You are here: HOME > Products (Machinery - Machine Tool) > Mitsui Seiki: Jig Grinder NC Type Series

Products (Machinery - Machine Tool)

Mitsui Seiki: Jig Grinder NC Type Series


Mitsui Seiki is part of the Mitsui Group, one of the most important business conglomerates in Japan. It is a manufacturer of machine tools with a particular specialization in precision machine tools.

It was founded in 1928 in order to establish a domestic supply of precision machine tools, of which Japan had previously been entirely reliant on an overseas supply. Since then, it has expanded throughout Japan and the rest of the world. It has a strong relationship with Toyota.

Jig grinders are one of the core products produced by Mitsui Seiki. Just as every peg needs a hole, machines cannot be built without jigs, the parts that guide and fix components and materials in the correct place for machines to function. A jig grinder is a type of precision machine tool used to grind and polish holes bored by drills, for example, in order to finish the inside of a hole with a defined diameter to a micron-level scale of accuracy. As with other precision machine tools, the level of experience of the operator can cause discrepancy in the finished dimensions. As a result, machines complete with computer numerical control (NC) systems have become the industry standard.

This kind of cylindrical grinding processing is crucial to the automobile, aircraft and space engineering fields. The level of precision demanded by such industries is extremely high, and the difficulty of the processing itself is also considerable. As a result, only a few manufacturers worldwide are able to produce machinery capable of meeting such high standards. Within Japan, Mitsui Seiki is the only machine tool manufacturer with the technology to produce NC jig grinders. The international share held by Mitsui Seiki for jig grinders currently stands at around 90%.

Mitsui Seiki NC jig grinders are outstanding for multiple reasons, introduced below.
As explained above, processing carried out by NC jig grinders needs to be highly accurate. This product series is characterized by the following two unique features, developed inhouse and incorporating into the manufacturing process in order to ensure the highest level of precision possible.

1) V-F sliding surfaces on the X- and Y-axe, spindle head and the top and bottom sides of horizontal bridges are finished with scrapers.
2) Low thermal expansion casting adopted for the head material.

The unique scraping process outlined in feature 1) above enables extremely high geometric precision. Feature 2) results in a significant decline in error due to heat displacement.
In addition, models in the series have been variously improved, as follows, in order to realize greater precision in processing.

1) All models excluding the 3GB: Z-axis is NC-controlled and two types of control (Z-axis as cutting feed and Z-axis as chopping cycle) are available.
2) 300G, 4GCN, 6GDN: the inclusion of a ball screw drive on the Z-axis chopping cycle has enabled high speeds of 200 cycles/min (at 25 mm stroke). Bottom dead center precision remains 2 µm at this speed.
3) 3GEN: a linear motor has been adopted for the Z-axis, the first such practical application for machine tools. A Z-axis chopping cycle of 400 cycles/min (at 25 mm stroke), impossible for traditional machines, has been realized to drastically reduce the process time of contouring cutting.

The aircraft and space engineering industries show signs of increasing expansion in the years to come. Amidst such demand, the Mitsui Seiki Jig Grinder NG Series will almost certainly become an increasingly significant product, unparalleled in quality and vital to much manufacturing. Further technological refinement is also expected.

Apr 13, 2011

About the author
Eriko Kinashi is a reporter for Japanest NIPPON
(Mitsui Seiki Kogyo Co., Ltd.)
Unit : 300G
X-axis(mm) 500
Y-axis(mm) 300
Table size(mm) 700×350
Maximum loading weight(kg) 300
Quill (Z-axis)
Chopping stroke(mm) 95