WO2000053389A1

WO2000053389A1 - Method and apparatus for improving gate removal from a mold

Info

Publication number: WO2000053389A1
Application number: PCT/US2000/005851
Authority: WO
Inventors: Thomas Skorch; Michael Bryan Smith
Original assignee: Conix Corporation
Priority date: 1999-03-09
Filing date: 2000-03-07
Publication date: 2000-09-14
Also published as: CA2364508A1

Abstract

The present invention provides an apparatus for molding articles wherein the apparatus includes a mold having at least two mold halves (8) defining therebetween a mold cavity, a plurality of gates (12A, 12B, 12C) for communicating molten plastic to the mold cavity from a source, and a recess formed in the mold for forming a tie strap (14) which connects at least two of the gates (12A, 12B, 12C) together to cause dependent movement of the at least two gates (12A, 12B, 12C) when at least one of the two gates (12A, 12B, 12C) is removed from the mold. The gates may be formed as cashew gates (12A, 12B, 12C). In addition, the invention provides a process for molding articles, wherein the process includes the steps of: a) providing a mold having a mold cavity and a plurality of passages for conveying molten plastic from a source to the mold cavity, the mold further including at least one tie strap recess (14) communicating between at least two of the passages; b) molding an article in the mold cavity, thereby forming a plurality of gates (12A, 12B, 12C) in the passages, at least two of the gates (12A, 12B, 12C) being connected by at least one tie strap formed in the tie strap recess (14); and c) removing at least one of the gates (12A, 12B, 12C) of the mold. The step of forming the gates (12A, 12B, 12C) may include the step of forming cashew gates (12A, 12B, 12C).

Description

METHOD AND APPARATUS FOR IMPROVING GATE REMOVAL FROM A MOLD

Field of the Invention

The present invention relates to injection molding methods and apparatus. More particularly, the present invention relates to injection molding methods and apparatus which provide improved efficiency and dependability in the automated removal of gates from a mold following a molding operation.

Background of the Invention

Injection molding in high production applications, such as those relating to mass production of automobile fascias and other plastic components, involve the use of automated equipment and high speed molding processes. Cycle times of less than 100 seconds to produce a single molded article are not extraordinary in these applications. Such state-of-the art processes involve the rather complex interaction of robotic equipment in precisely timed sequences to mold the article and remove it from the mold.

In general, injection molding processes involve the step of bringing two halves of a split mold together, introducing pressurized molten plastic into the mold cavity, allowing the plastic to cool or cure, and removing the molded product from the mold. The molten plastic is introduced through passages, known as gates, which provide fluid communication between the mold cavity and a molten plastic source. One form of gate, known as a "cashew" gate because its shape resembles that of a cashew nut, is especially useful in high-production applications. Cashew gates permit molding of parts and provide a clean break when the molded article is removed from the mold, thereby eliminating or reducing the need for trimming of the molded article and thus reducing cycle times. Removal of the molded article from the mold results in a "clean break" of the article from the cashew gates, which typically remain embedded in the mold core. These gates must be removed before another article is molded. Removal is accomplished with robotic equipment, including pneumatic ejection devices which partially eject the gates from the mold to a position where they can be gripped by robotic devices known as "grabbers" and pulled from the mold. In state-of-the-art molding processes, precise alignment of the grabbers with respective gates is accomplished with expensive automatic alignment equipment. Moreover, since each gate moves independently of other gates, each grabber must be sufficiently aligned with a corresponding gate to ensure removal of that gate from the mold. If even one gate is missed by a grabber, that gate will remain in the mold, thereby obstructing the passage to the mold cavity and resulting in what is known as a "tool crash" when the machinery attempts to mold another article. What is needed is an invention which improves the efficiency and dependability of existing injection molding methods and apparatus to remove gates from a mold.

Summary of the Invention

The aforementioned problems are eliminated and desired advantages are realized by the present invention, which contemplates a new and improved method and apparatus for ensuring removal of gates from a mold. Specifically, the invention provides one or more tie straps formed integrally with a number of gates in the molded article, thereby linking the gates together. The tie straps prevent one or more gate elements from "lagging" behind the others when the gates are ejected from the mold and gripped by robotic grabbers. Thus, if one gate is ejected to the appropriate position, all gates attached to the tie strap move to positions in which they can be quickly and easily grabbed by robotic equipment.

In one aspect, the invention may be defined as an apparatus for molding articles, the apparatus comprising a mold having at least two mold halves defining therebetween a mold cavity, a plurality of gates for communicating molten plastic to the mold cavity from a source, and a recess formed in the mold for forming a tie strap which connects at least two of the gates together to cause dependent movement of the at least two gates when at least one of the at least two gates is removed from the mold. More particularly, the invention may be defined as the aforementioned apparatus wherein the gates are formed as cashew gates. In another aspect, the invention may be defined as a process for molding articles, the process comprising the steps of: a) providing a mold having a mold cavity and a plurality of passages for conveying molten plastic from a source to the mold cavity, the mold further including at least one tie strap recess communicating between at least two of the passages; b) molding an article in the mold cavity, therby forming a plurality of gates in the passages, at least two of the gates being connected by at least one tie strap formed in the tie strap recess; and c) removing at least one of the gates from the mold. More particularly, the invention may be defined as the aforementioned process, wherein the step of forming the gates includes the step of forming cashew gates.

