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Manufacturing Industry

High speed machining, Italian style

Modern Machine Shop, Dec, 2002 by Mark D. Albert

One of the highlights of BI-MU, Italy's recent biennial machine tool show, was the number of innovative machine tools (and related technology) focusing on high speed machining. The show, held in Milan in even numbered years, indicated some clear trends in high speed applications for die/mold and aerospace customers. The high speed machines on display at BI-MU show that larger machines are getting faster. Large structures that can sustain high rates of acceleration and deceleration are emerging, apparently due to advances in computer analysis leading to more rigid designs along with a growing use of linear motors. Linear motors are now gaining in efficiency but are becoming more economical.

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Rigid designs combined with spindles capable of delivering high torque values at high spindle speeds are allowing high speed roughing and high speed finishing to occur on the same machine in one setup. Simultaneous five-axis machining is also growing in prevalence, especially in configurations utilizing tilting and rotating tables. Some machines feature five-axis spindle heads that can be locked into place for greater rigidity in three-axis roughing operations.

There is a trend toward longer worktables on some models, allowing more than one workpiece to be Set up for extended operation in the untended mode. In some cases, enclosures allow one end of the table to be closed off so that operations can resume while finished work is removed from the other side of the table.

Italian builders tend to favor Fidia, Heidenhain or Siemens CNGs for their high speed machines, but many are now offering Fanuc control units as an appeal to the North American market, where this brand is well established. Even a small selection of high speed milling machines on display at BI-MU attests to the dynamic level of development efforts in Italy.

Interesting Approach To Roughing

FPT's Dino is designed for both high speed roughing and high speed finishing. According to developers, this portal-style machine has the rigidity for roughing along with the nimbleness for finishing. Roughing is performed with a 45-hp fixed vertical spindle (top speed of 12,000 rpm). The company is promoting a concept that favors roughing with a relatively small tool at lighter depths (a 50-mm cutter at 1.0 mm DOC, for example) making many passes, thus avoiding the stresses too severe for machines designed for finishing only. While this strategy does not reduce overall roughing time compared to more conventional roughing with a larger tool at heavier cuts, it does reduce semi-finishing to essentially a remachining operation that cleans up material unreachable with the roughing tool. Overall machiningtime is reduced.

Semi-finishing and finishing are performed with a universal head that allows an HSK-63A tool to be oriented in five axes to cut with the most efficient part of the cutter. This 24-hp spindle has a top speed of 18,000 rpm for semi-finishing. For finishing, this spindle accepts a 34,000-rpm, 22.8-hp electrospindle for HSK-40E tooling. The universal head rotates 50 degrees to reach mild undercuts in molds or dies that might otherwise require a second setup.

Lining Up With Linear Motors

MECOF's new Prima machining center is equipped with linear motors in the X, Y and Z axes for 1.1 g acceleration and cutting speeds as high as 60,000 ipm (100,000 ipm for rapid traverse). The machine can change heads automatically, switching from a 40-hp fixed vertical head for roughing at a top speed of 18,000 rpm, to a rotary head with an electrospindle for finishing. The rotary head can be one of two types--a two-axis continuous model for five-axis machining at 26,000 rpm, or a two-axis positioning model for three-axis machining at 30,000 rpm.

With a 65 by 31.5 by 55-inch workzone, the Prima is targeted to die/mold and small aerospace components. For graphite electrodes, a dust suction system can be installed. For larger aerospace parts, MECOF offers the AirOne series, which is essentially the same machine configured with additional worktable modules that extend the X axis up to 945 inches long.

Perhaps the most ambitious use of linear motors appears in the Estrema milling machine introduced at the show by Gruppo Parpas. Along with the X, Y and Z axes, linear motors are used for the tilting and rotating table, giving it the speed to keep up with the other three axes. The rotary table is located off to one side of the extra long table so that the other side can be used for three-axis machining.

High Speed Or Multi-Purpose

Well established as a builder of milling machines for marble and stone, Breton only recently began designing and building machines for the metalcutting industry. The company's Xceeder and Ultrix machines are especially interesting. These machines are basically the same platform configured either for high speed machining or for multipurpose machining. These portal-type, traveling-column machines feature a "Metalquartz" base consisting of a steel frame filled with a quartz polymer composite for rigidity, vibration damping and resistance to thermal distortions.

Manufacturing Industry

High speed machining, Italian style

Modern Machine Shop, Dec, 2002 by Mark D. Albert

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