JPS6260254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for observing molding process variables within a molding die and controlling an injection molding machine using the information.

In the injection molding process, various factors have a complicated relationship with each other. For this reason, a control method is needed to control unstable elements involved in the injection molding process and continuously mold stable molded products. Particularly in the injection filling process of molten resin, the timing of switching from the primary injection pressure to the holding pressure, the pressure inside the mold of the molten resin, etc. affect the final filling state of the molded product, and have a large impact on the quality of the molded product. For this reason, various control methods have been proposed to control these factors.

For example, conventionally, there is a control method described below.

(1) A method in which the resin pressure in the mold is detected by a pressure sensor via an extrusion pin, etc., and when the resin pressure reaches a set value, the control is switched to the pressure holding process at that point.

(2) A method of detecting the hydraulic oil pressure supplied to the injection cylinder and switching control to the pressure holding process when the hydraulic oil pressure reaches a set value.

(3) A method in which the amount of opening of the mold parting surface or the amount of displacement of the mold due to resin pressure during injection is detected, and when these measured values reach a set value, the control is switched to the pressure holding process at that point.

These methods are expected to yield relatively good results when the molding die consists of one cavity, or when it consists of multiple cavities that have approximately the same shape. can. However, in the conventional method described above, in the case of so-called simultaneous molding of different shapes, in which the molding die is composed of multiple cavities with greatly different shapes such as wall thickness and dimensions, individual control of each molded product is not necessary. It is possible. As a result, even though the molded products that are managed and controlled are of good quality, other molded products may have variations from shot to shot or molding defects such as burrs and shot shots. Particularly in the case of simultaneous molding of different shapes, since the filling conditions of individual cavities are different, the margin for variation in molding conditions is smaller than in single-cavity molding. Therefore, the risk of molding defects occurring due to slight variations in molding conditions increases.

The present invention was made in view of the above-mentioned drawbacks in the prior art, and its purpose is to stabilize the molding condition between each molded product cavity during the filling process and the pressure holding process, and It is an object of the present invention to provide a control method and apparatus for an injection molding machine that can eliminate molding defects and molding defects and continuously obtain proper molded products.

In order to achieve this objective, the control method of the present invention measures the internal pressure of each cavity in the molten resin filling process and pressure holding process, and also measures the filling pressure increase gradient in the filling process and the holding pressure drop gradient in the pressure holding process. Each target value is set in advance, and in the filling process, the gradient of increase in mold pressure in each cavity is compared with the target value of the gradient of filling pressure increase, and a cavity exhibiting intermediate behavior is selected. In order that the mold pressure behavior of the cavity traces the set target value, and in the pressure holding process, the drop gradient of the mold pressure of each cavity is compared with the target value of the holding pressure drop gradient.
The feature is that a cavity exhibiting intermediate behavior is selected, and the pressure and flow rate of hydraulic oil supplied to the injection cylinder are controlled so that the in-mold pressure behavior of that cavity traces a set target value.

The present inventors observed the fluctuating behavior of the molten resin in the mold by varying the molded product shape, molding material, and injection molding conditions, and examined in detail the correlation between molding conditions and molded product quality. . As a result, it was found that the filling pressure rising gradient and holding pressure falling gradient in the filling process have a large contribution rate to the quality of the molded product. That is, it was confirmed that by controlling the injection molding machine so that the filling pressure rising gradient and holding pressure falling gradient were always kept constant, the quality of the molded product was stabilized and good products could be continuously supplied. The present inventors have focused on this phenomenon and have invented a method and device that can control the pressure pattern inside the mold by adjusting the pressure and flow rate of hydraulic fluid supplied to the injection cylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and apparatus for controlling an injection molding machine according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an apparatus for carrying out the control method of the present invention. In this figure, 16 is a molding die, 1a to 1
c is a cavity constructed in this molding die 16. Reference numeral 13 denotes an injection molding machine, which is composed of an injection screw 14, an injection cylinder 15, and a hydraulic pressure source 12 that supplies hydraulic oil to these. The control device of the present invention can be divided into a detection section, a calculation section, and a control section according to their functions. The detection unit includes a plurality of mold pressure sensors 3a to 3c that detect molten resin pressure in the cavities 1a to 1c via mold pressure transmission pins 2a to 2c;
A plurality of mold pressure transducers 4a to 4 that amplify the signals detected by the mold pressure sensors 3a to 3c.
c, a displacement sensor 7 for detecting the displacement of the injection screw 14, a displacement transducer 8 for amplifying the signal detected by the displacement sensor 7, and a filling pressure gradient for defining the state of the pressure pattern in the mold. Setting devices 5a to 5c, holding pressure gradient setting devices 6a to 6
c. A speed pattern setting device 19 for defining an injection speed pattern. The calculation section also includes a controller 9 that issues control signals for the molding machine based on these input information, and the control section further includes a power amplifier 10 that amplifies these control signals and converts the control signals into state quantities of hydraulic fluid. It is composed of an electro-hydraulic control valve 11.

