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Of all the calls you make as a design engineer, the ones related to materials selection can impact a product's overall cost the most. In Nick Dewhurst's experience, the influence of materials ranges from about 20 percent to almost all of the piece-part cost. He should know. His software and consulting firm, Boothroyd Dewhurst, has helped OEMs fine-tune thousands of products for manufacturability and cost reduction.
"The cheapest material oftentimes is not the most efficient in terms of overall cost," says Dewhurst, who notes that part failures, warranty issues, and manufacturing difficulties can easily offset even large price advantages.
Yet looking for lower-cost alternative materials can be a valid strategy under the right circumstances. Redesigns of first-generation products, which may have been conservatively engineered to start with, provide the most obvious opportunities to switch to lower-cost materials. "They're the low-hanging fruit," Dewhurst says. New products can also be designed from the get-go to make use of lower-cost materials. And when you spec in lower-cost materials from the start, you don't have to worry that tooling or other manufacturing changes will nibble away at the cost advantage.
Any effort to control materials costs should always start with a meaningful comparison of materials properties, price ranges, and manufacturability. One common mistake in plastics, for example, is neglecting the cost of tooling changes when a lower-cost plastic flows differently or has a different mold shrinkage than the higher-cost material. Or in metals, a lower-price alloy can quickly lose its cost edge if it takes longer to machine or form than a more expensive alternative.
Making these kind of informed judgments about price versus design capabilities and manufacturability involves plenty of research. One way to do that research is to individually collect data on all the materials you're looking at, dump it in a spreadsheet, and hope the best material rises to the top. Or you could save some time by starting with an online materials database. These databases, some free and some not, act like materials search engines to speed up your hunt for the right material.
A couple of new ones stand out. For those interested in metal powder alloys, the Metal Powder Industries Federation this month will launch a free online database that includes physical and mechanical property data on metal powder alloys from the worlds' major suppliers. It will give users the mechanical and physical property information they need to make "apples to apples" comparisons between material candidates, says James Dale, the federation's executive vice president. For plastics, IDES Inc. has added a feature to its Prospector database that allows users to search for alternative materials based on selected properties and to solicit price quotes. It helps users not only search for alternatives across different families of plastics but can also identify low-cost suppliers within a given material category.
Boeing Longbow Apache Helicopter
5 sheet metal parts 1 high-speed machined part
19 rivets 2 hrs manufacturing
20 tools needed 10% less weight
32 hrs manufacturing 45% less cost
Tooling cost virtually eliminated
|Consolidate Parts: Nothing cuts piece-part costs like not having to make the part in the first place. In this example, like many others in the real world, parts consolidation required a rethinking of not just the part design but also materials and manufacturing process.|
Mike Kmetz, IDES' founder and president, has seen his share of eye-opening savings related to plastic parts, where the resin typically represents 60 to 70 percent of piece-part cost. A growing number of prospector users, when their application requirements allow, have switched from higher-cost engineering plastics to lower-cost alternatives like polypropylene. Another user managed to achieve a 15 percent savings on the cost of acetal by identifying an offshore supplier with "very aggressive pricing," Kmetz says. Still another user who thought he needed a nearly $10/lb PEEK for his high-temperature application found that a phenolic costing less than $0.50/lb would fit the bill just as well.
This kind of price-conscious savings won't always pan out , but you never know until you at least try to identify some low-cost alternatives that might work in your application. "You shouldn't make any decisions in a vacuum," Kmetz says.
If you find low cost materials that do the trick, good going. But usually you have more work to do. "Reductions in material cost don't necessarily yield reductions in piece-part cost," Kmetz says. In fact, he and other materials selection experts agree that the opposite is often true. Materials exert a strong influence on such big-ticket cost drivers as manufacturability and assembly. For example, materials influence cycle times, which in turn influence piece-part costs and capital expendiures for manufacturing equipment. You can also trace a host of indirect costs back to materials choices, Dewhurst points out. These include storage, handling, lifecycle costs, and even some design-engineering overhead since some materials need more engineering attention than others.
|The Early Bird Saves Money: Nail down design decisions early to keep costs at bay. "The cost of change goes up exponentially throughout the development cycle," says Mark Matsco, manager of application engineering for Bayer Material Science.|
Materials choice also helps or hinders your efforts to create designs with fewer parts, which represents the single most important cost avoidance strategy. "You don't have to pay for components that you don' t have to make," Dewhurst says. Because successful parts consolidation tends to up the ante on the remaining components' functional requirements, these designs can call for higher- performing materials and advanced manufacturing processes.
That's true for plastics. Mark Matsco, manager of applications engineering for Bayer Material Science, explains that stiffer, stonger materials may seem to cost more. But these higher-performing plastics can enable thinner wall sections and ribs, which tips the cost scales in two ways-by cutting materials usage and reducing molding cycle times. Advanced processes can make a difference, too. Matsco estimates, for example, that gas assist molding can reduce piece-part costs by as much as 30 percent in the right applications. How? It hollows out parts, so they cool faster and use less material.
The same sort of cost logic applies to steel too. "People want to consolidate parts for the sake of cost while still meeting safety, NVH, and weight requirements," says Bart DePompolo, a technical manager at U.S. Steel. Reconciling these conflicting design goals has started to fuel the use of tailor-welded blanks made partially or entirely from different grades of advanced high strength steels. These blanks might cost more upfront, even double the cost of traditional blanks, DePompolo concedes. But they have a long list of cost benefits. "If you make three fewer parts, that's three presses you're not tying up and three sets of dies you no longer need to build and maintain," he says. Plus, you have fewer parts to weld, creating further direct labor, capital equipment and energy savings. DePompolo says further indirect savings-mostly related to logistics, weight reduction, and performance improvements-also favor tailored blanks
|Number Crunching: Software from Boothroyd Dewhurst helps engineers look at their designs through a lens that can see costs related to a given design's manufacturing and assembly methods.|
Once you consider manufacturing and indirect materials costs, plenty of materials that once seemed expensive start to look like a real bargain. Consider titanium, for example. "Sure it's considered expensive," says Tom Zuccarrini, who manages consumer and medical applications for Dynamet, a leading titanium supplier. But he estimates that titanium's price may represent as little as 3 percent of the total cost of a complex finished titanium component. On less complex shapes, that raw material cost might climb to 20 percent. So where does the rest of cost come from? Largely from machining and related costs, it turns out. And over the past few years, even the cost of machining has fallen. Dynamet, for example, offers "engineered shapes," rolled titanium rod and bar stock whose tight dimensional tolerances can lessen the amount of machining versus traditional bar stock.
So how do you know if that seemingly expensive material will produce a big enough bang for the buck? The same way you know whether that cheap material will do the trick. Go the extra mile on research. Dewhurst argues that too many companies blindly favor what they know and don't take enough time to look at alternative materials and processes. "Engineers sometimes have to stick their neck out and try something different," he says.