Compression molding against an insert

A flash free, compression molded object which includes an insert and is formed using only one mold plate is disclosed. Molding compound is trapped in a mold cavity between the insert and mold plate. An extrusion vent allows excess molding compound and curing gases to escape from the mold cavity. Systems for forming a pin hole within the molded object and removing the molded object from the mold plate are also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates generally to a method for compression molding. 
Specifically, the present invention relates to molding to an object called 
an insert and to entrapping the molding compound in a cavity formed 
between the insert and a single mold plate. 
Three techniques of conventional molding are known: compression, transfer, 
and injection. Each technique differs from the others in the type of 
molding compound typically used and the approach taken to load the 
compound into a mold cavity. Thermosettting resins, which become 
permanently rigid when heated, are typically used in compression and 
transfer molding. Compression molding requires individual handling of the 
compound. However, in transfer molding the compound is automatically 
forced into one or more mold cavities by an independent part of the mold 
structure. On the other hand, injection molding typically uses a 
thermoplastic compound, which softens when heated and hardens when cooled. 
Furthermore, injection molding uses an external structure to automatically 
force the compound into a tightly closed mold that may contain several 
cavities connected together by a series of branch passages. 
Compression molding offers certain advantageous over the other molding 
techniques. The tooling costs are lower because no mechanism is required 
to automatically load molding compound. Further, the molding compound 
escapes being masticated by automatic loading mechanisms. Thus, the molded 
objects demonstrate higher mechanical properties. This is especially 
significant when the molding compound contains internal fibers for 
strenghtening the molded object. Such fibers tend to remain randomly 
oriented and unbroken, and thus produce stronger molded objects having 
tighter ID and OD tolerances. 
The existing compression molding methods require the use of a mold 
comprised of at least two complimentary mold plates constructed so that 
the plates are mated together a mold cavity remains between the plates. 
First, the mold is heated to a predetermined temperature, and a 
predetermined quantity of a thermosetting resin is measured. Then, the 
mold is opened and the measured quantity of thermosetting resin is placed 
in the mold cavity between the mold plates. Next, the mold plates are 
clamped together and remain clamped for a predetermined period of time. 
During this period the heat in the mold and the clamping pressure transfer 
to the thermosetting resin causing the resin to assume the shape of the 
cavity and to undergo an irreversible chemical reaction known as curing. 
Next, the mold plates are momentarily separated to allow curing gasses to 
escape from them mold cavity, a step known as breathing, and then the 
plates are clamped together again for another predetermined period of 
time. Finally, the mold plates are again separated and the resulting 
molded object is removed typically by using ejector pins. The use of 
ejector pins poses a problem because they tend to make scarring marks on 
the molded object. Flash, which forms during curing when excess resin 
escapes the cavity at the parting line between the mold plates, poses an 
additional problem because it must then be removed from the finished 
object. 
The existing compression molding methods contain several disadvantages 
which are improved in the present invention. Specifically, the multiple 
mold plates, the breathing step, the use of ejector pins, and the 
formation of flash are all seen as causing an unnecessary complication, 
expense, and waste of time in a method for compression molding, and are 
thus addressed in the present invention. 
SUMMARY OF THE INVENTION 
The present invention relates to a method for compression molding to an 
insert. The method defined in the present invention uses a mold which 
needs to be comprised of no more than a single mold plate containing a 
mold cavity. This mold cavity could be considered to consist of two 
portions, an upper portion which defines the shape of the molded object, 
and a lower portion which mates with an insert. The insert is likewise 
defined to have a shape corresponding to the lower portion of the mold 
cavity. The present invention further defines steps for loading a molding 
compound and for pressing the insert into the mold cavity so that the 
insert mates with the mold cavity. 
One key feature, which provides several benefits for the present invention 
over existing methods, concerns the use of the insert. In the present 
invention the insert, which becomes part of the resulting molded object, 
replaces the second mold plate required by existing methods. Hence, a 
simplification occurs through the elimination of a complicated mold plate 
and through the elimination of the step for removing the resulting molded 
object from that plate. Further, since the present invention uses only one 
mold plate, no flash occurs at a parting line between multiple mold 
plates. Another simplification occurs by the elimination of a step for 
removing such flash from the resulting molded object. Another benefit 
results from the insert becoming a part of the resulting molded object. 
