JPH0339814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a molding control method for an injection molding machine, and particularly to control of an injection process.

(Prior art) The injection process of an injection molding machine can be roughly divided into a filling process from the start of injection of molten resin until the resin reaches the end of the mold cavity, and then a filling process in which the molten resin inside the cavity is cooled and solidified. It consists of a pressure holding process that compensates for the shrinkage.

Conventionally, a so-called programmed injection method has been known in which this filling process is controlled by controlling the injection speed of an injection screw (or plunger) according to a predetermined program. Therefore, the filling speed of the molten resin is controlled by changing it.
Furthermore, in the pressure holding process, a method for controlling the holding pressure in which the holding pressure is controlled in multiple stages using a timer is also known. Furthermore, a method is adopted in which the switching from the filling process to the pressure holding process is performed by changing the position of the screw, that is, the set position of the screw in the filling process. Furthermore, a method is also known in which the switching of this process is controlled by the injection ram (hydraulic pressure) or the resin pressure in the mold cavity. Recently, a switching method that involves a reduction in the moving speed of the screw has also been used.

On the other hand, the screw setting position immediately before the injection process, which is the initial position of the screw, is determined by the setting value of the molten resin metering position and the screw withdrawal (hereinafter referred to as suction back) stroke to prevent the molten resin from drooling from the nozzle. It is determined. The set position of the screw immediately before the injection process is set by a screw most retracted position setting device.

(Problems to be Solved by the Invention) On the other hand, during actual injection molding, it is usually unavoidable that the position of the screw immediately before the injection process deviates from a preset value.

For example, as shown in FIG. 2, the molten resin pressure in the cylinder 1 at the measurement completion point or the suction completion point is higher on the screw flight 2-d side than on the screw tip 2-a side before and after the backflow prevention ring 2-b. (right side in Figure 2) is higher, so even if it is after the completion of measurement or the completion of back-up,
A small amount of the molten resin flows from the screw flight 2-d side to the screw tip 2-a side as shown by the arrow 2-c. At this time, the screw 2 is pushed toward the injection ram 3 by the reaction, and the position of the screw 2 changes.

That is, the value set in the screw most retracted position setter and the actual screw position immediately before the injection process are different. Furthermore, the actual screw position immediately before the injection process varies depending on various conditions such as the molding cycle, the screw rotation speed, its rotational inertia, and back pressure. On the other hand, the fact that this value fluctuates means that during the injection process, the position at which the injection speed is switched is determined by the absolute position of the screw with respect to the cylinder, which causes a fluctuation in the injection amount up to the position at which the speed is first switched. become. During this injection process, fluctuations in the injection amount up to the injection speed switching position are maintained until the end of the injection process, which eliminates the problem of causing fluctuations in the surface condition of the molded product, and fluctuations in the dimensions and weight of the molded product. have.

Furthermore, in the prior art in which the absolute position of the screw with respect to the cylinder is set in advance and switching control is performed by comparing the set value and the detected value of the screw position detector, depending on the screw position,
This means that it is difficult to detect when filling is actually completed. That is, the filling amount of molten resin is determined by the injection volume, and the volume is given by the following equation.

V=π/4・D ²・S V: Injection volume D: Screw diameter S: Stroke Therefore, the injection volume is magnified by the fluctuation of the injection stroke, so the actual filling amount is , even a slight change in the screw position will cause a large error. That is, in order to appropriately perform the above-mentioned switching control based on the screw position, extremely delicate settings are required, and furthermore, the injection molding machine itself is required to have repeatability based on this strict positional accuracy. If this delicate position setting deviates even slightly, the resin will reach the end of the cavity and filling will be completed at a point before switching to the pressure holding process, or conversely, the process will be switched to the pressure holding process before filling is completed. In the former case, the cavity peak pressure rises to the set pressure during injection speed control, causing molding defects such as burrs, and in the latter case, the filling speed decreases before the resin filling is completed. Defects such as flow marks occur, and in any case, repeatability of the molding operation is inhibited. Since this problem has been known for a long time, a method has been adopted, for example, of switching from the injection speed control area to the pressure control area before filling is completed. In this method, the filling speed of the molten resin into the cavity before the filling is completed is controlled by pressure, and is not directly controlled by the injection speed. On the other hand, the injection speed is an important factor in controlling the surface condition of the molded product, and therefore, in order to obtain a high-quality molded product, the above method has to become unstable immediately before filling is completed. I don't get it.

Next, in the conventional technology that switches from the filling process to the pressure holding process using the injection ram pressure mentioned above, as the mold is filled with molten resin, the load pressure increases, so this is detected and the filling completion point is reached. This is to find out and switch to the pressure holding process. However, when the injection speed pattern is controlled in multiple stages during the filling process, this method detects the injection ram pressure because the change in the injection ram pressure, that is, the load pressure increases and decreases with the change in the injection speed. In order to control the process by switching to the pressure holding process, it was necessary to provide a restricted area for detecting the injection ram pressure and switching to the pressure holding process.

