JPH0866944A - Speed control method for injection molding machine - Google Patents

Abstract

PURPOSE: To provide a speed control method for injection molding machine wherein adverse effect due to irregular closing property of a check valve in an injection charge process is minimized so as to stabilize quality of a molded piece. CONSTITUTION: In an injection molding machine equipped with an injection control device for controlling speed of a charging process with an injection speed of a plurality of stages by inputting an injection screw position and an injection pressure detected through a position detecting device and a pressure detecting device, when the injection pressure reaches a check valve determining pressure Pj which is set to an optional point in the charging process previously, a difference ΔS1 (or ΔS2 ) between the injection screw position and an injection screw position at a reference shot is computed and stored. At each speed changing and shifting after setting of the determining pressure Pj, corrections are added to reference changing and shifting positions mn , mn+1 mn+2 ,... so as to perform speed shifting by position shifting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control method for an injection molding machine, and more particularly to a speed control method for an injection molding machine, which is designed to minimize the adverse effects of variations in the check valve closing characteristics during injection. Regarding control method.

[0002]

2. Description of the Related Art Conventionally, in injection molding of molten resin,
As shown in FIG. 3, the horizontal axis represents the position S or time t of the injection screw, the vertical axis represents the forward speed V or pressure P of the injection screw, and the filling step S for filling the molten resin into the mold cavity at high speed. ₁ and injection control is performed by a pressure-holding step S _{2 in} which pressure is applied to the resin in the mold cavity after molding with molten resin to mold the resin. In many cases, the filling step S ₁ sets the pressure control valve of the hydraulic circuit to high pressure. Set so that the opening of the flow control valve is changed over time so as to change the speed in multiple stages based on the elapsed time from the start of injection or the forward position of the injection screw, or according to the stroke position of the injection screw. Then, the injection speed of the piston of the injection cylinder, that is, the injection screw is controlled by adjusting the flow control valve, and the molten resin is melted at such a high speed that the resin in the cavity does not entrap air. Shall fill into the cavity, after the molten resin has been filled in the cavity is secured to a relatively small opening the flow control valve, a pressure-holding step S ₂ of adjusting the hydraulic pressure by the pressure regulating valve, the pressure-holding step S ₂ changes the opening of the pressure adjusting valve so that a predetermined pressure can be applied to the molten resin filled in the cavity with the passage of time, and the molten resin is cooled in the cavity so that the resin shrinks. The product shape and size are prevented from causing an error with respect to the cavity shape size, and a large residual stress is not generated inside the product.

Generally, in the injection process control in the filling process, the control target values of the injection speeds of a plurality of stages are switched when the detected value of the injection screw coincides with the preset injection speed position as described above. FIG. 4 shows an embodiment of this case, in which three speed setting values V are set in the filling step S ₁ .
_It shows the situation of changes in the injection speed V and the pressure P when the switching control is performed to ₁ , V ₂ and V ₃ . By the way, the operation of the check valve for preventing the molten resin in front of the injection screw from flowing backward to the injection screw side during injection is not always the same at every shot, and is slightly different.

[0004]

As described above, although there are some rare cases where the changeover of the injection speeds in the filling process is performed in the past, in most cases, the injection screw is changed at a preset position. Position changeover was performed at all the changeover change points when the point reached. In this case, when the closing of the check valve is delayed, the amount of resin filled in the mold cavity at the same screw position becomes smaller as much backflow occurs than when the closing of the check valve is early. Therefore, since the preset pressure switching is generally performed at the V-P switching point where the filling process shifts to the pressure holding process, in the shot when the check valve is closed late,
The injection screw position where V-P switching is performed (hereinafter, V-
The P switching position) is closer to the screw forward limit side. In this way, the region controlled by the set speed at the final stage of the filling process becomes longer. From Figure 4, compared to the last stage injection region S _A early shot A of閉Ri of the check valve, it can be seen that a large final stage exit area S _B of the slow shot B of閉Ri of the check valve. In particular, when a resin material such as nylon having a low melt viscosity and a strong temperature dependence of the melt viscosity is molded, the check valve closing characteristic varies more greatly from shot to shot than the other resin materials. −
The P switching position also varies, the variation width of the region controlled by the final stage set speed increases, and the variation width of the final stage injection time also increases. FIG. 5 shows a situation in which the final stage injection speed time in conventional position switching varies from shot to shot due to variations in closing of check valves. In this way, in shots where the check valve closes slowly, the injection time becomes longer and the resin in the mold cavity is cooled more by the longer injection time, and the flow resistance in the mold cavity is reduced. As the size of the mold becomes larger, the amount of filling in the cavity is insufficient, and a light defective molded product is produced. As described above, conventionally, the variation in the closing characteristics of the check valve, which is different for each shot, causes the resin filling amount in the cavity to be inconsistent, which causes the variation in the weight of the molded product and the variation in the molding quality.

