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From: Ed.Harris@p0.f417.n109.z1.fidonet.org (Ed Harris)
Subject: Re: Quality Parts AR-15
Keywords: casting
Date: Mon, 18 Jun 90 19:20:38 GMT

In article <1990May29.172051.233@ism.isc.com> rats@ihuxz.att.com (D. Woo) writes:
>According to a mechanical engineer whom examined the receivers, he said
>that the EA receivers were sandcasted. I am not certain if anyone would
>want to trust their life on an Aluminum sandcasted receivers...

I think you might be confusing sand casting with investment casting.
The sand casting process not been used in the firearms industry except
for making non-stressed parts like barrel bands and buttplates on
blackpowder guns. The investment casting process used for precision
high-strength parts is done by making an injection moulded wax form of
the part to be cast. These parts are then gated together to form a
"tree" which may be grouped to contain maybe 30-40 rifle receivers or
60-80 rifle bolts, or several hundred small parts. The "tree" is then
dipped in a slurry of silica and water, alternating with layers of
granular silica and more of the silica "mud" until the "vestment" is
strong enough to withstand normal handling in the foundry. After air
curing the forms are fired in a kiln, which burns out the wax, hence
the name "lost wax" often used to describve the process. In casting the
parts the forms are heated in a has furnace and then filled with molten
steel, aluminum, titanium, or what have you. Small parts are usually
done in a centrifugal caster which spins the trees to ensure good
fillout, whereas large pieces are poured similarly to casting a BIG
bullet, except that aluminum and most stainless steels are cast in a
controlled atmosphere, usually argon, or nitrogen, to avoid oxidation
and to control shinkage porosity. When I was at Ruger the high-strength
parts, such as rifle receivers and bolts or revolver frames were all
X-ray quality and ultrasonically tested. They are in fact stronger than
forged parts made by traditional stock removal machining methods.

--

	Ed Harris at The Black Cat's Shack (Fidonet 1:109/401)
	Internet:  Ed.Harris@p0.f417.n109.z1.fidonet.org
	UUCP:      ...!uunet!blkcat!417.0!Ed.Harris



From: Ed.Harris@p0.f417.n109.z1.fidonet.org (Ed Harris)
Newsgroups: rec.guns
Subject: Re: Forged vs. investment casting
Keywords: metallurgy
Date: 6 Aug 90 18:41:14 GMT

In article <7860@orca.wv.tek.com> dmunroe@copper.wr.tek.com (David
Munroe) writes:

>Once in a while I'll hear about guns manufactured by the "Investment Casting
>Process."  Could someone explain what that is and why it is named that?  How
>does it compare with forged parts?  I notice that Springfield Armory seems
>[...]
>
>Also, while I was reading a book on machine guns, I saw an occasional
>unfavorable remark about the use stamped metal parts -- is this separate
>from the forged vs. investment casting issue?

I became very familiar with the investment casting process when I
worked at Sturm-Ruger. To describe all the facets of it would fill a
book, but I can give you a brief description. The parts to be cast
start as an injection moulded wax model of the part, which is done with
great precision, with the dimensioning of the die calculated to control
the shrink rate of the wax and the size mould it will make when the wax
is burned out and the silica shell surrounding it is fired. The wax
pieces are gated together in assemblies of maybe several hundred small
parts, or about 12-15 rifle receivers or revolver framed, sometimes
combining smaller parts in the assembly which is called a "tree",
because it looks somewhat like a tree when finished. This assembly is
first dipped in a thin slurry of silica dust and water, then
alternately coated with progressively larger sizes of silica and more
slurry until a heavy shell is built up around it which will stand
normal handling in the foundry. Groups of the trees are cured until
dry, and after a correct period of time they are fired in a kiln which
burns out the wax form, hence the name "lost wax" used to describe the
process. The fired shells are stored until needed, and prior to casting
are heated red hot in a gas furnace, while the steel alloy is melted in
an electric induction furnace. Stainless steel parts are often cast
with vacuum melted steel in a controlled atmosphere such as nitrogen or
argon to control oxidation. Common alloy steels such as 4140 chrome
moly are cast in normal ambient atmosphere, but the open mould sinks
are covered immediately with a de-oxidant compound. After casting the
silica shell is broken off and the individual parts cut away from the
connecting gates. The parts are then cleaned, usually by sandblasting,
then visually inspected, and criticial parts such as rifle bolts,
revolver frames and rifle receivers are inspected by x-ray and/or
ultrasonically, before being annealed, straightened, and lotted up in
groups to be sent to the machine shop. In my experience I feel that
investment casting as done at Ruger is far superior to forging because
it reduces the stock removal necessary to make the finished part, and
permits use of alloys which cannot be machined by common stock removal
methods. Consequently, Ruger can use materials of a very low sulphur or
selenium content with a high hardenability which provides greater
tensile and compressive strength than the lower alloys other
manufacturers much use because their manufacturing processes require
use of additives like sulphur or selenium to obtain acceptable
machinability. I feel that resulphurized steels should not be used in
thin sections or in applications where extensive machining is required,
because of their greater notch sensitivity. We routinely subjected
Ruger rifles and revolvers to testing which destroyed competitor's
products.  Good forgings of quality material can be very strong, but
are very expensive to produce into complex parts. Investment casting
permits economical manufacture of large production runs of like parts
which offer strength equal to any other manufacturing method, if the
correct alloys and methods are used. Stamped sheet metal parts are not
the same as forged, because the working is done cold rather than hot,
and the grain structure of the steel is not changed. Stampings are
seldom used for highly stressed parts, although they can be used as a
receptacle to hold assemblies of high strength parts together, as in
the HK roller-locked weapons.

--

	Ed Harris at The Black Cat's Shack (Fidonet 1:109/401)
	Internet:  Ed.Harris@p0.f417.n109.z1.fidonet.org
	UUCP:      ...!uunet!blkcat!417.0!Ed.Harris

 
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