No longer a technical curiosity, metal injection molding still has a long way to go before it catches up to plastics. But companies committed to MIM are hoping to copy plastics' success with the process, by producing parts with lower energy input and faster turnaround times. More than a role model, plastic makes MIM possible by serving as a carrier, or binder, for the ultrafine metal powder during molding. Like plastic, the feedstock - generally a mix of fine metal powder with organic plastic binder and surfactants - is heated in the barrel of the machine. Whether metal or plastic, the injection process uses the same presses - with modifications such as harder-wearing barrels and screws for metal - but most metal molders say the similarities end there.
``With plastic, you mold it and you're done,'' said Sandy Alves, owner of Engineered Sinterings & Plastics Inc. ``You mold the MIM part and you're only beginning.''
Next, the plastic must be purged from the metal part, which is then sintered in a high-temperature furnace.
At its Watertown, Conn., plant, ESP injection molds both plastics and metals, including stainless steel, high-speed steel, ferritic stainless and a 2 percent nickel-steel, with MIM parts making up just 10 percent of its total business.
Though uncommon, companies like ESP and Phillips Plastics Inc. injection mold both materials. Phillips' MIM business is based at its innovative Origen Center, which opened last fall in Menomonie, Wis. Mark Rasmussen, who heads that unit, declined to be interviewed for this story.
RJG Associates Inc., a longtime consultant in plastics technology, also began molding metal last year at its Traverse City, Mich., plant; next month it plans to add plastics to that operation.
The MIM market lowdown can vary, depending on who's talking. For the most part, companies like to keep mum about their MIM sales and customers, though they don't mind talking technology. Overall, the U.S. market - which competing firms estimate at anywhere from $50 million to $100 million - is growing, some say, by 30-40 percent a year.
As in the plastics industry, that growth is driven largely by original equipment manufacturers, and MIM promoters are working hard at proving that their process is a ``faster, better, cheaper'' way to produce metal parts, according to Robert Merhar, who heads market development for Parmatech Corp., a MIM outfit in Petaluma, Calif.
However, most OEMs and their design engineers still don't know what MIM can and cannot do, Merhar said by telephone. Worse, many don't know the process exists, according to Marshall Maudlin, head of marketing for Advanced Forming Technology Inc. in Longmont, Colo.
Regardless, during the past five to 10 years, MIM has become more commercially viable. Its domain covers small, detailed, precision parts with complicated geometries that need the strength and wear of metal. Part weight can range from a fraction of an ounce to about 5 ounces. The process is most competitive when the volumes are high, such as for computer disk drives, Maudlin said. AFT has run as many as 1 million units of a single part in a month.
But can MIM compete for parts already cornered by plastics injection molding?
Gerry Mooney says yes. His company, Endex Polymer Addi-tives Inc. of Ajax, Ontario, sells a metal-plastic pelletized compound that Mooney claims is generating great interest among OEMs, mainly in high-volume, bread-and-butter applications, such as gears and self-lubricated bushings.
Rather than burning off the plastic binder, Endex technology incorporates it into the finished MIM product, eliminating the expensive, time-consuming steps of debinding and sintering.
During sintering, the metal part typically shrinks 15-17 percent, increasing its density. Because the unsintered Endex parts do not shrink much, they can contain as much as 93 percent metal by volume, Mooney said.
Endex, a 20-year supplier of foaming agents to the plastics industry, has a 50-ton Battenfeld press, which it dedicates mainly to metal injection research and development for OEMs with in-house molding operations. The company is working to develop a metal-nylon gear to supplant an all-nylon version manufactured by an undisclosed U.S. customer. For another project, it is converting a plastic aerosol valve.
But Maudlin says Mooney's compound is more accurately a metal-filled plastic, and his technology is not really MIM.
``He's in the plastics industry, in my mind,'' Maudlin said. ``The strength of his part is going to be as strong as the nylon that holds it together.''
Though MIM feedstocks typically contain just 50-70 percent metal by volume, the finished part is 100 percent metal - with all the properties of the metal -since the binder, which makes up the rest of that volume, is burned off. Common binders include polyethylene, polypropylene and polymethyl methacrylate.
