JP2929364B2 - Control method of pre-plastic 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 a control method for a pre-plastic injection molding machine provided with an accumulator for accumulating plasticized resin during non-weighing by a delivery plunger and a storage cylinder and sending the resin during metering.

[0002]

2. Description of the Related Art In general, a plasticizing device for plasticizing a molding material by a screw and a heating cylinder, a storage device for accumulating a plasticized resin during non-weighing by a delivery plunger and a storage cylinder, and sending the resin during metering, 2. Description of the Related Art A prepra-type injection molding machine including an injection device for measuring a resin supplied from a plasticizing device and a storage device by using an injection plunger and an injection cylinder and injecting the measured resin is known. This type of pre-plastic injection molding machine accumulates plasticized resin extruded from a plasticizer in a storage device and supplies the accumulated resin to the injection device in addition to the resin extruded from the plasticizer when measuring. Therefore, the plasticizer can be continuously operated, and the plasticization time is prolonged, so that there is an advantage that more uniform plasticization and shortening of the molding cycle time can be achieved.

Conventionally, such a pre-plastic injection molding machine (control method) is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 4-28661.
No. 7 is known a continuous plasticizing type injection molding apparatus, and the injection molding machine is configured such that even when the plunger of the storage device is at the extrusion limit position, the outflow passage of the plasticization device is connected to the storage cylinder. In addition to controlling the pressing force applied to the plunger of the storage device and the plunger of the injection device to a value that allows each plunger to retreat regardless of the position of the plunger of the storage device with respect to the resin sent from the outflow passage, the resin is opened inside. , Into the storage device or the injection device.

[0004]

However, the above-described conventional pre-plastic injection molding machine (continuous plasticizing injection molding machine)
The control method is to set the amount of resin to be stored in the storage device to be smaller than the total amount of resin required for one measurement, and to discharge the resin stored in the storage device at the time of measurement, thereby extruding from the plasticizing device. The delivery of the accumulated resin in addition to the resin ended earlier than the end of the metering process.

For this reason, depending on the position of the resin to be measured, there are a portion where the accumulated resin is mixed with the resin extruded from the plasticizer and a portion where only the resin is extruded from the plasticizer. However, it is not possible to obtain a uniform resin in a molten state from the side at the time of mixing, and pressure fluctuations occur in the resin extruded from the plasticizing device. There was a problem that a uniform resin could not be obtained.

The present invention has been made to solve the problems existing in the prior art, and it is possible to obtain a homogeneous resin in a molten state at the time of weighing, thereby achieving a homogenized and high quality molded article. An object of the present invention is to provide a control method for a pre-plastic injection molding machine.

[0007]

In particular, the control method according to the present invention comprises a plasticizing device 20 for plasticizing a molding material by means of a screw 21 and a heating cylinder 22, and a delivery plunger 31 and a storage cylinder 32, when non-weighing. The accumulating device 30 that accumulates the plasticized resin and sends it out at the time of measurement, the injection plunger 41 and the injection cylinder 42 measure the resin supplied from the plasticizing device 20 and the accumulating device 30, and inject the measured resin. In the pre-plastic injection molding machine 1 provided with the injection device 40, the theoretical rotational speed No of the screw 21 required to measure the total resin amount Qo corresponding to the target measured value and the heating cylinder 22 are extruded by the screw 21 in advance. By calculating the theoretical extrusion amount qo of the resin per one rotation to be performed, and by rotating the screw 21 according to the rotation speed No during molding, By detecting the actual rotation speed Nd at the time of stacking and calculating the actual extrusion amount qd per rotation, and comparing the detected Nd with the set No and the calculated qd with the set qo, respectively. ,
If any one of them does not match, the rotational speed No of the screw 21 in the measuring process is corrected, and the corrected rotational speed Ns
The rotation of the screw 21 is controlled by the following.

