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June 15, 1999

3 Min Read
IMMC Plant Tour:Keeping tolerance over time

For the past 12 yearsCitizen Watch has been the number one watchmaker in the world.Founded in 1930, the company today owns a 26 percent share ofthe entire world market in watch production, thanks largely tothe quality, design, and functionality of the products it producesfor citizens everywhere. For the past 12 years Citizen Watch alsohas been a PIM molder. Draw your own conclusions.
Its 15-building manufacturing complex is called "KawaguchikoSeimitsu." "Kawaguchiko" is the name of a lake;"Seimitsu" means precision parts maker. Citizen's PIMplant on the premises produces 8 million parts per month, up to80 percent of which are precision molded in ceramics. CIM wasa 10-billion yen market in Japan last year.
The rest of Citizen's PIM parts are in metals, like titanium andhard metals. Nearby in the complex, Citizen's plastics injectionmolding facility produces 80 million parts per month, parts likemicromolded acetal gears. But that's another story. Let's tour.


Running Like a Clock
The molding shop floor is spotless, quiet, and well lit from aceiling considered to be high by Japanese standards. Citizen'smolding machines are arranged in two rows with utilities fromoverhead. A 500 kg crane spans their clamps. The fully air-conditionedfurnace rooms are equally pristine, a bit more roomy, and arealso serviced from overhead utilities. BASF and Pacific Metalsare among the major materials suppliers to Citizen's PIM plant.
The molding machines operate in self-contained automated manufacturingcells. Machinery is well maintained and tuned to perfection. Eachcell is supported by parts-removal and degating robots, and fixedautomation devices. Each cell also has a beside-the-press setterfor startup rejects and a Nikon microscope for visual inspections.
Citizen has a large all-CNC/DNC toolroom on the grounds with 30moldmakers working in two shifts. Equipment there includes 10Sodick and Mitsubishi sinker and wire EDMs. Mold bases are outsourced.Some hot sprues are used in PIM, but Citizen mostly uses three-platemolds with pinpoint gating.


Measures of Perfection
In addition to its own clockwork and components for its otherproducts, Citizen custom molds a number of other types of precisionPIM parts for others in a number of different markets. Years ofexperience enable it to precisely match its feedstocks to customerspecs in such areas as magnetic properties, thermal conductivity,and thermal expansion. And its process expertise empowers Citizento consistently hold the extremely tight tolerances required forpart functions, even when producing millions of these small, complexparts per month.
For example, its highest volume part, a head for floppy disk drives,is molded in calcium titanate
ceramic. The design consolidates three parts into one part moldedin eight- and 16-cavity tooling. Automatically aligned on theirsetters, 160,000 heads go into a kiln in each batch. The headshave a small rec-tangular slit. The slit is 3,820µm long.Tolerances are consistently held to within ±15µmat a 2.57 CpK. And the slit's 335µm height is held to within±10µm with a 1.64 CpK (see box, p. 48).
Citizen Watch plans to expand its PIM business significantly inthe next three years. It expects most of this growth will be pulledby demand for its custom precision molding capabilities. The biggestchallenge is improving part quality while reducing part costs.Hot runners and more extensive use of automation are possiblesolutions.


Citizen Watch demonstrates its 12 years of precision PIMmolding experience in its ability to hold tolerances over time.The hole diameter for this iron watch cam is 653µm, ±5µm.The accuracy data represented in the graph was recorded over asix-month time period, including variance among cavities. Toleranceswere held to within ±2µm. Citizen Watch has yet toreceive a complaint in the six years the part has been in production.

Contact Information
Citizen Watch Co. Ltd.
Tokyo, Japan
Ken-ichi Yoshikawa
Phone: +81 (3) 424 68 4582
Fax: +81 (3) 424 68 4544
E-mail:[email protected]

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