JPS60169738A - Defective product detecting method of injection molded product - Google Patents

Abstract

PURPOSE:To judge the quality of synthetic resin products under production accurately and automatically, by measuring the weight of the injection molded product for every one shot continuously, and comparing the weight of the molded product with the weight of the molded product in the previous shot. CONSTITUTION:In the injection molding process of a synthetic resin, the weight of the molded product in the first shot is measured by an electronic scale. Then the weight of the molded product in the second shot is measured. Then, whether the weight of the second-shot molded product is within the allowance or not with respect to the weight of the first-shot molded product or not is operated by an upper limit comparator and a lower limit comparator. For example, when the weight of the first-shot molded product is 200g, the allowance is made to be 0.3-0.5g. Even though a metal-mold temperature 3 is adjusted at a specified temperature, the temperature of an injection molding machine is increased with the number of shots during the operation. The weights of the molded products at the higher number of the shots become light as shown by a line 1. The weights of the molded shot products are measured continuously and compared with those of the previous molded shot products. Whether the weights are within the allowance or not is operated and the selection is performed. Therefore the quality of the molded product can be automatically judged accurately.

Description

[Detailed Description of the Invention] <Technical Field of the Invention> The present invention relates to a method for detecting defects in injection molded products, and particularly to a method for detecting defects in injection molded products that can accurately distinguish between non-defective products and defective products. be.

Background of the Technology and Problems in the Conventional Problems When synthetic resin products are continuously injection molded using an injection molding machine, sometimes defective products such as 7-pieces and 9-pieces are sometimes molded. Even in injection molding machines equipped with highly improved control mechanisms in recent years, the above-mentioned phenomenon occurs, but this is due to the effects of so-called external disturbances such as opening and closing of the molding room door and changes in room temperature. It is believed that the main cause is
It is extremely difficult to completely prevent such disturbances.

If injection molding equipment is fully automatic and operated unmanned, there is a high risk that defective products molded due to the above disturbances will be disposed of as non-defective products. , Accurate determination of defects has traditionally been a major problem in quality control.

<Purpose of the Invention> The present invention has been made by focusing on such conventional problems, and its purpose is to eliminate defective products from B when a defective product is molded during the injection molding operation of synthetic resin products. It is an object of the present invention to provide a method for detecting defects in injection molded products that can automatically and accurately determine the characteristics of a defective product, and can perform separation processing of defective products without error, thereby solving the above-mentioned conventional problems.

<Structure of the Invention> In order to achieve the above object, the present invention measures the weight of a molded product in a shot (referred to as a first molded product for convenience) in a synthetic resin injection molding process, and Based on the weight of the first molded product, determine the allowable weight range of the next molded product (this is referred to as the second molded product), measure the weight of this second molded product, and compare it with the above reference weight. While detecting defects, if there are no defects, the weight of this second molded product is used as a reference to detect serious defects in the next molded product (this is called the third molded product). That is.

The characteristics of the present invention are based on the following analysis results conducted by the present inventor on injection molded products.

Generally, when molded products that are defective due to sink marks or short shots are weighed, they are slightly lighter than other non-defective products. For example, the standard weight is 200
Looking at g molded products, in most cases defective products are 0.3
~05g lighter. However, contrary to the above example, even if molded products look the same on the outside and have no functional abnormalities, their weight can vary depending on the molding conditions. In terms of products, even a difference of 0.5 g (or more) may not cause any practical problems. In other words, in the latter case, even though the molded product is 0.5g lighter than the standard product, there are no sink marks or short shots during injection molding, and it should be judged as a "good product". It is. In order to find out why the former "defective products" and the latter "good products" appear, the present inventor investigated the relationship between the total temperature inside the mold and the weight of the molded product at each shot, and as a result, the results shown in Figure 1 are as follows. A graph like the one shown in was obtained. As is clear from this graph, the weight of the molded product gradually decreases as the overall temperature inside the mold increases. This means that when injection molding of synthetic resin products is performed continuously, the standard weight for the molded product changes (specifically, it gradually decreases) as the number of stitches increases. do. When starting molding, even if the mold temperature is kept constant using a mold temperature controller, the molded product is affected by the temperature of the inside surface of the mold, that is, the surface where the injected molten resin comes into contact with the mold. Therefore, no matter how you adjust the mold temperature, the tendency shown in Figure 1 cannot be avoided. Therefore, by simply setting a standard weight, measuring the weight of the molded product, and comparing it with this standard weight, it is not possible to accurately determine whether the product is good or bad. According to the above-mentioned gist of the present invention, when the weight of the molded product is continuously measured for each shot, the weight of the molded product changes very slightly, but not suddenly, as shown in FIG. However, it is within a certain tolerance range (indicated by the dotted line in Figure 1), so if you set the tolerance range from the results for each shot, anything that deviates from the tolerance range will be a sink mark or short shot. It can be determined that there is a risk of such defects. The present invention utilizes such molding characteristics to determine whether a molded product is defective by comparing the weight of each shot with the molded product from the previous shot. It has the characteristics of

<Description of Embodiments> FIG. 2 is a diagram showing an embodiment of a control circuit for carrying out the method for detecting defects in injection molded products of the present invention. In this figure, reference numeral 1 denotes an electronic scale for measuring the weight of a molded product made by injection molding, and the measured values from this electronic scale 1 are input to a storage section 2 and a comparison section 3. The comparison section 3 is equipped with an upper limit comparator 3a that detects the upper limit of the allowable weight of the molded product, and a lower limit comparator 3b that detects the lower limit of the allowable weight.

