METHOD AND APPARATUS FOR CONTROLLING INJECTION MOLDING

Abstract: A technique of controlling injection molding is provided wherein the amount of mold opening formed by the injection pressure of a melted resin is measured, and the maximum value of the mold opening is used as judgement factor. Since the amount of mold opening is directly related to the quality of a molded article, and the change of the molding factors of an injection molding machine is also concerned in mold opening, control of an injection molding can be carried out only by detecting the maximum value of mold opening without detecting other molding factors.

Description: DESCRIPTION METHOD AND APPARATUS FOR CONTROLLING INJECTION MOLDING Technical Field The present invention relates to a technique of controllin injection molding that uses thermoplastic resins, and mor particularly to a method of controlling injection molding b grasping generally the molding on the basis of informations tha can be detected simply, and a controlling apparatus therefor. Background Art Injection molding of synthetic resins is generally carrie out by injecting a melted resin into a mold that has bee clamped, then cooling the resin to allow the resin to solidify and opening the mold to remove the molded article. Therefore in order to control molding, it is required to monitor the ra material system and the molding machine system. With respect t monitoring of the raw material system, there are informations for example, on the plasticizing temperature of the syntheti resin, the plasticizing time, the injection amount per injection and the injection pressure, and with respect to monitoring of th molding machine system, there are informations, for example, o the clamping pressure of the mold, the temperature in th cavities, the cooling temperature of the mold, and the coolin speed. In conventional control of injection molding, thes informations are measured for each article to be molded, each ra material to be used, and each molding machine to be used, and th control is effected on the basis of the measured results However, in the actual molding, ever-changing various factor such as a change in the temperature of the cooling water, change in the feed of the cooling water, a change in th temperature of the hot runner section, a change in the ga escaping from the cavities, a change in the physical propertie of the raw material such as the viscosity, an obstruction due t adhesion of foreign materials onto the gate or the like, a chan in temperature and humidity of the surroundings, and a change i the oil temperature of the cylinder for clamping are involve thereby causing accidental failure which will result in shor molding, formation of burrs, etc. If such failure occurs, al the products must be checked, inevitably leading to temporar suspension. Sometimes the dimensional accuracy of some product scatters outside the standard even if short moldings or burrs o the products are not formed, then in that case, check of th appearance such as check of short moldings or burrs cannot b carried out, and the sizes of all of the products are needed be measured. Further in the case of products whose functi cannot be confirmed by the measurement of the size or the lik there is not other test than the destructive test, and sinc recent molded articles are required to have not only a functio as, for example, a container but also an additional composi function, check to identify whether an article is good one o defective one is quite important. As measures against that, is considered to detect the above variable factors and to ta measures according to the amounts of the changes. However, is not practical to check all these factors, since it is requir not only to provide a number of detecting means such as sensor which will enlarge the controlling apparatus, but also to chan the design of the molding machine. Particularly, it i impossible to check all the factors in the case of multi-cavi molding for obtaining a plurality of molded articles in a singl injection, since the number of checks increases. Further, i such check is carried out, it is impossible to prevent defective from being produced. This is because not only the above factor are combined but also the frequency of use of the molding machin and the mold, and other factors will be added, which results i the formation of defectives. The present invention has taken the above situation int consideration, and is intended to provide a method of controllin injection molding wherein the control of the molding is possibl without checking a number of factors that vary at the time o molding and a controlling apparatus therefor. Particularly, th present invention is intended to provide a controlling method an a controlling apparatus wherein in the case of multi-cavit molding that uses a mold having a plurality of cavities, positiv control is performed on the basis of informations that can b detected easily. Disclosure of the Invention The present invention detects the maximum value of th amount of mold opening between a stationary mold and a movabl mold that are opened inevitably by injection pressure, and judge whether the injection molding