Estimating the cost of an engineered cast metal component can seem like trying to solve an advanced algorithm. It’s a complex process with a wide range of numbers to factor in and just as many variables to account for—and there are no shortcuts. Similar to solving the advanced mathematical equation, if you don’t do your homework, it shows. But a failing grade in the process of costing a casting can be more serious and drastically affect your bottom line. 
Similar to most other products, the more that goes into a cast component and the more that is expected from it, the more costly it will be. It’s no longer possible to determine the price per pound of a particular alloy and accurately estimate the casting cost based on that figure. While that is one aspect of the estimation formula, there is much more to factor into the equation.

“There is more to the price of a casting than just the components or raw materials coming in,” said Robert Creese, who is a professor of industrial and management systems in engineering at West Virginia Univ., Morgantown, W. Va., and has authored a book on cost estimation for the manufacturing industry. “What you have to remember is that costs go up for the processing of the materials and for overheads. It is not only labor costs and material costs, but the overhead costs—and those tend to be the major cost component.”

This article details the factors affecting the cost of a casting and provides tips for designing the best casting at the lowest cost.

In the Beginning

The process of costing a casting involves a number of different factors, but many of them are intertwined. Often, once one decision is made, another falls into place. The starting point of the complex estimation process boils down to a simple question: what does the casting need to do? The functionality of the component will drive many of the other factors in the estimating process. Before making a decision on alloy, casting process or post-casting treatment, ask the question, how will the casting be used in the final application?

Fig. 1

Metal type plays a significant role in the cost of a casting. But there are not always options when selecting an alloy. The type of metal used is directly related to the desired properties and characteristics of the casting. Sometimes, certain materials can match engineering characteristics of other materials at a reduced cost. But many times, only one alloy meets those requirements. Generally speaking, casting cost is directly linked to process and production requirements. 

Figure 1 compares the tolerances offered by a variety of molding processes. The processes offer varying capabilities and constraints, with certain processes better suited to specific designs and applications. Within a given process, different methods may exist that lend themselves to greater efficiencies at different production levels. Processes utilized for tight dimensional tolerances, thin sections and casting complexity tend to be more costly.

Design complexity and the component’s end use have a direct impact on selecting the appropriate molding method. Understanding the functionality of the component is crucial at this stage because different molding processes can offer different benefits, such as tight dimensional tolerances, excellent surface finish and ease of casting complex shapes.

“Each process has its limitations,” said Bill Marlatt, Grede Foundries Inc.—Vassar Foundry, Vassar, Mich., who has cost estimating experience as an industrial engineer and production controller. He also has held positions in purchasing and sales. “There are processes that are phenomenal at obtaining high strength and high pressure with no shrinkage and minor microporosity,” he said. “But there is a price to be paid for that type of technology. If you are making aerospace-quality components, you have to select a process that will give you that near-perfect, defect-free casting. But in a lot of applications, as long as a defect, such as porosity, don’t open up during machining, it won’t affect structural integrity.”

To avoid needless expenses, it is important to determine what is necessary and then decide what you are willing to pay for features, such as good surface finish, tight dimensional tolerances, complex shapes and internal passageways. This requires design engineers to resist the temptation to over-engineer the component. Often, by thinking, “if a little is good, then more must be better,” costs will needlessly increase. 

“Consider all possible design and process tradeoffs for your requirements,” said Rex Weinbender, Fluor Global Services, Greenville, S.C. , who has authored several articles on industrial engineering and costing topics. “When it comes down to it, you could make the perfect part by lost foam or investment casting, but do you need to? You can cast a near-net-shape component with excellent surface finish and minimal machining required, but is this necessary if the casting will be used as a heavy truck suspension component?”

Quantity also will drive the molding process selection. Evaluate the life cycle of the part. If it is a high-volume component with specific requirements, you may naturally gravitate toward a particular processes. Also, because of the high tooling costs incurred in certain processes, high-volume components with a long life cycle become more economically justifiable. 

Once a molding process has been selected, total costs of ownership must be evaluated.