Ingersoll Milling Machine Co.Rockford, Ill.

Machine tools, the next generation

In technology, Americans yearn for the spectacular breakthrough. Yet in older industries - such as machine tools -- slow, small, and laborious improvements have been the rule. Too often, anything spectacular is either the last gasp of a failing firm such as the classic Cord automobile of 1936 or a brilliant idea such as the electronic calculator that was born outside the mechanical calculator market it replaced. The spectacular octahedral hexapod is neither. Instead, this unusual design for a high-performance machine tool comes from Ingersoll Milling Machine Co., an old-line, privately held builder of specialty machine tools employing 4,000 in Rockford, Ill., and in Germany. It was not designed or built using government grants, although Edson I. Gaylord, chairman, admits almost with an air of embarrassed pride that after a prototype was designed and built, a grant was offered by the National Institute of Standards & Technology. "We told them we would accept only if no strings were attached," he says. "We didn't expect a response, much less a grant, but they came back with one with no strings attached. As a taxpayer, I personally feel it is not the best way to fund or encourage technological development, but we will make good use of the money for further development." The octahedral hexapod is also unusual, explains Mr. Gaylord, because it was designed and built without a specific customer in mind -- an uncommon practice at Ingersoll or for the machine-tool industry in general. "For example, when we developed our first transfer line in 1924 [an equally significant development], we had a specific automotive customer in mind. We think our customers would surely object if we routinely added 20% to quotes even if we explained that it was funding special machine-tool projects." Actually, in terms of the development's precision and performance, the company may have been thinking of all of its future customers when its board of directors authorized building the prototype in 1987. As an engineering exercise, the design represents an especially creative assault on the problem of achieving a rigid structure. A basic issue in building any machine tool, structural rigidity becomes a critical need as users turn to shaping tough materials such as ceramics and space age alloys. Ingersoll believes that dealing with materials of the future will require more than an incremental approach to improving machine-tool capability. By combining an octahedral structural frame with a hexapod actuator, Ingersoll's researchers believe they have created the stiffest, most rigid machine tool possible. In the machining process, stiffness and rigidity determine surface finish, tolerances, and tool life. The octahedron, the "space frame" structure, consists of 12 beams of similar length that are joined together at six junction points. Like a geodesic dome, the structure is a self-supporting, closed structure with minimal foundation requirements. The hexapod, the mechanism that guides the spindle, resembles the floating platform of a mechanical flight simulator (the Link trainer). It consists of six telescoping arms joined at the spindle with their opposite ends attached at the top of the octahedron, two to each of the three corners. Any loads they exert are transmitted either as tension or compression, so no bending forces occur to affect accuracy. Not only is the structure rigid, but its stiffness and accuracy represent at least a fivefold improvement over conventional machine-tool designs, says Dennis S. Bray, vice president of technology. A unique part of the design challenge was in the software that converts the conventional XYZ coordinate information into machine motions. For example, to move the spindle, it is necessary for all six struts of the hexapod to move. Dr. Bray terms the task as nontrivial software development! Part programming, however, is straightforward and simple, he adds. The octahedron, by concentrating all the forces of the machining process within its frame, offers a unique installation advantage -- no need for a special foundation. Designing and installing a foundation can be a substantial cost of a conventional machine tool, adds Dr. Bray. The company has demonstrated the machine's foundation independence by using a crane to lift one corner during a machining sequence. Accuracy wasn't affected. Another advantage is scalability of the design. Dr. Bray foresees versions of the design varying in size from table-top models for the semiconductor industry to units so large that the octahedron frame would also form the building structure. While Ingersoll is showing its six-axis, laboratory prototype with a spindle for metal cutting, Dr. Bray hopes customers will see beyond the machine's obvious in-contour machining capability. "It could be equipped with a laser for cutting and welding, or it could be set up for high-pressure water-jet cutting," he explains. "Representing the ultimate in stability, it could be ideal as a shop-floor coordinate-measuring machine." Dr. Bray believes the machine's self-contained nature makes it a natural for machining in space, on the moon, or in other low-gravity environments. "Discovering and implementing the potential of the design may be our biggest challenge," adds Fred C. Wilson, group president. "For example, consider its potential for portability. Not only is this a machine that could be taken to the job, but that job could be in a remote oil field as well as in a different part of a manufacturing plant." Additional potential of the machine derives from its simplicity and ease of manufacture. The part count in the prototype is only about 100. "Compare that with the 1,000 or so in the conventional machine tool," notes Dr. Bray. "The other characteristic is that many are duplicate parts." He believes that suggests more than cost-effectiveness. "Assembly is so easy and takes so little time that the octahedral hexapod could be sold as a kit." He believes those advantages play right into the popular "flexible" and/or "agile" manufacturing scenarios. (Flexible he defines as the ability to react to planned changes; agile as the ability to react to unplanned changes.) "Either way, the mechanical simplicity of the design plus its foundation independence gives users the ability to quickly reconfigure production lines with the easy option of storing the machines disassembled when they aren't needed."

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