Knowhow from the Okajima Plant Blossoming in Southeast Asia

Kubota builds engines through an integrated system encompassing operations from design and development to engine part casting, machining and assembly.

Through mutual collaboration between each of these divisions, we have achieved high-mix, low-volume production while maintaining a high level of quality. At the same time, we have continuously manufactured approximately 3,000 kinds of engines.

At the Okajima Business Center (Okajima Plant, commonly known as) in Osaka and Siam Kubota Metal Technology Co., Ltd. (SKMT, for short) in Siam, Thailand, we utilize casting technology to produce parts such as crankcases said to be the "body" that holds all the parts of the engine together.

Concerning the Okajima Plant, Thailand and future casting technology, we spoke to the Okajima Business Center's former director who worked at the plant from the 1980s and who was instrumental in launching SKMT in Thailand.

The Okajima Plant

Kubota's Okajima Business Center is located in Minami Okajima, Taisho-ku, Osaka City, Osaka Prefecture.

In 1917, in response to rapid growth in military production from WWI, the main plant (Minami-ku, Osaka City) became a dedicated factory for the machinery division, while the iron pipe department was transferred to the Amagasaki Plant. Also, the casting manufacturing department, which had facilities scattered throughout Japan, was consolidated into the Okajima Plant, which was built in Minami Okajima-cho, Nishi-ku, Osaka City (currently Taisho-ku, Osaka City).

Kubota began manufacturing agricultural engines in 1922, and to this day, has carried out production at the Okajima Plant for cast parts making up the greater portion of engines' basic structures.

We use casting technology to manufacture the crankcases known as the "body" that holds all the parts of the engine together. By combining the best of the Okajima Plant's casting technology cultivated by our company across many years, we have realized the durability, rigidity, and precise and complex interior structures of Kubota's compact, high-output engines, earning high regard from customers worldwide.

The Basics of Casting Technology

The name Okajima is said to be derived from Kaheiji Okajima, the developer of this land during the Edo Period. To honor and thank him, the local magistrate who oversaw this area changed the spelling of Kita and Minami Okajima so that "Oka" now means "with gratitude" when written in kanji (Chinese characters).

Meeting the Challenges of Technology and Enhanced Quality through an Integrated System

The former director of the Okajima Business Center was assigned to that location after entering Kubota in 1984.

-- "When I entered the company, I was greatly involved in interactions with the engine design team. Due to engines' base sections being created through casting, we received all kinds of demands from the design team. We were asked to improve cooling performance, for example."

In order to boost power output while maintaining the small-sized housing of Kubota's signature compact, high-output engines, we must improve cooling performance around the cylinder piston area. For that reason, the shapes required for passing water within crankcases, known as water jackets, have become increasingly complex.

The desire to boost engine performance and the difficult problem of producing something so complicated have spurred the engineers of Okajima to challenge the impossible.

-- "There was a remarkable foreman at that time who was a Naniwa master (Osaka Prefecture award given to distinguished technicians). He really honed the techniques used in casting.. We had to ensure 3 mm cavities to allow for water channels to pass through, but they did not hold up because we were pouring in iron exceeding 1,400 degrees Celsius. Even if we made cores, they would break, and the cores' sand was insufficient on its own. We then created shapes using steel plates, packed them with sand and first made the water channels. We kept repeating steps such as these."

The engineers adopted a scheme through which the outer frame of the steel plates supports the cores' sand. However, while outer frames and cores expand when high temperature iron is poured in, they do so at different rates. This in turn caused breakages, preventing the process from being completed successfully. As there were also no x-ray tests at that time, they could not conduct inspections with sufficient precision on water jackets with complex shapes allowing for water passage.

-- "Ceramic sand first appeared at that time. It expands at a quite low rate and provides a clean surface. Later sand processing can also be completed cleanly. From that point, we were able to use instruments like fiberscopes during testing, and we could then mass produce engines solving the cooling problem."

Through this repeated process of trial and error, the engineers carried out a great deal of hard work to implement many ideas over many years and thereby meet the demands of the design team.

-- "In the 1990s, we made numerous minor changes due to emission regulations. The design team would ask us whether we were capable of accomplishing various things. We actively exchanged opinions without holding back, for example by telling them that a certain design would make burr removal very difficult."

While the design and casting departments engage in close collaboration, they leave no room for compromise so as to create engines with even greater performance. This is the strength of Kubota's integrated system.

