Trends in Lightweighting With Metal Castings Opportunities for lightweighting with metal castings abound through material choice and smart designs. ANDREW HALONEN, MAYFLOWER CONSULTING LLC Note: This article is based on a presentation the author was scheduled to make at the 2020 Metalcasting Congress in April, which was unfortunately cancelled due to the coronavirus. etal castings are found in almost all industrial markets, and certainly in 4 KEY the transportation business. Cast- ings can be produced in many materials and processes, each offer- ing its uniqueness in properties, in WAYS tolerances and in the ability to seek M efficiencies. Efficiency becomes the ability to design and produce to an LIGHTWEIGHTING WITH optimized shape, minimizing material and post-processing. New tools METAL CASTING IS MET and new foundry techniques, combined with the long-honed skills of the metalcaster, are a winning combination for the future. WITH RESISTANCE Lightweighting is a term that encompasses the task of reducing material to achieve weight reduction. There are motivations to cut weight, just as there Cost is king. is resistance to cut weight. Improving performance and assembly ergonom- ics, reducing part count, and reducing material costs are some of the motiva- System over tions. Yet considering these factors, it does take considerable effort to reduce component. component weight. Changing the Cost Is King supply chain. Low cost usually wins. In ground vehicle transportation, lightweighting activity is constant, yet it is usually delivered as cost neutral. If there is an Other material appetite to cut weight, we often ask, “How much per pound will you pay?” innovations. which sounds like a straightforward question, yet it is often difficult to 32 | CASTING SOURCE | MAY/JUN 2020 answer. The product developer may the presentation, I reached out to value weight on the wheel more my global network and received than weight on the cab. I contend success stories from the U.S., Bul- that if the target value is $1-2/ garia, Sweden, France, and Canada. lb., then the lightweight solution Metalcasting lightweighting ex- remains within the incumbent amples were categorized as material supply chain; iron to ductile iron or conversions, sheet metal-to-castings, austempered ductile iron (ADI); or multi-metal, generative design, aluminum to stronger aluminum. powertrain influence, and process Target values exceeding $3/lb. may optimization. Last, we found two allow iron to aluminum conver- new alloy developments that will sions. Seldom do I hear of a ground Fig. 1. The steering knuckle conversion enable lightweight castings. vehicle willing to pay more than from an aluminum forging to a ductile iron The best applications in light- $5/lb. for weight savings, though in casting achieved a 40% cost savings and weighting cut costs while improv- 30% reduction in weight, while improving specialized commercial trucking— strength and stiffness by 20% and 25%. ing performance. Waupaca Foundry those carrying cryogenic fluids—I (Photo courtesy of Waupaca Foundry) (Waupaca, Wisconsin) achieved was told they would pay $12/lb. for success on an automotive steering weight savings. knuckle, converting an aluminum Recognize that the cost increase forging to an optimized ductile includes the cost at the foundry; at iron design that is 20% stronger, the machine shop if different than the more change that is required, the 25% stiffer and 40% lower cost, the incumbent, at the producer, at more resistance to make the change, while narrowing the weight delta to the assembler, and at the OEM to regardless of the upside efficiencies. an acceptable 1.32-kg increase over the customer. That does not leave Other Material Innovations the forging. much margin for the foundry to Again, cost is king in most ap- innovate, which is one reason why As we look at the entire vehicle plications, and this example shows despite the wide range of high per- through the lens of the chief engi- that delivering a lower weight than formance alloys, the transportation neer, there are many lightweighting the incumbent is not mandatory to business often selects the vanilla- options. Should we optimize the win the sale. grade alloys. steering knuckle, or should we ad- dress the windows? Converting the Sheet Metal Conversions System Over Component rear window from tempered glass to You may hear this phrase in In the electric vehicle (EV) polycarbonate offers a 40% reduc- the automotive market, “If they market, for example, the new tion in weight. This may be a much can stamp it, they will.” Metal powertrain costs are immense, easier conversion than reengineering stampings are popular in vehicle which doesn’t leave much cash to a safety critical component that of- construction, yet the innovative buy lightweight materials. Even fers similar weight reduction. foundries and engineers are