Note: This article is Part 2 of 2 of the author’s Hoyt Memorial Lecture presented at the 2023 AFS Metalcasting Congress in April. Part 1 appeared in the September issue of Modern Casting.

The metalcasting industry is impacted in no small way by the surge in all-electric vehicles (EVs). About half of the castings currently deployed in internal combustion engine (ICE) vehicles are eliminated in EVs. With our customers, we must “innovate or die.”

The EVs have no tailpipe emissions—that’s good. The electric motors are about 80% efficient—that’s good. They weigh, on average, 500kg more than comparable internal combustion vehicles—that’s bad. Electric vehicles cost significantly more than ICE vehicles because they contain about $10,000 worth of extra energy embodied in their battery powertrain … that’s significant. So, what do we do? Our government issues $7,000 tax credits to artificially induce EV sales by hiding the cost of the embodied energy that you are paying for up-front.

The typical, modern ICE vehicle is powered by a 40% efficient powertrain. You put carbon fuel in the tank (gasoline/diesel) and net 40% of the energy to operate the vehicle. The EV uses electricity produced by the power company. Let’s say the power company is a forward-thinking concern that has deployed a new 60% efficient natural gas, combined-cycle system to produce electricity. The power station is fed with natural gas, 60% of the energy is turned into electricity, 5% is lost in transmission to the end user’s charger and into the vehicle. Then the EV’s 80% efficient motors put the power to the road. The overall efficiency of the EV can be calculated as follows:

60% x 95% x 80% = 46% energy efficiency

That 46% EV headline efficiency is better than the ICE vehicle’s 40% efficiency but, remember, with the EV you buy $10,000 worth of energy (perhaps 100,000 kwh) upfront, embodied in the vehicle’s manufacture, and the EV weighs 500kg more than the comparable ICE vehicle requiring, perhaps, greater than 10% more power to propel the EV. So, is an EV more efficient than a comparable ICE vehicle? Does it produce more or less CO2 during its lifetime?

The EV push is based on a goal of zero carbon. No EV will ever be zero carbon (or zero emissions). And, propulsion type should not be a binary decision (carbon or no-carbon). It may be novel, but how about choosing the most efficient powertrain for the application? 

General Motors’ CEO Mary Barra has set the corporate goal of “zero emissions, zero congestion, zero crashes.” They have (arbitrarily) saddled their customers with that binary decision—zero carbon or nothing. General Motors (GM) is currently marketing a 4,500kg electric Hummer. How is that helping anything? GM also markets the lowest price EV in the U.S., the $26,500 Chevy Bolt, a small sedan weighing in at a hefty 1,640kg. Conversely, Toyota, the No. 2 vehicle manufacturer in the world and the leading manufacturer of hybrid vehicles has espoused another path. At an October 2022 press conference, Toyota CEO Akio Toyoda said that their goal “remains the same, pleasing the widest possible range of customers with the widest possible range of powertrains.”

The EVs are torquey. They don’t require oil changes. They reduce smog in city centers. They are perfect for some people. They are not for everyone. The metalcasting industry has helped their customers develop and produce the current generation of high-quality, efficient, powerful, vehicles. We should not stand idly by while well-intentioned, misinformed regulators kill our customers’ products.

Ironically, EVs, with their additional mass, will require truck-like suspensions and brakes. That means more robust gray iron brakes and stronger/stiffer suspension components, both opportunities for metalcasters.

Contrary to pronouncements by politicians and some automotive CEOs, ICE vehicles will continue to dominate the vehicle market for decades. On the ICE vehicle side of the ledger, the practical options for increasing vehicle efficiency are to further increase powertrain efficiency, reduce coefficient of drag, and to reduce the mass of the vehicle. The ICE vehicle designers/manufacturers must continue to “innovate or die.”

Embodied Energy: Industry 4.0, Design, and Metalcasting Innovation

The most efficient way to reduce the embodied energy in an iron casting is in the melting method. Cupola melting can be done for an average 33MJ/kg while induction melting takes an average 42MJ/kg. As it turns out, a properly scrubbed cupola uses, on average, 21% less energy than induction melting but produces up to 5% more CO2. You can weigh the tradeoff for yourself.

After melting, the two most efficient techniques to reduce melt process embodied energy are increasing mold yield and eliminating scrap.

Increasing mold yield is sometimes considered casually, and last, in the process model, but modeling a small increase in mold yield has a large effect on the casting’s embodied energy.

Scrap is waste. If a metalcasting business does everything right, they make a net 10% profit. One scrap part not only wastes the energy that went into that piece, but it reduces the capacity of the system to produce one more. In the end, 10 good parts need to be produced just to make up for the profit (and energy) lost in that one scrap piece.

Computer models today can help us to get parts “right the first time.” In a production foundry, modeling to increase a plant’s “right the first time” is a quick return on investment. Modeling will, over time, become more automated and come down in cost, expanding its use to short-run casting applications and further improving casting process efficiency.

