JP2762346B2 - Injection molding method and injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and an injection molding machine for performing molding by injection molding a molten resin into a mold cavity by an injection device.

[0002]

2. Description of the Related Art Conventionally, when a molten resin is injected and filled into a mold cavity from an injection device, the molten resin is filled while a gas pressure is applied to the mold cavity, and the gas pressure is changed. Method (counter pressure method) that controls the degree of foaming of the molded product
Are known, for example, from JP-A-4-308713 and JP-A-5-278058.

[0003]

However, in the above-mentioned conventional molding method, the gas pressure is controlled by paying attention to the pressure applied to the tip of the molten resin filled in the mold cavity. Although the effect of being able to freely control the degree of foaming can be obtained, on the other hand, pressure fluctuation factors when injection filling the molten resin into the mold cavity, for example,
Since the increase in resin pressure due to the flow length, which gradually increases with the progress of filling, is not taken into account, this type of pressure fluctuation factor and the gas pressure are combined, and the fluctuation range of the resin pressure in the mold cavity during the filling period The problem is that sufficient molding quality cannot be obtained, for example, when the resin becomes excessively large or the resin pressure is over-pressurized, resulting in variations in the weight of the molded product due to fluctuations in the filling amount and defective skin layers due to the density difference. was there.

The present invention has been made to solve the problems existing in the prior art, and it is an injection molding method capable of resolving a variation in weight of a molded article and a defective skin layer, and dramatically improving molding quality. And an injection molding machine.

[0005]

According to the injection molding method of the present invention, a molten resin R is injected into a mold cavity 3 by an injection device 2.
When performing molding by injection filling, the tip portion Rs of the molten resin R filled in the mold cavity 3 is applied to a pressurized medium, for example, an inert gas G, air A, a liquid or a pressurized body B, or the like. While the pressure is applied by the pressure medium, the pressure (gate pressure Pg) of the molten resin R in the vicinity of the gate 3g is detected, and the detected gate pressure Pg is set in advance to a predetermined pressure characteristic C, for example, during the filling period of the molten resin R. The present invention is characterized in that the pressurizing force of the pressurized medium is feedback-controlled so as to be a constant target value Ps.

As the pressurized medium, an inert gas G,
Any of air, liquid, and pressurized body B can be used. In this case, the pressurized medium is supplied and discharged from the end portions 3s and 3s of the mold cavity 3, and the pressing force of the pressurized medium is The supply / discharge amount of the pressurized medium to / from the mold cavity 3 is variably controlled. Alternatively, the air A in the mold cavity 3 can be used as the pressurized medium. In this case, the pressurized medium is discharged from the end portions 3s of the mold cavity 3 and the pressure of the pressurized medium is increased. Controls the discharge amount of the pressurized medium from the mold cavity 3 variably. Further, the pressing body B can be used as the pressing medium.

On the other hand, in the injection molding machine 1 according to the present invention, in particular, the tip portion Rs of the molten resin R filled in the mold cavity 3 is pressurized with an inert gas G, air, liquid or a pressurized body B. A pressurizing function unit 4 for pressurizing with a medium, a gate pressure detecting unit 5 for detecting a pressure (gate pressure Pg) of the molten resin R in the vicinity of the gate 3g, and a detected gate pressure Pg having a predetermined pressure characteristic C, for example, During the filling period of the resin R, a pressurization control unit 6 that performs feedback control of the pressurizing force of the pressurized medium so as to have a predetermined constant target value Ps is provided.

When any of the inert gas G, air and liquid is used as the pressurizing medium, the pressurizing function section 4
Is provided with a pressurized medium supply / discharge unit 7 for supplying / discharging the pressurized medium from the end portions 3s of the mold cavity 3. In this case, the pressurizing control unit 6 controls the pressing force of the pressurized medium by changing the amount of supply and discharge of the pressurized medium to and from the mold cavity 3.
When the air A in the mold cavity 3 is used as the pressurized medium, the pressurized medium discharge unit for discharging the pressurized medium from the end portions 3s of the mold cavity 3 to the pressurizing function unit 4. 7o is provided. In this case, the pressurizing control unit 6 controls the pressure of the pressurized medium by changing the discharge amount of the pressurized medium from the mold cavity 3.