That is, this restricted region is a region in which switching control to pressure holding is not performed before a certain predetermined point after the completion of filling, even if the injection ram pressure reaches the switching set value.

These problems occur not only when switching to holding pressure based on injection ram pressure, but also when switching to holding pressure by detecting resin pressure at the tip of the screw cylinder or resin pressure in the mold cavity, or detecting a drop in injection speed. It was hot.

(Means for Solving the Problems) In order to solve the problems of the conventional method, if the switching signal is generated by a value that monotonically increases with the time elapsed from the start of injection as a control factor, it is possible to solve the conventional problems. There is no need to provide limited ranges such as pressure detection or injection speed detection. Furthermore, since it is a monotonically increasing value, it can be used not only as a switching signal for pressure holding but also as a switching signal for injection speed (filling process).

In order to solve the above problems, the present invention detects the actual amount of molten resin injected into the mold after injection starts, and changes the injection speed or injection pressure depending on the amount (filling amount). Alternatively, switching to the pressure holding process is performed.

The present invention, as a first solution, detects the movement stroke (denoted as ΔS) of the screw during the injection process, and the moving speed of the screw (denoted as f(v)) that changes from time to time.f(v) is a function of time), and this f is detected along with the injection start signal.
It attempts to time-integrate the value of (v) (blocking ∫f(v)・dt), and when this time-integrated value matches a preset value, it emits a signal, and this signal The aim is to control the injection process. This means that if the movement stroke (△S) of the screw is detected during the injection process, the inner diameter of the cylinder is constant at the part where the screw moves during the injection process, and the cross-sectional area A of the inner cylindrical part of the cylinder is constant. Therefore, the injection volume of the molten resin is expressed by A·ΔS.

(Function) According to the configuration of the present invention, the actual injection speed, injection pressure, or switching to the pressure holding process is determined by the actual injection speed, injection pressure, or switching to the pressure holding process, regardless of how the position of the screw immediately before injection changes. This makes it possible to keep the amount of resin constant for each shot.

Example 1 A first embodiment of the invention is shown in FIG. 1a.

4 is a screw speed detector that detects the injection speed, that is, the moving speed of the screw 2 during injection.
The moving speed f(v) of the screw 2 is converted into voltage by a speed voltage converter 5. (The value after this conversion is defined as fe(v).) Next, the value of fe(v) is sent to the integrator 7 by a signal emitted by the integration start trigger transmitter 6 at the same time as the injection starts. Then, time integration starts (integral value is ∫fe(v)・dt). At the same time, the integral value (∫fe(v)・
dt) is constantly compared by a comparator 9 with a value previously set by a reference value setter 8, and when the two match, a signal 10 is generated.

This signal 10 allows switching to the injection speed, injection pressure, or pressure holding process, which is one of the injection process controls.

(Effects of the Invention) Normally, when an injection molding machine is operated, it is difficult to avoid a deviation between the screw position immediately before the injection process and the set value of the most retracted position, but according to the present invention,
Regardless of the deviation, not only the entire stroke of the injection process of the screw but also each stroke of each process in which the speed is changed corresponds to a predetermined value, and the injection amount becomes constant. Also, during injection molding, a cushion amount is usually left behind to maintain pressure in order to prevent sink marks on the molded product, but this cushion amount increases as the deviation of the screw position immediately before the injection process increases toward the ram side. As the size decreases, the volume and weight of the molten resin filled into the cavity as an actual molded product remain constant.

Furthermore, according to the present invention, if the molding conditions are such that a cushion amount remains, the injection conditions can be held constant no matter how the measured value is set, so it is necessary to pay close attention to the setting of the measured value as in the past. Nor.
(In other words, even if the measurement value is set incorrectly and set to a large value, overpacking will not occur as in the past.)
Therefore, it is also useful for preventing damage to the mold.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. Second
The figure is a diagram explaining the flow of molten resin in the screw when measurement is completed. DESCRIPTION OF SYMBOLS 1... Cylinder, 2... Screw, 3... Injection ram, 4... Screw speed detector, 5... Speed voltage converter, 6... Integration start trigger transmitter, 7... Integrator, 8... Reference value setter, 9... Comparator, 10...signal.

Claims (1)

[Claims] 1. In a method for controlling the injection process of an injection molding machine,
The moving speed of the injection screw is detected by a speed detector, the detected speed value is converted into an electrical signal, and the electrical signal is integrated over time at the start of injection, and when the integrated value matches a preset value. A molding control method for an injection molding machine, characterized in that a signal is emitted, and injection speed switching, injection pressure switching, or holding pressure switching is performed based on the signal.