is good or not on the basis of th detected value. In the present invention, when molding i judged to be defective, the resulting defective article i treated differently from good articles thereby improving th effect of injection molding. Mold opening reaches its maximum when the cavities a filled with the injected resin, and after the completion of t injection, the molds return to the original positions and t mold opening disappears. The inventors have found that if t maximum value of mold opening is within a prescribed range, go molding can be attained, while if the maximum value is outsi the prescribed range, defective articles will be formed. Th is, if the amount of mold opening is excessive, the mold article will have burrs, and if the amount of mold opening is t small, short molding will occur. This is because if the amou of mold opening is more than a needed amount, the melted res will leak outside the cavities, and on the other hand if t amount of mold opening is less than the needed amount, t cavities will not be filled sufficiently with the melted resi and will lack in the melted resin. Thus, mold opening required to a certain degree in injection molding, but if mo opening falls outside a certain range, defective articles will formed. Further, the inventors have studied and found that wh a resin is injected into cavities, the amount of mold openi varies depending generally on a combination of the clampi pressure, suffered deterioration of and suffered damage to t steel of the clamping machine structure, the injection pressur the injection speed, the amount of injection, the mo temperature, the oil temperature, the cooling water temperatur the amount of cooling water, the difference of the physic properties of the raw material, and other factors. That i mold opening will be caused by a combination of variable facto involved in injection molding, and if the maximum value of t amount of mold opening is detected and is use as an index f judging the quality of articles, other factors are not requir to be checked. This makes the control particularl advantageously easy in the case of multi-cavity molding where many items must be checked conventionally. Brief Description of the Drawings Fig. 1 is a general diagram of an injection molding machin and controlling apparatus suitable for carrying out the presen invention; Fig. 2 is a perspective view of an embodiment of measuring apparatus for measuring mold opening; Fig. 3 is characteristic diaga showing mold opening; Fig. 4 is schemati views of an article molded in Example 1 of the present invention Fig. 5 is a sectional view of parts of the molds used in Exampl 1; Fig. 6 is a front view of the arrangement of sensors; Fig. is schematic views of several examples of unfavorable molde articles; Fig. 8 is a schematic view of the article molded i Example 2; Fig. 9 a sectional view of parts of the molds used i Example 2; and Fig. 10 is a front view of the mold showing th arrangement of sensors. The Best Mode for Carrying out the Invention The present invention will now be described with referenc to the accompanying drawings. Fig. 1 is a diagram showing the constitution of a embodiment of an injection molding machine equipped with controlling apparatus for carrying out the present invention. stationary mol d 2 is mounted to a stationary side mounting bloc 1, and a movable mold 4 is mounted to a movable side mounti block 3. Cavities 5 that are in conformity with an article be molded is formed between the opposed surfaces of th stationary mold 2 and the movable mold 4. A synthetic resin a melted state is injected into the cavities 5 from th stationary mold 2 via a supply pipe (not shown) , and is cool and solidified in the cavities 5. The movable side block 3 which the movable mold 4 is mounted is abutted and clamp against the stationary side mounting block 1 by power of driving section such as a hydraulic cylinder, and then molding carried out. After the molding, the movable side block 3 retracted from the movable side mounting block 1 to open t cavities 5. With the cavities 5 opened, the molded articles a taken out by a robot hand (not shown) . The removed mold articles are transported on a conveyer, and are packed into box. The reference numeral 6 indicates a driving means carrying out the above operation. The driving means 6 equipped with a movable side mounting block driving section for moving back and forth the movable side mounting block 3 a for adjusting the clamping under a prescribed pressure, a res supply section 6b for injecting the melted resin into t cavities 5, a cooling temperature adjusting section 6c f adjusting the cooling rate of the melted resin and for adjusti the cooling temperature, etc., a cooling water supply section for carrying out the supply and discharge of cooling water, a sub-adjusting sections 6e, 6f for carrying out other drivin than the above drivings concerning the molding. These drivin are controlled by control signals from a control means 7 where a prescribed program is stored. In addition to the abo constitution, in this Example, a controlling apparatus provided that is equipped with a detecting means 20, a setti means 30, a judging