JPS634925A - Quality discrimination monitoring of injection molded form - Google Patents

Abstract

PURPOSE:To permit an easy and correct detection of the quality of an injection molded form, by a method wherein at least two physical data among the physical data of a molder and the physical data of molten resin in a mold are detected to operate a relation with the molded condition of a product. CONSTITUTION:When molten resin, which is reserved at the tip end of an injection screw for an injection molder under a condition shown by a point F in a diagram, is filled into the cavity of a mold at a temperature as it is and a pressure in the mold is 600 kg/cm<2>, then the condition of the resin is changed to the point G in the diagram. In this case, the specific volume of the resin becomes 1.15 cm<3>/g. The resin in the mold is cooled and the condition thereof is shown by the point H in the diagram, thercafter, the specific volume is changed as the temperature thereof is reduced under a condition that the pressure is 1 kg/cm<2>, a molded form is unloaded from the mold at a temperature lower than a glass transition point I, then the resin takes the condition J of a normal temperature finally and the specific volume thereof becomes 1.095S cm<3>/g. In this case, a difference between the specific volumes at the point G and the point J is developed as the volumetric shrinkage of the molded form, therefore, the molded form smaller than the size of the cavity may be obtained.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for detecting the quality of injection molded products, particularly a monitoring method for determining quality of injection molded products that can easily and accurately distinguish between non-defective products and defective products. It is related to.

Conventional technology In recent years, the dimensional accuracy required for molded products has become stricter, and on the other hand, automation and unmanned molding processes are also desired. It tends to be in demand.

An example of the conventional pass/fail determination method described above will be described below with reference to the drawings. Figure 12 is JP-A-69-7
This figure shows the injection pressure with respect to the screw position according to the pass/fail determination method proposed in No. 1836, in which curve 1 shows the normal one, and curves 2, 3''-' and 3 show the abnormal ones. Here, the comparison start position and comparison end position are determined during the stroke of the screw, and the pressure is monitored only when it is within this interval. By setting the upper pressure limit to Hl, the molded products of curves 2 and 3 are treated as defective. It is possible to determine.

In addition, as shown in Japanese Patent Application Laid-Open No. 59-194822,
The change curve of mold internal pressure during the filling process during injection molding is temporarily stored in a storage device, and the shot data when a good product is obtained is used as a reference value, and the detected value after setting the reference value and the reference value are A method has also been proposed in which the deviation or its absolute value is accumulated in multiple arbitrarily determined areas during the injection process, and an alarm is issued when the accumulated data exceeds the allowable value in the multiple areas. There is.

Problems to be Solved by the Invention However, with the above configuration, when determining the range of critical conditions for determining a molded product as a non-defective product, product characteristics (for example, dimensions) are only viewed in relation to one molding condition. Part 1
It is difficult to find appropriate conditions because the two conditions are not fully expressed as product characteristics and the correlation between them is not clear.

In addition, if an appropriate limit condition width is not set, for example, if the limit condition width is too small, even a good product may be determined to be defective, and if the limit condition width is too wide, some good products may be defective. You will end up getting mixed up.

Means for Solving the Problems In order to solve the above-mentioned problems, the quality determination monitoring method of the present invention is applied to a molding method in which resin is injected and filled from the outside into a mold. By detecting at least two physical quantities from among the physical quantities of pressure, velocity, and temperature of This method is characterized by ranking and monitoring the degree of occurrence of phenomena that greatly affect quality.

A second aspect of the invention is further characterized in that in the monitoring, a quality determination is made based on 5'-ji by comparing it with a set value of a rank of non-defective products.

Effect The present invention has the above-described configuration, so that the degree of occurrence of the current situation (especially dimensions), which greatly affects the quality of each shot of molding, is controlled by the pressure, speed, and
Physical quantities of temperature for 1 hour, pressure and speed of molten resin in the mold,
Based on the results of detecting at least two of the physical quantities of temperature and calculating the relationship between them and the molding state of the product, the dimensional tolerance of the molded product can be monitored based on rankings that more closely match the actual situation. Based on this, it is possible to easily and reliably set the limit condition range for determining a molded product as being non-defective.

