"DoN. Nichols" wrote in
:


There are things which are die cast and then machined to final
dimensions in some places like automobile engine pistons.


Automobile engine pistons are _not_ die cast. They are permanent mold
gravity cast. Die casting does not generate the required micrograin
structure for this application of aluminum alloy.
Die casting is "Pressure Casting". The molten "shot" of aluminum is
forced into the die at extreme pressure.
Permanent mold gravity casting is more of a traditional casting
technology, except the mold is a semi-permanent one made of (typically, a
special alloy of H13) steel. Although there are variations, most are of
the 5 piece inner core mold type.
There are up to 12 pieces that make up the mold, 5 inside, up to 7
outside, depending on whether the part requires flip cores or not.
Inside:
Center wedge - A tapered piece and the heart of the inner mold core. this
is a 4-way wedge.
2x side cores - these make up the inside window shape (ribs, pockets,
inner pin bore shape, etc)
2x middle cores. These are also wedge shaped to a small degree, and go
between the window cores.
2x outside cores. these make up the OD of the casting, and have a hole
for the pincores.
(optional) 2x flip cores. these are hinged outer window cores used for
generating pockets up under the 3rd groove above the pin bore for weight
reduction. These replace part, but not all of the outside cores.
2x pincores. these create the cast pin hole
1x head core. this creates the crown geometry.

After the part has solidified enough to be handled, the center wedge
pulls down, as the center wedge pulls down, it pulls the middle cores
toward the empty space left by the center wedge then down, then the side
cores are pulled inward to relase the casting. All of this is made as one
assembly. Then the head core releases. If flip cores are used, they swing
away, then the outside cores retract. The part is then removed from the
mold. Close all mold parts, insert new screen, and pour another part.

This type of mold allows you to cast pockets and other features inside
the casting that have negative draft.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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