means 31, a takeout means 32, an alarm mea 33, a stopping means 34, a display means 35, and a recordi means 36. The detecting means 20 is a means of detecting t amount of mold opening caused by the injection pressure of t resin, and consists of sensors 8 and an arithmetic section 9 The sensors 8 are provided on the outer surfaces of th stationary side mounting block 1 and the movable side mountin block 3, are opposed to each other, and can detect opening tha is brought about between the stationary side mounting block 1 an the movable side mounting block 3 by the injection pressure o the resin thereby detecting the amount of the mold openin between the stationary mold 2 and the movable mold 4. I compliance with the structure of the molds, in some cases, it i most effective that the sensors 8 are directly mounted to th stationary mold 2 and the movable mold 4. As these sensors, us can be made of, for example, (1) magnetic sensors that use th fact that magnetic lines of force change in accordance with th distance, and detect a change in exciting current due to th magnetic lines of force, (2) photosensors for detecting th number of slits that are moved by the mold opening, and othe sensors. In this case, it is preferable to use a sensor havin a detecting sensitivity on the order of mirometers since the mol opening is on the order of tens of micrometers. The arithmeti section 9 converts the detection signal outputted from th sensors 8 into the amount of mold opening. From the amount mold opening obtained by the conversion, its maximum value calculated and is outputted into the judging means 31. T judging means 31 compares the maximum value of the amount of mo opening outputted from the arithmetic section 9 with the s value inputted from the setting means 30. In the setting mea 30, the upper limit value and the lower limit value of the amou of mold opening between the stationary mold 2 and the movab mold 4 are set previously and stored. The upper limit value a the lower limit value are set as critical points where defecti molding will take place. Specifically, the upper limit value an amount of mold opening immediately below the amount of mo opening where burrs will be formed, and the lower limit value an amount of mold opening immediately over the amount ' of mo opening where short molding will occur. The upper limit val and the lower limit value will be depend on a combination factors at the time of molding such as the clamping force, t injection pressure of the melted resin, and the amount injection, and are difficult to be fixed absolutely. Therefor it is practical and more quickly adaptable to carry out sever tests before actual molding and to specify the upper limit val and the lower limit value from the test results. Thus, it preferable that the upper limit value and the lower limit val of the amount of mold opening involved can be suitably renew before a molding series, and the setting means 30 is equipp with memory means such as RAM for allowing this renewal. On t other hand, the judging means 31 detects the upper limit val and the lower, limit value of the amount of mold opening set the setting means 30, compares them with the detected values f the arithmetic section 9 of the detecting means 20, and jud whether they are within the range between the upper limit va and the lower limit value that are set. It is preferable t this judgment is carried out for every injection molding, but is allowable that this judgment is carried out for sever injection molding operations or tens of injection moldi operations. The case where the latter judgment is allowable based on an experimental rule that formation of burrs or sho molding generally does not occur accidentally but takes pla gradually as the number of the injection molding operatio increases, and if the latter judgment is carried out for certain number of injection molding operations, advantageous the amount of information can be reduced, and the statistics the information can be taken and arranged easily. The result judged by the judging means 31 in the abo manner is outputted into the control means 7. Although t control means 7 is a means of controlling the driving means 6 f driving essentially the injection molding, the control means 7 this Example is constructed in such a manner that it controls t driving means 6, and in addition, it controls the takeout mea 32, the alarm means 33, the stopping means 34, the display mea 35, and the recording means 36. The control of the takeo means 32, the alarm means 33 and the stopping means 34 amo these means is carried out when a defective article is produce and on the other hand the control of the display means 35 and t recording means 36 is carried out for the injection moldi generally irrespective of a normal article or a defecti article, and these means constitute a control system differe from the driving means 6 for carrying out essentially t injection molding. Therefore, the control means 7 may separated into a control section for controlling the drivi means 6, and a control section for controlling the takeout mea 32, the alarm means 33, the stopping means 34, the display mea 35, and the recording means 36, with