In addition, by ranking the products in this way and comparing them with the set value of the rank of non-defective products, it is possible to accurately determine non-defective products based on an appropriate limit condition width that is neither too much nor too little.

Example Examples of the present invention will be described below.

6''-FIG. 1 is a system configuration diagram showing an injection unit, a mold, and a control system of an embodiment of an apparatus for determining pass/fail by the pass/fail determination method of the present invention. Injection screw 1 like a general injection molding machine
A resin material is supplied from a pumper 3 between the pump and the heating cylinder 2, and the rotation of the motor 4 is transmitted to the injection screw 1 by gears 5 and 6, and the resin material is mixed and melted while being fed forward along the screw groove. Molten resin is stored in front of the injection screw 1. At this time, the directional control valve 7 is operated by the solenoid 7a.
is excited, and the space inside the injection cylinder e is filled with pressure oil at the pressure set by the control valve 8, and the force that pushes the injection screw 1 due to the pressure generated in the resin stored in front of the injection screw 1 is applied to the injection ram 11. When the pushing force of the pressure oil increases, the injection screw 1 moves backward while rotating, and the molten resin is stored. Note that 12 is a pump.

After that, the fixed mold 14 and movable mold 16 of the mold 13 are closed by a mold clamping mechanism (not shown), and a large pressure is set with the control valve 8 to open the valve 7'' to allow a suitable flow rate. If so, the space 1o is filled with high-pressure oil, a large force acts on the injection ram 11, the injection screw 1 moves forward, and the molten resin fills the sprue 16° cavity 17 in the mold. In the present invention, the above injection ram 11 and injection screw 1 together represent an injection drive body. The above configuration and operation are common to general injection molding machines, but in this embodiment of the present invention, the movable mold 16 is equipped with a pressure detection bottle 18 having a tip extending into the cavity 17, and a pressure detection bottle 18 that comes into contact with the end of the pressure detection bottle 18. A pressure detection bottle 2o having a tip extending into the cavity 17 is provided in the same cavity 17 at a position farther from the gate as well as a pressure detection bottle 2o and a pressure detection bottle 2o that comes into contact with the pressure detection bottle 2o. In the present invention, a combination of the pressure detection bottle 18, 20 and the pressure quadrature transducer 19, 21, or a piezo type pressure transducer that is directly attached to the mold, is referred to as a pressure signal conversion means. The pressure detector 22 converts the electrical signals obtained from the pressure transducers 19 and 21 into meaningful electrical signals as pressure values, and the two pressure signals sent from the pressure detector 22 are A pressure comparator 23 compares the pressure values, and a timer 24 measures the time until both reach the same pressure value, and a one-hour difference between the pressures is sent to a calculator 26.

The computing unit 26 stores the 1 hour difference in pressure and the storage device 26.
Based on the molding conditions, resin material physical property data, molded product shape data, etc. stored in give.

The command unit 27 converts the received signal into a current for controlling the reversing shooter 28 and sends it to the reversing shooter 28.

At the same time, the display device displays the calculation result of the dimensions of each shot and the number of the section in which the ranking has been performed.

The following describes how it operates in relation to the above configuration, the position of the pressure signal transducer in the mold, and material property data.

FIG. 2 is a sectional view of an example of a mold to which the quality determination method of the present invention can be applied, in which 29 is a fixed side mounting plate, 9 pages 3o are sprue bushes, and 31 is a sprue bush 30.
32 is a runner stripper plate, 33 is a fixed side mold plate, 34 is a runner connected to the sprue hole 31, 35 is a pressure detection bottle seen in the runner 34, 36 is a pressure-quadrant juicer, 37 is a A pressure detection bottle is provided at a position where the resin flows after the pressure detection bottle 36, 38 is a pressure fluid transducer, 39 is a gate connected to the runner 34, 40 is a cavity connected to the gate, 41 is a movable side template, and 42 is a 43 is a spacer, 44 and 45 are ejector plates, and 46 is a movable side mounting plate.

