Ceramics as an engineering material?
When you think of ceramics, the usual images that come to mind are refractories, porcelain or even pottery. But recent advances in materials and injection molding technology are making ceramics one of the hottest growth areas for the toughest possible jobs.
One example is the ceramic printhead that enabled Hewlett-Packard’s scalable ink-jet technology, a five year, $1.4 billion R&D project aimed at improving the speed and precision of photo printing. The Photosmart 8250 Photo creates 4 x 6-inch prints in 14 sec because the printhead features 3,900 nozzles that allow more ink dots on a specific space, boosting image quality.
Ceramic is used because of its hardness and mechanical strength, as well as wear and corrosion resistance and high working temperature. Generally speaking, the maximum use temperature for most ceramics is 600C.
“The key is the capability to produce intricate shapes with a high quality surface without secondary machining,” says Paul Manison, project manager for ceramic injection molding at Morgan Advanced Ceramics in Stourport-on-Severn, England.
New Developments
Until recent years, that was not possible with ceramics. Advances in materials and injection molding know-how are creating more opportunities to make intricate net shape ceramic parts. One other factor fueling ceramics growth now is entry into the field by plastic injection molders looking for new market niches. Two examples are Oechsler AG of Ansbach, Germany and Phillips Plastics of Hudson, WI. Even the most well-known ceramic injection molders generally have 12 or fewer presses and more that can be used with a screw-and-barrel swap.
Many advocates of ceramic molding will tell you the process is like plastic injection molding. But it’s similar in only the most superficial of ways. Yes, materials are plasticized in a barrel and then pushed under high pressure into a mold cavity where a part is formed. But all metal surfaces — screw, barrel, mold components — that come in contact with the highly abrasive ceramic composite must be extra tough. Tools must be specially ventilated. Parts must be designed differently. There’s proprietary technology in the composite material, in the debindering process and in the sintering process. Companies such as Small Precision Tools of Petaluma, CA that are doing the most demanding molding use submicron ceramic particles (most are 3 to 5 microns), employ proprietary processes from A to Z and even use tungsten carbide to make their tiny tools.
A German manufacturer of injection molding machinery, Arburg, is encouraging molders to consider entering the ceramic powder molding arena. Arburg has operated a powder materials development lab in its Black Forest manufacturing plant since 1991.
The global market for ceramic injection molding parts (CIM) is dwarfed by plastics, but some molders say it is growing as much as 20 to 30 percent per year. Uwe Haupt, a CIM expert at Arburg, estimates overall growth at a more sane 5 percent per year. The ceramic molding market is four to five times larger than the market for its close cousin, metal molded parts.
Key applications for molded ceramic parts are nozzles for spraying systems, such as the HP printhead, implantable structures, particularly dental, electrical and electronic parts, and components that require good wear characteristics in chemical processing or industrial machinery. Coorstek, a spin-off of Adolph Coors Co. based in Golden, CO, makes molded ceramics for electrochemical surgical tips and high-end digital projection equipment to maintain extreme positional accuracy.
The Vertu Phone
Design engineers in Europe are looking at molded ceramic parts as much for their aesthetic qualities as their functional attributes.
Vertu, an English-based manufacturer of luxury cell phones priced as high as $310,000, incorporates ceramics into its designs. The Vertu Ascent Ti features a scratch-resistant sapphire crystal face and highly polished ceramic. “From the start the Vertu Ascent has been heavily influenced by the power, energy and sheer precision of a beautiful car; with the Vertu Ascent Ti, this vision has been developed further using the high grade materials, design detail, technical superiority and unsurpassed performance associated with the luxury sports car industry,” says Frank Nuovo, principal designer.
Swiss watchmaker Rado uses advanced materials to achieve a futuristic and exotic look. The original attraction of ceramic was its scratch-proof characteristics, one of the hallmarks of Rado watches. Now, Rado representatives say the feel and bioinertness of ceramics are also factors.
At the Swiss watch show held late last year, Rado introduced the all-ceramic Ceramica series, topped by the Chronograph Jubilé which is adorned with diamonds. The ceramic is offered in both matte and polished finishes.
In the U.S., the focus is more on functional, industrial uses of molded ceramics.
One example is a nozzle used in a new line of flow cytometry-based cell sorter systems developed by BD Biosciences, a unit of Becton-Dickinson. In the new approach, cells are analyzed in a cuvette. The most important component is a tiny nozzle that separates the flow into precise droplets. Prototypes using metal alloys failed, primarily because they corroded in an ionic solution. Project engineers created a nozzle with orifices smaller than the diameter of a human hair from yttria-stabilized zirconia. Traditional machining couldn’t cut it.
“Our nozzle orifice size pushes the edge of machining and molding technology,” says Vijay Kumar, associate staff specialist on the BD project. The internal geometry of the orifice starts with a wider diameter and tapers down with a very smooth surface. The tapering forms the jet coming out of the nozzle.
The nozzle is now being successfully molded by Small Precision Tools, which specializes in micro ceramic shapes. “The geometry is so small and the material is so hard that if you tried to fabricate it, it would be virtually impossible to produce,” says Travis Ayers, manager of the SPT plant in Petaluma, CA. SPT makes its own compounds from ceramic powders that are less than one micron in diameter.
Powder injection molding dates back to at least 1973 when an engineer named Karl Zueger left Fairchild Semiconductor to develop precise, ceramic capillary tubes for wire-bonding integrated circuits. Zueger patented the process of ceramic injection molding (CIM) and metal injection molding (MIM), also called powder injection molding (PIM).
He founded Small Precision Tools and then Parmatech in Petaluma, CA, which remains a leading supplier of ceramic and metal and injection molded parts. Most companies that mold metal power, such as Parmatech and Phillips Plastics, also have capabilities to mold ceramic powders. Phillips recently took delivery of a sintering oven and landed its first major commercial order.
Phillips also boasts a major innovation department that is leading development of porous interconnected structures made of ceramic and other materials that can be used for orthopedic implants, even in tandem with umbilical cord stem cells.
Design Guidelines
There are several issues to consider when designing ceramic parts:
1) Invest extra time in the earliest stages of design to ensure net shape. Secondary machining is very expensive for ceramics and dramatically changes the economics of the process. Ceramics are abrasive, reducing cutting tool life. Ceramic materials are also expensive, often from $11 to $60 a pound.
2) Ceramics are very sensitive to notches and sharp corners. Large radii help ensure component life.
3) Ceramic parts shrink 20 percent and more as binders are removed in a sintering process.
4) Take special steps to protect and maintain tools. Consider plating certain surfaces and use especially hard tool steel. Tool components should be precision spark eroded and micro blasted. Demolding draft angles should be 1 to 3 degrees, which is more generous than drafts for plastic parts. Design ejector sections as large as possible. Ventilate cavities and consider evacuation.
Types of Materials
These materials are most commonly used for ceramic injection molding:
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Zirconia-stablized alumina combines the best properties of both materials (hardness and toughness). It’s available in white and black. It costs about $26/lb.
Major suppliers include BASF (Catamold), Clariant , Coorstek, and Zschimmer & Schwartz. Molders with roots in the ceramics industry, such as Morgan, produce their own ceramic composites. Coorstek, last year, opened a new materials technology center in Golden, CO to develop new ultrapure ceramic materials, with a particular eye on new demands in the semiconductor industry as it moves beyond 45 nm devices.
Another materials option is cermet, a composite of ceramic and metal powders.
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