The upper limit comparator M3a is connected to the upper limit weight setting section 7 and the calculation section 4 in parallel via manual/auto switching switches S1 and 83, and the lower limit comparator 3b is connected to the manual/auto switch S1 and 83. - The lower limit weight setting section 8 and the calculation section 5 are connected in parallel to each other via the auto-switching switches S2 and 84. When defective molded products are detected by manual setting, switches S, . . . S2 are turned on, and when detection is performed by automatic operation, switches S, . The calculation units 4 and 5 are both connected to the storage unit 2 via the switch S5 so that the weight data from the storage unit 2 is sent thereto. A range unit 6 for setting upper and lower allowable values is connected.

When manually detecting defects in a molded product using such a control circuit, first the upper limit weight setting section 7 is set to an upper limit weight allowed for the molded product, while the lower limit weight setting section 8 is set to a lower limit weight. Then, when the switches Sl and S2 are turned on, the weight of the molded product measured by the electronic scale 1 is stored in the storage section 2, and is also set in the upper limit weight setting section in the comparison section 3 using the lower limit comparator 3a. The molded product is compared with the data from the lower limit weight setting unit 8 using the lower limit comparator 3b, and whether the molded product is good or bad is detected. When it is determined that the product is good, the switch S5 is turned on 9, and the weight stored in the storage unit 2 is sent to the calculation units 4 and 5, where the upper and lower allowable values set in the range unit 6 are added. Alternatively, the reference value for the next shot is determined by subtraction. When changeover switch S is set to auto, switch S3. S4 is turned on and switch S,...
Since S2 is turned off, the weight of the molded product at this stage is compared with a reference value based on the previous weight of the molded product in the upper and lower limit comparators 3a and 3b, and it is detected whether the weight exceeds the weight. If the changeover switch S is set to auto in this way, the above process is repeated for each shot and the weight of the molded product from the previous shot can be constantly compared, but if an abnormal shock occurs during the molding operation, switch S5 Since it remains off, the weight of the molded product measured in the previous simulation remains set in the calculation units 4 and 5, and is used again as the reference weight value. Therefore, the weight of the molded product obtained from an abnormal shot is not used as a reference weight to detect defects in subsequent molded products, and the weight of the molded product is completely automatically monitored for each shot to detect defects in the molded product. can be detected.

<Effects of the Invention> As explained above, according to the present invention, the weight of the molded product is continuously measured for each shot, and in each shot, the weight of the molded product is compared to the weight of the molded product of the previous shot. Since defects in the molded product are detected by comparison with the number of juts, it is possible to accurately detect defects in consideration of the molding characteristic in which the weight of the molded product gradually increases or decreases as the number of juts increases.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the change in temperature inside the mold and the weight of the molded product for each shot from the start of injection molding of synthetic resin, and Fig. 2 is a graph showing the change in the molded product weight for each shot from the start of injection molding of synthetic resin. FIG. 3 is a diagram showing an example of a control circuit. 1...Electronic scale, 2...Storage unit, 3...
Comparison section, 4.5... Calculation section, 6... Range section, 7, 8... Manual setting section. Patent applicant Orion Kasei Co., Ltd. Procedural amendment (voluntary) 1. Indication of the case 1982 Patent Application No. 25607 2 Name of the invention Method for detecting defects in injection molded products 3 Person making the amendment Relationship to the case Patent applicant Orion Kasei Co., Ltd. 4 Agent address 105 Tokyo 1-20-5, Toranomon 1-chome, Minato-ku, Section 6 of “Detailed Description of the Invention” of the specification to be amended, Contents of the amendment

Claims (1)

[Claims] 1) In the injection molding process of synthetic resin, the weight of the first molded product in the shot is measured, and
The weight of the second molded product to be shot next is determined based on the weight of the molded product, and the weight of the second molded product is measured and compared with the reference weight to detect defects. If not, use this second
The third shot is then shot based on the weight of the molded product.
A method for detecting defects in injection molded products, characterized in that defects in the molded products are sequentially detected by determining a permissible weight range for the molded products. 2) When a defect in the molded product is detected by comparing the molded product weight with the reference weight, the reference weight is further used as the reference weight for the next injection molded product. A method for detecting defects in injection molded products according to claim 1.