Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)15“M-CM5BG” Large Engine Part-Compatible Horizontal
Machining Cell for Mass Production Processing Lines

YOHEI KOMATSU*1

KEISUKE YOSHIKAWA*1

HIROYUKI WAKAMOTO*1 KAZUTO NAKAMURA*2

HIDEFUMI OMOKAWA*2

The present machine tool market has no machining centers capable of completely processing
the parts of a 13,000 cc displacement–class engine (1,000 mm in total length), the largest size
offered by domestic truck/bus manufacturers. It is, therefore, necessary to build a dedicated line
equipped with special purpose machines, and existing processing lines were poor in terms ofbenefit-cost ratio and are inflexible. Crank-hole drilling on a cylinder block as a key engine part
requires the long tool called a line borer. To meet this requirement, Mitsubishi Heavy Industries,Ltd. (MHI) developed the M-CM5BG horizontal machining cell with equipment that automaticallyreplaces long tools of a maximum of 1,350 mm (and stores four tools at one time). Along with ahigh-rigidity bed for which the Z-axis stroke of 1,700 mm needed for long tool machining has beenrealized by supporting it at three points, the technologies mounted on this machine formaintainability, automation and labor saving are featured in this paper.

|1. Introduction
For cylinder blocks (hereinafter CB) and cylinder heads (hereinafter CH), which are key
components of the engines used in trucks/buses fabricated by domestic manufacturers, a machining
center (hereinafter MC) capable of totally processing a 10,000 cc displacement- (800 mm total
length) class model workpiece is being placed on the market in numbers. Nevertheless, there is no
MC capable of totally processing a 13,000 cc displacement- (1,000 mm total length) classworkpiece as the largest size, and despite its lower output than the 10,000 cc displacement class(800 mm total length), it requires, as processing equipment, a dedicated line using special purpose
machines to be installed, raising the problems of a poor benefit-cost ratio as well as inflexibility inthe production line. This is why the development of a high-productivity MC capable of totallyprocessing 13,000 cc displacement- (1,000 mm total length-) class engine parts (CB/CH) is instrong demand on the market. Meanwhile, due to its high maintainability as well as possible
automation/labor saving and in prospectively coping with the trend toward aluminum forlighter-weight parts to improve fuel efficiency, making high-load processing by an MC compatible
with high-speed processing also further in demand.
In meeting such market needs, MHI developed the M-CM5BG horizontal machining cellnote,
which shows high productivity in processing the parts of a medium- or large-sized engine to bemounted on trucks/buses. Table 1 shows the principal specifications.
The mounted technology’s characteristics and performance are described below.
Note: The machining cell is a machining center specialized for mass-production lines and is included as acomponent of the mass production line or cell production system, particularly because of its improved
productivity, reliability and space efficiency.

*1

Engineering Department, Machine Tool Division, Machinery, Equipment & Infrastructure*2

Chief Staff Manager, Engineering Department, Machine Tool Division, Machinery, Equipment & InfrastructureMitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)16

Table 1 Principal specifications of the M-CM5BG
StrokeSpindle

Feed speed

X axis
Y axisZ axis (standard/option)
Taper shape
Maximum rotational speed
Diameter(6000/15000 min-1)
Fast feed speed(accelerated speed)

APC

Pallet size
Maximum loading mass(including pallets)
Number of pallets
Long
Number of tools to be storedATC
Maximum tool length
Maximum tool diameterStandard
Number of tools to be storedATC
Maximum tool length
Maximum tool diameter
APC : Automatic Pallet Changer
ATC : Automatic Tools Changer

mmmmmmmin-1

1250
12001150/1700
HSK-A100/KM10080
6000/15000mm

φ120/φ100

X axis mm/min (G)Y axis mm/min (G)Z axis mm/min (G)mm

60（ 0.4）60（ 0.6）50（ 0.6）□800kg

2500

sheet
unit
mmmm
unit
mm
mm

241350φ140120800
φ350|2. On-board M-CM5BG technology
2.1(1)

Machining work specific to cylinder block
Issue
Machining work specific to cylinder blocks is the crank hole drilling shown in Figures 1and 2. At present, special purpose machines are adopted for this drilling, and so that MC can
implement this process, it is necessary to enable automatic replacement of long tools and securesuch a stroke as allows a long tool to be removed/inserted (1,350 mm in total length of the tool,
80 kg in tool mass and 1,700 mm in Z-axis stroke). To realize this, long and heavy tools must
be stored stably without being dropped or affected by pot friction. In addition, the tool shape is
not always the same since it is designed to match the workpiece shape. There is another issue of
space saving to make the frontage as narrow as possible in further consideration of its possible
application in a mass production line. Table 2 summarizes issues as well as solutions.

