Method for controlling temperatures in hot runners of multi-cavity injection mold, method for warning, and control system based on those methods

A method for controlling temperatures in hot runners of a multi-cavity injection mold, a warning method, and a control system based on those methods are provided, in which a temperature sensor is positioned at the same location as each of the cavities of the mold, one of the cavities is chosen as a standard cavity, and a standard filling time is defined. Besides, in every injection cycle, a calculating and controlling module is to calculate the differences between the standard filling time and the filling times of the cavities, and according to the differences, the temperatures in the hot runners may be adjusted by a temperature-adjusting device and a warning device may be started. So, the volumetric filling of the cavities can be balanced very quickly, the process can avoid fluctuations of external environment so as to reduce the time for product development, and the quality of production can be maintained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to multi-cavity injection molding and more particularly, to a method for controlling temperatures in hot runners of a multi-cavity injection mold, a warning method for a multi-cavity injection mold, and a control system based on those methods.

2. Description of the Related Art

The industries of semiconductor, optoelectronics, and ICT (information and communication technology) develop so fast that the market demand for varied specifications of consumer electronics and optoelectronics, which are light, thin, high-precision, and exquisite, is increasing. Therefore, domestic and foreign injection molding factories think highly of multi-cavity injection molding which has the advantages of mass production within a short time and resultant cost savings. However, it is subject to the defects of short shot, warpage, and different weights of the products, which result from the filling of the multi-cavity injection mold is unbalanced, which means that the volumetric fillings of individual cavities of the multi-cavity injection mold are not uniform, so that the production has low yield rate and needs long time for development.

To resolve the above-mentioned problems, a conventional method for controlling temperatures in hot runners of a multi-cavity injection mold is first positioning a temperature sensor at the end of the filling path of each cavity to send a temperature signal to a temperature controller, and then adjusting the temperatures in the hot runners by the temperature controllers so as to balance the volumetric filling of the cavities. Furthermore, a foreign-developed controlling method is defining a standard filling time as the average of the maximum and minimum filling time of the cavities which are spent on filling up the cavities respectively, and adjusting the temperatures in the hot runners after each injection cycle to make the filling time of the cavities of the next cycle closer to the standard filling time of the present cycle. As a result, the aforesaid method can balance the volumetric filling of the cavities after several injection cycles.

However, in aforesaid method, before the volumetric filling of the cavities is balanced, a new average was worked out after every injection cycle, which means that the standard filling time is changed constantly and susceptible to fluctuations of external environment. Besides, products made in the balanced condition may not meet the quality requirements, so the process parameters should be further adjusted. As a result, the product development of multi-cavity injection molding based on the conventional method not only requires a very long time but fails to work out satisfactory products.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the above-noted circumstances. It is an objective of the present invention to provide a method for controlling temperatures in hot runners of a multi-cavity injection mold and a control system based on the method, which can avoid fluctuations of external environment and balance the volumetric filling of the cavities very quickly so as to reduce the time of product development.

To attain the above objective, the present invention provides a method for controlling temperatures in hot runners of a multi-cavity injection mold which comprises steps of: (a) positioning a temperature sensor in the same location of each of several cavities of the multi-cavity injection mold; (b) choosing one of the cavities as a standard cavity and defining a standard filling time as time required from the beginning of injecting a material into the standard cavity till the material contacts the temperature sensor in the standard cavity; (c) injecting the material into the cavities through the hot runners which are connected with the cavities respectively, measuring time from the beginning of injection till the material contacts the temperature sensor in each cavity as a filling time of the cavity, and calculating the difference between the standard filling time and the filling time of each cavity as a temporal offset of the cavity; (d) if the temporal offset of at least one of the cavities is larger than a first preset value, adjusting the temperature in the hot runner which is connected with said cavity; and (e) repeating the steps (c) and (d) until the temporal offset of each cavity is smaller or equal to the first preset value.

Furthermore, the present invention provides a control system based on the aforesaid method for controlling temperatures in hot runners of a multi-cavity injection mold. The control system comprises several temperature sensors positioned in several cavities of the multi-cavity injection mold respectively for generating a temperature signal each; a calculating and controlling module for receiving the temperature signals generated by the temperature sensors and calculating temporal offsets of the cavities; and a temperature-adjusting device controlled by the calculating and controlling module for adjusting temperatures in the hot runners which are connected with the cavities respectively.

