the motor 31. The screw 29 is provided with a thrust bearing 32.
Is rotatably connected to the slider 33 via
A ball screw screw 34 is threaded through the slider 33. The ball screw 34 is connected to an output shaft of a servomotor 36 via a gear train 35. With this configuration, when the output shaft of the servo motor 36 rotates,
The rotation is transmitted to the ball screw 34 via the gear train 35, and the screw 29 moves forward or backward together with the slider 33 with the rotation of the ball screw 34. The control means 9 is connected to the motors 31 and 36 via driving means 37 and 38, respectively, for the control thereof. A load cell 39 for detecting the pressure applied to the screw 29 is incorporated in the thrust bearing 32, and the control means 9 is connected to the load cell 39 via a detection means 40. The advance and retreat of the screw 29 is controlled according to the position and speed of the screw 29 detected based on the rotation of the servomotor 36, or according to the pressure and time detected by the load cell 39. Is controlled.

Next, the configuration of the mold 50 will be described with reference to FIG. This mold is a hot runner mold
50, a fixed mold 51 attached to the fixed platen 1 and a movable mold attached to the movable platen 3
52 for forming a cassette half of a VHS video tape. When the mold closing device 5 is driven, the fixed mold 51 and the movable mold 52, which are mold members, are opened and closed with the movement of the movable platen 3, and between the fixed mold 51 and the movable mold 52 when the mold is closed. This is to form a cavity 53 having a product shape. At the same time, the fixed mold 51 and the movable mold 52 are provided with a predetermined, for example, 150 t, mold clamping force in a state where they are closed by the mold closing device 5. In the fixed mold 51, a fixed-side mounting plate 58 is fixed via backing plates 55 and 56 and a spacer block 57 to the back of a fixed-side mold plate 54 that forms a cavity 53. A manifold 59 is provided between the plate 58 and the plate 58. A sprue bush 60 to which the nozzle 22 of the molding machine is connected is fixed to the fixed side mounting plate 58 in a penetrating state, and the inside of the sprue bush 60 is a sprue 61. A heater 62 is provided around the sprue bush 60. Further, the sprue 61 is provided in the manifold 59.
Is formed, and a heater 64 is provided. Further, a through hole 65 is formed in the fixed mold plate 54 and the receiving plates 55 and 56, and the through hole 65 is formed in the through hole 65.
A spear 67 is provided in a bush 66 embedded in 65. The runner 63 of the manifold 59 communicates with the bush 65. Further, the tip of the through hole 65 is a gate 68 that opens to the cavity 53. On the other hand, in the movable mold 52, a movable mounting plate is fixed via a receiving plate and a spacer block, not shown, on the back surface of the movable mold plate 69 forming the cavity 53,
A protruding plate is provided between the receiving plate and the movable-side mounting plate. The fixed mold 51 and the movable mold 52 include:
A cooling water passage 70 is formed surrounding the cavity 53.

Next, an injection molding method using the molding machine and the mold 50 will be described. On the molding machine side,
The measuring step, the injection step, and the pressure holding step are sequentially repeated. In the measuring process, the rotary valve 23 is
With the 22 closed, the pallet of the thermoplastic resin supplied into the heating cylinder 21 is melted by the heating by the heater 27 and the shearing force accompanying the rotation of the screw 29.
A predetermined amount of the resin melted in this way is accumulated at the front end in the heating cylinder 21 by the retreat of the screw 29 while rotating. The injection step is performed after the end of the measuring step and when the mold is closed. In this injection step, after the rotary valve 23 is opened, the screw 29 advances and the molten resin in the heating cylinder 21 is injected from the nozzle 22 into the mold 50. Following the injection step, a pressure holding step is performed, and a predetermined pressure is applied to the screw 29 forward. Thereafter, the rotary valve 23 closes and the measuring process starts again. As shown in Table 1, the screw 29
Is controlled according to the speed and the position in the injection step, and is controlled according to the pressure and the time in the pressure holding step.

[0012]

[Table 1]

In Table 1, V is the speed of the screw 29,
HP is the holding pressure, which is expressed as a percentage of the maximum speed and the maximum pressure, respectively. The unit of the position S is mm and the unit of the time T is seconds. At the end of the weighing process, screw 29
Is at the position of S0. In the injection process, the speed of the screw 29 switches to four stages, and Sn (n = 1, 2, 3, 3)
The screw 29 advances at the speed of Vn to the position 4). When the screw 29 reaches the position of S4, a pressure-holding step is performed, and the screw 29 is pressurized with HP pressure for T seconds. As shown in FIG. 1, the injection process ends in about 0.75 seconds. Further, the rotary valve 23 closes 0.2 seconds after the end of the injection step. Further, the weighing process starts 0.3 seconds after the rotary valve 23 is closed.