[0009]

According to the injection molding method and the injection molding machine 1 of the present invention, since the pressurizing function section 4 includes the pressurized medium supply / discharge section 7, the pressurized medium such as the inert gas G, air, and liquid can be used. Are supplied into or discharged from the mold cavity 3 from the end portions 3s of the mold cavity 3. Therefore, a predetermined pressing force by the pressurized medium is applied to the front end portion Rs of the molten resin R filled in the mold cavity 3. Note that air A present in the mold cavity 3 may be used as the pressurizing medium. In this case, the pressurizing function unit 4 is provided with a pressurizing medium discharging unit 7o, so The medium is discharged from the end portions 3s of the mold cavity 3.

On the other hand, the gate pressure detector 5 detects the pressure of the molten resin R near the gate 3g (gate pressure Pg).
Is detected, and the detected gate pressure Pg is applied to the pressurization control unit 6.
Is given to Further, a predetermined pressure characteristic C, for example, a target value Ps for maintaining the gate pressure Pg at a constant value during the filling period of the molten resin R is set in the pressure control unit 6 in advance.

Thus, the pressurizing control section 6 supplies and discharges the pressurized medium to and from the mold cavity 3 based on the detected gate pressure Pg such that the gate pressure Pg matches the target value Ps. Or the discharge amount), and the pressure of the pressurized medium is feedback-controlled.

Therefore, the gate pressure Pg at the time of injection filling in the mold cavity 3 is maintained at a predetermined constant target value Ps.
The adverse effects such as an excessively large fluctuation range of the resin pressure in the inside and an occurrence of an overpressure state in the resin pressure are prevented, and as a result, variation in the weight of the molded product and defective skin layer are eliminated.

[0013]

Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the configuration of the injection molding machine according to the present embodiment will be specifically described with reference to FIG.

In FIG. 1, reference numeral 1 denotes an injection molding machine according to the present invention (embodiment). The injection molding machine 1 includes an injection device 2 and a mold 10 supported by a mold clamping device (not shown).

The injection device 2 has a heating cylinder 13 having an injection nozzle 11 at a front end and a hopper 12 at a rear part, and a screw 14 is built in the heating cylinder 13. Further, the rear end of the heating cylinder 13 is connected to the screw driving unit 15. The screw drive unit 15 includes an injection cylinder 16 containing a single rod type piston 16p and a piston 16p
An oil motor 17 having a rotary shaft spline-coupled to a rear end thereof is provided. A piston rod 16 r projecting from a front end of the injection cylinder 16 is coupled to a rear end of the screw 14.
Reference numeral 18 denotes the oil pressure of the rear oil chamber in the injection cylinder 16,
That is, it is a pressure sensor that detects the injection pressure.

Reference numeral 19 denotes a hydraulic circuit. Reference numeral 20 denotes a hydraulic circuit, which includes a hydraulic source 21 having a built-in hydraulic pump, an oil tank 22, and control valves 23, 24, and 25. Thereby, the hydraulic pressure source 21 and the oil tank 22 are selectively connected to the front oil chamber and the rear oil chamber of the injection cylinder 16 via the control valves 23, 24, 25, respectively. It is selectively connected to the motor 17. Further, a central controller 26 having a computer function has a function of controlling various controls of the entire injection molding machine 1. Reference numeral 27 denotes a hydraulic controller that controls the hydraulic power source 21, and is connected to the central controller 26. Note that 28
Is a pressure sensor that detects the discharge pressure of the hydraulic pressure source 21,
This detection result is provided to the hydraulic controller 27.
Reference numeral 29 denotes a position sensor for detecting the position (speed) of the screw 14, and the detection result is given to the central controller 26.

