Metal Molding Shapes up as Appealing Market
By: Greg Valero
MIM is attractive because it produces consistent, complex-geometry components
for high-volume, high- strength, and high-performance applications," says
Andrew Hanson, vice president of sales and marketing at
Advanced Forming Technologies
(AFT), which specializes in
metal injection molding (MIM)
and
Thixoforming
(patented method for injection molding magnesium).
The driving force behind MIM's growing popularity in the molding community is that it allows molders to broaden the services and capabilities they offer end users. Experts say that molders can sometimes be frustrated trying to meet customers' needs with only thermoplastic materials and processes. These customers may require better properties than plastics alone can offer.
"If their existing customer base requires MIM-type parts and (plastic molders) are not afraid of the capital outlay, steep learning curve, and increased operational cost, metal injection molding can be an interesting possibility," suggests Neal J. Goldenberg, vice president, marketing, Polymer Technologies. "[A processor] may want to consider buying a metal injection molding operation, or a joint venture with a current supplier."
MIM applications run the gamut across all industries, from medical device and telecommunications to textile machinery and hardware. The process is well suited for the manufacture of relatively small, complex components requiring high strength and economic viability. "You do leverage some of the same process technology in MIM that you do in plastics molding," says Bill Ellerkamp, VP of market development at MedSource Technologies Inc., a Minneapolis-based plastics and metal injection molder.
MIM
competes directly against other types of metal processes, such as machining and casting. "Machined parts require a considerable amount of labor and a lot of material is lost during the process," Ellerkamp says. "You can introduce a MIM part as an alternative."
The technology offers advantages over conventional metal forming processes where high volume, complex geometries, and low cost are required. Noting the technology has been available commercially for only about 20 years, "MIM is one of the fastest growing types of [metal forming] processes," says Tony Pelke, engineering manager at Phillips Plastics' MIM facility. The company is a custom injection molder of plastic and metal. "I think more people are understanding the process and trying it out."
MIM parts typically weigh up to 25g and are no larger than a human fist. The more complex the part, the more cost reduction the customer can realize, experts say. "You can make bigger parts, but what you run into is the cost to manufacture the powder for the part becomes prohibitive for many geometries," said Robert Cornwall, president of Innovative Materials Solutions (State College, PA), which provides market and training services for the powder injection molding industry.
Molders can realize even bigger profits when parts are molded in mass quantities. Industry experts say metal injection molding carries profit margins up to three times higher than plastic injection molding, depending on the part size and quality. Compared with typical plastics, metal parts have very low viscosity, high thermal conductivity, and sell for roughly 10 to 20 percent more.
According to the Metal Injecting Molding Assn., the basic process uses pressure and heat to form precision metal parts and shapes. The metal is supplied in powder form, which is combined with a thermoplastic binder. This mixture is then heated and injected into a mold. Following ejection from the mold, this "green" part is immersed in liquid (usually a solvent) that removes the debinder, leaving a part comprised of microscopic lattice-work metal. This part is then passed through a sintering furnace, which fuses and shrinks the metal, creating a basically solid metal component.
For molding, the binder is an important part of manufacturing quality parts. "Most binder systems are proprietary,"
AFT's
Hanson says, noting there are numerous systems in use today. "Millions of dollars have been spent on developing various binders that maintain component shape as they're being removed during the debinding and sintering processes."
During sintering, shrinkage control is a critical part of the process. Molders must ensure the initial mass of powder-typically 15 to 25 percent larger than the finished part-shrinks to spec when heated in the high-temperature, controlled-atmosphere furnace. "There are software packages available that predict shrinkage," Goldenberg points out.
"The process of MIM introduces an element of porosity and the Holy Grail is to eliminate that," MedSource's Ellerkamp adds. "Most standard MIM processes result in less than 97 percent density, or three percent porosity. Every time you increase that, you start to address a new set of critical applications, such as load bearing, which requires a higher mass to avoid stress fractures."
MIM
is much more capital intensive compared to plastic injection molding, due to the additional process steps after the components are molded. "Finished metal parts in the range of 95 to 99 percent density can be, among other things, machined, plated, or heat treated to meet specifications," Hanson says.
A molder can expect to invest about $500,000 to several million dollars in MIM, depending on the level of commitment. The bulk of this investment is in equipment, binding, feedstock systems, and a sintering furnace. Additional expenses include materials, secondary operations, and quality control.
"There are companies out there that provide expertise, essentially for binding and sintering metal products," says Cornwall. "So you don't have to do the entire business [by yourself]."
For this reason, the majority of companies acquire MIM operations, rather than start from scratch. "There aren't many plastic molders that have the know-how to jump into this technology with their existing staff," Cornwall says. "There's a huge learning curve."
In addition to financial and technological considerations, molders must build up a clientele sufficient to support the business. This is easier said than done, experts caution, as prospective customers want to see samples of quality craftsmanship. "MIM requires considerably more up-front attention to marketing, customer education, part selection, mold design, and metallurgical material selection," Goldenberg notes. "The activities after molding the part are extensive, difficult to control, and capital intensive."
Because plastics and metal are made from two different processes, insiders advise molders to maintain the separation. "We have found that MIM is not a direct extension of IM, as was originally thought," Goldenberg says. "It's a different business with different economics."
At MedSource, a wall is the most permanent fixture separating plastics from metal molding. The atmospheres are segregated to prevent ultrafine metal powders from cross-contaminating the plastics, and the controlled molding environment is fully climate-controlled with a dedicated air-handling system.
"We run it as a separate department," Ellerkamp says. "It's part of our core unit, which is a combined plastic and metal injecting molding business."
This article was reprinted from Modern
Plastics.
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