Site: Morikawa Industries Corporation 150, Imojiya Koshoku City Nagano 387, Japan Date Visited: January 12, 1996 WTEC Attendees: T.S. Piwonka (report author), H.W. Hayden Hosts: K. Ohta, General Manager K. Yamazaki, General Manager H. Kubota, Executive Director T. Koshi, Director T. Sunohara, Section Manager, R&D, Casting
Morikawa Industries is a 50-year-old enterprise, which is now partially (less than 10%) owned by the Honda group. Morikawa has been a principal supplier of machined gray and ductile iron castings to Honda for more than 25 years. It operates an alloy iron and ductile foundry, employing 350 and occupying a 30,000 m2 plant. The plant uses cope and drag and Disa green sand molding, shell mold and lost foam casting, and induction melting. The primary customer is Honda, and typical products are bearing caps, differential gear cases, exhaust manifolds, and cylinder sleeves. The plant has a 1,500 ton/month capacity and was operating at a level of 1,350 tons/month at the time of the WTEC visit. Morikawa has a U.S. subsidiary, American Morikawa, available to offer licenses for its patented lost foam process to U.S. companies.
The WTEC team did not see or discuss current R&D activities in casting, other than a passing mention by the hosts that they are looking at rapid prototyping. Morikawa did install a new Disa molding machine during August 1996 for which automatic pouring was planned.
The focus of the visit was the "Dream" process, which is the Morikawa variation on the lost foam process. In the "Dream" process, the vapors from the burning pattern material are burned off above the mold, using gas burners. The advantage of this process is that the burning effluent draws a vacuum on the mold, eliminating the need for a vacuum to be pulled on the mold mechanically, as is done in some "conventional" lost foam operations. One possible disadvantage is that the vacuum which can be pulled on the mold by this method is limited to about 35 inches, which means that only short clusters can be used. While this process minimizes the amount of sand that must be placed in the flask, it also limits the number of castings which can be poured on a single cluster. (The clusters the WTEC team saw had only one layer of castings; most conventional lost foam clusters in the United States will have two or three layers of castings.) The process has been licensed to four other Japanese foundries.
The pattern material is "Clearpor," a tri-polymer consisting principally of methyl metacrylate (MMA) -- 75%, and polystyrene (EPS) -- 25%, with a small amount of alpha methyl styrene. Clearpor was developed, at the behest of and with strong encouragement from Morikawa, by the Research Division of Mitsubishi Yuka Badische, a Japanese joint venture of Mitsubishi Chemical of Japan and Badische of Germany. Morikawa collaborated in this effort by making trial castings using various phases of the pattern material during its development.
Patterns are injected, assembled into clusters, and coated in a separate plant located about three miles from the foundry. Patterns are injected in machines using horizontal parting planes, and sprue components are injected in machines using vertical parting planes. The patterns drop softly into a water tray upon ejection from the pattern dies. After a two hour drying period, the patterns are assembled, using people and pick-and-place robots. Gluing is done automatically. Robots assemble the clusters, and the clusters are coated in tanks in which the coating slurry rises automatically over the patterns. Coated clusters are shipped to the foundry for pouring.
The Morikawa lost foam process uses a square flask. A layer of silica sand (Japanese specification JIS 6) is vibrated into the flask, the cluster is placed on it, and the flask is filled while it is vibrated to achieve compaction. Castings are poured manually. At shakeout the clusters are placed in a fixture and castings are removed from the downsprue by hydraulic rams.
Morikawa does not use any solidification simulation software, because company engineers do not know of any program which can handle lost foam. Morikawa management considers it too expensive presently to set up its own rapid prototyping facility.
None of the molding and pouring lines in Morikawa used automatic pouring at the time of the WTEC visit, although Morikawa representatives mentioned that they planned to install automatic pouring on the Disa line in 1996. They reported pouring exhaust manifolds with 3 mm walls on their cope and drag line.
Some spent sand (particularly fines) is sold to the cement industry. Sand disposition costs are approximately ¥7000-8000 per ton. WTEC's hosts pointed out that one of the advantages of lost foam is that it generates only 20% of the spent sand that green sand molding does. They mentioned that sand disposal in Japan is becoming more difficult each year.
Morikawa reported that although 100 foundries in Japan are currently experimenting with lost foam, only 20 are in production. The largest tonnage of lost foam castings in Japan is for water and drainage hardware castings.