Ultra-Flexible ManufacturingLine with a Finishing Machining
Center for Cylinder Blocks
NORITAKA FUJIMURA*1
YUICHIRO TANAKA*1
TAMAYA SUGANO*1

The mass producers of equipment for automotive parts increasingly need to acquire and effectively use parallel
process flexible lines for the manufacture of variable products in variable quantities. Mitsubishi Heavy Industries,Ltd. (MHI) has been responding to this need by actively proposing and developing a line composed of machining cells
for mass production processing. While this type of line has many advantages, its flexibility in manufacturing is still
limited by the use of special purpose machine tools for the final finishing processes. Quite recently, MHI has constructed an ultra-flexible manufacturing line composed of machining cells with performance equivalent to that ofspecial purpose machine tools for the finish processing. Production with this line requires no special purpose machine tools whatsoever.
it proposes a new flexible production line using this finishing machining center developed.

1. Introduction
MHI started to manufacture special purpose machine
tools in 1950 and developed Japan's first transfer machine in 1953. The company has continued to
manufacture mass production machining equipment for
automotive manufacturing ever since. Even since spinning off Mitsubishi Motors Corporation in 1970, thecompany has effectively responded to the needs of auto
and auto parts manufacturers by introducing FTL (flexible transfer line) and machining cells (machining centersexclusively for mass production lines).
This report is organized into three main parts. First,
it describes tendencies, case examples, and challenges
for automotive parts production lines. Second, it introduces the features and performance of the finishingmachining center developed for cylinder blocks. Lastly,

2. Changes in the automotive parts production line
In earlier years, conventional production lines for automotive parts were required to produce small numbersof products in large quantities. The mainstream units
for these lines were transfer machines with multi-spindle
special purpose machine tools designed with priority on
productivity. Nowadays, however, carmakers are producing a wider range of car models to meet diversifying
customer needs. Though the total output remains unchanged, the number of cars produced per model hasFigs. 1 and 2
suddenly decreased (Figs.
2).
Meanwhile, customer preferences are changing fasterthan ever and product lifecycles have noticeably shortened. The auto industry has been responding by shiftingfrom the manufacture of small numbers of products inlarge quantities to the manufacture of wide varieties ofproducts in medium quantities, or to the manufacture ofvariable products in variable quantities.
: A-company: B-company: C-company

Number of cars
produced per model: Number of car models: Number of cars produced

19801990

2000

PresentFig. 1 Changes in the number of cars produced by major
car companies and the number of car models
More car models are now being produced, the number of cars
produced remains unchanged.

1980

1990

2000

PresentFig. 2 Number of cars produced per model
The number of cars produced per model has decreased greatly.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)*1 Machine Tool Division1This has generated an increasing need for flexible
production lines capable of easily responding to designchanges and equipment diversions.
And with the shortening of lifecycles, automakers needto adopt parallel process production lines to reduce therisks of production line investment. Conventional serial process type production lines require special purpose
equipment for each process. As these lines require maximum production sizes to gain economic advantage, thecosts are substantial during production startup, periodsof decreased production, and production wind-down.
In contrast, the parallel process type allows a single
machine to engage in multiprocess machining, thus en-abling production startup with minimum equipment according to the required production quantity, as well as
ongoing production according to the volume of sales withphased investments.
Better still, this type of system also helps manufacturers equalize production equipment among different
lines in anticipation of equipment diversion. One challenge with parallel process lines is machining quality.
If multiple machines do the same machining in parallel,
accuracy variations among machines may lead to deviations from unit to unit. When this is the case, high-grade
production equipment also needs to be introduced forFig. 3 and T
able 1
these lines (Fig.
Table1).

Drawbacks to the serial process type
Necessary expenditures in fixed cost and variable cost are large.
Because investments are made based on the production scheduleat the maximum capacity, risks during decreased production are large.

9 000

F+Vcost (yen/car)

Investment (million yen)

10 000: Serial process type
: Parallel process type

7 000
5 000
3 000

: Serial process type
: Parallel process type

8 000
6 000
4 000
2 000

1 000
050100150200250

300

350

050100150200250

300

350

Production quantity (thousand cars/year)

Production capacity (thousand cars/year)(b) Cost comparison(a) Break point in investment

Fig. 3 Comparison of production systems: 1The figure shows drawbacks to the serial process type production system.

