Method for controlling fluctuation in flow property of resin in injection molding machine

• US 5,419,858 A
• Filed: 11/30/1992
• Issued: 05/30/1995
• Est. Priority Date: 11/28/1991
• Status: Expired due to Fees

• Current Assignee: KAO Corporation
• Original Assignee: KAO Corporation
• Inventors: Hata, Masaharu, Nonomura, Akira
• Primary Examiner(s): Vargot, Mathieu D.
• Application Number:
  US07/983,140
• Time in Patent Office: 911 Days
• Field of Search: 264/40.1, 264/40.5, 264/40.6, 264/328.14, 264/328.15, 264/328.16
• US Class Current: 264/40.5
• CPC Class Codes: B29C 45/76 Measuring, controlling or regulating measuring in general G01; controlling or regulating in general G05
• CPC Class Codes: B29C 45/77 of velocity or pressure of moulding material

Abstract

Molded articles having a constant quality can be obtained at all times irrespective of a fluctuation in resin properties (especially flowability). An output signal from an injection pressure sensor is sampled by a sampling circuit, and an injection-pressure waveform is obtained from injection-pressure data by means of a processing unit. If injection time fluctuates in the injection-pressure waveform, a constant-pressure injection process is judged to be in effect. If the maximum value of injection pressure fluctuates, then the process is judged to be a constant-speed injection process. The set temperature in a temperature setting unit is changed in dependence upon a fluctuation in injection time in the constant-pressure injection process and in dependence upon a fluctuation in the maximum value of injection pressure in the constant-speed injection process. The resin temperature is controlled by controlling heaters via temperature controllers. As a result, injection time or the maximum value of injection pressure is held substantially constant at all times, and so is the flowability of the resin.

Claims

1. A method of judging a molding process for controlling a fluctuation in resin flow property in an injection molding machine, comprising the steps of:

(a) obtaining a signal representing injection pressure from a sensor provided in at least one of an injection cylinder of the injection molding machine and a hydraulic circuit for driving the injection molding machine;

(b) sampling said signal from said sensor for a period of time beginning prior to a start of an injection stage of a molding cycle and extending for an amount of time which exceeds a likely injection time;

(c) detecting a rise in injection-pressure data obtained by said step of sampling, and judging that a point in time corresponding to the rise is an injection starting time;

(d) detecting a peak value of the injection-pressure data other than a peak of the injection-pressure data which may appear immediately after the injection starting time;

(e) judging that a point in time corresponding to the peak value, determined by said step of detecting a peak value, is an injection end time;

(f) calculating, as an injection time, a period of time from the injection starting time to the injection end time;

(g) obtaining the peak value of the injection pressure and the injection time in a molding cycle of the injection molding machine over a plurality of molding cycles by repeating above steps (a) to (f);

(h) examining whether a fluctuation in flow property of a resin material supplied to the injection molding machine appears as a fluctuation in the injection time or as a fluctuation in the peak value of the injection pressure; and

(i) judging that a constant-pressure injection process is in effect when the fluctuation appears as a fluctuation in the injection time and a constant-speed injection process is in effect when the fluctuation appears as a fluctuation in the peak value of the injection pressure.

2. A method according to claim 1, wherein when it is judged that a constant-pressure injection process is in effect, said method further comprising the steps of:

measuring actual injection time;

obtaining a degree of fluctuation in the measured actual injection time with respect to a standard injection time;

judging whether the degree of fluctuation obtained exceeds a predetermined value; and

adjusting injected resin temperature so that actual injection time will become substantially equal to the standard injection time if the degree of fluctuation obtained exceeds the predetermined value.

3. A method according to claim 1, wherein when it is judged that a constant-speed injection process is in effect, said method further comprising the steps of:

measuring the peak value of actual injection pressure;

obtaining degree of fluctuation in the peak value of measured actual injection pressure with respect to a peak value of standard injection pressure;

judging whether the degree of fluctuation obtained exceeds a predetermined value; and

adjusting injected resin temperature so that the peak value of actual injection pressure will become substantially equal to the peak value of standard injection pressure if the degree of fluctuation obtained exceeds the predetermined value.

4. A method of judging a molding process for controlling a fluctuation in resin flow property in an injection molding machine, comprising the steps of:

measuring an injection-pressure waveform in a molding cycle of the injection molding machine over a plurality of molding cycles;

examining whether a fluctuation in flow property of a resin material supplied to the injection molding machine appears as a fluctuation in actual injection time or as a fluctuation in a maximum value of actual injection pressure in the injection-pressure waveform;

judging that a constant-pressure injection process is in effect when the fluctuation appears as a fluctuation in actual injection time;

measuring an actual injection time;

obtaining a degree of fluctuation in the actual injection time with respect to a standard injection time;

judging whether the degree of fluctuation obtained exceeds a predetermined value; and

adjusting injected resin temperature so that actual injection time will become substantially equal to the standard injection time if the degree of fluctuation obtained exceeds the predetermined value.

5. A method of judging a molding process for controlling a fluctuation in resin flow property in an injection molding machine, comprising the steps of:

measuring an injection-pressure waveform in a molding cycle of the injection molding machine over a plurality of molding cycles;

examining whether a fluctuation in flow property of a resin material supplied to the injection molding machine appears as a fluctuation in actual injection time or as a fluctuation in a maximum value of actual injection pressure in the injection-pressure waveform;

judging that a constant-speed injection process is in effect when the fluctuation appears as a fluctuation in said maximum value of actual injection pressure;

measuring the maximum value of actual injection pressure;

obtaining a degree of fluctuation in the maximum value of actual injection pressure with respect to a maximum value of standard injection pressure;

judging whether the degree of fluctuation obtained exceeds a predetermined value; and

adjusting injected resin temperature so that the maximum value of actual injection pressure will become substantially equal to the maximum value of standard injection pressure if the degree of fluctuation obtained exceeds the predetermined value.