JP2015231676A - Molding quality determination method for hollow molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of determining presence or absence of occurrence of a resin leak inside a hollow molding with good accuracy in molding a hollow molding by die slide injection.SOLUTION: In a molding quality determination method for hollow moldings, a pressure sensor for detection of the internal pressure of a mold is provided, and, in a previous step, a change of the internal pressure of the mold when a hollow molding is molded normally is recorded as the reference internal pressure change. In an actual operation, with the dwelling step (H) after the lapse of a 1/6 of the total time for the dwelling step (H) taken as the monitor target period (K), occurrence of a resin leak is determined when the internal pressure of the mold decreases from the pressure change rate of the reference internal pressure change by a specified value. For example, in the monitor target step (K), occurrence of a resin leak is determined when the pressure change rate of the internal pressure of the mold decreases from the pressure change rate of the reference internal pressure change by a specified value.

Description

  In the present invention, a pair of semi-molded products placed in respective recesses of a pair of molds are clamped together so that the respective joint end faces each other, and a resin is injected to inject a pair of semi-molded products. The present invention relates to a method for determining the quality of a molded product in a method for molding a hollow molded product to obtain a hollow molded product.

  As a method for forming a hollow molded product in a mold, so-called die slide injection is well known. The mold used in this method is configured such that the other slides relative to one mold, and can be clamped at at least two positions according to the slide position. When the mold is clamped at the first slide position, two cavities are formed. When the mold is clamped at the first slide position and the resin is injected by primary molding, a semi-molded product obtained by dividing the hollow molded product into two is molded in each cavity. That is, a pair of semi-molded products is obtained. These half-molded products are formed with joint end faces to be joined to the other half-molded product. The mold is opened so that one half-molded product remains in one mold and the other half-molded article remains in the other mold. Next, the mold is slid and clamped at a position where the pair of semi-molded products face each other, that is, at the second slide position. Then, the pair of semi-molded products are abutted with each other at the respective joining end surfaces. Resin is injected by secondary molding to join a pair of semi-molded products. When the mold is opened, a hollow molded product is obtained.

  In the general die-slide injection as described above, the pair of semi-molded products formed by the primary molding are left in the mold without being completely removed from the mold, and the mold is left at the second slide position. The secondary molding is performed by tightening. However, as in the method described in Patent Document 1, a recess for inserting a semi-molded product into the mold, that is, a recess for insert may be provided, and the semi-molded product may be inserted into the insert recess from the outside. . The method of Patent Document 1 is a method in which the die / slide injection is deformed. In this way, after the semi-molded product is inserted from the outside into the concave portion of the mold, the mold is clamped to perform secondary molding. Even if the resin is injected, a hollow molded product can be obtained.

  A hollow molded product obtained by joining by injection molding from a pair of semi-molded products is characterized in that the joint is fused smoothly by the resin to be injected, so that the joint is formed smoothly and has excellent aesthetics and high strength. is there. However, since molding by an injection molding machine is affected by changes in various conditions such as mold temperature and outside air temperature, it is determined whether the molded hollow molded product has a desired quality and whether the molded product is good or bad. There is a need. There are various determination methods. For example, the quality of the hollow molded product can be determined by visual observation, and the method of determining the quality by measuring the weight of the hollow molded product is also well known. That is, if the measured weight of the hollow molded product exceeds the reference range, it is determined as a defective product. In addition, when a hollow molded product is obtained by secondary molding, a method of obtaining an injection pressure by torque that drives a screw in an injection device and monitoring this is also well known. If the change in the monitored injection pressure deviates from that in the normal state, it is estimated that an abnormality has occurred in the secondary molding, and the molded hollow molded product is determined to be defective.

