M. A. Daha, G. A. Nassef, I. A. Abdallah, and H. M. AbouSeeda
Production
Engineering Department, Faculty of Engineering, Alexandria University,
Alexandria, Egypt Structural Engineering Department, Faculty of Engineering,
Alexandria University, Alexandria, Egypt
Published
at : International Journal of Engineering and
Technology Volume 2 No. 4, April, 2012
ملخص:
لقد تم في هذا البحث استحداث نموذج العناصر المحددة
ثلاثي الأبعاد لتقدير شكل و أبعاد وصلة اللحام وتحليل توزيع درجة الحرارة و دورات
الحام الحرارية و الإجهادات المتبقية الناتجة في وصلات DSS 2205 الملحومة بالبلازما.
كما تم إقترح مصدر حرارى تكيفى لنموذج
التحليل العددي للعملية، أخذن بعين الاعتبار ملامح تكون وصلة لحام البلازما
"بوق". فقد كشف التحليل الحراري ملامح درجة الحرارة التي تشير إلى الحجم
والشكل الهندسي لمنطقة الأنصهار وقد كشف التحليل الحراري ملامح درجة الحرارة التي
تشير إلى حجم وهندسة المنطقة حام الانصهار (FZ) .
منناحية أخرى، فقد تم التحقق من صحة النماذج الأولية
مقارنة بالبيانات التجريبية، وظهرت علاقة جيدة للغاية، هذة العلاقة الجيدة دليل
على صلاحية النموذج العددي لأنتقال الحرارة والنموذج التحليلي لسريان المعدن.
كما تم
دراسة تأثير المحتوى الحرارى على شكل و أبعاد منطقة انصهار الحام.
Abstract:
A
three-dimensional thermal transient finite element model has been developed to
estimate the weld geometry and to analyze the temperature field due to the
keyhole plasma arc welding (PAW) in 2205 duplex stainless steel. An adaptive
heat source model is proposed for the numerical analysis of the process,
considering the “bugle-like” configuration feature of keyhole PAW welds. The
thermal analysis has revealed temperature contours that indicate the size and
geometry of the weld fusion zone (FZ). The initial models are validated against
experimental data and show very good correlation. Such good correlation
indicates the validity of the numerical heat transfer model and the analytical
fluid flow model. A variety of welding heat inputs are then simulated. Effect
of welding heat input on the size and geometry of the weld fusion zone are
established.
Results
:
1- It is noticed that all of the material
with in the fusion zone rises in temperature above the melting point, reaching
3623 K for a heat input of 1.96 kJ/mm . This high temperature is the main
attribute in the formation of the keyhole, converting liquid to vapor.
2- The curves indicate the pattern of heat
flow in the weldment. These curves are drawn for V = 28 Volts, I = 140 A, η =
0.50 and a welding speed = 0.002 mm/sec. A study of the isotherm sequence
provides the theory about the nature of heat flow in the
keyhole plasma weldment. To observe the molten-zone growth, the isotherm
corresponding to the liquidus temperature (1773 K) is plotted and examined. The
isotherm corresponding to 1773 K will show how fast the fusion zone is growing.
Heat input to the welding pool is transferred quickly, first in the thickness
direction and then in the width direction to reach a uniform distribution. The
isotherms at time (t= to + 0.60 S)
indicating that thefusion zone (T = 1773 K) has the shape of a reversed bugle.
The fusion zone is completely formed at (t = to + 1.15 S), the half fusion zone
width is 5.20 mm on the top surface and 1.25 mm on the bottom surface for a
heat input of 1.96 kJ/mm. Thus, the numerical results are in good agreement
with the experimental measurements.
3-Effect
of heat input can be easily studied using the thermal finite element model. The
inner isotherm, representative of the liquidus temperature, demonstrates the
geometrical characteristics of the weld pool. In this study, different values
of heat input were obtained by changing the welding speed. It can be noted that
the heat input has a minor effect on the temperature distribution on the top
surface of the welded plates.
Conclusion and Outlook :
The
following conclusions may be drawn from this analysis:
1- It is possible to analyze the three-dimensional
transient thermal analysis for the Keyhole PAW process using the finite element
method combined with an adaptive heat source model.
2- The predicted
weld pool geometry and size utilizing the optimized values for certain
parameters agree well with the corresponding experimentally determined values,
indicating the accuracy of the approach.
3- The effect of
fluid flow and solidification of the weld pool are considered analytically;
therefore, good predictions of the transient isotherms and the weld pool
geometry are obtained.
4- The results of
the built model can be used for the optimization of Keyhole PAW processes to
achieve sufficient energy and deep penetration.
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