the latter controlli section made optional. Thus, the system and the program of t apparatus as a whole may be simplified, and can be generally us for other molding machine. The latter control in the contr means 7 is carried out on the basis of the result of the judgme of the judging means 31. That is, if the detected value fr the arithmetic section 9 of the detecting means deviates ' from t range of the set value of the setting means 30, the control mea 7 controls the takeout means 32, the alarm means 33, and t stopping means 34. The takeout means 32 consists of a rob hand for taking out molded articles from the cavities 5, conveyer for taking out the molded articles to the outside of t system, etc. , and if a deviation signal is inputted into t judging means 31, the control means 7 judges the molded artic as a defective, and controls the particular molded article to taken out through a route different from that for normal mold articles. For example, the molded articles taken out from t cavities by the robot hand may be dropped in a port separat from the conveyer, or in the case wherein the molded articles a dropped under their own weight without using the robot hand, t conveyer may be driven reversely to take out the particul molded articles toward the side opposite to the side for t normal molded articles. The particular molded articles ta out through the route different from that for the normal mol articles are discriminated to be good or defective ones by operator. The alarm means 33 is equipped with alarm membe such as a buzzer, a lamp, etc. and when a deviation signal fr the judging means 31 is inputted into the control means 7, t control means 7 controls them and actuates them. Thus, t operator's attention is aroused, and the judgment of quality the article molded at the time when an alarm is issued facilitated. The stopping means 34 is a means of stopping t movable side mounting block 3, and when a deviation signal fr the judging means 31 is inputted into the control means 7, t control means 7 actuates the stopping means 34, and controls t stopping means 34 in such a way that the movement of the movab side mounding block 3 in the next molding may be stopped. By t stoppage of the movable side mounting block 3, the driving other members including the injection cylinder, etc. is al synchronously stopped. Therefore, the injection molding temporarily stopped, and the investigation or removal of t cause of the deviation signal is performed by the operator. this case, if the deviation signal is inputted, the operation the stopping means 34 is not performed until the molding at t time of the inputting of the signal is completed, and t operation of the stopping means 34 is effected after the moldi at the time of the inputting of the signal is complete Consequently, the article molded at the time when the deviati signal is inputted is taken out from the cavity. On the other hand, the display means 35 and the recordin means 36 display and record the state of the injection moldin regardless of the signal from the judging means 31. The displa means 35 displays data concerning the mold opening in th injection molding on a display or the like, which will be used a a guide for the operation by the operator. As the way o displaying use can be made of a digital display using 7-segmen LED or the like, or an analogue display wherein the amount o mold opening is lit along a prescribed curve. As the displayin method, the display can be made in such a way that since, i addition to the maximum value of the amount of mold opening there are, for example, information of the amount of opening a the time of clamping, and information of the return amount at th time when the molds have returned from the state of the maximu mold opening, these may be displayed side by side, or only th maximum value of the amount of mold opening may be displayed The operator can grasp the state of injection molding b monitoring these displays, so that for example the cause can b investigated before the occurrence of a defective and can b removed beforehand. The recording means 36 is a means of recording the amount o mold opening in injection molding. In injection molding for example a change in mold opening due to the clamping an injection, and mold return due to cooling occur in every molding and the amount of mold opening in each of these states i recorded every time by the recording means 6. Further, th maximum value of the mold opening detected by the arithmet section 9 is also recorded. The data thus recorded serve reference data concerning the particular injection moldi machine and can be used as guides by which the injection moldi machine can be controlled to prevent a defective from bei formed. Fig. 2 shows a measuring apparatus 40 equipped with t display means 35 and the detecting means 20. This measuri apparatus 40 is constructed separately from the injection moldi machine, and has an power source such as a battery therein make it of a handy type thereby allowing the measuring apparat to be used for a different injection molding machine. T measuring apparatus 40 has, in the front panel, an power sour switch 41, and a power source switch 42 