In this case, the rotation speed Ns is Ns [rpm].
= ｛[60 · Qo [cc]]-[Nd [rpm] · qd
[Cc / time] · ti [sec]]｝ / qd [cc / time]
[Tc [sec]-ti [sec]] (where ti
Is the injection time, and tc is the molding cycle time). The screw 21 is continuously rotated. On the other hand, the forward speed V of the delivery plunger 31 at the time of delivery from the storage device 30 is V [mm / sec] = L [mm] / [tc [s
ec] -ti [sec]] (where L is the storage device 30
It is desirable to set by the retreat distance of the sending plunger 31 at the time of accumulation. Further, the allowance time that can be arbitrarily set is tr, and the forward speed V of the delivery plunger 31 is
V [mm / sec] = L [mm] / [tc [sec
c] -ti [sec] -tr [sec]]. The margin time tr can be set according to the time required for refreshing the resin by rotating the screw 21 after the feed plunger 31 is moved forward most.

[0009]

According to the control method of the pre-plastic injection molding machine of the present invention, the theoretical rotational speed N of the screw 21 during molding is adjusted.
o, the screw 21 is rotated to detect the actual rotational speed Nd, and based on this, the actual extrusion amount qd is calculated. The detected Nd is set to No, and the calculated qd is set to qo. Are compared with each other, and if any of them does not match, the rotational speed No of the screw 21 during the measuring process is set to Ns (Ns = ｛[60
・ Qo] − [Nd · qd · ti]｝ / qd · [tc-t
i)), the screw 21 rotates at the corrected rotation speed Ns in the measuring step, and the required resin amount Qs is extruded from the extrusion port 23.
Therefore, the total resin amount obtained by adding the resin amount Qd sent from the storage cylinder 32 and the resin amount Qs coincides with the total resin amount Qo corresponding to the target measured value, and continuous plasticization for continuously rotating the screw 21 is possible. become.

The forward speed V of the delivery plunger 31 at the time of delivery of the storage device 30 is represented by V = L / [tc-t].
i], desirably, the margin time that can be arbitrarily set is tr, and if V = L / [tc-ti-tr] is set, the delivery plunger 31 can store the accumulated resin in the entire period of the measurement time required for the measurement process. Is sent out at a constant flow rate, the end of the metering process coincides with the end of sending out the resin stored in the storage cylinder 32.

Therefore, the resin discharged from the storage cylinder 32 and the resin extruded from the heating cylinder 22 are uniformly mixed at all positions, and the fluctuation of the resin pressure in the resin passage 51 is suppressed. From the aspect of the plasticizing ability of the device 20, the molten state of the resin becomes uniform.

[0012]

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

First, the configuration of a pre-plastic injection molding machine 1 according to the present embodiment will be described with reference to FIGS.
In the units of the physical quantity in the examples, the resin amount is [cc], and the resin amount per screw rotation is [cc /
Times], the number of rotations is [rpm], the time is [sec], the speed is [mm / sec], and the distance is [mm].

FIG. 2 shows a configuration mainly including a mechanical system of the pre-plastic injection molding machine 1. In the figure, reference numeral 20 denotes a plasticizing device, which includes a heating cylinder 22 into which a screw 21 is inserted. At the front end of the heating cylinder 22, there is provided an extrusion port 23 for plasticized resin, and at the rear, a hopper 24 for supplying molding material.
Having. A screw drive unit 25 is connected to the rear end of the heating cylinder 22. The screw drive unit 25 includes a screw motor 26, and a rotating shaft of the screw motor 26 is coupled to a rear end of the screw 21 via a coupler 27. Reference numeral 28 denotes a rotary encoder that detects the rotation speed of the screw 21.

