Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
2000-08-24
2003-07-01
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S328100, C425S155000, C425S542000
Reexamination Certificate
active
06585919
ABSTRACT:
This application is based on Japanese Patent Application No. 11-258800 filed on Sep. 13, 1999, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and an apparatus of an injection molding, which are arranged to successively mold articles made of a resin material. More particularly, the present invention is concerned with a novel method and a novel apparatus of an injection molding, which assure a sufficiently high degree of stability of a heat history of the resin material and a temperature of a mold, in every molding cycle, while permitting an execution of a successive injection molding of the resin material with high stability.
2. Description of the Related Art
As one type of an injection molding machine, there is known an injection molding machine, such as an inline-screw-type injection molding machine, a plunger-type (torpedo-type) injection molding machine and a preplasticating injection molding machine, wherein an injection screw or plunger which is reciprocally movably disposed in a bore of a heating cylinder is rotated so that a resin material is heated to be molten and metered in the heating cylinder. Successively, the injection screw or plunger is moved so as to inject the resin material into a mold cavity of a mold which is clamped by a suitable clamping device. The resin material filling the mold cavity is held within the cavity under a predetermined holding pressure and then cooled for a predetermined period of time. Then, the mold is opened and the molded product is ejected or released from the mold cavity, thereby obtaining a desired molded product. Such an injection molding machine is operated to perform repeatedly a cycle of molding operations so as to successively form a multiplicity of desired products.
In order to produce successively the desired products with a desired good quality, by means of the injection molding machine, there is required that a molding condition is kept substantially constant in every molding cycle. In particular, it is important that a heat history of the resin material and a temperature of the mold are kept substantially constant in every molding cycle.
However, one molding cycle includes various kinds of steps such as a cooling step wherein a time of the step is controlled, a mold closing and opening step wherein an operation velocity of the injection molding machine is controlled by adjusting an amount of discharge of a hydraulic pump, and an injection step wherein an injection pressure or a position of the injection screw are controlled. Therefore, it is difficult to keep the injection molding condition substantially constant, and a conventional injection molding machine inevitably is likely to suffer from variation in heating conditions and heating times of the resin material or the mold, leading to difficulty in keeping the heat history of the resin material and the temperature of the mold substantially constant in the every molding cycle, upon performing the above-indicated successive injection molding. Due to this drawback, the conventional injection molding machine may be insufficient in attaining a desired degree of stability in quality of the products, depending on kinds of the products.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method of injection molding for successively producing a resin product by repeatedly performing an injection molding cycle, which method permits a high degree of stability of molding conditions in terms of a heat history of a resin material and a temperature of a mold, in every molding cycle, thereby permitting successive production of the resin products with a stabilized quality thereof.
It is a second object of the invention to provides an injection molding apparatus which is novel in construction and which permits that molding conditions such as a heat history of a resin material and a temperature of a mold are kept substantially constant, during its successive injection molding operation, thereby permitting a successive production of desired resin products with a stabilized quality thereof.
The first object may be achieved according to a first aspect of this invention, which provides a method of injection molding for repeatedly performing an injection molding cycle including the steps of closing and clamping a mold having a mold cavity, injecting a resin material into the mold cavity, cooling and solidifying said resin material filling the mold cavity, and opening the mold so as to remove a molded product, in order to successively form the molded product, the method comprising the steps of: (a) measuring a cycle time at at least one measuring point in the injection molding cycle to thereby obtain a measurement of the cycle time; (b) obtaining a difference between the measurement of the cycle time and a predetermined reference cycle time; and (c) executing a time compensation on the basis of the difference at a time controlled step which is arranged to be executed before the next measuring point comes.
In the injection molding method according to the first aspect of the invention, the entire time required to execute one injection molding cycle is suitably controlled to be made substantially constant, although the injection molding cycle includes steps which are not controlled based on time. Therefore, the present method is capable of restricting or reducing an amount of variation in the cycle time of each injection molding cycle, making it possible that a period of time required from a current injection action to a next injection action is kept substantially constant. Thus, the present method permits a substantially constant molding conditions in terms of the heat history of the resin material and the temperature of the mold, in the every molding cycle.
For the above reasons, the present injection molding method assures an improved stability in quality of the products formed by the successive injection molding, while effectively attaining a sufficiently reduced ratio of reject of the molded product and an improved yield of the molded product.
It is noted that the measuring point for measuring the cycle time may be previously fixed to a point or points in the injection molding cycle, but not particularly limited. For instance, the measuring point may preferably be set to any point in the cycle at which an electric signal is generated. In this case, the electric signal is advantageously utilized to measure the cycle time. More specifically, the measuring point is set to a point in the cycle at which the injection molding cycle changes its steps. Namely the point may preferably be an initiation or a completion point of a mold clamping operation, an initiation or a completion point of an injection operation, for example. In this respect, the electric signal may be an output signal of a positioning sensor like a limit switch, an output signal of a timer or a time counter, for example.
The reference cycle time may be set to a desired value by a manual operation. It is preferable that the cycle time is timed in every molding cycle and if a desired product is obtained, then the timed cycle time is set as the reference cycle time. It is noted that the reference cycle time may be suitably changed taken into account molding conditions or the like.
The time compensation based on the obtained difference between the measurement of the cycle time and the reference cycle time may be executed at any one or more of the time controlled step(s) in the injection molding cycle. In this respect, the time controlled step should be interpreted as a step wherein a time or period of the step is controlled. For an effective time compensation, the time compensation is executed as follows: In this case where an injection molding cycle includes a plurality of measuring points for measuring the cycle time, if the difference is obtained in a current measuring point, then the time compensation based on the obtained difference should be executed until the next measu
Heitbrink Jill L.
Kabushiki Kaisya Meiki Seisakusyo
Oliff & Berridg,e PLC
LandOfFree
Method and apparatus for injection molding wherein cycle... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for injection molding wherein cycle..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for injection molding wherein cycle... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3089580