such as LED, etc. as wel as displays 43, 44, 45. These displays 43, 44, 45 display th change of the amount of mold opening in injection molding fo every prescribed item, and for example the display 43 display the amount of opening immediately after the clamping, the displa 44 displays the maximum value of the mold opening detected at th time of the injection, and the display 45 displays the retur value at the time of the cooling. On the other hand, a cord 4 is led from the measuring apparatus 40, and the end of the cor 46 has a sensor (not shown) . The sensor is supported by supporting member that can arbitrarily attached to the stationar side and movable side mounting blocks 1, 3 (Fig. 3) of th injection molding machine, and can be suitably attached to o detached from the injection molding machine to be measured. I this case, as the supporting member preferably use can be made o a structure that allows easy attachment or detachment through magnetic attracting force of a magnet or the like. T reference numeral 47 indicates a switch button provided on t side panel of the measuring apparatus 40 , , and dictates the sta of display on the displays 43, 44, 45, and the switch button is pushed when the displaying is to be terminated. For exampl when the switch button 47 is pushed after the clamping, t amount of opening at the time of the end of the clamping displayed on the display 43. Thereafter, when the melted res is injected and the mold opening starts, the display 44 displa its numerical change. Then, when the maximum value of the mo opening is detected, the display 44 stops the display at th numerical value. Then, after the stage is moved to a cooli step, and when the switch button 47 is pushed again, t operation becomes possible such that the display 45 can displ the return value. Since such a handy type measuring apparat 40 can be attached for different injection molding and c perform the measurement easily, it can be made convenient investigate the characteristics of every injection moldi machine. Now, an example of the control will be described below. Fig. 3 is a characteristic diagram obtained by measuring t sensor output along the time axis in injection molding. In th example, the sensor output is in proportion to the distan between the movable mold 4 and the stationary mold 2. The poi A indicates the point wherein the stationary mold 2 and t movable mold 4 are closed and clamped by the movement of t ovable side mounting block 3, the point B indicates the poi wherein the melted resin is injected into the molds, and t point C indicates the point wherein the molds are released allow the molded articles to be removed. In the characterist curves a, b, c, and d, the maximum peak appeared between B and is the maximum value of the amount of mold opening brought for by the injection of the melted resin. In the case of t characteristic curves a and b wherein this maximum value fal within the prescribed range D, good product can be molded. the other hand, in the case of the characteristic curve c that above the range D, the molded article will have burrs, and in t case of the characteristic curve d that is below the range D, short molded article will be obtained. Therefore, if t maximum value deviates from the range D, since the molded artic becomes defective, based on the signal from the judging means t control means 7 carries out the following control. (1) The driving of the molding machine is stopped. That is, the stopping means 34 is actuated. Thus, t operator conducts a cause removal process by cleaning the mol to remove soil such as adhered resin, or investigates the cause. (2) The molded articles from the molds are removed from t production line. By controlling the takeout means 32, for example t conveyer for the molded articles are driven reversely, or using the robot hand or the like, the molded articles are tak out into a discarding port. Thus, defectives can be prevent from being included. (3) An alarm is issued by the buzzer, lamp, etc. There are some cases wherein if the maximum value of t amount of mold opening deviates from the prescribed range, go articles are molded, and in those cases an alarm is issued arouse the operator's attention. The operator judges t quality of the molded article based on the alarm, and can ta measures such as suspending or stopping of the molding operati on the basis of the result of the judgment. The above controls can be made separately or may be ma simultaneously, or other measures may be taken. Next, t relationship between the maximum value of mold opening and t quality of the molded article will be described based on specif Examples. Example 1 Fig. 4 (a) and (b) show an Example wherein a filter ' casset container 10 for coffee will be injection molded, the contain 10 having a gate in the center of the bottom. Fig. 5 sho parts of molds therefore, wherein a cavity 14 for molding t container 10 is defined between a cavity block 12 and a co block 13. The reference numeral 15 indicates a stripper ri plate for pushing out the end of the molded article to relea the molded article from the core block 13. Sensors 16, 17 f detecting the mold opening are oppositely provided on