The resulting molded object may be removed from the mold plate by pulling 
on the insert instead of pushing the molded object out of a mold using 
ejector pins. Thus, the resulting molded object will contain scar marks 
caused by ejector pins. 
Another key feature of a preferred embodiment of the present invention 
concerns providing an extrusion vent between the upper portion of the mold 
cavity and the exterior of the mold plate. The provision of an extrusion 
vent obviates the breathing step required in existing methods. Therefore, 
the present invention is simplified over existing methods through the 
elimination of this step. Additionally, the extrusion vent provides an 
escape path for excess molding compound. In existing methods this excess 
causes flash which must later be removed in a separate step. Hence the 
benefits of flash, such as uniformity between resulting molded objects, 
are obtained without the flash. 
Yet another key feature of a preferred embodiment of the present invention 
concerns the formation of a pin hole within the resulting molded object. 
Such a pin hole allows the insertion of small pin-like objects into and 
removal from the resulting molded object. 
Still another key feature of a preferred embodiment relates to a technique 
for removing the resulting molded object from the mold plate. This 
technique provides for automatically gripping the insert as the insert is 
pressed into the mold plate. A camming means performs the gripping by 
moving a cam member toward the insert as the insert moves into the mold 
plate. Thus, no gripping occurs before the insert begins to move into the 
cavity and the insert can be easily mounted in and removed from the 
camming means. But, as the insert moves into the mold plate and mates with 
the lower portion of the mold cavity, the gripping action becomes 
sufficient to allow removal of the resulting molded object by pulling it 
from the mold plate. 
Other important features of this invention will become apparent from a 
study of the following specification, claims, and the attached drawings.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates the major parts of a specific embodiment of the present 
invention and the cooperation of these major parts. This cooperation 
describes the basic molding operation. Insert 10 is shown mated with mold 
plate 12. Molding compound 11 is entrapped within mold cavity 16 between 
insert 10 and upper portion of mold cavity walls 18A. Molding compound 11 
represents the substance that is molded in the molding operation and may 
comprise a thermosetting, thermoplastic, or other material. 
The present invention additionally relates to a procedure which causes 
these major parts to successfully cooperate with each other. The procedure 
produces a resulting molded object which is comprised of insert 10 bonded 
to molded molding compound 11. 
General Procedure 
The first step concerns setting up the apparatus used in conjunction with 
the present invention. This embodiment of the present invention adapts to 
a standard mold press (not shown), such as one with a seven inch diameter 
ram. The set up step requires attaching mold plate 12 to such a standard 
press. 
The next step of the procedure requires heating mold plate 12. In this 
embodiment heating is needed because molding compound 11 is a 
thermosetting resin which needs heat as a catalyst before the 
thermosetting chemical reaction starts and results in the curing of 
molding compound 11. A standard mold press provides the means for heating 
mold plate 12. Mold plate 12 acts as a heat reservoir since it is a 
relatively large metal mass compared to the size of the object to be 
molded. In this specific embodiment molding compound 11 is molded into a 
general conical shape approximately 1.2 inches in height with a base 
diameter of approximately 0.6 inches. The mold plate measures 
approximately three inches by seven inches by seven inches and is heated 
to a temperature in the 300-350 degrees F. range. Thus when molding 
compound 11 is entrapped within mold cavity 16, heat contained in mold 
plate 12 transfers to molding compound 11 thereby causing the 
thermosetting chemical reaction to occur. 
The application of a suitable lubricant (not shown), such as silicone, to 
mold cavity walls 18 aids the removal of the resulting molded object from 
mold plate 12 by minimizing the object's tendency to stick within mold 
plate 12. Additionally, the lubricant eases the task of cleaning mold 
cavity walls 18. 