The pressure signal when molded with this mold is as shown in Figure 3. When time t is plotted on the horizontal axis and pressure P is plotted on the vertical axis, the value obtained by amplifying the signal from the pressure-quadrant juicer 36 by the pressure detector 22 is curve A, and the value obtained by amplifying the signal from the pressure-quadrant juicer 38 is shown by curve A. Depicted by B. t is the time point when the resin is filled up to the gate, and the pressure increases rapidly as the resin passes through the narrow gate. After that, the pressure value continues to rise, and even at time t2, when filling of the resin into the cavity 10'' is completed, the pressure suddenly rises.The period up to t2 is called the filling process, and the period after t2 is called the pressure holding process, and both are included in the injection process. The pressure comparator 23 receives the signals of curve A and curve B, reads the pressure value of curve A at the moment when a slight pressure increase is felt on curve B, converts the pressure difference ΔP into a signal, and sends it to the calculator.Timer 24 is the time from the point at which curve A slightly rises (that is, the point at which the resin touches the pressure detection bottle 36) to the point at which the curve B slightly rises (the point at which the resin touches the pressure detection bottle 37) Δt
is measured and sent to the computing unit 25. The radius r of the cross section of the length 11 of the runner from the pressure detection bin 36 to the pressure detection bin 37 is input into the storage device 26, and this pressure difference 422 hours Δt.

Based on the runner length l and the runner cross-sectional radius r, the calculator 2
6 calculates the viscosity of the resin that has passed through this runner section and the shear rate at that time. That is, the viscosity is according to formula (1),
The shear rate follows equation (2).

11 "' 47? On the other hand, if the relationship between the viscosity, temperature, and shear rate of the material to be molded as shown in FIG. 4 is stored in the storage device 26, for example, the viscosity is η1, and the shear rate at that time is j
, the resin temperature is 20 as shown in Figure 4.
It can be seen that the temperature is 0°C. Pressure difference ΔP for each shot
and the time Δt, and as a result, the temperature passing through the runner portion of each shot can be detected. Here, Pmax indicates the maximum pressure value in the pressure holding process.

Furthermore, if the PVT characteristics of the resin material to be molded are stored in the storage device 26 as shown in FIG. 4, it becomes possible to estimate the weight of the molded product and, by extension, the dimensions of the molded product.

Diagram M6 is a graph showing the relationship between the specific volume of the amorphous resin and the pressure and temperature, and shows the relationship between the temperature and the specific volume using pressure as a parameter.

The state of the molten resin stored at the tip of the injection screw of an injection molding machine is, for example, point F (resin temperature 200°C).

Specific volume 1, 3cr/Vfl, pressure IH/cat)
Suppose that it is shown as

If the mold cavity is filled at the same temperature and the pressure inside the mold is 600 #/crA, the state at point G will be taken. At this time, the specific volume is 1.15cIVg. The weight of the molded product is obtained by multiplying the reciprocal of this specific volume (ie, density) by the volume of the cavity. The resin in the mold is cooled to a state at point H (i.e. resin temperature 126°C, pressure 1
ky/cril, specific volume 1.16), and after this, the specific volume changes as the temperature decreases at a pressure of 1 #/crl, and the molded product is removed from the mold at a temperature lower than the glass transition point. and finally at room temperature (pressure 1
#/cr;f, temperature 26℃, specific volume 1.09esc
rtfyy>. At this time, the difference in specific volume between points G and I appears as volumetric shrinkage of the molded product, resulting in a molded product smaller than the cavity dimension.

When actually determining the dimensions, the specific volume V of the molten resin is determined by the following PVT relational expression in the molten state using the already obtained molten resin temperature Tm and 5P-Pmax detected as the peak pressure.