[0005]

In order to solve the above problems, according to the present invention, a position detector for detecting the position of an injection screw, a pressure detector, and an injection stroke detected through the position detector. In the injection molding machine that is equipped with a speed calculator that calculates the time differential value of or the injection speed detector of the injection screw and that controls the speed of the injection screw at multiple injection speeds during the filling process, close the check valve. The preset judgment pressure is set to an arbitrary point in the filling process in advance, and the injection screw position when the injection pressure reaches the judgment pressure after the start of filling and the injection screw position when the judgment pressure reaches the preset reference shot. The difference is calculated and stored, and among the switching switching points of the injection speeds of the plurality of stages, the switching before the judgment pressure is reached is based on a preset injection screw reference. The speed is switched at the further switching position, and when switching after reaching the judgment pressure, the speed is switched by the position switching by the injection screw position corrected by increasing / decreasing the difference to the preset reference switching position of the injection screw. Decided to do.

[0006]

According to the present invention, the speed switching at the plurality of injection speed change switching points is performed by position switching according to a preset reference change switching position.
Set the check valve closing judgment pressure at any point in the filling process,
The difference between the injection screw position when the injection pressure reaches this judgment pressure after the start of filling and the injection screw position at the judgment pressure at the preset reference shot is calculated and stored. After the judgment pressure is reached, the speed switching is performed for each stage at the position where the reference change switching position is corrected by the difference. Therefore, shots with slow closing of the check valve are delayed by the difference in speed switching position as a whole, and shots with fast closing of the check valve are advanced by differences with respect to each speed switching position. Regardless of the slow speed, the final stage injection time is almost constant and the filling amount in the cavity is kept constant, so that the quality of the molded product is stable with each shot.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and 2 relate to an embodiment of the present invention,
FIG. 1 is a configuration diagram of an injection control device in an injection molding machine, and FIG.
FIG. 4 is a characteristic curve diagram showing injection process control. 1, an injection molding machine 100 includes a heating cylinder 2 having a hopper 1, an injection screw (screw) 3 which is rotatably and movably arranged forward and backward. The connected connecting rod 4 penetrates the frame 7, and the connecting rod 4 and the screw 3 are rotated by the hydraulic motor 6 fixed to the rear end of the frame 7. The frame 7 is connected to the piston rods 5b of the pair of left and right injection cylinders 5, and the piston 5a is configured so that the piston rod 5b, the frame 7, the connecting rod 4 and the injection screw 3 can reciprocate integrally.
The position of the injection screw 3 is measured by the screw position detector 30 by measuring the movement of the lever 7a connected to the frame 7. On the other hand, the injection cylinder 5 is connected to the oil pressure source 10 and the oil pressure unit 20 connected thereto by a pipe, and the working oil pressure is measured by the pressure detector 40.
The nozzle 2a at the tip of the heating cylinder 2 is pressed against the nozzle opening of the mold 9 to supply the molten resin inside the heating cylinder 2 to the cavity 9a. The injection controller 50 includes a speed calculator 50a, a differentiator 50b, and a pressure calculator 50.
c is built in, the position information of the screw 3 and the pressure information of the injection cylinder pressure are input, and the speed command and the pressure command are output. Explaining the operation of the injection molding machine 100,
The resin material is supplied from the hopper 1 into the heating cylinder 2 by rotating the injection screw 3 by the hydraulic motor 6, and the resin material is heated and melted while passing through the groove space formed by the heating cylinder 2 and the screw 3. Then, it is stored in front of the screw 3. At the same time, the screw 3 is gradually retracted, and when the screw 3 reaches a predetermined position, the hydraulic motor 6 is stopped and the measuring process is completed. Next, a servo valve (not shown) installed in the vicinity of the injection cylinder 5 is controlled to send hydraulic oil to the injection cylinder 5, and the screw 3 is advanced to inject the molten resin into the cavity 9 a of the die 9. In the initial stage of the injection process, the forward movement of the screw 3 causes a part of the molten resin in front of the screw 3 to flow back through the screw groove, but thereafter, the check valve 8 is seated on the check seat 8a to prevent the backflow. The operation of the check valve 8 seating on the check seat 8a is related to the forward movement of the screw 3 and the accompanying pressure difference before and after the check valve due to the backward flow of the molten resin in front of the screw, and the timing thereof varies from shot to shot. In the injection process (filling process), the injection speed of the screw 3 is controlled, and the pressure holding process (pressure holding process)
Is one of the oil pressure of the injection cylinder, the resin pressure, and the pressure inside the mold (in the embodiment of FIG. 1, the injection cylinder pressure is adopted).
Control the pressure of.

