Quality. Weight. Cost. All three aspects are key elements to the success of an engineered product. Whether designing for automotive, heavy-duty truck or the industrial/agriculture industry, these three elements remain a top priority from both commercial and engineering perspectives.
As the product development begins, balancing such closely linked elements is tricky. Does low weight necessarily mean low cost? Does high cost necessarily mean better quality? What levels of tradeoff for weight is one willing to make for the cost, or even quality, of the product? The answers to these questions are a pinnacle point during the development of many components in the manufacturing industry. Given that, selecting the right design and material is critical to balancing all three elements, with the end goal ultimately the launch of an optimized product.
Iron Casting Tradeoffs
The heart-and-soul process of the manufacturing industry. A process that leads directly to discussion about balancing the engineering requirements during system development and optimization. As customers continue to trend toward aggressive, short development cycles, engineering teams are often forced to make early directional decisions on whether to pursue iron or aluminum for their product design. The industry has witnessed trends where weight savings as minimal as multiple grams outweighed the mechanical properties and piece price savings of iron, only to evolve in future model years to accept the change in weight in order to reap the benefits of piece price savings and additional strength properties.
The electric vehicle (EV) market is a perfect example where lightweight components are crucial to balance the battery weight to keep the driving range competitive. Weight, short development cycles and cost pressures add complexity to an already extremely complex industry. The answer is not so simple on product direction, either; in many cases, the end system drives which element will have the highest priority. However, there are ways to minimize the weight impact of iron while benefiting from the financial and product robustness aspects.
First, let’s take a step back and review the benefits of ductile iron material in its mechanical properties. The key characteristics for selecting the best material are ultimate tensile strength, yield strength, elongation percentage and stiffness. An optimal solution can be found in the variety of ductile iron grades available.
From a purely mechanical standpoint, the various grades of ductile iron, with its wide range of mechanical properties, offers flexibility the application may require, as shown in Figure 1.
The range in the iron grades covers a much larger scope of potential applications. For example, a selection of high strength ductile iron may provide a product design that matches or exceeds the mechanical requirements of an aluminum design with only minimal weight impact.
As the EV market continues to evolve and expand well beyond luxury sedans and sports cars, high strength ductile iron becomes an ideal solution. Take Rivian, for example. It is a company that is launching a vehicle that not only needs to push the boundaries of driving range and cost, but also is entering a niche market that focuses on off-roading and “rugged” attributes. High-strength ductile iron not only provides and exceeds all the robustness requirements of these types of vehicles due to its natural mechanical properties—it can hit the weight targets of the demanding specifications of these EV vehicles. Its unique mechanical properties allow for material and weight reductions compared to standard ductile iron.
Understanding application requirements and the primary characteristics that drive the design (stiffness, strength, fatigue, loads, etc.) are essential to selecting the optimal material for the product.
Other factors, such as material hardness for machinability, datum structure for dimensional integrity before and after machining, and casting manufacturability play roles in the product design direction, product cost and quality.
Of course, this is common knowledge among engineering teams tasked with selecting between iron or aluminum. Yet determining the best material still does not come so easy. Material knowledge alone is not the only crucial factor in the development and engineering of an optimized product design. Short development timelines in today’s manufacturing create obstacles to adequately evaluate materials and designs. Given this, engagement of suppliers in the early development phase when deciding on aluminum or iron is vital to making the most informed decision.
Key Design Decisions Early
In the casting industry, the term “build-to-print” is both frequently understood and practiced. By challenging this philosophy, there is opportunity for the end customer to benefit from the mechanical strength properties and lower piece price of iron, while minimizing the impact on weight.
Grede, a dominant player in the ductile iron industry, has focused on creating this opportunity. The strategy is simple and streamlined: engage with the system-responsible engineering team early in the development process. Engineering teams must continue to strive for partnerships where together the roduct is optimized to offer the best combination of quality, weight and cost.
What benefits can be realized from the casting expert working side by side with the end customer? These include:
Material selection that is best suited for the application.
Optimization of the design for cost and function,
- Product yield
- Dimensional integrity
Shared product engineering resources between supplier and customer for early design direction.
Structural efficiency (finite element analysis (FEA)/optimization) completed by the supplier.
Stronger mechanical properties of ductile iron provide opportunity to eliminate other components (cost savings for the system) associated with aluminum.
One of many existing current ongoing examples of this activity is shown below.
An Example Program X
The figure above shows a steering knuckle for an automotive application produced by Grede Product Engineering. This exercise was done with a customer to determine if carryover product was sufficient, or if a redesign would be beneficial. From the exercise, one can conclude that with the integration of the supplier upfront, both the design and material can be optimized.
Early integration with the supplier (Grede) provided the engineering insight that led to using high-strength ductile iron, which in turn allowed for a significant reduction in weight.
Although aluminum provided a similar reduction in weight, the cost impact was too high.
Overall, by integrating the supplier in the advanced engineering phase, quality was maintained, cost was neutral and weight significantly reduced.
Quality. Weight. Cost.
In order to achieve the optimized balance of these three key elements, it’s time to change the way the commodity of castings is viewed, and to continue to shake and challenge the industry to push the optimization envelope. Early in development, prior to concept freeze of the design (during advanced vehicle development), the customer and supplier need to be collaborating to optimize these three key elements: quality; weight; and cost.
It is imperative to conduct a thorough comparison early in the development phase to avoid the need to redesign the product after the vehicle has hit production—which is a resource and cost drain. Suppliers must continue to invest in application and development engineering teams at the supplier level to provide the resources for customers to capitalize on the iron casting benefits. There is no question as to whether lighter weight iron casting designs are achievable. Whether the market is automotive or not, the key to success is selecting the proper material, the proper engineering expertise and integrating customers and suppliers during the early development phase.
Susan Bear is director of engineering, program management and quality at Grede.