T h e S t a r t i n g Po i n t fo r
“CREATION”–“MACHINING CENTERS” Otherwise
Known as “MOTHER MACHINES”
Yesterday, Today, and Tomorrow–
HEKI KASUGAIAKIHIKO FUJIWARA
HIROAKI SASAIMASARU KAJIYAMA

Fig. 1to the market at that time (Fig.
1).
The Japanese economy entered a low growth period
triggered by the "dollar shock" in 1971 and the "oil shock"in 1973. During this sluggish period, MHI developed the"MPA-50," "MPA-70," "MPA-40," and "MPA-100" machining centers in 1974 as forerunners to automatedmachining centers.
After that, MHI developed the "MPA-50A," "MPA50B," "MPA-60A," and "MPA-80A" type machining
centers in 1979, which mounted Automatic Pallet
Changer (APC) and which allowed unmanned operationin response to FMS (Flexible Manufacturing System).
Four times as many machining centers in the series wereshipped than the preceding MPAs.
In 1983, MHI entered the market of vertical machining centers, which was occupied into the die and moldindustry. The "MPA-V45," "MPA-V55," and "MPA-V65"
machining centers introduced at this time, were having
a function to compensate thermal displacement automatically for the first time in this industrial world, andto have dedicated automatic programming system. The
MPA series was well received in the market.

1. Introduction
A machining center is known as a "machine that
manufactures machines" or a "mother machine." Suchmachining centers have contributed to the developmentof industry as an essential machine that facilitates the
manufacture of industrial products. As a machine that
manufactures machines, there are many diverse typesof machining centers in the world, including NC lathes.
The history of machining centers began in 1958 when
Kearney & Trecker Corp of the U.S. developed the "Milwaukee-Matic Model II," the first practically applicablemachining center. The name "machining center" wasgiven at that time.

2. Machining centers - Yesterday
Mitsubishi Heavy Industries, Ltd. (MHI) began to
study the introduction of NCs into the machining centeraround 1958. Responding to increasing industrial needs
for rationalization during and after 1965, MHI developed two types of horizontal machining centers, the"MPA-10" and "MPA-15," in 1968, and introduced them

MPA-40

MPA-10

MPA-50 A
MPA-100

1968
Fig. 1 History of machining centers

1974
1979
Progress in horizontal type machining centers during the initial stage of development

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With the availability of unmanned operation of machining centers, the commercial product lineup of
Flexible Manufacturing Cell (FMC) and FMS systems
became fulfilled, and their systematized products were
further developed. MHI developed the "Free Flow Manufacturing System (F-FMS)" in 1985. Systems that require
no complex controller gained a high reputation among
domestic and overseas users, resulting in the delivery ofFig. 2a large number of F-FMS lines (Fig.
2).
Since then, MHI continued to introduce further
model changes in machining centers based on the core
concept of increasing productivity in response to demand for higher speed and higher accuracy, centering
on improvements in feed rate and in main spindle
speed. The increased main spindle speed and improved
main spindle rotating accuracy are absolutely essential to a built-in motor. To this point, the horizontal
machining center "M-HE Series" and the vertical machining center "M-VE Series", which were introduced
to the market during the period from 1995 to 1996,
fully adopted built-in motors to drive the main spindle.
Along with the increases in the speed of the main
spindle, MHI also enhanced the speed of the feed system and improved motion of the system. One example
of such improvements is the introduction of a horizontal
machining center by MHI with a pallet size of 800 x 800
mm (31.5 x 31.5”) class that achieves a feed rate of 40 m/
min (1 575 in/min).

Fig. 2 F-FMS (free flow manufacturing system) line

machining center that machines turbine blades.
(3) Aerospace
High speed and high performance machining centers (such as five-axis machining center) in this field
include machining centers that can be used to machine aluminum materials into three-dimensional
shapes at high speed, as well as high rigidity machining centers for machining materials that are difficult
to cut similar to those in the power generation equipment field.
(4) Automobiles
Machining centers in this field include high speed
machining and feeding machining centers that can beused to machine aluminum die casts, etc.; high rigidity and high speed machining centers for use inmachine casting and steel, and the like.
3.1 Technologies supporting the die and mold fieldThe Σ Series of vertical machining centers is a gradethat has been developed with the specific aim of being
applied to the die and mold field. The development ofthe Σ Series began from understanding the jobsite inwhich the die and mold production process takes placein order to actualize high quality die and mold machining. In case of machining die and mold, the improvementin accuracy in the shapes and quality of the machining
surface is important because a ball end milling is used
to machine a shape through repeated cutter passes. For
this reason, it was necessary to process the data of thecommands to move the point groups on each three-dimensional shape at high speed, and to accurately correct
delays in tracking the movement of the feed axis.
Studies of the main spindle rotating at high speed
while inducing less vibration were conducted in order toimprove the high quality of the machining surface. The
criteria of rigidity evaluation with respect to a shape being machined in which frequent repetition of highacceleration and deceleration of feed occurs was reviewed
with the aim of minimizing variations in machine attitudes during high acceleration and deceleration.
Furthermore, MHI developed an FM control function tocontrol high speed processing of the data of commands
to move point groups and a function to correct delays in

