Sonotrode for ultrasonic machining device
BACKGROUND OF THE INVENTION 
     Ultrasonic machining devices usually comprise a vibration exciter, for example, a piezoelectric vibration exciter, a coaxial sonotrode, and a tool that is also coaxial. The sonotrode is a rotationally symmetrical body and acts as a spring-mass system. By means of the vibration exciter the sonotrode is excited to longitudinal autooscillators, which form around a nodal surface. Frequently the sonotrode has on the input side a larger cross section than on the output side. Thus, it acts as an amplitude intensifier. 
     The known ultrasonic devices are relatively long in the axial direction of vibration, so that workpieces that are difficult to access are often hard to machine. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the problem of providing a sonotrode which enables a shorter overall length in the direction of vibration of the tool. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional view of a sonotrode with attached vibration exciter and tool. 
     FIG. 2 is a representation of the vibration of the sonotrode. 
     FIG. 3 is a side view of the sonotrode, and 
     FIG. 4 is a variation of the sonotrode. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The ultrasonic machining device according to FIG. 1 comprises a vibration exciter 1 with a piezo quartz thickness vibrator 2 and two metal cylinders 3 whose faces are connected to the vibrator, an amplifier or booster 4, a sonotrode 5 and a tool 6. The vibration exciter is cylindrical and performs harmonic longitudinal vibrations along its axis 10 with a nodal surface in its axial longitudinal center. The maximum amplitude occurs at the end faces of the vibration exciter 1. The thicker face of the coaxial amplifier 4, which is designed as a body of revolution, is attached to the one end face. The amplifier 4 tapers off in the direction of its other face and also oscillates at its natural frequency longitudinally around a nodal surface. The vibration amplitude is amplified by means of the tapering. 
     The sonotrode 5 is designed as an annular bending vibrator with a cylindrical outer surface 15, a coaxial, cylindrical inner surface 16, and an axis 11. The thinner end of the amplifier 4 is screwed into an input 17 of the sonotrode, the input being designed as an internal thread. The input 17 is coaxial to the axis 10 and radial to the cylindrical outer surface 15. The output 18 of the sonotrode 5 is designed as a bore, in which the tool 6, which is tubular here, is firmly connected (e.g. soldered in). The output axis 19 is also radial and intersects the input axis 10 forming an angle of about 90°. A coaxial tube 20, which communicates with a bore 21, penetrating the vibration exciter 1 and the amplifier 4, is moulded to the sonotrode. The tube 20 is connected to the axial bore 23 of the tool 6 by way of a hose 22. During ultrasonic machining, abradant can be drawn off through the bore 21, the hose 22 and the hollow tool 6 from the face 24 of the tool 6, acting as the working face, or the abradant can be supplied to the face 24. 
     The natural bending frequency of the sonotrode 5 is equal to the natural longitudinal vibration frequency of the amplifier 4 and the vibration exciter 1. The sonotrode vibrates around four nodal points 33 to 36. FIG. 2 shows the vibration of the neutral fibers of the sonotrode. When the cross section of the sonotrode 5 is the same over its entire circumference, the output amplitude 31 of the sonotrode vibration is equal to the input amplitude 30 (except for friction loss). As is evident, the output amplitude is at its maximum when the output axis 19 is at a right angle to the input axis 10, although the output amplitude is still near the maximum value when the angle deviates slightly, e.g. ±20° between 70° and 110°. 
     It is especially advantageous if the cross section of the sonotrode 5 increases from the output 18 in the direction of both sides up to the diametrically opposite point, as depicted in FIG. 3. The sonotrode thus projects conically in the direction of the input axis 10. With such a configuration the sonotrode also acts as an amplifier, and the output amplitude 31 is greater than the input amplitude 30. 
     FIG. 4 shows a variation where the tool 6 is detachably connected to the sonotrode, e.g. screwed from the top into a female thread 18&#39;. As is apparent from FIG. 4, abradant can also be supplied by way of an additional bore 40 in the amplifier 4, another hose 41 and a ring nozzle 42 enveloping the tool 6. 
     The goal is reached with the sonotrode 5 designed according to the invention as an annular bending vibrator that the tool 6 vibrates at an angle to the axis 10 of the vibration exciter 1 and the amplifier 4. Thus, even difficult to access workpieces can be machined efficiently with ultrasonics. 
     If the tool 6 is also to vibrate laterally relative to the longitudinal vibrations, it can be bent away from its axis. 
     Under some circumstances other natural bending vibrations with more than four nodes are also suitable for the sonotrode 5. In this case the angle at which the axes 10, 19 intersect is not 90°. For six nodes, for example, the axes 10, 19 could intersect a about 120°.