Method for injection molding of high quality parts

• US 6,287,488 B1
• Filed: 02/02/1999
• Issued: 09/11/2001
• Est. Priority Date: 02/02/1998
• Status: Expired due to Term

• Current Assignee: Superior Industrial, Inc., Thomas C. Dougherty, Thomas J. Dougherty
• Original Assignee: Thomas J. Dougherty
• Inventors: Dougherty, Thomas J., Dougherty, Thomas C.
• Primary Examiner(s): HEITBRINK, JILL LYNNE
• Application Number:
  US09/240,711
• Time in Patent Office: 952 Days
• Field of Search: 264/328.7, 264/2.2, 264/102, 425/808, 425/810, 425/150
• US Class Current: 264/2.2
• CPC Class Codes: B29C 2045/567 Expelling resin through the gate
• CPC Class Codes: B29C 45/561 Injection-compression moulding
• CPC Class Codes: B29L 2011/0016 Lenses
• CPC Class Codes: B29L 2017/005 CD''s, DVD''s

Abstract

A method and apparatus for injection molding of high quality thermoplastic parts is such that a conventional movable mold half is mounted on a movable platen of the injection molding machine, and a special stationary mold half is mounted on the stationary platen. The stationary mold half includes a stationary plate secured to the stationary platen, with the stationary plate including stationary mold inserts. Each stationary mold insert has a stationary mold insert surface. An A-half parting line plate is movably attached to the stationary plate, with the A-half parting line plate being movable with respect to the stationary plate and the stationary mold inserts. A driving device, such as a hydraulic cylinder, is disposed between the stationary plate and the A-half parting line plate, with the driving device driving the A-half parting line plate toward and away from the stationary plate. A control circuit is provided for controlling the driving device to control a movement of the A-half parting line plate with respect to the stationary plate.

Claims

1. A method of injection molding thermoplastic parts, said method comprising the steps of:

providing a movable mold half to be mounted on a movable platen of an injection molding machine, said movable mold half including a B-half parting line plate and at least one movable mold insert surface thereon;

providing a stationary mold half to be mounted on a stationary platen of the injection molding machine, said stationary mold half including a hydraulic cylinder plate which is configured to be fixedly attached to the stationary platen, at least one stationary mold insert fixedly attached to the hydraulic cylinder plate, and an A-half parting line plate movable with respect to said hydraulic cylinder plate by a moving device, said moving device linearly varying a distance between the A-half parting line plate and the hydraulic cylinder plate, wherein a movement of the A-half parting line plate is controlled by a control circuit;

attaching the movable mold half to the movable platen of the injection molding machine;

attaching the hydraulic cylinder plate of the stationary mold half to the stationary platen of the injection molding machine;

extending the moving device of the stationary mold half so that the A-half parting line plate is extended by a predetermined distance away from the hydraulic cylinder plate;

moving the movable platen of the injection molding machine toward the stationary mold half until the B-half parting line plate contacts the A-half parting line plate, thereby creating an expanded mold cavity between the at least one movable mold insert surface and a surface of the at least one stationary mold insert;

injecting a predetermined percentage of an injection shot of molten material into a runner system formed by the movable mold half and stationary mold half, said predetermined percentage of the injection shot traveling through the runner system and into the expanded mold cavity,

further moving the movable mold half in such a way as to decrease the predetermined distance between the A-half parting line plate and the hydraulic cylinder plate; and

injecting a remaining percentage of the injection shot into the injection cavity, wherein upon completion of the movement of the movable mold half the injection cavity has reached a final cavity size, and the mold insert surfaces have reached a final clamp position;

cooling the molten material in the mold cavity; and

removing a molded part from the injection cavity.

2. A method as recited in claim 1, said method including a step of sensing a movement of the A-half parting line plate relative to the hydraulic cylinder plate.

3. A method as recited in claim 1, said method including a step of controlling a movement of the A-half parting line plate with respect to the hydraulic cylinder plate by controlling a hydraulic pressure in a hydraulic circuit connected to the hydraulic cylinder plate while sensing a relative position of the A-half parting line plate with respect to the hydraulic cylinder plate.

4. A method as recited in claim 1, wherein said predetermined percentage of the injection shot comprises approximately 93-96%.

5. A method as recited in claim 1, wherein the remaining percentage of the injection shot and the predetermined percentage of the injection shot equals 100%.

6. A method as recited in claim 1, wherein said step of injecting the remaining percentage of the injection shot is performed simultaneously with the step of further moving the movable mold half in such a way as to decrease the predetermined distance between the A-half parting line plate and the hydraulic cylinder plate.

7. A method as recited in claim 1, wherein said step of injecting the remaining percentage of the injection shot is performed after the step of further moving the movable mold half in such a way as to decrease the predetermined distance between the parting line plate and the hydraulic cylinder plate.

8. A method as recited in claim 1, wherein said step of moving the movable platen includes a step of applying a counterpressure on a hydraulic system associated with the A-half parting line plate and the hydraulic cylinder plate, and wherein the step of further moving the movable mold half includes a step of venting the counterpressure in the hydraulic circuit, thereby allowing hydraulic pistons associated with the stationary mold half to collapse, enabling movement of the A-half parting line plate toward the hydraulic cylinder plate by the movable platen.

9. A method as recited in claim 8, wherein said relieving of said pressure in said hydraulic circuit includes opening a pressure relief valve when the pressure in the hydraulic circuit exceeds a preset pressure threshold of the pressure relief valve.