3. Machining centers - Today
During the recent period of shifting of global manufacturing sites to Asia led by China, MHI introduced theΣ Series vertical machining centers "M-V50" and "MV50-FM" in 2001 as high value-added machining centers.
After the vertical Σ Series, MHI introduced the horizontal Σ Series machining centers "M-H60" and "M-H80"
in 2002, further adding the "M-V70" and "M-V70-FM" tothe Σ vertical machining centers as table size products(one grade larger than the preceding series).
Depending on the characteristics of the workpiece, theapplications of the Σ Series were developed considering
four core fields: die and mold, power generation equipment, aerospace, and automobiles (including othergeneral use parts).
(1) Die and mold
The machining centers cover a range of molds inthis field from aluminum molds to hard metal molds.
The machining centers can be used to machine freecurved shapes at high speed, high accuracy, and highquality.
(2) Power generation equipment
The machining centers in the field of power generation equipment include high rigidity machines thatcan be used to machine materials that are difficult tocut, and high performance machines such as five-axis

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Conventional machine
M-V50-FM
Fig. 3 Enlarged view of surface machined by ball end milling
Comparison of the grade of machined surfaces between a conventional
machine and a M-V50-FM (giving superior grade)Fig. 4 Model of the ventilation of air into the machine body
Air is ventilated into the machining center body to make the body temperature equalization.

tracking the movement of feed axis with the aim of conFig. 3
tributing to the high quality of any machining (Fig.
3).
The former function estimates the acceleration anddeceleration of points during the working of a parts shapein the data of the infinitesimal point group beforehand,
thereby generating commands of the optimal value foracceleration and deceleration that are appropriate to therigidity of the machine.
In its efforts to reduce vibration of the main spindle,
MHI developed a main spindle that rotates at a speed of
30 000 min-1 after extensive design and analysis of methods of suppressing vibration over the entire rotational
speed range.
Owing to this development, MHI has developed a technology to evaluate and analyze the whole machine (therotating body of main spindle and further including themachine base parts supporting the main spindle) to reflect the technology onto the overall machine. This is
the first time that vibration evaluation (vibrational
analysis) over the entire rotational range has been successfully carried out in the industry.
Moreover, MHI has successfully developed a pre-load
switching mechanism for the main spindle bearings at
both the low speed and high speed ranges to increase
the rigidity of the main spindle in the low speed range,
thereby achieving stable heavy machining at the low
speed range and machining at the high speed range.
These technologies are the result of the MHI exclusive
analysis technology on rotational bodies for power generation equipment parts etc.
In order to assure the accuracy and stability of themachine, a three-point support bed has been adopted.
Several measures have been adopted to suppress thermal displacement. First, the temperature of the machine
body has been made equalization through the ventila-

