Daniel Danks


March 1985

Document Type


Degree Name



Dept. of Materials Science and Engineering


Oregon Graduate Center


Although the capacitor discharge welding process has many applications, it has been limited to studs less than 3/8" in diameter. This limitation comes from an incomplete understanding of the fundamental process and key variables that influence the resulting fusion joint. The objective of this investigation was to conduct a fundamental study of the capacitor discharge welding process in order to develop a model of the basic weld cycle. The following parameters were systematically varied to determine their effect on the weld: voltage, capacitance, drop height, drop weight, ignition tip geometry, shielding gases, base plate surface condition, and polarity. The weld cycle was studied by recording and analyzing the welding current and arcing phenomenon, the impact of the stud on the base plate with an accelerometer, and with high speed videography. Weld mechanical strength was checked by tensile testing. Fracture surface, cross section, and microstructural examinations were conducted with optical and scanning electron microscopy. From the work the following generalized conclusions have been made: 1. The optimum voltage for carbon steel is approximately 100 volts. 2. The capacitance is dependent on the cross sectional area of the stud. 3. Wetting agents enhance weld strength and consistency. 4. Similarly, shielding the weld with certain gases improve weld integrity. 5. The drop weight and height influence both the speed and force of impact. It is important to co-ordinate these two parameters to insure proper weld cycle timing. 6. Using the fundamental understanding developed, full strength 1/2" diameter welds, previously unweldable, were successful.





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