In the present invention, as shown in FIG.
A plurality of injection speeds in the filling process (in the embodiment of FIG.
1-step speed set value V₁, Second stage speed setting value V₂, 3rd speed
Degree set value V₃, Final stage speed setting value V_Four4 steps)
The change of the injection speed is switched according to the following procedure. Well
In the same way as the conventional speed control method,
Change change is based on a previously assumed reference shot (the most normal shot).
In the shot showing the switching operation procedure that seems to be out)
The actual injection screw at the set position of the injection screw 3.
The so-called position that performs speed switching when the vehicle reaches
It is for switching the position. However, as shown in FIG.
As shown in Fig.
Closed due to variation in closing operation of check valve 8 immediately after start
Slow motion occurs, like curve A and curve B respectively
It will be in a state where it shifts slightly with each shot. Therefore,
Reference change switching position m set in quasi-shot₁, M₂, M
₃, M_FourInstead of switching the position with, check at any point in the filling process.
Check valve closing judgment pressure P_J(In the example of FIG.
Changeover position m₁And reference change switching position m₂Between)
Then, the injection pressure P is the judgment pressure P._JIs measured when
Position of injection screw 3 and assumed curve M of reference shot
Is the judgment pressure P_JDifference from the injection screw position when reaching
The difference is calculated and stored in memory, and the check valve closing judgment pressure
Power P_JEach reference change switching position after reaching m
_n, M_{n + 1}, M_{n + 2}, ... are each corrected by this difference.
Correct, and execute speed switching at each corrected switching position.
Give. Switching the speed by the above operation
As a result, for example, shot B in which check valve 8 closes slowly
Then, the difference when reaching the judgment pressure ΔS₁Only one after another
It will be later than the expected curve M, and VP
Switching point S_CAlso, the reference change switching position m_FourMore difference
Min △ S₁V-P switching is implemented at a position delayed by
, The final stage injection speed area S_BIs almost the end of the reference shot
Step injection speed area S_MIs equal to Conversely, the check valve is closed
In the quick shot A, the difference is ΔS₂As soon as V-P
Change occurs, the final stage injection speed area S_AIs still S_MAlmost to
Will be equal. As described above, the final stage set speed is the same.
Therefore, the final stage injection speed area S_M, S _A, S_BIs almost the same
If the same, the final-stage injection time tf is the closing of the check valve 8.
The values are almost the same regardless of variations in characteristics. that's all
By performing speed switching like
Shot B or check that the check valve closing operation was delayed during the period
Even in shot A where the valve closes quickly, reference shot M
At the same time, the final stage injection speed range and the final stage injection time
Is kept almost constant, and as a result, inside the mold cavity 9a
Since the amount of resin filled into
Molded product quality is stable.

In other words, the intent of the present invention is to set the check valve closing judgment pressure P _J even if the closing operation of the check valve 8 which operates at the beginning of the filling process is delayed or, conversely, becomes faster. At the reference speed switching position m _n after the setting, the difference between the injection screw position when reaching the check valve closing determination pressure P _J provided in the middle and the injection screw position in the reference shot is calculated and stored,
In the subsequent reference change switching positions m _n , m _{n + 1} , m _{n + 2} , ... By correcting this difference and switching the position,
Even if the injection first speed injection time differs from shot to shot, the cavity filling amount is kept constant by making the subsequent injection time, especially the final stage injection time, almost constant. The difference in the check valve closing timing, which has variations, is not reflected in the final stage injection time. That is, it is intended to determine whether the initial check valve closing operation of the first speed of injection is early or late by the position of the injection screw at the judgment pressure P _J , and the injection pressure reaches the judgment pressure P _J. Occasionally, a shot whose injection screw position is on the backward side of the injection molding machine is a shot with a quick check valve closing, and a shot with an injection screw position on the forward side is a shot with a late check valve closing. It is intended to correct the subsequent reference change switching position by the difference and to make other injection times, especially the final stage injection time, constant. As a result of various tests, the variation in the final-stage injection time for each shot, which is seen in FIG. 5 in which all speed switching is position switching, is significantly reduced by performing the method of the present invention, and the fluctuation range is reduced. About 2 except the initial stage
It became as small as 0%. The method of the present invention, particularly for a resin material having a strong temperature dependence of melt viscosity such as nylon,
In the conventional control method, the final stage injection time varies due to the variation in the closing of the check valve, and as a result, the same V
In the case of a shot in which the pressure is changed to the P switching pressure P _C and the final stage injection time is long even in the pressure holding process, the temperature of the molten resin in the mold decreases, the viscosity increases, and the flow resistance increases. Since it increases, there is a hindrance to filling, and it is possible to eliminate the problem that the quality of the molded product is not stable because it is not possible to keep the total mold filling amount constant at the time of V-P switching. As described above, the final-stage injection time is almost constant by delaying the difference ΔS ₁ or advancing the difference ΔS ₂ even at a certain reference change switching position m ₄ .
Molded product is stable.