Brief Description of the Drawings The accompanying drawings which are incorporated into and form a part of the specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating preferred embodiments of the invention and are not to be construed as limiting. In the drawings, in which like numbers refer to like parts throughout:

FIG. 1 is top view of a bottom mold half for molding an automobile air dam member showing cashew gates and tie straps according to a preferred embodiment of the invention;

FIGS. 2A and 2B are representations of a mold cross-section showing steps of forming and removing cashew gates and a tie strap according to a preferred embodiment of the present invention; and

FIG. 3 is an isometric illustrating the initial stage of a gate removal step utilizing a tie strap according to the present invention.

Description of the Preferred Embodiment

FIG. 1 is a top view of a bottom mold half 8, sometimes termed a mold core, for a molded article 10, in this case, an air dam for an automobile. Those of ordinary skill in the art will recognize that the mold core 8 includes portions which project outward from the plane of the page of the illustration and mates with a top mold half (not shown) sometimes termed a "hat." Extending from the molded article 10 are a plurality of cashew gates 12 which communicate molten plastic material from an injection nozzle (not shown). According to the invention, tie straps 14 are molded integrally with the cashew gates 12 using a recess 16 formed in the bottom mold half 8. Typically, gates 12 will have a width of about inch while straps 14 will have a width of about 3/16 inches.

FIG. 2A corresponds to a cross-section of a mold, such as that illustrated in FIG. 1 , during a molding process. A top mold half 18 and bottom mold half 8 define a mold cavity 22 where the molded article 10 is formed. The mold halves also define a cashew gate 12 for conveying molten plastic from an injection nozzle 24 to the mold cavity 22. Injection nozzle 24 cooperates in a known manner with the mold and is typically reciprocally movable in a vertical direction. Moreover, in automated equipment, mold halves 8 and 18 are moved into and out of a molding position by robotic devices.

As can be seen from FIG. 2A, cashew gate 12 tapers at its left end to a reduced cross-section. Due to this reduced cross-section, molded article 10 may be separated from the gate 12 without the need for trimming. Also illustrated in FIG. 2A is a tie strap 14 shown in cross-section and extending generally perpendicular to the plane of the page. Preferably, tie strap 14 is of a semi-circular cross-section. It will be recognized that tie strap 14 connects two or more gates 12, although only one gate is illustrated in FIG. 2A.

Referring in addition to FIG. 2B, following the molding process stage illustrated in FIG. 2A, the injection nozzle 24, upper mold half 18 and the molded article 10 have been removed, leaving the cashew gate 12 embedded in the mold bottom half 8. The next step in the cycle is removal of the gates 12, which typically occurs with the use of pneumatic equipment (not shown) cooperating with bottom mold half 8 and which applies an air stream underside of the gate 12 through a passage (not shown) in the mold bottom 20. Pneumatic ejection of the gate 12 cause it to assume the position illustrated in FIG. 2B where it may be gripped with robotic grabbers and pulled from the mold.

Referring additionally to FIG. 3, in accordance with the present invention, the tie strap 14 ensures that adjacent gates 12 move effectively in unison from the mold bottom half 8. FIG. 3 illustrates the initial stages of ejection of a first gate 12A. As can be seen, tie strap 14 is ejected from the mold bottom half 8 along with gate 12A. As gate 12A emerges further from the mold bottom half 8, tie strap 14 will ensure that adjacent gates 12B and 12C are also ejected from the mold bottom 8. It will be understood that adjacent gates 12B and 12C will also be subject to pneumatic ejection forces. However, without tie strap 16, there is increased potential for one or more adjacent gates 12B and 12C to "lag" behind other gates. This may be due, for example, to gates "sticking" in the mold bottom 8, or experiencing reduced pneumatic forces due to slight clogging of the pneumatic implements used to eject the gates 12. Thus, tie strap 16 causes all gates 12A, 12B, 12C and those not illustrated to move to the same general location where they may be gripped by a respective robotic "grabber." Those of ordinary skill in the art will recognize that the dimensions of tie strap 14 will depend, at least in part, on the materials used in the molding operation. The dimensions should be such that the potential for severing the tie strap 14 during gate removal is remote. It will also be recognized that the use of tie straps 14 in accordance with the invention may eliminate the need for robotic "grabbers" for each and every gate in the mold. That is, only a single "grabber" may be used to grip and remove two or more gates from the mold. Moreover, the tie straps 14 may be used as gripping surfaces themselves, thereby permitting reduced tolerances for alignment of robotic equipment with the tie strap 14.

Although the preferred embodiment of this invention has been described hereinabove in some detail, it should be appreciated that a variety of embodiments will be readily available to persons utilizing the invention for a specific end use. The description of this invention is not intended to be limiting on this invention, but is merely illustrative of the preferred embodiment of this invention. Other products, apparatus and methods which incorporate modifications or changes to that which has been described herein are equally included within this application. Additional objects, features and advantages of the present invention will become apparent by referring to the above description of the invention in connection with the accompanying drawings.

Claims

What is claimed is:Claims

1. An apparatus for molding articles, the apparatus comprising: a mold having at least two mold halves defining therebetween a mold cavity, a plurality of gates for communicating molten plastic to the mold cavity from a source, and a recess formed in the mold for forming a tie strap which connects at least two of the gates together to cause dependent movement of the at least two gates when at least one of the at least two gates is removed from the mold.

2. The apparatus of claim 1 wherein the gates are formed as cashew gates.

3. A process for molding articles, the process comprising the steps of: a. providing a mold having a mold cavity and a plurality of passages for conveying molten plastic from a source to the mold cavity, the mold further including at least one tie strap recess communicating between at least two of the passages; b. molding an article in the mold cavity, thereby forming a plurality of gates in the passages, at least two of the gates being connected by at least one tie strap formed in the tie strap recess; and c. removing at least one of the gates from the mold.

4. The process of claim 3, wherein the step of forming the gates includes the step of forming cashew gates.