On the other hand, the mold 10 comprises a fixed mold 10c and a movable mold 1c.
0 m. A mold cavity 3 is provided between the fixed mold 10c and the movable mold 10m, and the mold cavity 3 has a gate 3g. In addition, 3s and 3s in the mold cavity 3 indicate end portions, and R indicates the molten resin being filled in the mold cavity 3.

On the other hand, reference numeral 30 denotes a gas system circuit, which includes a pressurizing function unit 4 and a pressurizing control unit 6 which constitute essential parts of the present invention.

The pressurizing function section 4 has a function of pressurizing the tip portion Rs of the molten resin R filled in the mold cavity 3 with an inert gas G (pressurizing medium). The pressurizing function unit 4 includes a pressurized medium supply / discharge unit 7. Pressurized medium supply / discharge unit 7
Are provided with main gas cylinders 31 and 31 containing an inert gas G (nitrogen gas, carbon dioxide gas, etc.), a gas recovery cylinder 32 and a spare gas cylinder 33 containing an inert gas G, and the main gas cylinders 31. Is connected via a check valve 35, and the gas recovery cylinder 32 and the spare gas cylinder 33 are connected via a control valve 34. In this case, the gas recovery cylinder 32 has a double structure including a rigid outer cylinder 32o and a flexible inner cylinder 32i formed of rubber or the like, and the inner cylinder 32i is connected to the control valve 34 and the check valve 35. . The outer cylinder 32o is configured to be connectable to the discharge side of the hydraulic power source 21 or the oil tank 22 via the control valve 36. In the mold 10,
A gas passage 37 for supplying the inert gas G from the end portions 3s of the mold cavity 3 into the mold cavity 3 is provided. The gas passage 37 is connected to an output port of a servo valve 39 via a control valve 38. One input port of the servo valve 39 is connected to the gas recovery cylinder 32 (the inner cylinder part 32i) via the check valve 40, and the other input port is connected to the main gas cylinder 31.

On the other hand, the pressurization control section 6 includes a gas controller 41 for controlling the servo valve 39, and the gas controller 41 is connected to the central controller 26. A pressure sensor 42 detects the pressure of the inert gas G supplied to the mold cavity 3, and the result of the detection is given to the gas controller 41. In the vicinity of the gate 3g in the mold 10, a gate pressure detector (pressure sensor) 5 for detecting the pressure of the molten resin R (gate pressure Pg).
Is arranged. The detection result of the gate pressure detector 5 is provided to the gas controller 41. Further, the gas controller 41 has a function of setting a target value Ps, and sets an optimum gate pressure near the gate 3g in advance as the target value Ps. The detection result of the pressure sensor 28 attached to the injection cylinder 16 is also given to the gas controller 41.

Next, an injection molding method according to the present invention including the operation of the above-described injection molding machine 1 will be described with reference to FIGS.

Now, it is assumed that the measuring step and the mold clamping step are completed and the injection step is started. In this state, the control valve 34 shown in FIG. 1 is switched to the upper symbol, the control valve 36 is switched to the left symbol, and the control valve 38 is switched to the right symbol. As a result, the inert gas G stored in the main gas cylinders 31 is supplied to the mold 10 through the servo valve 39 and the control valve 38, and further from the end portions 3s of the mold cavity 3 through the gas passage 37. It is supplied into the mold cavity 3. Therefore, the mold cavity 3
A predetermined pressure is applied by the inert gas G to the tip portion Rs of the molten resin R filled in the resin. The gas pressure at this time is detected by the pressure sensor 42 and applied to the gas controller 41.

