E-shots Web Exclusive: Ceramic molding may not be easy, but this molder sees the future in it

Editor’s note: In the December 2002 IMM we showed how SLG, a molder in Germany’s Black Forest, won a job away from a low-labor-cost area using creative engineering. That creativity is also taking them into entirely new technology and markets.

In 1996, Dieter Stockkamp, the general manager of SLG Kunstoff-Fabrik und Formenbau in Bernau, Germany, met with a university professor researching new molding technologies such as metal injection molding (MIM) and ceramic injection molding (CIM). SLG already had some experience with MIM, but the area of ceramics caught Stockkamp’s attention. SLG saw that the finished products offered a unique property profile and had wide application potential. Moreover, with only two other companies in Germany into CIM at the time, SLG saw a market window, too.

They soon discovered that the learning curve for ceramic molding resembled a ski jump…seen from the bottom. Serious development work was needed on both processing and materials. SLG had solid molding experience that would help them with the processing.

They were also good moldmakers, a skill they correctly foresaw as critical for CIM. Rather than do it all themselves, they decided to partner closely with BASF on materials so they could concentrate on processing. That strategy worked, and within a few years SLG was being told its processing skills were leading the field. A lot of trial and error went into the learning, says Stockkamp, and they learned the most from the errors. SLG began its CIM development using an older Arburg molding machine, which is still working, and second-hand debindering and sintering ovens. It took over two years for the first product line, surgical forceps, to reach normal production.

There are now eight molding machines on the side of the building where ceramics are produced. Four Arburgs are used almost exclusively for ceramics, while four Demag Ergotechs, are switched between ceramics and plastics by changing barrels—in tune with demand.

The "waiting time" took some getting used to, says Stockkamp. Results are visible only after the entire process cycle—molding, debindering, sintering—is complete. Molding cycles are about the same as plastic, but debindering takes 8 to 20 hours and sintering up to 30 hours. And it is not just the waiting. While "green" molded parts can be handled easily, debindered parts are not only fragile but must go straight from the debindering oven to the sintering oven. SLG discovered that simply opening a door during the change was enough to flaw the products, which you could not discover until a day later.

CIM MARKETS VARIED AND GROWING
SLG targets its CIM technology at four markets. Medical-surgical products are well underway. The forceps line, which has reached four products, has been joined by a line of scalpels. Ceramic material is nonconductive and nearly inert. Metal, by comparison, can trigger reactions in many people—serious problems. Many medical experts see metal almost vanishing from surgical areas within 10 or 15 years by virtue of ceramics. Other advantages are that scalpels never need resharpening, and that ceramics can be sterilized by standard hospital techniques.

A second market, dental equipment, might seem related to medical but is very different. Ceramic drill bit holders and a variety of other generally small mechanical components are steadily replacing metal. A major reason why is ceramics wear resistance. It is so hard—up to 2000 HV for aluminum oxide; and up to 1300 HV for zirkon oxide—that designers have to learn that whatever the ceramic is contacting will wear out first.

A third major market, commercial knives, exemplifies the company’s hard-earned processing expertise. Think about the wall thickness and flow length ratio of a kitchen knife blade, including the long tang inside the handle. It is not easy to move CIM material that far in such a narrow path, and should a non-homogenized bit of material temporarily freeze during flow, it will almost certainly create a weak point that will not be evident until after debindering and sintering. Manfred Hauser, SLG project manager for CIM: "We were told that it ‘definitely’ could not be done, and that was great motivation." Most other ceramic knives on the market are machined from sheet stock, not molded.

The current dream goal for the blade, says Hauser, is increased flexibility. At present, dropping the knife can snap the blade. But for those who love to cook, a blade that always stays super-sharp and is easy to clean is worth the careful handling. Sharpening the blades took significant development work by SLG. A CIM blade will wear away a sharpening stone. Because what the market had to offer at the time was not specific to their product, and was expensive, SLG decided to develop proprietary sharpening technology, a competitive advantage you will not see described here or in any other article. Machining the knife handles from Dupont Corian provides enough weight that a dropped knife will likely hit the floor handle first, and thus not break the blade.

A fourth market, technical industrial components, is where SLG sees the greatest range of possibilities. The dimensional stability of ceramics, its hardness, chemical resistance, and ability to hold very small tolerances, are highly valued properties for pumps, compressors, specialty textile cutters, and a lot more. Hauser says SLG’s biggest job currently is educating designers as to what can be done with CIM. After that happens, applications multiply quickly. A large percentage of new applications are very small parts. Holding a cylindrical pump housing, Hauser says, "We were told this .4-mm wall thickness was impossible, too." SLG developed its micromolding skills to support ceramic processing, and tolerances of .01 mm are now found in many small parts.

A NEW WORLD OF PROCESSING
The CIM processing window is narrower in virtually every parameter than what SLG was used to with plastic. Normal melt temperature is around 135?C with a window of only ±2.5 degrees. SLG, which makes all its CIM tools in house, developed special gate designs and overflow cavities to cope with these problems and more. Multiple cavity sensors monitor the process. Cooling via drilled channels is the norm. Removing heat fast, they say, is not the problem. Maintaining homogeneous flow is far more critical. Single-cavity molds prevail here, though the knife blade molds are two-cavity hot-runner designs.

Virtually all demolding and handling of ceramic parts is done manually. Automation will be installed to speed up and stabilize the process and for quality assurance, much as it happened in SLG’s plastic operations. Early in 2001, a graduate engineering student did his thesis by documenting all of SLG’s hard-won ceramic processing know-how. The 160-page book is now an invaluable and closely guarded reference and training tool. Hauser says new process knowledge developed since the book was written can fill an even larger volume. That knowledge is their edge, and they are increasing it.

You could think SLG simply saw an opportunity and took it, which would be true, but their thinking goes much deeper and longer term. SLG has done well as a custom molder of medium- to large-sized plastic parts. Yet, near the end of the IMM meeting, Dieter Stockkamp noted, "We are uncertain about the future of custom molding in Europe." To better position itself, SLG sees the advantage of special niches, be they by market, technology, or a combination of the two. The CIM department will soon have needed growth space on the second level of a new addition to the factory. Plans for the current ceramics molding space are undisclosed for the moment.

Dieter Stockkamp, Director
SLG Kunststoff-Fabrik und Formenbau GmbH
Gewerbegebiet Gässle 1
D-79872 Bernau, Germany
Phone: +49 (7675) 9 05 10
Fax: +49 (7675) 90 51 50