Production of injection molding tooling with conformal cooling channels using the three dimensional printing process

A Solid Freeform Fabrication Process called Three Dimensional Printing is a pplied to the fabrication of injection molding tooling with cooling channel s which are conformal to the molding cavity. The tool is created by spreadi ng layers of stainless steel powder and selectively joining the powder in t he layers by ink-jet printing of a binder material. Unbound powder is remov ed from without and within the green part thus defined. The green part is s intered and infiltrated with a copper alloy to produce a fully dense tool. The infiltrant is kept out of the cooling channels by elevating the tool ab ove the free surface of the pool of infiltrant in the crucible, thus creati ng a controlled negative pressure within the infiltrant. An upper Limit to the separation of tooling cavity and cooling channel was derived based on t ransient heat transfer considerations. A tooling set was created to mold a split ring shape and conformal cooling channels were placed in both the cav ity and core sides of the tool. The performance of this tool was compared a gainst the performance of a tooling set with straight cooling channels. The rmocouples buried in the core and cavity showed that the conformal tool had no period of transient behavior at the start of molding, while the tool wi th straight channels took 10-15 cycles to come to an equilibrium temperatur e some 40 degrees C above the temperature of the coolant. The conformal too l was also found to maintain a more uniform temperature within the tool dur ing an individual molding cycle. The gap in the molded split rings did not change from cycle to cycle with the conformal tool, while it did with the c onventional tool. A 2-D finite difference model accurately captured the obs erved temperature histories of the mold with conformal cooling channels.