JP 2008-221575 A JP 2009-137073 A

  In Patent Document 2, although the molded product to be judged is not a hollow molded product, a pressure sensor is provided in the mold, and this sensor monitors the resin pressure in the mold, that is, the mold internal pressure, in the injection process and the pressure holding process. And the determination method which determines the quality of a molded article is described. When injection molding is carried out normally, the mold internal pressure reaches the maximum value in a short time in the injection process, and when switching to the pressure holding process, the mold internal pressure decreases to the vicinity of the set holding pressure in a short time. The mold internal pressure decreases gradually after being maintained at a constant value. However, when a short shot occurs, there is an abnormality in the mold internal pressure immediately after the start of the pressure holding process. That is, when switching from the injection process to the pressure holding process, the mold internal pressure decreases immediately after that, but at this time, the mold internal pressure once becomes lower than the set pressure holding pressure and then increases to the pressure holding pressure. That is, undershoot. If this undershoot is detected, it is determined that a short shot has occurred. This determines the quality of the molded product. In Patent Document 2, the timing of occurrence of this undershoot is not mentioned, but judging from the graph of this document, 1/6 of the total time required for the pressure-holding process has elapsed since the start of the pressure-holding process. Undershoot has occurred by the time. The cause of undershoot is due to the gap that is not filled with resin in the cavity, and the pressure of the resin as a reaction from inside the cavity that is obtained when the cavity is filled normally is the gap that is not filled This is because the pressure temporarily decreases due to the cushion. That is, it can be said that the initial stage of the pressure-holding process in which the resin fluidity is relatively high is a problem, and this initial stage is monitored.

  The quality of the hollow molded product can be judged by visually observing the appearance of the hollow molded product, and the quality of the hollow molded product can also be judged by other conventional methods. The quality of the hollow molded product can also be determined by the method described in Patent Document 2. However, there are some problems to be solved. Specifically, there is a problem that when a pair of semi-molded products are joined to form a hollow molded product, it is not possible to determine the molding abnormality of the resin leak that causes the resin to leak into the hollow molded product. In general, when a hollow molded product is formed from a pair of semi-molded products by secondary molding, it is desirable to mold at the last injection pressure that does not cause resin leakage inside the hollow molded product. This is for obtaining sufficient bonding strength. However, since the injection pressure is high, resin leakage may occur. In this case, it is important whether or not this abnormality can be accurately determined. First, in the conventional method of judging the quality of a hollow molded product from its appearance, the internal state that cannot be visually recognized cannot be judged, so the presence or absence of resin leakage cannot be judged. In the method of measuring the weight of a hollow molded product and comparing it with a reference value, even if the weight is within the reference range, the molded product is not necessarily a good product, and a part of the resin is There is also a possibility of leaking inside. In the method of measuring injection pressure with an injection device in secondary molding and monitoring this, it is possible to determine the quality of molding to some extent, but the accuracy of the determination is not sufficient. That is, even when the injection pressure changes normally in the secondary molding, resin leakage may occur. On the other hand, in the method described in Patent Document 2, since it is possible to directly measure the internal pressure of the mold rather than the injection pressure and monitor this, it is likely that the presence or absence of the occurrence of the resin leakage can be accurately determined. Subject is limited to short shots. That is, the resin leakage inside the hollow molded product cannot be determined.

  An object of the present invention is to provide a method for determining the quality of a hollow molded article that solves the above-described problems, and specifically, a pair of half-molds that are placed in respective recesses of a pair of molds. In the molding method of a hollow molded product, a mold is clamped so that the molded product is abutted with each other at each joining end face, and a pair of semi-molded products are joined by injecting resin to obtain a hollow molded product. It is an object of the present invention to provide a molding quality determination method that can determine the quality of a molded product by detecting the presence or absence of resin leakage.

  In order to achieve the above object, the present invention provides a pressure sensor in a pair of molds obtained by joining a pair of semi-molded products by injection molding to obtain a hollow molded product, thereby obtaining an internal pressure of the mold. Like that. First, as a preliminary process, a change in the mold internal pressure when the hollow molded article is normally molded is recorded as a reference internal pressure change. In each molding cycle, the pressure holding process after 1/6 of the total time required for the pressure holding process has been set as a monitoring target period, and the mold internal pressure is a predetermined amount compared to the reference internal pressure change in the period. If it falls, it will comprise so that it may determine with resin leak having generate | occur | produced in the hollow molded product. For example, in the process to be monitored, if the pressure change rate of the mold internal pressure is reduced by a predetermined value compared to the pressure change rate of the reference internal pressure change, it is determined that a resin leak has occurred in the hollow molded product. Alternatively, resin leakage occurs in hollow molded products when the time integrated value of the mold internal pressure in a predetermined time zone in the monitoring period is smaller by a predetermined amount than the time integrated value of the change in the reference internal pressure in the corresponding time zone. It is determined that