Table 1 Comparison of production systems: 2
Serial process type

Parallel process type

Stable quality

A workpiece must be frequently installedand removed.

Machining is possible with chucking done only
once. This eliminates the need for frequently
installing and removing a workpiece.

Quality control

Quality control is easy.

The use of multiple machines for machining
makes quality control difficult.

Amount of investment(Fixed cost)

The amount of contingent time, such astransportation time, is large. The number ofmachines installed is therefore increased.

The amount of contingent time, such astransportation time, is small. The number ofmachines installed can therefore be reduced.

Variable cost

Due to the above, more machines areinstalled. The necessary expenditures aretherefore large.

Due to the above, fewer machines are installed.
The necessary expenditures are therefore small.

Handling of loss
cost during decreased
production

Only the operation time is adjusted.

The operation time and number of equipment
units in operation are both adjustable. The rateof line capacity use can be easily maintained.

Ease of variablequantity productionLinearity for variation in the number ofmachines is insufficient.

Variation in the number of machines can be
implemented linearly.

Equipment diversion
during decreased
production

Equipment diversion is difficult because
equipment is directly connected by one line.

Equipment diversion is easy because multiple
machines are used.

Investment risk

Investments are made based on theproduction schedule at the maximum
capacity. This increases risks during
decreased production.

Phased investments can be made.
This lets automakers spend more time toassess the investment timing.

Evaluation item

QualityCost

Flexibility

Management

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

2Machining cell

Special purposemachine tools
Fig. 4 Case example of car production line
Special purpose machine tools are used forthe finishing process.

is to use machining cells for the processes now handled
by special purpose machine tools. This will require thedevelopment of machining cells that provide the samefunctions as special purpose machine tools. MHI has
accomplished this finishing machining cell into practical use. The following section introduces some of thecharacteristics and achievements of this equipment.
4.1 Features of the machining cell for finish cuttingof cylinder blocks
The M-CM5AL is a machining cell for finish cuttingof cylinder blocks. This machining cell is capable of carrying out multiple processes conventionally only possible
with conventional special purpose machine tools designed
exclusively for finishing.
Finish boring of crank bores using a long boring bar(About 850 mm in length)
Accuracy measurement for cylinder bores and a crankbore
Automatic-correction finish cutting of cylinder bores
Finish milling of top surfaces
Finish reaming of dowel holes in each surface
Fig. 5 shows a view of the machine plan. The MCM5AL has the characteristics shown below.
The machine is equipped with a special tool changer
capable of exchanging long boring bars automatically.
The long boring bar is a special tool for the finishingof crank bores, as shown in Fig. 66.
The Z-axis stroke is 1200 mm, enabling automatic
exchange of long boring bars and machining.
The machine is equipped with two measurement systems, one for measuring cylinder bores and one formeasuring crank bores.
The machine is equipped with a tilt index table capable of machining five workpiece surfaces (Fig. 6).
Because the machine is capable of providing arbitrary
positioning, it can also handle a wide variety of different workpieces, such as V6 engines and V8 engines.

3. Recent production lines for automotive parts
Fig. 4 is a layout diagram of a machining line for aluminum cylinder blocks that MHI delivered in 2004. Thisline is made up of two parts: a rough cutting line withmachining cells for mass-production machining arranged
in series, and a finish cutting line with special purpose
machine tools (transfer machines) arranged in series.
The machining cells in the rough cutting line are capableof flexibly adapting to changes in machining processes.
The special purpose machine tools (transfer machines)
in the finish cutting line are arranged with a priority on
high-accuracy machining and production efficiency inimportant processes (crank bore finishing, cylinder borefinishing, finishing of front and rear surfaces, top surface finishing, etc.). Customers have highly evaluatedthe flexibility, machining accuracy, and productivity of
the latest production lines designed to exploit the advantages of both the machining cells and transfermachines. Challenges with this type of line are foreseen in the future, however, as customers are expected
to increasingly request "parallel process lines" and the"manufacture of variable products in variable quantities."
The rough cutting line is a parallel process line consisting entirely of machining cells capable of producing
a mix of multiple models and flexibly responding tochanges in workpiece design with relative ease. The finish cutting line, on the other hand, is a serial process
type line consisting of special purpose machine tools. For
this reason, the latter can handle only a limited variety
of workpiece types and sometimes requires substantial
modification for workpiece design changes.

