Tech Talk
What is “Angle Approach Grinding”?
Situations often arise where grinding of a side face requires both a fine finish and a precise angle, face to diameter, relationship. It is not good practice to grind with the side of a parallel grinding wheel unless the side face of the grinding wheel is relieved. Therefore, angle approach grinding is generally used where the wheelhead of the machine is angled and dressed to grind the correct shape of two or more angled faces. The grinding wheel is plunged at an angle into the workpiece, achieving the final size on both the face and diameter with precise correlation of those surfaces. The process is very fast and accurate.
There are many advantages of angle approach grinding. Two or more surfaces may be completed more efficiently and in one plunge. The grinding marks on the face of the shoulder will also be concentric. This is desirable because seal faces with grinding marks, which are anything but concentric, aggravate a seal and cause heavy wear. Because the grinding wheel is grinding with its periphery, there is no side grinding/rubbing and, therefore, less chance of burning on the face. The large area of contact between the face and the diameter also tends to dampen any regenerative chatter which might occur. Angle ground is a splined shaft or has a key-way to interrupt the cut. The splines, during a combination angle approach grind on a face and splined shaft, will induce a pulse into the system, which will transfer into the surface of the face grind as noticeable radial marks. Such a grind is best performed in two separate grinding operations, first the face and then the splined shaft.
A common problem in cylindrical grinding is the occurrence of regenerative chatter, due to either the lack of rigidity of the machine system or the lack of rigidity of the workpiece. Regenerative chatter is a vibration due to the cyclic variation in the grinding wheel depth of cut, initiated by a machine vibration which occurs at a natural frequency of the machining system. Once the grinding wheel/workpiece system begins to vibrate at a resonant frequency, the grinding wheel and workpiece will cycle radially towards and away from one another. The motion creates a wave pattern around the workpiece which corresponds to the frequency of vibration. The wave pattern on the workpiece, caused the original vibration, produces cyclic forces on the system. The cyclic forces occur at the critical frequency initiated by the varying depth of cut of the wave pattern. As the natural frequency of vibration is regenerated by the crests and valleys, its amplitude increases and the machine can be heard and, in some severe cases, seen to vibrate. Once regenerative chatter has begun, it is extremely difficult to eliminate.