find- internal combustion engine vehicles Success Stories ing ways to convert to castings. are adding new levels of autonomy Here are four examples: and data sharing, all adding to Despite the resistance, metalcast- 1. Meridian Lightweight vehicle cost. Mayflower Consulting ers are a hardy crowd and still find Technologies (Strathroy, is studying suspension components successes in lightweighting. Com- Ontario, Canada) converted now, and we will soon see what ma- municating success is much easier an eight-piece steel stamped terials are selected for a few EVs, to me in pictures than words, as and welded assembly to a and dozens of SUVs and pickups. was intended at the Metalcasting one-piece magnesium casting Congress 2020. In preparation for Changing the Supply Chain Imagine as a buyer, you have been working with a gray iron foundry for years, and now the engineers de- signed the next component iteration in ADI or aluminum. This forces you to seek out new suppliers, to learn their business, the differentia- tors between good and bad casting, and the robustness of the processes. Fig. 2. Tesla is replacing 70-piece steel weldment in its Model 3 (left) with two large castings in Change is difficult for everyone, so the Model Y (right). MAY/JUN 2020 | CASTING SOURCE | 33 ter·mi·nol·o·gy to cut the weight of the inner panel on the Jeep Wrangler RheocastingRheocasting Metalcasting process where liquid metal is agitated during initial rear swing gate by 6.7 kg. 2. Automotive shock towers are stages of solidification to produce a semisolid structure that transitioning from steel stamp- remains highly fluid after 60% solidification. ings to high pressure die cast (HPDC) aluminum with a weight savings on the vehicle as high as 24 kg. This is not shared a success story in an A bi-metal brake disc with a a new story, yet this applica- industrial plant where a 50-kg unique method of joining is 25% tion is evolving into non-heat hot-rolled steel fabricated lighter than the baseline 350-mm treated aluminum alloys to ramp was redesigned in 80- outer-diameter, one-piece gray iron avoid distortion in heat treat. 55-06 ductile iron, cast in lost disc. The aluminum flows around I project shock towers will foam with just 3.2mm walls, the iron peg, joining the two pieces. eventually be produced in and reduced to 15.8 kg. The Called COBADISK, the center aluminum via rheocasting, big winner was the shop floor of the brake disc is low-weight and further converted to a personnel, as the lightweight aluminum while the wear ring is new alloy, magnesium via high ramp could be moved by just gray iron. pressure diecasting. one person. 3. The Tesla Model Y has two Powertrain Effect on Metal extremely large castings in the Multi-Material Integration Castings: Internal Combustion rear compartment, replac- “Put the best material in the best Engines ing 70 steel stampings and location,” is the thought behind multi- It was enlightening to learn a made with an AlSiMg alloy material integration. Two interesting compact graphite iron (CGI) engine in HPDC. For a view of this examples include the following. block could enable a lower weight casting, refer to the “mega Steel and aluminum automo- engine than one using an alumi- casting” in this benchmarking tive subframes, uniquely joined by num block. Compare the stats and video by Munro & Associ- friction stir welding, achieved 25% images in Figure 4. Both are 3.0 ates, www.youtube.com/ weight savings and are 25% more L engines, yet because CGI has a watch?v=KVGvwLnNyF0. rigid in its third generation on the higher modulus of elasticity (stiff- 4. Skuld LLC (Tipp City, Ohio) 2018 Honda Accord. ness) than aluminum, it enables a smaller engine block for the same output. Even though the CGI block is heavier than the aluminum block, the reduced size requires smaller components to produce the complete engine, thus the total package is both smaller and lighter. Engine compart- ments are always space limited, and most IC engine vehicles are over- weight in the front. It sounds like a great application for CGI. Powertrain: Electrification In battery electric vehicles, there is considerable conversation and development activity in battery box housings and structures. Most of the battery boxes are made with alumi- num sheet and extrusions. It is interesting to see the growth in the “skateboard” chassis, such as the one in Figure 7 from Rivian (Plymouth, Michigan). The skateboard chassis offers Fig. 3. This bi-metal brake disk is 25% lighter than the baseline iron disc. (Photo courtesy of significant versatility in building Saint Jean Industries.) vehicles; over the top of the chassis, 34 | CASTING SOURCE | MAY/JUN 2020 one can build an SUV, a pickup, or a delivery truck. Rivian has taken considerable investment from Ford Motor Company and Amazon, and they received an order from Amazon to provide 100,000 delivery vans.