GRAPHITE PERMANENT MOLDS - GPM

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Designing:

Similar to other permanent molds, two mold halves with cavities cut in each half are pressed together, molten metal is injected into the mold under low pressure and are then held together throughout the solidification stage.  The mold halves are then separated and the casting is removed.  The process is then repeated.  Being a permanent mold process, the molds are used over and over with life-time cycles of 10,000-40,000 parts.

The following should be considered when designing components for this process:

• CASTING SIZE – Lengths to 16 inches, widths to 12 inches and depths to 4 inches.  These dimensions are maximum limits and are not to be combined.  Weights range from a few ounces to 10 pounds.

• TOLERANCES – Generally, +/-.005” for the first inch.  Additional inches:  +/-.002” per inch.  Across parting line:  +/-.005”.

• MINIMUM WALL THICKNESS – Usually .125”, however, .060” is possible on small sections.

• MINIMUM DRAFT – 2 degrees on all surfaces perpendicular to the parting line.

• SURFACE FINISH - Castings generally demonstrate much better than 125 RMS but finishes can vary depending on specific location and design.

• ANNUAL VOLUMES – 500-15,000 pieces per year.  Higher or lower volumes are acceptable but may not be as competitive as another process.

• LETTERING AND LOGOS – Raised details can be reproduced.  When used on a surface that cannot contain these protrusions, a block with the graphics can be recessed.

• EJECTOR PIN MARKS – Ejector pins are used to facilitate removal of the castings from the mold.  These pins will leave their impressions on one or both sides of the casting.  Acceptable surfaces for these marks should be specified.

• SHARP CORNERS – Minimum as-cast corner and edge radii should be .015-.032 inches.

• HEAVY CAST SECTIONS – Sections over .380” located in the interior of the part should be avoided, unless feeding ribs can be accommodated.  Perimeter heavy sections should have access to feeding gates.

• SLIDE CORES – Generally, only one slide core is practical in order to properly feed the part.  Internal cores are currently not permissible.

Cost Savings:

Savings in reduced machining operations can be realized due to the dimensional uniformity and cast precision of the castings.  Excellent surface finishes also reduces some secondary operations such as polishing. 

Contact Castechnologies, Incorporated for more information about the Graphite Permanent Mold Process.