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

Abstract

A Solid Freeform Fabrication Process called Three Dimensional Printing is applied to the fabrication of injection molding tooling with cooling channels which are conformal to the molding cavity. The tool is created by spreading layers of stainless steel powder and selectviely joining the powder in the layers by ink‐jet printing of a binder material. Unbound powder is removed from without and within the green part thus defined. The green part is sintered 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 above the free surface of the pool of infiltrant in the crucible, thus creating a controlled negative pressure within the infiltrant. An upper limit to the separation of tooling cavity and cooling channel was derived based on transient heat transfer considerations. A tooling set was created to mold a split ring shape and conformal cooling channels were placed in both the cavity and core sides of the tool. The performance of this tool was compared against the performance of a tooling set with straight cooling channels. Thermocouples 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 with straight channels took 10–15 cycles to come to an equilibrium temperature some 40°C above the temperature of the coolant. The conformal tool was also found to maintain a more uniform temperature within the tool during 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 conventional tool. A 2‐D finite difference model accurately captured the observed temperature histories of the mold with conformal cooling channels.

Design for Additive Manufacturing: Trends, opportunities, considerations, and constraints

“…13). Early research [280] [359][129] [267] showed that conformal cooling in injection molding tooling improves process efficiency and quality. Industrial injection molding case studies have confirmed these benefits with reports of reduced lead time, more uniform temperature distributions, reduced cycle times, improved quality, reduced reject rates, reduced corrosion, longer maintenance intervals, and overall cost savings [98][108] [112].…”

Capabilities and Performances of the Selective Laser Melting Process

“…They showed that the conformal cooling channels technique led to significant improvements and a general reduction of the cycle time while increasing heat transfer (Ring et al, 2002). A comparison between conformal channels and drilled cooling channels has also been conducted by Sachs et al Their analysis shows that the conformal channel mould reaches operational temperature faster than the conventional one, attaining a more uniform temperature distribution with efficient heat transfer capacity (Sachs et al, 2000). While the use of conformal cooling channels on the one hand greatly enhances the injection molding process, on the other hand it is much more complicated fabricate them on respect of the straight ones.…”

Layered Manufacturing: Challenges and Opportunities

“…Enhanced heat extraction, increased production rate and reduced cost can thus be achieved. Conformal cooling channels can be made by depositing sacrificial material, which is later removed as with MITs 3DP process [37], or can be made while fabricating the part as with Optomec's LENS process [16]. Another example of part complexity is the casting for a fuel cross over made for Rocketdyne by Soligen's 3DP process [36].…”