Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1998-07-17
2001-12-11
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S266000, C264S273000, C264S275000, C264S279000, C264S319000, C264S328700, C264S328800, C264S294000, C425S130000
Reexamination Certificate
active
06328920
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to injection molding and injection compression molding, and particularly to a process for combining the advantages of injection molding and injection compression molding to form complex shapes.
BACKGROUND OF THE INVENTION
Injection molding is a major plastic part process. The mold is a two-section tool that has a hollow cavity in the center. The hollow form is filled with plastic to make the part. The injection molding process has as its general steps closing of the mold, application of clamping force, injection of plastic, curing of plastic, opening of the mold, and removal of the part. This process is then repeated. The mold halves close and a clamp force is applied to keep the two halves closed to resist the injection pressure inside the mold. The plastic flows in the hollow form to make the part.
Injection compression molding is similar to injection molding, with the major difference being that the plastic is injected without clamping pressure applied on the mold. The plastic is injected while the mold is not fully closed. During the final phase of the injection, the mold is closed and clamping force is applied to compress the plastic to make the shape. Thus, injection compression molding requires less clamping force because force is not needed to resist the pressure in the injection phase. The general steps of this process include injection of plastic in a slightly open mold, closing of the mold, curing of the plastic, opening of the mold, and ejection of the part.
Injection molding can be used to make complex parts, but its disadvantage is that the clamping force increases with the complexity and size of the part. Injection compression molding has the advantage of reduction in clamping force, a reduction of approximately 50-70%, but its disadvantage is that the part is smooth in shape.
It is seen then that there exists a need for a new process which combines certain advantages of both injection molding and injection compression molding, but eliminates certain disadvantages of each process.
SUMMARY OF THE INVENTION
This need is met by the injection-compression molding process, according to the present invention, wherein existing injection molding and injection compression molding are combined for manufacturing, using one mold for the two steps.
In accordance with one embodiment of the present invention, a method is provided for forming a part having a first layer which is a complex structure and a second layer which is a smooth structure. Initially, a single mold is provided, the mold having an interior cavity and a runner reaching from an exterior of the mold to the cavity. The mold is closed, and a quantity of a first plastic material is injected via the runner into the interior cavity to form a first layer of the plastic part. In this step, the appearance of the complex structure is non-critical and does not form the overall shape of the part. The mold is then partially opened, creating an increased interior cavity section, into which a quantity of a second plastic material is injected, via the runner, to form a second layer, as a smooth structure. The complex structure provides strength and function to the smooth structure. The solidified plastic part can then be ejected from the mold.
It is an advantage of the present invention that it can produce complex shapes with reduced clamping force. It is a feature of the present invention that the injection molding step and the injection compression molding step both use the same mold. That is, the process of the present invention combines both molding steps to make one part in one mold. The part requirement is a complex surface or side (containing structures for strength, stability and fastening functions) and a smooth surface or side for the sake of appearance. This is, of course, typical of many plastic parts and housings in the audio, video and automotive industries. Finally, it is an advantage of the present invention to make a relatively large part without using a large machine.
For a full understanding of the nature and objects of the present invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings and the appended claims.
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Sam Lam B.
Uchiyama Yuichi
Haushalter Barbara Joan
Honda Engineering North America, Inc.
McDonald Alan T.
McDowell Suzanne E.
Silbaugh Jan H.
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