On the other hand, reference numeral 30 denotes a storage device, which comprises a storage cylinder 32 into which a delivery plunger 31 is inserted. The front end of the storage tube 32 is provided integrally with the front end of the heating tube 22, and the storage tube 32 stands up. In addition, at the front end of the storage tube 32, there is a resin entrance 33, and the direction of the entrance 33 is
At right angles to Further, at the rear end of the storage cylinder 32,
A delivery cylinder (hydraulic cylinder) 34 is connected, and a ram 35 built in the delivery cylinder 34 is provided with a delivery plunger 3.
Bind to 1. Reference numeral 36 denotes a position scale for detecting the position of the delivery plunger 31.

On the other hand, reference numeral 40 denotes an injection device disposed below the plasticizing device 20 and includes an injection cylinder 42 into which an injection plunger 41 is inserted. The front part of the injection cylinder 42 is connected to the front ends of the heating cylinder 22 and the storage cylinder 32 via the opening and closing mechanism 50. Further, an injection nozzle 43 for injecting a resin into a mold (not shown) is provided at a front end of the injection cylinder 42, and an injection cylinder 44 is connected to a rear end. The injection cylinder 44 incorporates a ram 45, which is coupled to the injection plunger 41. Reference numeral 46 denotes a position scale for detecting the position of the injection plunger 41.

The opening / closing mechanism 50 includes a resin passage 5 therein.
1, the outlet of the resin passage 51 communicates with the inside of the injection cylinder 42, and the inlet is at a right angle to the extrusion port 23.
In addition, they communicate with the entrance 33 on the same straight line. on the other hand,
Reference numeral 52 denotes an opening / closing cylinder, which opens and closes the resin passage 51 by displacing an opening / closing valve 53 disposed at an intermediate portion of the resin passage 51.

Further, a resin pressure adjusting mechanism 55 is provided in front of the extrusion port 23. As shown in FIG. 3, the resin pressure adjusting mechanism 55 has an opening adjustment valve 56 disposed to face the extrusion port 23, and has a displacement portion 57 for moving the opening adjustment valve 56 forward or backward, Opening control valve 56
The opening of the extrusion port 23 can be adjusted by moving forward or backward. Thus, for example, even if the pressure of the resin delivered from the storage cylinder 32 fluctuates, the pressure of the resin extruded from the heating cylinder 22 can be maintained at a predetermined level, and adverse effects on the plasticizing characteristics can be prevented.

On the other hand, reference numeral 60 denotes a hydraulic circuit, and reference numeral 80 denotes a controller that controls the entire injection molding machine. The position scales 36 and 46 are connected to the controller 80.

Next, the configuration of the hydraulic circuit 60 will be described with reference to FIG.
This will be described with reference to FIG. 5 shows a configuration mainly including a hydraulic system of the pre-plastic injection molding machine 1, and FIG. 6 shows a block diagram of the configuration.

In the hydraulic circuit 60, reference numeral 61 denotes a hydraulic pressure source, and the discharge side is connected to an inlet 62 i of a switching valve 62. The first outlet 62a of the switching valve 62 is connected to the open / close cylinder 5
2 and a first oil outlet 62a and an oil tank 63 are connected to a rear oil chamber 34r and a front oil chamber 34f of the delivery cylinder 34 via a switching circuit 64.
Connect to On the other hand, the second outlet 62b of the switching valve 62
While connected to the front oil chamber 52f of the opening / closing cylinder 52,
Further, the second outlet 62b and the oil tank 63 are connected to the rear oil chamber 44r and the front oil chamber 44f of the injection cylinder 44 via the switching circuit 65. The hydraulic pressure source 61 includes a variable discharge hydraulic pump 66, control valves 67 and 68, a relief valve 69, and the like. Further, the switching circuit 64 includes switching valves 70, 7
The switching circuit 65 includes switching valves 73 and 74 and an electromagnetic proportional relief valve 75.

Next, the operation of the pre-plastic injection molding machine 1 according to the present embodiment will be described with reference to FIGS.

