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Die Casting News & Updates
Improvements in Aluminum Alloys
The mechanical properties of aluminum die casting alloys has greatly improved over the last few years. Many advances have been in gating and shot control, but the biggest gains have come from improvements in melt quality control. If dirty or gassy metal is pushed through a shot tube, the castings will never approach the quality achieved with metal of uniform composition, freedom from inclusions of many bad forms, and low gas levels. Most die casters now recognize that while increased shot pressures will partially compensate for faulty melt control, the best castings are created with metal that meets high quality standards. The presence of inclusions and gas in the metal ladled into the shot tube can negate all down-stream efforts to improve mechanical properties of castings.
In recent years many process improvements have been developed to resolve the negative factors associated with inclusions and gas content. The combination of rotary degassing and flux injection is the most popular method, and combines economy with the added advantage of yielding minimal interruptions to metal delivery to the holders and die casting machines.
Concurrent with the adoption of advanced cleansing processes, the tools used to monitor the processes have also undergone changes. The accuracy of the old reduced pressure testing methods has been greatly improved with automation and better control instrumentation, especially when coupled with density measurments of the test coupons. The test results have moved from subjective operator estimates to quantitive numbers that are the basis for new specifications. While chemical analysis changes do influence the density of the samples, changes in the gas or inclusion levels will have a more immediate effect upon density of the samples, with a direct impact upon down-stream casting mechanical properties.
The net result of all of the process changes and developments has been the production of stronger castings, and general improvement in the overall quality level.
Aluminum Versus Iron
Aluminum castings started making significant inroads on iron castings almost as soon as the price of aluminum began to make it economically feasible, albeit a stretch. Momentum changed dramatically with the implementation of mandatory fuel economy standards for light vehicles.
CAFÉ legislation was passed in 1975, not to reduce what was already recognized as high levels of pollution created by automobiles, but to address the 1973 Arab oil embargo. The rules were challenged, plaintiffs were granted extensions and economic issues delayed comprehensive implementation until the mid-1980’s. The standards continue to tighten with the EPA requiring vehicles to meet a target of 63 grams of carbon dioxide equivalent per mile in model year 2025. It is most conveniently and understandable when expressed in miles per gallons but that is not the correct form.
Taking weight out of vehicles is one of the easiest ways to meet EPA regulations. Aluminum is a very good way to take weight out. Initially, iron castings including engine blocks, heads, intake manifolds and transmission housings were converted to aluminum. In addition, steel wheels were largely replaced by cast aluminum wheels. In 1975, aluminum content in light vehicles was about 80 pounds. In 2012, aluminum content rose to an average of 343 pounds. About 85% of that weight is in the engines (130 pounds), wheels (67 pounds), transmission and drive chain(70 pounds) and radiators (32 pounds). Eighty percent of engine blocks are aluminum, 99% of cylinder heads, 100% of radiators and transmissions and 70% of road wheels are aluminum. Small percentages of aluminum castings are used in suspension arms/links (14%), bumper beams (17%), steering knuckles (27%) and hoods (30%).
The 263 pound of aluminum added to vehicles from 1975 to 2012 came at the expense of 765 pounds of iron castings.
It is generally accepted in the automotive industry that $2 in additional vehicle cost is reasonable to reduce weight by one pound. Ford Motor’s 2015 F150 Pickup is the first “all aluminum” vehicle. There is about $1000 in added cost due just to the use of aluminum. While the use of aluminum in light vehicles will continue to grow only a small portion will be aluminum castings. Most of the growth in the use of aluminum will be extrusions and sheet.
Most reports compare iron and aluminum castings based either on tons (weight) or sales dollars. Neither makes any sense in the comparison. Iron weighs 491 pounds per cubic foot and aluminum weight 169 pounds per cubic foot. A comparison based on weight substantially understates the volume of aluminum cast relative to iron. In 2012, the average aluminum casting sold of $2.358 per pound compared to $.641 for ductile iron, a multiple of 3.7 times the price of ductile iron. A comparison based on sales dollars overstates the importance of aluminum.
An “apples to apples” comparison is a comparison of the cubic feet cast.
As the chart shows, aluminum is a larger share of the market than recognized when weight is used as a comparison. Several factors impact the volumes cast in any one year. For both iron and aluminum, automotive is the “900 pound gorilla.” In 2012, 8.9% of gray iron castings were for automotive, 12.2% for ductile iron and 30.5% for aluminum. In die casting aluminum, fully 55% of production is for automotive applications. The significant drop in aluminum production that began in 2008 and started to reverse in 2010 was due to the drop in automotive production.
Each of the iron alloys and aluminum alloys have properties that can determine which is best in a particular application. There are times the materials are interchangeable with reasonable or no modification to the part design. As proof of this, consider the conversions of iron castings in automotive to aluminum. When the materials are substantially interchangeable, price becomes the determining factor. Aluminum is a preferable material from the standpoint of ease of processing.