The application of an adhesive 40 to insert bonding surface 15 prevents 
molding compound 11 from spinning relative to insert 10 in the resulting 
molded object. Insert bonding surface 15 defines that surface of insert 10 
which bonds to molding compound 11. In this embodiment a "B" staged epoxy 
serves as adhesive 40. This "B" staged epoxy behaves similarly to a 
thermosetting resin in that it is partially cured when applied to insert 
bonding surface 15 and requires heat as a catalyst to become activated and 
completely cure. Thus, this epoxy cures in the same manner as the 
thermosetting resin used for molding compound 11 in this specific 
embodiment. It will of course be understood that other means of preventing 
relative rotary movement might be used, such as protrusions, fins, etc. 
extending from insert 10 into molding compound 11. 
Next, a suitable quantity of molding compound 11 is measured. The volume 
remaining in mold cavity 16 after insert 10 is mated with lower portion of 
mold cavity walls 18b, the characteristics of molding compound 11, and the 
density of the resulting molded object all combine to define the amount of 
molding compound required. Measuring a quantity slightly greater that the 
amount required provides desirable effects. A precisely correct quantity 
of molding compound 11 is very difficult to obtain due to variations in 
insert 10 dimensions, variations in measuring molding compound 11, and 
variations in the quantity of molding compound 11. However, such a 
slightly greater than required amount insures that mold cavity 16 will be 
completely filled when molding compound 11 is entrapped within mold cavity 
16 regardless of such variations. The present invention refers to that 
amount which is greater than required as excess 44. To achieve uniform 
dimensions and uniform density between different resulting molded objects, 
excess 44 must be allowed to escape mold cavity 16. The present invention 
provides a sufficient path for this escape through extrusion vent 24, but 
some care must be taken in measuring molding compound 11 to prevent excess 
44 from being too great. In this specific embodiment, between 7.0 and 7.5 
grams of molding compound 11 satisfies the measurement step. 
Another step in the procedure concerns placing the insert in the mold 
press. A standard mold press (not shown) typically accommodates two mold 
plates. The present invention only requires one mold plate. Thus, in this 
embodiment insert 10 adapts to a standard mold press through a pressure 
plate 30, which as shown in FIG. 2 simulates a second mold plate. 
Yet another step relates to loading the measured molding compound 11 
between insert 10 and mold cavity walls 18. Loading is the term given to 
transferring molding compound 11 to the location in the mold where it will 
be formed into a molded object. In this embodiment, minimizing internal 
stress problems and tolerance variations between resultant objects, and 
maximizing resultant object strength and surface smoothness are design 
goals which affect both the type of molding compound 11 used and this 
loading step. This specific embodiment utilizes a thermosettting resin 
with embedded fibers 42 for molding compound 11. The achievement of these 
design goals requires that embedded fibers 42 be substantially randomly 
oriented within molding compound 11. Molding compound 11 typically comes 
supplied with the fibers substantially randomly oriented. Thus, the 
loading step should employ means that insure the fibers remain 
substantially randomly oriented. In this embodiment molding compound 11 is 
measured and placed on insert bonding surface 15 by hand, and then 
transferred to mold cavity 16 as insert 10 is mated with lower portion of 
cavity walls 18b. However, it will be understood by those skilled in the 
art that many methods of loading the mold can be utilized and that 
different types of molding compound may adapt to different loading 
methods. 
Next, insert 10, mates with mold plate 12. The mating of insert 10 with 
mold plate 12 requires a significant amount of force because excess 44 of 
molding compound 11 tends to cause the amount of molding compound 11 
present in mold cavity 16 to be slightly greater than the given volume 
accommodates. A standard mold press (not shown) provides the necessary 
force, which in this specific embodiment is approximately 300 pounds. When 
insert 10 is mated with mold plate 12 at lower portion of cavity walls 
18b, molding compound 11 is entrapped within mold cavity 18 under a 
substantially pressure. This pressure causes molding compound 11 to adapt 
to the shape defined by upper portion of cavity walls 18a. Again, care in 
measuring molding compound 11 should be taken to insure that excess 44 is 
not too great. Too large a quantity of excess 44 could prevent insert 10 
from becoming properly registered against lower portion of cavity 
walls18b, or could cause damage to insert if the force exerted by the mold 
press increasews to drive insert 10 into proper registration regardless of 
the amount of excess 44 of mounting compound 11. 
