Prise winners list

Development of new resin molding system without ejector pins, drastically improving production efficiency of high-precision hard silicon lenses

Watari-cho, Miyagi Prefecture
Maxell Finetech Ltd.
Other award winners
Maxell Finetech Ltd. / Ichiro Iibuchi, Yukihiro Ogasawara, Daisuke Koide, Yorio Hachiya, Hiroyuki Hirama, Naoaki Watanabe
Nippon Future Co., Ltd. / Tomomasa Imai
Recommended by
Industrial Technology Institute, Miyagi Prefectural Government
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Suzuishi, Mitsunobu  (48)
Miyagi Precision Dept.
Die and Mold Technology Center
Deputy Center Chief

We study any new idea, discuss and test it. We study a new idea till the end before giving it up. Then a breakthrough will be found.
summary

Silicon resin has prominent characteristics as an optical material, namely high resistance to heat and ultraviolet ray. However, silicon resin could not be used for continuous mass production because its viscosity is too low when it is molded and its products are brittle after they are cured. The problems were found with the ejector pins, which released the products from a mold. After trial and error, they succeeded in releasing the products from a mold by using vibration. They used many protective measures for the equipment. They adopted quake-absorbing structure to prevent vibration from transferring to the sections other than the mold, and heat-insulated between the high-temperature mold and the heat-sensitive ultrasonic oscillator. As a result, production efficiency of hard silicon lenses was drastically improved. Currently hard silicon lenses are mainly used for light diffusion lenses for LED flashes installed on mobile phones. They will also be used for automobile light in the near future.

summary

The common knowledge about injection molding cannot be used. Although it has prominent characteristics, silicon resin cannot be used for mass production

It was 2005 when Mr. Suzuishi and other engineers started development of mass production technology for hard silicon resin because of its prominent characteristics as optical lens material. Their target was production of light diffusion lenses for LED flashes installed on cameras of mobile phones. Silicon resin has two prominent characteristics best suited for that purpose as follows. 
"First of all, although it is resin, hard silicon can withstand high temperature of two hundred and several tens of degrees. In the manufacturing process of mobile phones, the printed circuit boards are exposed to very high temperature in soldering. Needless to say, the silicon resin can withstand heat generated by super luminosity LED." 
Silicon is thermosetting resin, which is heated up to 170C in a mold to harden it. Therefore its products also have high heat resistance.

"Secondly, it has high resistance to ultraviolet ray. Although it is also thermosetting, epoxy resin turns yellow and deteriorates when it is exposed to ultraviolet. However, silicon resin does not lose transparency. This is a prominent characteristic for lenses for super luminosity LED flash, which emits wavelength close to that of ultraviolet ray. The same thing can be said also for automobile and street lights which are exposed to sunshine outdoors."

However, silicon resin had a critical defect for mass production. Silicon resin material is thick like slime at normal temperature of 25C. However, when it is heated to flow it into a mold, it becomes thin like salad oil. Therefore people said, "it flows even into very small clearances due to its low viscosity. It leaks from joints and its products are miserable because they have conspicuous burrs."

More serious problem was found with the ejector pins within a mold. In an injection machine, products are pushed out by the pins after the mold is opened. Silicon resin flowed even into between the pins and their guide holes. Therefore we had to stop the molding machine six times a day to maintain it. In addition, the products were so brittle that they broke easily like cookies just baked when they were pushed out. "We had to move the pins so slowly and take out the products so carefully that we felt irritated. The yield rate was nearly 90% but the production efficiency was too low."

Idea of "vibration" struck us, but quake-absorbing structure and heat insulation were the problem we had to clear.

Although we improved the working accuracy wherever possible to prevent flowing in of the resin, it still flowed into clearances. We changed the shape of pins but it took too much time to machine them. To begin with, the problem of breakage cannot be solved as far as the pins are used. We studied and tried all the methods but they all failed, and we were quite at a loss what to do. Then "the God of Technology" helped Mr. Suzuki. "A new idea struck me while I was commuting. Isn't it possible to use vibration to take out the molded products? It was quite a new idea."

Ultrasonic wave came to my mind. The vibrate mode of mobile phones uses vibration of ultrasonic motor. We produced a test machine in which a mold was set on an ultrasonic oscillator. Then the products could be successfully removed from the mold…but they still broke easily. "Anyway, finding that vibration could be used effectively, we pursued this new method and finally succeeded in removing the products from a mold without breaking them."

On the other hand, ultrasonic vibration was spread through the whole injection machine and caused a failure. After trial and error, we solved this problem by adopting "quake absorbing structure" for the supporting section of the mold and the ultrasonic oscillator. However, we had to solve another problem. As mentioned above, silicon resin must be kept at 25C as a material but at 170C when it is flowed into a mold. However, an ultrasonic oscillator is easily affected by heat and destroyed at 50C. Temperature adjustment to solve this problem was difficult. If each section was heat-insulated too much, vibration could not be transferred to the mold. It was difficult to find the proper balance."

We finally completed the mass-production injection machine in 2007 and started continuous mass production. Production quantity increased as much as 40% because the time for mold release was shortened and maintenance work was so simplified that it had to be conducted only once a week. It seems that idea of "vibration" solved all the problems. According to Mr. Suzuki, however, we should not forget fact that all our team members studied numerous ideas very hard to solve the problems. Inspiration that brings about a breakthrough is a prize awarded by "the God of Technology (Monodzukuri)" to those who can continuously strive and study to solve a problem.

Maxell Finetech Ltd.

Established:
May. 1963
Capital:
One billion yen
Employees:
324 (as of Dec. 2009)
Brief information:
Based on its own skill for die machining, the company is trying to develop a new technology by combining the technology for resin molding and metal working and the optical design technology.

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Image1
Image2

Right: silicon resin at normal temperature, sticky as slime, left: heated silicon resin just before flowed into a mold, thin like salad oil

Image3

Silicon resin lenses released from mold

Image4

Ultrasonic oscillator set on the test die