Measuring Temperature Distribution Of Laser Induced Plasma In Deep Penetration Laser Welding

Keyhole effect is the essential characteristic of deep-penetration laser welding,the research of keyhole mechanism is the hot and difficult point in laser welding field.Laser induced plasma densely cover the keyhole,so detecting laser induced plasma is very helpful for keyhole mechanism research and has guiding significance in practical application of laser welding.Temperature is one of the most important parameters of plasma,any other parameters can be expressed by plasma temperature and electron density.The article designs a multi-channel spectral measurement system to research the status inside laser induced plasma by measuring the temperature distribution of plasma inside the keyhole and above the workpiece surface.Creative designs a measurement system based on multi-channel optical fiber detecting assembly,measures line integral curve of plasma intensity of plasma and computes 2-D temperature distribution of the plasma inside the keyhole and above the workpiece surface by Abel inverted transform.Analyzing influence of welding parameters to temperature distribution above the workpiece surface by orthogonal experiment,and first gets the 2-D temperature distribution of the plasma inside the keyhole by experimental method based on "sandwich" method.The results show that plasma temperature above the workpiece surface is below 10000K, and the average temperature decrease with height increasing;the temperature distribution of plasma above the workpiece surface is non-uniform and unstable,and the temperature change is smaller and more stable;the plasma inside the keyhole has much effect on plasma above the workpiece surface;the temperature distribution is low in middle area and front of welding area is always high than back;different welding parameters have different effect on the temperature distribution of plasma.The plasma maximum temperature inside the keyhole is above 15000K,the intensity of middle area is weak,but temperature is much higher.The state inside keyhole including solid,liquid,gas and plasma,and has different trend between front and back of the welding keyhole.