JPH04332621A - Injection molding machine possessing estimation function of temperature of resin eithin mold - Google Patents

Abstract

PURPOSE:To enable highly acculately calculation of a temperature of resin within a mold. CONSTITUTION:The title machine is provided with a resin temperature sensor (43) within a reservoir in a heating cylinder, a temperature sensor (42) of a mold, a timer (30) measuring a time from completion of injection of resin to the foregoing mold or starting of dwell, a parameter input device (33) for setting up of an estimation value of resin in a terminal condition as parameter and an estimation device estimating a resin temperature within the foregoing mold until the lapse of a fixed time from starting of timing of the foregoing timer by signals from the foregoing parts each. Then the estimation device performs estimation of the resin temperature within the foregoing mold based on a formula obtained by superposing the first index function having lowering time constant of the resin temperature within the mold for its index and the second index function having lowering time constant of a mold temperature for its index upon each other.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine, and more particularly to an injection molding machine having a function of estimating resin temperature within a mold.

0002

2. Description of the Related Art Generally, injection molding is carried out through the following steps: plasticization of resin, injection into a mold, holding pressure in the mold, and cooling. The quality of the molded product obtained through such a process is particularly influenced by the resin pressure and temperature control within the mold during the pressure holding process. Of these, the resin pressure can be detected and controlled with high precision by a pressure sensor installed in the mold. However, regarding the resin temperature, the temperature at the surface of the mold cavity is insufficient, and it is difficult to install a temperature sensor inside the cavity, making it impossible to control the temperature using actual measured values. Conventionally, resin temperature control in the mold has been performed by obtaining the resin temperature by estimation.
The following two methods have been proposed as methods for estimating resin temperature. The first method is to use the formula for heat conduction in a flat plate, and the estimated value of the resin temperature is calculated using the following formula 1.
It is determined by

0003

[Math 1]

[0004] However, Tm (t) is the mold temperature, θr is the resin temperature in the heating cylinder at the start of injection, a is the thermal diffusion coefficient, s is the typical thickness of the molded product, π is the circumference, and t is the injection This is the time since the start. The second method is a method that uses temperature measurements at two points: the surface of the mold cavity and the inside of the mold, and the estimated value Eθm is determined by the following formula. Eθm =x·Tf −y·Tw where Tf is the temperature of the cavity surface and Tw is the temperature inside the mold. Further, x and y are constants determined by the mold and resin, respectively, and are determined as follows. First, molding is performed, and a temperature sensor embedded near the cavity surface in the mold determines the cavity surface temperature Tf.
1, and the mold internal temperature Tw1 is measured by a temperature sensor embedded in the mold. Next, the mold temperature is changed and the cavity surface temperature Tf2 and mold internal temperature Tw2 are measured, respectively. As the estimated value Eθm, the temperature inside the heating cylinder (torpedo head temperature or flange part set temperature) is entered, and x and y are determined as solutions of simultaneous equations.

For example, when the resin temperature is 200°C (Eθm =
200℃) and molding with the mold temperature set to 40℃T
Assume that f1=60°C and Tw1=40°C were actually measured. 200=60x-40y

(1) Next, keep the resin temperature as it is and increase the mold temperature to 5.
When molded at 0℃, Tf2=70℃, Tw2=5
Assume that 0°C is actually measured. 200=70x-50y

(2) Solving equations (1) and (2) to find x and y, we get
x=10, y=10. In this way, x and y are determined, and the estimated value Eθm is calculated by measuring the cavity surface temperature Tf and the mold internal temperature Tw during molding.

[0006]

[Problems to be Solved by the Invention] In the first method described above, it is difficult to determine the parameters a and s, and because the approximation is based on a single exponential function, it is difficult to determine the parameters a and s with high accuracy over the entire time range of the injection process and pressure holding process. Estimates are difficult to obtain. On the other hand, in the second method as well, when temperature estimation is performed during continuous molding, resin temperature fluctuations within the heating cylinder are not reflected in the estimated value, which means that the accuracy of the estimated value is reduced. In view of the above-mentioned problems, an object of the present invention is to provide an injection molding machine having an in-mold resin temperature estimation function that can calculate an estimated value of the in-mold resin temperature with high accuracy.

[0007]

[Means for Solving the Problems] An injection molding machine according to the present invention includes a resin temperature sensor in a reservoir in a heating cylinder, a temperature sensor in a mold, and a temperature sensor that detects the temperature of the resin from the time of completion of injection of resin into the mold or the start of pressure retention. a timer for measuring time, a parameter input means for setting an estimated value of resin temperature under terminal conditions as a parameter; a first exponential function whose index is a time constant of decrease in resin temperature in the mold; and a second index whose index is a time constant of decrease in mold temperature. The method is characterized in that the temperature of the resin in the mold is estimated based on a formula superimposed with a function.

[0008]

[Operation] In the present invention, test molding is carried out after completion of determining the molding conditions. Then, the estimated value of the resin temperature under the final condition is set as a parameter, and actual continuous molding is started. During this continuous molding operation, the estimating means estimates the resin temperature within the mold during the time specified by the timer for each molding cycle as a time profile, and performs temperature control based on this profile.

[0009]

[Embodiment] First, an injection molding machine to which the present invention is applied will be explained with reference to FIG. This injection molding machine 100 includes an injection device 1 for injecting molten resin, a mold 2 for solidifying the molten resin to obtain a desired molded product, and a control system 3 for the injection device 1. In the injection device 1, the screw 11 is rotationally driven to send the molten resin to the reservoir 13 provided at the tip of the heating cylinder 12. This process is called the metering process. Thereafter, in the injection process, the control system 3 determines the amount of operation to be performed on the servo valve 4, and operates the servo valve 4. By this operation, the molten resin in the reservoir 13 is filled into the mold 2 through the gate.