Thus, in order to achieve the above-described object, the invention according to claim 1 is configured such that a pair of half-molded products that are clamped in a pair of molds and inserted into the recesses of the pair of molds are projected at the respective joining end surfaces. When molding a hollow molded product by injecting resin and joining a pair of semi-molded products, the pressure inside the mold is the pressure inside the mold by the pressure sensor provided in the mold This is a molding quality judgment method for judging the quality of the hollow molded product, and records the change in the mold internal pressure when the hollow molded product is normally molded as a preliminary process as a reference internal pressure change, and the molding In the pass / fail judgment method, for each molding cycle, the pressure holding process after 1/6 of the total time required for the pressure holding process has been set as the monitoring target period, and the mold internal pressure changes in the reference internal pressure in the monitoring target period. Only a certain amount compared to Configured as a molding quality determination method of a hollow molded article and judging the resin leaks into the hollow molded article After beating occurs.
According to a second aspect of the present invention, in the determination method according to the first aspect, in the monitoring target step, the pressure change rate of the mold internal pressure is only a predetermined value compared to the pressure change rate of the reference internal pressure change. If it falls, it will determine with resin molding having generate | occur | produced in the hollow molded product, It is comprised as a shaping | molding quality determination method of the hollow molded product characterized by the above-mentioned.
According to a third aspect of the present invention, in the determination method according to the first aspect, the time integrated value of the mold internal pressure in a predetermined time zone in the monitoring target period is a value of the reference internal pressure change in the corresponding time zone. It is configured as a molding quality determination method for a hollow molded product, wherein it is determined that a resin leak has occurred in the hollow molded product when it is smaller by a predetermined amount than the time integrated value.
According to a fourth aspect of the present invention, in the determination method according to the first to third aspects, the pressure sensor is provided on the upstream side of the gate in the mold or on a tab immediately after the gate. This is configured as a molding quality judgment method for a molded product.

  As described above, according to the present invention, a pair of molds are clamped so that a pair of semi-molded products placed in the recesses of the pair of molds are abutted on each joint end surface, and a resin is injected. When molding a hollow molded product by joining a pair of semi-molded products, a pressure inside the mold is used to obtain a mold internal pressure that is the pressure of the resin in the mold, thereby It is configured as a molding quality judgment method for judging quality. That is, the pressure is determined by a pressure sensor that can directly detect the pressure of the resin in the mold. In the present invention, the change in the mold internal pressure when the hollow molded article is normally molded as a preliminary process is recorded as the reference internal pressure change, and the molding pass / fail judgment method of the present invention is maintained for each molding cycle. The pressure holding process after 1/6 of the total time required for the pressure process has been set as the monitoring target period, and when the mold internal pressure decreases by a predetermined amount compared to the change in the reference internal pressure during the monitoring target period, resin is formed into the hollow molded product. It is configured to determine that a leak has occurred. That is, among the pressure-holding processes, the mold internal pressure is monitored as a monitoring target period after a predetermined time has elapsed since the pressure-holding process has started, and compared with the reference internal pressure change recorded when molding is performed normally. The presence or absence of resin leakage is determined. As will be described in the embodiment for carrying out the invention, the resin leakage of the hollow molded product occurs within this monitoring target period, and when the resin leakage occurs, the mold internal pressure rapidly decreases. Therefore, if it determines like this invention, the presence or absence of the resin leak can be determined accurately and reliably.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the metal mold | die which concerns on embodiment of this invention, The (a) is front sectional drawing of a pair of metal mold | die which concerns on this embodiment, The (a) and (c) are this metal mold | die. It is front sectional drawing of a metal mold | die which shows each process when shape | molding a hollow molded product using. It is a graph which shows the change of the mold internal pressure in an injection process and a pressure-holding process, The (a) and (I) are the graphs which show the change of the mold internal pressure in a tab just after a gate and a mold just before a gate, respectively. It is. It is a graph which shows an experimental result, The (a) and (b) are graphs which show the change of the die internal pressure of the injection process and the pressure-holding process at the time of normal time and a resin leak, respectively.