On the other hand, the control valve 23 in the hydraulic circuit 19 of the injection device 2 switches to the right symbol, and the control valve 24 switches to the left symbol. As a result, the pressure oil discharged from the hydraulic pressure source 21 is supplied to the rear oil chamber of the injection cylinder 16, so that the screw 14 moves forward. At this time, the forward position of the screw 14 is detected by the position sensor 29, and the forward speed (injection speed) of the screw 14 is obtained by converting the position data detected by the position sensor 29. The hydraulic system controller 27 controls the screw 14
The feedback control of the discharge flow rate from the hydraulic power source 21 is performed based on the detected forward speed of the screw 14 so that the forward speed of the screw 14 coincides with a preset target speed.

As a result, the molten resin R measured in front of the screw 14 is injected and filled into the mold cavity 3. Then, at this time, the pressure of the molten resin R (gate pressure Pg) near the gate 3g is detected by the gate pressure detection unit 5, and the detected gate pressure Pg is applied to the gas controller 41. The gas controller 41 (pressurization control unit 6) determines that the detected gate pressure Pg
The servo valve 39 is controlled so as to match the set target value Ps. Further, the servo valve 39 controls the supply amount of the inert gas G to the mold cavity 3 or the discharge amount of the inert gas G from the mold cavity 3, and the gate pressure Pg is the pressure characteristic C shown in FIG. Is maintained constant during the filling period so as to reach the target value Ps.

When the inert gas G is supplied, the inert gas G in the main gas cylinders 31 is supplied into the mold cavity 3, and when the inert gas G is discharged, the inert gas G in the mold cavity 3 is supplied. Gas recovery cylinder 32 (inner cylinder 32
Collected in i). Therefore, the recovered gas of the gas recovery cylinder 32 is supplied with the pressure oil from the hydraulic pressure source 21 into the outer cylinder 32o by switching the control valve 36 to the symbol on the right side, and from the inner cylinder 32i to the main gas cylinder 31 ... side. Will be returned. When the inert gas G in the main gas cylinders 31 decreases, the control valve 34 is switched to the lower symbol, so that the inert gas G is replenished from the spare gas cylinder 33 to the main gas cylinders 31. .

When the inert gas G is not supplied into the mold cavity 3, the flow length gradually increases as the filling amount of the molten resin R into the mold cavity 3 increases. Therefore, as shown in the pressure characteristic indicated by Co in FIG.
As the screw 14 advances, the gate pressure Pg increases. However, in the present invention, since the pressurizing characteristic of the inert gas G changes as shown by Cg in FIG. 2, the gate pressure Pg becomes constant during the filling period like the pressure characteristic C. When the inert gas G is not supplied into the mold cavity 3, the pressure characteristic (resin conversion value) of the injection cylinder 16 is Co.
c, and the pressure characteristic of the tip pressure of the screw 14 is Coh
However, when the inert gas G is supplied according to the present invention, the pressure characteristic (resin conversion value) of the injection cylinder 16 becomes C
c, and the pressure characteristic of the tip pressure of the screw 14 also becomes constant as Ch.

Therefore, the gate pressure Pg at the time of injection filling in the mold cavity 3 is maintained at a predetermined constant target value Ps, so that the fluctuation range of the resin pressure in the mold cavity during the filling period is excessive. The adverse effects such as an increase in the pressure and an overpressure state in the resin pressure are prevented. As a result, variations in the weight of the molded product and defects in the skin layer are eliminated, and the molding quality is dramatically improved.

In the embodiment shown in FIG. 1, the inert gas G is exemplified as the pressurized medium. However, air may be used instead of the inert gas G, or a liquid such as silicon oil may be used if necessary. Is also good.

Next, a modified embodiment according to the present invention will be described.
This will be described with reference to FIGS.

FIG. 3 shows a modified example of the pressurized medium supply / discharge unit 7. In the embodiment shown in FIG. 1, the inert gas G discharged from the mold cavity 3 is configured to be recovered by the gas recovery cylinder 32. However, in the modified embodiment shown in FIG. The pressurized medium discharged from the inside is discharged as it is. In this case, when the inert gas G or air is used, it can be released to the atmosphere as it is, and when a liquid is used, it can be collected in an open container or the like. In FIG. 3,
Since the other configuration can be the same as that of the embodiment shown in FIG. 1, the same parts as those in FIG. 1 are denoted by the same reference numerals, the configuration is clarified, and the detailed description is omitted.

