Introduction of Aircraft Door
Center that Applies Epochmaking Flexible Production
SystemTAKAYUKI YONEDA* 1
TETSUYA SODA* 1

The volume of orders received for the production of doors for civil aircraft is increasing along with their diversity oftypes. In order to successfully overcome competition for such orders, an epoch-making concept that departs from theconventional assembling method had to be introduced. Various consultations were held with specialists, production plants
and other parties concerned, and the idea for an integrated line called a Door center characterized by flexible manufacturing was adopted. Notable characteristics of such an approach include mixed production and increased efficiency in handling as well as flexible layout, producing from the assembly of small parts to the packaging of products. At present, twomodels and three types of base flexible assembling lines have been built. The basic concepts and beneficial effects of theselines are introduced here.

1. Introduction
Orders for the doors of civil aircraft received by
Mitsubishi Heavy Industries, Ltd. (MHI) in recent years
Fig. 1include the entrance doors and cargo doors (Fig.
1) forBoeing B767 and B777 as well as Airbus A330 and A380
aircraft. The types and sizes of the doors ordered arequite diversified. A brief overview of conventional door
assembly operation is first presented before the epochmaking concept of flexible assembly is explained.

2. Conventional door assembly operation
Fig. 1 A330 cargo door
Typical product produced with the door center

2.1 Flow of operations
The first step in door assembly operations consists ofconstructing of a framing for the door. The framing ismanufactured by setting several pieces of frames passing in the vertical direction and several beams passingin the longitudinal direction in a lattice shape and joining the intersections of each piece to each other withrivets. Next, the framing is moved to next, and a skin islocated onto the completed framing. This is done by drilling some 2 000 or more joining holes into the skin andthe framing from the skin side, and then joining skin to
the framing with rivets. After the skin is joined to theframing, inner skins are installed onto the inner surfaceof the framing. The inner skins are also joined to theframe with rivets. This completes the main steps in theassembly of the basic door structure.
Next, the completed structural assembly is moved tothe painting area, for paint operations. After painting
has been completed, work begins on the installation of
the various mechanical parts that comprise the final door
system. Here handles, hooks, rods, shafts for releasing
the door lock and other door components are installed in
the door. Finally, a dimensional inspection is performedof the entire door before it is shipped. This is the general flow of the door assembly operation.
2.2 Problems with the conventional assembly methodIn the conventional assembly method, a new production line is required each time the number of new door
models is increased, because a special production line foreach type of aircraft and type of door needs to be set basedon the particular specifications for each door assembly
operation. Further, if variation in the number of aircraft
produced occurs, the number of jigs must be increased ordecreased and the arrangement of the jigs needs to bechanged, accordingly. The amount of investment necessary to fabricate and maintain such lines is quite large.
Aside from equipment, since workers perform operations for a specified time on a given dedicated line, there
is a limit to how much operation time can be successivelyreduced. In order to compete with worldwide low laborcost, a new assembling method has become necessary. Inaddition, another factor contributing to an increase in theoverall amount working time is handling work using general-purpose cranes and dollies.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)*1 Nagoya Aerospace Systems Works1

3.2 Increase in efficiency and automation of handling
The second concept is an increase in efficiency andautomation of handling.
Generally, moving the position of a product does notprovide added value to the product. Thus, if a generalpurpose crane is used in the category of incidental
operations, it is an operation that cannot be neglected
as it is performed by four or five workers (five to six
times for each product) and comprises about 7 to 8% of
the total cost for assembly. In addition, MHI considered that handling operations must be improved since
there is a risk of damage to the product in the eventthat any human error were to occur during handling.
As a first measure, the painting area was positioned
adjacent to the plant to join the painting area to theassembly area by a monorail, thereby eliminating theneed for dolly transportation of the product to the nextstage of production.
Next, automated guided vehicles, monorails, andspecial cranes according to work characteristics at eachposition and the layout of the plant building wereplanned and constructed for complete automation (semiand full-automation) of operations. As a result, the costof handling could be reduced to less than 1% of the total cost for assembly.
For reference, the main features of each of the handling equipment used and the reason for why thesevarious pieces of equipment were adopted are briefly
introduced below.
Automated guided vehicle: This piece of equipment
reduces the risk of products being dropped, enables
unmanned handling, and makes it possible to easilychange the layout by replacing a magnetic tape. Accordingly, the vehicle is applied to a commonly used
position area where rate variation occurs frequently
and the times of changes in layout are expected toFig. 2
occur frequently (Fig.
2).

3. Three basic concepts of aircraft door centerTo address the above problems, a variety of measures were examined from various angles such as
manufacturing method, layout, jigs, and equipment.
As a result, MHI finally arrived at the idea of developing a flexible production line (aircraft door center)having three basic concepts.
3.1 Increase in efficiency through flexible
production
The first of the three basic concepts is to increase
the efficiency of production through the effective application of flexible production.
Generally, the total number of man-hours needed
to produce a given product decreases as workers become more proficient and accustomed to producing theproduct. In small lot production such as for aircraft,however, the length of time needed for workers to become proficient and accustomed to the manufacture ofeach product becomes longer.
As a result, similar increases in effectiveness interms of shortened production man-hours cannot beexpected in a short period as can be realized for othermass-produced products. Accordingly, in the flexible
production approach, similar steps were unified andsimilar operations are performed at the same positionon each line.
As a result, the amount of time needed for workers
to produce products of similar types as they became
more proficient and accustomed to producing eachmodel could be shortened to 1/2 for the second modeland 1/3 for the third model. Significant reductions incost could thus be realized as production could become
more stabilized.
For example, when a worker performed an operation for one type of product in four days, the worker
would become accustomed to a production cycle of fourdays. (If two types of products were moved down thesame line at the same time, the worker would learn
the operation in four days.)
However, if the operation was divided into two parts
with operations performed by two workers, the amountof work that must be learned by one worker would behalved, which would be equivalent to work for twodays. The operation time can be thus reduced earlier
with a cycle of two days.
In this case, however, a major point is the similarity of the two products. Since the line cannot beapplied to a range of operations with significantly
different design concepts for each door such as theinstallation of an opening/closing mechanism, theoperations performed at the flexible position must
be carefully examined before being incorporated inthe line.