Figure 1

Cylinder block section

Figure 2

Crank-hole drilling

Table 2 Automatic long tool changer: issues and solutions
Issue
Dropping of a long tool during automatic
replacement operation
The pot to store tools is less durable.
(Pot friction affects stable operation.)
Crank-hole drilling to be flexibly worked on foreach different-size workpieceSpace needs to be saved

Solution
A dedicated carrier with the tool supported at two
points or at both ends was developed.
A fixed rack is used instead of the storage pot.
With only the tool-end locating portion designed
for exclusive use, tool diameter/length difference
has now been flexibly handled.
Using dead space, a dedicated storage rack wasarranged (instead of a standard magazine).

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Solution
Although concept development and mechanical planning for each piece of equipment arenormally the tasks of the design sector, a cross-function team (CFT) was organized for thisdevelopment. The members were summoned from not only design, but also the assembly,
procurement and production management sectors and the team grasped and analyzed the“functions” to be fulfilled by the equipment from the perspective of users using the VE (valueengineering) method and figured out a variety of ideas about means to achieve these goals inthe search of optimum solutions to the aforementioned issues.
As a result, the selected automatic long tool replacement structure shown in Figure 3
safely composed the equipment without widening the installation, utilizing dead space asshown in Figure 4, thereby enabling the frontage to become 500 mm narrower than in the casewhere tools were stored in standard magazines. Moreover, by placing tools on fixed racks, theinfluence of pot wear could be excluded. Furthermore, in coping with different tool shapes tomatch each workpiece, a tool receptacle system as shown in Figure 5 was adopted and only thetool-end locating portion was designed for exclusive use, developing a structure that canquickly respond to a change of workpiece.

Figure 3

Automatic long tool changer

Figure 4

Tool storage using dead space

Figure 5Tool receptacle

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Easier maintenance and accuracy preservation

(1)

Issue
Machine tools have the problem of the need to suppress the deterioration of machineaccuracy due to changes in its foundation over time, as well as to facilitate accuracy adjustment
when deteriorated. But machining with a long tool necessitates a stroke of 1,700 mm as
mentioned in Section 2.1, and with this level of stroke, a multipoint-supported bed is normallyused. A multipoint-supported bed has the problem of time-consuming jack adjustment
accompanied by deterioration in maintainability.
(2) Solution
The 3D models of the entire machine and the three-point support bed shown in Figures 6and 7 were prepared, and using a numerical analysis approach (finite element method: FEM),
the rib shape, thickness and arrangement within the casting structure were optimized, thereby
successfully coming up with the three-point supported bed that maintained compatibility with a
1,700-mm stroke.
This robust bed has not only excluded the effects of changes in foundation level tosuppress machine accuracy deterioration, but also limited changes in the straightness of the1,700-mm stroke within 3.2 μm as shown in Figures 8 and 9, maintaining the high accuracy ofthe machine.

Figure 6

3D Model built in

Figure 8 Changes in Z axis straightness (YZplane)

2.3(1)

Figure 7

3-point supported bed

Figure 9 Changes in Z axis straightness (XZplane)

Efforts for automation/high productivity

Issue
A processing line well responsive to different kinds/different volumes must ensure highproductivity for multiple workpieces. But the aforementioned line with special purpose
machines has the issue of having been forced to replace the setup for different workpiecemachining after once bringing the production line to a halt. For medium-/large-sized engine
parts, a heavy workpiece/fixture setup (workpiece mass of 500 kg, fixture mass of 1,500 kg andpallet mass of 500 kg, totaling 2,500 kg) is required to be replaced in a short time. In addition,
workpieces/fixtures are not always the same and changes in size or mass dependent upon thesituation must be properly complied with.
(2) Solution
In this machine, the 2APC method (method of allowing two pallets to turn for automaticreplacement) shown in Figure 10 to automatically replace the setup containing fixtures as-is(including pallets) was employed, thus proposing a measure in favor of automation and high

