JPS637129B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides control when starting automatic or semi-automatic operation of an injection molding machine when the mold and resin temperatures have not yet reached a steady state where good products can be continuously obtained. Regarding the method.

The above-mentioned steady state in which good products are continuously obtained is achieved when the injection molding machine is operated automatically or semi-automatically and high temperature molten resin is injected into the mold at regular intervals during molding, resulting in the mold being heated and reaching a predetermined level. Generally speaking, when the molding operation starts, the mold has not yet reached the predetermined temperature, and the steady state is not reached until molding continues for several shots.

At the start of molding, the mold temperature is low and the resin does not flow easily, resulting in a so-called short shot in which the resin does not flow sufficiently into the mold.

Regarding the resin being molded, during continuous molding, a certain amount of raw resin is fed into the barrel from the hopper during each plasticizing process, and after a certain period of time, it is injected into the mold. If there is any resin remaining in the barrel during the temperature rise in preparation for starting, this remaining resin will be heated for a longer time than the resin in a steady state, so its viscosity will drop and it will flow more easily. ing. In such a case, molding results in so-called overpacking in which too much resin is forced into the mold, resulting in burrs or excessive weight of the molded product.

Here, the relationship between time from the start of operation, mold temperature, and resin viscosity is shown in the graphs in Figure 1 A and B, respectively, and the mold approaches a predetermined temperature in a quadratic manner. , the resin viscosity linearly reaches a predetermined viscosity.

As explained above, there are various problems before the mold temperature and resin temperature reach a steady state at the start of molding operation, and until a steady state molded product is produced, the weight will be about 20 to 30 shots heavier than a good product. It is common practice to mold defective products with different dimensions, etc., and in some cases these are discarded as defective products.

The present invention has been developed in view of the above-mentioned circumstances, and eliminates the disadvantage of producing many defective products when automatic or semi-automatic operation is started before reaching a steady state. It is an object of the present invention to provide a control method for an injection molding machine that operates under conditions different from the molding conditions and gradually approaches the steady-state molding conditions to prevent molding defects or to reduce molding defects as much as possible.

Next, one embodiment of the present invention will be described using FIG. 2 as an example of a method of switching from the filling process, which is one of the molding conditions, to the holding process by changing the plunger position in the barrel. An injection plunger 2 is inserted into the injection cylinder 3 so as to be movable forward and backward by pressure oil acting on an injection cylinder 3. Reference numeral 4 is an electromagnetic proportional flow control valve which adjusts the flow rate by varying the magnitude of the voltage acting thereon, controls the amount of pressure oil flowing into the injection cylinder 3, and determines the moving speed of the injection plunger 2. Reference numeral 5 denotes a potentiometer that electrically detects the position of the injection plunger 2 as the injection plunger 2 moves back and forth. Reference numerals 6 to 9 indicate speed switching position setters, and the speed switching setting positions 6 to 9 are set when the injection plunger 2 is in the injection stroke.
When passing through, change the speed and set the respective speed setter 1
It is configured to move at speeds set between 0 and 14, and the signals set in the speed setters 10 through 14 act on the electromagnetic proportional flow control valve 4 via the speed signal switch 15. There is.
16 is a speed switching signal comparator that compares the position of the injection plunger 2 detected by the potentiometer 5 with the value set in the speed switching position setter 6 to 9, and outputs a signal when the two values match. Emits,
It acts on the speed signal switch 15. Each time the speed signal switching device 15 receives the coincidence signal, it sequentially switches the set values set in the speed setters 10 to 14, so that the electromagnetic proportional flow control valve 4 is controlled by the set values. ing. Reference numeral 17 is for adjusting the hydraulic pressure of the injection plunger 3 by adjusting the strength of the voltage applied by an electromagnetic proportional pressure control valve. Reference numeral 18 is a comparator for controlling the switching from the filling process to the pressure holding process, which indicates the position of the injection plunger 2 detected by the potentiometer 5 and the switching position of the injection plunger 2 to the pressure holding process, which is one of the molding conditions. is compared with the setting value set in the switching condition setting device 19, and when the two values match, it acts on the speed signal switching device 15 and the pressure signal switching device 20, which will be described later, to switch from the filling process to the pressure holding process. The switch is about to take place.

