• An Analytical Model for Prediction of Solidification Cracking Susceptibility in Aluminum Alloys Taking into Account the Effect of Solidification Rate   (1398/7/15)
    An Analytical Model for Prediction of Solidification Cracking Susceptibility in Aluminum Alloys Taking into Account the Effect of Solidification Rate Solidification cracking in pulsed laser welding of aluminum alloys has been the subject of a number of researches. The purpose of this study is to analyze the possible effects of high solidification rates involved in pulsed laser welding on the solidification path of aluminum alloys and solidification cracking sensitivity. For the analysis, conditions at the interface are not necessarily considered to be at equilibrium. Accordingly, the solidification path is modified taking into account the effects of solidification rate on the solidus, liquidus, and eutectic temperatures, the liquidus slope, and the interface parameters, including the partition coefficient, the cell/dendrite tip radius, and the liquid composition in the cellular dendrite tip. In line with the previous researches, cracking susceptibility is assumed to be proportional to the range of temperature squared for solidification crack formation (DT2). مشاهده ادامه
  • Effect of laser welding mode on the microstructure and mechanical performance of dissimilar laser spot welds between low carbon and austenitic stainless steels   (1398/6/28)
    Effect of laser welding mode on the microstructure and mechanical performance of dissimilar laser spot welds between low carbon and austenitic stainless steels This paper aims at investigating metallurgical and mechanical characterization of dissimilar laser spot welds between low carbon and austenitic stainless steel sheets. Microstructural examination, microhardness test and quasi-static tensile–shear test were performed. Mechanical properties of the welds were described in terms of peak load. The effects of laser mean power on the performance of dissimilar laser spot welds have been studied. It was found that increasing laser mean power leads to the transition of laser welding mode from conduction to keyhole. This transition causes a significant growth of the fusion zone size in the lower sheet, i.e. the low carbon steel sheet; since, the keyhole acts as an effective trap for the laser beam and will greatly increase the energy absorption from the incident laser beam. It is also shown that the fusion zone size in the weaker sheet, i.e. the low carbon steel sheet مشاهده ادامه
  • Study on Cracking Behaviour in Pulsed Nd:YAG Laser Welding of 2024 Aluminium Alloy   (1394/7/26)
    Study on Cracking Behaviour in Pulsed Nd:YAG Laser Welding of 2024 Aluminium Alloy Cracking behavior in pulsed laser welding of AA2024 is investigated. It is established that the weld metal can be divided in two zones with respect to cracking behavior. The first zone corresponds to the weld metal nucleated and grown on the wrought base metal. The second zone corresponds to that part of the weld pool which is grown on the weld metal of the previous spot. It is established that the partially melted zone between the weld metal and the wrought base metal acts as a strong initiation site for solidification cracks. However, the partially melted zone of the fusion line between two consecutive weld spots is immune to acting as initiation site for solidification cracking. Overall, the study shows that partially melted zone microstructure and its relation to the welding stresses has an overriding effect on what is known as solidification cracking in the weld metal of AA2024. مشاهده ادامه
  • بررسی تاثیر پارامترهای لیزر بر سخت کاری سطحی فولاد زنگ نزن مارتنزیتی 420 توسط لیزر Nd:YAG پالسی   (1394/7/26)
    بررسی تاثیر پارامترهای لیزر بر سخت کاری سطحی فولاد زنگ نزن مارتنزیتی 420 توسط لیزر Nd:YAG پالسی لیزر به عنوان یک چشمه حرارتی پر شدت قابل کنترل می تواند موجب استحاله سریع فولادها شود. گرم کردن سریع توسط لیزر و سرد شدن سریع خود قطعه موجب می شود تا سطح قطعه به صورت موضعی با صرف انرژی ورودی اندک سخت گردد. هدف این مقاله بررسی اثر پارامترهای مختلف لیزر Nd:YAG پالسی بر ویژگیها و نمایه سختی و مشاهده ریزساختار سطح سخت شده فولاد AISI 420 با لیزر است. پارامترهای موثر بر این فرایند در لیزر تپی شامل توان متوسط عرض تپ بسامد و قطر لکه می باشند. در شرایط بهینه حاصل از این تحقیق سختی سطح تا 2.5 برابر حالت آنیل همین فولاد یا 90% حداکثر سختی کوره ای افزایش یافته است. Keywords: Pulsed Nd:YAG laser, laser surface hardening, , martensitic stainless steel مشاهده ادامه
  • جوشکاری Ti-6Al-4V با استفاده از لیزر Nd:YAG تپی یکصد وات   (1394/7/26)
    جوشکاری Ti-6Al-4V با استفاده از لیزر Nd:YAG تپی یکصد وات تیتانیوم و آلیاژهای آن از مهمترین و مرسوم ترین مواد به کار رفته در صنایع پیشرفته هستند و روشهای اتصال آنها از چالش های امروز دنیاست. در این تحقیق سعی برآن است تا با به کارگیری لیزر Nd:YAG تپی یکصد وات پارامترهای بهینه جوشکاری این آلیاژ مشخص شوند. Titanium and its alloys are from the most applied materials in progressed industries and today their joining methods are challenges of the world. This research attended to determine the improved parameters for welding of this alloy by application of one hundred pulsed Nd:YAG Laser source.Three main and effective parameters, peak power; energy per pulse; pulse overlapping percentage, on the depth of the weld pool were studied and at the end a useful combination of these three important parameters was introduced and a weld by hemogenus microstructure and defect free was obtained. . مشاهده ادامه
