Surface conditioning of a grinding wheel generally includes the two requirements of truing and dressing. Dressing replaces worn (dulled) cutting edges with sharp edges by fracturing the worn grains and regenerates a wheel face loaded with swarf by removing a layer from the face with a dressing tool. Dressing a superabrasive wheel is much more difficult than dressing a conventional wheel and is not always possible. A special process known as ELID was introduced to allow the grinding of hard ceramics and is discussed in more detail in this chapter.
The necessity for dressing increases costs in grinding. In addition, the loss of abrasive particles from the wheel surface is expensive due to the high cost of superabrasive wheels and the associated loss of wheel life. Consequently, it is very important to use superabrasive wheels effectively to minimize waste of the wheel as well as to reduce dressing time.
14.1.4 ELID G RINDING
The new ELID technique has attracted special interest because it eliminates conventional dressing times while improving the quality of ground surfaces. In ELID grinding, the grinding wheel is connected to a positive electrode and a negative electrode is mounted in proximity to the wheel with a gap of 0.1 to 0.3 mm. During predressing or grinding, a power source provides a pulsed direct current.
The gap is filled with an electrolyte grinding fluid to obtain an electrochemical action. The direct current pulse ionizes and removes conductive bond material. As the action proceeds, the surface of the wheel becomes coated with a nonconducting layer such as iron oxide or hydroxide. The nonconducting layer has the effect of preventing excessive electrolytic action. The rate of electrolytic action is an essential aspect of process control to ensure adequate protrusion of the grains while avoiding excessive wheel wear.
14.1.5 Advantages of ELID
Advantages of ELID include:
• Elimination of dressing time by in-process dressing.
• Elimination of the need for conventional dressing tools and, hence, reduced dressing costs.
• Elimination of physical or mechanical damage to the dressed grains.
• A significant reduction in normal grinding force with ELID grinding compared with conventional grinding.
• Extremely smooth surfaces can be achieved by use of ultrafine abrasives.
• High precision parts can be achieved with excellent process efficiency.