JPH0478090B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a metering control device for an injection molding machine, and in particular, to the metering of an injection molding machine, that is, after injection, raw resin is transferred from a hopper to the front of a heating cylinder by screw rotation, kneaded, and kept constant. The present invention relates to a control device in a metering process for measuring a quantity and preparing for the next cycle of injection. [Prior Art] Among the qualities of injection molded products, one of the most important is the stability of the weight of the injection molded product. To this end, it is required that the amount of raw material resin injected by the injection molding machine is always constant, and a prerequisite for this is accurate metering (charging). Conventionally, in an injection molding machine, as shown in FIGS. 2 and 5, raw resin in a hopper 9 is fed into a heating cylinder 1, where it is melted and charged to the tip of a screw 2. At this time, the front end surface of the annular check ring 7 is pushed by the resin flow and comes into contact with the screw tip 2a, but due to the flow groove 2b provided on the outer surface of the screw tip, The liquid is charged into the charge chamber 8 at the tip of the screw. In the injection process, when the screw tip 2a moves forward, the check ring 7 does not move forward, but instead comes into contact with a check sheet 8 forming the leading edge of the screw, thereby preventing backflow of molten resin. . [Problems to be Solved by the Invention] However, in conventional injection molding machines, there is a phenomenon in which the screw 2 gradually retreats by about 0.5 to 1.0 mm even after the metering process is completed and the rotation of the screw 2 is stopped. This phenomenon is caused by the screw 2 shown in Figure 5.
The plasticized and kneaded raw material resin is sent to the charge chamber 8 on the front side of the screw 2 by the rotation of the screw 2, but even if the rotation of the screw 2 is stopped, it remains in the valley of the screw 2 and near the check sheet 8. It is considered that the pressure P ₁ of the molten resin in the molten resin is somewhat higher than the pressure P ₂ of the resin fed into the charge chamber 8, and that there is a relationship of P ₁ >P ₂ . Therefore, even when the metering process is completed and the screw 2 stops rotating, the molten resin is sent into the charge chamber 8, and when the screw 2 moves back slightly and P ₁ = P ₂ , the screw 2 is completely retracted. Stop at. Moreover, in the hydraulic system diagram shown in FIG. 3, the above-mentioned screw retraction phenomenon can be solved by returning the four-way switching valve 34 to the neutral position at the time of completion of the metering process, and simultaneously stopping the rotation of the screw 2 and injecting the injection cylinder 3.
There is also a method of forcibly preventing the screw 2 from retreating by blocking the oil path that communicates with the tank from the head side of 5, but since P ₁ > P ₂ remains, the resin pressure in the charge chamber 8 will further rise. It is not possible to prevent the liquid from flowing out of the machine through the nozzle passage, causing drooling (a droopy nose phenomenon) and causing defective molded products. The purpose of the present invention is to solve the problems of the prior art described above, to prevent the screw from retreating after measurement is completed, and to manufacture molded products of excellent quality by avoiding phenomena such as drooling. The object of the present invention is to provide a metering control device for an injection molding machine that can perform the following steps. [Problems to be Solved by the Invention] The above objects are: a heating cylinder, a screw disposed in the heating cylinder so as to be rotatable and movable back and forth, and position detection for detecting the backward position of the screw as it is charged. and a charging chamber predetermined by at least the conditions of the nozzle part and the molding material when entering the metering control stroke section l immediately before the completion of charging during the metering stroke from the charging start point to the charging completion point. pattern selection means for selecting a back pressure reduction pattern; and a metering control stroke section l using the position detection means.
and means for lowering the back pressure in the charging chamber based on the signal from the pattern selection means when it is detected that the charging chamber has entered the charging chamber. [Function] Metering control stroke section l immediately before charge completion
If the screw rotation stops when metering is completed, if the back pressure in the charging chamber is lowered using a back pressure lowering pattern predetermined depending on at least the nozzle conditions and the type of molding material. , the resin pressure in the charge chamber (P ₂ ) is almost equal to the molten resin pressure at the rear of the check sheet (P ₁ ),
Outflow of resin into the nozzle passage is stopped. [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is an explanatory diagram showing an example of processing in the metering control device according to the present invention. In an injection molding machine, the total metering stroke S is usually divided into 3 to 4 stroke sections, and the screw rotation speed V and the proportional electromagnetic relief valve 39 shown in FIG. The back pressures BP generated by the operation are V ₁ , V ₂ , ...V ₄ , BP ₁ , BP ₂ , respectively, as shown in Figure 1.
...It is configured so that BP ₄ can be set. In the present invention, after entering the final stroke section of the metering stroke, which is the _S4 section in the embodiment shown in FIG. 1, the metering control stroke section 1 is entered. Then decide. l = α・S・BP ₄ ... (1) α: Coefficient S: Total metering stroke (mm) BP ₄ : Back pressure in the final stroke section (Kg/cm ² ) In other words, the metering control stroke section l is the charge This is considered to be a stroke that applies braking to the screw that is being weighed, but the larger the total metering stroke S, the larger the amount of resin that accumulates in the charge chamber 8, and the viscoelasticity of the resin causes the screw 2 to retreat after metering is completed. The effect is also considered to be large, and S is considered to be proportional to l. Also, if the set back pressure BP ₄ in the final stroke section increases,
The amount of back pressure reduction also increases, so it is proportional to BP ₄ .
is necessary. Therefore, from the above two points, the calculation formula for the stroke l is set as the above equation (1). Here, α is a constant with a dimension of [cm ² /Kg], and even if BP ₄ is set to about 20Kg/cm ² ,
It is set to a small value that does not satisfy ≧S ₄ . The present invention lowers at least the back pressure in the charging chamber in a fixed pattern when entering the metering control stroke immediately before the completion of charging among the above-mentioned total strokes S, and at the same time lowers the screw rotation speed. How the back pressure BP ₄ is lowered in the metering control stroke section 1 is determined by the cooling of the resin in the nozzle hole. In other words, the fluidity of the resin in the nozzle hole decreases depending on the type of resin, the nozzle temperature setting, and the size and shape of the nozzle hole (straight or reverse taper), and the effect of preventing the drooling phenomenon from occurring differs. Therefore, this allows the operator to select one pattern from, for example, the patterns shown in FIG. 1 and determine it manually. The rotational speed of the screw is determined by the amount of oil fed from the hydraulic source that rotates the hydraulic motor during metering, that is, the signal voltage to the proportional electromagnetic flow control valve 33 shown in FIG. Set it to a constant low rotation speed Vl at a certain point. FIG. 2 is a schematic configuration diagram of a metering control device for an injection molding machine according to the present invention. In this metering control device, a rack 4 and a pinion 5 are provided to an actuator of an injection molding machine via a connecting bar.
A position detector (potentiometer, encoder, etc.) 6 that rotates in synchronization with the pinion 5 is installed, and its output is input to a control device 10. These rack 4, pinion 5
In addition, the position detector 6 constitutes a position detecting means. The control device is a computer system that includes an arithmetic processing unit CPU, memory devices ROM, RAM, input/output interfaces IN and OUT, and a keyboard.
KB and analog-to-digital converter A/D are provided. In FIG. 2, a position detector 6 measures the current position S _x of the screw using a voltage analog value. This analog signal is converted to a digital signal by an A/D converter, and then sent to the arithmetic processing unit via the interface IN.
Input to CPU. General molding conditions are set on the keyboard KB, and the following digital values necessary for the present invention are input.

