Injection molding thermoplastic patterns having ceramic cores
AssigneeUnited Technologies Corporation
InventorRichard A. Myllymaki
Life of this patent
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Abstract
Disclosed is a method and apparatus for fabricating thermoplastic patterns for investment casting. The patterns define hollow objects and have contained within a very precisely located ceramic core. Thermoplastic is injected into the pattern die on either side of the core, thereby avoiding distortion, movement or breakage of the core. Multiple sprues are used; the sprues are individually fed from a nozzle having a single central bore. The configuration of the nozzle tip and the cavity from which the sprues emanate is such that a gate or bridge is not formed at the entrance to the die assembly. Accordingly, removal of the pattern from the die may be effected by pulling the part coaxially with the sprues, thereby avoiding the necessity of splitting the die where the sprues are located.
Claims9
In the process of fabrication of a ceramic investment casting mold containing a thin and brittle ceramic core, wherein a thermoplastic polymer is injection molded into a die to form an expendable pattern in a die cavity, wherein a portion of the mold defines a shape of the airfoil of a gas turbine, the improvement which comprises simultaneously injecting the polymer on either side of the core from an end of the die through at least two sprues with balanced flow that minimizes hydrostatic force on the core.
In injection molding using a nozzle with a single port and a die with multiple ports, the method of preventing solid material from forming between the die ports which comprises providing a higher surface area in a portion of the nozzle than in a portion of the die with which the nozzle mates, said die and nozzle portions being those which cooperatively define a liquid cavity connecting the multiple ports.
In apparatus for injection molding the combination comprising a single port nozzle having a surface relief channel intersecting the port and a multiple ports die, the nozzle and die defining a liquid carrying cavity when mated, the portion of the nozzle which defines the cavity having a higher surface area than the portion of the die which defines the cavity.
Apparatus for injection molding, within a cavity in a multi-part die, a thermoplastic polymer pattern having therewithin a precisely located thin ceramic core, for defining the shape of a thin walled article such as a hollow turbine blade, comprising:
- a source of molten polymer;
- a nozzle having a central bore running to a port at its tip and a surface relief portion intersecting the port, the nozzle connected to the source to provide polymer at the tip;
- a socket in the die surface, the socket having at least two ports therein, the socket adapted to receive the nozzle and form a liquid tight seal therewith, the surface relief portion of the nozzle forming, when mated with the socket, a cavity connecting the central port of the nozzle with the die ports;
- and
- means for conveying polymer separately from each socket port to the pattern cavity in the die.
Dependencies are inferred from the claim text.