Screw vibration assisted tapping device

Abstract

A vibration assisted tapping device includes an elastic frame for translating axial vibration to a vibration having both axial and torsional components. The elastic frame has flexural members that connect an upper plate to a lower plate with a vibratory actuator preloaded therebetween. The flexural members are inclined relative to an axis of the frame in a direction calculated to result in translated vibration substantially aligned with the lead angle of the thread being cut. Also disclosed is an automated system for applying different vibration patterns to the tap/workpiece interface during tapping and for recording the tapping torque associated with each vibration pattern. The disclosed system permits identification of the vibration frequency and amplitude that results in the greatest reduction in tapping torque. The automated system may be configured as an adaptive machine tool to first identify and then apply the optimum vibration pattern.

What is claimed is:  
     
         1 . A screw-vibration assisted tapping device for tapping threads having a lead angle, said vibration assisted tapping device comprising: 
 an upper plate for supporting a workpiece or tap;    a lower plate axially spaced from said upper plate;    a vibratory actuator fixed to one of said upper or lower plates and arranged to exert a reciprocal axial vibration on the other of said upper or lower plate; and    a plurality of flexural members connecting said upper plate to said lower plate, each said flexural member inclined relative to a longitudinal axis at an angle equal to or greater than the lead angle of the threads to be tapped,    wherein the reciprocal axial vibration is translated into a screw-vibration having axial and torsional elements.    
     
     
         2 . The screw-vibration assisted tapping device of  claim 1 , wherein said upper plate, lower plate and plurality of flexural members are formed from a single piece of metal.  
     
     
         3 . The screw-vibration assisted tapping device of  claim 1 , wherein said vibratory actuator is a piezoelectric actuator.  
     
     
         4 . The screw-vibration assisted tapping device of  claim 1 , wherein said vibration has a frequency of between approximately 400 Hz and approximately 800 Hz.  
     
     
         5 . The screw-vibration assisted tapping device of  claim 1 , wherein said vibratory actuator has a first axial stiffness and said upper plate, lower plate and flexural members are connected to form an assembly with a second axial stiffness of approximately equal to said first axial stiffness.  
     
     
         6 . The screw-vibration assisted tapping device of  claim 1 , wherein the plurality of flexural members comprise six or more flexural members integrally connecting the upper plate to the lower plate.  
     
     
         7 . The screw-vibration assisted tapping device of  claim 6 , wherein the flexural members are arranged around the periphery of said upper and lower plates and the vibratory actuator is arranged along the axis of the device.  
     
     
         8 . The screw-vibration assisted tapping device of  claim 6 , wherein said flexural members are angled such that the motion induced in the plate supporting the workpiece or tap is substantially aligned with a helix defined by the thread to be cut.  
     
     
         9 . An adaptive machine tool comprising: 
 a vibration assisted cutting tool, said vibration assisted cutting tool having a vibration pattern comprising a frequency and an amplitude that are variable in response to a driving signal;    a sensor for measuring the specific energy of material removal by the vibration assisted cutting tool; and    a computer programmed to apply a plurality of driving signals to said vibration assisted cutting tool to produce a plurality of vibration patterns with different frequencies and/or amplitudes, said computer further programmed to record the specific energy of material removal for each of said plurality of vibration patterns,    wherein said computer is programmed to identify the vibration pattern that has the smallest specific energy of material removal and to apply that vibration pattern to the vibration assisted cutting tool.    
     
     
         10 . A method for optimizing the vibration assistance applied to a tapping operation comprising: 
 applying a plurality of vibration patterns to a tap/workpiece interface of the tapping operation, each vibration pattern comprising a vibration frequency, a vibration amplitude and a vibration direction, said plurality of vibration patterns comprising a stepwise decrease or increase in the vibration frequency and/or vibration amplitude over a range of vibration directions centered on a lead angle of the thread being tapped;    recording torque data comprising a tapping torque associated with each said vibration pattern; and    using the torque data to identify the optimum vibration frequency and vibration amplitude for the operation by identifying the vibration pattern or patterns associated with the lowest tapping torque.    
     
     
         11 . A screw-vibration assisted device for performing drilling, wrenching or other machining process having a lead angle, said vibration assisted device comprising: 
 an upper plate for supporting a workpiece;    a lower plate axially spaced from said upper plate;    a vibratory actuator fixed to one of said upper or lower plates and arranged to exert a reciprocal axial vibration on the other of said upper or lower plate; and    a plurality of flexural members connecting said upper plate to said lower plate, each said flexural member inclined relative to a longitudinal axis at an angle equal to or greater than the lead angle appropriate for the process to be performed,    wherein the reciprocal axial vibration is translated into a screw-vibration having axial and torsional elements.    
     
     
         12 . The screw-vibration assisted tapping device of  claim 1 , wherein said vibratory actuator is selected from the group comprising ultrasonic drives, magnetostrictive drives, electrostrictive drives and mechanical drives.  
     
     
         13 . The screw-vibration assisted device of  claim 11 , wherein said vibratory actuator is selected from the group comprising ultrasonic drives, hydraulic drives, magnetostrictive drives, electrostrictive drives and mechanical drives.  
     
     
         14 . The screw-vibration assisted tapping device of  claim 1 , wherein the plurality of flexural members comprise more than three flexural members integrally connecting the upper plate to the lower plate.  
     
     
         15 . The screw-vibration assisted device of  claim 11 , wherein the plurality of flexural members comprise more than three flexural members integrally connecting the upper plate to the lower plate.  
     
     
         16 . The adaptive machine tool of  claim 9  wherein said vibration assisted cutting tool is incorporated into a workpiece support element such as a work table or a work surface.  
     
     
         17 . The adaptive machine tool of  claim 9  wherein said vibration assisted cutting tool is incorporated into a holder element such as a tool holder, chuck or collet.