Drilling down to a field I’m very familiar with, cast iron, the initial automotive industry approach has been to convert from ferrous components to aluminum to reduce mass. This has proven to be expensive and energy intensive. Low specific gravity does not always translate to lower component weight or volume.

Dawson et al. have demonstrated that clever compacted graphite iron (CGI) design can produce diesel engines that are smaller and lighter than their aluminum counterparts. This doesn’t necessarily happen because the CGI block weighs less, but that the CGI design (with its higher stiffness) shortens the engine making the entire system substantially lower in mass than the longer, aluminum engine. Recently published, by Dawson, Ferrarese and Marquard, was the case of a diesel hybrid engine developed by TUPY with a CGI block mated with a polymeric casing replacing aluminum at equal mass and significantly lower embodied energy (Figure 2).

Zhu et al. compared the life-cycle energy for an automotive upper control made from either ductile iron or cast aluminum and found the life cycle analysis (LCA) energy of the ductile iron design to be “40-43%” lower than that of a cast aluminum design. They further compared an ADI design to a stamped/welded steel design and found the ADI’s life-cycle energy to be 7% lower.
The cast iron family tree is 3,000 years old with many interesting branches. Gray iron, malleable iron, compacted graphite iron, ductile iron, high-silicon-molybdenum iron, austempered ductile iron and high-silicon, solution strengthened, ferritic ductile irons all have unique properties and mature markets. Relatively high stiffness and strength-to-weight ratio make cast irons a lightweighting choice, if we choose to take maximum advantage of those properties during the design process.

As was mentioned earlier, metalcasting is the lowest energy method to produce a metallic product. That implies that all forgings, weldments, and multi-piece assemblies would be candidates for conversion to metal castings. Here, metalcasters have historically been lazy. It is very easy to sell a specific cast material/process to people already buying and using that material. It is much more difficult, albeit more profitable, to sell castings to customers buying weldments, forgings, and assemblies or another cast material/process combination. As my colleague, Kathy Hayrynen, once said, “We need to stop being order takers and start being order makers.” Why aren’t all metallic products castings?

With the sophisticated Industry 4.0 technology that we have for design, why do we still design parts that are extruded and evolved geometric shapes? The flowers in my garden have designs evolved over eons. The stems are perfectly designed to be sufficient to support the flower in a 50-mph wind. The stems are not extruded geometric shapes. How can we take the cue from nature?

A particularly interesting corner of Industry 4.0 is the use of Integrated Computational Materials Engineering (ICME). This technology holds the promise of designing alloys, heat treatments, and surface treatments at the individual crystal level, substituting atoms and modeling the effect on the macro properties of the material. Cast iron, with its silicon content, allows carbon atoms to be mobile in the matrix. It should be a perfect vehicle for ICME work. Unfortunately, cast iron is considered “old tech” and it is hard for researchers to get funding related to cast iron research of this type. We know that new branches of the cast iron tree await. We should lobby for application of ICME work to cast irons.

For example, to reduce embodied energy and keep iron costs down, we will need to figure out how to use less pig iron (15MJ/kg) and more steel scrap (6MJ/kg). Most steel scrap has 0.60-0.90% Mn and ductile iron producers target under 0.35% Mn for good properties, no carbides, and good machinability. What might be the path to, for example, high-quality ductile iron with 0.60% Mn? A former colleague of mine, Bela Kovacs, used to say: “Manganese would be the best alloying element if you could just take a rake and rake it out smoothly across the entire matrix.” Without a rake, it tends to segregate at the last-to-freeze/cell-boundary areas, reducing ductility and machinability. Over the years, we have seen producers that make very good ductile iron with 0.40% Mn by using special inoculants forcing nodule counts in excess of 400/mm2. What if we could make 1,000 nodules/mm2? Inmold? In-stream? We’re working on it and encourage our friends in the cast iron field to join us.

We spent years looking for new austempered ductile iron conversions, with a good deal of success. However, ADI’s exceptional strength-to-weight ratio leaves it with technical and commercial limits. To fully exploit its exceptional strength-to-weight ratio we would need to achieve much thinner section sizes. High-production foundries are loathe to produce sections under 5mm for dimensional and metallurgical reasons. Carbides can form in critical sections with substantial negative effect on properties. Draft requirements hold the designer hostage. In one research project, we observed a 4% reduction in mass on a lightweighted design if draft could be eliminated.

To further exploit the high strength-to-weight ratio of ADI, we concluded that we needed to produce carbide-free, 3mm wall castings and apply that capability to organic, draft-free designs, like the aspirational aluminum design in Figure 3—perhaps beyond the capabilities of conventional molding/casting. That work is crucial, and ongoing.

Sand additive manufacturing (Figure 4) could be the path to organic designs, but current additive manufacturing (AM) devices are expensive and slow. The technology needs to be faster and cheaper—perhaps an order of magnitude faster and an order of magnitude cheaper. Perhaps twice the speed at half the price is a good start. Stay tuned.   

Click here to view the article in the digital edition of October 2023 Modern Casting.