〔Effect of the invention〕

As described above, according to the present invention, precise injection molding can be performed by avoiding the stroke retraction phenomenon after the completion of the metering process and ensuring an accurate charge amount.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of processing in the metering control device of the injection molding machine of the present invention, FIG. 2 is a schematic configuration diagram of the metering control device of the injection molding machine of the present invention, and FIG. This hydraulic control system diagram, FIG. 4, is a flowchart showing an example of the processing of the present invention, and FIG.
The figure is a schematic sectional view of the screw part of the injection molding machine. 1... Heating cylinder, 2... Screw, 3...
...Injection cylinder, 4...Rack, 5...Pinion, 6...Position detector, 7...Check ring,
8...Charge room, 9...Check sheet, 31
... Hydraulic source, 32 ... Proportional electromagnetic relief valve, 33
...Proportional electromagnetic flow adjustment valve, 34...Direction switching valve,
35...Injection cylinder, 36...Hydraulic motor for screw drive, 37...Relief valve, 38...4
Directional switching valve, 39... Proportional electromagnetic relief valve (for back pressure setting).

Claims (1)

[Scope of Claims] 1. A heating cylinder, a screw disposed within the heating cylinder so as to be rotatable and movable back and forth, and a position detection means for detecting the backward position of the screw as it is being charged, from the time when charging starts. During the metering stroke up to the completion of charging, when entering the metering control stroke section l immediately before the completion of charging, a pattern of lowering the back pressure in the charging chamber predetermined by at least the conditions of the nozzle part and the molding material is set. A pattern selection means for selecting a pattern, and means for lowering back pressure in the charging chamber based on a signal from the pattern selection means when the position detection means detects that the metering control stroke section has entered. injection molding machine.