Borgo San Dalmazzo, Italy. It was a huge challenge for a small precision machining company, but Costruzioni e Lavorazioni di Precisione dared to take on an order to manufacture a massive component for a nuclear reactor.
Horizontal boring mill, working on an external body of a pump for a nuclear reactor.
“Don’t sell the bear’s skin before you have caught the bear” is a popular proverb in the province of Cuneo in northwestern Italy. It’s been a long time since much bear hunting took place here, however. Today the area specializes in food products such as Castelmagno cheese, Barolo and Barbaresco wine and the meat of the fat ox of Carrù. Still, Luca Giordano, managing director of Costruzioni e Lavorazioni di Precisione (CLP) in Borgo San Dalmazzo quotes the proverb when he talks about taking on a new project to manufacture a massive component for a nuclear reactor. In essence the company, situated about 50 miles south of Turin, was contravening the proverb’s wisdom when it agreed to the task. Giordano says, “We were selling the bear’s skin before it was killed.” It was a decision that took considerable courage – and a strong partner in Sandvik Coromant.
Costruzioni e Lavorazioni de Precisione
CLP has no standard production range. Instead the company works as contractor for various companies operating in industries such as energy, nuclear research, civil engineering, machine tool
Face milling head that helped CLP save $42,000 for each lot of pieces machined.
manufacturing and aviation. Drawings and unfinished castings go into the factory and finished parts come out, ready for assembly or further machining.
The company specializes in steel structural work and high-precision mechanical machining of large-size parts. Tolerances of hundredths of millimetres are accomplished in parts that are so large they must arrive and depart by special transport – often at night when the traffic is lightest. Pump bodies for nuclear reactors, components for an experimental fusion reactor and excavators for the excavation of penstocks or underground railway tunnels are just some of the recent projects CLP has had a hand in. And whenever the company takes on a new project, the estimating stage is crucial. The duration of the inserts, the path followed by tools in areas of the part to be machined where there is limited room for movement, the characteristics of materials such as stainless steel and cast iron or the presence of siliceous inclusions (a very hard foundry residue capable of rapidly wearing the inserts) in the castings are all factors that can have a great impact on the times and costs involved in the production process. It’s here, says Giordano that CLP’s 10-year-long relationship with Sandvik Coromant really pays off.
Replacing the side milling cutting head with the high-performing R300, which has inserts that are 0.79 inches in diameter.
“The presence of a partner that can assist special tools can we ‘sell the bear’s skin before we have killed the bear.’”
CLP recently machined the external body of a pump intended for installation in a nuclear reactor. The part, 12 feet in diameter with a spherical external surface, arrived unfinished and had to be milled and lathed to the final internal dimensions (the exterior would be subjected to further machining by the client once the structure was subjected to X-ray examination and pressure tests).
At the CLP workshops in Borgo San Dalmazzo the component was subjected to three machining processes – two on a gantry machining center and one on a boring mill (see sidebar). Sandvik Coromant technical personnel provided assistance for each process, but in particular it worked with CLP on the second process.
“When CLP asked for our advice with regard to using the gantry machining center’s rotary table, we suggested the use of a Coromant Capto C8 clamping unit [the manual version] mounted on a purpose-built block to be integrated with the machine’s ram in order to perform the internal and external turning operations required,” explains Giorgio Signori, northwest area manager for Sandvik Coromant in Italy. “We transformed the center into a vertical lathe.”
CLP, which specializes in steel structural work and high-precision mechanical machining of large-size parts, has had a 10-year relationship with Sandvik Coromant
Sandvik Coromant Customer Service
The pump body was turned during this stage, but it was also milled externally – an operation complicated by the type of material, the casting crusts and the shape of the piece. Simone Guglielmetto, area specialist at Sandvik Coromant, explains that the solution adopted in agreement with CLP’s technical personnel involved the use of an R300 milling cutter with a .79-inch-diameter insert, which allowed higher tool contact times and work parameters than expected.
On completion of this stage, the pump body was transferred to a Lazzati milling machine for milling the internal parts. However, the Lazzati is certified for use with milling cutters of only up to 6.3 inches in diameter, and the machining process required here called for the use of a milling cutter that was 21.7 inches in diameter.
“We advised CLP to use an N331 special disk milling cutter, 21.7 inches in diameter,” recalls Valter Angius, technical sales person at Sandvik Coromant. “It is designed with positive geometries that do not affect the stability of the machine.”
With the increased tool contact time and longer insert duration CLP was able to save $42,000 for each lot of pieces machined.
“This shows how the service supplied is much more important than the cost of the tool itself,” says Giordano. “The value of advice provided by the Sandvik Coromant technical personnel gives their product an excellent quality/price ratio, even though the price in itself may appear high at first glance. This is why we use Sandvik Coromant products for more than 80 percent of our requirements and for 100 percent of our requirements related to reactor pump body machining.”
Learn more about Customer Service at Sandvik Coromant.
Technical Insight
CLP asked the technical staff at Sandvik Coromant to help create a way to mill and turn a large, unfinished casting (measuring about 12 feet in diameter) of a pump body. But there were several aspects to CLP’s request that required unconventional solutions. The company wanted to use a machining center as a lathe (even though it offered lower performance than a proper lathe would) and at the same time it wanted to use a 21.7-inch milling cutter, a much larger diameter than what the machining center was approved for, without compromising on machining precision. CLP also wanted to increase production by shortening work times, both in terms of machining and machine placement.
“Together with CLP’s technical personnel we were able to test the tool path on three-dimensional models,” says Simone Guglielmetto, area specialist at Sandvik Coromant. “We decided to use short, large-diameter milling cutters to prevent vibrations from affecting machining precision.”
An R200 toroidal milling cutter with round inserts was used for the first machining stage (milling on the machining center), which was then replaced with the high-performing R300 with an insert of 0.79 inch in diameter in September 2009, as soon as that insert was launched on the market. A Coromant Capto C8 clamping device was used for the second stage, allowing the turning of some of the internal and external areas to be accomplished using the center’s rotary table. Sandvik Coromant also assisted during the second stage, in which a milling cutter machined various internal areas.
“The machine’s manufacturer approved the machine for use with milling cutters with a maximum diameter of 6.3 inches,” says Guglielmetto. “With CLP we experimented with the application of a purpose-designed and manufactured disk-milling cutter, the N331, which was 21.7 inches in diameter. Excellent results were obtained, and the demand for precision fully complied with.”
Learn more about Milling at Sandvik Coromant.
Originally published in Metalworking World 1.2011, a business magazine published by Sandvik Coromant.
