Measuring Tool Length For Micron Accuracy

When the smoothness of a mold surface or the dimensions on a partfeature are toleranced to the micron level, measuring the length Cemented Carbide Inserts of thecutting tool in the spindle to the same level of precision becomescritical. Makino(Mason, Ohio) has introduced a method for accomplishing this task. Themethod takes into account not only the position of the tool tip butalso the effects of thermal displacement in the spindle. This requiresmeasuring the cutting tool in the spindle at a static (non-rotating)state and then measuring the spindle end while rotating with thecutting tool in place at the speed programmed for machining. Becauserotating the spindle inevitably causes some slight thermal growth ordeformation, this method can measure that change and, if necessary,factor it into the calculations for tool length compensation values.

Becausethis method involves contact and non-contact sensing devices, it iscalled a hybrid automatic tool-length measuring system. Carbide Inserts According todevelopers, applying this system allows cutting tools to be changed andstill hold variations in dimensional and surface roughness to 1 micronor less from tool to tool. This is possible because the system canadjust for thermal displacement of the spindle rotating at differentspeeds along with the slight inaccuracies in tool tip positionresulting from automatic tool changes. Thus, the results ofsemifinishing and finishing operations that call for cutting tools ofvarious length are not affected by the tool changes.

This system is available as an option only on the company’s Hyper2J, V22 and V33 vertical machining centers. After the machine’sautomatic tool changer has changed a tool, initiating a macro routinemakes the spindle move to the measurement unit mounted on the machine’stable, where a retracting cover exposes a contact sensor. Thenon-rotating spindle touches the tip of the cutting tool on the pad ofthe sensor and determines the tool length from the spindle end. Verylittle force is required to trigger the measurement. Therefore,extremely delicate tools, which may be under a millimeter in diameter,are protected.

The spindle moves away and begins torotate at the rpm set for that cutting tool. It then moves to anon-contact sensor located adjacent to the contact sensor in the sameenclosure. Because the spindle is rotating at speed, the effects ofthermal displacement become apparent and can be detected by thenon-contact sensor. The macro directs the spindle to make multiplepasses at the sensor in 30-second intervals until three consecutivereadings do not deviate from each other above a set limit. This ensuresthat the spindle has reached a stable condition before deriving thelength of the spindle end.

By comparing the positions ofthe tool tip and the spindle end, the system can determine if the toollength value should be adjusted to compensate for apparent spindlegrowth. For example, if the difference between the non-rotating androtating tool length is greater than 1 micron or whatever limit theuser sets, then an adjusted tool length value will be used in tool compcalculations.

The hybrid system is designed for users whomust maintain very accurate blending of surfaces from tool to tool inmicromachining applications. In mold work, achieving these smoothsurfaces greatly reduces or eliminates polishing.

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