MIM can't touch plastics injection molding on costs, but metal meets certain needs. For high-temperature, high-strength, dura-ble parts, plastics can't rival metals, and metals can't match cera-mics, said Sundar Atre, a professor in Penn State University's metal injection molding program.
``I have seen a minuscule amount of plastic [business] being taken away by metal. I don't really see it as a threat,'' he said.
On the metal playing field, MIM competes mainly with labor-intensive discrete machining, and with investment casting of smaller parts, with some benefits being better surface finishes, thinner walls and tolerances within 0.003 inch per each inch of dimension, Merhar said. For simpler metal shapes, a process such as die compaction is more economical.
Hard steel, which is difficult to machine, is a good candidate for MIM, said Mike Groleau, RJG technical director.
``It all gets down to the dollar,'' Merhar said.
Well-established in the firearms industry, MIM is forging inroads with newer, emerging markets. Automotive holds huge potential for the process, Maudlin said - as does medical, Groleau said.
Remington Arms Co. in Ilion, N.Y., which has a captive MIM operation for its gun business, also makes custom components for cars and computers.
Maudlin said that when AFT started up in 1988, it saw MIM as ``a niche nobody else was out there to fill.'' The Longmont firm is breaking into automotive with parts for anti-lock brakes and airbags. Its 10-plus Battenfeld small-tonnage presses and 115 workers also make parts for orthoscopic instruments, connectors for fiber optics, gun parts, and biopsy cups so small that ``you could lay a couple of them on the tip of a pencil eraser,'' he said.
ESP first entered MIM in the late 70s, left, then re-entered the business. In 1993, it beefed up by buying New Industrial Tech-niques, a metal injection molder in Coral Springs, Fla.
ESP owner Alves said he has invested more than $1 million so far in that company's MIM operations. In addition to MIM and other powdered metal processes, ESP does both thermoset and thermoplastic molding. It em-ploys 225.
MIM makes a good match for ES&P by combining the firm's 43 years of experience in powder metallurgy with 28 years of injection molding close-tolerance plastic parts, Alves said. Plus, he noted, some of its OEM customers were requesting it. One of its prime MIM projects is a shell covering for a drill used in deep-hole dril-ling of gas and oil.
But, as Alves points out, the process still is defining its limits. For example, in parts with too many cross-sections of various thicknesses, the tolerances are hard to maintain, much more so in MIM than with plastic, he said.
``MIM can't be a cure-all for everyone's application. We are moving in a direction of being more selective in the type of work we want to do,'' he said.
``So much of it is an art, not a science,'' Alves said, noting that one iffy area involves controlling and predicting shrinkage, to get the right dimensions in the finished, sintered part. ``The most difficult part of MIM is to make a profit.''
Like ESP, RJG does a good bit of development work, though it also is making parts commercially, Groleau said. About a year ago the company turned its consulting savvy with injection molding into a custom molding enterprise: a partnership with Krupp Engi-neering Inc. of Dexter, Mich., that has RJG molding the metal parts and Krupp finishing them.
The two firms teamed up when Krupp had trouble manufacturing a part using stamped powder metallurgy, according to Groleau.
RJG invested a fraction of the $1 million to $2 million it would have needed to set up a complete MIM operation, he said. Also important to the setup, BASF Corp. supplies the feedstock.
Groleau explains it this way: While other MIM operations must have expertise in four separate areas - mixing feedstock, injection molding, debinding and sintering - RJG can stick to its specialty. The company's real expertise is in controlling the injection molding process inside the mold cavity, and the parameters that affect the molding of plastic parts are magnified with metal, he said. On the sintering side, Krupp offers a patented process, F2, that it claims produces fully dense high-speed steel parts.
In Traverse City, RJG runs four 10-50 ton machines for MIM, and soon will add four more presses for plastics, focusing on hard-to-mold materials. The firm's consulting clientele are its main customers.
Keeping overhead down played a big factor in RJG's decision not to go it alone, Groleau said, since sintering and debinding costs can be prohibitive.