  Hereinafter, a method for determining the quality of a hollow molded product according to an embodiment of the present invention will be described. First, a pair of molds for molding a hollow molded product according to the present embodiment used for molding will be described. The pair of molds according to the present embodiment is a mold for forming a hollow molded product, and is configured in substantially the same manner as a conventional mold for so-called die-slide injection. That is, as shown in FIG. 1A, the pair of molds includes a fixed mold 1 attached to a fixed plate of a mold clamping device (not shown) and a movable mold attached to the movable plate. It consists of two. The movable mold 2 slides up and down relatively with respect to the fixed mold 1, and these molds 1 and 2 are clamped at the first and second slide positions. It is like that. A first core 4 protruding to a predetermined height is formed on the upper part of the parting line of the fixed mold 1, and the first core 4 having a predetermined depth is formed on the lower part. The recessed part 5 is formed. A second recess 7 is formed in the parting line of the movable mold 2 at a predetermined depth at a position corresponding to the first core 4, and a predetermined height is set at a position corresponding to the first recess 5. A second core 8 protruding in the direction is formed. Accordingly, when the mold is clamped at the first slide position, cavities are formed by the first core 4 and the second recess 7 and by the first recess 5 and the second core 8, respectively. Thus, a pair of semi-molded products having a shape obtained by dividing the hollow molded product into two can be molded. The fixed mold 1 is provided with a first runner 9 for injecting resin in primary molding and a second runner 10 for injecting resin in secondary molding. The first and second runners 9 and 10 are branched from a common sprue, and the resin injected from an injection device (not shown) is branched from the sprues and selectively sent to these runners 9 and 10. It is like that. However, the sprue is omitted in FIG.

  The fixed-side mold 1 and the movable-side mold 2 according to the present embodiment are provided with two exceptional pressure sensors in order to perform the molding quality determination method for the hollow molded product according to the present embodiment. ing. The first pressure sensor 12 is provided in the second runner 10 of the fixed mold 1 and is located on the upstream side of the gate 13 in the secondary molding. That is, the mold internal pressure which is the pressure of the resin immediately before the gate 13 can be detected. On the other hand, the second pressure sensor 14 is provided in the vicinity of the second recess 7 of the movable mold 2. A small shallow recess 16 is formed in the portion where the second pressure sensor 14 is provided, and similarly a shallow recess 18 is also formed in the vicinity of the secondary molding gate 13 of the fixed mold 1. . When the mold is clamped at the second slide position, a single tab is formed from these shallow recesses 16 and 18, and in the secondary molding, a gold pressure that is the pressure of the resin immediately after passing through the gate 13 The in-mold pressure can be detected.

  The fixed side mold 1 and the movable side mold 2 according to the present embodiment can form a hollow molded product in the same manner as a conventional die / slide / injection mold. First, primary molding for molding a pair of semi-molded products is performed. That is, as shown in FIG. 1A, the molds 1 and 2 are first clamped at the first slide position. Then, cavities are formed from the first core 4 and the second recess 7 and from the first recess 5 and the second core 8, respectively. When resin is injected from the first runner 9 via the sprue and filled into these cavities, a pair of semi-molded products 20 and 21 obtained by dividing the hollow molded product into two are molded. In this primary molding, these semi-molded products 20 and 21 are formed with joined end faces to be joined to each other. This state is shown in FIG. After cooling and solidification, the molds are opened so that the pair of semi-molded products 20 and 21 remain in the second and first recesses 7 and 5, respectively. It slides to a 2nd slide position so that a pair of semi-molded products 20 and 21 may oppose. When the mold is clamped at this position as shown in FIG. 1C, the pair of semi-molded products 20 and 21 are brought into contact with each other at the joining end surfaces. When the resin is injected from the second runner 10 via the sprue by secondary molding, the resin is injected in the vicinity of the joining portion of the pair of semi-molded products 20 and 21, and these are joined to form a hollow molded product. The When a hollow molded product is molded in the secondary molding, an abnormality that the resin leaks inside may occur. In FIG. 1C, the resin 23 when a resin leak occurs is indicated by a dotted line. However, in the method for determining whether or not a hollow molded product is molded according to the present embodiment, such a resin leak occurs. The presence or absence of is detected.

