A DUAL-FREQUENCY ELECTROMAGNETIC SENSOR FOR NONCONTACT DILUTION EVALUATION IN LASER CLADDING AND ALLOYING PROCESSES

In laser surface cladding and alloying processes, the properties of th e cladding/alloy layer produced may change due to dilution by the subs trate. At the same time the thickness of the cladding/alloy layer may vary. A dual-frequency electromagnetic sensor has been developed to en able the simultaneous, non-contact, non-destructive measurement of the magnetic reluctance of the workpiece and air gaps. This has been appl ied to monitoring the level of dilution (the degree of contamination b y substrate) in laser cladding/alloying processes. For certain types o f cladding/substrate combinations such as those having large differenc es either in magnetic permeability or in conductivity, the sensor can indicate the level of dilution of the cladding/alloy. The effects of m agnetic flux leakage, edge fringing, eddy currents, cladding/alloy thi ckness, surface temperature, operating frequency and signal processing are discussed. Both theoretical analysis and experimental data are pr esented. Good agreement between the theory and experiments has been ac hieved.