Versatile VMC line

Author William Leventon
December 02, 2021 - 01:00pm

Called the J series for “jig,” a line of CNC machines introduced by Mitsui Seiki Kogyo Co. Ltd. in Japan is said to combine jig borer accuracy and machining center productivity.

The company designed the vertical machining centers to handle precision boring, milling, drilling and tapping. The J series includes four basic machines to accommodate a wide range of workpieces for the medical, optical, aerospace and mold and die industries.

“The large-frame machines are suited for doing large mold-base work and things of that nature,” said Bill Malanche, chief operating officer at Mitsui Seiki USA Inc. in Franklin Lakes, New Jersey. “But we also make (smaller) J-style machines for doing things like ultraprecise medical components.”

Included in the J series are the PJ812 (PJ stands for “profile jig”), which offers the least axis travel and the lowest table load capacity of the group; the J1220; the J1230, which presents the most x-axis travel; and the J1625, which has the highest table load capacity. X-axis travel provided by the different machines ranges from 1,200 mm (47.2") to 3,000 mm (118.1"), y-axis travel runs from 800 mm (31.5") to 1,600 mm (63"), and table load capacity ranges from 1,500 kg (3,307 lbs.) to 6,500 kg (14,330 lbs.). Z-axis travel for all the machines is 500 mm (19.7"). The line furnishes positioning accuracy and repeatability of ±1 µm (0.00004"), according to Mitsui Seiki.

J series VMCs are designed to offer both machining center technology and jig-milling precision. Image courtesy of Mitsui Seiki USA

The component accuracy offered by J series machines is attributed partly to an automatic thermal compensation system that employs sensors on the machine face plate and inside the spindle to minimize the effects of temperature changes. Mitsui Seiki says the system reduces temperature-related displacement by 60% and cuts z-axis thermal growth and deflection by 30%.

Other design features include a proprietary design element that increases the static rigidity of the z-axis to more than six times that of conventional z-axis arrangements, the company reports. In addition, machine precision and rigidity get a boost from hardened and ground tool-steel box slideways and contact elements designed to improve acceleration, reduce stick-slip and allow feed accuracy of 0.1 µm (0.000004"). Malanche explained that the contact elements are part of the gib system, which was modified to reduce the effective weight on the ballscrew during machining to allow the machine to move more precisely.

The company says another feature that distinguishes J series machines from the competition is the way in which the guide ways are attached to the machines. After hand-scraping cast machine surfaces to a true, flat condition, Mitsui Seiki bolts on the steel guide ways from underneath.

“A lot of machine tool designers put those bolts through the top of the way, down to the casting material, and then put little plastic caps or something like that over those holes,” Malanche said. “We completely eliminate any kind of obstruction there by doing it the opposite way and bolting on the guide ways from underneath the axes.”

J series machines also benefit from a special cooling system for slideways and ballscrew cores aimed at increasing axis feed precision. He pointed out that slideways and ballscrews traditionally have been lubricated with either a heavy grease pack or a heavy lubricant. By contrast, Mitsui Seiki cools these components with an air-and-oil atomization system.

“Instead of drowning the ballscrews and slideways with liquid,” Malanche said, “we’re spraying a light mist with cold air as well.”

For some potential users, one of the most attractive features of J series VMCs may be their ability to do more complete component machining.

“In a lot of cases, people tend to not use their precise machines for roughing and finishing,” Malanche said. “But because of the construction of these machines, they are capable of doing the whole job. They’re heavy and rigid enough to do roughing work. And they can move ultraprecisely for the finest elements that need to be done.”    


Related Glossary Terms

  • boring


    Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

  • centers


    Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

    Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

  • face plate

    face plate

    Flat, round workholder with slots used to hold regular- or irregular-shaped stock. If stock is markedly asymmetrical, counterbalances may be needed to prevent vibration.

  • feed


    Rate of change of position of the tool as a whole, relative to the workpiece while cutting.

  • flat ( screw flat)

    flat ( screw flat)

    Flat surface machined into the shank of a cutting tool for enhanced holding of the tool.

  • gang cutting ( milling)

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • jig


    Tooling usually considered to be a stationary apparatus. A jig assists in the assembly or manufacture of a part or device. It holds the workpiece while guiding the cutting tool with a bushing. A jig used in subassembly or final assembly might provide assembly aids such as alignments and adjustments. See fixture.

  • machining center

    machining center

    CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.

  • milling


    Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

  • tapping


    Machining operation in which a tap, with teeth on its periphery, cuts internal threads in a predrilled hole having a smaller diameter than the tap diameter. Threads are formed by a combined rotary and axial-relative motion between tap and workpiece. See tap.