Process Analysis of Manufacturing of Sewing Scissors by All Forging Process and Understanding of Its Sharpness

In Japan there are several types of scissors such as pruning scissors, flower scissors, U-shaped scissors, and sewing scissors and so on. Among them sewing scissors was introduced when the black ships of Commodore Perry came from the United States in the last Edo period almost 160 years ago. The shape and size of sewing scissors have been changed to fit Japanese people. Yakichi Yoshida started Japanese sewing scissors by his own manufacturing process; all a forging process. His technique was distributed to many persons who learned his process through implicit knowledge base. According to the family tree starting with Yakichi, there has been a spread to the manufacturing family of 23. However at present only one person is remained. He is still making the cutlery which has very good reputation among high ranking wear making persons and other high quality manufacturing persons. In order to preserve this manufacturing technique the process analysis was performed through video recording and the records were put in this paper. The process was divided into 9 steps such as Preparation, Making the ring, Making part of the blade, Making the neck part, Grinding, Finishing machinery, Quenching, Finish grinding, Post finishing, Normally the expert needs dozens of years for the whole process, therefore the number of products per day is very small. In the case of cutting some materials two blades contact each other at very small part. Small as possible makes sharp cutting because of stress concentration at the cutting point. In order to create this phenomenon the inside of the blade should not be a flat surface; instead the surface is required to be dented. This dented surface was made at the third step, and particularly only one sub process can make it. Our further study will be made for more accurate time analysis and also the bending process will be focused to understanding the secret of sharp cutting.