The switching condition setter 19 is controlled by a counter 21. The counter 21 compares the molding conditions in a steady state with the molding conditions at the start of operation, and calculates the difference in a linear or quadratic manner so that the molding conditions at the start of operation gradually approach those at the steady state. , set in advance how many shots it takes to eliminate the difference, count the number of shots from the start of the molding operation, and each time correct the setting value of the switching condition setting device 19 to reach the preset count number. When the switching condition setter 1
The injection plunger position set at 9 is made to match the steady state molding conditions. Reference numeral 22 denotes a pressure setting device for the filling process, which controls the electromagnetic proportional pressure control valve 17 until a switching signal to the pressure holding process from the comparator 18 is applied to the pressure signal switch 20. Reference numeral 23 denotes a pressure setting device for the holding pressure process, which is controlled by the counter 21 like the switching condition setting device 19 described above, and when the count number set in the counter 21 is counted out, the holding pressure setting device 23 is set. The holding pressure that has been maintained becomes the steady state holding pressure.

The switching from the filling process to the pressure holding process can be performed not only by the position of the injection plunger as in the above embodiment, but also by detecting the hydraulic pressure of the injection plunger as shown in FIG.

Regarding the method shown in FIG. 3, only the differences from the previous embodiment will be described.
A counter 27 having the same function as in the previous embodiment corrects the set value of the signal transmitter 26 for each shot so that it is in a steady state within a predetermined number of shots, and a predetermined number of shots is counted. When it is turned off, that is, when steady state hydraulic pressure is achieved, a switching signal is generated from the comparator 18 and acts on the signal switching device 20.

As explained above, although the molding conditions are explained using switching control from the filling process to the pressure holding process as an example, there are various molding conditions, and the present invention can be applied to any of the molding conditions.

In addition, even if automatic or semi-automatic operation is interrupted for some reason and restarts, a timer is provided that starts the timing when operation is interrupted and completes the timing when operation is resumed, and the timer The molding conditions can be set as the relationship between the length of time counted, and the number of shots corresponding to the interruption time can be determined by setting, for example, how many shots it takes to return to a steady state after an interruption of one hour.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between time from the start of operation, mold temperature, and resin viscosity. Figures 2 and 3 show an example in which the molding conditions according to the present invention are controlled to be switched from the filling process to the pressure holding process, and Figure 2 is an example diagram in which the switching is performed by controlling the position of the injection plunger. . FIG. 3 is a diagram of an embodiment in which switching control is performed by hydraulic pressure of an injection plunger. 2...Injection plunger, 4...Solenoid proportional flow control valve, 5...Potentiometer, 6-9...Speed switching position setter, 10-14...Speed setter,
15... Speed signal switch, 17... Electromagnetic proportional pressure control valve, 19, 26... Switching condition setter, 20...
...Pressure signal switch, 21, 27...Counter, 2
2... Filling pressure setting device, 23... Holding pressure setting device.

Claims (1)

[Claims] 1. When starting automatic or semi-automatic molding operation in an injection molding machine, the molding conditions are different from the steady state molding conditions in which automatic or semi-automatic operation is continued for a certain period of time and good products are continuously obtained. A method for controlling an injection molding machine, comprising setting molding conditions, starting a molding operation, and gradually bringing the set molding conditions closer to steady-state molding conditions. 2. The method according to claim 1, wherein the molding conditions set at the start of the operation are linearly approximated to the steady state molding conditions. 3. The method according to claim 1, wherein the molding conditions set at the start of the operation are brought quadratically close to the steady state molding conditions. 4 The molding conditions set at the start of the operation are set values for the switching control from the filling process to the pressure holding process and the set values for the hydraulic pressure of the injection plunger immediately after the process switching, and both the above set values are set individually or both at the same time. 4. A method according to any one of claims 1 to 3, wherein the method comprises: 5 A timer is provided in the control circuit that starts timing when the automatic or semi-automatic operation of the injection molding machine is interrupted, and completes the timing when the operation is restarted, and the set value of the molding condition set at the start of the operation. 5. The method according to claim 1, wherein: is expressed as a function of the length of time counted by the timer.