-- "Surely, the benefit of conducting casting in-house is that we can take on extremely difficult requests. At a different company, it would probably be impossible to make such requests. First of all, we can pursue such challenges without regard for cost. Since we have the capacity to test whether or not we can accomplish various things, we can take up even higher-level challenges."

The Okajima Plant has recently introduced 3D printers. Thanks to this change, the production of prototypes, which took two or three months until now, can be completed in one or two weeks. It is expected that this will contribute considerably to shortening the product development cycle and achieving functional improvements.

Building a Foundry in Thailand

Upon entering the 2000s, the demand for engines rose rapidly. Unable to supply the required engines through the Okajima Plant alone, Kubota needed to construct a new foundry.

-- "Deciding that Kubota's next new plant should be built overseas rather than in Japan, Kubota chose to build a foundry in Siam, Thailand. I worked in Thailand from 2010 to 2016 as a manager for that plant."


Kubota founded Siam Kubota Metal Technology Co., Ltd. in Siam, Thailand (SKMT, for short) in 2010. Kubota's first task was to develop our human resources. Prior to conducting operations at SMKT, we initially hired ten workers locally and carried out training at the Okajima Plant.

-- "We started by assembling together and training young people who just graduated high school in Thailand. We began by teaching them to observe regulations, rules and everyday manners."

Nevertheless, when initially launching operations, it was very difficult to ensure that staff carried out work in a stable manner.

With ten years passing since that time, the quality of casting at SKMT has now improved thanks to the training and dedicated hard work undertaken by Kubota staff with a respect for the differences in culture and lifestyle. Productivity has also risen, allowing for production surpassing the 30,000 tons manufactured annually at the Okajima Plant.

-- "Recently, we have conducted measures such as providing regular training at the Okajima Plant to five workers, so as to transfer Japanese manufacturing expertise. SKMT's production volumes have risen and it has undertaken a larger role. It has become increasingly capable of handling casting products in difficult shapes beyond simple crankcases, and the capabilities of the plan could now be said to be at a similar level as the Okajima Plant, for the most part."

Crankcases and cylinder heads are parts that cannot be made quickly anywhere. Their production requires considerable knowhow and technical expertise.

Without the capacity to manufacture these items in-house, it would not be possible to develop new engines or to endure fluctuations in production volumes.

The diligent, hard work of skilled craftspeople at the Okajima Plant spanning 100 years has now blossomed in Thailand. These efforts not only doubled production output, they also yielded considerable value beyond that.

The Future of Kubota's Casting Technology

Renovations to New Casting Lines

The Okajima Plant's ES (airflow press molding) line began operating in 1997, meaning 25 years have already passed since that time.

-- "We replace production lines with new ones about every 25 years. Although core generation and finishing processes will not change, melting furnaces and cast parts will be replaced."

We plan to operate the new casting line to handle mass production starting in FY2024. For the melting of casting materials, we will upgrade from one cupola furnace to four electric furnaces. With a firm eye on carbon neutrality measures, we will promote decarbonization through the conversion to electric furnaces from a cupola furnace emitting considerable volumes of carbon dioxide (CO2) during combustion. Additionally, we are forecasting a casting production capacity of 36,000 tons annually, a 20% rise in comparison to current levels.

Initiative to Produce Large Engines

Although the greatest strength of Kubota's engines is said to be the high output produced by their compact size, we also developed large-displacement industrial diesel engines within the 200-Plant known as the casting workshop, where junior employees can learn about traditional casting techniques.

Here, through practical work, they learn for themselves skills such as the process of producing casting molds and foundry cores, factors such as temperature and timing for pouring, and other fundamental casting skills.

It's not only for the line workers — finishing and maintenance staff also take part in practical training here so that they can take Japan's national casting certification test. (The casting workshop at the Okajima Plant is an accredited test center for Osaka Prefecture, and the foremen and supervisors are qualified members of the certification committee. People from other companies also visit the workshop to take the test.)


"Even if someone is assigned to a fixed post, by studying here, they can see the line as a whole and, based on a different perspective, reconsider what kind of role is served by their position. It may also become possible to move to another post, and most of all, casting itself will become more interesting."

“Casting Itself Becomes More Interesting”
Although the phrase "becomes more interesting" may sound like a rather trivial expression, it may describe one of the motives behind the innovations of Kubota's casting technology.

As long as we pursue and further explore the field of casting, within which many things remain unknown, and as we continue to carry out interesting initiatives, we will surely achieve the further evolution of Kubota's for another 100 years.