User manual

Appendix I

ZCast Design Guide - 25

 Creating a runner bar, for example, across the heat sink fins would help to facilitate

proper filling; however mold vents must still be provided for adequate exhausting of any

gas.

6.6 Parting Lines

The process for creating a mold in CAD software typically involves taking an object (the casting)

and subtracting it from a larger, encompassing object (the mold). The mold must then be split

along a generated surface or a plane. Traditionally, the parting line is very carefully chosen to

create a pair of patterns to form the cope and drag without undercuts, and minimize the number

of cores necessary.

Since ZCast molds are printed using the 3D printing process, the choice of a parting line

becomes a much less demanding chore. The parting line can theoretically cut through any

portion of the mold cavity without regard for undercuts. Below is a list of the few things to

consider when choosing a parting line:

• Avoid thin edges – thin edges can break easily: during either handling or pouring.

• Keep cores intact – splitting cores will leave flash where the parting line passes through

resulting in metal fouling the core vent.

• Cores can sometimes be incorporated directly into either mold half - these ‘internal cores’

possess the benefit that they are always aligned and that no requirement exists that

venting pass through a parting surface.

• Position parting line where flash can be tolerated and/or ground off – putting the parting

line across a complex region without room to grind will limit the possibilities of finishing

the part.

• Keep parting line as far away as possible from core vents – since some metal can leak

along the parting line, be careful that it does not reach the openings for core vents. Metal

will potentially leak out of the mold and into the core, preventing the vent from performing

its function.

• Minimize the number of jogs – keep the design as simple as possible. The more angles

and steps in the parting line, the more difficult it will be to assemble the mold accurately.