Grinding Journal - Fall 2007 - (Page 18)

1. Conventional Creep Feed Part, Feature: Turbine blade, dovetail form Machine: 3-axis CNC Wheel: 2"-wide aluminum oxide & ceramic Wheel speed: 3,500 surface feet per minute (SFM) Roughing parameters: 0.03" depth of cut (DOC) at 10 inches per minute (IPM) Finish parameters: 0.002" (DOC) and 20 (IPM) Coolant: Water base emulsion, 60 GPM, CNC axis movement variable PSI to profile wheel form Cycle time: 5 minutes (formed roller dress) 9 minutes (single-point diamond disk dress) Dressing method: Rotary diamond roller, formed or disk Workholding: Manual clamping Q Prime: 3-5 mm3/sec This dressing approach uses a standard single point diamond disk to create a variety of shapes on the grinding wheel on demand. Perfect for quick setup on prototypes and small batches. For creep feed grinding, a 3-axis CNC machine is required to control the in-feed depth, cross speed, and table stroke. The wheel is dressed after every pass via the single point CNC method. A rotary diamond disk (a steel disk with a single layer of diamonds around the exterior) creates the required wheel form via X-Y-Z movement across the wheel guided by the CNC program. Depth of dress is empirically derived pending form tolerance and geometry and typically ranges from .002"to .010"per dress. Another approach is to use a full form roll to dress the form into the wheel. The workholding in this case is typical of a flexible job shop application, using manual clamping fixtures that are effective as far as flexibility and cost. This application is typical of a job shop where the customers’ demands continually change. It’s a low volume and low investment situation, because job shops often don’t have the capital or time to order long-lead tooling. The limitations of this process include an inability to grind very complex forms such as radial geometries or some groove and slot forms that would be possible with a five-axis machine. It’s also not the most productive way to produce high volume parts due to the amount of dressing and wheel changing that have to occur. The Single-point CNC dressing method enhances flexibility because it eliminates the need to purchase Fall/Winter 2007 Diamond disk a custom-formed diamond roller, which for this application might take six to eight weeks to have designed and built. Here, the CNC program shapes the wheel within minutes once the design is entered into the control. Low cost and flexible Addressing the five variables outlined earlier, this application features a relatively low investment in capital equipment, namely a basic 3-axis machine. The flexibility of the dressing process complements a job shop/prototype approach, although the need to return the wheel for dressing after each pass negatively affects cycle time, and repeated dressing increases wheel consumption. Coolant consumption is moderate and water-based coolant is environmentally preferred. The individualized nature of the process helps maintain high part quality. Low-volume job-shop production makes manual workholding a practical choice.

Table of Contents Feed for the Digital Edition of Grinding Journal - Fall 2007

Grinding Journal - Fall 2007 Contents From Virginia: Apparently no credit crunch for machine tools Why measure cutting tools Other perspectives on CNC tool measuring Productive grinding of superalloys SUPER service grinding BIG rolls Problem Solver

Grinding Journal - Fall 2007

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