In this embodiment utilizing a thermosetting resin, a curing cycle time is 
observed once insert 10 mates with mold plate 12. This cycle time allows 
the thermosetting resin, of which molding compound 11 is comprised, to 
become partially cured. Curing refers to the thermosetting chemical 
reaction that causes molding compound 11 to harden and become infusible. 
In this step the curing needs only sufficient completion to allow removal 
of the resulting molded object from mold plate 12 without damage to the 
resultant object. This specific embodiment uses a 3 minute cycle curing 
time. 
Another step of the procedure relates to removing the resulting molded 
object from mold plate 12. This embodiment of the present invention uses 
only a single mold plate. Therefore, both mold plate 12 and insert 10 are 
designed to insure that the resultant object is removable. Thus, the 
resultant object is removed by gripping insert 10 and pulling insert 10 
out from mold plate 12. The resultant object may tend to stick within mold 
plate 12 in spite of lubrication efforts at minimizing the sticking. 
However, a standard mold press (not shown) grips insert 10 and provides 
the necessary pulling force. 
Finally, this embodiment performs a post-curing step by placing the 
resultant object in an approximately 350 degree F. oven (not shown) for 
four hours. Since the curing is completed in an oven, the time molding 
compound 11 spends in mold plate 12 is minimized, and the mold plate 12 is 
efficiently used. 
The parts used to accomplish the molding procedure in this embodiment of 
the present invention have specific characteristics, as illustrated in 
FIG. 2, which allow the parts to successfully cooperate with each other. 
The Parts 
Mold plate 12 adapts to a standard mold press (not shown) and serves as a 
heat reservoir. As discussed above, mold plate 12 is dimensioned 
accordingly and constructed of a suitable material. Further, mold plate 12 
contains mold cavity 16 which serves as a mate for insert 10 and defines 
the shape of the resultant object, and mold plate 12 contains extrusion 
vent 24 which serves as an escape path for curing gases and excess 44 of 
molding compound 11. 
Removing a portion of mold plate 12 from one of the mold plate 12 surfaces 
forms mold cavity 16. Mold cavity walls 18 are defined as the boundary 
between mold plate 12 and mold cavity 16. Mold cavity walls 18 consist of 
two sections corresponding to the two functions performed by the mold 
cavity. 
Upper portions of mold cavity walls 18a represent the boundary between mold 
plate 12 and that portion of mold cavity 16 which defines a predetermined 
outline of the resulting molded object. Upper walls 18a exist as an 
integral part of mold cavity walls 18 and are located adjoined with and 
toward the inside of mold plate 12 from lower portion of mold cavity walls 
18b. As shown in FIG. 1, the intersection of upper walls 18a and lower 
walls 18b occurs where insert bonding surface 15 contacts mold cavity 
walls 18. Although the precise shape of upper walls 18a depends on the 
shape of the resulting molded object, in this embodiment upper walls 18a 
circumscribe a portion of mold cavity 18 which generally tapers from a 
large cross-sectional area toward the outside of mold plate 12 to a 
smaller cross-sectional area toward the inside of mold plate 12. This 
taper allows the removal of the resultant molded object from mold plate 
12. 
Lower walls 18b mate with the first surface 14 of insert 10. Therefore, 
lower walls 18b are shaped recriprocally to first surface 14 of insert 10. 
When insert 10 is properly mated with mold plate 12, first surface 14 
tightly registers against the recriprocally corresponding lower walls 18b. 