.
.
..
.
.
.
.
.

4. Production lines for automotive parts in the future
The key to realizing "parallel process line" capable of"manufacturing variable products in variable quantities"

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)3

TableBedToolLong boring bar

Machinining units

Special automatic tool changer

SpindleWorkpiece

Table

Cylinder boremeasurement
head
Crank boremeasurement
headLine bar(Crank boremachining)
ZColumn

Z-axisZ-axis
BedTools to be stored

ColumnX
Movable unit (X-axis, Z-axis)

RackSpecial automatic tool changer

XZ

Special tool changer

Fig. 5 Structural diagram of machining cell for finish cutting
cylinder blocks
The machining cell is made up of the machining units and special
tool changer.
JigTools to bestored

Z-axisWorkpiece (V6, aluminum)

Movable unit(X-axis, Z-axis)

YZ
Tilt index table

Fig. 7 Structural diagram of special tool changer
The apparatus has two movable shafts and accommodates three special tools.

Long boring bar.

speed response and good positioning accuracy.
To keep the unused tools clean, the special toolchanger is provided with a shutter designed to separate
the tool rack and machining chamber. Fig. 9 shows thestructure of the shutter. The shutter in this machine isdivided into three parts to shorten the tool exchange timeby realizing concurrent motions and increasing the opening and closing speeds. Two design features have madeit possible to reduce the tool exchange time to as little
as eight seconds: shutter A is opened and closed by aservomotor-driven cam, and shutters B and C open andclose as they move with the rack into the machine.
4.3 Measurement system
MHI has developed a system capable of making measurements in two lines for the measurement of crankbores and of cylinder bores after finishing. The presentmachine is equipped with an A/E converter, control devices, and two measurement heads, one exclusively forcylinder bores and the other exclusively for crank bores.
Using this system, machining results are measured on
the machine immediately after machining to check if themachined products conform to specifications. And withregard to cylinder bores, the machine also feeds backthe change in the hole diameter due to tool wear andcarries out corrective machining for the next workpiece.

SpindleFig. 6 Long boring bar
The long boring bar is used for finish cutting crank bores.

The control axes for high-accuracy positioning enable
the use of MHI's own scale (MP scale) for all straightand rotary axes.
The following section describes the special toolchanger and measurement system, the key technologies
for this machine.
4.2 Special tool changer
Fig. 7 outlines the features of the special tool changer
recently developed by MHI. The apparatus is installed on
the side surface of the machine body and is equipped witha biaxial movable unit and a rack for storing up to threetools. The body of the rack moves directly into the machine and carries out tool exchange with the spindle. The
method for tool exchange is shown in Fig. 8
8. In the example given here, the three tools installed in the rack area line bar for machining crank bores, a head for measuring
crank bores, and a head for measuring cylinder bores. Theservomotor used to drive the apparatus ensures a high-Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

4Spindle

Shutter opened

Z-axis

Machiningunit
X-axisAutomatictool changer
X
MovableLong boring barunit
Z(a) Before insertion of tool

XZ(b) After insertion of toolFig. 8 Tool exchange procedure
The body of the special tool changer moves into the machine and delivers tools to the spindle.
Shutter AShutters Band CMeasurement
headMaster gauge formeasurement

Movableunit(a) Top view
Long boring bar
Fig. 10 Measurement head as stored
The measurement head, inserted into the master gauge for measurement, is stored in the special tool changer.

Shutter B

Rack

Movable unit

Shutters B and C move with the rack, opening or closing
simultaneously with the beginning of rack movement
Fig. 9 Structural diagram of shutter
The shutter is divided into three parts and opens or closes simultaneously with the movement of the special tool changer.

