Instrumented spot welding electrode

• US 4,472,620 A
• Filed: 04/01/1983
• Issued: 09/18/1984
• Est. Priority Date: 04/01/1983
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Nied, Herman A.
• Primary Examiner(s): Shaw, C. C.
• Application Number:
  US06/481,171
• Time in Patent Office: 536 Days
• Field of Search: 219/109, 219/110, 219/119, 219/120
• US Class Current: 219/120
• CPC Class Codes: B23K 11/3009 Pressure electrodes
• CPC Class Codes: B23K 35/0205 Non-consumable electrodes; C-electrodes

Abstract

An instrumented spot welding electrode significantly improves the weld quality available from production resistance spot welding machines by providing real time measurements of key multivariable resistance welding parameters. The real time data provided may be used as inputs to adaptively control welding machines and dynamically adjust welding system operation responsive to the sensed variables. A number of sensors are positioned within a cavity specially formed into a water cooled electrode tip to obtain the desired measurements while being protected against physical damage. The sensors are advantageously placed in good thermal and electrical contact with a plug element which bears directly on the workpieces being welded to enhance the accuracy of the sensed variables. This specially configured and instrumented sensor cavity is ideally suited for use with all end types of electrodes including spherical, truncated, offset, flat and the like.

Claims

1. An instrumented resistance spot welding electrode comprising:

(a) a body member terminating in an end face, said body member having a central elongated longitudinal channel extending along its axis and through the end face;

(b) a high thermal diffusivity, low electrical resistivity plug member fitted into said channel at said end face location;

(c) means for thermally and electrically insulating said plug member from the inner walls of said channel; and

(d) at least two sensing means disposed in said channel and in contact with an interior portion of said plug for simultaneously sensing at least two predetermined resistance welding variables, wherein at least one of said sensing means comprises a piezoelectric device in pressure bearing relationship with said plug within said channel for providing pressure data indicative of the compression load applied by said electrode on a workpiece in contact with said end face during a weld operation.

2. An instrumented resistance spot welding electrode comprising:

(a) a body member terminating in an end face, said body member having a central elongated longitudinal channel extending along its axis and through the end face;

(b) a high thermal diffusivity, low electrical resistivity plug member fitted into said channel at said end face location;

(c) means for thermally and electrically insulating said plug member from the inner walls of said channel; and

(d) at least two sensing means disposed in said channel and in contact with an interior portion of said plug for simultaneously sensing at least two predetermined resistance welding variables, wherein at least one of said sensing means comprises a piezoresistive device in pressure bearing relationship with said plug within said channel for providing pressure data indicative of the compression load applied by said electrode on a workpiece in contact with said end face during a weld operation.

3. A multivariable resistance spot welding electrode of the water cooled type comprising:

(a) a copper-based body member terminating in an end face and having a central elongated longitudinal channel extending along its axis and through the end face;

(b) a high thermal diffusivity, low electrical resistance plug member fitted into said channel at said end face location and thermally and electrically insulated from the inner walls of the channel by an insulating member;

(c) a plurality of sensing means in said channel and in contact with an interior portion of said plug member for simultaneously monitoring at least two predetermined resistance welding variables, said sensing means comprising;

(i) a first sensor including an electrical conductor in electrical contact with said plug for providing a means of deriving data indicative of the voltage gradient in a workpiece in contact with said plug exterior surface during a weld operation;

(ii) a thermocouple device placed in contact with an interior surface of said plug for providing temperature data indicative of the surface temperature of a workpiece in contact with an exterior surface portion of said plug during a weld operation;

(iii) a piezoelectric device in pressure bearing relationship with said plug within said channel for providing pressure data indicative of the compression load applied by said electrode on a workpiece in contact with said end face during a weld operation; and

(iv) a Hall effect device in said channel for providing magnetic field strength data indicative of the current flow through said electrode during a resistance welding operation.

4. The instrumented electrode of claim 3 wherein said electrode further comprises conductors connected to said sensing means and a radial channel connecting said longitudinal channel with the exterior of said electrode body for routing said conductors externally of said electrode.

5. An instrumented multivariable resistance spot welding electrode comprising:

(a) a copper-based body member having chambers for water cooling, an end face, and a central elongated longitudinal channel extending along its axis and through said end face;

(b) a high thermal diffusivity, low electrical resistivity plug member of silver-based material fitted into said channel and means for thermally and electrically insulating said plug member from the inner walls of said channel, said plug member having a first surface wholly interior to said channel, a second surface insulated from the inner walls of said channel, and a third surface forming an exterior surface portion of said end face and conforming to the shape of said end face; and

(c) a plurality of sensing means disposed in said channel and in contact with an interior portion of said plug member for simultaneously sensing resistance welding variables, said sensing means comprising;

(i) a first sensor including an electrical conductor in contact with said plug and providing a means for deriving data indicative of the voltage gradient in a workpiece in contact with said exterior surface portion of said plug during a resistance weld operation; and

(ii) a second sensor comprising at least one thermocouple device in contact with said plug interior surface for providing temperature data indicative of the surface temperature of the workpiece.

6. The instrumented electrode of claim 5 wherein said sensing means further comprises a piezoelectric device in pressure bearing relationship with said second surface of said plug for providing pressure data indicative of the compression load applied by said electrode on a workpiece in contact with said end face during a resistance weld operation.

7. The instrumented electrode of claim 5 wherein said sensing means further comprises a piezoresistive device in pressure bearing relationship with said second surface of said plug for providing pressure data indicative of the compression load applied by said electrode on a workpiece in contact with said end face during a resistance weld operation.

8. The instrumented electrode of claim 5 wherein said sensing means further comprises a Hall effect device in said channel for providing magnetic field strength indicative of the current flow through said electrode during a resistance welding operation, said Hall effect device being mounted on an axis displaced from the central longitudinal axis of the electrode.