FIG. 4 shows a process chart in one molding cycle. Now, assume that the weighing process is completed. In this case, the delivery plunger 31 is at the most advanced position, and the screw 21 continues to rotate (plasticizing step). In addition, a measured resin is accommodated in an injection cylinder 42 in front of the injection plunger 41. On the other hand, the switching valve 62
In FIG. 5, the symbol is switched to the symbol on the left. Therefore, the pressure oil supplied from the hydraulic pressure source 61 is supplied from the second outflow port 62b to the front oil chamber 52f of the opening / closing cylinder 52,
It is supplied to a switching circuit 65 connected to the injection cylinder 44. As a result, the opening / closing valve 53 is displaced in the closing direction to close the resin passage 51, and the operation of the injection process can be controlled. That is, the supply of the pressure oil to the injection cylinder 44 is interlocked with the closing operation of the resin passage 51.

Therefore, the switching valve 74 is set to the left symbol,
Further, when the switching valve 73 is switched to the symbol on the right side, the injection plunger 41 advances, and the injection control for the mold is performed (injection step). At this time, the other switching circuit 64 functions as a meter-out circuit, and meter-out control (back pressure control) is performed on the delivery cylinder 34.

On the other hand, even during the injection process, since the screw 21 in the plasticizing device 20 continues to rotate, the plasticized resin is accumulated in the accumulation cylinder 32 of the accumulation device 30 through the extrusion port 23 (accumulation). Process). At this time, the switching valve 70
And 71 are switched to the symbols on the right side, respectively, and the back pressure control for the delivery plunger 31 is performed. The screw 21 is rotating at a corrected rotation speed Ns described later.

When the injection step is completed, the switching valve 62 switches to the right symbol in FIG. Therefore, the pressure oil supplied from the hydraulic pressure source 61 is supplied to the first outlet 62
From a, it is supplied to the rear oil chamber 52r of the opening / closing cylinder 52 and to the switching circuit 64 connected to the delivery cylinder 34. As a result, the opening / closing valve 53 is displaced in the opening direction to open the resin passage 51, and the operation control of the sending step of sending the resin accumulated in the storage cylinder 32 to the resin passage 51 becomes possible. That is, the supply of the pressure oil to the delivery cylinder 34 is interlocked with the opening operation of the resin passage 51.

When the switching valve 71 is switched to the left symbol and the switching valve 70 is switched to the right symbol, the delivery plunger 31 moves forward, and the resin accumulated in the storage cylinder 32 passes through the resin passage 51. The resin is sent out to the injection cylinder 42, and at the same time, the resin extruded from the plasticizing device 20 is supplied to the injection cylinder 42 through the resin passage 51, and the measurement control is performed (delivery step and measurement step). At this time, the other switching circuit 65 functions as a meter-out circuit, and meter-out control (back pressure control) is performed on the injection cylinder 44.

In this case, the forward speed of the delivery plunger 31 and the rotation speed of the screw 21 are set as follows.

First, a method of setting the forward speed of the delivery plunger 31 will be described. The retreat distance L (see FIG. 2) of the delivery plunger 31 during accumulation in the accumulation device 30 is detected by the position scale 36, and the molding cycle time tc and the injection time ti are measured by a timer provided in the controller 80. Therefore, the forward speed V of the delivery plunger 31 is basically V = L / [tc−t
i]. In this case, any margin time tr
It is desirable to set the transmission plunger 3
If the margin time tr is set based on the time required for refreshing the resin by rotating the screw 21 after the first forward movement of No. 1, the forward speed V becomes V = L / [tc-ti-t.
r].

Therefore, the delivery plunger 31 sends out the accumulated resin at a constant flow rate during the entire measuring time te required for the measuring process. Is uniformly mixed at all positions and the fluctuation of the resin pressure in the resin passage 51 is suppressed, so that the molten state of the resin becomes uniform from the aspect of the plasticizing ability in the plasticizing device 20. In addition, depending on the setting of the surplus time tr, for example, the storage cylinder 32
If the resin sent from the storage tube ends earlier than the end of the measuring step, the resin pressure sent from the storage cylinder 32 is adjusted by the resin pressure adjusting mechanism 55.

