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January 6, 2003

9 Min Read
The pressure is on for lower-cost materials

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Resin suppliers are focusing on new grades aimed at specific applications and markets. For example, Bayer created an easier flowing grade of its Durethan nylon for thin-walled automotive applications, such as this engine cover for the V5 2V engine in the VW Passat. As a result, the number of resin choices has expanded greatly.

Future shock has definitely set in when it comes to material selection, and that goes for all plastics processes. In short, choosing a resin from among the 40,000-plus grades available today requires more than a passing acquaintance with polymer families, properties, and data sheets. Moreover, an increasing number of OEMs are coming to expect that processors will find the lowest-cost material that meets an application?s requirements.

The road to lower-cost resins is by no means a straight one. Applications that have been designed with a particular material in mind can suffer failures and processing problems when a substitute polymer, even one in the same generic family, is used. Minor changes in properties such as density and modulus can have major impacts. Changes in fillers or additives can likewise affect the behavior of a part in service.

Yet, the pressure on processors to find a way to lower material costs continues. To examine the issue, PM&A spoke with two industry experts?Mike Sepe, technical director at Dickten & Masch Mfg. Co., a custom molding and moldmaking firm, and Mike Kmetz, president of IDES, a materials database firm.

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Roof appliqués molded from a new grade of PET (Rynite RE5309 from DuPont) on Saturn?s VUE sport utility vehicle meet requirements for Class A finish, long-term precision fit, and easy assembly. This grade was developed specifically for such applications, and combines dimensional stability, low coefficient of linear thermal expansion (CLTE), and warp resistance.

Progress, Not Perfection
Kmetz believes the resin selection process has become more complex in recent years because the sheer number of available grades has ballooned. ?There are simply more choices now. Our database is evidence of that. We?ve exceeded 40,000 materials, all active materials on the market, and we?re finding more all the time,? he says. (See sidebar, p. 19.)

Why so many grades? Resin suppliers continue to tailor resins for new market opportunities, bringing new grades into being. ?This is the beauty of plastics, the ability to meet application requirements in an almost custom manner,? Kmetz notes.

But along with the choices comes a higher degree of complexity. ?If you were to ask a plastics industry veteran, he would say that selecting materials isn?t complex,? he says. ?For someone with experience, the choice becomes intuitive to a degree. But with downsizing, a lot of expertise has left the industry. Companies haven?t done a good job of capturing that knowledge.?

Kmetz acknowledges that distributors and major suppliers can offer support in selecting substitute materials, but the catch here is that the assistance they give is based on the materials they offer. In short, it?s hard to get an objective opinion.

For most processors, substitution usually means selecting an alternative resin within the same generic polymer family. ?We?re hearing a lot about substituting lower-cost resins now, especially in Detroit,? Kmetz explains. ?Auto OEMs are putting such a squeeze on processors that they?ve taken out margins almost entirely. So the processors are looking for lower-cost materials to substitute. Without redesigning the part, the obvious choices lie in the same product family.?

Making the Switch
When the heat is on to find a lower-cost material, what guidelines should processors follow? According to Kmetz, they need to understand the criteria that drove selection in the first place. ?Often, a processor has a material and a distributor in mind when it bids on a job. But there are other considerations. Are there approvals to be met? Does the material need to be FDA approved, for example? Are there any regulations in place that govern material selection? These should be covered up front before a material is selected.?

IDES has worked with processors who say they need a higher-flow substitute, and also want to replicate fillers or additives used in the existing material. Most of the time they look at only a few key properties to find a substitute. That can be dangerous if the higher-flow material does not interact with the filler or additive in the same way as the original resin. Digging a bit deeper into multipoint data on properties is the answer here.

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To produce molded-in-color body panels that look like the painted sheet metal equivalent, automotive molders can choose from several resins in the Surlyn Reflection Series from DuPont, which contains alloys based on ionomer and nylon chemistry.

Mike Sepe believes that most material substitutions require the input of an experienced designer who can help translate material properties into part performance. ?While automated tools to select materials do exist, and have simplified the lives of countless designers and processors, there is a danger in relying solely on the numbers,? he says. ?For example, how do you translate a requirement for a 10-ft drop test onto concrete into notched Izod impact numbers? This is not a straightforward process.?