  • Effect of Wire Feed Position on 2024 aluminum alloy pulsed Laser Welding with Filler Wire   (1394/7/26)
    Effect of Wire Feed Position on 2024 aluminum alloy  pulsed Laser Welding with Filler Wire The utilization of the laser welding process whit filler wire addition is often considered a difficult and complicated process. This study shows the effect of most important welding variables to the quality of 2024 aluminium alloy laser welding when welding whit filler wire. Wire feeding position to work piece surface, laser beam focal point to work piece surface, wire feeding position to laser beam focal point, Wire feeding direction to welding direction and shielding gas were from investigated variables in this study. Used from Argon and helium as shielding gases. Spattering occur intensely in the welds which were performed with argon. The misalignment of wire in the transverse direction to welding direction and laser beam optical execs cause problems that the may lower quality of weld. The wire feeding direction should be at the welding direction and the wire feed toward the weld bead. مشاهده ادامه
  • اثر پارامترهای لیزری در آلیاژسازی سطحی الومینیوم با لیزر Nd:YAG تپی   (1394/7/26)
    اثر پارامترهای لیزری در آلیاژسازی سطحی الومینیوم با لیزر Nd:YAG  تپی آلیاژسازی لیزری با استفاده از لیزر Nd:YAG تپی با تابش انرژی 10 تا 12 ژول بر سطح الومینیوم پیش پوشش داده شده با نیکل انجام شده است. در این تحقیق اثر پارامترهای لیزری نظیر انرژی تپ ، قطر پرتو، و سرعت روبش بر میکروساختار و خواص لایه آلیاژی شده بررسی شده است. آلیاژ تشکیل شده در این تحقیق شامل فازهای سخت بین فلزی نیکل آلومیناید می باشد که سختی حاصل از این آلیاژسازی تا حدود 10 برابر سختی الومینیوم زیرسازه افزایش یافته است. Surface alloying of aluminum pre coated with nickel was carried out using a pulsed Nd-YAG laser. In this article, effect of laser and process parameters such as pulse energy, beam spot diameter and scan speed on microstructure and properties of alloyed layer was studied. During this research, the Ni-Aluminide intermetallic hard phases were formed. The hardness of the obtained alloyed layer after laser surface processing is about 10 times the hardness of Al substrate.  مشاهده ادامه
  • بررسی تاثیر پارامترهای فرایند جوشکاری آلومینیوم آلیاژی 2024 توسط لیزر Nd:YAG پالسی   (1394/7/26)
    بررسی تاثیر پارامترهای فرایند جوشکاری آلومینیوم آلیاژی   2024 توسط لیزر Nd:YAG پالسی در این مقاله اثر پارامترهای فرایند جوشکاری آلومینیوم آلیاژی 2024 با استفاده از لیزر Nd:YAG پالسی بر ابعاد حوضچه جوش مورد بررسی قرار گرفته است. تاثیر دو پارامتر انرزی پالس و قله توان بر عمق و عرض حوضچه و همچنین تغیی حالت جوشکاری از هدایتی به سوراخ کلیدی مورد بررسی قرار گرفته است. Abstract- In this paper effects of aluminum alloy welding process parameters pulsed laser on the weld bead dimension were investigated. The effect of energy pulse and peak power on the deep and width of weld bead and change in welding mode from conduction to keyhole were studied. The results shows that both energy pulse and peak power effect on welding mode change. Also the increasing of overlapping cause the weld bead dimensions increase but its effect is lower than effect of pulse energy and peak power. Variations of work piece distance cause change in welding mod because of power density variation. Keywords: aluminum alloy 2024, laser welding, weld bead shape, pulsed Nd:YAG laser. مشاهده ادامه
  • Sealed Off Operation of a High Repetition Rate TEA CO2 Laser   (1394/7/26)
    Sealed Off Operation of a High Repetition Rate  TEA CO2 Laser Abstract: Design and construction of a high repetition rate miniature TEA CO2 laser using low purity industrial gases is reported. An abnormal drop in laser power around input pulse energy of Ein=150-200 mj was observed. In spite of gas velocity importance in attaining uniform plasma under high voltage discharge pulse at high frequency operation it has no influence on this anomalous treatment. Degradation of gas molecules in plasma region at present of arc free glow discharge was considered. After 3×10Exp5 shots laser output power is decreased around 10% while working in closed-cycle laser gas mixture. مشاهده ادامه
  • تحلیل عددی بهینه سازی برش لیزری فولاد نرم با گاز کمکی اکسیژن   (1394/7/26)
    تحلیل عددی بهینه سازی برش لیزری فولاد نرم با گاز کمکی اکسیژن در این مقاله یک مدل ریاضی برای برش ورق فولاد کم کربن با استفاده از لیزر CO2 پیوسته موج بهمراه گاز کمکی اکسیژن پیشنهاد شده است. این مدل بر اساس حل همزمان معادلات پایستگی جرم، اندازه حرکت و انرژی در حالت ایستا گسترش یافته است. شیوه جدیدی برای تخمین سرعت بیشینه برش در این مقاله معرفی شده است. مشاهده ادامه
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