Total Cost of Ownership

Within each molding process lies another set of factors that can affect the cost of a casting. These total costs of ownership can add up over time, but they also can be controlled when designing a casting. The key is to remember that the more that goes into it, the more it will cost in the end. 

“You should look beyond piece price; you have to consider tooling costs, which include not only patterns but also coreboxes and other items, such as fixtures,” Weinbender said. “The cost of these items should be factored on a per-unit basis, based on estimated tooling life and life cycle demand for the part. Thus, quantative analysis of casting price should include piece price plus costs for any peripheral costs relative to it. It’s not just the casting price, it’s anything upstream or downstream relative to the component.”

Tooling is arguably the biggest cost in this area. It also provides many options that affect casting cost. Variables that affect casting cost include: pattern material, pattern design, type of molding machine and cored versus non-cored.

Pattern Material—Wood and plastic are suitable for many applications, but high-volume jobs that require the pattern to hold up over long periods of time may need the added strength of machined aluminum, iron or steel. Also, aluminum, iron and steel patterns tend to hold tighter tolerances because they are less susceptible to breakage than wood. But keep in mind that the durability of a robust pattern material will increase the total cost of the component. 

“If you are looking at a low-volume part that is going to run 5,000 pieces/yr., then you may want to consider a mounted polyurethane pattern,” Weinbender said. “But, if you are producing 1 million parts a year, then you are going to want to use a machined steel pattern because you will need that durability. Tooling specifications should be matched to the anticipated production requirements.”

Pattern Design—Options for patterns include plate-mounted impressions versus pressure cast impressions and separate cope and drag patterns versus a matchplate design. The size and number of impressions also play a role in tooling cost. A cost-effective option is a “rider,” which occurs when additional, smaller castings can be produced when patterns are mounted onto existing tooling. This can be a cost-effective option because the only cost of the “rider” is the additonal metal.

“Pattern and corebox commonality is a possibility, too,” Weinbender said. “If you are looking at a family of parts, engineering the tooling to incorporate changeable inserts may allow you to produce multiple part numbers form common tooling, which can help reduce the overall cost.”

Type of Molding Machine—The type of molding machine used is typically dictated by the volume of castings to be produced. Larger automatic molding machines can allow for the inclusion of several castings on a single pattern.

“Typical order quantities over the life of the casting will determine the types of molding centers that are most cost-effective,” Weinbender said. “Try to match the production requirements to the metalcasting facility’s capabilities and align them as closely as possible.”

Cored vs. Non-Cored—Cores are used in metalcasting processes to help form the complex geometries of cast metal components, such as internal passageways. They are beneficial because they have the ability to minimize some secondary operations, such as machining. If cores are needed, there will be an additional expense to build coreboxes and produce cores. Similar to patterns, coreboxes can be made from a variety of materials that offer different benefits and costs. The cores themselves can be produced in a variety of methods (shell, coldbox, nobake, etc.) that offer different benefits and costs. It’s also important to remember that the use of cores can help bring down the price of the casting because they have the potential to eliminate expensive machining operations.

“Try and combine things, such as cores,” Creese said. “If you can get one core instead of two, it’s one piece going in instead of two. Improving productivity not only decreases unit labor costs, it also reduces the unit overhead costs.”