the out surfaces of the cavity block 12 and the core block 13 by bracke 18 respectively. As the sensors 16, 17, magnetic sensors a used, and the sensor 17 is a detecting side sensor, while t sensor 16 is a starting side sensor. In this case, the starti side sensor 16 can be adjusted to be spaced from the sensor 1 The cavity block 12 and the core block 13 are provided on t opposite sides of a hot runner (not shown) , and the block 12 a the block 13 positioned on the opposite sides serve as a movab mold and a stationary mold respectively. In this Example, cavities are formed, so that 8 articles can be formed by o injection, and the sensors 16, 17 are attached for the respecti cavities as shown in Fig. 5. Hereinafter, the cavities a designated #1 to #8, and the maximum values of the amount of mol opening at the time of clamping and injection, and the interval between the stationary mold and the movable mold after th returning from the mold opening are shown in Table 1. The uni of the numerical values is μm. Table 1 after 20 min of kickoff after 8 hours of kickoff Maximum of Return from Maximum of Return from Cavity Clamping mold opening mold opening Clamping mold opening mold opening Table 1 shows numeral values of continuous operation of 1 shots after the kickoff. The column under "Clamping" shows t intervals at the time of clamping under a pressure of 150 t, t column under "Maximum of mold opening" shows the maximum valu of mold opening assuming the value of mold opening at the time the above clamping to be "0", and the column under "Return fr mold opening" shows intervals assuming the value of mold openi at the time of clamping to be "0". In Table 1, after 8 hours kickoff, since the column under "Clamping" shows sever micrometers, it will be inferred that resin residue adhered the parting surfaces of the molds, which will be used as a gui for cleaning the molds. Table 2 shows the results of the measurement of the maxim values of the mold opening in respective shots that were obtain when injection molding was effected using the above molds. T clamping force was 150 t for all the shots. In the case of t cavity #1, from the seventh shot, the temperature of the h runner section changed from 250 °C to 235 °C, and in the case the cavity #6, from the thirteenth shot, the hot runner secti changed similarly. After that change, in the case of the cavity #1, from t ninth shot, and in the case of the cavity #6, from the fifteen shot, the maximum value of the amount of mold opening lowere and short molded articles appeared wherein part of them wer missing as shown in Fig. 7 (a). In this connection, as reaction, the amount of mold opening of the cavity #4 and th cavity #7 located diagonally opposite to the cavity #1 and th cavity #6 was increased, but the increase in this amount did no cause the molded articles to have burrs. From this it can understood that, in the case of the cavity wherein the maxim value of the amount of mold opening drops sharply, som unpreferable change arises, making the molded article defective. Table 2 8 10 11 12 13 14 15 16 17 18 19 20 #1 25 25 25 26 25 25 24 20 10 11 10 10 10 11 10 10 10 10 10 10 #2 27 27 27 27 26 27 25 27 27 27 27 28 28 28 28 28 27 28 28 28 #3 26 26 26 26 26 26 26 27 27 27 27 27 27 27 28 28 28 28 29 29 #4 26 26 26 26 26 26 27 27 35 35 36 35 36 36 36 36 36 36 35 36 #5 28 27 28 28 27 28 27 28 29 28 28 28 28 28 29 28 28 27 27 28 #6 27 26 27 27 27 27 26 27 27 27 27 27 23 21 11 10 10 11 10 10 #7 25 25 25 25 26 25 24 26 26 26 26 26 27 30 37 36 35 35 36 35 #8 26 26 26 27 26 26 25 27 27 27 27 26 27 27 28 28 28 28 28 28 Table 3 shows the maximum values of the amount of mol opening in the case wherein only the clamping force was adjust to 150 t, and other factors including the heating of the h runner section, the temperature of the melted resin, and t cooling rate were set to carry out the molding. In Table 3, t mark "*" and the mark "Δ" are attached to the maximum values th changed sharply. The mark "*i" indicates the case wherein sho molding in which part was missing as shown in Fig. 7 (a occurred, the mark "*2" indicates the case wherein large sho molding as indicated in Fig. 7 (b) occurred, the mark "*3 indicates the case wherein more larger short molding as shown Fig. 7 (c) occurred, and the mark "*4" indicates the case where short molding occurred that brought about a molded article th did not form a container. The mark "A" indicates the cas wherein a molded article having burrs blocking completely t opening in the bottom of the container was formed, and the ma ,,A " indicates the case wherein a molded article having bur partially blocking the opening in the bottom of the container w formed. Table 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 #1 25 25 25 25 26 25 23 20 10* 1 10* 1 8* 2 7* 2 5* 3 5* 3 5* 3 2* 4 3* 4 2* 4 3 3 #2 27 27 27 26 27 26 26 26 28 28 38 39 60 Δ 61 63 68 68 69 68 Λ 68 #3 26 26 26 26 26 26 26 27 27 28 37 40 62 Δ 60 62 69 69 68 68 A 69 Λ A A A Δ Δ Δ Δ Δ Δ Δ #4 26 26 27 26 26 26 27 28 35 36 80 88 80 78 75 70 70 70 70 69 #5 28 27 28 28 28 28 28 28 28 27 40 39 6^ 60 61 6^ 69" 69 69^ 70 Δ Δ Δ Δ Δ Δ Δ Δ #6 27 27 26 27 26 27 27 27 27 27 39 40 60 61 62 66 68 68 