``The compounding equipment is expensive. The debinding equipment is expensive. Some of the furnaces can run upwards of $1 million,'' Maudlin said. ``The R&D in metallurgy is not inexpensive.''
Merhar said such alliances may designate the next phase for MIM. But, he emphasized, some companies out there already are seeing a profit.
AFT, which has been injection molding metal parts since 1987, holds the largest piece of the U.S. market for MIM sales, according to Neal Nordstrom, Parmatech's general manager. Though Parma-tech claims second place in the slim lineup of 20-25 players, Nordstrom would not say how much the firm has grown since 1994, when it reported sales of $6.5 million. Merhar said it runs eight presses and employs 100. About 20 percent of its current sales are in injection molded ceramics.
Both AFT and Parmatech have publicly held parents that help carry the costs. In October, Carpenter Technology Corp. of Reading, Pa., bought Parmatech. Last year Carpenter had sales of $758 million in specialty metal parts. In 1991, AFT was acquired by Precision Castparts Corp., a Portland, Ore., firm with $550 million in sales, mainly in investment castings.
Peter Johnson, spokesman for the Metal Injection Molding Association, said such buys may indicate a trend. MIMA, based in Princeton, N.J., has 15 U.S. members and 22 worldwide.
``Larger companies, both overseas and here, are moving into the [MIM] business, providing greater capital and resources,'' Johnson said.
Nordstrom agreed that large metal manufacturers like Pre-cision Castparts and Carpenter lend credibility and technical backing to the MIM process.
``It signals to potential customers that the industry is moving out of the R&D stage and into the commercial,'' he said. Seven licensees worldwide use Parma-tech's MIM technology.
Parmatech, like many metal injection molders, compounds its own feedstocks.
``The concept of feedstocks is a big secret in the industry,'' Mer-har said, with more and more patents emerging around the binders - most of which are plastic-based - and their removal systems.
Two New Jersey firms are among those that supply metal powders: BASF Corp. of Parsip-pany and International Specialty Products Inc. of Wayne. The two families of metal used in MIM are high-density atomized powders and carbonyl irons and nickels - only ``the finest of the fine powders,'' having diameters of 5-30 microns, with less than 10 microns being ideal, Merhar said.
ISP product manager Sotiri Papoulias said it is not practical from a business standpoint for his firm to make feedstocks for MIM, because the combinations of metals are limitless. BASF offers 10-12 feedstocks, using carbonyl metals and a polyacetal binder, which is removed as a gas via a patented catalytic debinding system. Most binders are re-moved in a liquid state. Allied-Signal Inc. is working on a water-based binder for MIM, which it plans to have out within two years.
Penn State's Atre said he thinks the absence of the major material suppliers hurts MIM's credibility in the marketplace. Penn State, in State College, Pa., is a hub for MIM technology transfer and home to a powder injection molding consortium for both metal and ceramics. PolyVisions Inc. of York, Pa., supplies a specialty PP binder to Penn State's MIM program and to its consortium members, according to Larry Bour-land, co-owner of the firm.
Bourland credits small entrepreneurial firms, like his own, with developing the binder technology. The company also makes specialty resins and compounds for the plastics industry.
He believes the MIM market will catch up to the vast R&D work being done, as processors and material suppliers define a wider range of compounds.
``There's a tremendous amount of opportunity in this area,'' Bourland said. ``But you have to have a multidiscipline company for this technology.''
He noted that several ceramic injection molders also have inquired about PolyVisions' bin-ders. ``They're even more secretive,'' he said.
Ceramics make up the other side of the powder injection molding industry. Both Carpenter and Precision Castparts own ceramics injection molding companies. Even Dow Plastics owns a compounding injection molding machine specially designed for ceramics.
Dow's hybrid machine has a Betol twin-screw compounder attached to a Dassett plunger-style injection unit. Dow would say only that it is using the machine for R&D on advanced materials. The system, tagged Osciblend, also is being tested on metals and ceramics, using plastic-based binders, at the Wolfson Centre for Materials Processing at Brunel University in Uxbridge, England.