Fig. 4tion of air into the body (Fig.
4). An insulation coverhas been installed to prevent heat from any machining from affecting the machine body, and multi-pointtemperature measurement and compensation function
have been adopted in order to reduce any thermal displacement within ±0.005 mm (±0.0002”). In addition,a thermal analysis program based on the three-dimensional CAD plays a significant role in the effectivenessof these thermal analysis technologies.
3.2 Technologies supporting the power generationequipment field
Parts such as blades in the power generation equipment field used under high temperature environment are
represented by heat-resistant alloys (titanium, Inconel,etc.) and stainless steels. These materials are difficult
to cut and have complex three-dimensional machining
shapes. Moreover, they must have high profile accuracy.
The machines for these difficult to cut parts not only
need to have high static rigidity but also high dynamic
rigidity. In addition, they must maintain stable accuracy over a long period of time, thus making it essentialthat the machine have highly stable accuracy, including
minimum thermal displacement.
In order to meet such requirements, the fundamental
technologies briefly outlined below have been adopted
in the horizontal machine centers of the Σ Series "MH60" and "M-H80".
(1) Development of high torque and highly rigid main
spindleIn order to realize a high torque and highly rigid
main spindle, the main spindle motor torque was increased, and a high pre-load was adopted for the main
spindle bearings. A mechanism to cool the bearing
from the inside of the main spindle was applied as atechnology to prevent temperature increases in the
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bearing under the increased pre-load of the main
spindle bearing.
(2) Feed mechanism having both a dynamically rigid sliding guide and a motion performance of the rollingguide
MHI has developed all feed axes hydraulic staticpressure sliding mechanism in which static load supports have been adopted on both the loading side andthe counter-loading side in order to assure the highdynamic rigidity of the feed system.
The mechanism has eliminated variations in machine attitude, which are observed in conventional
feed mechanisms that use resin sliding face material.
The MHI mechanism is suitable for the machining ofworkpieces which require strict shape accuracy. A feed
speed of 50 m/min (1968 in/min) was realized because
the coefficient of friction is small.
3.3 Technologies supporting the aerospace field
The aerospace field also uses parts that are difficult
to cut, as represented by heat-resistant alloys and stainless steels. Thus, the improvement of machining
performance is also an issue of common concern withthe power generation equipment field. To this point, the
M-H Σ Series, which adopts a hydraulic static pressure sliding mechanism, assures high productivity inthis field, as well.
In aerospace, machined parts manufactured fromlightweight form materials of aluminum and magnesiumcomprise a large share of the main component parts.
Notable features of these parts are the increased variety of accuracy of the final products and the increased
variety of shapes that cannot be machined by linear
three-axis machines. From the standpoint of machining
parts by making a shape using point group data, theseparts also share a common feature with die and molds.
A notable difference from die and mold machining,
however, is that the die and mold is machined by die
sinking and has rigidity of the workpieces. Many aerospace parts, on the other hand, have numerous ribs withthin thicknesses in shape [around 2 mm (0.078”)], andthe rigidity of the workpiece is weaker than that of the
cutting tool so that vibration is likely to occur duringmachining. In addition, importance is placed on fast machining to achieve specified shape.
3.4 Technologies supporting the automotive field
Advances in technologies that support the automotive field in recent years include the adoption ofaluminum die casts as major parts and the adoption ofresin parts enhanced by reductions in weight and thenumber of parts. For die cast parts, which have smallermachining margins, the minimization of non-cutting time
is further pursued through the adoption of a main spindle
with a high rotational speed and high rates of acceleration and deceleration together with the adoption of a highspeed feed mechanism. In this field, more machining

needs to be done to develop element technologies that
respond effectively to the increases in speed, such as linear motors.
MHI has shifted to machining cells (machining centers for mass production lines) developed fromexclusive-use machining lines as part of its efforts to introduce machines that respond effectively to these mass
production fields. MHI introduced the "M-CM4A" (mainspindle rotational speed of 12 000 min- 1 with an acceleration of 1 G) to the market in 2002 in order tocontribute to high efficiency production.
3.5 Technologies that support the operation of auser's machines
Technologies that assure high operating rates are essential to customers who have adopted machining centers
as a means of competing in fierce cost battles. Such technologies add to the functionality and performance of themachining center itself.
From the beginning of its development, the Σ Series
was subjected to Mean Time Between Failures (MTBF)
and Mean Time To Repair (MTTR) evaluations in order
to assure that the machines would have hard-to-fail characteristics and be durable under a variety of working
conditions. In addition, designs emphasized Total Productive Maintenance (TPM) in order to gather equipment
requiring regular maintenance to a single location, so
as to improve the ability to carry out visual inspections
and maintenance more effectively. Furthermore, themachining centers of the Σ Series emphasize energy savings as a part of measures to realize ever greater
environmental conservation.
A remote diagnostic system utilizing the most advanced communication infrastructures has also beenbrought into practical application. The system connects
a machining center at a user site with the Service Section of the MHI Machine Tool Division via the Internet
or Personal Handyphone System (PHS) to provide direct diagnosis of any failures that occur at the machining
center at a distant location. This kind of IT-utilizing function is expected to be further developed and distributedin the future.
In the event that a failure does occur, the CS Centerof MHI provides support to the user. The CS Center
manages the Service Section and the Technology Sectionof MHI, and controls the integrated process down to problem solving from the viewpoint of the customer.