69 68 Δ Δ Λ Δ Δ Δ Δ Δ #7 25 25 25 25 25 25 25 26 26 27 37 38 61 60 6(T 68 68 68 69 69 Δ Δ Δ Δ Δ Δ Δ #8 26 26 26 27 26 27 27 27 27 27 38 40 57 57 59 68 68 69 70 69 Then, using the molds shown in Fig. 5 and Fig. 6, article were injection molded continuously for 96 hours. The moldin conditions were as given below. (1) The clamping force was 15 t, and 5.6 sec were used for the clamping, the molding, and th removal (dropping under their own weight) in all. (2) Takin the allowance range of the size of the mold opening at the tim of clamping to be 15 μm, and in the case when the clampin exceeding this range continued 5 shots, the driving of th molding machine was stopped and the molds were cleaned. (3 Setting the allowance range of the change of the maximum value o the mold opening at the time of shot to be down to 5 μm but up t 50 μm, the molded article falling outside this range wa discharged automatically as a defective article from the lin into the discarding port (i.e., discharged on the side opposit to the side where normal articles were placed by reversel driving the conveyer) . (4) Taking the allowance range of th opening size at the time of returning from the clamping to be μm, the molded articles deviating from this range were discharge into the discarding port. (5) When the driving of the moldin machine was stopped for 5 min or over, until 10 shots wer completed after the resuming of the driving, the molded article were discharged into the discarding port. As a result of the molding under the above conditions, ther were 8 molding operations falling under condition (2) , producin 320 molded articles, all of which were confirmed by the check b the operator that they were good articles. There were 1 molding operations falling under condition (3) , and of 128 molde articles, 16 articles were defective, and the remaining article were good ones. There were 20 molding operations falling un condition (4) , and of 160 molded articles, 26 molded artic were defective, and the remaining articles were good on There were 5 molding operations falling under condition (5) , of 400 molded articles, 123 molded articles were defective, the remaining articles were good ones. Thus, the total num of the defectives was 165. The molded articles that we outside conditions (2) to (5) were all good, and the total numb thereof was 489,112. Therefore, the good ones were 489,955 all including obtained under conditions (2) to (5) . Since t theoretical number of articles that would be produced continuous production for 96 hours was 493,714, the yield of t molding was 99.25 %. Example 2 In this Example, flat trays 26 as shown in Fig. 8 we injection molded. As mold, use was made of one having caviti 24 defined by a stationary side cavity block 21, a movable si cavity block 22, and an ejector core 23. The reference numer 25 indicates an ejector port for the removal of the mold article. This mold has two cavities 24 as shown in Fig. 10, a two molded articles can be obtained by a single injectio Sensors 17 were attached in such a way that two sensors 17 we attached to the upper part and the lower part of the cavity # respectively, and two sensors 17 were attached to the upper pa and the lower part of the cavity #12 respectively there measuring the amount of mold opening. Thus, hereinafte abbreviations "upper #11," "lower #11," "upper #12," and "low #12 " are used. Table 4 and Table 5 show the clamping after kickoff, th maximum value of mold opening, and the return from mold openin after kickoff, which correspond to Table 1 in Example 1. I Table 4, the clamping was made under a pressure of 210 t, and i Table 5, the clamping was made under a pressure of 187 t. Table 4 after 20 min of kickoff after 24 hours of kickoff Maximum of Return from Maximum of Return from Cavity Clamping mold opening mold opening Clamping mold opening mold opening 0 5 8 0 0 6 10 0 0 7 10 0 0 6 8 0 Table 5 after 20 min of kickoff after 24 hours of kickoff Maximum of Return from Maximum of Return from Cavity Clamping mold opening mold opening Clamping mold opening mold opening 0 6 26 0 0 7 27 0 0 8 26 0 Table 6 shows the results of the measurement of the maxim values of mold opening for respective shots in the injecti molding using the molds shown in Figs. 9 and 10. In this cas the clamping force was 187 t, and after the second shot t temperature of the hot runner section was decreased from 250 to 230 °C. As apparent from Table 6, when the temperature the hot runner section changes, then the maximum value of mo opening becomes small. After the fourth shot, short mold articles were obtained. Therefore, by measuring the maxim value of mold opening, the change in the temperature of the h runner section can be monitored indirectly, and also t formation of defective articles can be detected. Table 6 Shot Cavity Upper #11 25 24 20 Lower #11 27 26 21 Upper #12 26 25 20 Lower #12 24 24 19 Table 7 shows the results of the maximum values of t amount of mold opening for respective shots when the temperatu of the hot runner section to the cavity #11 was increased fr 235 °C to 260 °C at the second shot. In the case of the cavi #11, molded articles having burrs were obtained after the