군수용 방탄도어씰 제작을 위한 CMT 용접공정 최적화

Abstract

ABSTRACT

Optimization of CMT Welding Process for Manufacturing of Military Bulletproof Door-seal

Nam-Ho Hong Advisor : Prof. Bang, hee-seon, Ph.D. Department of Welding and Joining Science Engineering, Graduate School of Chosun University

Threre are many problems with GMAW(Gas Metal Arc Welding) which makes lots of sppatter and produces problems about quality. Welding the base metal, the produced heat transfer to the welding zone that makes deformation of products. In this situation, the next generation tactical military vehicles are being developed from 2015 and some models of them will be applied with bulletproof materials. Bulletproof materials are made of ultra high strength steel(1,700) and have 6 thickness. They have good performance of the strength but not good formability. Hence many straight parts are need to assemble the products and there are weaknesses when doing the ARC welding, penetration is not good enough. In this paper, the CMT(Cold Metal Transfer) welding process was used for making the military bulletproof door-seal and welding conditions are derived for ultra high strength steel(1,700), ARMOX 500T(6.0). And then the weldability was evaluated in terms of mechanical and metallurgical characteristic. The CMT + PULSE mode of the CMT welding process was used, and when wire feeding speed is 7.6, the angle of torch is 75°, the flow rate of shield gas composed Ar 80 + CO2 20 is 15, welding speed is 6, groove is 40° and gap is 1, the weldability was most excellent. Quality of the welded joint was evaluated according to ISO 5817. The result for welded joints was obtained quality level for stringent(B). And the average result value of the yield strength was about 800MPa and fracture occurred in the weld zone. The Vickers hardness were found above 500HV for base metal, and 272HV for welded joints. It looks like that grain coarsening was occurred in HAZ by the welding heat. Derivation of CMT welding process is used for creating two weling mechanism process and applied to the short welding course, 20 in field welding atmosphere. And then the weldability was evaluated. To prevent excess back bead, ARC starting current is adopted 105% of the main current during 0.1 sec and to remove the creator of the terminal area, final current is adopted 5% of the main current during 2.5sec. Developed welding mechanism and three types of the welding sequences were applied to making the prototype of the military bulletproof door-seal. The measurement of the deformation was carried out with the inspection fixture and then the results were exchanged to 100 points by the test reports. From these reports, the minimum cooling time in the room temperature was calculated. In the last result, the overlap of the deformation came from welding heat makes the width of the product larger. And the cooling at least 5 minutes at room temperature by the grouped welding method is the most economical and can produce high quality products.