surface grinding operations - m m robinson high school e ：表面研磨操作- m m鲁滨孙高中e

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.PowerPoint to accompanyKrar Gill SmidTechnology of Machine Tools6th EditionSurface Grinding Operations Unit 82 Objectives Set up various workpieces for grinding Observe the safety rules to operate the grinder Grind flat, vertical, and angular surfaces2Surface Grinding Primarily for grinding flat surfaces on hardened or unhardened workpiece Perform operations such as form, angular, and vertical grinding Good results depend on several factors:Proper mountingProper wheel selection for job3Mounting Workpiece for Grinding Flat Work or Plates Remove all burrs from surface of work Clean chuck surface with clean cloth Place piece of paper slightly larger than workpiece in center of magnetic chuck face Place work on top of paper, and be sure to straddle as many magnetic inserts as possible If workpiece warped, shim work to prevent rocking Turn handle to on position Check work to see it is held securely4Thin Workpieces Tend to warp because of heat created during grindingMinimize by mounting workpiece at angle of 15 to 30 from side of chuck Reduces length of time wheel in contact with work Use adapter if available and mount work at an angle5Short Workpieces Work that does not straddle three magnetic poles generally not held firmly enough for grinding Advisable to straddle as many poles as possibleSet parallels or steel pieces around work to prevent it from moving Parallels should be slightly thinner than workpiece6Grinder Safety Before mounting a grinding wheel, ring test wheel to check for defects Be sure grinding wheel properly mounted on spindle See wheel guard covers at least one-half wheel Make sure magnetic chuck has been turned on by trying to remove work7 See that grinding wheel clears work before starting grinder Be sure grinder operating at correct speed for wheel being used When starting grinder, always stand to one side of wheel Never attempt to clean magnetic chuck or mount and remove work until wheel has stopped completely Always wear safety glasses when grinding8Procedure to Grind a Flat (Horizontal) Surface Remove all burrs and dirt from workpiece and face of magnetic chuck Mount work on chuck, placing piece of paper between chuck and workpiece Check to see that work held firmly Set table reverse dogs so center of grinding wheel clears each end of work by 1 in.9 Set crossfeed for type of grinding operation roughing cuts, .030 to .050 in.; finishing cuts, .005 to .020 in. Bring work under grinding wheel by hand, having about 18 in. of wheel edge over work Start grinder and lower wheelhead until wheel just sparks work Wheel may have been set on low spot of work.10 Cutting fluid should be used whenever possible to aid grinding action keep cool Start table traveling automatically and feed entire width of work under wheel to check for high spots Lower wheel for every cut until surface is completed roughing cuts, .001 to .003 in.; finishing cuts, .0005 to .001 in. Release magnet and remove workpiece by raising one edge to break attraction11Table 82.1: Surface grinding problems, causes, and remediesGrinding Problem Cause Possible RemedyBurning or Wheel is too hard. Use a softer, free-cutting wheel.discoloration Decrease wheel speed.Increase work speed.Coarse-dress the wheel.Take lighter cuts and dressthe wheel frequently.Use coolant directed point of contact between wheel, workBurnished Wheel is glazed. Dress the wheel.work surface Use a coarser-grit wheel.Use a softer wheel.Portion of tabletaken from text12To Grind the Edges of a Workpiece Edges ground square and parallel so edges may be used for further layout or operations Flat surfaces ground first, permits them to be used as reference surfaces for setups Clamp work to angle plate so two adjacent sides ground square without moving workpiece13Setting Up the Workpiece Clean and remove all burrs from workpiece, angle plate, and magnetic chuck Place piece of paper slightly larger than angle plate on magnetic chuck Place one end of angle plate on paper Place flat-ground surface of workpiece against angle plate so top and one edge of work project 12 in. beyond edges of angle plate14 Hold work firmly against angle plate and turn on magnetic chuck Clamp work to angle plate and set clamps so they will not interfere with grinding operation Turn off magnetic chuck and carefully place base of angle plate on magnetic chuck Carefully fasten two more clamps on end of workpiece to hold work securely15Grinding Edges of Workpiece Square and Parallel Raise wheelhead so it is about 12 in. above top of work Set table reverse dogs so each end of work clears grinding wheel by about 1 in. With work under center of wheel, turn crossfeed handle until about 18 in. of wheel edge overlaps edge of work16 Start grinding wheel and lower wheelhead until wheel just sparks work Move work clear of wheel with crossfeed handle Raise wheel about .005 to .010 in. in case wheel has been set to low spot on work Check for high spots by feeding table by hand so entire length and width of work passes under wheel17 Engage table reverse lever and grind surface until all marks removed Depth of cut for roughing cuts .001 to .003 in. Depth of cut for finishing cuts .0005 to .001 in. Stop machine and remove clamps from right-hand end of work Turn off magnetic chuck and remove angle plate and workpiece as one unit Clean chuck and angle plate18 Place angle plate (with attached workpiece) on end, with surface to be ground at top Fasten two clamps to right-hand side of workpiece and angle plate Remove original clamps from top of setup Repeat steps 1 to 8 and grind second edge Remove assembly from chuck and remove workpiece from angle plate19Grinding the Third and Fourth Edges First two edges used as reference surfaces to grind other two sides Clean workpiece, angle plate, and magnetic chuck thoroughly and remove any burrs Place clean piece of paper on magnetic chuck20 Place ground edge of workpiece on paper If work 1 in. thick and long enough to span three magnetic poles on chuck, and no more than 2 in. high, no angle plate required If work less than 1 in. thick and does not span three magnetic poles, fastened to angle plate Place ground edge on paper and place angle plate no higher than workpiece against workpiece Turn on chuck and clamp work to angle plate Grind third edge to required size Repeat operations 1 to 3 and grind 4th edge21Grinding a Flat Surface with a CBN Wheel Grind hardened tool and die steels more efficiently than aluminum oxide wheels Increase productivity, improve work quality, and reduce grinding costsWear slow, uniform and life longNot necessary to dress wheel frequently Grind cool so stay sharp longer22Conditioning CBN Wheels For best performance, important they are conditioned (trued and dressed ) properly TruingOperation of making grinding wheel round and concentric with spindle axisUsually leaves grinding surface smooth DressingOperation of removing some of bond material from surface of trued wheel to expose abrasive crystals and allow wheel to cut23Properties of a Trued and Dressed Wheel Produce accurate workpieces and good surface finish Use minimum of grinding power Produce work without burn, surface damage, or chatter marks Increase material-removal rates and lower grinding costs24Procedure for Truing a CBN Wheel Example assumes use of an impregnated diamond wheel to true SBN resin-bond (100% concentration) wheel Mount CBN wheel on grinder, snug up flange nut, and indicate wheel circumference to within .001 in. or less runout Tighten flange nut securely25 Clean magnetic chuck and place diamond holder on left-hand side of chuck Cover as many magnetic inserts as possible Energize chuck Adjust grinder table to locate diamond nib about 12 in. to left of wheel centerline Lock table in position Lower wheelhead by hand until just touches piece of paper held between wheel and diamond26 Turn grinder crossfeed handle so diamond clears edge of wheel Lightly coat wheel surface to be trued with wax marking crayon Start grinder spindle and feed wheelhead down in .0004 in. increments until contact made with diamond Direct coolant to wheel-diamond interface Feed diamond across wheel face at 3 to 12 in./min C