Knowledge Bank

Basic Considerations For Die Castings

• Dimensional tolerances depend on part configuration. They are dependent on moving die members, the size of the part (projected area), and whether dimensions run across the parting line of the die. Never specify dimensional tolerances closer than are essential and practical to the die cast process.
• When dimensioning part always specify
  A. Amount of draft.
  B. Where dimension is to be held (does dimension increase or decrease because of draft).
• Provide the maximum permissible radii on all corners and try to stay away from sharp corners wherever possible.
• Keep wall sections a uniform thickness.
• Raised engraving on part is desirable and less costly than depressed lettering.
• Minimum machine stock is very important. Over .030 per side could result in opening up porosity.
• Stay away from holes smaller than 4-40 for the following reasons:
  A. Cannot core.
  B. Porosity is a problem in dig drilling and tapping holes this size or smaller. (Minimum hole diameter as a rule is .125 for aluminum and .093 for zinc.)
• Allow a minimum of three (3) times the pitch of thread beyond depth of required tapped hole depth, to allow for tap lead.
• Stay away from undercuts at base of thread.
• Cast threads are possible in class 1 gage limits, allow a flat at 180° if possible for trimming.
• Use roll taps where possible on depth holes. In the case where a thru hole requires a stronger thread, use a roll tap, but hole should have a cast countersink at both ends to prevent bulge.
• Use heli-coils where excessive assembly and disassembly of bolts is required.
• Utilize cast-in inserts for extreme wear areas.
• Close tolerance machined castings should be stress relieved.