?We wrestle with this all the time,? adds Kmetz. ?Processors get a spec that says the part needs to have high impact characteristics, yet there is no Izod number that tells them how high.?

The biggest problems that Sepe finds are where material substitution appears to be a no brainer, ?for instance, going from one HDPE to another with the same melt flow. It seems easy enough, but it is not as straightforward as just picking numbers. It has to do with design and processing.?

In an actual example of substitution, an OEM and processor agreed to substitute one HDPE for another on gas tanks for lawn and garden vehicles. The only change in properties was a minimal density difference. When the tanks were tested, instead of bending as the original material had done, the part cracked.

On paper, the change in density was minimal. However, density does influence mechanical properties relating to strength and stiffness, so the switch caused further property changes during long-term operation. ?Those numbers on a data sheet represent short-term properties at room temperature, not long-term properties in operation,? Sepe says. ?Yield point can?t be reached in operation without product failure, so we need to know what happens before that point.?

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Automotive OEMs are pressuring suppliers for lower cost parts, which often means a switch to lower-cost engineering resins such as those used by GE plastics in this Peugeot.

Design Input
Both Sepe and Kmetz agree that the phenomenon of material selection based strictly on cost is so new that there is little infrastructure to support the process. To get to the lowest-cost material that will meet an application?s needs, processors often must solicit the input of part or product designers.

?If a processor takes on design responsibility, it has to understand properties and how they relate to application requirements,? says Kmetz. ?It needs designers in the organization, or a processor on staff who has the experience juggling performance requirements against material properties.?

Needless to say, this is always a balancing act. Don?t even think about finding the perfect material, because trade-offs are a given.

In the case of automotive applications, the top requirement is to meet a certain specification designated by the automotive OEM. Designers usually come up with no more than six requirements, and these are rarely a narrow band but more often a range of properties. Processors can look at materials that meet that range, and then find a match based on cost.

Using an analysis tool at this point can uncover problems before they show up on the shop floor. Moldfilling analysis can help predict processing problems and performance snafus such as warpage and stress cracking.

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New resin blends introduced within the past year include Xylex from GE Plastics, a blend of PC and aliphatic polyester for better chemical resistance and cost efficiencies. One of the first applications for the new resin was the DragonRake sunglasses by Dragon Optical, designed for snowboarding, mountain biking, and other action sports.

Kmetz believes it is counterproductive to list more than three must-have properties because it cuts out a lot of possibilities. ?You need to look critically at whether certain parameters are necessary or not,? he says. ?For example, a processor was using a PEEK material at $10/lb primarily for its high temperature resistance, but also because it met other nonessential needs. Upon inspection, it was found that a phenolic at pennies per pound would have also done the trick.?

Material selection is also industry specific in many cases, so every market looks at it differently. For a consumer products company, impact resistance and electrical characteristics might be at the top of the list. Medical devices must meet a plethora of regulatory statutes. ?Be aware of the top three requirements before making any substitutions,? says Kmetz.

DES, Laramie, WY; Mike Kmetz
(307) 742-9227; www.ides.com  

Dickten & Masch Mfg. Co.
Nashotah, WI; Mike Sepe
(262) 369-5555; www.dicktenplastics.com

40,000 and counting

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Polycarbonate and ABS terpolymer blends can be tailored to meet property requirements by varying the ratio of PC and ABS for applications such as automotive body panels and instrument panels, computer housings, and cellular phones.

If you had a dollar for every resin on the market today, not including custom compounds, you?d have nearly enough cash to buy that new Porsche Boxster that?s been calling your name. At IDES, a leading supplier of technical plastic materials data, the number of available grades across all plastics processes in its database now exceeds 40,000.

Next on the agenda at IDES is to segment its material selection tools for specific markets. Automotive is one of them, and the company is also looking at medical device development as a niche. ?Any time a processor bids on an automotive project, it receives a print with a material spec that relates to the company,? says Mike Kmetz, president, ?such as for General Motors, GM345. There isn?t any easy way to find out which materials meet the spec, however. Distributors can help, but they are not completely unbiased. There needs to be a comprehensive way for a processor to look this up.?

Plans are also in the works for additional capabilities in the company?s Sourcing feature, which tells users who makes a specific material and lists all the distributors for it. ?In the near future, Sourcing will include a feature whereby IDES will locate a material source for those materials not listed as offered by a distributor,? says Kmetz.

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