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Reducing Costs & Lead Time Through The Graphite Permanent Mold Process


Casting ZA-12 in Graphite Molds  
 

Designing

When designing or upgrading a product for the Graphite Permanent Mold (GPM) process, we highly recommend consulting with CASTECHNOLOGIES' engineers;  their assistance will simplify the design process, thereby reducing engineering and development costs.

This process is simple:  Two mold halves with cavities cut in each half are pressed together, molten metal is injected into the mold under low pressure and held at pressure 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.

CNC Machining

The combination of graphite's high rate of thermal conductivity and the low pressures used to fill the mold cavities effects many specific casting parameters.  Therefore, the following should be considerd 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.
• 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 surfaces perpendicular to the parting line.
• SURFACE FINISH - Castings generally demonstrate much better than 125RMS but 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 casting 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, depending on location.
• HEAVY SECTIONS - Sections over .38" located in the interior of the part should be avoided, unless feeding ribs can be accomodated.  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 no permissable.

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. Casting sizes range from a few ounces to 10 lbs.
Contact us now in Attleboro, Massachusetts, for more information about permanent mold casting.

Contact us now in Attleboro, Massachusetts, for more information about permanent mold casting.