Grinding Journal - Summer 2007 - (Page 19)

Summer 2007 concentrically distributed. It is when the deviations become unbalanced and the round becomes an oval that problems are most apparent. The piece can move in the workhead or tailstock centers when the grinding wheel is touching the part. Cleaning the center with a center-hole sharpening wheel can sometimes be the answer to this problem. However, some parts cannot be salvaged and become scrap. Achieving straightness is a second geometrical challenge. ends of the workpiece, and the traverse speed. Finally, you may need to change the wheel and workpiece speed, plus wheel dressing to ensure it’s a sharp, open wheel. Coolant is usually critical Coolant plays a large part in proper grinding and improper coolant can cause a wide range of problems. Always use coolant during dressing to increase diamond life and ensure proper wheel truing. And ensure you have adequate coolant flow into the grinding zone, because insufficient or incorrect coolant destroys the workpiece surface and also increases wheel wear. One sign of insufficient coolant is the presence of sparks. There shouldn’t be any! Proper spark quenching may require additional coolant from below, or increased coolant pressure. Rules of thumb for coolant requirements: • Per 1 HP spindle power, approximately 1 US gal/min emulsion is necessary • Per 1 inch wheel width 6.5 – 20 US gal/min emulsion is necessary • The pressure of the pump should be at least 14.5 PSI (normal approx. 70 PSI) • The thermal conductivity of oil is half that of an emulsion (4.2 J/K° versus 1.9 J/K°). Therefore you need to DOUBLE the amount of oil to dissipate the heat The Art of Grinding™ is just that, an art that must be perfected with experience. As this article shows, each component in the process is linked and has an affect on the others. As with analyzing any other process, keep it simple. Begin with the obvious and proceed from there. Author/engineer John Richard “grew up grinding” at Studer. He now serves as their Sales Manager for North America. Studer’s theme is The Art of Grinding.™ The Art of Grinding. Workpiece after grinding without steady rest One unwanted outcome is a larger diameter in the middle of the workpiece than on the ends. Possible causes include: • bending forces during the grinding process, • incorrect infeed, • incorrect wheel overlapping, • coolant pressure on the workpiece (especially when working with thin parts), • tailstock or workhead misalignment, or • dressing issues (wheel isn’t sharp and requires too much grinding force). Overcome bending forces during grinding by using a steadyrest. As a rule of thumb, use a steadyrest if the part is 10 times longer that the smallest diameter. Mount the steadyrest on the smallest diameter. This rule can also be applied to determine if multiple steadyrests are needed. Infeed and wheel overlap create straightness issues when the wheel wears from traversing the workpiece. To fix this error when working on a single diameter workpiece, plunge from both ends of the workpiece and traverse in both directions. To grind multiple diameters on your workpiece, always plunge the wheel on the shoulder of the larger diameter and traverse out to the end of the workpiece. This will help assure straightness and alignment of the two diameters. Make sure to over-travel a minimum of 1/3 the wheel width. You may also want to change the spark-out time on the INFO grinding.com John Richard • 41-33-439-1360 john.richard@studer.com Grinding Journal 1 http://www.grinding.com http://www.grinding.com

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

Contents My Thoughts Exactly When Lives Are at Stake Walter Consolidating Production The Art of Grinding: Knowing the Source of Grinding Errors and How to Fix Them The How and Why of Conventional Vitrified Grinding Wheel Selection Grinding Glass Flat Problem Solver

Grinding Journal - Summer 2007

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