As a result, the aforesaid control system and method can be applied in the development stage of a product, avoid fluctuations of the external environment, and balance the volumetric filling of the cavities very quickly. Besides, the temperature parameters of the hot runners worked out in the method can be used in the subsequent production of the same product, and the products from each cavity can meet the quality requirements so that the product can proceed to the production stage. In other words, the control system and the method can efficiently reduce the time of product development.

It is another objective of the present invention to provide a warning method for a multi-cavity injection mold and a control system based on the warning method, which can supervise the quality of the products.

To attain the above objective, the present invention provides a warning method for a multi-cavity injection mold, which comprises steps of: (a) positioning a temperature sensor in the same location of each of several cavities of the multi-cavity injection mold; (b) choosing one of the cavities as a standard cavity and defining a standard filling time as time required from the beginning of injecting a material into the standard cavity till the material contacts the temperature sensor in the standard cavity; (c) injecting the material into the cavities through the hot runners which are connected with the cavities respectively, measuring time from the beginning of injection till the material contacts the temperature sensor in each cavity as a filling time of the cavity, and calculating the difference between the standard filling time and the filling time of each cavity as a temporal offset of the cavity; and (d) repeating the step (c) several times, and then starting a warning device if the temporal offsets of at least one of the cavities worked out in a plurality of continuous times of the step (c) are larger than a second preset value.

Furthermore, the present invention provides a control system based on aforesaid warning method, which comprises several temperature sensors positioned in several cavities of the multi-cavity injection mold respectively for generating respective temperature signals; a calculating and controlling module for receiving the temperature signals generated by the temperature sensors and calculating temporal offsets of the cavities; and a warning device controlled for activation by the calculating and controlling module.

In light of the above, the aforesaid control system and warning method can be applied to the production stage of products. In the continuous production process, the activated warning device can alert the engineers that something is wrong with the products, thus supervising the quality of the products.

DETAILED DESCRIPTION OF THE INVENTION

As shown inFIG. 1, a control system10in accordance with a preferred embodiment of the present invention includes several temperature sensors20, a calculating and controlling module30, a temperature-adjusting device40, and a warning device50.

The control system10is installed into several cavities (not shown) of the same shapes and into several hot runners (not shown) connected with the cavities respectively. In the molding process, a molten material is injected into the cavities through the hot runners respectively, and then the products of the same shape are formed in the cavities respectively.

In the embodiment, a mold with four cavities is instanced, and the temperature sensors20are positioned at the same locations of the cavities respectively, which means that the control system10has four temperature sensors20. It is preferable to position each temperature sensor20in the final part, especially where the filling path of the cavity reaches 95-98%, so that the temperature sensors20can sense a sudden rise in temperature when contacting the molten material so as to indicate that the cavity is almost full.

The calculating and controlling module30can receive the temperature signals generated by the temperature sensors20and calculate the time intervals between the beginning of injection and when the temperature sensors20senses a sudden rise in temperature respectively, i.e. when the temperature sensors20contacts the molten material. Then, the filling time for each of the cavities is inferable based on the time interval. Besides, the calculating and controlling module30can control the temperature-adjusting device40for adjusting the temperatures in the hot runners. The warning device50is also controlled by the calculating and controlling module30to emit lights, sounds or other signals to call attention, or to stop the operation of the production equipment.

The aforesaid control system10can take a method for controlling temperatures in hot runners of a multi-cavity injection mold to be applied to the product process development. The method is shown inFIG. 2and includes the steps described below:

(a) Position a temperature sensor20in the same location of each of multiple cavities of the multi-cavity injection mold. In the embodiment, the mold has four cavities.

(b) Choose one of the cavities as a standard cavity and define a standard filling time60as a time interval between the beginning of injecting a material into the standard cavity and when the material contacts the temperature sensor20in the standard cavity. The standard cavity and the standard filling time60can be defined through simulation and experiment, numerical methods based on the properties of plastics, or another customized way. In the embodiment, the cavity No. 2 is taken as the standard cavity, so the standard filling time60is the time required for filling the cavity No. 2.

(c) Inject the material into the cavities through the hot runners which are connected with the cavities respectively, measure the time from the beginning of injection till the material contacts the temperature sensors20in the cavities Nos. 1-4 and define it as a filling time61,62,63, or64of the cavity respectively, and then calculate the difference between the standard filling time60and each filling time61,62,63, or64as a temporal offset of the cavity respectively.

