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One reason might be the sheer complexity of the process-more than simply buying a new piece of machinery, switching to injection molding requires a change in the entire manufacturing cycle. High-quality powders must be selected and might require additional preparation to meet product specifications. A suitable binder designed specifically for injection molding must then be carefully formulated or selected and homogenously mixed into the powder, and the resulting formulation must be converted into feedstock that can be fed into the injection molding machine. Injection molded parts must then be dewaxed (binder removed) and sintered to complete the production cycle.
Each stage requires knowledge and expertise to achieve success. For companies that are comfortable with more traditional forming processes such as extrusion or cold isostatic pressing, the idea of switching to injection molding can be intimidating.
"There are a lot of different variables involved in injection molding, and a lot of places where things can go wrong," notes Jay Thomas, product manager for Tosoh USA, Inc., a subsidiary of the Tokyo, Japan-based Tosoh Corp. "But for manufacturers that produce high volumes of small, detailed parts, injection molding can provide a lot of advantages compared to conventional forming methods."
From Powders to PartsTosoh, which is well known in the ceramic industry for the manufacture of high-purity zirconia powders, also has an impressive track record in injection molding. In 1988, it formed a subsidiary called Tosoh Ceramics Co. Ltd. to produce injection molded ferrule blanks and other components.
"Prior to 1988, Tosoh's ceramic business was exclusively in powders. But as the fiber optics industry grew in the '80s, so did the need for connectors and ferrules," Thomas explains. "The ferrules used in the connectors at that time were stainless steel, glass, plastic and alumina ceramic, but zirconia soon became the material of choice; its small sintered grain size permitted the high-precision finishing that was required for low loss connections. This was a perfect fit for Tosoh's high-purity zirconia powders, so the company began compounding its powder and injection molding ferrule and sleeve blanks to meet market demands."
Why injection molding? According to Thomas, Tosoh Ceramics used other forming techniques such as cold isostatic pressing for other components. But for the small, detailed ferrule blanks, other techniques simply weren't cost-effective.
"With injection molding, the detail can be built into the tooling to produce as-molded features. For example, the back end of Tosoh's ferrule blanks, where the fiber is inserted, has the V-hole molded in during the injection molding process. The only other way to effectively produce these components might be extrusion, but then the ferrules would have to be cut apart and the V-hole would have to be machined into them, which adds extra steps and costs," Thomas explains.
With injection molding, the company found a competitive niche, and its business in ferrule and sleeve blanks was soon booming. But as Tosoh gained experience in injection molding, the company began to see significant potential for the technology in other markets-markets that it didn't necessarily want to pursue as a ceramic manufacturer. When some of Tosoh's powder customers began approaching the company several years ago for solutions to produce small, complex ceramic parts, the company began to reevaluate its options. Why not capitalize on its powder and injection molding expertise to supply ready-made compounds that would simplify the injection molding process for other manufacturers?
Simplifying Injection MoldingIn 2001, that's precisely what Tosoh decided to do. The company initially offered two standard "off-the-shelf" compounds for high-pressure injection molding based on its high-purity zirconia powders-one for dewaxing in air, which featured good dewaxing performance and slow beginning flow in the injection molding machine; and the other for dewaxing in nitrogen, which featured a faster beginning flow. A short time later, Tosoh introduced a third compound that featured both good beginning flow and good dewaxing performance for dewaxing in air.
Each compound is composed of high-purity zirconia powders and a proprietary binder formulation (approximately 50 vol %) developed for the intended dewaxing environment. According to Thomas, the binder is crucial to ensuring high-quality injection-molded components. "The binder is removed from the part during the dewaxing stage, but since half of the part's mass is composed of binder, the part experiences a lot of shrinkage in the dewaxing process. The binder must be formulated specifically for the intended dewaxing atmosphere to ensure that the amount of shrinkage is precise and repeatable with each batch of parts," he explains.
The company adds its proprietary binder to the powders and homogeneously mixes the formulation. The resulting taffy-like mixture is dried and pelletized to produce the injection molding compound that is delivered to the ceramic manufacturer.
"In the past, injection molding was a much more difficult process because a company would have had to create or purchase its own binder system, and formulate and mix its own compounds. Now, companies can just buy the injection molding equipment and purchase ready-made compounds, so it's a much simpler process," says Thomas.
But Tosoh's involvement doesn't necessarily stop at supplying the compounds. "Tosoh is unique because it has ceramic powder production under its total control, along with experience in formulating that powder into injection molding compounds and using those compounds to mass-produce sintered parts. We've been doing that for more than 10 years. We've encountered virtually every problem there is, and we've solved it. That gives us valuable experience, and we're willing to support our compounds with that experience, from the starting powder all the way to the sintered product going out the door," Thomas explains.
For example, the company has developed a process in injection molding to recycle 100% of the compound so that none of it goes to waste. According to Thomas, Tosoh is willing to share that process with its customers.
The company is also willing to partner with ceramic manufacturers to develop formulations based on materials other than zirconia. "Our binder system is tried and true, and we have the experience," says Thomas. "Companies can supply us with the material, or tell us the specifications of the material they want to use if it's something other than zirconia. We will do that, and then we can help them mold, dewax and sinter the components to ensure the highest possible quality. We want companies to know that if they have the markets, we have these products and the experience to help them produce high-volume, detailed, small parts in the most cost-effective way possible.
New OpportunitiesAs ceramic manufacturers look for ways to become more competitive on a global scale, technologies such as injection molding are worth a second look.
"Molded shape vs. final shape is the driving force behind using injection molding. It's all about what steps you can cut out of the process to get the same end product," notes Thomas.
In many cases, however, it's also about creating new products that can expand a company's market share. For example, a black zirconia injection molding compound has been used to manufacture high-end covers for cell phones, as well as wear parts for robotic optical systems. Injection molding has also been used to manufacture cutting tools, tooling and cores for investment casting, and a variety of other components.
Several years ago, a university professor who had performed extensive research in ceramic injection molding noted, "As the understanding of the ceramic injection molding process continues to evolve, the market for these ceramic components has the potential to increase exponentially."1
Today, with the availability of new ceramic injection molding compounds and a wealth of expertise, this level of growth appears to be within reach.
For more information about injection molding compounds, contact Tosoh USA, Inc., 3600 Gantz Rd., Grove City, OH 43123-1895; (866) 844-6953 or (614) 277-4348; fax (614) 875-8066; e-mail firstname.lastname@example.org; or visit http://www.tosohusa.com.