Plastic article or earthenware shaping or treating: apparatus – With apparatus assembly or dismantling means or with idle part – Pivotally joined housings or housing sections enclosing...
Reexamination Certificate
1999-08-20
2001-12-11
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
With apparatus assembly or dismantling means or with idle part
Pivotally joined housings or housing sections enclosing...
C249S079000, C249S102000, C425S190000, C425S19200R, C425S547000, C425S556000
Reexamination Certificate
active
06328552
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to injection molding and more particularly to a structure and method enabling a mold base to be alternately used for different parts production.
BACKGROUND OF THE INVENTION
Injection molding of parts, e.g., produced from plastic, involves the use of a press and a mold. In accordance with the present invention, the mold is a block having mated top and bottom sections referred to as a mold base. The mold base is provided with a pocket, part of which is in each of the top and bottom sections for receiving mold inserts, also in two-part top and bottom sections, in which a cavity is cooperatively formed to define a part to be molded. The mold base also includes a sprue that receives molten plastic and conveys the molten plastic to an inter-connected passage in the mold insert that leads to the cavity. Other ports or openings in the base provide access for connection of cooling water fittings secured to passages in the insert to cool the molten plastic in the cavity. Following the cooling and thus the setting of the plastic, the two sections of the mold base are separated (the plastic part residing in the bottom section of the mold insert which resides in the bottom section of the mold base). Ejector pins are extended from the mold base and through the mold insert to engage and unseat the plastic part. The plastic part having been removed from the cavity, the ejector pins are then reseated with the reseating of the two sections of the mold base. The cycle is then repeated.
The locations of the ports (for connection to the molten plastic and water) and the ejector pins are optimally located for the particular part being molded. As will be appreciated, such ports and ejector pin locations require cooperative design as between the mold base and mold insert. Thus, it has been customary that for every part that is to be produced, a mold base and mold insert therefore is custom designed and that mold base and mold insert is dedicated to the production of that part only.
BRIEF DESCRIPTION OF THE INVENTION
It has been determined that a substantial savings can be achieved if a mold base could be adapted to receive alternate mold inserts for different parts. It is, accordingly, an objective of the present invention to provide a generic mold base with a variation of ports or openings (for both water cooling and plastic injection) and having the capacity to provide different patterns of ejector pins.
Also, because the mold inserts have to be precisely seated in the pocket of the mold base, they have been precision sized and essentially press fit into the pocket of the mold base. This inhibits removal and interchange of the mold inserts and thus a further objective is to provide a design that enables precise seating of the mold inserts in the pocket but also ready removal thereof.
A further problem results in the use of alternate mold inserts in a common mold base. The ejector pins need to be fully retracted back to molding position following ejection of each part. The ejector pins are carried by a pusher plate and the plate is moved upwardly in its own chamber in the mold base beneath the mold insert. Return of the ejector pins is accomplished by the reseating of the two mold base sections. Return pins carried by the pusher plate protrude upwardly from the bottom section of the mold base and when the mold base sections are reseated, the top section engages the return pins and pushes the pusher plate to its retracted position as well as the ejector pins carried thereby.
However, the two mold base sections are not designed to be abutted one against the other. For reasons which are not pertinent to an explanation of this invention, the part line spacing between the seated mold base sections will vary. Thus, in one case the ejector pins will be retracted a different distance than the other. This can cause damage to the pins (and failure of the part) and thus it is a further objective to provide full retraction of the pusher plate and thus the ejector pins regardless of the part line spacing.
In a preferred embodiment wherein all of the above objectives are satisfied:
(a) The mold base is provided with ports or openings that adapt to different configurations of the water cooling passages in the mold inserts and multiple sprue openings that selectively connect to anticipated infeed passages in the inserts for directing molten plastic to the cavities.
(b) The mold inserts are designed to have a designated side edge and a designated end edge that is to be securely abutted against a corresponding side edge and end edge of the pocket in the mold base. The insert may be provided so that it can only fit in the pocket in this relationship with the mold base. A relief (spacing) is provided at the opposing end and side edges of the mold insert and wedge members fitting the relief are seated between the mold insert and corresponding end and side edges of the pocket. Screws are provided to force the wedges into the corresponding relief areas and then screws are screwed through the insert into the mold base to secure an accurate positioning of the mold insert in the pocket. Removal of the mold inserts is enabled by removing the screws, allowing for removal of the wedges and then the mold inserts.
(c) The pusher plate is typically provided in upper and lower plate segments. The upper segment carries the ejector pin holes that receives the pin and pin heads. The lower plate segment is secured to the upper plate segment and traps the ejector pins to hold them in place. The mold base is provided with a peripheral seat or land for supporting the mold inserts and define a center opening through which the ejector pins protrude into the inserts. The ejector pins can be located wherever desired within the confinement of the center opening. The pusher plate is configured to fit through the opening and thus can be removed and exchanged to provide different ejector pin arrangements with removal and exchange of the mold inserts. Whereas the center of the mold insert is not supported by the mold base, strategically placed pillars are positioned to project through clearance holes in the pusher plate and into engagement with the insert to provide the needed support. The pillars are removable and replacement pillars at different locations can be provided with interchange of the mold inserts and pusher plates.
(d) The top section of the mold base is provided with pusher plate reseating pins aligned with the pusher plate return pins in the bottom section of the mold base. The upper reseating pins are spring biased to a protruded position from the bottom of the upper base section so that upon seating of the two sections of the mold base, the upper reseating pins engage the lower return pins and pushes the pins and the pusher plate to its fully retracted position. When the pusher plate is fully retracted, continued movement of the upper reseating pins is resisted and the spring behind that pins are compressed to whatever extent is required to accommodate whatever part line spacing is designed for the mold inserts.
As previously discussed, the invention provides a unique and cooperative arrangement between mold base and mold insert whereby the same mold base will accommodate a variety of mold inserts and thereby the production of different parts. This is accomplished by identifying the features that have to be customized to a specific part. Such features includes water cooling passages and ejector pin locations. The former are provided in the inserts which of course is also provided with the customized cavity. By considering the likely water cooling passage layout for a variety of part cavities, the desired locations for water connection accessibility for the variety of mold inserts can be predicted. The mold base can then be provided with the openings necessary to provide that water connection accessibility for the different inserts. The ejector pins and pusher plate are replaceable with the replacement of the mold inserts by provision of the enlarged opening in the support plate of the
Booth Lloyd
Hendrickson Glen D.
Sarkinen Larry R.
Harrington Robert L.
Luk Emmanuel
Nguyen Nam
WBNL DBA AIMMCO
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