Production Machining

MAY 2018

Production Machining - Your access to the precision machining industrial buyer.

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finish, material honed, honing pressure, surface speed and operator technique, but should always be consistent, part to part. In a production environment where the same parts are honed one after another, the stone wear ratio should be very stable, reflecting the consistent bond structure of a quality honing abrasive. If the honing oil does not adequately lubricate the honing chip and grit, the abrasive grain wear will become erratic. This will affect the stone wear ratio and cause the finished part size to vary unless in-process gaging is used to stop the honing cycle. Low performance honing oil allows welding of metal chips to the workpiece, which are then sheared off, causing a larger total surface roughness than expected for a given abrasive grit size. The consequence is unwanted random scratches on the workpiece deeper than those normally produced during honing opera- tions. The results are lost productivity, material waste, part rejects and lost profit. Metal specks in the abrasive surface are a sign of honing oil with low lubricity. e oil fails to fully lubricate allowing chips to lodge into the abrasive surface. e embedded chips will hold the abrasive away from the workpiece and prevent uniform grit penetration into the base metal, preventing material removal. e metal carried in the abrasive surface can scratch or tear the honed surface as the abrasive sweeps the chips along the honing tool path. If this "loading" of the abrasive surface is minor, it may go unnoticed, however, productivity will begin to drop off. When the loading is more severe, it leads to fracture of the abrasive. e trapped chips are forced against the part wall by the honing stone. If the chip re-welds to the part, it can scratch or chip the honing stone. When embedded metal that is near the leading edge of the abrasive welds to the workpiece, the abrasive is loaded in compression and will seldom break. Instead, the welded metal cuts a groove in the abrasive. If embedded metal that is near the trailing edge of the abrasive re-welds to the workpiece, the abrasive has less support to resist the tearing motion and will break away, leaving a chip on the trailing edge. Low performance honing oil can create catastrophic welding between the workpiece and the mandrel shoe :: Like most metalworking processes in today's metalworking shop, honing involves numerous disciplines, which must work together to deliver the accurate parts in the most efficient manner possible. METALWORKING FLUIDS 32 PRODUCTION MACHINING :: MAY 2018

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