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Next-generation turning
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Third-generation CNC lathe/turning center offers flexible productivity and cycle time reduction The lathe is probably the oldest machine tool, stemming from the early "tree" lathe which was turned by a rope passed around the work a few times and attached to a springy tree branch overhead. Then, about 200 years ago the Englishman Henry Maudslay built the first screw cutting lathe. Now, at the dawn of the 21, century, the traditional lathe is fading from the manufacturing scene. It has been replaced largely by increasingly versatile and highly productive CNC turning centers and the still more advanced turn/mill centers. For more than 30 years, Valco Instruments Co. Inc. (VICI), Houston, TX, has been the leading designer and manufacturer of standard and custom valves and fittings for precision analytical, biomedical and biocompatible instrumentation. The firm's product line also includes a wide range of related products such as pneumatic and electric actuators, tubing and sampling loops, heated enclosures, valve sequence and temperature controllers, gas purifiers and digital interfaces. In the manufacturing of these components, Valco uses a wide range of corrosion-resistant alloys that include such difficult to machine materials as tough Hastelloy (Ni-Cr-Mo-Fe-W alloy), the slightly more machinable Nitronic 60 (Ni-Cr-Mn) austenitic stainless steel and the conventional 300-series and 4400 stainless steels (Cr-Ni), all of which can be also tough to machine. Even though widely recognized as being gummy or stringy, Valco routinely machines these nickel alloys and stainless steels. The complexity of Valco's parts increased markedly over time and about a year ago, the need arose for a turning machine with an opposing subspindle to machine parts with similar features at each end. Other requirements were to find a machine with Yaxis milling capability and a large capacity tool turret with live tools. Last and though not really a machining feature, it was considered desirable to have a machine with a smaller footprint. In the company's search such a machine, Frank Stearns, Valco VP, investigated the availability of such machines and choose the good reputation of Mori Seiki's products. Valco then decided to invest in a Model SL150SY continuous machining, dual-- process turning center. "Even though we've had our SL150SY for a little more than half a year," says Stearns, "we use it routinely to produce as few as ten parts and as many as 5,000 parts. Typically, the parts machined by Valco measure only 1.25" (31.75 mm) long and 1.75" in diameter (44.45 mm). It isn't the size of the part, but more so the tiny holes that must be drilled which presents the challenge." Stearns adds: "I can consistently drill 0.006- diameter (0.152 mm) holes in 316 stainless steel. High-pressure water soluble coolant through the tool goes a long way toward increasing drill life. Of course, it's also important to remember that the holes are not all that deep, some only 0.079- (2 mm) in depth. Keep in mind that a No. 80 drill is 0.0135" (0.343 mm) in diameter. For these operations, spindle speeds are generally below 8,000 rpm with 6,000 rpm being more typical." Cutting tool material for the tough nickel alloys routinely turned at Valco is generally carbide but cobalt tool steels are also used. For example, Nitronic 60 will be turned at about 400 sfm (120 m/min) using carbide and drilled at 150 fpm (45 m/min), both of which are well within the capabilities of the SL-150SY. For turning and nondrilling operations, coated carbide is generally used but there are occasions when cobalt steel cutting tools are called for. Valco, in an effort to minimize setup time, has developed multiple position quick-change tool holders so any given part engineered for this machine can be completely machined in one operation. The tools can have as many as six positions on each turret face (72 tools in a setup). "It really works well," says Stearns. Next-generation turning The SL-150SY is a third-generation machine in Mori Seiki's line of turning centers. It is more than a turning machine. It is a true multi-function machine tool combining the features of both turning and machining centers. It is a high performance machine that is capable of producing extremely complex workpieces in one set-up with its driven tools and X, Z, C and Y-axes. The Y-axis feature permits off-center machining. Everything about the new machine is faster, including turret indexing, acceleration and deceleration, C-spindle connection and live tools. The traverse rates are exceptionally fast. The 708 ipm (18 m/min) for the X-axis is 50 percent faster and the 945 ipm (24 ni/min) for the Z- axis is 60 percent faster than on earlier similar machine. This represents a very significant improvement in manufacturing performance. The B-axis also comes in at 945 ipm (24 m/min) and the versatile Y-axis functions at 236 IPM (6 m/min). Combining all of these features provides a significant reduction in cycle times, which, of course, also translates into a comparable increase in productivity. One of the features is that manufacturing engineers can apply the CNC programs from a second generation SL machine, run these on the new machine and benefit from the same reduction in cycle times. As with the whole range of SL Series turning centers made by Mori Seiki, the SL-150SY uses a very solid and rigid time proven Meehanite casting slant bed design. The wide stance and solid rectangular shape result in a rugged and very thermally stable machine. To further counteract heat and thermal stress, the coolant tank and chip pan is a removable unit that slides into the bed casting. The torque tube construction absorbs any twisting, bending or shock of cutting forces. The versatile tool turret can carry both fixed and live tools. Turret indexing maintains accuracy by using a true Gleason CURVIC coupling. Taking advantage of servo motor technology has increased the speed of indexing. Servo motors also drive the live tooling. The turret indexing mechanism is a non-rise type and is similar to the mechanism used for table indexing in horizontal machining centers. All mechanical action takes place internally. The clamp and unclamp action never lifts the turret, it simply rotates. An advantage of this design is that the mechanism is protected from chips and coolant. Tool indexing, station to station is only 0.2 second. Live tools can be rotated at 3,000 rpm, with 4,000 rpm optionally available. When switching from turning to milling, there is a 0.2 second Z-axis connection time. For heavy-duty cutting a disc brake is used to clamp the C-- axis. Frank Stems' enthusiasm for the SL150SY after only six months centers on the rapid cycle times and the versatility of the Y-axis. Valco has already asked for a quotation on another one. http://findarticles.com/p/articles |
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