AE07.pdf

1 the frequency bandwidth is wide 2 resonant

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1. The frequency bandwidth is wide. 2. Resonant frequency and flat band frequency transducers can be used in a wide bandwidth, such as 0.1 to 1.0 MHz. 3. The frequency characteristics of the acoustic emission signal are dominated by the frequency characteristics of the acoustic emission transducers. The transducer placement in acoustic emission testing is also a major concern in grinding applications. Except for surface grinding and many other machining processes, both the cutting tool (grinding wheel) and workpiece are in rotation in the grinding process. The rotation of the spindles makes it difficult to attach the transducer to a grinding area. If a transducer is placed in a stationary location, such as a bearing supporter, the bearings or gears generate a lot of noise. The actual acoustic emission signal generated during grinding is usually smaller than the background bearing noise and is hard to distinguish from noise. Moreover, a stationary place where a transducer can be attached is probably too far from the grinding zone and signal attenuation is significant. Alternatively, other noncontact transducers, such as noncontact signal transmitting transducers and coolant coupled transducers, have been used. The coolant coupled transducer seems to be most viable for acoustic emission detection during grinding and dressing. During acoustic emission testing, a coolant fitting transducer is not directly in contact with either the grinding wheel or the workpiece. Instead, it serves as a part of the coolant system of the grinding machine. The coolant jet from the T fitting directs to either the workpiece or the grinding wheel. It not only plays a role for cooling the grinding zone but also the coolant jet serves as a waveguide, creating a path that allows the acoustic emission signal to reach the acoustic emission test transducer inside the T fitting. There are several advantages of such a configuration: 1. It is convenient to place the transducer close to the grinding and dressing zone. No machine retrofitting work is needed for transducer installation. 2. Noises induced by dynamic movement components, such as bearings, gears, belts and lead screws, can be greatly reduced. 3. The distance from the grinding zone to the transducer location is fixed so that the wave traveling distance stays constant, unaffected by changes in the relative position of wheel and workpiece. 4. More importantly, this configuration can be used in many kinds of grinding and dressing processes where a contact transducer cannot get a high enough ratio of signal to noise because of the influence of rotary parts (wheel, dresser and workpiece) in cylindrical grinding (internal, external and contour), centerless grinding and rotary tool dressing. Figure 32 shows some examples of how coolant coupled transducers are applied to different grinding and dressing processes (internal grinding on Figs. 32a and 32b, centerless grinding on Fig. 32c, external grinding on Fig. 32d, single-diamond tool dressing on Fig. 32e, contour tool dressing on Fig. 32f, rotary diamond truing on Fig. 32g and rotary diamond dressing on
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