Next, a method of setting the rotational speed of the screw 21 will be described with reference to a flowchart shown in FIG. First, the theoretical rotational speed No and the extrusion amount qo of resin per one rotation extruded from the heating cylinder 6 are obtained and set in advance based on the performance of the pre-plastic injection molding machine 1 and the setting conditions and the like. . Then, first, the screw 21 is rotated at the theoretical rotational speed No to perform molding (step S).
1). At this time, the actual rotation speed Nd is detected by the rotary encoder 28. After the end of the accumulation step in which the resin is accumulated in the accumulation cylinder 32, the actual extrusion amount qd per rotation of the screw 21 can be calculated based on the total accumulation amount Qd of the resin. That is, ti is the accumulation time (injection time)
Then, since Qd = [Nd / 60] · ti · qd, the extrusion amount qd is represented by qd = Qd · 60 / [Nd · t
i] (step S2). On the other hand, the detected Nd is compared with the set No, and the calculated qd is compared with the set qo. Steps S3 and S4). On the other hand, if any of them does not match, the rotation speed No is corrected, and the rotation of the screw 21 is controlled by the corrected rotation speed Ns (steps S4 to S6).

In this case, the correction for the rotational speed No is performed as follows. Now, the total resin amount based on the target measurement value of the injection cylinder 44 is Qo, and the measurement process (after the accumulation process is completed,
In the period until the next injection process starts), the heating cylinder 22
Assuming that the required amount of resin extruded from the extrusion port 23 is Qs, the relationship of Qs = Qo-Qd is established. Therefore,
Assuming that the corrected rotation speed is Ns and the corrected extrusion amount is qe, Qs is Qs = [Ns / 60] · te · qe = [N
s / 60] · [tc-ti] · qe, so Q
o is Qo = Qd + Qs = ｛[Nd / 60] · ti · q
d｝ + {[Ns / 60] ・ [tc-ti] ・ qe｝. This equation is Ns = ｛[60 if qd = qe is considered.
・ Qo] − [Nd · qd · ti]｝ / ｛qd · [tc−
ti]｝, the required rotational speed Ns for the screw 21 can be obtained from this equation (step S5).

Therefore, in the measuring step, the corrected rotational speed N
The screw 21 is rotated by s, and the required resin amount Qs is extruded from the extrusion port 23 (step S6). Therefore, the total resin amount obtained by adding the resin amount Qd sent from the storage cylinder 32 and the resin amount Qs matches the total resin amount Qo based on the target measured value, and continuous plasticization for continuously rotating the screw 21 is enabled. And the end of the weighing process and the storage cylinder 3
The end of the delivery of the resin accumulated in 2 can be matched.

On the other hand, during the measuring step, a cooling step and a mold opening / closing step are performed on the mold side. In FIG. 4, to indicates the cooling time in the cooling step, and tm indicates the mold opening and closing time in the mold opening and closing step.

On the other hand, when the measuring step is completed, the switching valve 6
2 is switched to the left symbol in FIG. This allows
The pressure oil supplied from the hydraulic pressure source 61 is supplied from the second outlet port 62b to the front oil chamber 52f of the opening / closing cylinder 52, and is also supplied to the switching circuit 65 connected to the injection cylinder 44, and shifts to the above-described injection step. I do.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment,
The detailed configuration, method, and the like can be arbitrarily changed without departing from the gist of the present invention.

