 Forging Raises the Bar on Magnesium Die Casting
With
magnesium emerging as "the new aluminum" due to
its exceptional light weight, hot chamber magnesium die
casting is gaining popularity in the manufacturing world.
The process produces magnesium parts with precise dimensions
in a variety of configurations, but it can be demanding
on die casting machines, particularly on the gooseneck that
delivers the molten magnesium to the die. Sloan Industries,
Inc., a Wood Dale, IL-based precision machine shop who supplies
wear parts to the magnesium die casting industry, has discovered
that using forged, rather than the more commonly cast goosenecks,
will yield better machine performance and part quality.
Together with Scot Forge of Spring Grove, IL, the company
has begun supplying forged goosenecks to the industry-and
they are able to do so at competitive costs, due to creative
engineering.
"It was critical for us to supply an improved product
to support our growing customer base in the magnesium die
casting industry," says Henry Slowinski, the company's
president. He notes, "They're making magnesium parts
for everything from laptops to supermarket scanners."
Magnesium is becoming the lightweight manufacturing material
of choice in high tech, space, auto and other industries
because of its excellent strength-to-weight ratio, good
dimensional stability, and recyclability. "It isn't
as brittle as aluminum," Slowinski adds.
The hot chamber magnesium die casting process uses a gooseneck
and piston to inject molten magnesium into a die. The gooseneck
is submerged into molten magnesium, and through the side
fill holes, the gooseneck cavity is filled with molten magnesium.
The piston then forces the molten metal down from the top,
delivering the metal through the gooseneck's vertical delivery
hole, nozzle and into the die without exposure to the environment.
After the metal turns solid inside the die cavity, the die
opens, the part is ejected and at the same time the piston
retracts to its initial position above the fill holes. Then
again, the die is closed, and the gooseneck is filled with
molten metal and ready for the next injection.
Improving the Goosenecks
Sloan Industries supplies goosenecks to various customers
in sizes ranging from 80 to 528 tons. Sloan machines the
goosenecks with precision quality. All of the goosenecks
must be able to withstand temperatures of 1300 degrees,
and must hold up against magnesium, which is highly abrasive.
Until recently, the goosenecks that Sloan provided were
made from sand castings. But imperfections in the cast goosenecks
were causing cracking, porosity, and machining problems.
"Specifications called for DIN 1.2888 cast steel,
which would hold up under the chemical and high temperature
demands, but it was expensive and difficult to cast,"
says company vice president Adam Niedospial. "The inconsistency
of cast goosenecks, unexpected porosity and shrink pockets
caused difficulties and delays in machining."
He
continues, "As many as 40% of the castings had to be
scrapped before we supplied our customers. This was costly
for us, and affected our on-time delivery."
Sloan looked for an alternative to castings, and considered
switching to making the goosenecks from solid bar. This
method would require excessive material, extensive machining,
and as a result, the cost would be non-competitive.
Forging Fits the Bill
Forging was an attractive alternative for the cast goosenecks.
In the forging process, a solid billet can be shaped on
open die presses, which consolidate the ingot center and
eliminate porosity.
Sloan Industries has teamed with Scot Forge, a leading
open die and rolled ring forging company, on previous parts.
Scot Forge uses presses ranging from 750 to 5500 tons, and
can produce shafts with any combination of round (cylindrical),
square, flat or polygonal dimensions. Sloan believed that
Scot Forge could create the right shape and inquired about
the goosenecks.
A Proactive Partnership
Providing a high-quality, cost-efficient forging solution
was right up Scot Forge's alley. Scot Forge offers a "Proactive
Partnership" program in which they work with machine
shops and metal part buyers to optimize part quality, while
minimizing waste and reducing costs. The program, led by
an experienced metallurgist, was designed to discover ways
for producing high quality parts less expensively using
the forging process. It identifies and eliminates unnecessary
processing while improving part strength, often by combining
multiple components into one higher-strength part.
In this case, the gooseneck dimensions called for a spindle
with a square head. If Scot Forge could make this shape,
Slowinski thought, Sloan could then machine the gooseneck
at a much more cost-effective price than from solid bar.
"Two-in-One" Part Saves
Costs
Scot
Forge sales engineers not only confirmed that they could
forge the square-headed spindles; they proposed a creative
"two-in-one" solution that yielded cost and material
savings. Tim Peglow of Scot Forge explains: "When the
Scot Forge sales team saw the dimensions, they knew they
could save costs by making one forging that would yield
two goosenecks. We start with a billet on one of our open
die hydraulic presses; make a square center section, then
use a fuller tool to mark the stepdowns on either end. We
then shape the stepdowns into round journals. Forging the
goosenecks this way makes machining and processing much
easier at Sloan."
Material Assistance
In addition to Scot Forge's Proactive Partnership offering,
the company also assists metal buyers with material selection,
specialty alloys, and custom melts.
"Scot
Forge helped us find an alternative to the DIN 1.2888 steel
specified for casting," Slowinski says. "The alternative
had to stand up under the chemical abrasiveness of magnesium.
Scot Forge's metallurgists worked with us to find a strong
stainless-based alloy to replace the original specification."
Results
Sloan Industries has been pleased with the results and
the cost savings. "With Scot Forge's engineering expertise
and two-in-one concept, we've had no more porosity problems,"
Slowinski says. "With less rework, we save time and
material costs."
He adds, "Now we are able to deliver a superior finished
product that is more reliable and lasts longer for our customers."
For more information go to: http://www.modernmachineshop.com
Photos courtesy of Gardner Publications, Inc.
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