Mehtap HIDIROĞLU, Unal KAHRAMAN, Nizamettin KAHRAMAN

AC ve MFDC nokta direnç kaynak teknolojilerinin yeni nesil otomotiv çeliklerinin mekanik özelliklerine etkisi

Özellikle ultra yüksek mukavemetli çeliklerin kullanımı son yıllarda arttıkça, araç gövdesi, üreticileri nokta direnç kaynak ekipmanı için iki akım türü arasında seçim yapma zorluğu ile karşı karşıya kalmıştır. Bu çalışmanın amacı, alternatif akım (AA) ve orta frekans doğru akım (OFDA) güç kaynak makinelerinden elde edilen kaynaklı bağlantıların mekanik performans üzerindeki etkilerini karşılaştırmaktır. Preslenmemiş 22MnB5 ve DP600 çelik saclar arasındaki bağlantı için iki farklı kaynak ekipmanı AA ve OFDA teknolojisi kullanılmıştır. Hem AC hem de OFDA işlemi için preslenmemiş (22MnB5) ve çift fazlı (DP600) çelik arasındaki nokta direnç kaynaklı bağlantıların mikro sertlik sonuçları, çekme makası ve çapraz gerilim testleri ayrıntılı olarak açıklanmaktadır. Sonuçlara göre, OFDA teknolojisi ile elde edilen kaynaklı örneklerin kaynak metali ve ITAB bölgelerinde AA teknolojisine kıyasla nispeten daha düşük sertlik değerleri gözlenmiştir. AA teknolojisine göre OFDA teknolojisi ile kaynak yapılmış numunelerin mukavemet ve uzama değerlerinde pozitif etki gözlenmiştir. Çapraz çekme ve çekme makaslama testi sonuçları değerlendirildiğinde, OFDA teknolojisine sahip kaynaklı numunelerde %5'ten fazla iyileşme gözlenmektedir. Bu makalenin özgünlüğü hem AA hem de OFDA prosesinin preslenmemiş 22MnB5 ve DP600 arasındaki farklı bağlantının performans özelliklerine etkisini inceleyen karşılaştırmalı bir çalışma sunmaktır.

Anahtar Kelimeler:

Nokta direnç kaynağı, Preslenmemiş 22MnB5, DP600, AA ve OFDA nokta direnç kaynağı

The effect of AC and MFDC resistance spot welding technology on mechanical properties of new generation automotive steels

Usage of UHSS (ultra high-strength steels) had increased in recent years, automobile Body in White-BIW- manufacturers had faced the challenge of choosing between two types of currents for resistance spot welding equipment. The objective of this work is to compare the effects of welds obtained from both AC and MFDC (alternate current-AC- power source and medium frequency constant current one-MFDC) machines on mechanical performance. Two different welding equipment had been used for making joints between as-delivered 22MnB5 and DP600 steel sheets. The micro-hardness results, tensile shear (TS) and cross tension (CT) tests of resistance spot welded (RSW) joints between as - delivered (22MnB5) and double phase (DP600) steels for both AC and MFDC process are detailed. According to the results, comparatively lower hardness values were observed in the weld metal and heat effected zones of the welded samples obtained by MFDC technology compared to AC technology. The positive effect was observed in the strength and elongation values of the samples welded with MFDC technology according to AC technology. When the CT and TS test results were evaluated, more than 5% improvement is observed on welded samples with MFDC technology. The originality of this paper presents a comparative study of joint performance properties effect for both AC and MFDC process on dissimilar joints between as-delivered 22MnB5 and DP600.

Keywords:

Resistance spot welding, As delivered 22MnB5, DP600, AC and MFDC resistance spot welding,

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