Die Casting News

Outstanding Achievement: Magnesium Strut Tower Brace

Excerpt from the Modern Casting May 2020 article.

This year's American Foundry Society named 2 foundry castings with their top honors as well as 8 others for outstanding achievement. One of those companies achieved outstanding achievement for their unique cold chamber high-pressure die-cast magnesium strut tower brace. 

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As lightweight automotive design fuels more diecasting applications, faster die-spraying is cutting cycle times, and more uniform adhesion is improving process reliability.

Excerpt from the June 2020 article from Foundry Management & Technology

Cost optimization and improved productivity and product quality are driving die casting strategies, particularly in the face of global competition and the need to produce more complex components. Automotive design and manufacturing are prompting to die casters to take on more complex, lightweight, components for powertrain, chassis, and structural parts. In turn, this has guided investments in larger high-pressure die casting machines and more expensive tooling, which has manufacturers seeking to improve productivity, process reliability, and product quality, and to extend die service.

The main purpose of a die-release agent is to allow clean part release and provide a release film that minimizes die soldering, and uniform coverage is critical to both process reliability and the finished product quality.  Standard water-based lubricants evaporate in contact with a hot steel die, leaving a lubricant coating. This is a critical stage, because too much lubricant means liquid cannot evaporate quickly enough when molten metal is injected; and too little lubricant may result in poor material flow (i.e., "die soldering"), and then causing surface defects and porosity that reduce finished product quality.

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Current simulation tools account for the physics of fluidity, and should be capable of predicting castability too. Investigating thermal resistance shot sleeve heat loss effect of conventional HTC values.

Excerpt from the December 2014 article from Foundry Management & Technology by R. Bhola and S. Chandra

The term "thin-wall castings" for the HPDC process has been investigated for well over two decades.  However, the perception of what is considered a thin-walled part has changed over the years and continues to change.  Historically, 3-mm wall thickness was considered a thin HPDC part and that number decreased over the years to 2 mm, and further to 1 mm. Currently, there is a push for even thinner walled parts in the electronics industry, with thickness demands as low as 0.6 mm.  The automotive industry has been looking to make ultra large castings (ULC) using various processes, including semi-solid, permanent mold, and HPDC processes, with target thickness in the range of 1 to 2 mm^[2].

Thin-walled parts are difficult to cast because the melt cools rapidly upon contact with the relatively cold die steel and can solidify quickly before die filling is complete.  The distance a given molten material travels before it freezes and stops moving is commonly referred to as "fluidity".  The dominant variables affecting fluidity are: thermophysical properties of the melt; the temperature of the melt above liquidus (superheat); and mold coating release agent^[3,4].  Much of this work on quantifying fluidity was based on experiments under low pressures, generally not exceeding 15 psi to force the liquid metal through a passage. 

Further, die temperature and the heat-transfer coefficient at the die surface do not seem to be considered properties that define fluidity, though Dewhirst^[4] acknowledged that the heat-transfer coefficient at the mold surface does play a significant role in the measured flow lengths for a given alloy type under given test conditions.

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Problems with conventional approaches to forging-die lubrication can be eliminated with a system that uses PLC-controlled positive-displacement pumping systems.

Excerpt from the November 2007 Forging Magazine article by the Forging staff

In the forging process, friction between die and part, consistency of friction from part to part, and consistency of die temperature all affect not only the part quality and part tolerances, but also die life, and hence operating efficiency and operating costs.

Indeed, die life is affected not only by thermal cycling but also by friction between the die and the part being formed, variations of which greatly affect the severity of thermal cycling itself. Die designers base their designs on assumed, given friction. Presses also are designed based on loads caused by formation of parts, and these loads are affected significantly by friction, in addition to temperature and material being formed. Even billet weight is based on estimated material flow which, again, is greatly impacted by temperature and friction.

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