FIG. 4 shows a case where air A present in the mold cavity 3 is used as it is as a pressurized medium. In this case, instead of the pressurized medium supply / discharge unit 7, a pressurized medium discharge unit 7o having only a function of discharging the pressurized medium from the end portions 3s of the mold cavity 3 is provided. Specifically, a control valve (relief valve) 5 is provided in the gas passage 37 of the mold 10.
1 and the air A discharged from the mold cavity 3
To control emissions. That is, since the air A is compressed by filling the mold cavity 3 with the molten resin and the internal pressure of the mold cavity 3 is increased, the principle of variably controlling the internal pressure by varying the discharge amount of the air A is used. It is. In FIG. 4, since other configurations can be the same as those of the embodiment shown in FIG. 1, the same portions as those in FIG. 1 are denoted by the same reference numerals, the configuration is clarified, and the detailed description thereof is omitted. Omitted.

FIG. 5 shows a modification of the mold. FIG.
In the embodiment shown in FIG. 5, a general mold 10 is used, but the modified embodiment shown in FIG. 5 is applied to a mold 10p for injection compression molding. In this case, the mold 10p is the movable mold 1
0 pm is previously opened by a predetermined amount, and during or after injection filling, mold compression is performed to move the movable mold 10 pm in the direction of arrow F. In FIG. 5, the other components are the same as those in FIG.
Since the configuration can be the same as that of the embodiment shown in FIG. 3, the same parts as those in FIG. 3 are denoted by the same reference numerals, the configuration is clarified, and the detailed description thereof is omitted.

On the other hand, FIG. 6 shows a pressing body B,
For example, a pressure rod Br is used. In this case, the type of molded product that can be applied is limited to the form of a bar or the like,
It can be carried out in the same manner as the above embodiment. The modified embodiment shown in FIG. 6 exemplifies a case in which a piston rod 53 which is moved forward and backward by a pressurizing cylinder 52 provided on a mold 10 is directly used as a pressurizing rod Br. Further, since the pressurized oil of the hydraulic pressure source 21 (FIG. 1) can be supplied to the pressurized cylinder 52, the pressurized medium supply / discharge unit 7 shown in FIG. 1 is not required. In FIG. 6, reference numeral 54 denotes a control block including a pressure control unit and a pressure function unit. Note that the modified embodiment shown in FIG. 6 can also be configured basically in the same manner as the embodiment shown in FIG. Therefore, the same portions as those in FIG. 1 are denoted by the same reference numerals, the configuration is clarified, and the detailed description is omitted.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment.
For example, as the pressurizing medium, another pressurizing medium other than the illustrated one can be used. Further, the gate pressure is controlled to be a predetermined constant target value during the filling period of the molten resin, but may be controlled to have an arbitrary pressure characteristic (change characteristic) as necessary. Furthermore, each component in each embodiment including the modified embodiment can be replaced and implemented as necessary. In addition, it is possible to arbitrarily change the detailed configuration, method, and the like without departing from the gist of the present invention.

[0036]

As described above, in the injection molding method (injection molding machine) according to the present invention, when the injection molding is performed by injecting the molten resin into the mold cavity by the injection device, the molten resin filled in the mold cavity is filled. The distal end portion of the resin is pressurized with a pressurized medium, and the pressure (gate pressure) of the molten resin near the gate is detected, and the pressure of the pressurized medium is set so that the detected gate pressure has a predetermined pressure characteristic set in advance. Since the pressing force is feedback-controlled, there is a remarkable effect that the variation in the weight of the molded product and the failure of the skin layer can be eliminated, and the molding quality can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram including a block circuit of an injection molding machine according to the present invention,