The tightness of the registration is maintained in the area of lower walls 
18b which is nearer the inside of mold plate 12. At all points along a 
plane at the intersection of upper walls 18a and lower wall 18b, this 
registration sufficiently maintains the required pressure when a proper 
quantity of molding compound 11 is inside mold cavity 16. Additionally, 
this registration sufficiently prevents molding compound 11 from escaping 
mold cavity 16 at the area of registration. Further, in this embodiment 
the area of lower walls 18b that meets the tight registration requirements 
also tapers similarly to that of upper walls 18a to facilitate the removal 
of the resultant molded object from mold plate 12. 
Extrusion vent 24, which connects mold cavity 16 to exterior 26 of mold 
plate 12 terminates on one end at relatively small opening 46 in upper 
portion of cavity walls 18a and tapers to relatively large opening 48 in 
the exterior of mold plate 12. While molding compound 11 cures, excess 44 
of molding compound 11 (see FIG. 1) and curing gasses (not shown) escape 
mold cavity 16 through extrusion vent 24. 
A further consideration of extrusion vent 24 relates to small opening 46. 
As mentioned above, a sufficient pressure must be maintained within mold 
cavity 16 during the curing cycle time. Small opening 46 maintains that 
pressure by remaining as small as possible. Conversely, small opening 46 
is also large enough to allow a sufficient amount of excess 44 along with 
the curing gasses to escape mold cavity 15 during the cycle curing time. 
In this specific embodiment small opening 46 is an approximate 0.040 inch 
diameter hole in upper walls 18a. 
Another consideration of extrusion vent 24 relates to the taper of the 
passageway from smaller opening 46 to larger opening 48. This taper tends 
to prevent small opening 46 from becoming clogged with excess 44 of 
molding compound 11 as compound 11 begins to cure and harden during the 
curing cycle time. The taper further tends to prevent clogging of small 
opening 46 from one curing cycle to the next. 
Insert 10 contains several features which are significant in the present 
invention. In this specific embodiment insert 10 is made from aluminum and 
is manufactured in a particular shape. As mentioned above, insert 10 
contains a first surface 14 which mates with lower portion of mold cavity 
walls 18b and conforms to the shape dictated by lower walls 18b. First 
surface 14 is a tapered surface enclosing a generally conically shaped 
volume in which the cross-sectional area of the cone decreasingly tapers 
toward insert bonding surface 15. The use of this shape for first surface 
14 tends to ease insert manufacturing requirements, assure a tight 
registration with recriprocally shaped lower walls 18b, and ease removal 
of the resulting molded object from mold plate 12. 
A bond strengthening umbrella 28 located on insert bonding surface 15 of 
insert 10 aids the attachment of molding compound 11 to insert 10. When 
molding compound 11 cures between umbrella 28 and bonding surface 15, the 
resulting bond between molding compound 11 and insert 10 is stronger than 
would otherwise occur without umbrella 28. Umbrella 28 both causes an 
increase in bonding area and necessitates a part of cured molding compound 
11 to break away from the rest of molded compound 11 before the molded 
compound can separate from insert 10. Both are factors responsible for the 
increase in bonding strength. 
This specific embodiment of the present invention contains a small 
aproximately 0.0675 inch diameter pin hold through insert 10 extending 
into molded compound 11 approximately three-fourths the distance of molded 
compound 11 in the resulting molded object. In this embodiment, the pin 
hole is used to retain small pin-like objects inside the resulting molded 
object. Thus, insert 10 contains aperture 20 for forming this pin hold. 
Aperture 20 extends through the central area of insert bonding surface 13 
and bond strengthening umbrella 28. 
The formation of the pin hole alters the above described molding procedure. 
In this specific embodiment, steel pin 22 passes through aperture 30 in 
the direction of mold cavity 16 and extends beyond insert 10 for a 
distance corresponding to the length of the pin hole. The lubricant 
application step also includes applying the lubricant to pin 22. The 
measured molding compound 11 is then applied to insert 10 by forming 
compound 11 around pin 22. As insert 10 is mated with mold plate 12, pin 
22 is retained in position by pressure plate 30. After the resultant 
object is removed from mold plate 12 it is then removed from pin 22 
leaving the pin hole formed through the interior at the resultant object. 