4. Machining centers - Tomorrow
The trend of shifting the production bases of machining centers to locations outside Japan is expected toincrease further, if not accelerate. Nevertheless, parts
for testing during the research and development stage
and high added value parts that support the most advanced technologies will continue to be manufactured
domestically in Japan as an exclusive industry.
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Consequently, the application of five-axis machining
technology (combined machining technology) is absolutely necessary to minimize initial setup andpreparatory work before machining and to ensure highly
accurate machining. To this point, MHI plans to introduce a five-axis machining center that is optimum for
Fig. 5working to the market (Fig.
5).
4.3 Automobile field - Tomorrow
MHI has extensive experience in production lines thatare exclusive to automobile parts. To this field, MHI will
provide machining cells that have flexible line structures
and that run at super high speed thereby providing highproductivity to accommodate medium to large volumesof parts production. In addition to parts produced in exclusive production lines, MHI will also develop small
scale and highly accurate versatile machining centers
for producing various types of medium to small lots ofparts.
4.4 Technologies utilizing machining center Tomorrow
In order to support the future of customers who utilize machining centers, it is very important not only toprovide high functional machining centers but also to
support the overall production activities of customers.
(1) Support for production technology
With the increase in high speed machining, optimal machining conditions become more difficult tograsp. On this point, MHI continues to accumulate
the machining technology know-how (production
methods, tool application engineering, conditions formachining, and measuring and evaluation technology)
that maximizes the performance of MHI machining
centers. MHI is planning to establish a system to provide the accumulated know-how to customers from the
Manufacturing Technology Center (MTC) of MHI Machine Tool Division.
(2) Action to improve operating ratio
Intelligent machines are a keyword to improving
the technology of machining center utilization in the
future. Measures in this field include easy maintenance adopting the TPM concept, reduction of
non-productive operating time of peripheral devices
and equipment, full application of self-diagnostic functions with strengthened sensing functions, and full
application of remote diagnosis utilizing network inf r a s t r u c t u r e s . M H I M a c h i n e To o l D i v i s i o n i s
promoting the development of these basic technologies jointly with MHI Technical Headquarters.
(3) Production control systems including production atoverseas locations
A system currently known as Manufacturing Execution System (MES), which is widely adopted inother production fields, will be introduced to the machine working sector in the near future. In responseto the trend towards ever greater globalization, pro-

Fig. 5 Head-tilting five-axis machining center

Given this background, MHI continues to develop highvalue added machining centers in the four fields described above on the basis of the Σ Series with the aimof shortening the lead time in production of these highvalue added parts.
4.1 Die and mold field - Tomorrow
In order to shorten the lead-time of the mold machining of hard materials and stainless steels, MHI has begun
the research into fundamental technologies on high rigidity linear motors. In addition, MHI is promoting
studies into increasing the more high speed and reducing the vibration of the main spindle with the aim ofeliminating hand-finishing processes.
Furthermore, in order to improve the efficiency of thetotal process of die and mold production, MHI is examining ways of improving efficiency over the entire process,not only with respect to improving the efficiency of theworking process of the machining center but also withrespect to the automated preparation of optimum cutting programs using CAD/CAM and automatedinspection processes, in short covering activity from thedesign stage to the inspection stage.
4.2 Power generation equipment and aerospace
fields - Tomorrow
Tomorrow
MHI has systematically identified the relation between tool wear and the dynamic rigidity of the machine
in high speed machining of materials that are difficult
to cut such as heat resisting materials. Based on theseresults, MHI has begun a range of studies into the selection of optimum tools and methods to be reflected in thedesign process.
On the machine side, MHI has selected a criteria ofevaluation of machine rigidity applicable to high speed
machining of materials that are difficult to cut, and has
begun studies into fundamental technologies for improving machine rigidity.
The shortening of lead-times for machining aluminumalloys into complex shapes is an issue of critical concern.

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duction data at individual production bases will used
jointly throughout the world. Based on these expectations, MHI is in the process of establishing a
production control system that includes existing FMC
and FMS together with further high-level systems.

cal Headquarters. The effects of these investigations into
basic technologies are reflected in the machining centers produced by MHI. Through continued technologicaldevelopment, MHI is confident of its ability of being able
to provide machining centers that will be welcomed andhighly regarded by customers wherever they may be.

5. Conclusion
Near future, the manufacturing industry in Japan is
expected to concentrate upon the high-level products andindustries toward pursuing higher added value, high accuracy machining and high-level machining methods.
Accordingly, identification and creation of fundamental
technologies necessary to satisfy these high-level machining are required.
MHI produces products in the power generation equipment, aircraft, and aerospace facility fields that pursue
further high accuracy and high durability. By taking partin the production technology development from the initial stage of these products, for solving prompt problem,
MHI can achieve identification and abstraction of basic
technologies promptly.
Furthermore, in order to satisfy these requirements,
MHI Machine Tool Division promotes studies in basic
technologies in close cooperation with the MHI Techni-

MACHINE TOOL DIVISION

General Manager,
Machine Tool Division
Heki Kasugai

Akihiko Fujiwara

Hiroaki Sasai

Masaru Kajiyama

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.1 (Feb. 2003)

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