Cao Biao

Approximate entropy—a new statistic to quantify arc and welding process stability in short-circuiting gas metal arc welding

Based on the phase state reconstruction of welding current in short-circuiting gas metal arc welding using carbon dioxide as shielding gas, the approximate entropy of welding current as well as its standard deviation has been calculated and analysed to investigate their relation with the stability of electric arc and welding process. The extensive experimental and calculated results show that the approximate entropy of welding current is significantly and positively correlated with arc and welding process stability, whereas its standard deviation is correlated with them negatively. A larger approximate entropy and a smaller standard deviation imply a more stable arc and welding process, and vice versa. As a result, the approximate entropy of welding current promises well in assessing and quantifying the stability of electric arc and welding process in short-circuiting gas metal arc welding.

Digital control system of high frequency bipolar pulse power supply for acid pickling process

Acid pickling is one of the industrial processes used for removal of scales. To overcome some severe problems when using aggressive acids, such as corrosion of metallic substrates and hydrogen embrittlement phenomenon, a digital control system of high frequency bipolar pulse power supply has been designed. The load characteristic of the acid pickling system is analyzed and the corresponding output current waveform scheme has been put forward. The main circuit topology, which is on the basis of two-stage inverter structure, and its working principle are described. A digital control system based on digital signal processor (DSP) is proposed. Control schemes of inverter circuits and control algorithm are also explained in detail. A prototype with a peak output power up to 15 kW has been constructed and tested. The power source can output anodic direct current (DC), high frequency bipolar pulse and cathodic DC waveforms. The pulses have a repetition rate up to 10 kHz, and the current pulse is influenced by loop electrical parameters. The experimental results demonstrate that the high frequency bipolar pulses are very effective for acid pickling of steel.

Fuzzy control system of constant current for spot welding inverter

To avoid the instability of small parts welding, the paper proposes a new type of spot welding inverter, mainly controlled by digital signal processor(DSP) dsPic30F6010A. The system enables stable constant current through fuzzy control. The paper introduces the component , principle and design of the system in details. The experimental result shows that the fluctuation ratio of output current under different service voltage and load conditions is 2% by using the fuzzy control designed.