FIG. 2 is a pressure characteristic diagram of each part when an injection molding method according to the present invention is performed,

FIG. 3 is a configuration diagram showing a part of an injection molding machine according to a modified embodiment of the present invention,

FIG. 4 is a configuration diagram showing a part of an injection molding machine according to another modified embodiment of the present invention,

FIG. 5 is a configuration diagram showing a part of an injection molding machine according to another modified embodiment of the present invention,

FIG. 6 is a configuration diagram showing a part of an injection molding machine according to another modified embodiment of the present invention,

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Injection apparatus 3 Mold cavity 3s Terminal part 3g Gate 4 Pressure function part 5 Gate pressure detection part 6 Pressure control part 7 Pressurized medium supply / discharge part 7o Pressurized medium discharge part R Molten resin Rs Molten resin G Inert gas A Air B Pressurized body C Pressure characteristics Ps Target value Pg Gate pressure

Claims (16)

(57) [Claims] In an injection molding method for performing molding by injection-molding a molten resin into a mold cavity by an injection device, a tip portion of the molten resin filled in the mold cavity is pressurized by a pressurized medium and a gate is formed. An injection molding method comprising detecting a pressure (gate pressure) of a molten resin in the vicinity, and performing feedback control of a pressing force of a pressurizing medium so that the detected gate pressure has a predetermined pressure characteristic set in advance. 2. The injection molding method according to claim 1, wherein any one of air, an inert gas, and a liquid is used as the pressurized medium. 3. The pressurizing medium is supplied and discharged from an end portion of the mold cavity, and the pressure of the pressurized medium is controlled by varying the amount of supply and discharge of the pressurized medium to and from the mold cavity. The injection molding method according to claim 1 or 2, wherein 4. The injection molding method according to claim 1, wherein the pressurized medium uses air in a mold cavity. 5. The pressurizing medium is discharged from an end portion of the mold cavity, and the pressure of the pressurized medium is controlled by varying the discharge amount of the pressurized medium from the mold cavity. The injection molding method according to claim 1 or 4, wherein: 6. The injection molding method according to claim 1, wherein a pressurized body is used as the pressurized medium. 7. The gate pressure is set during the filling period of the molten resin.
2. The injection molding method according to claim 1, wherein the control is performed such that a predetermined target value is set. 8. A pressurizing function section for pressurizing a tip portion of a molten resin filled in a mold cavity with a pressurized medium in an injection molding machine for performing injection molding of a molten resin into a mold cavity by an injection device. A gate pressure detector for detecting the pressure (gate pressure) of the molten resin in the vicinity of the gate; and a pressure control unit for performing feedback control of the pressure of the pressurized medium so that the detected gate pressure has a predetermined pressure characteristic set in advance. An injection molding machine comprising a pressure control unit. 9. The injection molding machine according to claim 8, wherein the pressurized medium uses one of air, an inert gas, and a liquid. 10. The injection molding machine according to claim 8, wherein the pressurizing function unit includes a pressurized medium supply / discharge unit that supplies / discharges a pressurized medium from an end portion of the mold cavity. 11. The pressurizing control unit controls the pressing force of the pressurized medium by changing the amount of supply and discharge of the pressurized medium to and from the mold cavity.
Injection molding machine according to 0. 12. The injection molding machine according to claim 8, wherein the pressurized medium uses air in a mold cavity. 13. The injection molding machine according to claim 8, wherein the pressurizing function unit includes a pressurized medium discharge unit that discharges the pressurized medium from an end portion of the mold cavity. 14. The injection molding machine according to claim 8, wherein the pressurizing medium uses a pressurizing body. 15. The pressurizing control unit controls the pressing force of the pressurized medium by varying the discharge amount of the pressurized medium from the mold cavity.
The injection molding machine as described. 16. The pressurizing control unit during the filling period of the molten resin,
9. The injection molding machine according to claim 8, wherein the gate pressure is controlled so as to become a predetermined constant target value.