Plastic and nonmetallic article shaping or treating: processes – With step of making mold or mold shaping – per se
Reexamination Certificate
2000-06-15
2001-10-09
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of making mold or mold shaping, per se
Reexamination Certificate
active
06299814
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a method of fabricating a silicon rubber-based mold and, more particularly, to a method of fabricating a silicon rubber-based mold which contains minimum amount of silicon rubber and improves molding characteristics of the product to be formed.
(b) Description of the Related Art
Generally, rim molds or vacuum casting molds that are mainly used for the casting purpose involve high production cost and retarded production time because they should be fabricated separately in accordance with the shape of the required products. Therefore, in case various kinds of products should be formed in a small scale, the molds based on silicon rubber or epoxy resin have been extensively used.
FIGS. 3A
to
3
D illustrate the processing steps of fabricating a silicon rubber-based mold according to a prior art. As shown in
FIG. 3A
, a jig
112
, and a master model
114
of products to be formed are first made. Thereafter, as shown in
FIG. 3B
, the master model
114
is mounted onto the jig
112
. As shown in
FIG. 3C
, the master model
114
mounted on the jig
112
is inserted within a casting enclosure, and then, silicon rubber is injected onto the master model
114
to thereby form a lower half mold
116
. The lower half mold
116
is overturned, and the jig
112
is separated from the master model
114
. Thereafter, silicon rubber is again injected onto the master model
114
to thereby form an upper half mold
118
. Finally, the master model
114
is removed from its place while leaving out an empty space for forming the required products there.
Silicon rubber used in such a process is flexible, and coefficient of thermal expansion thereof is up to 0.01. Therefore, considering that the product formation using a mold is performed under the high pressure of 1-1.5 MPa, the above structured mold that is entirely based on silicon rubber is liable to suffer serious transformation due to its high thermal expansion, and causes poor dimensional precision of the resulting products.
On the other hand, the mold based on epoxy resin involves complicated processing steps due to physical properties of the epoxy resin. Furthermore, since the required flexibility is absent in the epoxy resin-based mold, serious transformation of the product is generated at mold release.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of fabricating a silicon rubber-based mold which can enhance dimensional precision of the product to be formed.
This and other objects may be achieved by a mold fabricating method including the first step of making a master model of products to be formed, and a jig. The master model is mounted onto the jig, and a lower pad is formed on the master model. A plurality of round bars are inserted onto the lower pad. A lower frame is made by injecting a backing material onto the lower pad. The lower pad and the round bars are removed from their places while leaving out an empty space and silicon injection paths there. Silicon rubber is injected into the empty space via the silicon injection paths to form a lower silicon layer, thereby completing a lower half mold. The lower half mold is then overturned. The jig is separated from the master model, and an upper pad is formed on the master model. A plurality of round bars are inserted onto the upper pad. An upper frame is made by injecting a backing material onto the upper pad. The upper pad and the round bars are removed from their places while leaving out an empty space and silicon injection paths there. Silicon rubber is injected into the empty space to form an upper silicon layer, thereby completing an upper half mold.
A metallic mesh may be fixed to the upper frame before the step of injecting silicon rubber into the empty space. The metallic mesh is to securely fix the upper silicon layer to the upper frame.
Silica or a mixture of resin and silica may be used as the backing material for forming the upper and lower frames.
REFERENCES:
patent: 2434780 (1948-01-01), Wiss et al.
patent: 2615229 (1952-10-01), Blackburn et al.
patent: 3053713 (1962-09-01), Juras
patent: 3064314 (1962-11-01), Gagne et al.
patent: 3270110 (1966-08-01), Downie et al.
patent: 3509250 (1970-04-01), Knipper
patent: 4104347 (1978-08-01), Ohashi et al.
patent: 4349498 (1982-09-01), Ellis et al.
patent: 4-224904 (1992-08-01), None
Christie Parker & Hale LLP
Hyundai Motor Company
Kuhns Allan R.
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