.

Fig. 2 Automatic guided vehicle
Automatic handling is possible.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

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Fig. 4 Monorail
Mechanism installation position and dimensional inspection position

Conventional fixed jig system(Independent production)

Flexible common position system(integrated production).Large-scale fixed jig.Door is fixed to a detachable special jig frame,

and two-storied steps
are required for eachmodel door

put on a common general purpose jig frame,and work is performed on a facilitated step
Detachable baseframe (special)

Detachable
special jig frame

General purpose
jig framecommon tomultiple
models.Capable of easily coping with new projects andFig. 3 Special crane
Safe rotation of product is possible.

Fig. 5 Jig frame concept

variations in rates through ready replacementof the detachable base frame and detachable
special jig frame.

Special crane: This equipment has the function of rotating products. It is used for loading and unloading
items from an automatic riveter (described later),which is difficult and dangerous to do using a genFig. 3eral-purpose crane (Fig.
3).
Monorail: This equipment is operated by man. However, it can reduce the number of workers necessary
for transportation. Once products are set on the monorail, operations can be performed in that state without
loading or unloading items from a support fixture. Accordingly, it is used in areas for painting andFig. 4
mechanism assembly positions (Fig.
4).
3.3 Flexibility of layout
The third concept is that flexibility is given to layout.
In the production of aircraft, the rate and types of models produced very rapidly. In order to minimize any
increases or decreases in the number of jigs and changes
in the arrangements of jigs for each production process,which were problems in the conventional production
method, the special assembly jig used for framing work
was modified to separate the special jig frame designed
for each model from the frame used as a base so that it
could be readily changed.

.

Fig. 6 Common support fixture and work step with lifting function

As a result, even if a new door project is started in
the future, the jig can cope with it easily merely by reFig. 5
placing the detachable special jig frame (Fig.
5).
In addition, a support fixture commonly usable for allmodels has been prepared in the common position area,
Fig. 6and a work step (Fig.
6) with a lifting function has beenarranged around it. Since the fixture can accommodate
all models, it can flexibly cope with a variation in production rates and the receipt of new orders in the future.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

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4. Introduction of NC automatic riveter
In the design of the door production center, the lines
were created aiming at an increase in efficiency. Cost
reduction by the latest automatic assembly equipment
was also considered to be critical factors, and was introduced in the basic concept for the production center fromthe beginning. One of the devices thus introduced wasFig. 7
an automatic riveter for panels (skins) (Fig.
7).
Due to the complicated structure (shapes of frame andbeam) of the components, an automatic riveter was not
used for joining the door panels. Accordingly, drilling,deburring, and riveting operations by two workers wereperformed manually and as such were one of the tasks
which took a long time to complete.
The NC automatic riveter, however, can move to a riveting position rapidly with high accuracy by fully
numerically controlled operation, drilling in a short time
without deburring, and can perform riveting quickly andreliably. Namely, it has the effect of remarkably reducing working time.
In addition, since the quality of riveting is better ensured and consistent, the need for re-riveting which wasrequired by manual operation has been eliminated. The
beneficial effects of the device are tremendously large.
In particular, it is expected that the riveter will be applied to a wide range of uses in the production of cargodoors for the Airbus.

Fig. 7 NC automatic riveter

6. Conclusion
This plan was established as a prototype for integrated assembly of similar products. It seemed that doors
could be put together easily because they were smallproducts. However, problems arise in the assembly of avariety of doors on the same line. Quantities demanded
may be larger than expected, and consultations could
not be performed in many cases to the extent considered
beforehand. However, a base flexible manufacturing line
capable of assembling two models and three types of products could eventually be established.
A brief overview of the line concept and equipment
have been explained above. However, it is true that cost
reduction relying on them is limited. MHI considers that
it is more important to create an easy-to-manufacture
product from the design phase and make full use of itseffect. It can be said that, in the severe cost competitiveness in the future, the manufacturer and designer must
work more to create low cost products in cooperation witheach other.

5. Future of door center
In constructing the door center, MHI set a goal of enhancing price competitiveness to global levels. It aims
to remarkably reduce costs less than those associatedwith conventional assemblies. At present, MHI has been
actively moving towards this goal.
MHI is confident that this goal has been achieved by
the full operation of the automatic riveter. The conceptof the door center has just begun. In the future, MHI
plans to continue making every effort to increase thevolume of new orders received for the construction ofaircraft doors and fill its assembling line with doors thatbest meet every customer need as early as possible.

Takayuki Yoneda

Tetsuya Soda

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

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