1. Field of Invention
This invention relates to an improved method for molding articles in an injection molding apparatus.
2. Description of Related Art
It has become increasingly popular to manufacture automobile and truck trim and body parts such as fenders, bumpers, rocker panels, body panels, doors, filler panels, wheel covers, dash boards, arm rests, chin spoiler and other parts via injection molding techniques. In conventional injection molding systems and methods, an injection molded part having a show surface is formed using a mold, comprised of a first mold portion and a second mold portion that combine to form a mold cavity. Moreover, to minimize the emission of VOC compounds and to improve the aesthetic appearance of many such injection molded plastic parts, a paint film laminate covering the show surface may be placed in the mold cavity as is known in the art. The paint film laminate is placed so that a painted side of the film faces towards one of the mold portions, whereas the backing sheet of the paint film faces towards the other mold portion. The mold is then clamped closed with the paint film laminate in place, the mold cavity being formed in the space between the first and second mold portions.
A charge of thermoplastic molten resin is injected into the mold cavity so as to flow in an upstream to downstream direction. The resin fuses with the paint film in and forms the desired injection molded plastic part. After the part has been cooled in the mold, and one of the mold cavity support surfaces is displaced from the other, the part is then ejected by the use of pneumatically or hydraulically actuated lifters and the like. The lifters cooperate with one side of the mold (usually that side contiguous with the plastic substrate) and ejects or “pops” the finished part out of the mold so that another molding production cycle can occur.
When parts having narrow edges or corners are produced, such as in the case of rocker panels, chin spoilers, bumpers, etc., the flow of the plastic material tends to entrap air in the mold cavity leading to the formation of a blister or bubble in the plastic material in these corners or edges. The bubbles or blisters results in undesirable blemishes on the part. Additionally, the flow of the plastic material is inclined to push up the tip of the paint film laminate and seep between the laminate and the mold surface. The seepage of the plastic material between the paint film laminate and the mold surface forms an undesirable overflow scrap on the part. These blemishes detract from the aesthetic appearance of the part and in some instances render the part unsuitable for use. An improved molding process and system would therefore be desirable to reduce the formation of such blemishes.
The invention is accordingly directed to methods and an apparatus for injection molding plastic parts, and more specifically for distributing the plastic material into the confined crevices in the corners and edges of the mold cavity. The methods and apparatus of the invention are designed to inhibit the formation of surface blemishes on the part that otherwise often occur as the thermoplastic plastic resin is injected into the mold cavity.
One aspect of the invention is directed to a method of molding an automobile or truck plastic part. The method includes providing a mold cavity formed by at least two mold portions, wherein the mold cavity has at least one confined crevice and one of the mold portions has at least one diverter positioned adjacent the at least one confined crevice. The method also includes injecting a charge of the plastic into the cavity such that a portion of the charge of plastic flows over the diverter and into the confined crevice of the mold cavity.
Another aspect of the invention is directed to molding apparatus. The apparatus includes a first mold part and a second mold part, the first mold part and the second mold part when positioned adjacent each other defining a mold cavity therebetween, wherein the mold cavity has at least one confined crevice. The apparatus also includes a plastic injection runner communicating with the mold cavity and adapted to inject a shot of molten plastic into and along the cavity from an upstream to a downstream direction. The apparatus also includes at least one molten plastic flow diverter extending from the first mold portion, the at least one diverter located adjacent the at least one confined crevice and configured to direct the molten plastic flow into the crevice.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.
The above mentioned and other features of this invention will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawing, wherein:
Corresponding reference characters indicate corresponding parts throughout the views of the drawings.
The invention will now be described in the following detailed description with reference to the drawings, wherein preferred embodiments are described in detail to enable practice of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. But to the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description.
Turning now to
In the illustrated embodiment, the injection of plastic material proceeds from the runner 18 at an upstream end of the cavity 25 to a downstream end 26 of the cavity 25 to form a molded part having a plastic substrate. The ejection molding apparatus 10 is used in accordance with conventional injection molding techniques, and when a film laminate 29 is used to create a painted “show” face, conventional co-molding techniques, wherein the paint film laminate 29 is placed in the mold cavity 25 with the charge of plastic material injected into the mold along the backside of the paint film laminate. Typically, the plastic for the plastic substrate is chosen from a host of various thermoplastic and thermoset plastic materials with more common plastic substrates comprising polyvinyl chloride, polyolefins, such as polypropylene, polyacrylates such as poly(methyl)methacrylate, polyvinyl acetate, polyamides, polyimides, polyesters, phenol-formaldehyde polymers, amino polymers, polyurethanes, etc. It should be noted that the phrase paint film laminate as used herein is intended as a generic description of any film, monolayer, laminate or otherwise that is intended to impart a desired aesthetic appeal to the show surface of the part. The paint film laminate 29 can comprise a color imparting layer or layers, a transparent cast, a metallic luster or a metallic flake appearance.
Pistons 28, 30 are operatively associated with the second mold portion 24 so that this mold portion 24 may be reciprocated along rails 31, 33 between a mold formation station and a station in which the mold portion 24 is retracted upwards with regard to
Turning also now to
Upon operation of the molding apparatus 10, the paint film laminate 29 is first inserted into the mold machine 10 along a portion of the cavity 25 defined by the contoured configuration of the second mold portion 24. Then, a sufficient shot of plastic material is injected into the molding apparatus 10 in an upstream to downstream direction from the sprue 16 and runner 18 towards the downstream end 26 of the cavity 25. As is conventional in the art, the injection of the plastic shot into the cavity 25 may be assisted via pressurized gas flow and the like, and a predetermined amount of the desired plastic material, at desired pressure and temperature is fed into the mold cavity 25. After the molded part is made in the mold cavity 25, the second mold portion 24 is retracted via the pistons 28, 30 to the open position. Then, pistons 102, 104 are actuated to move ejector plate 100, and the lifter pins 43 carried thereon toward the top to eject the part 27 out of the mold cavity 25.
Turning now to
Turning now to
In accordance with the invention, the diverter 130 is formed in one of the mold cavity surfaces creating a narrow restriction or throat 301 adjacent the crevice 126. As illustrated in the embodiment depicted in
Additionally, in embodiments where the film laminate 29 is provided in the co-molding process, the diverter 130 also diverts the flow of plastic material into the space 212 between the doubled or V-shaped layers of the film laminate 29 so as to adjust the angle at which the flow of plastic material impinges upon the tip 134 of the paint film laminate 29 (see arrows B representing direction of flow in
As seen in
Turning now to
While various exemplary embodiments of the invention are described herein, the invention is not limited to the precise forms of the lifter and methods described herein. It is evident based on the description provided that many changes, alterations, variations and changes to the invention can be made without departing from the scope of the invention as set forth herein.
This application claims the priority benefit of U.S. Provisional Patent Application Ser. No. 60/749,393 filed Dec. 12, 2005 and U.S. Provisional Patent Application Ser. No. 60/843,017 filed Sep. 8, 2006.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2006/044406 | 11/15/2006 | WO | 00 | 10/3/2008 |
Number | Date | Country | |
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60749393 | Dec 2005 | US | |
60843017 | Sep 2006 | US |