IMM Focus: Materials 20011IMM Focus: Materials 20011

Alvin Toffler, author of the book Future Shock, predicted that this century would offer people too many choices. His prophecy seems particularly meaningful when it comes to material selection. Choosing the optimum resin for an application from among the 40,000-plus grades available today can seem daunting.

Help is available, of course, from distributors and major resin suppliers as well as from materials database providers such as IDES and Campus. Likewise, moldfilling analysis can provide designers and molders with a means of comparing how candidate materials will behave during molding and what the effect may be on part performance. These tools are essential for new product design.

What happens, however, when the pressure is on to find a lower-cost substitute polymer for an existing product? 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.

To examine the issue, IMM spoke with three industry experts: Mike Kmetz, president of IDES, a materials database firm; Mike Sepe, technical director at Dickten & Masch, a custom molding and moldmaking firm; and Joe Muhs, VP at Prime Alliance, a resin distributor.

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. “We’ve exceeded 40,000 materials, all active on the market, and we’re finding more all the time,” he says.

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 says.

But along with the choices comes increased complexity. “If you were to ask a plastics industry veteran, he would say that selecting materials isn’t complex. 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,” he says.

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.

Currently, 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 says. “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 designers and processors follow? According to Kmetz, they need to understand the criteria that drove selection in the first place. “There are several 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.

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 one 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.”

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, [he or she] has to understand properties and how they relate to application requirements,” says Kmetz. “[A company] needs designers in the organization, or a processor on staff who has the experience of juggling performance requirements against material properties.”

Needless to say, this is a balancing act. Don’t even think about finding the perfect material, because trade-offs are a given.

In the case of automotive, the top requirement is whether a material meets 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 cost them out to find a match.

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

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.

The Distributors’ Role

In many ways, material selection expertise has always been a strong point among resin distributors. Carrying product lines from multiple resin suppliers, the distributor can present an unbiased opinion as to the best resin for the job. In addition, distributors typically hire technical support staff experienced in this area.

Joe Muhs, VP, Prime Alliance, explains that from a distributor’s standpoint, materials expertise is one of the main reasons customers want to work with them. “Often, when we meet a customer, they are looking at us because they don’t know what resin they need or what they can substitute,” he says.

One of the first questions designers and molders ask, according to Muhs, is how to get a lower-cost resin that still hits critical property targets. The second question, naturally, is what will the property trade-offs be if the switch is made?

“We’re increasingly taking on the role of specifying engineer, helping customers find what they need at the lowest possible cost,” he says.

Another main factor in the equation is that distributors don’t have to push any one product over another, so their recommendations aren’t clouded by vested interest. A major resin supplier, on the other hand, can only sell what it makes. “Customers know we won’t do that,” Muhs adds. “Instead, customers ask, ‘Which of 12 suppliers’ products do you recommend on a cost-performance basis?’”

Like Kmetz, Muhs generally begins a material search by nailing down the application’s special requirements, usually two or three critical properties that must be met at the lowest cost. “In today’s environment, everyone is looking for less-costly materials,” he says. “In the past, a part specified in PC might be reengineered for PC/ABS to take cost out. The next step would be ABS, and finally HIPS. Now, customers want to skip the intermediary steps and go directly from PC to HIPS.”

Resin supplier price increases help to foster this attitude as they force OEMs and molders to take a hard look at the cost and performance of existing resin choices. Oil prices recently peaked at $35/barrel, up from $24 last year, and natural gas has more than doubled, raising the cost of making polymers. As those increases are passed on to customers, many look for ways to avoid having to raise prices themselves.

For new parts, distributors are often called in to recommend a specific material. If that recommendation turns out to be overspecified, it will be replaced in short order, so making the right call is important. “Distributors need to find just the right mix of performance and cost based on experience and delving into what the application needs.”

For those who make material substitutions and find themselves in trouble, Muhs suggests calling a local distribution rep. “We can call suppliers for help, and usually we can get action almost immediately because we have a presence with the supplier.”

Also, when it comes to competing with Asia, he believes that OEMs and molders in the U.S. need to make use of the collective brainpower found at the distribution level. “Distribution reps have to deal in so many different materials, and are trained to do so. It makes sense to consult with them, because your competitors are consulting with everyone they can.”