[0037]

As described above, according to the control method of the pre-plastic injection molding machine according to the present invention, the theoretical rotational speed No. of the screw required to measure the total resin amount Qo corresponding to the target measured value is determined in advance. While calculating the theoretical extrusion amount qo of the resin per rotation extruded by the screw from the heating cylinder,
At the time of molding, by rotating the screw with the number of revolutions No, the actual number of revolutions Nd at the time of accumulation is detected and the actual extrusion amount qd per revolution is calculated. By comparing the set qd with the set qo, if any of them does not match, the screw rotation speed No at the time of the weighing process is corrected, and the screw is rotated based on the corrected rotation speed Ns. As a result, a uniform resin in a molten state can be obtained at the time of measurement, which has a remarkable effect that the homogenization and high quality of a molded product can be achieved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a setting procedure of a screw rotation speed in a control method of a prepra injection molding machine according to the present invention;

FIG. 2 is a partial cross-sectional view mainly showing the mechanical system of the prepra-type injection molding machine,

FIG. 3 is a partial cross-sectional configuration view of a resin pressure adjusting mechanism in the pre-plastic injection molding machine.

FIG. 4 is a process diagram of a molding cycle in the pre-plastic injection molding machine.

FIG. 5 is a hydraulic circuit diagram mainly showing a hydraulic system of the pre-plastic injection molding machine,

FIG. 6 is a basic block diagram of a hydraulic circuit in the pre-plastic injection molding machine;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pre-plastic injection molding machine 20 Plasticizing device 21 Screw 22 Heating cylinder 30 Storage device 31 Delivery plunger 32 Storage cylinder 40 Injection device 41 Injection plunger 42 Injection cylinder L Retraction distance of delivery plunger tc Molding cycle time ti Injection time tr Allowance time

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-131509 (JP, A) JP-A-5-337993 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) B29C 45/53-45/54 B29C 45/58 B29C 45/76-45/77

Claims (6)

(57) [Claims] 1. A plasticizing device for plasticizing a molding material with a screw and a heating cylinder, an accumulating device for accumulating plasticized resin during non-metering by a delivery plunger and a storage cylinder, and sending the resin during metering, and an injection plunger. In a control method of a prepra-type injection molding machine including an injection device for measuring a resin supplied from a plasticizing device and a storage device and injecting the measured resin by an injection cylinder, a total amount corresponding to a target measured value is determined in advance. The theoretical rotation number No of the screw required to measure the resin amount Qo and the theoretical extrusion amount qo of the resin per rotation extruded by the screw from the heating cylinder are determined, and at the time of molding, the rotation number No is determined. By rotating the screw, the actual rotation speed Nd during accumulation and the actual extrusion amount qd per rotation are calculated and detected. By comparing the obtained Nd with the set No and the calculated qd with the set qo, if any of them does not match, the rotational speed No of the screw in the measuring process is corrected, and the corrected A method for controlling a pre-plastic injection molding machine, wherein the rotation of a screw is controlled by the rotation speed Ns. 2. The number of revolutions Ns is Ns [rpm] = ｛[6
0 · Qo [cc]]-[Nd [rpm] · qd [cc /
Times] · ti [sec]]｝ / qd [cc / times] · [tc
2. The control method for a pre-plastic injection molding machine according to claim 1, wherein the calculation is performed by [sec] -ti [sec]] (where ti is an injection time and tc is a molding cycle time). 3. The control method for a pre-plastic injection molding machine according to claim 1, wherein the screw is continuously rotated. 4. The forward speed V of the delivery plunger at the time of delivery of the storage device is defined as V [mm / sec] = L [mm] /
2. The method according to claim 1, wherein the time is set according to [tc [sec] -ti [sec]] (where L is the retreat distance of the delivery plunger when the storage device is stored). 5. An arbitrary settable time is represented by tr,
Let the forward speed V of the delivery plunger be V [mm / sec] =
L [mm] / [tc [sec]-ti [sec]-tr
[Sec]], and is set according to [1].
A control method for the prepra-type injection molding machine described in the above. 6. The control of a pre-plastic injection molding machine according to claim 5, wherein the margin time tr is set according to a time required for refreshing the resin by rotating the screw after the feed plunger is advanced most. Method.