Causes and prevention of surface ripples in surface grinding
Surface grinding is mainly used for grinding plane and groove on surface grinder. There are two kinds of surface grinding: the grinding process with grinding wheel OD face is called peripheral grinding, generally on horizontal shaft surface grinder. When using form grinding wheel can also process various shaped surface; The grinding process with the wheel end face is called end face grinding, generally on vertical shaft surface grinder.
The surface grinding can get very good flatness, parallelism and roughness. If there are mistakes in the selection of grinding method, grinding wheel and grinding allowance, the processing quality will drop sharply and even waste products will appear. The appearance of surface ripples will greatly affect the surface roughness and aesthetic degree of the workpiece. Therefore, how to prevent and eliminate the surface schrathes is very important when grinding the workpiece.
The surface ripples types:
1.Equidistant straight line ripples
The straight line ripples with equal distance distribution on the surface of the workpiece during surface grinding show that there is forced vibration, and the vibration source mainly comes from the unbalance of grinding wheel or motor.We need to check the principal axis balance and the clamping with grinding wheel.
When the wheel lost cutting ability, it’s difficult to remove material freely. The grinding wheel will push workpiece surface but not cut. It will also get such ripples. We need to re-dress the wheel until feel coarse grainy by finger.
In surface grinding, if there is a single ripple on both sides of the workpiece or on one side, it means that impact occurs when the worktable changes direction,which makes the column of grinder shake. When the worktable is moved backward, the workpiece enters grinding again. At this time, the column is shaking, so there is a single ripple defect on both sides or one side of the workpiece. Therefore, the position of reversing block should be adjusted to make it appropriate, and the screw of reversing throttle valve should be adjusted to reduce the reversing impact of worktable.
When grinding the surface, if rhombic ripple appears, it means that the grinding wheel and the workpiece have vibration. Because the ratio of the number of revolutions per minute of the grinding wheel to the number of strokes per minute of the worktable is not an integer in most cases, the diamond shaped ripple is more likely to appear than the equidistant straight ripple. Therefore, the rigidity of the grinding wheel should be increased and the vertical feed rate should be appropriately reduced.
During surface grinding, the surface of the workpiece may be left with abrasive debris, or the debris and sand particles falling from the cover of the grinding wheel fall into the workpiece and move together with the grinding wheel,resulting in scuffing and scratching. The surface scratch can be prevented by improving the coolant nozzle and cleaning the wheel cover frequently.
In addition, in order to effectively prevent scuffing, reverse grinding is not suitable for plane creep feed finish grinding. If reverse grinding is used,grinding fluid is not easy to enter into the grinding area, and the detached abrasive particles will scratch the machined surface. Therefore, the smooth grinding should be adopted in the fine grinding. The cooling conditions are good, and the grinding fluid can be brought into the grinding area smoothly.
When the abrasive particles fall off, they will only fall on the machined surface and be washed away by the grinding fluid The machined surface will be scratched and a lower surface roughness will be obtained.
In addition, in order to make the grinding fluid enter into the grinding area without shunting during grinding, so as to prevent the workpiece from being burned, a guide plate should be installed at the position close to the part at the easy burn end to guide the flow. During the forward grinding, there is sufficient grinding fluid in the grinding area at the beginning of grinding because the surface to be machined can guide the flow. When the workpiece is grinded to the end, the grinding fluid begins to flow, resulting in burn and scuffing due to the lack of grinding fluid in the grinding area.
Therefore, the guide plate should be installed at the end of the workpiece during forward grinding. When reverse grinding, the guide plate should be installed at the beginning of the workpiece to prevent the workpiece from burning and scuffing.