Design Engineers Plan Push toward Injection Molding

Engineers are actively exploring new processing technology in an effort to reduce costs and improve performance of the products they are designing.

Topping the list is injection molding and half of the respondents to a Design News research survey say they are exploring plastics-for-metal substitutions.

One example of the tough new demands being placed on plastics is a compressor valve plate developed by Hoerbiger Corp., the world's largest independent compressor valve manufacturer. RTP Co. of Winona, MN developed an injection-moldable, low-flow, carbon-fiber-reinforced PEEK compound for the application.

“Valve plate materials must provide a high degree of physical strength while maintaining high impact and cyclic fatigue resistance,” says Tim Bremner, vice president of materials technology at Hoerbiger. “In many instances, compressor plates compress highly acidic or caustic gas streams, posing serious challenges for the chemical compatibility of the valve plate material.”

One theme that resonates loudly in 2009 for design engineers is a requirement for higher performance from plastics, metals and adhesives as they strive to find substitutions.

Engineers who participated in the study (who were promised confidentiality) are definitely interested in new carbon-fiber-reinforced materials, for example.

One issue; however, is quality control. “There's a need to improve the non-destructive means to determine internal flaws in pressure vessels and primary load carrying structure made from carbon epoxy composites,” said a consultant for advanced propulsion engineering.

Another engineer said there is a need for better industry standards on product forms and grades. A third said the costs of characterizing and qualifying composite materials are too high.

A Bennington, VT company called Plasan Carbon Composites recently established an R&D program to overcome obstacles with carbon-fiber composites.

“The target of our research is to take us from 7,000 vehicle sets a year to 50,000 or 60,000 a year,” says Gary Lownsdale, engineering manager for Plasan Carbon Composites. “We're getting down and really trying to understand what happens in the curing process so that individual resins can be tailored for the process.” The goals are to boost productivity, a chronic problem for any type of thermoset curing process, and to improve surface quality.

Here are examples of other areas where design engineers would like to see some very specific improvements. Results are from a recent study conducted for Design News by Reed Business Information's Research Dept. View a survey snapshot, and download the full survey results.

AISI 1018 cold-rolled steel (low-carbon, manganese-rich): “The material that I have been getting lately is not rolled into a true rectangular profile. One side of the longer edge is often slightly curved, near the shorter edge.”

Fluoroelastomers: “The current (thermal) limit is about 280C. Something that could survive 340C would be a better fit for exhaust-related seals.”

High-temperature resins (e.g. polyamide, PBT-type polyester): “I would like to see less moisture absorption without having to resort to extremely high-priced or difficult to mold resins.”

Rubber used for insulating: “They should have more capability at very high strain rates.”

Polymer blend of polyphenylene oxide and polystyrene: “Better UV resistance.”

There were also a few comments from design engineers dissatisfied with plating options.

“We need an environmentally friendly replacement with decent cost and performance,” says an engineer who designs equipment for in-house use. “These days, cadmium is effectively banned for environmental reasons, but none of the possible replacements meet all the performance requirements.”

Cadmium has been widely used as a plating material because it offers good corrosion resistance, cathodic protection of steel and galvanic compatibility with aluminum, as well as excellent lubricity. Cadmium can be dyed to many colors and can be used as a final finish or a paint base.

Inhalation of cadmium-containing fumes; however, can result in chemical pneumonitis, pulmonary edema and death. Human exposures to environmental cadmium are primarily the result of the burning of fossil fuels and municipal wastes. It's one of six substances banned by the European Union's Restriction on Hazardous Substances (RoHS) directive.

Electrolytic aluminum is used as an alternative to cadmium plating. The process takes place in a completely enclosed and inert atmosphere, making it much more capital-intensive to set up than a standard electroplate.

Boeing developed Zn-Ni electroplate as an alternative to cadmium plating for aircraft use. Because of hydrogen embitterment issues, this coating is not yet recommended for high-strength steels.

Many engineers have opted for stainless steel as a cadmium replacement, but stainless costs have been up and down like a roller coaster in the last 18 months.

Another comment on plating came from an engineer who designs portable tools. “I would like to see (polyacetal) modified to be plateable so we can adhere a copper layer to replace some of our decorative parts which are ABS and tend to stress crack. The stipulation here is Asian market availability and reasonable pricing.”

Asian availability is less of an issue than it was 10 years ago, but reasonable pricing is often a major stumbling block.

In general, substitutions mandated by new environmental requirements are a major activity right now in the design engineering community.

Another difficult area for engineers is flame-retardant systems for high-temperature applications in electronics applications.

Two brominated FR additives, penta-BDE (decabromodiphenyl ether) and octa-BDE, have been banned in the European Union. Use of decabromodiphenyl ether will be banned from use in computer and television housings in Maine starting next year. The state of Washington is also considering restrictions on use of deca-BDE.

There are several problems with alternatives, including:

• They typically do not have the same amount of testing;

• Reliability has not been confirmed in use;

• They require costs for conversion;

• Product availability is uncertain and; they are

• Generally higher in cost.

Many producers are developing proprietary solutions for targeted applications. For example, Arnite T-XG 510 PBT is halogen-free and has received approval for electrical insulating materials. Produced by DSM Engineering Plastics, the compound is aimed at connectors in washing machines, dryers and dishwashers.

Machining Winds Down

Another major trend under way is a shift toward rapid prototyping technologies and away from machining.

Sixty-seven percent of survey respondents say they now primarily use machining to produce prototypes, while 54 percent use rapid prototyping systems. Fifty-one percent said rapid prototyping will become more important in the next 12 months, while only 25 percent said machining will become more important.

There are two big reasons for the shift: Costs of rapid prototyping systems are falling, and capabilities of those systems are rising.

3D Systems Corp. is now selling the V-Flash Desktop Modeler, which is the first commercially available 3-D modeler priced under $10,000. The Dimension 3D Printing Group, a business unit of Stratasys Inc., sells the uPrint Personal 3D Printer at $14,900. uPrint builds models with Stratasys ABSplus — a material on average 40 percent stronger than the company's standard ABS material.

Dimension also recently reduced the base price of its Elite and 1200es 3D printers. The Elite, previously priced at $32,900 is now available for $29,900.