Next, in the pressure holding process, the control system 3 controls the resin pressure sensor 41 in the mold, the mold temperature sensor 42, and the reservoir 13.
The holding pressure set value is calculated based on each detection signal from the nozzle resin temperature sensor 43 installed in the servo valve 4 to determine the operation amount to the servo valve 4, and the servo valve 4 is operated. By this operation, the molten resin filled in the mold 2 is pressed. The control system 3 also estimates the change pattern of the resin temperature in the cavity of the mold 2 based on the detection signals from the mold temperature sensor 42 and the nozzle resin temperature sensor 43 using a method described later, and uses this estimation result. Based on this, the resin temperature is controlled. The amount of movement of the screw 11 and the oil pressure for driving the screw 11 are converted into electric signals by a movement amount detector 44 and an oil pressure detector 45, respectively, and sent to the control system 3 through amplifiers 46 and 47.
will be given feedback.

The control system 3 includes a timer 30 for measuring time, a CPU 31 having functions of pressure holding control and resin temperature estimation and control;
In addition to the memory 32, there is an input console 33 for inputting the estimated value of the resin temperature in the mold as a parameter for the termination condition.
It has an input/output interface 34 for exchanging data with. The control system 3 further includes a first A for converting detection signals from a resin pressure sensor 41, a mold temperature sensor 42, and a nozzle resin temperature sensor 43 into digital signals.
A second A/D converter 36 for converting the detection signals from the /D converter 35, the movement amount detector 44, and the oil pressure detector 45 into digital signals, respectively, and a digital command value for driving the servo valve 4. D for converting to analog signal
It has a /A converter 37 and an amplifier 38.

Next, an algorithm for estimating the resin temperature in the mold will be explained. The present invention calculates the resin temperature in the mold using the following formula 2, which is expressed by the superposition of two exponential functions.
Estimate based on The first exponential function is a function whose index is the time constant α of the resin temperature drop in the mold, and the second exponential function is a function whose index is the time constant β of the mold temperature drop.

[0013]

[Math 2]

[0014] However, Eθr (t) is the start of holding pressure (t=0
), θN (t0) is the detected value of the resin temperature in the reservoir 13 at the start of injection, A,
Both B are time constants expressed by formulas described below. The falling time constants α and β are expressed by Equations 3 and 4 below.

[0015]

[Math 3]

[0016]

[Math 4]

However, θm (0) is the detected value of the mold temperature at the start of pressure holding, tH is the pressure holding time, and t1 is the intermediate time in the pressure holding process, for example, t1=tH /2, Δ
θm is the time average value of the difference in mold temperature between the current molding cycle and the previous molding cycle. This difference Δθm
is expressed by Equation 5 below.

[0018]

[Math 5]

However, θm, i(n·ΔT) is the detected value of the mold temperature at sample time n·ΔT of the i-th molding cycle. Next, constants A and B are calculated as follows. (1) Assume that the following equation holds true at time t=0, which is the initial condition at the start of pressure holding. θr (t)=θN (t0)(A+B)=θN (t
0) This means (A+B)=1. (2) As a terminal condition, the following equation 6 holds true at time t=tH.

[0020]

[Math 6]

Here, since θr (tH) is given as a parameter from the input console 33, the constant A is given by the following equation 7.

[0022]

[Math 7]

Further, the constant B is given by (1-A). FIG. 2 shows measurement data of the resin temperature inside the mold when polystyrene was actually used as the material, and the results estimated using the above algorithm.

Next, the actual work procedure will be explained. (A) Set the molding conditions. (B) Input the estimated value of the resin temperature in the mold under the terminal conditions as a parameter from the input console 33. (C) Check estimated values and adjust parameters. (D) Continuous molding is started, and the resin temperature in the mold is estimated in a predetermined time range for each molding cycle, and the resin temperature is controlled based on this estimated value.

[0025]

As described above, according to the present invention, the temperature of the resin in the mold can be estimated with high accuracy. In particular, according to the estimation of the present invention, the number of parameters to be input is small and does not depend on the mold or physical properties. Furthermore, it is possible to calculate an estimated value that reflects fluctuations in both the resin temperature in the heating cylinder and the mold temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of an injection molding machine according to the present invention.

FIG. 2 is a characteristic diagram of estimated resin temperature versus time for explaining estimation of resin temperature according to the present invention.

[Explanation of symbols]

1 Injection device 2 Mold 3 Control system 4 Servo valve 13 Reservoir 41 Resin pressure sensor inside the mold 42 Mold temperature sensor 43 Nozzle resin temperature sensor

Claims (1)

[Claims] 1. A resin temperature sensor in a reservoir in a heating cylinder, a mold temperature sensor, a timer for measuring the time from the completion of injection of resin into the mold or the start of pressure holding, and a temperature sensor for resin in a reservoir at a terminal condition. A parameter input means for setting an estimated temperature value as a parameter, and a means for estimating the resin temperature in the mold from the start of timing of the timer until a predetermined time elapses based on signals from each of the parts, The estimating means calculates the amount of the metal based on a formula obtained by superposing a first exponential function whose index is a time constant of decrease in resin temperature in the mold and a second exponential function whose index is a time constant of decrease in mold temperature. An injection molding machine having an in-mold resin temperature estimation function, characterized by estimating an in-mold resin temperature.