  As is well known, the injection device includes a heating cylinder and a screw. When the resin is injected in the injection process, position control for controlling the screw position is performed, and in the subsequent pressure holding process, the screw driving torque is obtained. Pressure control is performed to control the injection pressure. Also in the secondary molding in which a hollow molded product is formed from a pair of semi-molded products, the position control of the screw position is performed in the injection process, and the pressure control of the injection pressure is performed in the pressure holding process. FIG. 2A shows changes in the mold internal pressure in the secondary molding injection step S and the pressure holding step H detected by the first pressure sensor 12. Similarly, (a) of FIG. 2 shows changes in the mold internal pressure in the injection process S and the pressure holding process H of the secondary molding detected by the second pressure sensor 14. The mold internal pressures detected by the first and second pressure sensors 12 and 14 change as indicated by the dotted line graphs 25 and 26. That is, in the injection process S, since the injection pressure increases rapidly, the mold internal pressure immediately before the gate 13 detected by the first pressure sensor 12 also increases rapidly. When the injection process S is switched to the pressure holding process H, the pressure control is changed, so that immediately after the pressure holding process H starts, the injection pressure rapidly decreases. As a result, as indicated by the graph of reference numeral 25, the mold internal pressure detected by the first pressure sensor 12 also rapidly decreases, but after a slight undershoot, the pressure is returned to a predetermined pressure, and then the pressure holding step. The mold pressure gradually decreases with the progress of H. On the other hand, the mold internal pressure in the tab immediately after the gate 13 detected by the second pressure sensor 14 hardly changes in the injection process S as shown by the graph of reference numeral 26, and pressure control is performed. In the pressure holding process H to be performed, the mold internal pressure suddenly increases, and then the mold pressure decreases gradually with the progress of the pressure holding process H. That is, the mold internal pressure immediately before the gate 13 and the mold internal pressure in the tub immediately after the gate 13 gradually decrease after reaching a predetermined value after a predetermined time has elapsed after the start of the pressure holding process H. Yes.

  The inventor of the present invention has found that an abnormality in the mold internal pressure occurs in the pressure-holding step H of the secondary molding when resin leakage into the hollow molded product occurs. Specifically, when a resin leak occurs, the mold internal pressure detected by the first and second pressure sensors 12 and 14 changes as indicated by solid line graphs 27 and 28. That is, after the pressure holding step H has elapsed for a predetermined time, the mold internal pressure, which should be gradually decreased, is decreased in a short time as indicated by reference numerals 30 and 31, and then the mold in a normal state. It changes at a value lower than the internal pressure. When a pair of semi-molded products are abutted at the joining end surfaces in the secondary molding, a seal is formed thereby, so that the resin does not leak into the interior of the hollow molded product. However, the occurrence of resin leakage is presumed to be caused by the temperature in the vicinity of the seal rising due to the resin injected in the secondary molding and the seal breaking. At this time, the mold internal pressure decreases. The inventor repeated experiments as will be described later, and this phenomenon occurs not immediately after the start of the pressure-holding process H, but when the pressure-holding process H has passed for a predetermined time, specifically, the pressure-holding process H is required. I found that it was after 1/6 of the time. In other words, it occurs in the 5/6 period that is closer to the rear in the entire period of the pressure holding process H. In view of this, the present invention has invented a determination method in which the mold internal pressure is monitored with this period as the monitoring target period K, and it is determined that a resin leak has occurred when it is lower than the normal mold internal pressure by a predetermined amount.

The method for determining the quality of a hollow molded product according to the first embodiment of the present invention monitors the rate of pressure change of the mold internal pressure. Specifically: First, secondary molding is performed so that a hollow molded product is normally molded as a preliminary process. Then, the mold internal pressure changes as indicated by reference numerals 25 and 26. Such a change in the mold internal pressure is defined as a reference internal pressure change. Next, the pressure change rate of the reference internal pressure change in the monitoring target period K is sequentially calculated as follows.
P ′ (t) = ΔP / Δt (1 formula)
However, P ′ (t): Pressure change rate of reference internal pressure change, ΔP: Difference of reference internal pressure change, Δt: Sampling time interval In other words, the pressure change rate of reference internal pressure change is obtained as a function of time. This is stored in the controller of the injection apparatus.
In this operation, when a hollow molded product is molded by repeating the molding cycle, the pressure change rate of the mold internal pressure is sequentially calculated in the monitoring target period K as follows.
p ′ (t) = Δp / Δt (2 formulas)
However, p ′ (t): Pressure change rate of mold internal pressure, Δp: Difference of mold internal pressure, Δt: Sampling time interval, and Pressure change rate p ′ (t) of mold internal pressure are stored in the controller Compared with the pressure change rate P ′ (t) of the reference internal pressure change, if the following relationship is detected, it is determined that a resin leak has occurred.
p ′ (t) <P ′ (t) −α (3 formulas)
Where α: Permissible change rate Unit is Pa / t
The change rate allowable value α is appropriately set according to the injection pressure of the pressure holding process and other conditions. For example, when the injection pressure of the pressure holding process is 15 MPa, the change rate allowable value α is 2 to 5 MPa / t. Set as follows.

