Tech Talk
What is “Plunge Cylindrical Grinding”?
Plunge grinding is a cylindrical grinding process where the grinding wheel plunges into the workpiece at right angles to the axis of the part and forms a shape on the cyclinder. Long and slender parts generally require special handling and fixturing, as the normal forces exerted on the workpiece during plunge form grinding are extremely high, high enough to deflect the workpiece and, in the extreme, deflect the machine tool. Therefore, it is necessary to use steady-rests to support the workpiece against the machining forces in order to minimize part deflection.
The center type cylindrical grinder is designed with four basic movements: the rotation of the grinding wheel, the rotation of the workpiece, the longitudinal traverse of the workpiece across the grinding wheel, and the infeed of the grinding wheel in either plunge or intermittent feed. These machines are not considered high-stock removal rate machines; they are precision finishing machines. However, as improvements are made in their design to improve rigidity and dynamic stability, their capability to remove large volumes of stock are creating new opportunities. One plunge grinding operation may take the place of a rough turning and finish grinding operation. A good example is the grinding of very delicate seal grooves. Turning such delicate seals generally causes distortion and very poor surface integrity, so the surfaces are generally finish ground. Plunge grinding can achieve both the full form seal in one plunge with no distortion, as the grinding forces are radial, and a superior surface integrity, which is generally associated with precision grinding.
Steady rests are essential, especially when plunge grinding, or grinding flexible or delicate workpieces. The steady rest performs the function of supporting the workpiece while it is being ground.
Steady rests are used to support workpieces which have insufficient rigidity to produce satisfactory results in longitudinal, plunge, or internal grinding. Part deflection, due to the mass of the workpiece or the grinding forces, is counteracted by the support from the steady rest. A further function of steady rests is to prevent workpiece vibration and so eliminate chatter.
