Ultrasonic sensor for on-line detection of cutting tool insert failure

• US 5,777,231 A
• Filed: 10/24/1996
• Issued: 07/07/1998
• Est. Priority Date: 10/24/1996
• Status: Expired due to Fees

• Current Assignee: Mcmaster University
• Original Assignee: Mohamed A. Elbestawi, Narendra D. Patel
• Inventors: Elbestawi, Mohamed A., Patel, Narendra D.
• Primary Examiner(s): Oda, Christine K.
• Application Number:
  US08/735,648
• Time in Patent Office: 621 Days
• Field of Search: 73/597, 73/599, 73/629, 73/660, 73/104, 73/862.06, 364/474.17, 340/679, 340/680, 340/683
• US Class Current: 73/660
• CPC Class Codes: G01N 2291/011 Velocity or travel time
• CPC Class Codes: G01N 2291/015 Attenuation, scattering
• CPC Class Codes: G01N 2291/02881 Temperature
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/22 Details , e.g. general constructional or apparatus details
• CPC Class Codes: G01N 29/24 Probes transducers for acoustic waves B06B, G10K; for measuring G01H

Abstract

An on-line ultrasonic sensor for monitoring and sensing failure in a cutting tool insert. The preferred embodiment of the sensor includes a piezoelectric film of aluminum nitride (AlN) deposited onto a tool insert or tool insert seat with the AlN film electrically connected to a signal generator and detection circuitry. A voltage pulse is applied to the AlN film to generate ultrasonic signal pulses in the AlN film which are transmitted through a tool insert to the vicinity of the cutting edge of the tool insert during use. Back-reflected ultrasonic signals from the edge of the tool insert induce a voltage signal in the piezoelectric film which is analysed and compared to signals characteristic of undamaged tool inserts. Temperature increases, wear and various types of tool failure can be readily detected during use of the insert with the sensor.

Claims

1. A method for on-line monitoring a tool insert having an edge portion which contacts a workpiece during use, comprising:

a) producing ultrasonic signal pulses in a coating of piezoelectric material contacting a tool insert and directing the ultrasonic signal pulses through the tool insert toward said edge portion of the tool insert;

b) detecting ultrasonic signal pulses reflected from said edge portion of the tool insert back into the piezoelectric coating; and

c) comparing said ultrasonic signal pulses reflected from said edge portion of the tool insert to reference ultrasonic signal pulses reflected from said edge portion before the tool insert is initially contacted to said workpiece.

2. The method according to claim 1 wherein the step of detecting the ultrasonic signal pulses comprises measuring a transit time of each one of the ultrasonic signal pulses from a source electrode to said edge portion and back to said source electrode.

3. The method according to claim 1 wherein the step of detecting the ultrasonic signal pulses comprises measuring an amplitude of each one of the ultrasonic signal pulses.

4. The method according to claim 1 wherein said piezoelectric coating is a film of aluminum nitride (AlN) having substantially <

002>

crystal orientation.

5. The method according to claim 4 wherein said AlN film has a thickness in the range from about 20 μ

m to about 150 μ

m.

6. The method according to claim 2 wherein said reflected ultrasonic signal pulses are analyzed to determine the transit time of the ultrasonic signal pulses in use and comparing said transit time to the transit time for the reference ultrasonic signal pulses.

7. The method according to claim 3 wherein said reflected ultrasonic signal pulses are analyzed to determine its amplitude and comparing said amplitude to the amplitude for the reference ultrasonic signal pulses.

8. The method according to claim 4 wherein the AlN coating is grown on a surface of an insert seat to which the tool insert is clamped so that in use the AlN coating is sandwiched between the tool insert and the insert seat.

9. The method according to claim 4 wherein the AlN coating is grown on a surface of the tool insert which is adjacent to a surface of an insert seat on which the tool insert is clamped so that in use the AlN coating is sandwiched between the tool insert and the insert seat.

10. The method according to claim 5 wherein the ultrasonic signal pulses have a frequency in the range from about 30 MHZ to about 150 MHZ.

11. An on-line ultrasonic sensor for monitoring a tool insert, the tool insert having an edge portion for contacting a workpiece and being mountable in an insert holder, comprising:

a) a piezoelectric coating in contact with a portion of said tool insert spaced from said edge portion;

b) means for generating ultrasonic signal pulses in the piezoelectric coating, the ultrasonic signal pulses being directed through the tool insert substantially toward said edge portion of the tool insert which contacts said workpiece in use; and

c) means for detecting and analyzing ultrasonic signal pulses responsively reflected from said edge portion of the tool insert back through the tool insert into the piezoelectric coating.

12. The on-line sensor according to claim 11 wherein the piezoelectric coating is a film of aluminum nitride (AlN) having substantially <

002>

crystal orientation.

13. The on-line sensor according to claim 12 wherein said AlN film has a thickness in the range from about 20 μ

m to about 150 μ

m.

14. The on-line sensor according to claim 12 wherein said insert holder includes a seat, the tool insert being clamped onto the seat in the insert holder, and wherein the AlN coating is grown on a surface of the seat to which the tool insert is clamped in use so the AlN coating is sandwiched between the tool insert and the seat and contacts both.

15. The on-line sensor according to claim 14 wherein said means for generating said ultrasonic signal pulses includes a voltage generator electrically coupled to said AlN coating.

16. The on-line sensor according to claim 15 wherein in use said signal analyzing means includes means for measuring a transit time of the ultrasonic signal pulses from a source electrode to the edge portion and back to the source, and comparing said transit time to a transit time for reference ultrasonic signal pulses reflected from said edge portion before the tool insert is contacted to the workpiece.

17. The on-line sensor according to claim 15 wherein said signal analyzing means includes means for measuring an amplitude of the reflected ultrasonic signal pulses and comparing said amplitude to an amplitude for a reference ultrasonic signal pulse reflected from said edge portion before the tool insert is contacted to the workpiece.

18. The on-line sensor according to claim 12 wherein said insert holder includes a seat, the tool insert being clamped onto the seat in the insert holder, and wherein the AlN coating is grown on a surface of the tool insert which is adjacent to the seat so that the AlN coating is sandwiched between the tool insert and the seat and contacts both.

19. The on-line sensor according to claim 18 wherein said means for generating said ultrasonic signal pulses includes a voltage generator electrically coupled to said AlN coating.

20. The on-line sensor according to claim 19 wherein said signal analyzing means includes means for measuring a transit time of the ultrasonic signal pulse from a source electrode to the edge portion and back to the source and comparing said transit time to a transit time of a reference ultrasonic signal pulse reflected from said edge portion before the tool insert is contacted to the workpiece.

21. The on-line sensor according to claim 19 wherein said signal analyzing means includes means for measuring an amplitude of the reflected ultrasonic pulses and comparing said amplitude to an amplitude of at least one reference ultrasonic signal pulse reflected from said edge portion before the tool insert is contacted to the workpiece.