Site: Mitsubishi Heavy Industries
Research Division
Nagoya Aerospace Systems Factory
10 Oyemachi, Minato-ku
Nagoya-shi, Aichi-ken 455, Japan

Date Visited: December 8, 1992

Report Author: B. Kramer

ATTENDEES

JTEC:

D. Wilkins
M. Ashizawa
J. Devault
D. Gill
I. Ahmad
X. Spiegel

HOSTS:

Mr. T. Tanioka

Mr. T. Ikeda

Mr. Y. Yamaguchi

Mr. K. Ogasawara

Mr. T. Yamamoto

Mr. Shiraishi

BACKGROUND

The Nagoya works employs 4,593 people. Mr. Shiraishi indicated that almost anything could be discussed at this meeting, except areas related to Japanese Defense Agency projects.

Mr. Ogasawara indicated that advanced composites work at MHI started in 1969. As a result, MHI is the world leader in co-curing technology, which is needed to reduce assembly cost.

General applications include the co-curing of very large and complex parts, including a new fighter wing torque box which is 160" by 80". It took 5 years to develop the technology to produce the wing torque box by co-curing. The part is autoclaved in the biggest unit in Japan: 18' diameter, 51' long, within 200 psi, 800øF capability.

RESEARCH & DEVELOPMENT ACTIVITIES

1. 3-D composites. Efforts are to improve interlaminar shear strength. They do the weaving for the project in-house.
2. Resin-transfer molding (RTM). It was indicated that they were investing "almost significant" research resources in the project. When asked what the biggest challenge in RTM was, they indicated that it was the resin. The JTEC team indicated that it thought weaving was the biggest challenge. However, our hosts replied that they have a low-cost method for manufacturing the preform. They also have many specialty weavers in Japan working on preforms. U.S. companies are coming to Japan for weaving technology.
3. Film infusion.
4. Material development. The emphasis is on thermoplastics and high temperature resins.

MHI representatives listed five key approaches to co-curing technology:

1. Finding the applicable range of co-curing. MHI engineers calculate the design/manufacturing/quality assurance (QA) trade-off for each part in order to optimize resources. When asked how the scrap rate is estimated for the model, they indicated that they assumed zero scrap. They have an effective repair method for fixing the defects they get. When asked about bag leakage, they indicated it almost never happens. For instance, only one failure in 240 speed brakes.
2. Assuring the strength of the co-cured interface for in-plane shear, tension and peel.
3. Minimizing thermal deformation. Finite element methods (FEM) analysis is used to adjust parts deformation.
4. Assuring achievable tolerance.
5. Assuring effective repair methods.

MHI employs five key methods for improving co-curing:

1. Each detail part is compacted before co-curing the assembly to remove air and water, to adjust the resin viscosity and to control the dimension and/or shape of the part. The parts are non-destructive evaluation (NDE) inspected by ultrasound after hot compaction.
2. A reliable, leak-free bagging system is used. The MHI system is made from unreinforced silicon rubber, reusable for 20 cycles. The company used to buy bagging rubber from a U.S. material supplier, but now makes its own. It has developed its own zip-lock system for bagging.
3. Dimensional stability is assured to minimize warpage. MHI uses invar tooling.
4. Pressure is transferred directly to the part using a molded bladder bag that has the same shape as the part.
5. Temperature uniformity is assured by uniform gas flow in the autoclave.

The MHI staff feels that 80% of their success is in the tool, but indicated that this assumes the use of high quality labor. For tooling research, film pressure transducers are used in the autoclave.

MHI is engaged in the following cost reduction activities:

1. Cooperation between research, design, manufacturing, and Q/A
2. Manufacturing development incorporating a zero-defect goal and emphasizing step-by-step development
3. Low cost manufacturing technology including:
   a. Automated cutting and nesting
   b. Automated layup
   c. Computer-controlled cure with temperature and pressure sensing but
   no supplemental tool heaters
   d. Net trim before cure with an NC trimming machine

SUMMARY

MHI representatives indicated that prepreg cost is important, that filament winding, pultrusion and thermoplastic composites are not used in production, and that CATIA data are shared by designers, automated layup, and tool fabricators. Our hosts expressed the view that a 50% decrease in cost could be attained with accumulated minor improvements, that no major breakthroughs were on the horizon, and that MHI has a special device (an intensifier) to prevent bleeder mark-off, but that they cannot discuss it. The method involves the use of carbon fiber slip-sheets.

They indicated that MHI wingbox technology has been transferred successfully to General Dynamics and that they do not use long, discontinuous fibers.

Composite organizations mentioned included JSCM and JSAMPE. Professor Maekawa of Kyoto Institute of Technology was mentioned as one of the leading university researchers.