Retrofitting CNC Machining Center With Auxiliary High RPM Spindle

Adding a high-speed electric-spindle system to an existing CNC vertical machining center can improve the machine's productivity by providing quick, infinitely variable speed selection and higher rpm capabilities. Integrating the auxiliary spindle permanently onto the machine allows a company to meet the constantly changing demands of machining fine details and still retain the main spindle's capabilities for larger cutters.

In a typical application, one company recently purchased a five-axis Fadal VMC 4020 vertical machining center and modified it so it could also be used for machining fluidic circuit prototypes. Modifications include a Precise SC 102-O high speed electric spindle system (Precise Corp., Racine, Wisconsin), a special mounting plate that allows the spindle to remain in place while the main spindle is in use, some tool changer and programming adaptations, and cable carriers to keep all fluid and electrical lines neat and manageable.

The high rpm capability makes it possible to use carbide end mills from as small as 0.009" diameter up to about 1/4-inch. To make the high spindle rpm needed for small diameter cutters readily available, the auxiliary Precise spindle is mounted permanently on the side of the machine's column. Offset approximately ten inches, the spindle's fixed location enables it to be programmed into operations with little or no special accommodation. The machine's main spindle remains intact to provide the higher power and lower speed range needed to use larger diameter cutters.

With the auxiliary spindle, tools are set up in their own quickchange toolholders. This makes it possible to preset all of the tools and quickly change from tool to tool as needed, roughing with a larger diameter end mill for part of the program and finishing with smaller diameter end mills.

The machine can be programmed so switching from the main spindle to the high speed spindle can be done quickly, without interruption. When the operator specifies a speed above the main spindle's 10,000 rpm limit, the custom postprocessor recognizes the condition and applies the fixture offset, negates the main spindle, turns on the auxiliary spindle, turns it off when the cycle is through and returns to the main spindle.

The Precise spindle is equipped for automatic tool changing but the toolholder release can also be operated manually. A conveniently located pushbutton that releases the toolholder is tied to a zero-speed sensor so the tool will not be released until the operator is ready. Pre-set tooling allows the cutters to be changed quickly. MMS

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