1.5
1.2
0.9
0.6
0.3
0.0
-0.3
-0.6-0.9-1.2-1.5Standard(b) Front view

Variation in measurement
value ( m)Shutter C#1 #2 #3

#4

#5 #6

#7

#8

#9 #10

Data numberThis measurement data is strung to the workpiece ID information and sent to the quality control system in thefactory. The use of this measurement system enhances traceability, one of the main challenges for the parallel processline, to a level where it can be controlled by customers.
The measurement head, inserted into the master
gauge for measurement, is stored in the special toolchanger described above. With comparative measurements of the master gauge for measurement andworkpieces, the temperature changes can also be factored
into the measurement calculations. Moreover, the master gauge is measured every time the measurement headis mounted on the spindle, to confirm normal mounting

Fig. 11 Repeated measurement accuracy of measurement device
Shows actual measurement values when ten successive measurements are taken.

and to ensure measurement reliability. As the measurement head is stored together with the master gauge, thisconfirmation can be quickly executed during a series oftool exchange motions to further ensure measurement
Fig. 10accuracy and save time (Fig.
10).
Fig. 1
1 shows the repeated accuracy of the measure11
ment device of this machine. The measurement device
itself has a guaranteed accuracy of 1.5 micrometer orless. With this system, MHI has been able to confirm
the reliability of the tool changer.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

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Cylinder bore circularity

4.4 Machining accuracy
Figs. 12, 13 and 14 show actual measurement values of the accuracy of cylinder bore and crank bore
machining, an important finishing process for cylinder
blocks. A machining accuracy equivalent to that of con-ventional special purpose machine tools is confirmed, ahigh Cpk is achieved, and the quality requirements forcylinders are fully met.

5. Proposal of new production lines
The use of this machining cell for finish cutting makes
it possible to construct production lines far more flexible than the lines of the past. Fig. 15 shows one example.
The upper and lower sections show a line using the conventional special purpose machine tools and a line using
the machining cells for finish cutting described here. The
following processes are set up in this example.
OP120
OP120: Finish milling and reaming of front and rearfaces, Crank bore finish boring and accuracy measurement
OP130
OP130: Cylinder bore finish boring, Accuracy measurement, Corrective machining, Upper face finish milling

Required tolerance
Cpk 7.2

123

45

678

9

10

Workpiece No.

Required tolerance

Crank bore coaxiality

Cylinder bore cylindricity

Fig. 12 Cylinder bore machining accuracy (Circularity)Shows actual measurement values of machining accuracy
when ten Cylinder bores are machined successively.

Cpk 3.0123456789Required tolerance
Cpk 2.5

11023

Workpiece No.

45678910

Workpiece No.

Fig. 13 Cylinder bore machining accuracy (Cylindricity)Shows actual measurement values of machining accuracy
when ten cylinder bores are machined successively.

Fig. 14 Crank bore machining accuracy (Coaxiality)
Shows actual measurement values of machining accuracy
when ten crank bores are machined successively.

OP120

OP130

C/T 60 seconds
Production model
Only one model(Straight 4)

Finishing process composed of special purpose machines
C/T 60 seconds
Production model
OP120

OP130

#1 Gantry loader

Two models(V6 and V8)#2 Gantry loader #3 Gantry loader

Finishing process composed of machining cells
Fig. 15 Case example of new production system
The finishing process is composed of machining cells for finish cutting.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

6

With this proposal, we have been able to obtain thefollowing effects.
(1) Cylinder blocks with completely different shapes, suchas the parts for V6 or V8 engines, are difficult to machine with conventional special purpose machine
tools. With this developed machining cell, those cylinder blocks can be easily produced with other cylinder
blocks in the same line.
(2) As with rough process, the finish cutting process line
can now be parallel process.
(3) Flexibility has been improved with no increases inline cost above the level with special purpose machines. This improves the cost performance.

Noritaka Fujimura

Yuichiro Tanaka

6. Conclusion
Parallel process flexible lines composed of machining
cells are now the mainstream as production lines forautomotive parts. While this type of line has many advantages, its flexibility in manufacturing was still limitedby the use of special purpose machine tools for the final
finishing processes. MHI has introduced machining cells
for finish processing capable of replacing the conventional special purpose machine tools. With these cells,
it has become possible to build parallel process ultraflexible lines.
MHI excels not only in the manufacture of machine
tools, but also full-turn type design and manufacturing,
including systems for entire lines. If you send us a request specifying the type of workpiece, production
quantity, and future plan, we can propose an optimum
line configuration to meet your requirements. In today's
vertiginously changing business environment, we at MHI
hope to continue supporting the auto industry and growthof automotive manufacturing technologies.

Tamaya Sugano

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

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