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

Die Cast 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.

Die Cast "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."

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