Modern Machine Shop

OCT 2018

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Page 87 of 147

MMS OCTOBER 2018 86 CREEP-FEED GRINDING Likely it is reasonable to think of your deep- grinding application as creep-feed, and you may have done grinding that was arguably creep-feed without realizing it. 2. Creep-feed is both a low-force and a high-force process. Mr. Rutkiewicz characterizes the creep-feed process by pointing to this seemingly contradic- tory depiction: The force in the cut is low from one perspective and high from another. While each cutting particle on the grinding wheel experiences a low force relative to other modes of grinding, the force imparted to the machine overall is likely to be high. Compensating for the heavy depth of cut in creep-feed is a traverse rate (feed rate) that is low, often on the order of 5 to 20 inches per minute. The low feed means the cutting force upon every individual grit of the surface of the grinding wheel is also low. Wheel life and power efficiency both poten- tially benefit from this. And yet, a lot of grits are engaged. The larger depth of cut of creep-feed means a longer arc of the wheel is submerged in the part, increasing force overall. As a result, the requirements of a grinding machine used in this process include spindle power of at least 15 to 20 horsepower per inch of grinding wheel width and a static loop stiffness of 100,000 pounds per inch for each inch of grinding wheel width. 3. Creep-feed offers advantages over conventional grinding. Compared to a conventional process that makes faster, lighter passes, creep-feed grinding offers the following benefits: Here is creep-feed defined in a simple illustration. Compared to surface grinding, creep- feed has a higher depth of cut and slower traverse rate. Norton Saint-Gobain places the minimum depth of cut at 0.005 inch, but others imagine the starting point to be deeper than this. Superabrasive wheels such as the Norton Winter Paradigm wheel seen here permit creep-feed grinding without a demand for continuous dressing. The unit for intermittent dressing is located on the machine's table and seen in the facing photo. Creep Feed Slow Traverse, Heavy Depth Conventional Surface Fast Reciprocation, Light Depth

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