The operation of the control device configured as described above is as follows. That is, in response to the injection start signal, the controller 9 adjusts the flow rate of hydraulic oil supplied to the injection cylinder 15 based on the information from the speed pattern setting device 19, and controls the pattern of the forward speed of the injection screw 14. Along with this, the molten resin is filled into the individual cavities 1a to 1c via the sprue 17 and the runner 18. The controller 9 constantly monitors these filling conditions via the mold pressure transducers 4a to 4c. Filling pressure control is then carried out from the time when the molding state satisfies the conditions for completion of speed control. In other words, so that the fluctuation behavior of the mold pressure traces the set filling pressure increase gradient,
Adjusts and controls the pressure and flow rate of hydraulic oil supplied to the injection cylinder 15. Further, pressure holding process control is carried out from the time when the mold internal pressure satisfies the conditions for completing the filling process. That is, the pressure and flow rate of the hydraulic oil supplied to the injection cylinder 15 are adjusted and controlled so that the variation behavior of the mold pressure traces the set holding pressure drop gradient. In these control processes, the method of determining control targets from multiple cavities is to measure the rising and descending gradients of all the cavities, and then select a cavity whose deviation between the measured value and the target value is in an intermediate state. This is done by automatic selection. These control steps will be explained in more detail with reference to the fluctuation behavior of the forming state shown in FIG.

FIG. 2 shows temporal changes in the molten resin pressure and screw displacement in the individual cavities 1a to 1c in the apparatus shown in FIG. 1. In FIG. 2, 50 is an injection process, 51 is a filling process, 52 is a pressure holding process, and 53 is a cooling process. In addition, 21 is a screw displacement curve, 22a-2
2c is the pressure curve inside the mold, and each cavity 1a to 1c
The fluctuation behavior of the pressure inside the mold is shown. 26a to 26c are filling pressure gradient target values for the molten resin in the cavities 1a to 1c, respectively, and these target values are the filling process start pressures 23a to 23c and the pressure holding process start pressure 24a.
~24c, and filling time 33.
Similarly, 27a to 27c are the holding pressure gradient target values of the molten resin in the cavities 1a to 1c, respectively, and these target values are the pressure holding process start pressure 24a to 24c, the pressure holding process completion pressure 25a to 25c, and the holding pressure time 34. Determined from

Based on the injection start point 28, the controller 9 controls the speed pattern of the injection screw 14 in the section from the plasticization completion position 32 to the filling process start position 35. Thereafter, control of the filling process starts from the filling process starting point 29, and the filling state of the molten resin is controlled. The controller 9 stores the filling pressure gradients set for the individual cavities 1a to 1c, and based on this information, compares the actual pressure behavior of the individual cavities 1a to 1c and displays an intermediate behavior between them. The filling process is managed using the cavity as the control target. That is, the controller 9 measures the in-mold pressure conditions of the individual cavities 1a to 1c, and calculates the deviation from the filling pressure gradient target values 26a to 26c. And the cavity 1a~ where these deviations are configured
A cavity having an intermediate value among 1c, for example, cavity 1b, is selected as a control target and controlled. The controller 9 sets the filling pressure gradient target value 26b whose target value is the control target in-mold pressure curve 22b.
If a deviation occurs, a corresponding correction signal is output, and the injection molding machine is controlled via the power amplifier 10 and the electro-hydraulic control valve 11. Next, the controller 9 determines the interval from the pressure holding process start point 30 to the pressure holding process completion point 31, which is the middle of the cavities 1a to 1c, where the deviation between the in-mold pressure behavior and the holding pressure gradient target values 27a to 27c is configured. Control similar to the filling pressure process is performed targeting a cavity having a certain value, for example, cavity 1c. Thereby, the molten resin in each of the cavities 1a to 1c is monitored throughout the filling and pressure holding process, and controlled so as to maintain the set target state at all times.