(d) If the temporal offset of at least one of the cavities is larger than a first preset value V1, adjust the temperature in the hot runner connected with said cavity whose temporal offset is too large via the temperature-adjusting device40. The first preset value V1can be set as any acceptable tolerance, or as the tolerance calculated from three sigma (standard deviation) rule, which is commonly applied to quality control, taking the standard deviation of the filling time61,62,63, or64calculated by taking the standard filling time60as the mean value. The purpose of adjusting the temperature in the hot runner by the temperature-adjusting device40is to make the filling time of the cavity in the next injection cycle closer to the standard filling time60. The temperature-adjusting device40is controlled by the calculating and controlling module30which is based on, but not limited to, the fuzzy control method.

(e) Repeat the steps (c) and (d) until the temporal offset of each cavity is smaller or equal to the first preset value V1.

In this way, the volumetric filling of the cavities is balanced and thus the products from the cavities are uniform and satisfactory. Because the standard filling time60is a constant in the whole process, the method can be excused from the fluctuations of the external environment so that the temperature parameters of the hot runners worked out in the method can be applied to many production lines to make the same products by means of the same molds. In other words, the product can proceed to the production stage.

The control system10can be further applied to the production stage for supervising the quality of the products by taking a warning method. The warning method is firstly to repeat the aforesaid step (c) several times, which means repeating injection cycle and in every injection cycle measuring the temperatures in the cavities by the temperature sensors20and calculating the temporal offsets of the cavities. Then, if the temporal offsets of the same one of the cavities worked out in a plurality of continuous times of the step (c) are larger than a second preset value, activate the warning device50by the calculating and controlling module30to emit warning signals to remind the engineers to do necessary check and adjustment.

In aforesaid warning method, the second preset value can be an acceptable tolerance identical to or different from the first preset value V1, or be the tolerance calculated in accordance with the three sigma rule. The activated warning device50can inform the engineers that something is wrong with the production line. It is possible that the problem occurred in the standard cavity, and in that event, adjusting the hot runner connected with the standard cavity by the temperature-adjusting device40can restore the production line to make satisfactory products.

Furthermore, the control system10can be applied to inspect if the temperature of the material in the cavities is out of a temperature range which can be set as the molding temperature range of the material. Specifically speaking, the warning device50can be set to start if the temperature sensor20in the same one of the cavities sense temperature out of the temperature range in a plurality of continuous times of the step (c).

In addition to aforesaid warning method for single cavity, the present invention also provides a warning method for multiple cavities, which is described below.

The warning device50can be set to start if the temporal offsets of an amount of the cavities worked out in a plurality of continuous times of the step (c) are larger than the second preset value to inform the engineers that several cavities have problems. Then, the temperatures in the hot runners can be all readjusted. The amount mentioned before can be set as an acceptable number, and in the embodiment, it is set as one third of the total amount of the cavities.

Besides, the warning device50also can be set to start if at least one third of the temperature sensors sense that the temperature rises beyond the molding temperature range of the material in a plurality of continuous times of the step (c). Then, the temperature in the hot runner connected with the standard cavity can be readjusted, or, the temperatures in the hot runners can be all readjusted.

In aforesaid warning methods for single cavity and multiple cavities, it is preferable to start the warning device50after said unusual situation occurred in three continuous times of the step (c). However, the number of times can be plural, not limited to three.

The aforesaid control system10and method for controlling temperatures can not only reduce the time of development of a multi-cavity injection molding product, but also maintain the quality of production. It can be learned from the above description that in the product development stage, the control system10can include none of the warning device50. Besides, in the production stage, the control system10can include none of the temperature-adjusting device40. In that event, the control system10can take another warning method which neither includes the aforesaid the steps (d) and (e), in which the temperatures in the hot runners may be adjusted, nor the process of adjusting the temperatures in the hot runners after unusual situation occurred, either. In other words, the warning method only function as warning the engineers of unusual situations in need of proper treatment so as to recover the quality of the subsequent products.

It is emphasized here that the control system10provided in the present invention centers on sensing the temperatures in the multiple cavities and the calculation. So, the control system10mainly includes the temperature sensors20and the calculating and controlling module30. If adjusting the temperatures in the hot runners is needed, the temperature-adjusting device40can be included into the control system10. If supervising the quality of the products by emitting warning signals is needed, the warning device50can be included into the control system10. Therefore, the control system10can be variously embodied.