A hypothetical casting weighing one pound in iron (.34 pounds in aluminum) that can be made identically in both iron and aluminum would cost $.641 in ductile and $.802 in aluminum. The price of aluminum is trending very slowly downward. When the cost of aluminum drops another 25%, the materials will be cost competitive. Aluminum is a much more prevalent element than iron in the earth’s surface. A breakthrough in processing technology that lowers primary aluminum cost could bring a dramatic price drop. Also, aluminum is very easily recycled. As more primary aluminum is put into use and products reach the end of their life cycle and are reprocessed the supply of secondary aluminum will increase. An increased supply of secondary aluminum will put downward pressure on material costs.
There do not appear to be any imminent breakthroughs in primary aluminum processing. The price of secondary aluminum is moving very slowly. It will be some time before aluminum, as a material in itself, is price competitive with iron.
There are certain categories of castings where there is no comparison between iron and aluminum castings. Aluminum castings top out at 3,500 pounds with a few somewhat larger. Iron castings top out at 200,000 pounds in the United States and even larger in Europe and China.
Brief History of Aluminum
Aluminum is the newest of the major metals in casting today. Aluminum is the world’s third most abundant element after oxygen and silicon. It makes up about 8.3% by weight of the Earths solid surface. Aluminum metal is very reactive so native specimens are rare. It is found combined in over 270 different minerals. The major ore used in the production of primary aluminum is bauxite.
The process for extracting aluminum was very complex and expensive until in 1886 when Oberlin College student Charles Hall and French engineer Paul Heroult separately and simultaneously developed a relatively inexpensive electrolysis process by which aluminum is extracted from aluminum oxide. Prior to that aluminum was considered a precious metal. During the reign of Napoleon III (1852 to 1870) privileged guests at state dinners were served on aluminum plates while less privileged guests were served on plates made of gold and silver. When the Washington Monument was capped with a 100 ounce aluminum casting in 1884, the cost was today’s equivalent of $300 per ounce or $4,800 per pound. The 6-1/4” pound casting was the largest ever produced at that time.
In 1919 the Smithsonian Institute reported that 80 tons of aluminum was produced in 1889 and that grew to 80,000 tons in 1917. The major use of the increased production was in the manufacture of aircraft and dirigibles. The development of low cost electricity production, especially hydro-electric, drove the cost of producing primary aluminum down to more reasonable levels. Production of primary aluminum in 2013 was 4.527 million metric tons.
Greater use of Aluminum
Ford’s decision to utilize aluminum body and bed panels in the 2015 F-150 put the automotive industry on notice as to the potential of the metal. Weight savings of 700 pounds in the new truck shows the potential for the use of aluminum for larger volume production vehicles. Audi and Jaguar pioneered aluminum in the A8 and XJ as primary structure and body components in the early 2000s with the metal finding its way into other models over time, mostly for hoods or trunk deck lids. Today, Land Rover, Range Rover and Tesla Model S utilize aluminum extensively. Late last year, Toyota jumped on the aluminum bandwagon announcing that selected future models will depend on aluminum to reduce weight. Chrysler also announced that the next generation Jeep Wrangler would also have an aluminum body.
The use of aluminum within the auto industry – at least in North America – could double by 2025 if there is sufficient supply of auto grade aluminum. This shift has started in larger and more expensive vehicles first but will migrate into more mainstream vehicles over time. As costs fall with working with the metal, the pace of models offering such aluminum structures and body panels is likely to increase at an increasing clip to gain fuel economy advantages. This means that new methods for vehicle construction – such as rivets and bonding and newer welding techniques will become more mainstream.
The steel industry seems to have been caught off guard by these moves to aluminum and is now feverishly working on lighter weight steel for the auto industry. Vehicles account for roughly 25% of steel consumption as the second largest category after construction globally.
A NADCA endorsed bill to provide more oversight of regulators is moving through the newly Republican controlled Congress. The small business Regulatory Flexibility Improvements Act has secured significant support in the House, and for the first time, has a chance of securing the sixty votes needed in the Senate for passage. The bill requires government regulators to include the indirect impacts on small business, in addition to the direct impacts of a rule, in any analysis when developing new regulations. The bill also forces the EPA and other federal agencies to hold a small business review panel when developing a rule impacts that impact small businesses. NADCA has repeatedly raised concerns over agencies skipping the review process and downplaying the number of small business they believe their rule will affect.
We have recently revised our Aluminum Alloy Characteristics sheet. See which alloy is best for your die castings by downloading your copy from our online Resource page. Aluminum Alloy Characteristics
Northwest Die Casting has recently expanded its facilities. We now have a total of 24,360 square feet available. With this expansion, we are able to accommodate new equipment and machines to better serve our customers.
Northwest Die Casting is proud to announce we have purchased our first CMM (Coordinate Measuring Machine). This new piece of equipment brings an even greater level of precision to our design and testing capabilities.
We will continue to update this page on a regular basis. Stay tuned for important news about Northwest Die Casting and other information concerning the die casting industry.