US 4,161,380 A · Injection molding process control

Abstract

Both a method and apparatus are disclosed for controlling a cyclically operated injection molding machine such that uniform, high quality molded articles are repeatedly produced from plasticized synthetic resinous material. The method and apparatus include integration of a sensed injection pressure with respect to time from the beginning of an injection stroke until plasticized material in a mold reaches a predetermined pressure. The integration defines a work index which is compared with a preset allowable range. If the work index lies outside the preset range, an adjustment is made to the back pressure acting on the plasticizing screw during the plasticizing portion of the subsequent molding cycle. The apparatus is permitted to make a predetermined number of adjustments in the back pressure after which a suitable indication is made that the molding apparatus is out of control itself. Other viscosity-affecting parameters may be controlled including injection screw rotary speed and injection screw velocity, and barrel temperature of the plasticizing apparatus. A mold cavity pressure sensor indicates that the cavity is full, and thereupon stops the integration and may also reduce the injection pressure to a lower value, sufficient to supply additional material to compensate for shrinking due to cooling, yet not high enough to introduce strains, or cause flashing.

Claims12

Dependent claims

In an automatically controlled injection molding apparatus having a process control means for producing uniform, high quality articles from synthetic resinous material, the improvement comprising:

material pressure sensing means for sensing the pressure of plasticized synthetic resinous material in the mold;
injection pressure sensing means for sensing the pressure of hydraulic fluid during the injection portion of the molding cycle;
integration means operable to integrate the work parameter of the injection molding apparatus during the injection portion of the molding cycle to obtain a work index;
initiating means for starting the integration means approximately with the inception of the injection portion of the molding cycle;
terminating means for stopping the integration means when the material pressure sensing means indicates a predetermined value;
and
feedback means for making a compensatory adjustment in a viscosity-affecting parameter of the molding apparatus during subsequent molding cycles thereof and being activated by a signal from said process control means in response to the value of the work index.

4 more elements

Apparatus for cyclically controlling an injection molding machine during injection molding of uniform, high quality articles from synthetic resinous material, comprising:

first sensing means for generating a first signal representing pressure of synthetic resinous material in a mold;
second sensing means for generating a second signal representing a work parameter;
adjustment means for changing a viscosity-affecting parameter of subsequent cycles in response to a command signal;
and
process control means for controlling a molding cycle having a plasticizing portion, an injection portion and a holding portion, the process control means including
an integrator for generating a work index by integrating said second signal with respect to time during said injection portion until said first signal attains a predetermined value,
a comparator for determining if the work index is within the predetermined allowable range, and
means for generating an appropriate command signal to said adjustment means when the work index is outside the predetermined allowable range, whereby the failure of the work index to lie within the predetermined allowable range effects a variation in the plasticizing portion of subsequent cycles such that the work index of subsequent cycles will more likely fall within the predetermined allowable range.

5 more elements

Dependencies are inferred from the claim text.

Injection molding process control

Life of this patent

Injection molding process control

Life of this patent

Abstract

Claims12