13''-' 1. to 2. to V-, 6.-P to T+, T2 where V
- Specific volume CcrV9) T - Melt resin temperature (°C) P - Peak pressure after completion of filling (bar) Kls - 8s - Material constant This specific volume V (7/g) and cavity volume v
The weight W of the molded article can be obtained from (d).

W=v・1/′v・・・・・・・・・・・・・・・
・・・・・・・・・(2) Next, the room temperature TG and the atmospheric pressure P
Using G, from the following PVT relational expression in the glass state,
Glass condition・・・・・・・・・・・・・・・・・・
...(3) Here, vG - specific volume in glass state (
d/g) TG - Normal temperature (°C) PG - Atmospheric pressure (bar) The difference between the specific volume vG obtained here and the specific volume (■) at the time of melting appears as volumetric shrinkage of the molded article. 14" In other words, the volume after contraction VG is the specific volume in the glass state ■G
From the already calculated weight W, vG: W@VG ......middle...
(4). If the volumetric shrinkage rate in this case is α, then a = V G/V ・・・・・・・・・
・・・・・・・・・It can be expressed as (6). Assuming that the rectangular parallelepiped molded body contracts uniformly in three-dimensional directions, there is a -
The side dimension l' is 4, where the cavity dimension is l.
'-3f''□1(6) However, in the above, 1s- is 88.v, l
and equations (1) to (6) are stored in the storage device.

When making a quality judgment, the average dimension l' of several shots molded using the above method is determined, the data is taken as basic data 4°, and lo is divided into an appropriate number of sections m. loO
With the value as the center, sections larger by 487m in the child direction are +1.487m, sections larger than 2・lO//m are +2, and sections are numbered sequentially by 1 around +20, and the same goes for the minus direction. After setting the nanno (ring) to about 120 and setting the classification section, it outputs the dimensions of each shot and also outputs which part of the numbered section it belongs to. do.

Then, it is compared with the dimensional standards input into the storage device to determine whether it is good or bad. This corresponds to the molding cycle time when performing this quality determination. The flow chart of FIG. 6 shows the flow of detection and calculation of each physical quantity.

A specific example of quality determination will be described below. In Figure 7,
It shows the shape of the molded product. 47 is a gate, and a is the size to be detected.

At this time, the average size of about 10 shots was 9.89, so 1. = 9, 89 wL, the number of section divisions is m = 10, OOQ, and 20 sections are set for each of the plus method and the minus method.Table 1 shows the section ranges and section numbers.

Table 1 Number of section divisions m = 10,000 section width t. /m=0.0
0098917'' Molding was performed for 1000 shots, and the results of which sections were determined at that time are shown in Figure 8.The variations are in the positive direction and negative direction, respectively, in 11 of the set sections.
I'm up to number one. The number m of sections to be divided must be determined to be an appropriate number depending on the shape of the molded product, etc., but if the distribution of dimensional variations in the molded product is within about 10 sections in each of the positive and negative directions. Good results were obtained. FIG. 9 shows the variation in dimensions when all the samples after molding were actually measured, and this distribution is slightly different from the discrimination results by the discrimination device described above. The reason for this is thought to be the sensitivity of the discrimination device, and as a result of analyzing the differences between the two, it was found that the differences occur with a certain regularity.

FIG. 10 is a graph showing the cause of the difference between the above discrimination result and the result of actual dimension measurement. When discrimination is performed in this way, the rank to which the actual dimension belongs is n. If the size is determined as n, then 6
It is thought that there are 4% r cases where the rank is determined to be 0, n+1 rank is 18''', 9% are determined to be the rank n+2, and about 1% are determined to be the rank n+1.

That is, when making a discrimination, it is necessary to fully understand this sensitivity.

From the above results, it has been found that there is an error (n+1) in the determination, so it is necessary to narrow the range for determining a good product by three sections on one side with respect to the product standard.