The molding quality determination method for a hollow molded product according to the second embodiment of the present invention monitors the time integral value of the mold internal pressure. Specifically: The target time zone for time integration, that is, the integration target time zone T is determined from within the monitoring target period K. The integration target time zone T can be any time zone as long as it is the monitoring target period K, but a relatively early time zone is preferable. For example, when 1/3 of the time required for the pressure holding process H has passed since the start of the monitoring target period K. This is because the resin leakage is likely to occur relatively early in the monitoring target period K. When the integration target time zone T is determined, first, as a preliminary process, secondary molding is performed so that a hollow molded product is normally molded. Then, the mold internal pressure changes as indicated by reference numerals 25 and 26. Such a change in the mold internal pressure is set as a reference internal pressure change, and a time integrated value of the reference internal pressure change in the integration target time zone T is calculated as follows.
∫P (t) dt = ΣP / n (4 formulas)
However, ∫P (t) dt: time integrated value of reference internal pressure change, ΣP: total value of all samplings of reference internal pressure change in integration target time zone T, n: number of samplings per unit time obtained reference internal pressure change The time integral value ∫P (t) dt is stored in the controller of the injection device.
In this operation, when a hollow molded product is molded by repeating the molding cycle, the time integral value of the mold internal pressure in the integration target time zone T is calculated as follows.
∫p (t) dt = Σp / n (Formula 5)
Where ∫p (t) dt: time integral value of mold internal pressure, Σp: total value of all mold internal pressure sampling in integration target time zone T, n: number of samples per unit time and the following relationship is detected If so, it is determined that a resin leak has occurred.
∫p (t) dt <∫P (t) dt-β (Equation 6)
Where β: Allowable difference unit is Pa · t
The difference allowable value β is appropriately set according to the injection pressure in the pressure holding process and other conditions. For example, the integration target time zone T is 2 seconds, and the injection pressure in the pressure holding process is 15 MPa. In this case, it is set to 3 to 6 MPa · t.

When a hollow molded product was formed from a pair of semi-molded products, an experiment was conducted to measure the mold internal pressure for each of a case where a normal hollow molded product was obtained and a case where resin leakage occurred.
(1) Experimental conditions Mold: The mold uses the fixed side mold 1 and the movable side mold 2 according to the present embodiment, but the number of gates and the number of pressure sensors are changed as follows. That is, the mold was provided with three gates for secondary molding, which were gates g1 to g3. Further, tabs t1 to t3 are provided immediately after the respective gates g1 to g3. Five pressure sensors for detecting the mold internal pressure were provided and arranged as follows. The pressure sensors s1 and s2 were provided immediately before the gates g1 and g2. And pressure sensor s3-s65 was provided in tab t1-t3.
Secondary pressure holding pressure step H: The pressure holding step H was performed at an injection pressure of 14.0 MPa for 12 seconds.
(2) Experiment Secondary molding was performed to mold a hollow molded product from a pair of semi-molded products. The hollow molded product did not cause resin leakage inside, and a good product was obtained. The pressure in the mold detected by the pressure sensors s1 to s5 in the injection process S and the pressure holding process H of the secondary molding was measured, and a graph (a) in FIG. 3 was obtained.
Next, a critical condition for causing resin leakage inside was searched for as follows. The molding of the hollow molded product was repeated such that the injection pressure in the pressure holding step H was increased from 14.0 MPa to 0.2 MPa. Only when the injection pressure in the pressure holding step H was 15.0 MPa, resin leakage occurred inside the hollow molded article. That is, it can be said that the injection pressure of 15.0 MPa in the pressure holding step H is a critical condition for causing resin leakage in the hollow molded product to be tested. At this time, the pressure in the mold detected by the pressure sensors s1 to s5 in the injection process S and the pressure holding process H of the secondary molding was measured, and the graph of FIG. As indicated by reference numeral 33, it was confirmed that the pressure inside the mold suddenly decreased.
(3) Simulation In order to confirm that resin leakage can be detected in any of the molding quality determination methods for hollow molded products according to the first and second embodiments of the present invention, the following simulation was performed on a computer.
The monitoring target period K was 2 seconds after the start of the pressure holding process H to the end of the pressure holding process H, and the integration target time zone T was 2 seconds from the start of the monitoring target period K. In addition, when the allowable change rate α is 2 MPa / t and the allowable difference value β is 3 MPa · t, and the molding quality determination method for the hollow molded product according to the first and second embodiments is simulated on a computer, In the method, resin leakage could be detected.