In the embodiment of the present invention shown in FIG. 2, V
The reference speed switching position m ₄ which is the −P switching point S _C is also the position switching in which the difference is corrected, but the VP switching point S _C
In can also be a pressure switch according to V-P switching pressure setpoint P _C as in the prior art (illustrated in FIG. 4) (where,
It is not desirable because the VP switching pressure P _C has to be set separately in addition to the judgment pressure P _J , and the control is complicated and cumbersome.

[0011]

As described above, according to the present invention,
Eliminates the difference in the length and time of the final stage injection speed region that varies from shot to shot, which is seen in conventional injection process control, in which all injection speed switching is preset position switching,
Even if the check valve closing characteristic varies, it is possible to prevent the variation in the weight of the molded product from shot to shot and the resulting variation in the quality of the molded product. Therefore, the quality of molded products is stable and reliable operation can be continued.
Productivity is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an injection control device of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram showing injection process control according to the embodiment of the present invention.

FIG. 3 is a graph showing an example of conventional injection control.

FIG. 4 is a characteristic curve diagram showing conventional injection process control.

FIG. 5 is an explanatory diagram showing data of final-stage injection time in conventional injection process control.

[Explanation of symbols]

1 Hopper 2 Heating Cylinder 3 Injection Screw (Screw) 4 Connecting Rod 5 Injection Cylinder 5a Piston 5b Piston Rod 6 Hydraulic Motor 7 Frame 8 Check Valve 8a Check Sheet 9 Mold 9a Cavity 10 Hydraulic Source 20 Hydraulic Unit 30 Screw Position Detector 40 Pressure detector 50 Injection controller 50a Speed calculator 50b Differentiator 50c Pressure calculator 100 Injection molding machine A Shot with a quick closing check valve B Shot with a slow closing check valve M Reference shot P Pressure P _C V-P Switching pressure setting value P _k Holding pressure setting value P _J Check valve closing judgment pressure V Injection speed V ₁ 1st stage speed setting value (1st injection speed) V ₂ 2nd stage speed setting value (2nd injection speed) V ₃ 3rd stage speed set value (3rd injection speed) V ₄ Final stage speed set value (4th injection speed) S Position S ₁ Filling process S ₂ Pressure-holding process S _A Final-stage injection area for shots with early closing of check valve S _B Final-stage injection area for shots with late closing of check valve S _M Final-stage injection area for reference shot m ₁ Reference change switching position m ₂ Reference change switching position m ₃ Reference change switching position m ₄ Reference change switching position (VP switching point) m _n Reference speed switching position after setting check valve closing judgment pressure t time tf final stage injection time N number of shots

Claims (1)

[Claims] 1. A position detector for detecting an injection screw position, a pressure detector, and a speed calculator for calculating a time differential value of an injection stroke detected through the position detector or an injection speed detector of the injection screw. In an injection molding machine that is equipped with and controls the injection speed of the injection screw at multiple injection speeds during the filling process, the check valve closing judgment pressure is set in advance at an arbitrary point in the filling process, and injection is performed after the start of filling. The difference between the injection screw position when the pressure reaches the judgment pressure and the injection screw position when the judgment pressure is reached in a preset reference shot is calculated and stored, and the change switching point of the injection speed of the plurality of stages is set. Among these, the switching before reaching the judgment pressure is performed by switching the speed at the preset change reference switching position of the injection screw, and when switching after reaching the judgment pressure. A speed control method for an injection molding machine, wherein speed switching is performed by position switching according to the injection screw position corrected by increasing / decreasing the difference to a preset reference switching position of the injection screw.