Apparatus and method for monitoring and evaluating weld quality

The method of controlling a stud welding process wherein a stud is initially raised above a metallic surface, an arc is generated between the stud and the metallic surface by the application of electrical power from a power supply through the stud to the metallic surface, and the stud is then lowered into a metallic pool that forms on the metallic surface from the heat generated by the applied electrical power, comprising the steps of:

• a) monitoring the current applied to the stud and producing a current signal related thereto;
• b) monitoring the voltage applied across the stud and metallic surface and producing a voltage signal related thereto;
• c) producing from said current and voltage signals a temperature signal related to the temperature of the metallic surface at the instant said stud is lowered into contact with the metallic pool during the welding process;
• and
• d) controlling the point in time during the welding process when the stud is lowered in accordance with said temperature signal.

A weld control circuit for controlling a weld process joining a first metallic member to a second metallic member at a weld zone, comprising:

• a power supply for supplying electrical power to said weld zone;
• a first circuit for producing an electrical temperature signal related to the temperature of said weld zone during the weld process;
• and
• a second circuit responsive to said temperature signal for producing an output signal indicative of the quality of the weld formed by the weld process;
• wherein said first circuit means produces said temperature signal in accordance with a current signal related to the total current supplied by the power supply to the weld zone and a voltage signal related to the voltage applied across the weld zone;
• wherein said first circuit produces said temperature signal by determining the total power supplied to the weld zone in accordance with said current and voltage signals, subtracting therefrom a heat loss factor, and dividing the result by a mass factor related to the mass of the first and second metallic members in the weld zone.

A process for controlling a weld process for joining a first metallic member to a second metallic member at a weld zone, comprising the steps of:

• a) applying electrical power to the weld zone,
• b) producing a temperature signal related to the temperature of the weld zone during the weld process, and
• c) evaluating the quality of the weld formed by the weld process in accordance with the value of said temperature signal;
• wherein said step b) includes the steps of producing a current signal related to the current applied to the weld zone, producing a voltage signal related to the voltage applied across the weld zone, and producing said temperature signal in accordance with said current and voltage signals;
• wherein said temperature signal is produced by determining the total power applied to the weld zone in accordance with said current and voltage signals, subtracting therefrom a heat loss factor, and dividing the result by a mass factor related to the mass of the first and second metallic members in the weld zone.