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productivity. By means of FEM analysis, a level of rigidity that can withstand the supposed
load was secured, and at the same time, supposed workpiece and fixture models were preparedto simulate the state where pallets were actually exchanged for arm shape and stand rigidity
optimization, thereby realizing a maximum loading mass of 2,500 kg and APC exchange timeof 30 seconds. Changing workpiece and fixture masses were to be coped with by servo motor
driving which changes the speed, depending upon the mass, for the permitted quickest
operation, to come up with a structure that contributes to time saving. Moreover, the adopted
method of replacing the setup containing fixtures as-is (including pallets) also facilitates thedevelopment of an automatic guided vehicle (AGV)-based palletized shipment-type flexible
manufacturing system (FMS).

Figure 102.4

2APC method

Efforts for labor saving(1)Issue
Labor saving at and around processing equipment faces the problem of the need tooptimize the line composition for line operation with the lowest possible personnel allocation,
as well as to alleviate short-term breakdowns (moment stops) on the order of minutes for adecrease in man-hours for equipment restoration. Many moment stops are caused by shavings.
Heated shavings bring about machine accuracy deterioration, deposited shavings induce themalfunction of fixtures and sensor failure, and the splashing of shavings result in on-board
equipment damage and other problems.
(2) Solution
This machine employs a stainless chute which prevents shavings from directly contacting
the bed as shown in the internal structure of the M-CM5BG in Figure 11, structuring it in sucha way as not to conduct the heat of the shavings to the bed and thereby suppressing thermal
displacement. Inside the machine, metal covers (ATC shutter and XY-/Z-axis slide covers)
were employed and have improved durability against direct hits from shavings. The
center-trough bed structure and the employment of a stainless chute have prevented shavings
from depositing within the machine and enabled them to be quickly discharged outside themachine. Further consideration is given to prevent shavings from being deposited by thewashing of the inside of the machine using MHI’s uniquely designed coolant curtain as shownin Figure 12.

Figure 11

Internal structure of the M-CM5BG

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Figure 12

2.5Coolant curtain

Future efforts

(1)

Issue
For truck/bus engine parts as well, it is necessary to cope with the trend toward aluminumfor lighter-weight parts to prospectively improve fuel efficiency. This raises additional needs tomake both high-load processing and high-speed processing compatible. Nevertheless, thegreatest problem with an increase in speed in a #50 taper spindle is the need to prevent bearing
seizure due to heat generation and minimize thermal displacement.
(2) Solution
By adopting MHI’s own jet lubrication and circulating coolant of the temperaturesynchronously controlled to that of the machine body through the spindle inside and casing,both the minimization of thermal displacement and the maximization of pre-loads on thebearing in the low speed zone were made compatible. Further total recovery and recycling of
bearing lubricant amounts have lengthened coolant life by eliminating unnecessary oiling,
reducing running costs and using a smaller amount of lubricants mixed in the coolant.(1) This
achieved the 15,000 min-1 specification in a #50 taper spindle, enabling high-efficiency
high-accuracy machining in the whole rotating area.

Figure 13

Internal cooling structure of spindle|3. Conclusion
The technologies mounted on the M-CM5BG horizontal machining cell were featured above.
They have been finished into a machine capable of handling the stages where medium-/large-sizedengine parts were processed by special purpose machines and this machine can perform all kinds ofprocessing by itself. Through the replacement of existing special purpose machines with theM-CM5BG, MHI will propose a more flexible and capable multiproduct variable quantity
production method, thereby maintaining its contribution to higher productivity at large parts
production sites. MHI further intends to understand the needs of various industries and provide
unprecedented solutions in an effort to contribute to the extensive development of themanufacturing industry.

Reference
1. Omokawa, H. et al., High-precision Machining Technology for Large Machining Centers Special Jet Lubrication and Advanced
Thermal Displacement Suppression System, Mitsubishi Heavy Industries Technical Review Vol. 49 No. 3 (2012) pp.35-38