An automated system for non-destructive inspection of a weld through the use of ultrasonic waves produced by an electromagnetic acoustic transducer (EMAT) The system includes: a computer control unit (31); a transport apparatus (32) having a first EMAT (24) for producing an ultrasonic SH shear wave and a second EMAT (26) for receiving an ultrasonic SH shear wave reflected from a butt weld (22); a data acquisition unit (33) and a calibration means (38) The computer control unit, which is in electrical communication with a welding apparatus, the transport apparatus and the data acquisition unit, coordinates the weld test with completion of the weld An edge detection sensor, which is affixed to the transport apparatus is used to automatically position the transport apparatus for a weld scan and to signal completion of the scan The system includes an electrostatic shield to protect the second EMAT from electromagnetic and radio frequency interference Other new and improved electronic features permit certain system components to be remotely located from the transport apparatus and the welding apparatus

Automated butt weld inspection system

A method of resistance spot welding is disclosed. The method includes providing a first metallic workpiece having a primary surface and a second metallic workpiece having a secondary surface. The method also includes positioning the primary surface into physical contact with a first electrode and a second electrode into physical contact with the secondary surface. The second electrode includes a secondary actuator. The method also includes measuring contact force between the first electrode and the second electrode, and initiating a current through the first electrode when the contact force reaches a preselected force value. The method also includes forming a weld nugget in at least the second workpiece and a depression in the primary surface of the first workpiece, and controlling the location of the weld nugget by using two different classes of electrodes. The depression in the primary surface is substantially undetectable by a visual examination. A resistance spot welding system is also disclosed. The system includes a fast follow-up electrode of one RWMA class mounted to one end of a pivot arm for squeezing a primary workpiece and a secondary workpiece together and for following the surface of the secondary workpiece as the weld is formed. A stationary electrode of another RWMA class is positioned opposite the fast follow-up electrode. A sensor is coupled to the stationary electrode for directly measuring the contact force between the fast follow-up electrode and the stationary electrode. A measuring instrument for measuring a depression formed in the primary surface.

Welding system and method

A process for on-line assessment of resistance weldings uses an ultrasonic source which impinges shear waves onto the weld region and an ultrasound receiver. The time at which the melting point of the weld material is reached and a weld nugget begins to form is determined from the output signal of the ultrasound receiver. The volume V of the weld nugget is calculated during the welding operation from the diminishment of shear waves after having reached the melting temperature.

Process for assessing welded joints

A method and apparatus for ultrasonic in-process monitoring and feedback of resistance spot weld quality uses at least one transducer located in the electrode assembly transmitting through a weld tip into an underway weld Analysis of the spectrum of ultrasonic waves provides the operator with an indication of the size, thickness, location, dynamics of formation and quality of the spot weld The method presents a fundamentally new physical approach to the characterization of the spot weld quality Together with transmission mode it includes new modes of operation of ultrasonic probes such as a reflection mode and simultaneous use of transmission and reflection modes, and a new physical interpretation of the signal analysis results

Ultrasonic in-process monitoring and feedback of resistance spot weld quality

Spot welding is one of the most important technologies for joining sheet metal While there are lot of approaches to non-destructive testing, quality assurance still mainly relies on welding parameter monitoring and destructive testing, leading to significant failure rates In this paper an approach to spot weld testing using flash thermography is presented The main focus of attention is on the identification of two typical error classes: stick welds and welds at the splash limit Besides investigating the principal feasibility of thermography for zinc plated samples the results of a series test of spot welds joining 1 mm thick TRIP steel are shown Based upon these results a statistical criterion is developed which allows a reliable classification of the named error classes

Thermographic testing of spot welds

Ultrasonic transducers spring biased into seating engagement in a pair of opposed spot welding tips transmit and receive ultrasonic waves and associated circuitry measures the time of flight between the transducers which is a function of tip separation, workpiece temperature and nugget size which are indicators of the progress of a weld. The rate of change of flight time is measured and the weld current is adjusted early in the weld cycle to maintain a preset rate of weld growth. The weld current is terminated later in the cycle if the transit time rate falls below another preset value. Otherwise the weld current and termination time follow a standard schedule.

Ultrasonic method and apparatus for spot weld control

Ultrasonic transducers (28) spring biased (36) into seating engagement in a pair of opposed spot welding tips (24) transmit and receive ultrasonic waves and associated circuitry (16,18) measures the time of flight between the transducers which is a function of tip separation, workpiece temperature and weld nugget size which are indicators of the progress of a weld. The rate of change of flight time is measured and the weld current is adjusted early in the weld cycle to maintain a preset rate of weld growth. The weld current is terminated later in the cycle if the transit time rate falls below another preset value. Otherwise the weld current and termination time follow a standard schedule.

John J. Ross

Papers

Ultrasonic method and apparatus for spot weld control

Method and apparatus for spot weld control

Method and device for controlling ultrasonic spot welding