Pressure plate 30 adapts insert 10 to a standard mold press (not shown) and 
transmits forces exerted by the mold press to insert 10 thereby causing 
insert 10 to mate with mold plate 12. Pressure plate 30 simulates the 
general outline of a mold plate only because this shape is accommodated by 
a standard mold press. Specific embodiments of the present invention which 
are not adapted to standard mold presses do not require such a pressure 
plate. Pressure plate 30 additionally contains pressure plate finger 31 to 
support internal areas of insert 10. Pressure plate finger 31 tends to 
prevent damage to insert 10 as the mold press exerts the force which 
causes insert 10 to mate with mold plate 12. 
The present invention also provides a camming means for gripping insert 10 
as insert 10 is pressed into mold cavity 16. In this embodiment, the 
camming means is comprised of cam members 32a and 32b which are mounted on 
pressure plate 30, guide pims 34a and 34b located on and extending beyond 
the surface of mold plate 12 which contains mold cavity 16, and guide pin 
receptacles 36a and 36b contained in cam members 32a and 32b respectively 
for mating with guide pins 34a and 34b respectively. 
When the mold press fully opens the cam members 32a and 32b are in a home 
position exercising little or no gripping action on insert 10. Thus, in 
this home position insert 10 is not retained within the camming means and 
can be easily removed from or placed on pressure plate 30. When insert 10 
is positioned on pressure plate 30 and the mold press begins to close by 
moving insert 10 toward mold cavity 16, guide pins 34a and 34b begin to 
mate with guide pin receptacles 36aand 36b respectively, thereby causing 
cam members 32a and 32b to move or cam in a direction toward insert 10, 
perpendicular to the movement of insert 10. As the mold press continues to 
close cam members 32a and 32b begin to grip insert 10. As the mold press 
fully closes the gripping action applied to insert 10 by cam members 32a 
and 32b is substantial enough that after a curing cycle time has been 
observed the resulting molded object is removed from mold cavity 16 by 
pulling cam members 32a and 32b away from mold plate 12. 
In this specific embodiment guide pins 34a and 34b are cylindrical rods 
positioned parallel to the direction of movement of insert 10 as insert 10 
moves into mold cavity 16. Guide pin receptacles 36a and 36b are enlarged 
holes in cam members 32a and 32b respectively, and each receptacle is 
angled away from insert 10. Receptacles 36a and 36b are angled so that the 
openings where guide pins 34a and 34b first encounter receptacle 36a and 
36b respectively are located closer to the insert than are the rest of 
receptacles 36a and 36b. The angling of guide pin receptacles 36a and 36b 
causes cam members 32a and 32b to move toward insert 10 as guide pins 34a 
and 34b mate with guide pin receptacles 36a and 36b respectively. Those 
skilled in the art will recognize that various combinations of guide pin 
shapes, angles, locations, and guide pin receptacle and locations will 
work to achieve the same camming action. 
In this specific embodiment the camming means of the present invention uses 
insert adapter 38. Insert 10 is threaded where cam members 32a and 32b 
would grip insert 10. Insert adapter 38 uses these threads by being 
screwed onto insert 10 and then having cam members 32a and 32b come into 
contact with adapter 38 instead of directing contacting insert 10. This 
arrangement prevents damage which may otherwise occur to insert 10 from 
the gripping forces exerted by cam members 32a and 32b. Adapter lips 39 
located on insert adapter 38 further prevent damage by providing a greater 
surface area to push and pull against while mating and removing insert 10 
from mold cavity 16. Additionally, insert adapter 38 allows inserts of 
various sizes to be adapted to a single standard size pressure plate. 
As mentioned above, this embodiment of the present invention uses a 
thermosetting resin with embedded fibers for molding compound 11. These 
fibers are constructed of fiberglass and account for approximately 20 
percent of the weight of the molding compound. Thermoset polyester 
material No.: 1412-A manufactured by the Glastic Corporation is an example 
of such a molding compound. 
The foregoing description uses various embodiments to illustrate the 
present invention. However, those skilled in the art will recognize that 
changes and modifications may be made in these embodiments without 
departing from the scope of the present invention.