As described above, according to the present invention, the pressure and flow rate of the hydraulic oil supplied to the injection cylinder are appropriately controlled, and the filling pressure rising gradient and holding pressure falling gradient, which have an important influence on molded product quality, are maintained at appropriate levels. This allows us to continuously supply good products, and since we are able to track and control the molding condition, we are able to minimize variations in the molding condition from one molding shot to another. This has the effect of reducing the molding defect rate to less than 1/5 of the conventional rate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a device for implementing the injection molding machine control method of the present invention, and FIG.
It is a graph showing the in-mold pressure and screw displacement behavior of each cavity in the device shown in the figure. 1a-1c...Cavity, 2a-2c...In-mold pressure transmission pin, 3a-3c...In-mold pressure sensor, 4a-4c...In-mold pressure transducer, 5a-5c
...Filling pressure gradient setter, 6a to 6c...Holding pressure gradient setter, 7...Displacement sensor, 8...Displacement converter, 9...Controller, 10...Power amplifier, 11...Electro-hydraulic control valve , 12... Working oil pressure source, 13... Injection molding machine, 15... Injection cylinder, 16... Molding mold, 19... Speed pattern setter, 22a to 22c... In-mold pressure curve, 23a
~23c...Filling process start pressure, 24a~24c
... Holding process start pressure, 25a to 25c... Holding process completion pressure, 26a to 26c... Filling pressure gradient target value, 27a to 27c... Holding pressure gradient target value, 33... Filling time, 34... Holding pressure time, 51
... Filling process, 52... Pressure holding process.

Claims (1)

[Scope of Claims] 1. In a method for controlling an injection molding machine that simultaneously molds a plurality of molded products using a mold having a plurality of cavities, the molds of each cavity in a molten resin filling process and a pressure holding process are controlled. The internal pressure is measured, and a target value for the rising gradient of the filling pressure of the molten resin determined from the filling time and the maximum mold internal pressure is set for each cavity. Compare the rising gradient of the filling pressure with the target value of the filling pressure rising gradient set above to find the respective deviations, select the cavity exhibiting an intermediate behavior among the cavities that are composed of these deviations, and calculate the internal pressure of the cavity. The pressure and flow rate of the hydraulic oil supplied to the injection cylinder are controlled so that the behavior traces the target value set above, and the pressure and flow rate of the hydraulic oil supplied to the injection cylinder are also controlled for the pressure holding time, molten resin pressure at the start of pressure holding, and A target value of the holding pressure drop gradient determined from the pressure inside the mold at the time of completion of holding pressure is set, and in the pressure holding process, the drop gradient of the pressure inside the mold of the cavity and the target value of the holding pressure drop gradient set above are set. Compare and find the respective deviations, select a cavity exhibiting an intermediate behavior among the cavities that are composed of these deviations, and supply it to the injection cylinder so that its in-mold pressure behavior traces the target value set above. A method for controlling an injection molding machine, characterized in that the pressure and flow rate of hydraulic oil are controlled. 2. In a control device for an injection molding machine that simultaneously molds a plurality of molded products using a mold having a plurality of cavities, an in-mold pressure sensor that detects the pressure of each molten resin in the cavity, and An in-mold pressure transducer that amplifies the signal detected by the pressure sensor, and a filling pressure that sets the target value of the filling pressure increase gradient of the molten resin determined from the filling time and the maximum in-mold pressure during resin filling. a holding pressure gradient setting device that sets a target value for a holding pressure drop gradient determined from the holding pressure time during holding pressure, the molten resin pressure at the start of holding pressure, and the pressure in the mold at the completion of holding pressure; In the filling process, the gradient of increase in pressure inside the mold of each cavity is compared with the target value of the gradient of increase in filling pressure set above to find the respective deviations, and the intermediate behavior of the cavity constituted by these deviations is determined. means for selecting a cavity with a pressure drop in the mold, and in the pressure holding process, comparing the drop gradient of the mold pressure in each cavity with the target value of the hold pressure drop gradient set above, and determining the respective deviations;
A means for selecting a cavity exhibiting an intermediate behavior among cavities constituted by these deviations, and a means for selecting a cavity exhibiting an intermediate behavior among the cavities configured with these deviations, and a method for determining the in-mold pressure behavior of the cavity exhibiting the selected intermediate behavior during the filling process and the pressure holding process. and a controller that issues a control signal to a control unit that controls the pressure and flow rate of hydraulic fluid supplied to the injection cylinder so as to trace the target values of the filling pressure increase gradient and holding pressure decrease gradient set above. Characteristic injection molding machine control device.