Understanding Grinding Fluid

Fluid use is very important in the grinding process because it reduces the effects of friction, removes heat from the work zone, and increases material removal. Most important, grinding fluid increases the material removal rate without increasing the damage to the surface of the workpiece.
Many cutting fluids are available today, so it is wise to choose the best option on the basis of application and material. With the goals being productivity improvement and cost reduction, shops must reduce scrap and create good, final parts. Properly selecting and applying grinding fluids can help manufacturers reach these goals. “The fluid reduces friction by lubrication, either by chemical lubricity or by the use of an oil,” explained Master Chemical Corp. District Sales Manager for Canada David Foster. “The lubricity can be in the form of a lubricant that decreases the friction between the surfaces or it can act as a contaminant and reduce the shear stress in cutting.”
Grinding fluid also acts as a coolant, and even oil has some heat-transfer capability, but not as much as water-based coolants. “Material removal is increased by the reduction in specific energy, which allows the stock removal rate to go up without increasing the surface damage to the workpiece,” said Foster. Because the grinding process creates a lot of heat, flood coolant is most appropriate. However, it is equally important that the fluid be delivered where it is needed the most: at the point of cut.
“The application [method] of the fluid is very important; it should apply the fluid to the interface where it is needed the most,” said Foster. “Fluid application is not just a matter of bathing the area in fluid and assuming that it will be in the right place. The application method has to be engineered properly to ensure that the fluid is applied properly.” Good final part quality relies on the fluid getting to the point of cut, in the correct volume, and at the proper velocity. Proper delivery allows the fluid to wet the wheel and the workpiece rapidly while providing the correct lubricity.
Examining the contact point is also important. The arc of contact in grinding is the portion of the circumference of the grinding wheel that is in contact with the workpiece. According to Foster, the longer the arc of contact, the more critical wetting becomes. “The correct velocity also is very important. A lot of people will flood the grinding area, but this is actually not beneficial. The coolant should be moving at least as fast as the tool is moving at the point of cut for maximum benefit,” said Foster.