Figure 11 shows how many non-defective products were found among the molded products that were determined to be defective after the product standard was narrowed down by three sections on each side to determine pass/fail. It shows whether it is included and what the actual size distribution is among non-defective products. In this case, compared to the true defective rate of 0.25%, the pass/fail discriminator judged 4.296% as defective, which is 4.296% for non-defective products. o4e
% are determined to be defective, but the probability that a defective product will be found among non-defective products is 0%, so it can be passed on to the next process without inspection.

19"' 1. As for the quality to be ranked and monitored,
The degree of occurrence of flow marks, which is determined by calculations based on resin temperature and flow velocity, or resin temperature and Raynozzle number,
There is Paris and short shot, which are calculated based on the resin temperature and peak pressure, and this judgment method can monitor not only the dimensions of the molded product but also a wide range and determine whether it is good or bad.

Effects of the Invention Since the present invention has the configuration and operation described above, the following effects can be obtained.

■ The quality of each shot can be estimated from sampling data based on the calculated values of the relationship between the molding state and at least two physical quantities involved in molding in the molding machine or mold, allowing accurate quality estimation. It can be identified and passed on to the next process without inspection.

■ Since the width of the pass/fail judgment can be set according to the dimensional tolerance of the molded product, it is easy to set the pass/fail judgment conditions.

■ When fully fitting other parts after molding, smooth fitting can be achieved by taking into account the dimensional variations of other parts and grading them according to size.

[Brief explanation of the drawing]

Figure 1 shows a system configuration diagram of an apparatus for determining quality according to an embodiment of the present invention, and Figure 2 is a sectional view of an example of a mold applicable to the system shown in Figure 1. Figure 2 is a graph of the pressure signal obtained with the pressure quadrangle juicer, Figure 4 is a graph showing an example of the relationship between resin viscosity, temperature, and shear rate, and Figure 6 is the resin specific volume, temperature, and pressure. Figure 6 is a flowchart of the quality determination in one embodiment of the present invention, Figure 7 is a perspective view of the molded product on which the quality determination experiment was conducted, and Figure 8 is the result of 1000 shots of molding. Figure 9 is a histogram diagram of the results of actually measuring the dimensions of the 1000 shots, and Figure 10 shows the degree of error that occurs when classifying. The histogram 21″-′ shown in FIG.
FIG. 12, which is a distribution diagram of the actual dimensions of molded products determined as good or defective, is a diagram showing the relationship between screw position and pressure in the conventional pass/fail determination method. 1...Injection screw, 13...Mold,
18゜2o...Pressure detection bottle, 22...Pressure detector, 19.21...Pressure quadrangle juicer, 25...Calculator. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
--11 and Z2 Liu f9.21 --- q l-7 scene z-j Figure 8 1-6 (τ+m) Figure 9 3k<mJ n±f---4 [1% Figure 11 0, I25% Q023% 95704%
2.023% 0.126Z Fig. 12 □ Screen position I

Claims (2)

[Claims] (1) In a molding method in which resin is injected into a mold from the outside, the physical quantities of the pressure, speed, temperature, and time of the molding machine that affect the quality of the molded product, and the pressure, speed, and temperature of the molten resin in the mold By detecting at least two physical quantities from among the physical quantities and calculating the relationship between them and the molding state of the product, the degree of occurrence of phenomena that significantly affect quality is quantified, ranked, and monitored. A monitoring method for determining the quality of injection molded products. (2) In a molding method in which resin is injected into a mold from the outside, physical quantities such as the pressure, speed, temperature, and time of the molding machine that affect the quality of the molded product, as well as the pressure and speed of the molten resin in the mold, By detecting at least two of the physical quantities of temperature and calculating the relationship between them and the molding state of the product, we quantify and rank the degree of occurrence of phenomena that significantly affect quality for monitoring. A monitoring method for determining the quality of an injection molded product, characterized in that the quality is determined by comparing it with a set value of the rank of a non-defective product.