  Various modifications can be made to the method for determining whether or not a hollow molded product is molded according to the first and second embodiments of the present invention. For example, in the method according to the first embodiment, the pressure change rate has been described as dividing the difference in the mold internal pressure by the sampling time interval as in formula 1 and formula 2, but only the difference in the mold internal pressure. You may make it give by. This is because, since the sampling time interval is constant, comparing the difference in mold internal pressure with the difference in reference internal pressure change is substantially equivalent to comparing the pressure change rate. In the method according to the second embodiment, the total value of all samplings of the mold internal pressure in the integration target time zone T is obtained by sampling per time when the time integrated value is obtained as shown in Formula 4 and Formula 5. Although it has been described that it is divided by the number n, it is not necessary to divide this by the number n of samplings per time. Since the sampling number n per time is constant, even if the total value of all samplings of the mold internal pressure in the integration target time zone T is compared with the total value of all samplings of the reference internal pressure change in the integration target time zone T, This is because it is equivalent to comparing the time integral values. Similarly, in the molding quality determination method according to the second embodiment, an average value may be employed instead of the time integration value. This is because the average value is nothing but the time integration value for the unit time.

DESCRIPTION OF SYMBOLS 1 Fixed side metal mold | die 2 Movable side metal mold | die 4 1st core 5 1st recessed part 7 2nd recessed part 8 2nd core 9 1st runner 10 2nd runner 12 1st pressure sensor 13 Gate 14 1st 2 Pressure sensor
20, 21 A pair of semi-molded products S Injection process H Holding pressure process K Monitoring target period T Integration target time zone

Claims (4)

The pair of molds are clamped so that the pair of semi-molded products placed in the recesses of the pair of molds are abutted at the respective joining end surfaces, and the resin is injected to join the pair of semi-molded products. When molding a hollow molded product, a mold internal pressure, which is the pressure of the resin in the mold, is obtained by a pressure sensor provided in the mold, thereby determining whether the hollow molded product is good or bad. There,
As a pre-process, record the change in mold internal pressure when the hollow molded product is molded normally as the reference internal pressure change,
In the molding pass / fail judgment method, for each molding cycle, the pressure holding process after 1/6 of the total time required for the pressure holding process has been set as the monitoring target period, and the mold internal pressure is the reference value in the monitoring target period. A method for determining good or bad molding of a hollow molded article, wherein it is determined that a resin leak has occurred in the hollow molded article when the pressure is reduced by a predetermined amount compared to a change in internal pressure.   The determination method according to claim 1, wherein, in the monitoring target step, if the pressure change rate of the mold internal pressure is reduced by a predetermined value as compared to the pressure change rate of the reference internal pressure change, resin leakage occurs in the hollow molded product. A method for determining good or bad molding of a hollow molded product, characterized by determining that it has occurred.   2. The determination method according to claim 1, wherein a time integrated value of the mold internal pressure in a predetermined time zone in the monitoring target period is a predetermined amount compared to a time integrated value of the reference internal pressure change in a corresponding time zone. A method for determining whether or not a hollow molded product has been molded is characterized in that it is determined that a resin leak has occurred in the hollow molded product when it is only small.   The determination method according to claim 1, wherein the pressure sensor is provided on the upstream side of the gate in the mold or on a tab immediately after the gate.

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