Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)
26

M-VB25 Fixed Rail Bridge Type Milling Machine Series,
Best Suited for 5-Face Machining of Thin Workpieces

YASUHISA ICHIKAWA*1 TAKAYUKI KUME*2

HIROYUKI TAUCHI*1

AKIHIKO MATSUMURA*3

HIROSHI OISHI*2

KEIICHI NORIYAMA*2

In cases mainly for the machining of roughly 500 mm-thick thin workpieces, a fixed rail
bridge type milling machine is the best choice in terms of function and cost. But existing machinesof the same type do not have sufficient ability to cut at the time of ram extension due to their poormachine stiffness. The developed M-VB25 fixed rail bridge type milling machine has materialized ahigh-stiffness bridge-shaped strong structure, which has been made to give full play to its highcutting ability at a substantial amount of ram extension. Along with the adoption of an
operability-improved/maintenance function-reinforced original control board as well as display,energy saving promotion-based reduction of CO2 emissions has also been realized. The features ofthe M-VB25’s technology are described below.

|1. Introduction
In fields such as industrial equipment, energy and electrical appliances,diversification/division into smaller lots and the upsizing of parts have advanced at processing sites
for small and mid-sized product parts in recent years, resulting in more cases where the table sizeor the stroke amount of each axis is insufficient in existing machining centers. Workpieces of thissize are thin, being generally 1 m or more in width and length and 500 mm or less in thickness, andsince the installed capacity of a bridge-type 5-face milling machine is too large for the machiningof such workpieces with this machine, there is increasing need to reduce investment in equipment
by limiting machine functions.
Mitsubishi Heavy Industries, Ltd. (MHI) developed the M-VB25 fixed rail bridge typemilling machine, which has a cutting ability sufficient to meet the needs of this market. Table 1
shows principal specifications. This machine successfully improved machine operability as asolution to increasingly younger operators, and realized a reduction in CO2 emissions forenvironmental load alleviation. The features of the M-VB25 are introduced below.
Table 1

M-VB25 specifications

WidthWorksurface
Table
LengthLoading capacity
Column bridge widthWork passage height
Ram size
SpindleSpindle speed
Spindle motor output (continuous)
Number of ATC tools*1mmmmton/mmmmmmm
min-1
kWtool (s)

1,500
3,000
12/3.0
2,050
1,200
□350
6,000
22/30 (low/high speed)
50Engineering Department, Machine Tool Division, Machinery, Equipment & Infrastructure*2

Chief Staff Manager, Engineering Department, Machine Tool Division, Machinery, Equipment & Infrastructure*3Manager, Engineering Department, Machine Tool Division, Machinery, Equipment & InfrastructureMitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)27|2. Stiffness improvement technology and cutting ability of theM-VB25
A rail-movable (equipped with rail elevating W axis) bridge-type 5-face milling machine
represented by MHI’s MVR-Ex allows the rail (W axis) to go up and down in accordance with thethickness (height) of the workpiece to be machined, and therefore is characteristically able to set
the amount of shortest ram extension (Z axis) for efficient machining. But in the case of a fixed rail(not equipped with rail elevating W axis) 3-axial bridge type milling machines represented by theM-VB25, since it is necessary to machine workpeices only by extending the ram, there was aproblem of the failure to obtain sufficient cutting ability due to the larger amount of ram extension
for the machining of thin workpieces compared with that of machines with an elevation axis.
Hence, structural reform into a bridge-shaped type was carried out to realize higher stiffnessof the machine so that sufficient cutting ability could be ensured even at the time of a substantial
amount of ram extension. Through this improvement, MHI commercialized a milling machine withexcellent cost performance.

2.1

Stiffness improvement technology

To enhance the cutting ability at the time of ram extension, the rib shape, thickness andlayout within the casting structure were optimized, utilizing the latest structure optimization
technology along with conventional FEM analysis for successful improvement into a strong
bridge-shaped structure with excellent dynamic stiffness.
Figure 1 exemplifies the structural analysis of a bridge-type machine. The latest structural
analysis permits the optimum rib structure within the column to be determined. In addition, theM-VB25 adopted an integral column and bridge casting structure to enhance the stiffness at thejoints.
Figure 2 shows a photo of the M-VB25’s casting structure. Furthermore, casting iron withexcellent damping performance was employed for all of its major structures, realizing avibration-resistant, high-stiffness structure. These stiffness improvement technologies realized acutting ability 1.4 times greater than before with considerable extension of ram at both the verticaland horizontal spindles.

Figure 1 Example of bridge-type machine’s structural
analysis

2.2

Figure 2 Integrated bridgeand column

Cutting ability

An example of machining where the test piece was SS400 general structural rolled steel,which is used for industrial equipment and other purposes, is introduced here. With this machine,
the amount of ram extension at the vertical-axis milling cutter is 919 mm, while that at thehorizontal-axis cutter of 631 mm permits heavy cutting of 5-mm cuts. With considerable extensionof ram, a cutting ability favorably compared with that of the higher-ranked MVR-Ex has beenacquired. Figure 3 and Table 2 exemplify milling cutter/endmill processing cases.

Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)
28

Model

Vertical/Material
horizontal
Verticalaxis

M-VB25

SS400
Horizontal
axis

Verticalaxis
MVR-EχHorizontal
axis

Figure 3

SS400

Table 2Cutting ability of the M-VB25

Tool

Spindlespeed(rpm)Cutting
speed(m/min)

420

211

130

5500

99

25

420

211

500

99420
420

φ160 face
milling cutter
φ63 end mill
φ160 face
milling cutter
φ63 end mill
φ160 face
milling cutter
φ160 face
milling cutter

Cutamount(cc)

Ramextension(mm)

1,100715

919

35300

263906130

51,100715

631

2535300

263708

211

130

5

1,100715

800

211

130

4

1,100572

800

Width ofcut
(mm)Depth of
Feed rate
cut(mm/min)(mm)

Milling|3. Operability
improvement
reinforcement of machineandmaintenancefunction

At processing sites, the rate of younger operators is increasing while the number of veteranengineers decreases. In addition, due to the higher performance of machines, their operation andrestoration methods are becoming more complex. With these factors in the background, there is
growing demand foramachine that dispenses with the need for skill in operation. Customer
demands are as follows:
Touch-panel and other intuitive/simple-to-operate control console/screen
Control console/screen easy to manually operate during automatic milling in small-lot work
processing
Expansion/facilitated operation of the maintenance functions so that even customers caneasily restore the machine.

3.1

Improved operability

Figure 4 illustrates the proprietary control console and operating screen that MHI developed
based on customer voices and human engineering. Being enabled with simpler/more intuitive
operation compared with that of conventional machines could prevent operators from making
mistakes and shorten non-processing time such as keypunching. The features of the developed
control console and operating screen are as follows:Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)
29

Figure 4 Control console and operating screen

(1)
(2)
(3)
-3.2

Easier to viewOperating screen expanded from 10.4 to 15 inches
Higher visibility of onscreen characters due to font/coloration optimization
Easier manual operation
Change from the unique key arrangement of the numerical control to that of QWERTY key
arrangement identical to a personal computer
Axis selection and override switches arranged at optimum heights/positions in considerationof operator posture for machine operation
Easier to use
Changed from single-screen to multi-screen (for coordinates, program, machine-specificand other information) display
Added function to customize the information to be displayed on a screen (including theselection of information to be displayed)

Enhanced maintenance function

Due to the increased sophistication of the machinery, it is also necessary to facilitate theoperation of maintenance functions including restoration once an alarm is sounded. Figure 5compares the M-VB25 with existing equipment in terms of the alarm display screen. Unlike
existing equipment using only text display of alarm contents, the M-VB25 provides a 3D birds’ eyeview of the machine with the alarm location highlighted, etc., realizing the visualization of theequipment for which the alarm has sounded, the cause of the alarm and troubleshooting methods.

Figure 5 Comparison between alarm display screen of conventional machine andM-VB25 (recovery facilitation)Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)30

Alarm fault recovery has also been facilitated. Figure 6 compares the recovery screen of theM-VB25 with that of existing machines. In existing machines, recovery is based on single
M-Code* operation concurrent with consultation with the operation manual, requiring time for thechecking of operational procedures and recovery itself. In the case of the M-VB25, the state of thetarget equipment’s actuator/interlock, as well as the recovery procedures, are indicated on theoperation screen to eliminate the need to check operational procedures, thereby enabling quick
recovery.
* M code: 2 or 3-digit number following M to direct the auxiliary movement of a machine tool

Figure 6 Comparison between recovery screen of conventional machineand M-VB25 (recovery procedure)|4. Power consumption reduction (energy saving) of machine
In the industrial world, a variety of approaches are being intensified to improve the efficiencyof energy consumption under the Energy Conservation Act, and there is growing demand to reduce
electricity consumption by production equipment including machine tools. Since the energyconsumed for the machining of workpeices depends upon the material of the workpiece and cutting
conditions including the kind of the tool, it becomes important for energy saving by a machine tool
to enhance the efficiency of equipment while the machine is in operation.

Figure 7

Energy saving measures for machine tools

Figure 7 shows how energy saving measures should be undertaken for machine tools, andFigure 8 illustrates an example of electricity consumption by existing machines. For the spindle
and feed motors with the highest energy consumption share, the latest numerical control technology
and high-efficiency motors were adopted, and for the oil cooler/multi-kind pumps as well,high-efficiency equipment complying with the Top Runner Program regulations were adopted,
thereby reducing electricity consumption.
For hydraulic motors, lubricating equipment and oil coolers, which regularly consume
electricity during machining, an idling stop function to monitor the state of the spindle temperatureand the operation state of the machine for automatically halting unnecessary hydraulic, lubricating
and cooling operations was developed and mounted on the M-VB25, achieving energy saving of
10% from the level of consumption by existing machines (energy conservation).

Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)31-Adoption of the latest numerical control technology/high-efficiency motors (3% reductionin power consumption in MHI’s in-house comparison)
Addition of idling stop function for hydraulic units, oil coolers and lubricating equipment(7% reduction in power consumption in MHI’s in-house comparison)
By reviewing operations of tool exchanging and attachment indexing to shorten the operatingtime, processing hours could be further reduced by 10% in total, thereby reducing fixed energy
consumption.

Figure 8 Power consumption of existing machines (example)|5. Conclusion
The newly-developed M-VB25 was designed to feature higher stiffness by applying
structural optimization technology, as well as through the integration of the column with the bridge.
As a result, a cutting ability as high as 1.4 times that of existing equipment with considerable
extension of ram was achieved. At the same time, the maintenance functions were strengthened
such as through the improvement of operability and the facilitation of recovery, enabling
non-processing time to be shortened. Also, the revision of machine operation and the addition of an
idling stop function permitted energy savings of 10% to be achieved in MHI’s in-housecomparison.