eig shot, and in the case of the cavity #12, short molded articl were obtained after the eigth shot. From this, it is consider that the cavity #12 underwent gradually the influence of the mol opening of the cavity #11, and the influence of the cavities up each other can be detected from the amount of mold opening. I Table 7, the mark "*l" falls within the range of good article though having thin burrs, and the mark "*2" indicates defectiv articles having apparent burrs. Table 7 Shot Table 8 shows the results of the measurement of the maxim values of the amount of mold opening in the case wherein from t second shot the temperature of the injection cylinder to melt t synthetic resin was increased by 10 °C, and in the case where from the ninth shot that temperature was increased by a furth 10 °C. In either any of the cavities, the molded articles h burrs from the eleventh shot. Therefore, by measuring t maximum value of mold opening, the change in the temperature the injection cylinder can be monitored indirectly, and also t formation of defective articles can be detected. Table 8 Shot In addition, the inventors have confirmed that other moldi conditions than those mentioned above for example the change i the temperature of cooling water, the change in the amount o cooling water, the change in the clamping force, the change i the amount of gas escaping from the cavity, and a combination o these could be grasped by measuring the maximum value of th amount of mold opening. Then, molding was carried out continuously for 96 hour under the same molding conditions as Example 1, except that th clamping force was adjusted to 187 t, and the period until th takeout of the molded article was 22 sec. In this case, ther were 4 molding operations under condition (2) stated in Exampl 1, and all 40 molded articles were good ones. There were n defective articles in the molding under conditions (3) , (4) an (5) stated in Example 1. There were 31,310 good molde articles, amounting to 31,350 good molded articles in all Since in this continuous molding, the theoretical number of th articles that would be produced was 31,418, the yield of th molding was 99.78 %. Industrial Applicability As stated above, the method of controlling injection moldin according to the present invention can control injection moldin by using as index only the maximum value of mold opening at th time of injection without needing monitoring of many factors tha will lead to the formation of defectives. Thus, the presen controlling method is suitable for injection molding machines fo judging the quality of molded articles with the operation simple, and particularly suitable for controlling multi-cavity injectio molding machines that are liable to have a composite cause many entwined factors. The controlling apparatus for injecti molding according to the present invention can be mounted to injection molding machine in addition to the essential functio can be applied to any one of all conventional injection moldi machines without changing the design, and can be used generally

Claims: CLAIMS 1. A method of controlling injection molding, characteriz in that the maximum value of the amount of mold opening between stationary mold and a movable mold opened by the injecti pressure due to the injection of a melted resin is detected, a this detected maximum value is used as a judgment factor f controlling the injection molding. 2. A method of controlling injection molding as claimed Claim 1, characterized in that multi-cavity injection molding f obtaining a plurality of molded articles in a single injection controlled. 3. An apparatus for controlling injection moldin characterized in that said apparatus is provided with a detecti means of detecting the maximum value of the amount of mo opening between a stationary mold and a movable mold opened the injection pressure of a melted resin, a setting means setting the upper limit value and the lower limit value of t amount of mold opening between the stationary mold and t movable mold corresponding to the quality of the molded articl a judging means of comparing the detection value of sai detecting means with the set value of said setting means and f judging whether the detection value is within the range of t set value or not, and a controlling means of performing contr to handle the molded article that has been molded when sai detection value deviates from the range of the set value. 4. An apparatus for controlling injection molding as claime in Claim 3, characterized in that said controlling means control the molded article that has been molded when said detection val has deviated from the range of the set value in such a way th said molded article may be taken out through a route differe from that for normal molded articles. 5. An apparatus for controlling injection molding as claim in Claim 3, characterized in that when said detection val deviates from the range of the set value, said controlling mea controls said apparatus to display to that effect.

Inventors: YOSHIKAWA YUKIO, YOSHIKAWA, YUKIO
Applicants: NAKAYAMA KOGYO CO LTD, NAKAYAMA KOGYO CO., LTD.
Application year: 1989
Main classification: B29C45
IPC codes: B29C45