In the case of the mold 50, the mold closing step is performed by the mold closing device 5 of the molding machine prior to the injection step. In this mold closing, the speed of the movable mold 52 with respect to the fixed mold 51 gradually decreases. The setting is gradually increased to 70 at maximum speed.
%, 60% and 40%. At that time, first, the movable mold 52 is generally closed with respect to the fixed mold 51 by the toggle mechanism 7. Next, the hydraulic drive mechanism 8 applies a sufficient clamping force of, for example, 150 t against the resin pressure to the fixed mold 51 and the movable mold 52. In terms of time, as shown in Fig. 1, 0.
In 6 seconds, the movable mold 52 comes into contact with the fixed mold 51 (mold touch). At this point, only the contact is made, and no mold clamping force is generated. At the end of another 0.3 seconds, the final predetermined clamping force is reached. Then, the injection process starts at the time of mold touch 0.6 seconds after the start of mold closing. In this injection process, the molten resin injected from the nozzle 22 of the molding machine is supplied to the sprue 61 and the runner 6 of the manifold 59.
3. The air passes through the periphery of the spear 67 sequentially and flows into the cavity 53 from the gate 68. During the injection process, the cavity 53 is filled with a molten resin. In the pressure-holding step subsequent to the injection step, pressure is applied to the resin in the mold 50 to prevent the backflow of the molten resin from the cavity 53, and to reduce the amount of shrinkage due to cooling and curing of the resin. It is supplemented in the cavity 53. Then, after the resin in the cavity 53, that is, the product is sufficiently cooled and hardened, the mold is opened and the product is taken out. In addition, on the molding machine side, the rotary valve 23 is opened for a certain time immediately before the mold is opened, and suckback is performed. FIG. 2 shows the timing of opening and closing the rotary valve 23 throughout one molding cycle.
The time for one molding cycle is about 13 seconds. Throughout the entire process, the sprue 61, the runner 63, and the resin in the through hole 65 of the mold 50 are always kept in a molten state by heating the heaters 62, 64.

As described above, the injection step starts before the final predetermined clamping force is applied to the fixed mold 51 and the movable mold 52, but the injection step in which the cavity 53 is not filled with the resin is performed. In the beginning, fixed type
The pressure applied to the fixed mold 51 and the movable mold 52 is low, and a large mold clamping force is not required to prevent the fixed mold 51 and the movable mold 52 from opening each other due to the resin pressure. There is no problem if the injection process is started before the mold clamping is completed. On the other hand, as the cavity 53 is filled with the resin, the force acting on the resin to open the fixed mold 51 and the movable mold 52 increases, but at this stage, the mold clamping has already been completed. Fixed type 51 and movable type 52
Since the sufficient mold clamping force is applied, the fixed mold 51 and the movable mold 52 are reliably prevented from opening against strong resin pressure.

During the period from the start of the pressure-holding step to the closing of the rotary valve 23, the molten resin in the mold 50 is directly pressurized by the screw 29 of the molding machine. However, direct pressurization by the screw 29 becomes ineffective. When the rotary valve 23 closes, the resin in the cavity 53 including the gate 68 has not been cured yet, and is in the middle of the pressure-holding step. However, during the period from the start of the pressure-holding step to the closing of the rotary valve 23, the pressing of the screw 29 causes the die 50
The pressure of the molten resin in the resin passage centered on the runner 63 of the manifold 59 in the inside is sufficiently increased. After the rotary valve 23 is closed, the resin pressure inside the runner 63 and the like is kept sufficiently high as described above, so that the resin in the cavity 53 due to the shrinkage due to the curing of the resin in the cavity 53 has a through hole.
It will be supplemented from inside 65 into cavity 53.

Thus, according to the configuration of the above embodiment, by starting the injection step at the time of touching the mold before the end of the mold clamping, the time from the start of closing the mold to the start of the injection step is reduced by 0.4 seconds compared to the conventional case. The molding cycle can be shortened. In addition, by starting the weighing step in the middle of the pressure-holding step, the time required for one molding cycle, which took about 19 seconds in the conventional method under the same other conditions, can be significantly reduced to about 14 seconds. In addition, as described above, even if the injection process is started at the time of touching the mold before the end of the mold clamping, there is no problem in molding. Also, due to the pressure of the molten resin in the mold 50,
Holding pressure can be performed reliably, and weighing is also possible with the rotary valve 23.
This is done after the nozzle 22 is closed, so make sure
I can do it. Such time reduction is possible without adding a special structure to a conventional molding machine or mold. Further
Until the weighing process starts during the pressure holding process,
Is controlled to pressurize at a certain pressure for a certain time.
It is not complicated and troublesome, but rather
Pressure and time used for holding pressure control at multiple stages
The control becomes simpler than that of the control.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made. For example,
The time of each process, mold clamping force, screw position and speed, setting of holding pressure, etc., according to the product to be molded and other conditions,
Of course it changes. Further, in the above-described embodiment, the rotary valve 23 is closed between the mold opening step and the mold closing step, but may be kept open as shown in FIG. Further, the mold and the molding machine are not limited to those of the above-described embodiment. For example,
The molding machine may be of an in-line screw type as in the above-described embodiment, or of a pre-plastic type. The mold closing device is not limited to the mechanical and hydraulic combined type as in the above-described embodiment, but may be any type such as a hydraulically driven direct pressure type and a double toggle type. Further, the mold may be of a valve system in addition to the spear system.

[0019]

According to the present invention, during the mold closing step, before the mold clamping force applied to the mold member reaches a predetermined mold clamping force and when a plurality of mold members abut against each other and come into contact with each other. Starts the injection process, and is added to the mold members during this injection process
Runode was reached the mold clamping force to the predetermined mold clamping force, without adding a special structure to the conventional molding machine and a mold, and is not required originally large clamping force at the beginning stage of the injection process As a result, the molding cycle can be shortened without hindering the molding, and the resin in the resin passage of the mold is plasticized.
With keeping, provided a valve for opening and closing the nozzle of the injection apparatus, the pressure holding process, a constant pressure in the injection apparatus
And presses the pressing member for a certain period of time.
After having put pressure sufficient to hold pressure in the resin in the mold, so to start the metering step by closing the valve, especially in the conventional molding machines and molds
No additional structure and complicated and cumbersome control
Molding cycles can be further reduced without compromising and without compromising the reliability of metering and dwelling.

[Brief description of the drawings]

FIG. 1, showing an embodiment of the present invention, is a timing chart showing steps from mold closing to weighing.

FIG. 2 is a timing chart for opening and closing the valve.

FIG. 3 is a schematic explanatory view of the injection molding machine.

FIG. 4 is a cross-sectional view of the mold.

FIG. 5 is a timing chart for opening and closing a valve according to another embodiment of the present invention.

[Explanation of symbols]

 5 mold closing device 20 injection device 22 nozzle 23 rotary valve (valve)29 Screw (pressing member)  51 Fixed mold (mold member) 52 Movable mold (mold member) 53 Cavity

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29C 45/20-45/23 B29C 45/46-45/57 B29C 45/64-45/70 B29C 45/76-45 / 77

Claims (1)

(57) [Claims] 1. A cavity between a plurality of mold members to be opened and closed.
As well as through this cavity and internally
A mold having a resin passage for keeping the resin in a plastic state, a mold closing device for opening and closing the plurality of mold members and applying a predetermined mold clamping force to the closed mold members, and a closed mold. Press the plasticized resin from the nozzle into the cavity formed between the mold members.
An injection device which is pressed by a pressure member and sent out, and using a molding machine having a valve for opening and closing the nozzle, a measuring step of storing a predetermined amount of resin in a plastic state in the injection device, and closing a plurality of mold members A mold closing step of applying a mold clamping force to these mold members; an injection step of sending a plasticized resin from the injection device after the measuring step into a cavity formed between the closed mold members; A pressure-holding step of applying pressure to the resin in the mold member from the injection device after the process, wherein the mold-clamping process is performed before the mold-clamping force applied to the mold member reaches the predetermined mold-clamping force. When the plurality of mold members abut against each other , the injection process is started, and the mold clamping force applied to the mold members during the injection process is reduced.
The predetermined mold clamping force is reached, and in the pressure holding step , a constant
Pressing the pressing member for a certain period of time with pressure
And applying a pressure sufficient to hold the resin in the mold, and then closing the valve to start the measuring step.